Microelectrochemical characterization of Zn, ZnO and Zn-Mg alloys with online dissolution monitoring Dissertation zur Erlangung des Grades “Doktor der Naturwissenschaften” an der Fakultät für Chemie und Biochemie der Ruhr-Universität Bochum vorgelegt von Sebastian Oliver Klemm aus Wuppertal Bochum 2011
157
Embed
Microelectrochemical characterization of Zn, ZnO and … · Microelectrochemical characterization of Zn, ZnO and Zn-Mg alloys with online dissolution monitoring ... rate of zinc based
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Chapter 0: Glossary
1
Microelectrochemical characterization of
Zn, ZnO and Zn-Mg alloys
with online dissolution monitoring
Dissertation
zur
Erlangung des Grades
“Doktor der Naturwissenschaften”
an der Fakultät für Chemie und Biochemie
der Ruhr-Universität Bochum
vorgelegt von
Sebastian Oliver Klemm
aus Wuppertal
Bochum 2011
Chapter 0: Glossary
2
Chapter 0: Glossary
3
1. Gutachter: Prof. Dr. Martin Stratmann
2. Gutachter: Prof. Dr. Wolfgang Schuhmann
Tag der Disputation: 31.8.2011
Chapter 0: Glossary
4
Gewidmet meinen lieben Eltern,
Elke und Reinhard Klemm
Chapter 0: Glossary
5
Acknowledgement The work presented was carried out at the Max-Planck Institut für Eisenforschung GmbH in
Düsseldorf in collaboration with ThyssenKrupp Steel Europe AG, Dortmund. My deepest
compliment for the excellent working atmosphere and the inspiring environment that I
experienced from the first moment on! I particularly express my gratitude to Prof. Dr. Martin
Stratmann for supervising this thesis, for his constant support and the challenging remarks
that proved to be a reliable guidance at all times. I furthermore thank Prof. Dr. Wolfgang
Schuhmann for kindly accepting to act as second reviewer and the time he invested for me.
Prof. Dr. Achim Walter Hassel deserves my explicit thankfulness for being a friendly and
inspiring mentor, and the constant backup on the scientific parquet. All the best for your new
position in Linz! My new group leader, Dr. Karl J. J. Mayrhofer, showed admirable care and
interest from the day I joined his group and I am deeply grateful for the exceptional benefit he
provided. Big thanks go to Dortmund, in particular to Dr. Bernd Schuhmacher, Dr. Janine-
Christina Schauer, Dr. Stefan Krebs, Maria Köyer and Jennifer Schulz from TKS Europe
for an excellent collaboration, many fruitful discussions, and the financial support. Further
thanks are given to Dr. Sascha E. Pust and Dr. Jürgen Hüpkes from the Forschungszentrum Jülich for a very effective and enjoyable collaboration on ZnO. I express my gratitude to the
excellent staff at the MPIE and thank Bernd Schönberger, Cornelia Arckel, Daniel Kurz,
Eberhard Heinen, Rebekka Loschen, Ulrich Wiebusch, the workshop team, and all the
others. Thanks to Bochum at this point, to Gundula Talbot from the Ruhr-Universität for her
great guidance on the admission side. I furthermore appreciate the brilliant scientific
environment I had the pleasure to work in with all colleagues, group leaders and the
fantastic Electrocatalysis-Group composed of Andrea Mingers, Angel Topalov, Anna
Schuppert, Claudius Laska, Hendrik Venzlaff, Ioannis Katsounaros, Josef Meier, Nicole
Fink, and Jay Srinivasan. One member is missing in the former list, but he happens to be the
best friend one can imagine and therefore deserves special mentioning: Arndt Karschin.
Besides him of course, there are many other great friends to thank at this point: Bastian
Huschens, Benjamin Schulte, Daniel Schiffer, Felix Fuge, Jan Lauckner, Jan Spitzley,
Leif Müller, Nils Koenen, Rüdiger von Dehn, and many more. Finally, my warmest
gratitude goes home, to my dear Julia Lengsfeld, for the unbelievable joy of sharing my life
with you! Also to my little brother Alexander Klemm, who I am really proud of at all times. In
the end, I want to mention my parents Elke & Reinhard Klemm, who gave me the greatest
possible trust and support throughout my life. In deep admiration, I dedicate this thesis to you.
Chapter 0: Glossary
6
Chapter 0: Glossary
i
Abstract The primary aim of this study is to utilize microelectrochemical techniques in combination
with time resolved trace analysis to correlate the electrochemical behavior and the dissolution
rate of zinc based materials in order to provide new insights into corrosion processes. For this
purpose, a fully computer controlled scanning flow cell setup is developed utilizing a two-
compartment capillary cell (theta type) with adjustable electrolyte flow. This setup is coupled to
a UV-VIS spectrometer downstream capable of providing time resolved electrolyte analysis. By
using Zincon as a complexing agent, online analysis of zinc and copper in the electrolyte stream
is achieved with a detection limit around 100 nmol l-1. A very good correlation between
electrochemical and spectroscopic data is demonstrated on the example of zinc and copper.
Furthermore, a detailed parameter screening is performed on metallic zinc, covering the impact
of sulfate and chloride anions on the electrochemical behavior and dissolution rate of zinc.
A focus is set on the effect of the pH value on the corrosion and electrochemical response
in aerated buffered and unbuffered electrolytes. The results on zinc are thereby complemented
by investigations on ZnO substrates with large similarities in borate buffered solutions. It is
shown that the dissolution proceeds through a surface oxide under these conditions, with the
electrochemical behavior mainly determined by the rate of oxide dissolution by proton
transport. The dissolution in unbuffered solutions on the other hand is mainly governed by
changes in the surface pH as a consequence of proceeding corrosion processes.
To take full advantage of the high throughput capabilities and the small surface demand of
the capillary tip (~200 µm diameter), Zn-Mg material libraries are prepared by thermal PVD
and characterized by a variety of surface analysis techniques. Linear scans along the
composition gradient reveal strongly non-linear behavior of the electrochemical and dissolution
behavior in both NaCl and borate buffered solutions. The results indicate that additions of
20 at. % Mg are most beneficial for the corrosion resistance of zinc based coatings in
unbuffered NaCl solutions, while a screening in borate buffer highlights the impact of various
magnesium contents on the surface oxides formed.
The high consistency of the obtained datasets underlines the feasibility to perform high
throughput material optimization with the integrated approach taken in this study. Moreover,
the picture presented emphasizes the importance of downstream dissolution monitoring for
correct evaluation of electrochemical data and provides innovations for electrochemical
corrosion testing methodologies.
Chapter 0: Glossary
ii
Content
Glossary ..................................................................................................................... v
As described in the experimental section (4.2.3), Zn and Mg was co-deposited by thermal
PVD onto steel substrates of approximately 10 x 2 cm2. The typical average thickness ranges
around 400 nm, while the exact thickness varies due to locally different deposition rates. As an
example, the thickness in the middle of the sample is approximately 30 % less than right above
the sources if Zn and Mg are deposited at equal rates assuming an average sharpness parameter
of 2.4.
The optical appearance of the samples is strongly non linear despite the continuous
(sigmoidal) increase of magnesium along the x-axis as shown in Figure 8.1. The image
additionally contains a schematic line scan illustrating a typical sequence of measurement
locations subsequently addressed by the SFC. It can be observed from the optical image that
the zinc rich area up to approximately 14 at. % Mg appears grey and matt due to a large surface
roughness. However, the optical roughness vanishes abruptly as the magnesium content is
further increased, accompanied by a dark appearance between around 18 and 45 at. % Mg. The
latter feature is not attributed to the surface roughness since the reflectivity remains. Moreover,
the surface structure or the oxides formed (dark ZnO, see [72]) may affect the optical
appearance. It will be shown later that this region indeed exhibits a pronounced growth of
native oxides.
Chapter 8: Corrosion of Zn-Mg alloys
102
0 20 40 60 80 1000
20406080
100
Magnesium
cont
ent /
at.%
position / mm
Zinc
Figure 8.1: Optical image of a Mg11Zn89-Mg95Zn5 material library with schematic insets illustrating
the locations addressed with the SFC. The composition along the x-axis is shown by an EDX line scan.
While the roughness is certainly a very important parameter for electrochemical studies, a
variation of the native oxide thickness needs to be considered as well because polishing
techniques to equalize the surface topography are not feasible on this kind of samples. All
observation therefore suggest a strong non-linearity that encourages further structural
investigations.
8.1.2 SEM imaging High resolution SEM images were taken at specific locations to clarify the structure of the
thin film formed during deposition. It is well known that zinc exhibits a high surface mobility
[209] (pp. 447) and grows voluminous in the hexagonal crystal system. Baker et al. showed that
the roughness of the film can be reduced by cooling of the substrate [74], which is not available
in the PVD system used. Therefore, a sponge-like film was obtained for pure zinc that
dominates the overall film structure up to approximately 14 at. % Mg, after which the co-
deposition significantly alters the film growth. Figure 8.2 shows a series of SEM images
following increasing Mg content from 0 to 91.2 at. %.
Chapter 8: Corrosion of Zn-Mg alloys
103
Figure 8.2: SEM images of thermally evaporated Zn-Mg alloys at 100 k magnification (acc. Voltage
12 kV). The images were taken on 3 different samples to cover the composition range presented.
A particularly interesting feature is the lamellar growth of upright standing plates, all being
horizontally oriented. The zinc source was located on top of each image while the magnesium
source was located on the bottom. Therefore, the orientation of the lamellas is in all cases
perpendicular to the connecting vector between the sources.
The rough morphology observed at high Zn contents dominates the structure up to around
13- 15 at. %, which is in exact agreement with the optical images. The surface is smoothed by
this structural change towards lamellar growth, probably being a consequence of the formation
of Zn-Mg intermetallics.
Further increase of the Mg content (χMg) causes the lamellas to tilt with respect to the
surface normal, ultimately leading to a smooth layer of plates lying flat on the substrate. This
change of lamellar orientation is again reflected by the optical appearance as the dark coloration
vanishes in this region, resulting in a mirror like appearance at all Mg contents exceeding
~44 at. %. The strong decrease of the number and size of the inclusions evident from the last 3
SEM images indicates that these are composed of a zinc rich phase, while the matrix
Chapter 8: Corrosion of Zn-Mg alloys
104
morphology is comparable to pure magnesium films obtained by sputter techniques reported
by Blawert [210].
8.1.3 XRD analysis To determine the crystallographic composition of the material libraries, X-ray diffraction
(see section 4.1) was performed along the gradient. The incidence angle was kept at 5° and the
sample was positioned in a way to ensure that the long side of the rectangular shaped
illuminated area (slit aperture) was perpendicular to the composition gradient (therefore,
parallel to the y-axis on the substrate). Due to the low incidence angle, the illuminated area is
comparably large and covers around 6.88 mm on the substrate in x-direction [122], causing the
diffraction patterns to correspond to a composition range. The following figures show an XRD
survey (step size 0.1°, integration 5 s) including a large number of compositions und three
detailed diffraction patterns recorded with high resolution and long integration times (step size
0.05°, integration 18 s).
30 40 50 60 70 80123456789
1011121314
ZnZn
Fe
Zn
Fe
Zn
log
(inte
nsity
/ a.
u.)
2 θ / degree
Mg
Fe
374453627178848992
Zn content / at. %
(a)
Figure 8.3:
Grazing incidence XRD along
the Zn-Mg material library with
a logarithmic intensity scale. The
individual patterns are shifted
along the y-axis for clarity. The
graph shows a survey covering a
large number of compositions
(mean value given, deviation
± 4 at. %).
Chapter 8: Corrosion of Zn-Mg alloys
105
30 40 50 60 70 801
2
3
4
5
6
7
8(b)
61.4 - 66.2 at. % Zn
77.0 - 81.1 at. % Zn
93.8 - 95.7 at. % Zn
MgZn2
ZnFe
Zn
FeZn
log
(inte
nsity
/ a.
u.)
2 θ / degree
FeZn
Figure 8.4:
Grazing incidence XRD along
the Zn-Mg material library with
a logarithmic intensity scale. The
individual patterns are shifted
along the y-axis for clarity. The
graph shows a detailed pattern
with high integration time to
resolve the low intensity MgZn2
peaks with the exact composition
ranges covered during the
experiment.
The survey shown in Figure 8.3 demonstrates a decrease of the metallic zinc pattern [211]
that completely vanishes for a zinc content of 53 ± 4 at. %. Further decrease of χZn results in
the emergence of a metallic Mg peak while the substrate material (Fe) is present in all cases. An
interesting observation is that the transition region shows neither Zn nor Mg features, but
instead a broad region of increased intensity that originates from several overlapping, poorly
resolved peaks. Figure 8.4 provides clarity for a composition range from 61.4 to 66.2 at. %
where a large number of low intensity peaks were detected that correspond to the intermetallic
MgZn2 [212]. The absence of metallic magnesium over a large composition range proves that
Mg is incorporated into the film as intermetallic. Given the stochiometry of MgZn2, it would be
expected that excess magnesium occurs at 53 ± 4 at. % in Figure 8.3 which is most probably
reflected by the slight increase of the XRD intensity at 34.5° in the respective dataset. The
presence of other intermetallics like MgZn and Mg2Zn11 [79] can be excluded within the
detection limit. The results presented are in full agreement to the literature stating MgZn2 to be
the dominant intermetallic formed under typical solidification conditions [213]. The presence
of amorphous material (especially Mg) can be excluded according to the low crystallization
temperature and ease of crystal formation during PVD deposition [214].
8.1.4 AES maps The formation of lamellas during the PVD process is the most noticeable feature of the Zn-
Mg material libraries and was shown to be roughly confined to a region between 90 and
50 at. %. zinc. This composition range is also characterized by the emergence of the
intermetallic MgZn2, which might be the origin of the structure observed through local
Chapter 8: Corrosion of Zn-Mg alloys
106
differences in composition, as long as these regions match the small size of the structural
features. To investigate this possibility, AES maps of high resolution (~15-20 nm) were
performed using a take off angle of 30°, an acceleration voltage of 25 kV and a current of
10 nA. Increasing intensity in the corresponding images is indicated by an increase in color
brightness.
Figure 8.5:
SEM image and corresponding AES maps of a
Zn79Mg21 alloy part of a Zn-Mg material library
deposited by thermal PVD. The image beside shows
the intensity difference between Zn and Mg indicating
regions of relative dominance of one particular element.
Please note that this measurement procedure only
allows for qualitative comparison.
Figure 8.6 shows the SEM image and corresponding AES maps on a Zn-Mg material library
at a magnesium content of 21 at. %. These maps only allow for qualitative comparison and the
peak/valley intensities of zinc and magnesium were matched to allow the illustration of the
local composition distribution in the difference map. While the Zn and Mg images themselves
strongly reflect the surface topography, the comparison in the last image corrects for that fact
and reveals regions of different composition that match the size of the lamellas considerably
well. It is therefore concluded from the XRD and AES data that phase separation between Zn
and MgZn2 is the major reason for the surface structure observed.
Chapter 8: Corrosion of Zn-Mg alloys
107
8.1.5 Native oxide thickness The thickness of the native oxide was estimated by means of X-ray photoelectron
spectroscopy (XPS) and sputter depth profiling. Peak locations and measurement procedures
were described in section 6.2.3.
The depth profiles on a Zn-Mg material library at three different compositional domains are
shown in Figure 8.6. The first observation is that the oxygen signal does not decay to zero
despite a leveling of the intensities with progressing sputter depth. Complementary EDX
analysis reveals an oxygen content in the complete film below 10 at. % as the sum of surface
oxides and oxides within the film formed during the deposition procedure. Therefore, the high
level of oxygen at large sputter depth is not assumed to reflect a high intrinsic level of oxygen
in the film itself, but is rather due to a topographic effect or an oxidation process during the
XPS measurement. It is to note that the exact determination of the oxide thickness is limited
because of the uncertainty regarding the exact sputter rate in comparison to SiO2, especially
because the etch rates of both metals and their oxides may all be different [29]. Therefore, the
data will be used for a qualitative comparison between different compositions only.
A well known effect during oxide formation on Zn-Mg alloys under environmental
conditions is the enrichment of magnesium at the surface due to its high affinity for oxygen
[79]. The data presented clearly reflects this fact by very low zinc intensities measured at the
surface (almost zero except for 6 at. % Mg). Furthermore, magnesium has the tendency to
oxidize deeper than zinc as shown by the emergence of metallic zinc prior to metallic
magnesium in sputter profiles presented by Hausbrand [29, 50]. The estimation of the oxide
thickness by e.g. the crossing point between zinc and oxygen therefore proves questionable.
However, the total intensity of oxygen and the slope of the signal decay during depth profiling
can be used for comparison and indicate that the native oxide thickness in the series presented
follows the order Mg6 < Mg37 < Mg19. This is surprising to some extend as a correlation
between Magnesium and oxygen content can not be concluded. The strong non-linearity
observed along the gradient previously demonstrated by different characteristics apparently
applies for the formation of native oxides as well.
Chapter 8: Corrosion of Zn-Mg alloys
108
0 5 10 15 20 25 30 35 400
20
40
60
80
Zn63Mg37
Mg
O
cont
ent (
at. %
)
Sputter depth / nmSiO
Zn
2
0 5 10 15 20 25 30 35 400
20
40
60
80
2
Zn81
Mg19
cont
ent (
at. %
)
Sputter depth / nmSiO
Mg
O
Zn
0 5 10 15 20 25 30 35 400
20
40
60
80
100
2
cont
ent (
at. %
)
Sputter depth / nmSiO
Zn94Mg6
Mg
OZn
Figure 8.6:
XPS depth profiles of the native oxide grown
on the material library at different
compositions. Carbon signals were only
observed prior to the first sputter step and are
not included.
8.1.6 Summary of the results Zn-Mg thin film obtained by thermal co-deposition exhibit a surface structure highly
dependent on the film composition. The rough morphology observed for very zinc rich
coatings vanishes quickly as the Mg content is increased above ~13 at. %, leading to the
formation of highly ordered lamellas. High resolution AES maps in combination with XRD
suggest the formation of MgZn2 intermetallics to be the origin of the structure observed. The
thickness of the native oxides on the material library estimated from XPS depth profiles was
shown to behave non linear along increasing Mg content.
Chapter 8: Corrosion of Zn-Mg alloys
109
8.2 Electrochemistry and dissolution 8.2.1 Unbuffered NaCl solution
Similar to the investigations on pure zinc presented in a former chapter (6.1, p. 54), aerated
0.1 M NaCl solution was used as a corrosive medium under steady electrolyte flow. It has been
presented in the respective chapter that open circuit potential measurements in combination
with downstream analytics constitute a very reliable way to measure ECorr and icorr, and the same
methodology is applied on Zn-Mg coatings in order to investigate the effect of magnesium on
the electrochemical behavior and dissolution rate of Zn-Mg material libraries.
8.2.1.1 Open circuit potentials A 1000 s OCP measurement was performed on a Zn-Mg material library ranging from
approximately 96 to 61 at. % zinc. The dominance of zinc along the whole library was chosen
because of the active nature of Mg in chloride containing environment, causing e.g. gas
evolution in the cell at very high Mg contents.
The measurement procedure was executed in a fully automated mode, and a linear array of
measurement locations (spacing 1 or 2 mm depending on the experimental run) was
programmed along the gradient vector (x-axis on the substrate, see Figure 8.1). Each location
was subject to 1000 s of OCP measurement, followed by a lifting of the cell and subsequent
purging for 1200 s. A steady electrolyte flow of 15.6 µl min-1 was maintained at all times. The
following figure shows a 3D graph of the recorded OCP in two independent experimental runs
after automated data processing, i.e. addition of the reference potential (212 mVSHE) and
conversion from position to composition (see page 33).
Figure 8.7: 3D OCP maps (1000 s) on a Zn-Mg material library displayed as a function of Zn content
(at. %) in 0.1 M NaCl solution under constant electrolyte flow. Two independent datasets are shown.
Chapter 8: Corrosion of Zn-Mg alloys
110
The corrosion potentials at high Zn content were stable within the duration of the
experiment and range around 780 mV. This value is well comparable to the literature [79] and
the data presented earlier on bulk samples of pure zinc (~760 mV, see p. 55).
As expected, a strong cathodic shift is observed at increasing Mg content within the first,
approximately 50 s of the experiment, which is attributed to the very active redox potential of
magnesium leading to rapid dissolution under these conditions [50]. Remarkably, this cathodic
shift is prolonged over a composition range between ~90 to ~70 at. % zinc, causing the system
to reach a stable potential value significantly later than 50 s. This delay shows a maximum
around 80 at. % Zn. It is probable that this behavior originates from an inhibition of the initial,
preferential dissolution of Mg by either compensatory dissolution of zinc or a generally
decreased corrosion current density. To further illustrate this effect, two-dimensional cuts at
fixed times were extracted from the datasets and are shown in the following figure:
50 60 70 80 90 100-900
-875
-850
-825
-800
-775
-750
OCP at 200 s series 1 OCP at 200 s series 2
OCP at 1000 s series 1 OCP at 1000 s series 2
Pote
ntia
l / m
VSH
E
Zn content / at. %
Figure 8.8:
Corrosion potentials of a
Zn-Mg material library as a
function of the composition
(at. % Zn given, rest Mg) at
different contact times
extracted from Figure 8.7.
It is clearly evident that the corrosion potential after 200 s of electrolyte contact exhibits a
minimum around 82 at. % in both replicates. This effective difference to the final potentials
measured at 1000 s vanishes for both high (> 90 at. %) and low (< 70 at. %) contents of zinc.
Local maxima are observed in the measurement at 200 s, reflecting peaks in the potential
transient as seen in Figure 8.7. The origin of this “overshoot” of the potential is purely
speculative and may originate from a temporary blocking effect of precipitates due to strong
magnesium dissolution expected during the anodic shift of the corrosion potential during the
Chapter 8: Corrosion of Zn-Mg alloys
111
initial seconds of the experiments. This effect can unfortunately not be clarified due to the
absence of magnesium detection.
8.2.1.2 Zinc dissolution monitoring Complementary zinc analysis, however, does provide information on the origin of the
prolonged cathodic potential region around 82 at. %. Because the preferential dissolution of
Mg in the respective region is assumed to proceed at lower rates, a decreased zinc signal would
immediately indicate lower total material dissolution. The measured zinc concentrations are
shown in Figure 8.9.
Figure 8.9: 3D illustration of the zinc concentrations detected downstream during an automated 1000 s
OCP scan on a Zn-Mg material library in aerated 0.1 M NaCl under electrolyte flow. Two different
perspectives are shown for clarification.
The shape of the dissolution profiles and the concentration range is well comparable to the
results obtained on bulk zinc under identical conditions (see section 6.1.1, pp. 57 ). However, at
very high zinc contents (> 90 at. %), the consistency of the data is relatively low compared to
the results in the following regions of increasing Mg. The partially large deviations observed
between neighboring dissolution profiles in the high-Zn region are not taken as reliable
differences in the dissolution behavior. Instead, the surface roughness, previously shown to be
very large in this region (Figure 8.2, p. 103), is assumed to cause irreproducible wetting that
immediately affects the dissolution rate, while the area independent corrosion potential remains
stable.
The most remarkable feature of the graphs shown in Figure 8.9 is the existence of a
minimum in dissolution rate that coincides with the maximal prolongation of the cathodic
corrosion potential shown in the two former figures. This is taken as a strong indication of a
reduced total dissolution rate of the material causing both reduced zinc liberation and a delay of
Chapter 8: Corrosion of Zn-Mg alloys
112
the preferential dissolution of magnesium. Even though the overall material loss covering zinc
and magnesium is not experimentally accessible with the setup presented, it can be roughly
approximated by including the film stochiometry into the dissolution profiles. The assumption
is that the homogeneity of the film causes the dissolution process to liberate zinc and
magnesium equal to the composition of the alloy if the experiment duration exceeds the region
of preferential dissolution of one particular component. The measured zinc concentration
therefore transform into a total dissolution rate through a division by the molar fraction of zinc
as shown in Figure 8.10 to compensate for an imposed linear decrease in zinc concentrations
that originates solely from reduced zinc content.
60 70 80 90 1000.0
0.5
1.0
1.5
0
10
20
30
40
50
60
[Zn2+
] t=10
00s Χ
-1 Zn /
μmol
l-1
Zn content / at. %
i Dis
s / μA
cm
-2
Figure 8.10: Dissolution transients from Figure 8.9 normalized to the molar fraction of zinc (left) and 2-D
cut at 1000 s with corresponding dissolution current densities (right).
As seen from the figure, decreasing zinc contents in the film lead to an up scaling of the
dissolution profiles especially evident at high magnesium fractions when comparing the graph
to the original dataset from Figure 8.9. The minimum in dissolution though is unaffected and
still falls in the region around 80 at. % zinc. The increasing trend towards the Mg-rich side
indicates dissolution rates that will most probably exceed the values observed at pure zinc.
In order to compare immersive and climate tests, it is important to consider the
observations made to bulk samples subject to climate chamber conditions (80 % RH, 20 °C, 28
days exposure after contamination with chloride) as reported by Prosek et al. [79]. The
following figure shows the weight loss as a function of the magnesium content after climate
corrosion tests:
Chapter 8: Corrosion of Zn-Mg alloys
113
Figure 8.11:
Weight loss of different cast model alloys (Mg
content in wt. %, rest Zn) subject to 28 days of
climate test after contamination with NaCl.
From [79].
Surprisingly, the weight loss minimum at 8 wt. % (19 at. %) Mg is in very good agreement to
the data presented in this study despite the large differences in sample preparation and
corrosion test methodology. The magnitude of the difference in weight loss between Zn and
ZnMg8 as shown in Figure 8.11 is large compared to the SFC based screening experiments.
This is most likely the consequence of the different testing procedures, which magnifies the
beneficial aspects of magnesium in case of climate tests (due to carbonate and hydroxide
buffering, see section 2.3.4, pp. 21).
Nevertheless, it is remarkable that short screening experiments with the SFC (1000 s) on
thermally evaporated Zn-Mg material libraries match long term climate tests (28 days) on cast
alloys to that extend. Furthermore, these results encourage investigations on technical
Zn80Mg20 (at. %) coatings to evaluate the performance as corrosion protection material.
8.2.2 Borate buffer pH 7.4 For pure zinc, it has been shown in a former chapter (6.2, pp. 66) that the existence of a
buffer system alters the corrosion mechanism significantly. Investigations at a steady pH value
are of high interest for Zn-Mg alloys as well, since Mg exhibits a different stability window
(stable at higher pH values than zinc, [4]) and is assumed to affect the surface pH during
corrosion processes [77, 96]. On the basis of the pH series presented earlier for zinc (Figure
6.12, p. 68), a borate buffer (0.1 M) of pH 7.4 was selected for experiments on Zn-Mg. This
specific pH value was chosen because of the comparably aggressive nature of the solution (high
dissolution rates) that nevertheless allows the characterization of surface films over a large
potential window due to kinetic passivity and the absence of pitting.
The experimental series performed consists of an OCP measurement for 600 s (the OCP
stabilizes quickly in this medium, p. 67) and an anodic sweep (5 mV s-1) starting at the OCP
with a current density of 650 µA cm-2 as stop condition. Figure 8.12 shows the recorded
corrosion potentials as a 3D illustration in a concentration range from 96.2 to 38.3 at. % Zn.
Chapter 8: Corrosion of Zn-Mg alloys
114
The extended range towards higher magnesium contents as compared to the experiments in
0.1 M NaCl solution is possible by the less active nature of Mg in near neutral, chloride free
environments.
8.2.2.1 Open circuit potentials
Figure 8.12:
3 D plot of the open circuit
potential measurements
(600 s) in borate buffer
(0.1 M) of pH 7.4 under
continuous electrolyte flow
(15.6 µl min-1) as a function
of zinc content.
It can be seen that the corrosion potentials are roughly 100 mV higher than in the
complementary experiment in NaCl solution. Furthermore, a strong cathodic shift of the initial
potentials is observed similarly, which is assumed to originate from preferential Mg dissolution.
However, a prolonged region of cathodic potentials as previously seen for NaCl solution in the
region between 70 and 90 at. % zinc is not found. Instead, the potentials recorded are very
stable and exhibit a high consistency along the composition axis.
In order to clarify the difference between the intermediate (30 s) and final (600 s) corrosion
potentials apparent from Figure 8.12, a two dimensional cut along the time axis was performed
at the respective times as shown in the following.
Chapter 8: Corrosion of Zn-Mg alloys
115
30 40 50 60 70 80 90 100-750
-735
-720
-705
-690
-675
-660
70 80
-705
-700
-695
-690
OCP at 30 s OCP at 600 s
Pote
ntia
l / m
VSH
E
Zn content / at. %
Magnified region(t=600 s) 65 - 86 at.%
Figure 8.13:
Two dimensional cut through
Figure 8.12 at t=30 s and
t=600 s. The inset magnifies
the local minimum observed
after 600 s in a region between
65 and 85 at. % zinc.
While the initial potentials at 30 s decrease with increasing Mg content until reaching a
stable value around -740 mV, the final values show a strongly non-linear behavior with a local
minimum around 80 at. % zinc. The extraordinary behavior of this composition was previously
observed in NaCl solution, even though the potential differences in borate buffer are of small
magnitude (several mV). This observation can therefore not be taken as direct evidence for a
specific surface process, but it is nevertheless remarkable that the region around 80 at. % zinc
behaves extraordinary in all experiments presented so far on Zn-Mg material libraries. It is to
note that the XPS results shown previously (Figure 8.6, p. 108) demonstrate an increased
thickness of the native oxides formed at the respective composition, which allows assuming
that the local potential minimum indicates a more active potential preserved over a longer time,
possibly due to a decreased barrier effect of the surface film formed.
8.2.2.2 Potential sweep experiments This question can be addressed by the potential sweep experiments performed subsequent
to the OCP measurement. The following graph summarizes the results in a 3D illustration:
Chapter 8: Corrosion of Zn-Mg alloys
116
Figure 8.14: Anodic sweep experiments (5 mV s-1) starting from the previously recorded OCP (600 s) with
dynamic end points at 650 µA cm-2 in borate buffer (0.1 M) of pH 7.4 under constant electrolyte flow
(15.6 µl min-1). The dataset is shown from two perspectives for clarification.
The passive current density increases significantly around 80 at. %, being further indication
of a decreased barrier effect of the oxides formed during anodization. Besides that, a striking
consistency along the composition gradient is observed that allows separating the dataset into
composition regions of continuous trends.
-0.5 0.0 0.5 1.0 1.5 2.00
100
200
300
400
500
600
700
i / μ
A c
m-2
E / VSHE
43.9
54.1
-0.5 0.0 0.5 1.0 1.5 2.00
100
200
300
400
500
600
700
0.0 0.5 1.0 1.5200
300
400
i / μ
A cm
-2
E / VSHE
i / μ
A c
m-2
E / VSHE
55.4
78.4
-0.5 0.0 0.5 1.0 1.5 2.00
100
200
300
400
500
600
700
-0.5 0.0 0.5 1.0 1.5
250
300
350
i / μ
A c
m-2
E / VSHE
i / μ
A cm
-2
E / VSHE
87.6
79.3
-0.5 0.0 0.5 1.0 1.5 2.0 2.50
100
200
300
400
500
600
700
-0.5 0.0 0.5
200
300
i / μ
A cm
-2
E / VSHE
88.7
96.3
96.3
i / μ
A c
m-2
E / VSHE
88.7
Figure 8.15: Regions of continuous trends extracted from Figure 8.14. The numbers indicate the zinc
content in atomic %.
Chapter 8: Corrosion of Zn-Mg alloys
117
The first composition range between 96.3 and 88.7 at. % is characterized by a strong increase of the
initial peak in current density. An initial barrier formation in the highly dynamic equilibrium
between oxide formation and dissolution (section 6.2.2, pp. 68, especially pH 7.1) is assumed to
cause the observed behavior. Because of the strong change in surface topography in the
respective composition region, it is not possible to correlate the behavior observed to the effect
of roughness or increasing magnesium exclusively. However, it is to note that the passive
current density is not lowered with increasing magnesium content even though the roughness
(and therefore the real area of the electrode) decreases strongly. This is not unexpected because
the possibility to use the SFC on the sample surface implies that the rough, sponge-like
structure is not completely wetted and soaked with electrolyte, which would instantly drain
massive electrolyte volumes from the cell.
Another noticeable feature in the first composition range is the transition from an
exponential increase in current density starting around 2.5 VSHE at 96.3 at. % towards a steeper
increase with earlier onset with increasing magnesium content. While in case of high zinc
contents the increase in current density is assumed to reflect film breakdown, the steep increase
around 1.7 VSHE is attributed to oxygen evolution most probably enabled by the existence of
intermetallics as shown during anodization of Al-Cu material libraries in another study [122].
This oxygen evolution reaction remains steady for all further measurements of increased Mg
content as evident from all other graphs included in Figure 8.15. This separation between film
breakdown and oxygen evolution will be later clarified by the results of downstream zinc
detection.
The second composition range from 87.6 to 79.3 at. % zinc is dominated by a steady increase in
passive current density most probably originating from a decreased barrier effect of the surface
film formed. As shown on pure zinc (Figure 6.18, p. 75), it has been confirmed by XPS that the
surface film is of oxidic nature with no hydroxide signal within the detection limit. This
observation in conjunction with the active OCP (local minimum) in this particular region is
surprising given the superior corrosion resistance in unbuffered NaCl solution. It suggests that
the active nature of magnesium is pronounced at these compositions which is apparently
beneficial in neutral, unbuffered solutions, but of inverse effect in borate buffer of pH 7.4.
The third composition range from 78.4 to 55.4 at. % zinc shows a decrease of the passive current
density while the current density during the initial approximately 800 mV of anodic polarization
remains constant. The latter appears to consist of two broad peaks, similar to the peak shape
observed on Zn-Mg intermetallics in NaOH by Hausbrand et. al [29] (also see [50], p. 46). The
exact electrochemical processes at this stage are not clarified. However, a major difference in
Chapter 8: Corrosion of Zn-Mg alloys
118
current density during anodic progression of the potential is observed decreasing from
~320 µA cm-2 at 78.4 at. % Zn to ~210 µA cm-2 at 55.4 at. % Zn. This decrease may reflect an
increased barrier effect of MgO in the film as suspected by Prosek et. al [79] and supports a
direct contribution of magnesium to the film properties rather than an indirect stabilization of
zinc precipitates.
The final region starting from 54 at. % zinc shows an increase of both the peak and plateau
current density with a strong additional peak evolving around 0 VSHE. Since the oxide layer is
dynamic at all times due to a continuous dissolution by the electrolyte, a selective oxidation of
either zinc or magnesium can not be confined to a defined potential because both metals exist
in an oxidized state at the outer layer. Experiments performed on 45 at. % zinc with varying
OCP times prior to the sweep showed the peak in question to be more pronounced with
shorter periods of free corrosion. Since the peak integral appears to grow with increasing
magnesium content in the alloy and magnesium tends to leech from the surface (therefore
explaining higher peak integrals with shorter OCP periods), the origin of the peak is assumed in
a process where metallic magnesium is involved, even though an immediate association with a
distinct electrochemical process can not be given.
Chapter 8: Corrosion of Zn-Mg alloys
119
8.2.2.3 Zinc dissolution monitoring
The dataset recorded parallel to the OCP-anodic sweep couple is shown in Figure 8.16. A
highly consistent trend towards lower zinc concentrations is observed with increasing
magnesium content for both the OCP dissolution as well as the dissolution during the anodic
sweep. Close examination of the final region of the zinc dissolution profiles around 96 at. %
Zn reveals a sharp peak at the end of the anodic sweep that originates from film breakdown.
The transition to the OER with earlier onset around 92 at. % (Figure 8.15) causes this peak to
vanish.
The initial region around 160 s, that is immediately after electrolyte contact when
subtracting the delay time (156 s), is characterized by a steady increase in zinc concentration for
zinc contents above approximately 85 at. %, but exhibits a small plateau as the magnesium
content is further increased. To illustrate this effect, the inset of Figure 8.16 magnifies the first
500 s of the dissolution profile for 91 and 72 at. % Zn. It can be seen that the initial rise of the
zinc concentration is comparable in both cases, but followed by a strong decrease of the slope
Figure 8.16:
3D plots of the zinc concentrations detected
during the OCP-anodic sweep couple in borate
buffer (0.1 M) of pH 7.4 under steady electrolyte
flow (15.6 µl min-1) as a function of zinc content
on a Zn-Mg material library. Two different
perspectives are shown with indication of the
measurement sequence on the time scale. The inset
shows the initial dissolution profile Zn91Mg9 and
Zn72Mg28 for the first 500 s of electrolyte contact.
Chapter 8: Corrosion of Zn-Mg alloys
120
in case of the higher magnesium content. This dissolution peak most probably originates from
surface film formation during the first seconds of electrolyte contact that inhibits further
dissolution. Selective removal of magnesium, therefore cathodic protection of zinc by
magnesium, is taken as another probable process, even though this would not account for the
existence of a peak.
While the generally decreasing trend of the dissolution profile with increasing magnesium
content is clearly demonstrated, the film stochiometry also needs to be taken into account
because Mg detection is not available. Two dimensional cuts at fixed times were taken from
Figure 8.16 showing the zinc concentration divided by the molar fraction of zinc as a function
of the zinc content. The first set corresponds to the OCP region (50-600 s) while the second
displays the increase in concentration during the potential sweep (750 and 1050 s) including the
final OCP values (600 s) for comparison. Please note that all times were corrected by the dead
time (156 s).
40 50 60 70 80 90 1000.0
0.4
0.8
1.2
1.6
0
40
80
120
i Diss
/ μA
cm
-2
[Zn2+
] χZn
-1/ μ
mol
l-1
Zn content (at. %)
600 s
200 s
50 s
linear fit 40-80 at. %
linear fit 80-97 at. %
40 50 60 70 80 90 100
1.2
1.6
2.0
2.4
2.8
3.2
80
120
160
200
240
i Dis
s / μA
cm
-2
[Zn2+
] χZn
-1/ μ
mol
l-1
Zn content (at. %)
1050 s
750 s
600 s
Figure 8.17: Zinc concentrations at given times corrected by td as a function of Zn content in the film
extracted from Figure 8.16. The dataset is separated into times during the OCP (50-600 s) and the anodic
sweep (750 and 1050 s). The right axis shows the corresponding dissolution current densites at a flow rate of
15.6 µl min-1.
An interesting observation is that the normalized dissolution rate quickly after electrolyte
contact (50 s) rises with increasing Mg content and levels around 80 at. % Zn, reflecting the
emergence of an initial peak. However, an inverse trend is observed for longer contact times,
while again reaching a steady dissolution rate. These results support the hypothesis of a barrier
formation (between 50 and 200 s) that reduces the increase of the dissolution rates as the
experiment proceeds. 80 at. % again constitutes an exceptional composition and appears to be
the onset composition (towards higher Mg contents) for the behavior observed.
Chapter 8: Corrosion of Zn-Mg alloys
121
The normalized concentrations measured during the potential sweeps indicate a higher
dissolution rate with increasing magnesium content at 750 s (approximately 0 VSHE), which
correlates to the generally increasing current density at the respective potential (Figure 8.15). At
1050 s, the anodic sweep progressed to approximately 1.55 VSHE, being the final region of the
passive range shortly before either film breakdown or the onset of the OER. Major differences
were observed in this area along the composition gradient, the most significant being the
maximum around 80 at. %. This behavior appears to be reflected by the dissolution rates since
the measurement curve at 1050 s in Figure 8.17 exhibits a local maximum around this
composition. The final increase of the normalized concentrations starting around 55 at % for
both 750 and 1050 s appears very steep and coincides with a high peak current density
recorded during potential sweeps. Remarkably, the dissolution rate in this region is independent
of the potential, evident from the identical dissolution current densities at 750 and 1050 s in
Figure 8.17. It is possible that the mixed oxides at the surface exhibit a composition at which
the dissolution rate at the interface is unaffected by the applied potential, a case reported by
Wagner on iron-oxide with the composition Fe2.67O4 [65]. However, a deeper investigation of
this effect would require exact knowledge about the electronic structure and crystal
composition of the respective oxides formed.
A composition of 80 at. % zinc is characterized by a low dissolution and corrosion potential
at the OCP, which is consistent with the data recorded in 0.1 M NaCl where Zn~80Mg~20
was found to exhibit prolonged cathodic corrosion potentials and low dissolution rates.
However, a high dissolution and passive current density during anodic sweeps was recorded for
this composition. It appears that the character of the oxide film as estimated from the passive
current density is not decisive for the dissolution under open circuit conditions. Moreover, a
difference in the oxides formed on the surface need to be assumed since precipitation is absent
in borate buffer of pH 7.4 as concluded from its purely oxidic nature (determined by XPS, see
p. 75) and the high solubility of both zinc- and magnesium hydroxide. To clarify the oxide
composition, XPS depth profiling after electrochemical treatment is performed in the following
section.
8.2.2.4 XPS Analysis XPS-depth profiling was performed on three different compositions each subject to 1000 s
OCP measurement and 100 s OCP with subsequent potential sweep to 500 mV anodic of the
corrosion potential at a scan rate of 5 mV s-1. The results are shown in Figure 8.18.
Chapter 8: Corrosion of Zn-Mg alloys
122
0 5 10 15 20 25 30 35 400
20
40
60
80
100
cont
ent (
at. %
)
Sputter depth / nmSiO2
Zn94Mg6 - 1000s OCP
Mg
O
Zn
0 5 10 15 20 25 30 35 400
20
40
60
80
100
cont
ent (
at. %
)
Sputter depth / nmSiO2
Zn94Mg6 - Sweep
Mg
O
Zn
0 5 10 15 20 25 30 35 400
20
40
60
80
100
cont
ent (
at. %
)
Sputter depth / nmSiO2
Zn81Mg19 - 1000s OCP
Mg
O
Zn
0 5 10 15 20 25 30 35 400
20
40
60
80
100
cont
ent (
at. %
)Sputter depth / nmSiO2
Zn81Mg19 - Sweep
Mg
O
Zn
0 5 10 15 20 25 30 35 400
20
40
60
80
100
cont
ent (
at. %
)
Sputter depth / nmSiO2
Zn63Mg37 - 1000s OCP
Mg
O
Zn
0 5 10 15 20 25 30 35 400
20
40
60
80
100
cont
ent (
at. %
)
Sputter depth / nmSiO2
Zn63Mg37 - Sweep
Mg
O
Zn
Figure 8.18: XPS depth profiles of different compositions on the material library after electrochemical
treatment as indicated in each graph. Carbon signals were only observed prior to the first sputter step and are not
included.
The comparison between 1000 s OCP measurement and potential sweeps yields a slight
increase in oxide thickness as a consequence of applied anodic potentials. In contrast, an
increase in magnesium content significantly increase the oxygen signal in the depth profiles for
both OCP and potential sweep experiments, demonstrating that magnesium enhances the
formation of mixed oxides on the surface. Of particular interest is that a selective leeching of a
single metal can not be observed. This effect is attributed to the instability of both oxides at a
pH value of 7.4, dissolving at equal and diffusion limited rates. The electrochemical behavior
described in the former section is therefore mainly determined by the electrical properties of
the oxidic material on the surface and the total extends of oxide formation. It is to note that the
Chapter 8: Corrosion of Zn-Mg alloys
123
thickness of the oxides formed during electrochemical treatment can not be exactly determined,
because comparably high amounts of oxygen are found in the native state of these materials as
shown previously (Figure 8.6, p. 108). However, it is apparent that thick layers of oxides form
on the surface with considerably constant stochiometry. Proton diffusion as rate determining
process for material dissolution therefore applies for Zn-Mg mixed oxides as well under the
conditions presented. This is supported by the considerably stable normalized dissolution
current density shown in Figure 8.17 at the OCP, with the increased rates at high Zn content
being a consequence of a significant surface roughness.
8.2.3 Summary of the results The corrosion behavior of thermally evaporated Zn-Mg material libraries can be effectively
investigated with the microelectrochemical system presented. The corrosion potentials and
dissolution rates in both NaCl solution and borate buffer for zinc rich compositions are
comparable to pure zinc samples presented in chapter 6. However, the effect of magnesium on
the corrosion behavior differs largely between unbuffered NaCl solution and borate buffer of
pH 7.4.
In 0.1 M NaCl solution, a strong decrease of the dissolution current density at the OCP was
observed up to magnesium additions of 20 at. %, that coincides with a prolonged cathodic
corrosion potential after electrolyte contact. Further increase of χMg increases the corrosion rate
and reduces the duration of the initial cathodic corrosion potential, with only minor influence
on the potentials established after 1000 s of electrolyte contact. These findings are in good
agreement with climate test reported by other authors, which is surprising given the large
differences in methodology, sample preparation and time consumption. The results presented
demonstrate that material optimization procedures can be strongly supported by the integrated
microelectrochemical system presented and encourage the use material libraries for
combinatorial investigations. The most beneficial composition for the corrosion in aerated
NaCl solution was shown to range around 20 at. % magnesium.
In borate buffered solution however, fundamentally different results were obtained. The
dissolution rates at the OCP in borate buffer of pH 7.4 are well comparable to the bulk Zn
counterpart, with deviations only in the zinc rich region that exhibits an intrinsically high
surface roughness. The oxides formed are several tens of nm thick and do not show large
alteration in composition during depth profiling. However, the electrochemical behavior during
anodic potential sweeps shows an impact of the magnesium content, being strongly non linear
along the composition axis. The electrical properties of the mixed oxides formed on the surface
are taken as the most plausible cause for the observed differences.
Chapter 9: Comprehensive discussion
124
9 Comprehensive discussion The majority of the experiments presented in this work are based on a novel
microelectrochemical setup that has been developed within the scope of this study. The
primary experimental challenge was the integration of a steady electrolyte flow into a capillary
microcell with a tip diameter around 200 µm and the implementation of downstream UV-VIS
analytics. Due to the novelty of the measurement procedure, a comprehensive system
characterization has been the foremost aim to prove the validity of the data obtained. During
these efforts, it has been shown on the example of oxide formation on valve metals and
platinum that the validity and reproducibility of microelectrochemical data is high and well
comparable to literature values. A comparison to a classical channel electrode has been
achieved by correlating the transport limited current density of the oxygen reduction reaction
on platinum with the volume flow rate. This investigation clearly demonstrates that the
transport limit is a function of the cube root of the volume flow, a dependency well known for
classical channel electrodes.
Downstream analytics have been successfully integrated using Zincon as a complexing agent
and a UV-VIS flow cell. The detection limit was shown to range around 10-7 mol l-1 and the
dead time between substrate and detector was about 156 s. The successful coupling of micro
electrochemistry and downstream detection was demonstrated on copper, where the
electrochemically released amount of metal ions was quantitatively detected in the
spectroscopic system. This correlation proved the calibration procedure and measurement
sequence to be valid. The three initially formulated aims of (i) a high reproducibility and
comparability of data, (ii) a miniaturized and fully automated setup and (iii) a high sensitivity
and reliability of downstream detection were achieved.
The fundamental investigation of pure zinc was performed subsequent to the system
characterization with the aim to investigate the impact of different parameters on zinc
corrosion with both electrochemical and spectroscopic data. It was shown that an increase of
the chloride content from 0.01 to 1 M gradually increases the corrosion current density under
constant electrolyte flow, even though high amounts of chloride increase the equilibration time
of the system. It was further shown that the corrosion potentials shift cathodically, which was
attributed to a shift in the reversible potential of zinc dissolution because of nearly identical
Tafel slopes measured. Furthermore, a variation of the volume flow rate of the electrolyte
revealed an increased zinc dissolution profile with increasing electrolyte flow, originating from
an enhanced removal of precipitates from the surface. This was supported by the fact that the
Chapter 9: Comprehensive discussion
125
measured corrosion current densities lie well below the theoretically possible oxygen reduction
rates, indicating a strong hindrance of oxygen transport by surface films formed.
One of the key questions (I, see p. 24) on pure zinc was to evaluate the possibility to
accurately determine the corrosion current density from the dissolution profile. This was
confirmed by galvanostatic experiments, showing a very good correlation between dissolution
current as calculated from downstream zinc concentrations and imposed current. This finding
is of particular importance since it provides a method of measuring corrosion current densities
without driving the corroding system from its steady state. Potentiodynamic sweep experiments
(II) in contrast did not yield comparable corrosion current densities, but instead revealed a
linear variation of the results depending on the square root of the scan rate. This indication of a
diffusion controlled processes was interpreted on the basis of a local saturation of the
electrolyte with zinc as a consequence of the anodic dissolution, causing film formation and a
deviation from the steady state due to the time dependence of the corresponding processes.
The electrochemical and spectroscopic data presented provide a comprehensive picture of the
corrosion process of zinc in NaCl solution, being mainly determined by precipitate and surface
film formation and therefore susceptible to parameters with an immediate effect thereon.
Because the surface pH is of uttermost importance in this mechanism and affected by both
anodic and cathodic reactions, the effect of a buffer system was thoroughly studied.
There it was found that the corrosion mechanism changes fundamentally in borate buffered
solutions. The dissolution process in this medium is governed by proton diffusion and the
resulting decomposition of ZnO formed on the surface. The dissolution with hindrance by
corrosion products observed in NaCl solution therefore changes to dissolution through an
oxidic film, which was confirmed by surface analysis techniques. The corrosion current
densities are linearly dependent on the concentration of protons and proton carriers, and
comparably high in neutral borate buffer (0.1 M) under electrolyte flow. In contrast, the
corrosion potentials behave strongly non linear with passive values at pH 7.4 and above and
active values at lower pH. The strong cathodic shift of the corrosion potential at higher pH
values is taken as an indication that a closed oxide layer is formed, with a thickness depending
on the relation between film formation and dissolution. The presence of active sites and active
corrosion potentials accordingly, can be stimulated by the addition of sulfate anions, leading to
oscillations in the OCP at certain combinations of pH and sulfate concentration. While sulfate
is primarily regarded as a pitting anion, is has been shown that the steady state dissolution rate
is significantly increased by addition of these anions. The earlier onset for film breakdown is
therefore not the main effect, but the consequence of zinc complexation and solubility increase
caused by these species. It appears that the severe influence of sulfate ions and buffered
Chapter 9: Comprehensive discussion
126
electrolytes on zinc corrosion is often underestimated in the literature. The integrated zinc
detection presented however provides a very fundamental property that largely aids the
evaluation of electrochemical data.
In order to verify the dissolution mechanism of ZnO concluded from the results in buffered
solutions, polycrystalline, RF-sputtered ZnO:Al thin film were investigated with respect to the
chemical and electrochemical dissolution mechanism. It was accurately confirmed (I) that
proton transport is the rate determining process since the dissolution rate of ZnO is a linear
function of the buffer capacity at constant pH. Furthermore, this proton induced etching
initiates preferably at grain boundaries, causing a texturing of the surface along the grain
boundaries that vanishes at high dissolution rates. This chemically induced etching of ZnO was
shown to be very low in unbuffered NaCl solutions, clearly demonstrating that this process is
not decisive for the corrosion current densities of zinc in these electrolytes (II).
Due to the high conductivity of ZnO:Al, it was possible to investigate the electrochemical
decomposition processes taking place at high anodic potentials. These efforts were strongly
supported by the dissolution data of zinc, which allowed distinguishing between the two
competing oxidation processes of either water or lattice oxygen. It was shown (III) that pH
buffers significantly decrease the faradaic efficiency for dissolution from around 88 % in
unbuffered NaCl solutions to 61 % in 0.1 M acetate buffers of pH 6.5 and 7.0. This difference
illustrates that both water splitting and lattice decomposition trigger ZnO dissolution, while the
former can be significantly reduced by stabilizing the surface pH. It was concluded that protons
generated on the surface attack the lattice surprisingly effective, causing the stability window of
water to indirectly determine the stability of surface oxides prone to proton etching. The
surface texture obtained after electrochemical decomposition of polycrystalline ZnO:Al thin
films showed a unique degree of selectivity towards the grain boundaries, clearly demonstrating
that both water splitting and lattice decomposition proceeds at these sites exclusively. The
importance of the crystalline structure and phase composition of oxidic films is strongly
emphasized. Furthermore, these findings offer a novel tool for the modification of the optical
properties of ZnO:Al for solar cell applications.
The final aim of this study was to apply the new methodology on laterally graded Zn-Mg
material libraries and perform high throughput screening experiments with an exceptionally
high information depth, covering both electrochemical and dissolution behavior (I). This
application takes advantage of all features of the system presented as it combines high
throughput experimentation, local confinement and parallel electrochemical and spectroscopic
data acquisition. For sample preparation, a thermal PVD unit was modified to allow co-
deposition of a variety of metals onto large substrates (~10 cm length), and a mathematical
Chapter 9: Comprehensive discussion
127
deposition model was developed. An element mapping procedure was presented based on this
model to allow a precise and automated transformation of the measurement position into an
alloy composition. The Zn-Mg material libraries produced showed a complex crystal growth on
the surface and MgZn2 as dominant intermetallic, as shown by XRD, SEM and scanning AES
measurements. The electrochemical screening experiments revealed a strong impact of the
magnesium content on the dissolution behavior and corrosion potentials on 0.1 M NaCl
solution. The initial cathodic shift of the corrosion potential as a consequence of the active
redox potential of magnesium was prolonged at compositions from 90 to 70 at. % Zn, with
maximum duration around 80 at. %. The alloy dissolution was found to be significantly
lowered in this region, suggesting an increased corrosion resistance (II). These results were
found to be in surprising accordance to a recent study on bulk materials in climate tests by
other authors, and demonstrate the feasibility to utilize the complex setup presented for
material screening processes. The use of a borate buffer (III) however altered the results
significantly. The data is in good agreement with the previous investigations on Zn and ZnO,
demonstrating a change in the corrosion mechanism to chemically controlled dissolution of
thick oxidic surface layers. While XPS surface analysis revealed an oxide composition reflecting
the Zn/Mg ratio in the alloy, the electrochemical properties of the respective layers differed
strongly non linear along the composition axis. It was found that 4 at. % Mg is sufficient to
trigger oxygen evolution at approximately 1.5 VSHE independent of a further increase of the
magnesium content, while compositions with lower additions of Mg showed film breakdown at
more anodic potentials. Interestingly, a maximum in the plateau current density during
potential sweeps was observed at a composition around 20 at. % Mg, indicating low insulating
properties of the surface layer formed. The beneficial effect of magnesium is therefore strongly
dependent on the electrolyte system used, which further emphasizes the need to include the
effect of different media into corrosion testing procedures.
The scanning flow cell system presented may significantly contribute to the large
experimental demands resulting from this approach, as the high throughput capabilities and the
validity of the obtained data has been repeatedly confirmed within this study. It further allows
monitoring the zinc dissolution as a fundamental parameter and complementary analysis
technique parallel to electrochemical investigations, which has been shown to strongly aid the
interpretation of electrochemical data. The applicability of microelectrochemical systems with
online dissolution monitoring has been proven for Zn, ZnO and Zn-Mg alloys, and the
comparative data analysis conducted provided valuable information on the corrosion
mechanism of these materials in various electrolyte systems.
Chapter 10: Outlook
128
10 Outlook The technical developments achieved within this work constitute a solid basis for further
investigations. It would be valuable to thoroughly study the flow profile in the tip and optimize
the transport characteristics, possibly allowing to study electrochemical reactions involving
dissolved gasses. A detailed comparison to the rotating disc electrode would therefore be of
high relevance.
Furthermore, an extensive parameter screening on zinc with focus on the electrolyte
composition could largely contribute to the understanding of environmental corrosion
processes, as online dissolution monitoring and surface analysis techniques can be easily
conducted. It is to be expected that a combination of electrolyte constituents causes a different
corrosion behavior than estimated from combining the singular impact of each substance. An
example would be the coexistence of aggressive (e.g. Cl-, SO42-) and passivating anions (e.g.
CO32-) very commonly encountered in environmental conditions. Furthermore, a detailed
characterization of precipitates formed under various conditions would improve the
understanding of this highly complex process which is of uttermost importance for zinc
corrosion as repeatedly demonstrated in this study.
As a result of the combinatorial corrosion testing performed on Zn-Mg alloys, the most
promising composition for corrosion protection ranged around 80 at. % Mg. It would be
consequent to expose model alloys of the respective composition to a variety of technical
testing conditions, and to perform a comprehensive investigation of the effect of the electrolyte
composition on the corrosion behavior. This possibly enables to translate the scientific results
presented into technical coatings with broad profit in a variety of applications. These
investigations would furthermore significantly profit from additional analysis techniques of the
electrolyte downstream, covering both zinc and magnesium for alloy testing or multi element
analysis (e.g. ICE-OES) for a much broader range of possible investigations.
Chapter 11: Bibliography
129
11 Bibliography [1] D.A. Jones, Principles and prevention of corrosion, 2nd ed., Prentice-Hall inc., New York, 1996.
[2] X.G. Zhang, Corrosion and Electrochemistry of Zinc, Springer, New York, 1996.
[3] A.R. Marder, The metallurgy of zinc-coated steel, Progress in Materials Science, 45 (2000) 191-271.
[4] M. Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solutions, Pergamon, New York, 1966.
[5] M. Gmytryk, J. Sedzimir, Corrosion of Zn in Deaerated Sulphate Solutions at Different pH Values, Corrosion Science, 7 (1967) 683-695.
[6] C. Cachet, F. Ganne, S. Joiret, G. Maurin, J. Petitjean, V. Vivier, R. Wiart, EIS investigation of zinc dissolution in aerated sulphate medium. Part II: Zinc coatings, Electrochimica Acta, 47 (2002) 3409-3422.
[7] B.E. Conway, D.C.W. Kannangara, Zinc Oxidation and Redeposition Processes in Aqueous Alkali and Carbonate Solutions .2. Distinction between Dissolution and Oxide Film Formation Processes, Journal of the Electrochemical Society, 134 (1987) 906-918.
[8] Z. Zembura, L. Burzynska, Corrosion of Zinc in Deaerated 0.1 M NaCl in pH Range from 1.6 to 13.3, Corrosion Science, 17 (1977) 871-878.
[9] E. Tada, K. Sugawara, H. Kaneko, Distribution of pH during galvanic corrosion of a Zn/steel couple, Electrochimica Acta, 49 (2004) 1019-1026.
[10] M. Maja, N. Penazzi, R. Fratesi, G. Roventi, Zinc Electro-Crystallization from Impurity-Containing Sulfate Baths, Journal of the Electrochemical Society, 129 (1982) 2695-2700.
[11] V.S. Muralidharan, K.S. Rajagopalan, Kinetics and Mechanism of Corrosion of Zinc in Sodium-Hydroxide Solutions by Steady-State and Transient Methods, Journal of Electroanalytical Chemistry, 94 (1978) 21-36.
[12] N.A. Hampson, G.A. Herdman, R. Taylor, Some Kinetic and Thermodynamic Studies of the System Zn/Zn(II),OH-, Journal of Electroanalytical Chemistry, 25 (1970) 9-18.
[13] J.O.M. Bockris, Z. Nagy, A. Damjanov, Deposition and Dissolution of Zinc in Alkaline Solutions, Journal of the Electrochemical Society, 119 (1972) 285-295.
[14] L.M. Baugh, Corrosion and Polarization Characteristics of Zinc in Neutral-Acid Media .1. Pure Zinc in Solutions of Various Sodium-Salts, Electrochimica Acta, 24 (1979) 657-667.
[15] C. Cachet, F. Ganne, G. Maurin, J. Petitjean, V. Vivier, R. Wiart, EIS investigation of zinc dissolution in aerated sulfate medium. Part I: Bulk zinc, Electrochimica Acta, 47 (2001) 509-518.
[16] T. Hurlen, K.P. Fischer, Kinetics of Zn/Zn(II) Reactions in Acidified Solutions of Potassium-Chloride, Journal of Electroanalytical Chemistry, 61 (1975) 165-173.
[18] C.H. Hamann, A. Hamnett, W. Vielstrich, Electrochemistry (2 ed.), Wiley, 2007.
[19] I.A. Ammar, Prediction of pathways for the dissolution of iron, Corrosion Science, 17 (1977) 583-591.
Chapter 11: Bibliography
130
[20] J.W. Johnson, Y.C. Sun, W.J. James, Anodic Dissolution of Zn in Aqueous Salt Solutions, Corrosion Science, 11 (1971) 153-159.
[21] K.E. Heusler, Der Einfluss der Wasserstoffionenkonzentration auf das Elektrochemische Verhalten des Aktiven Eisens in Sauren Lösungen, Zeitschrift Fur Elektrochemie, 62 (1958) 582-587.
[22] J.O.M. Bockris, D. Drazic, A.R. Despic, The electrode kinetics of the deposition and dissolution of iron, Electrochimica Acta, 4 (1961) 325-361.
[23] T.S. Lee, Hydrogen Overpotential on Zinc Alloys in Alkaline-Solution, Journal of the Electrochemical Society, 122 (1975) 171-173.
[24] A.P. Yadav, A. Nishikata, T. Tsuru, Oxygen reduction mechanism on corroded zinc, Journal of Electroanalytical Chemistry, 585 (2005) 142-149.
[25] K.J.J. Mayrhofer, D. Strmcnik, B.B. Blizanac, V. Stamenkovic, M. Arenz, N.M. Markovic, Measurement of oxygen reduction activities via the rotating disc electrode method: From Pt model surfaces to carbon-supported high surface area catalysts, Electrochimica Acta, 53 (2008) 3181-3188.
[26] E. Yeager, Electrocatalysts for O2 Reduction, Electrochimica Acta, 29 (1984) 1527-1537.
[27] C. Deslouis, M. Duprat, C. Tulettournillon, The Cathodic Mass-Transport Process During Zinc Corrosion in Neutral Aerated Sodium-Sulfate Solutions, Journal of Electroanalytical Chemistry, 181 (1984) 119-136.
[28] H.S. Wroblowa, S.B. Qaderi, The Mechanism of Oxygen Reduction on Zinc, Journal of Electroanalytical Chemistry, 295 (1990) 153-161.
[29] R. Hausbrand, M. Stratmann, M. Rohwerder, The physical meaning of electrode potentials at metal surfaces and polymer/metal interfaces: Consequences for delamination, Journal of the Electrochemical Society, 155 (2008) C369-C379.
[30] K.G. Boto, L.F.G. Williams, Rotating-Disk Electrode Studies of Zinc Corrosion, Journal of Electroanalytical Chemistry, 77 (1977) 1-20.
[31] J.O.M. Bockris, A.K.N. Reddy, Modern Electrochemistry, 2nd ed., Kluwer Academic Publishers, New York, 2002.
[32] I. Katsounaros, J.C. Meier, S.O. Klemm, A.A. Topalov, P.U. Biedermann, M. Auinger, K.J.J. Mayrhofer, The Effective Surface pH during Reactions at the Solid-Liquid Interface, Electrochemistry Communications, 13 (2011) 634-637.
[33] H. Gerischer, Kinetik der Entladung einfacher und komplexer Zink-Ionen, Zeitschrift Fur Elektrochemie, 202 (1953) 302-317.
[34] H. Gerischer, Zum Entladungsmechanismus Von Komplex-Ionen, Zeitschrift Fur Elektrochemie, 57 (1953) 604-609.
[35] E.E. Abd El Aal, S.A. El Wanees, Galvanostatic study of the breakdown of Zn passivity by sulphate anions, Corrosion Science, 51 (2009) 1780-1788.
[36] E.E. Abd El Aal, Effect of Cl- anions on zinc passivity in borate solution, Corrosion Science, 42 (2000) 1-16.
[37] R. Grauer, W. Feitknecht, Thermodynamische Grundlagen der Zinkkorrosion in Carbonathaltigen Lösungen, Corrosion Science, 7 (1967) 629-644.
[38] M.C. Bernard, A. Hugotlegoff, N. Phillips, In-Situ Raman-Study of the Corrosion of Zinc-Coated Steel in the Presence of Chloride .1. Characterization and Stability of Zinc Corrosion Products, Journal of the Electrochemical Society, 142 (1995) 2162-2167.
Chapter 11: Bibliography
131
[39] C. Gabrielli, M. Keddam, F. Minouflet-Laurent, K. Ogle, H. Perrot, Investigation of zinc chromatation. I. Application of QCM-ICP coupling, Electrochimica Acta, 48 (2003) 965-976.
[40] T.E. Graedel, Corrosion Mechanisms for Zinc Exposed to the Atmosphere, Journal of the Electrochemical Society, 136 (1989) C193-C203.
[41] T. Prosek, D. Thierry, C. Taxen, J. Maixner, Effect of cations on corrosion of zinc and carbon steel covered with chloride deposits under atmospheric conditions, Corrosion Science, 49 (2007) 2676-2693.
[42] S. Morris, Electrochemistry at Semiconductor and Oxidized Metal Electrodes, Plenum Press, New York, 1980.
[43] J.A. Zuo, A. Erbe, Optical and electronic properties of native zinc oxide films on polycrystalline Zn, Physical Chemistry Chemical Physics, 12 11467-11476.
[44] P. Zu, Z.K. Tang, G.K.L. Wong, M. Kawasaki, A. Ohtomo, H. Koinuma, Y. Segawa, Ultraviolet spontaneous and stimulated emissions from ZnO microcrystallite thin films at room temperature, Solid State Communications, 103 (1997) 459-463.
[45] J. Kim, T. Kimura, T. Yamaguchi, Sintering of Zinc-Oxide Doped with Antimony Oxide and Bismuth Oxide, Journal of the American Ceramic Society, 72 (1989) 1390-1395.
[46] J. Hüpkes, B. Rech, S. Calnan, O. Kluth, U. Zastrow, H. Siekmann, M. Wuttig, Material study on reactively sputtered zinc oxide for thin film silicon solar cells, Thin Solid Films, 502 (2006) 286-291.
[47] J. Hüpkes, J. Müller, B. Rech, Texture Etched ZnO:Al for Silicon Thin Film Solar Cells, in: K.K. Ellmer, A.; Rech, B. (Ed.) Transparent Conductive Zinc Oxide: Basics and Applications in Thin Film Solar Cells, Springer, Berlin, 2008.
[48] C.A. Koval, J.N. Howard, Electron transfer at semiconductor electrode-liquid electrolyte interfaces, Chemical Reviews, 92 (1992) 411-433.
[49] M.A. Butler, D.S. Ginley, Prediction of Flatband Potentials at Semiconductor-Electrolyte Interfaces from Atomic Electronegativities, Journal of the Electrochemical Society, 125 (1978) 228-232.
[50] R. Hausbrand, Elektrochemische Untersuchungen zur Korrosionsstabilität von polymerbeschichtetem Zink-Magnesiumüberzug auf Stahlband, Ph. D. thesis, Ruhr-Universität Bochum, 2003
[51] S. Fletcher, The theory of electron transfer, Journal of Solid State Electrochemistry, 14 (2010) 705-739.
[52] B. Pettinger, H.R. Schöppel, T. Yokoyama, H. Gerischer, Tunnelling Processes at Highly Doped ZnO-Electrodes in Aqueous Electrolytes .2. Electron Exchange with Valence Band, Berichte Der Bunsen-Gesellschaft-Physical Chemistry Chemical Physics, 78 (1974) 1024-1030.
[53] S.R. Morrison, T. Freund, Chemical Role of Holes and Electrons in ZnO Photocatalysis, Journal of Chemical Physics, 47 (1967) 1543-1551.
[54] B. Pettinger, H.R. Schöppel, H. Gerischer, Tunnelling Processes at Highly Doped ZnO Electrodes in Contact with Aqueous Electrolytes .1. Electron Exchange with Conduction-Band, Berichte Der Bunsen-Gesellschaft-Physical Chemistry Chemical Physics, 78 (1974) 450-455.
[55] S.O. Klemm, S.E. Pust, A.W. Hassel, J. Hüpkes, K.J.J. Mayrhofer, Electrochemical texturing of Al-doped ZnO thin films for photovoltaic applications, Journal of Solid State Electrochemistry, (2011) 1-8.
[56] A.J. Bard, Photoelectrochemistry and Heterogeneous Photocatalysis at Semiconductors, Journal of Photochemistry, 10 (1979) 59-75.
Chapter 11: Bibliography
132
[57] J. Han, W. Qiu, W. Gao, Potential dissolution and photo-dissolution of ZnO thin films, Journal of Hazardous Materials, 178 (2010) 115-122.
[58] H.C. Gatos, Dangling Bonds in III-V Compounds, Journal of Applied Physics, 32 (1961) 1232-1234.
[59] A.N. Mariano, R.E. Hanneman, Crystallographic Polarity of ZnO Crystals, Journal of Applied Physics, 34 (1963) 384-388.
[60] H. Gerischer, N. Sorg, Chemical Dissolution of Zinc-Oxide Crystals in Aqueous-Electrolytes - an Analysis of the Kinetics, Electrochimica Acta, 37 (1992) 827-835.
[61] J.S. Wellings, A.P. Samantilleke, P. Warren, S.N. Heavens, I.M. Dharmadasa, Comparison of electrodeposited and sputtered intrinsic and aluminium-doped zinc oxide thin films, Semiconductor Science and Technology, 23 (2008) 7.
[62] H. Gerischer, N. Sorg, Chemical Dissolution of Oxides - Experiments with Sintered ZnO Pellets and ZnO Single-Crystals, Werkstoffe Und Korrosion-Materials and Corrosion, 42 (1991) 149-157.
[63] O. Fruhwirth, G.W. Herzog, J. Poulios, Dark Dissolution and Photodissolution of ZnO, Surface Technology, 24 (1985) 293-300.
[64] M. Valtiner, S. Borodin, G. Grundmeier, Stabilization and acidic dissolution mechanism of single-crystalline ZnO(0001) surfaces in electrolytes studied by in-situ AFM imaging and ex-situ LEED, Langmuir, 24 (2008) 5350-5358.
[65] C. Wagner, Models for Lattice Defects in Oxide Layers on Passivated Iron and Nickel, Berichte der Bunsengesellschaft für physikalische Chemie, 77 (1973) 1090-1097.
[66] M.M. Lohrengel, Thin Anodic Oxide Layers on Aluminum and Other Valve Metals - High-Field Regime, Materials Science & Engineering R-Reports, 11 (1993) 243-294.
[67] N. Valverde, C. Wagner, Considerations on the Kinetics and the Mechanism of the Dissolution of Metal Oxides in Acidic Solutions, Berichte der Bunsengesellschaft für physikalische Chemie, 80 (1976) 330-333.
[68] K.E. Heusler, The influence of electrolyte composition on the formation and dissolution of passivating films, Corrosion Science, 29 (1989) 131-147.
[69] T.P. Dirkse, Voltage decay at passivated zinc anodes, Journal of Applied Electrochemistry, 1 (1971) 27-33.
[70] M. Mokaddem, P. Volovitch, K. Ogle, The anodic dissolution of zinc and zinc alloys in alkaline solution. I. Oxide formation on electrogalvanized steel, Electrochimica Acta, 55 (2010) 7867-7875.
[71] E.E. Abd El Aal, Oxide film formation on zinc in borate solutions under open circuit, Corrosion Science, 50 (2008) 41-46.
[72] R.W. Powers, M.W. Breiter, Anodic Dissolution and Passivation of Zinc in Concentrated Potassium Hydroxide Solutions, Journal of the Electrochemical Society, 116 (1969) 719-729.
[73] Z.I. Ortiz, P. Diaz-Arista, Y. Meas, R. Ortega-Borges, G. Trejo, Characterization of the corrosion products of electrodeposited Zn, Zn-Co and Zn-Mn alloys coatings, Corrosion Science, 51 (2009) 2703-2715.
[74] M.A. Baker, W. Gissler, S. Klose, M. Trampert, F. Weber, Morphologies and corrosion properties of PVD Zn-Al coatings, Surface & Coatings Technology, 125 (2000) 207-211.
[75] G.K. Wolf, R. Munz, Corrosion studies of steels coated by means of PVD with Zn and Zn/Mn, Materialwissenschaft Und Werkstofftechnik, 37 (2006) 178-182.
Chapter 11: Bibliography
133
[76] M. Pushpavanam, S.R. Natarajan, K. Balakrishnan, L.R. Sharma, Corrosion Behavior of Electrodeposited Zinc-Nickel Alloys, Journal of Applied Electrochemistry, 21 (1991) 642-645.
[77] N.C. Hosking, M.A. Strom, P.H. Shipway, C.D. Rudd, Corrosion resistance of zinc-magnesium coated steel, Corrosion Science, 49 (2007) 3669-3695.
[78] R. Hausbrand, M. Stratmann, M. Rohwerder, Corrosion of zinc-magnesium coatings: Mechanism of paint delamination, Corrosion Science, 51 (2009) 2107-2114.
[79] T. Prosek, A. Nazarov, U. Bexell, D. Thierry, J. Serak, Corrosion mechanism of model zinc-magnesium alloys in atmospheric conditions, Corrosion Science, 50 (2008) 2216-2231.
[80] J. Swiatowska, P. Volovitch, K. Ogle, The anodic dissolution of Mg in NaCl and Na2SO4 electrolytes by atomic emission spectroelectrochemistry, Corrosion Science, 52 (2010) 2372-2378.
[81] E. Ghali, W. Dietzel, K.-U. Kainer, General and localized corrosion of magnesium alloys: A critical review, Journal of Materials Engineering and Performance, 13 (2004) 7-23.
[82] J.H. Greenblatt, A Mechanism for the Anodic Dissolution of Magnesium, Journal of the Electrochemical Society, 103 (1956) 539-543.
[83] G.L. Makar, J. Kruger, Corrosion Studies of Rapidly Solidified Magnesium Alloys, Journal of the Electrochemical Society, 137 (1990) 414-421.
[84] D.R. Sempolinski, W.D. Kingery, H.L. Tuller, Electronic Conductivity of Single Crystalline Magnesium-Oxide, Journal of the American Ceramic Society, 63 (1980) 669-675.
[85] L.N. Kantorovich, J.M. Holender, M.J. Gillan, The energetics and electronic structure of defective and irregular surfaces on MgO, Surface Science, 343 (1995) 221-239.
[86] A.R. Balkenende, A.A.M.B. Bogaerts, J.J. Scholtz, R.R.M. Tijburg, H.X. Willems, Thin MgO layers for effective hopping transport of electrons, Philips Journal of Research, 50 (1996) 365-373.
[87] C. Chen, S.J. Splinter, T. Do, N.S. McIntyre, Measurement of oxide film growth on Mg and Al surfaces over extended periods using XPS, Surface Science, 382 (1997) L652-L657.
[88] P. Bhattacharya, R.R. Das, R.S. Katiyar, Comparative study of Mg doped ZnO and multilayer ZnO/MgO thin films, Thin Solid Films, 447-448 (2004) 564-567.
[89] T.H. Kim, J.J. Park, S.H. Nam, H.S. Park, N.R. Cheong, J.K. Song, S.M. Park, Fabrication of Mg-doped ZnO thin films by laser ablation of Zn:Mg target, Applied Surface Science, 255 (2009) 5264-5266.
[90] X.H. Chen, J.Y. Kang, The structural properties of wurtzite and rocksalt MgxZn1-xO, Semiconductor Science and Technology, 23 (2008) 6.
[91] R. Lindström, L.G. Johansson, G.E. Thompson, P. Skeldon, J.E. Svensson, Corrosion of magnesium in humid air, Corrosion Science, 46 (2004) 1141-1158.
[92] S. Schürz, M. Fleischanderl, G.H. Luckeneder, K. Preis, T. Haunschmied, G. Mori, A.C. Kneissl, Corrosion behaviour of Zn-Al-Mg coated steel sheet in sodium chloride-containing environment, Corrosion Science, 51 (2009) 2355-2363.
[93] B. Schuhmacher, C. Schwerdt, U. Seyfert, O. Zimmer, Innovative steel strip coatings by means of PVD in a continuous pilot line: Process technology and coating development, Surface & Coatings Technology, 163 (2003) 703-709.
[94] S. Schürz, G.H. Luckeneder, M. Fleischanderl, P. Mack, H. Gsaller, A.C. Kneissl, G. Mori, Chemistry of corrosion products on Zn-Al-Mg alloy coated steel, Corrosion Science, 52 (2010) 3271-3279.
[95] T. Ishikawa, K. Matsumoto, A. Yasukawa, K. Kandori, T. Nakayama, T. Tsubota, Influence of metal ions on the formation of artificial zinc rusts, Corrosion Science, 46 (2004) 329-342.
Chapter 11: Bibliography
134
[96] P. Volovitch, C. Allely, K. Ogle, Understanding corrosion via corrosion product characterization: I. Case study of the role of Mg alloying in Zn-Mg coating on steel, Corrosion Science, 51 (2009) 1251-1262.
[97] D. de la Fuente, J.G. Castano, M. Morcillo, Long-term atmospheric corrosion of zinc, Corrosion Science, 49 (2007) 1420-1436.
[98] F. Thébault, B. Vuillemin, R. Oltra, K. Ogle, C. Allely, Investigation of self-healing mechanism on galvanized steels cut edges by coupling SVET and numerical modeling, Electrochimica Acta, 53 (2008) 5226-5234.
[99] K. Ogle, V. Baudu, L. Garrigues, X. Philippe, Localized electrochemical methods applied to cut edge corrosion, Journal of the Electrochemical Society, 147 (2000) 3654-3660.
[100] R. Hausbrand, M. Rohwerder, M. Stratmann, C. Schwerdt, B. Schuhmacher, G. Grundmeier, Model study on the corrosion of magnesium-containing zinc coat on steel sheet, Galvatech, (2001) 162-167.
[101] G. Binnig, C.F. Quate, C. Gerber, Atomic Force Microscope, Physical Review Letters, 56 (1986) 930-933.
[103] R. Shimizu, Quantitative-Analysis by Auger-Electron Spectroscopy, Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes & Review Papers, 22 (1983) 1631-1642.
[104] J.M. Hollande, W.L. Jolly, X-Ray Photoelectron Spectroscopy, Accounts of Chemical Research, 3 (1970) 193-&.
[105] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-ray Photoelectron Spectroscopy, Eden Prairie, 1995.
[107] K.C.A. Smith, C.W. Oatley, The Scanning Electron Microscope and Its Fields of Application, British Journal of Applied Physics, 6 (1955) 391-399.
[108] B.E. Warren, X-Ray diffraction, Dover Pubn Inc., Dover, 1991.
[109] M.G. Samant, M.F. Toney, G.L. Borges, L. Blum, O.R. Melroy, Grazing-Incidence X-Ray-Diffraction of Lead Monolayers at a Silver (111) and Gold (111) Electrode-Electrolyte Interface, Journal of Physical Chemistry, 92 (1988) 220-225.
[110] M. Berginski, J. Hüpkes, M. Schulte, G. Schöpe, H. Stiebig, B. Rech, M. Wuttig, The effect of front ZnO:Al surface texture and optical transparency on efficient light trapping in silicon thin-film solar cells, Journal of Applied Physics, 101 (2007) 074903-074911.
[111] S.O. Klemm, A.G. Martin, J. Lengsfeld, J.C. Schauer, B. Schuhmacher, A.W. Hassel, Theoretical simulation and preparation of binary and ternary combinatorial libraries by thermal PVD, Physica Status Solidi a-Applications and Materials Science, 207 (2010) 801-806.
[112] R. Zarnetta, D. Konig, C. Zamponi, A. Aghajani, J. Frenzel, G. Eggeler, A. Ludwig, R-phase formation in Ti39Ni45Cu16 shape memory thin films and bulk alloys discovered by combinatorial methods, Acta Materialia, 57 (2009) 4169-4177.
[113] A. Ludwig, J. Cao, J. Brugger, I. Takeuchi, MEMS tools for combinatorial materials processing and high-throughput characterization, Measurement Science & Technology, 16 (2005) 111-118.
Chapter 11: Bibliography
135
[114] A. Ludwig, R. Zarnetta, S. Hamann, A. Savan, S. Thienhaus, Development of multifunctional thin films using high-throughput experimentation methods, International Journal of Materials Research, 99 (2008) 1144-1149.
[115] M. Knudsen, The cosine law in the kinetic gas theory, Annalen Der Physik, 48 (1916) 1113-1121.
[116] M. Knudsen, The vaporisation of crystal surfaces, Annalen Der Physik, 52 (1917) 105-108.
[117] J.R. Shi, S.P. Lau, Z. Sun, X. Shi, B.K. Tay, H.S. Tan, Structural and electrical properties of copper thin films prepared by filtered cathodic vacuum arc technique, Surface & Coatings Technology, 138 (2001) 250-255.
[118] K. Stella, D. Burstel, S. Franzka, O. Posth, D. Diesing, Preparation and properties of thin amorphous tantalum films formed by small e-beam evaporators, Journal of Physics D-Applied Physics, 42 (2009) 9.
[119] T. Matsushima, Surface structural information carried by desorbing reaction products, Progress in Surface Science, 82 (2007) 435-477.
[120] X.Y. Liu, M.S. Daw, J.D. Kress, D.E. Hanson, V. Arunachalam, D.G. Coronell, C.L. Liu, A.F. Voter, Ion solid surface interactions in ionized copper physical vapor deposition, Thin Solid Films, 422 (2002) 141-149.
[121] D.E. Hanson, J.D. Kress, A.F. Voter, X.Y. Liu, Trapping and desorption of energetic Cu atoms on Cu(111) and (001) surfaces at grazing incidence, Physical Review B, 60 (1999) 11723-11729.
[122] S.O. Klemm, J.P. Kollender, A.W. Hassel, Combinatorial corrosion study of the passivation of aluminium copper alloys, Corrosion Science, 53 (2011) 1-6.
[123] Z.H. Cao, P.Y. Li, H.M. Lu, Y.L. Huang, X.K. Meng, Thickness and grain size dependent mechanical properties of Cu films studied by nanoindentation tests, Journal of Physics D-Applied Physics, 42 (2009) 6.
[124] F. Hunkeler, A. Krolikowski, H. Böhni, A study of the solid salt film on nickel and stainless steel, Electrochimica Acta, 32 (1987) 615-620.
[125] H. Lajain, Das elektrochemische Verhalten von Schweißverbindungen, Materials and Corrosion, 23 (1972) 537-545.
[126] H.S. Isaacs, Initiation of Stress-Corrosion Cracking of Sensitized Type-304 Stainless-Steel in Dilute Thiosulfate Solution, Journal of the Electrochemical Society, 135 (1988) 2180-2183.
[127] A.J. Bard, G. Denault, R.A. Friesner, B.C. Dornblaser, L.S. Tuckerman, Scanning Electrochemical Microscopy - Theory and Application of the Transient (Chronoamperometric) Secm Response, Analytical Chemistry, 63 (1991) 1282-1288.
[128] M. Etienne, A. Schulte, W. Schuhmann, High resolution constant-distance mode alternating current scanning electrochemical microscopy (AC-SECM), Electrochemistry Communications, 6 (2004) 288-293.
[129] T. Suter, H. Bohni, A new microelectrochemical method to study pit initiation on stainless steels, Electrochimica Acta, 42 (1997) 3275-3280.
[130] T. Suter, T. Peter, H. Boehni, Microelectrochemical investigations of MnS inclusions, Materials Science Forum, 192-194 (1995) 25-40.
[131] A. Moehring, Entwicklung einer elektrochemischen Mikrodurchflusszelle zur Untersuchung des Elektrochemischen Senkens (ECM, Electrochemical Machining), Ph. D. thesis, Heinrich-Heine Universität, 2004
Chapter 11: Bibliography
136
[132] M.M. Lohrengel, A. Moehring, M. Pilaski, Capillary-based droplet cells: limits and new aspects, Electrochimica Acta, 47 (2001) 137-141.
[133] M.M. Lohrengel, C. Rosenkranz, I. Klüppel, A. Moehring, H. Bettermann, B. Van den Bossche, J. Deconinck, A new microcell or microreactor for material surface investigations at large current densities, Electrochimica Acta, 49 (2004) 2863-2870.
[134] N. Birbilis, R.G. Buchheit, Electrochemical characteristics of intermetallic phases in aluminum alloys - An experimental survey and discussion, Journal of the Electrochemical Society, 152 (2005) B140-B151.
[135] A.W. Hassel, M.M. Lohrengel, The scanning droplet cell and its application to structured nanometer oxide films on aluminium, Electrochimica Acta, 42 (1997) 3327-3333.
[136] C.J. Park, M.M. Lohrengel, T. Hamelmann, M. Pilaski, H.S. Kwon, Grain-dependent passivation of surfaces of polycrystalline zinc, Electrochimica Acta, 47 (2002) 3395-3399.
[137] A.W. Hassel, M. Seo, Localised investigation of coarse grain gold with the scanning droplet cell and by the Laue method, Electrochimica Acta, 44 (1999) 3769-3777.
[138] A.I. Mardare, A.W. Hassel, Quantitative optical recognition of highly reproducible ultrathin oxide films in microelectrochemical anodization, Review of Scientific Instruments, 80 (2009) 046106.
[139] M.M. Lohrengel, A. Moehring, M. Pilaski, Electrochemical surface analysis with the scanning droplet cell, Fresenius Journal of Analytical Chemistry, 367 (2000) 334-339.
[140] K. Fushimi, S. Yamamoto, R. Ozaki, H. Habazaki, Cross-section corrosion-potential profiles of aluminum-alloy brazing sheets observed by the flowing electrolyte scanning-droplet-cell technique, Electrochimica Acta, 53 (2008) 2529-2537.
[141] A.W. Hassel, K. Fushimi, M. Seo, An agar-based silver | silver chloride reference electrode for use in micro-electrochemistry, Electrochemistry Communications, 1 (1999) 180-183.
[142] K.A. Lill, A.W. Hassel, A combined micro-mercury reference electrode/Au counter-electrode system for microelectrochemical applications, Journal of Solid State Electrochemistry, 10 (2006) 941-946.
[143] M. Osawa, K. Ataka, K. Yoshii, T. Yotsuyanagi, Surface-Enhanced Infrared Atr Spectroscopy for in-Situ Studies of Electrode-Electrolyte Interfaces, Journal of Electron Spectroscopy and Related Phenomena, 64-5 (1993) 371-379.
[144] K. Kunimatsu, T. Sato, H. Uchida, M. Watanabe, Role of terrace/step edge sites in CO adsorption/oxidation on a polycrystalline Pt electrode studied by in situ ATR-FTIR method, Electrochimica Acta, 53 (2008) 6104-6110.
[145] E.M. Sherif, R.M. Erasmus, J.D. Comins, In situ Raman spectroscopy and electrochemical techniques for studying corrosion and corrosion inhibition of iron in sodium chloride solutions, Electrochimica Acta, 55 (2010) 3657-3663.
[146] K. Ogle, S. Weber, Anodic dissolution of 304 stainless steel using atomic emission spectroelectrochemistry, Journal of the Electrochemical Society, 147 (2000) 1770-1780.
[147] M. Itagaki, F. Hori, K. Watanabe, UV/VIS spectrophotometry/channel flow electrode to determine anodic dissolution of metal, Analytical Sciences, 16 (2000) 371-375.
[148] D. Zoltzer, G. Schwedt, Comparison of Continuous-Flow (Cfa) and Flow-Injection (Fia) Techniques for the Photometric-Determination of Traces of Aluminum in Water and Soil Samples, Fresenius Zeitschrift Fur Analytische Chemie, 317 (1984) 422-426.
[149] J. Ghasemi, S. Ahmadi, K. Torkestani, Simultaneous determination of copper, nickel, cobalt and zinc using zincon as a metallochromic indicator with partial least squares, Analytica Chimica Acta, 487 (2003) 181-188.
Chapter 11: Bibliography
137
[150] J.F.C. Lima, C. Delerue-Matos, M.C.V.F. Vaz, Automation of iron and copper determination in milks using FIA systems and colourimetric detection, Food Chemistry, 62 (1998) 117-121.
[151] J. Kozak, J. Gutowski, M. Kozak, M. Wieczorek, P. Koscielniak, New method for simultaneous determination of Fe(II) and Fe(III) in water using flow injection technique, Analytica Chimica Acta, 668 8-12.
[152] H. Wada, A. Yuchi, G. Nakagawa, Spectrophotometric determination of magnesium by flow injection analysis with a ligand buffer for masking calcium, Analytica Chimica Acta, 149 (1983) 291-296.
[153] P. Richter, M.I. Toral, A.E. Tapia, E. Fuenzalida, Flow injection photometric determination of zinc and copper with zincon based on the variation of the stability of the complexes with pH, Analyst, 122 (1997) 1045-1048.
[154] M.A. Koupparis, P.I. Anagnostopoulou, Automated Flow-Injection Spectrophotometric Determination of Zinc Using Zincon - Applications to Analysis of Waters, Alloys and Insulin Formulations, Analyst, 111 (1986) 1311-1315.
[155] A.I. Mardare, High throughput growth, modification and characterization of thin anodic oxides on valve metals, Ph. D. thesis, Ruhr-Universität Bochum, 2009
[156] A.W. Hassel, Elektronische und ionische Transportprozesse in ultradünnen Ventilmetalloxidschichten, Ph. D. thesis, Heinrich-Heine Universität, 1997
[157] A.I. Mardare, A. Ludwig, A. Savan, A.D. Wieck, A.W. Hassel, Combinatorial investigation of Hf-Ta thin films and their anodic oxides, Electrochimica Acta, 55 (2010) 7884-7891.
[158] J.W. Schultze, M. Pilaski, M.M. Lohrengel, U. Konig, Single crystal experiments on grains of polycrystalline materials: Oxide formation on Zr and Ta, Faraday Discussions, 121 (2002) 211-227.
[159] J.J. Vandeemter, F.J. Zuiderweg, A. Klinkenberg, Longitudinal Diffusion and Resistance to Mass Transfer as Causes of Nonideality in Chromatography, Chemical Engineering Science, 5 (1956) 271-289.
[163] U. Bertocci, D. Turner, in: A.J. Bard (Ed.) Encyclopedia of Electrochemistry of the Elements, Marcel Dekker, New York, 1974.
[164] T.I. Quickenden, X. Jiang, The Diffusion-Coefficient of Copper-Sulfate in Aqueous-Solution, Electrochimica Acta, 29 (1984) 693-700.
[165] G. Brümmer, K.G. Tiller, U. Herms, P.M. Clayton, Adsorption Desorption and/or Precipitation - Dissolution Processes of Zinc in Soils, Geoderma, 31 (1983) 337-354.
[166] R.A. Reichle, K.G. McCurdy, L.G. Hepler, Zinc Hydroxide - Solubility Product and Hydroxy-Complex Stability-Constants from 12.5-75 Degrees C, Canadian Journal of Chemistry-Revue Canadienne De Chimie, 53 (1975) 3841-3845.
[167] F.A. Uribe, T.E. Springer, S. Gottesfeld, A Microelectrode Study of Oxygen Reduction at the Platinum/Recast-Nafion Film Interface, Journal of the Electrochemical Society, 139 (1992) 765-773.
[168] R. Halseid, T. Bystron, R. Tunold, Oxygen reduction on platinum in aqueous sulphuric acid in the presence of ammonium, Electrochimica Acta, 51 (2006) 2737-2742.
[169] J.P. Hoare, Oxygen Overvoltage Measurements on Bright Platinum in Acid Solutions .4. Methanol-Containing Solutions, Journal of the Electrochemical Society, 113 (1966) 846-&.
Chapter 11: Bibliography
138
[170] D.A. Scherson, Y.V. Tolmachev, Z.H. Wang, J. Wang, A. Palencsara, Extensions of the Koutecky-Levich equation to channel electrodes, Electrochemical and Solid State Letters, 11 (2008) F1-F4.
[171] P.M.S. Monk, Fundamentals of electroanalytical chemistry, John Wiley & Sons Ltd., Manchester, 2005.
[172] W. Feitknecht, Studies on the Influence of Chemical Factors on the Corrosion of Metals, Chemistry & Industry, (1959) 1102-1109.
[173] H. Leidheiser, W. Wang, L. Igetoft, The Mechanism for the Cathodic Delamination of Organic Coatings from a Metal-Surface, Progress in Organic Coatings, 11 (1983) 19-40.
[174] R.P. Bell, J.E. Prue, Kinetic Studies in Heterogeneous Buffer Systems .1. The System Zinc Hydroxide and Zinc Sulphate, Transactions of the Faraday Society, 46 (1950) 5-13.
[175] G.S. Frankel, Pitting corrosion of metals - A review of the critical factors, Journal of the Electrochemical Society, 145 (1998) 2186-2198.
[176] M. Stern, A.L. Geary, Electrochemical Polarization 1. A Theoretical Analysis of the Shape of Polarization Curves, Journal of the Electrochemical Society, 104 (1957) 56-63.
[177] F. Mansfeld, Tafel slopes and corrosion rates obtained in the pre-Tafel region of polarization curves, Corrosion Science, 47 (2005) 3178-3186.
[179] G.W. Walter, Corrosion rates of zinc, zinc coatings and steel in aerated slightly acidic chloride solutions calculated from low polarization data, Corrosion Science, 16 (1976) 573-586.
[180] F.H. Assaf, S.S. Abd El-Rehiem, A.M. Zaky, Pitting corrosion of zinc in neutral halide solutions, Materials Chemistry and Physics, 58 (1999) 58-63.
[181] S.O. Klemm, J.-C. Schauer, B. Schuhmacher, A.W. Hassel, A Microelectrochemical Scanning Flow Cell with Downstream Analytics, Electrochimica Acta, (2010).
[182] T. Hurlen, Corrosion of Zinc - Effect of pH, Acta Chemica Scandinavica, 16 (1962) 1346-1352.
[183] T.H. Muster, I.S. Cole, The protective nature of passivation films on zinc: surface charge, Corrosion Science, 46 (2004) 2319-2335.
[184] J. Guśpiel, W. Riesenkampf, Kinetics of Dissolution of ZnO, MgO and Their Solid-Solutions in Aqueous Sulfuric-Acid-Solutions, Hydrometallurgy, 34 (1993) 203-220.
[185] C. Fenster, M. Rohwerder, A.W. Hassel, The impedance-titrator : A novel setup to perform automated pH-dependent electrochemical experiments, Materials and Corrosion-Werkstoffe Und Korrosion, 60 (2009) 855-858.
[186] J.E. Castle, D. Epler, Chemical-Shifts in Photoexcited Auger-Spectra, Proceedings of the Royal Society of London Series a-Mathematical Physical and Engineering Sciences, 339 (1974) 49-72.
[187] D.R. Baer, M.H. Engelhard, A.S. Lea, P. Nachimuthu, T.C. Droubay, J. Kim, B. Lee, C. Mathews, R.L. Opila, L.V. Saraf, W.F. Stickle, R.M. Wallace, B.S. Wright, Comparison of the sputter rates of oxide films relative to the sputter rate of SiO2, Journal of Vacuum Science & Technology A, 28 (2010) 1060-1072.
[188] M.N. Hull, J.E. Ellison, J.E. Toni, Anodic Behavior of Zinc Electrodes in Potassium Hydroxide Electrolytes, Journal of the Electrochemical Society, 117 (1970) 192-&.
[189] N. Fink, B. Wilson, G. Grundmeier, Formation of ultra-thin amorphous conversion films on zinc alloy coatings Part 1. Composition and reactivity of native oxides on ZnAl (0.05%) coatings, Electrochimica Acta, 51 (2006) 2956-2963.
Chapter 11: Bibliography
139
[190] I. Odnevall, C. Leygraf, The formation of Zn4SO4(OH)6·4H2O in a rural atmosphere, Corrosion Science, 36 (1994) 1077-1087.
[191] E.E. Foad El Sherbini, S.S. Abd El Rehim, Pitting corrosion of zinc in Na2SO4 solutions and the effect of some inorganic inhibitors, Corrosion Science, 42 (2000) 785-798.
[192] D.M. Brasher, Role of Anion in Relation to Metallic Corrosion and Inhibition, Nature, 193 (1962) 868-869.
[193] V.K. Gouda, M.G.A. Khedr, A.M.S. El Din, Role of anions in the corrosion and corrosion-inhibition of zinc in aqueous solutions, Corrosion Science, 7 (1967) 221-230.
[194] S.S.A. El Rehim, E.E. Fouad, S.M.A. El Wahab, H.H. Hassan, The influence of some sulphur-containing anions on the anodic behaviour of zinc in an alkaline medium, Journal of Electroanalytical Chemistry, 401 (1996) 113-118.
[195] S.A. Awad, K.M. Kamel, Mechanism of corrosion-inhibition and corrosion-promotion of zinc by phosphate ions, Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 24 (1970) 217-225.
[196] J. Augustynski, F. Dalard, J.C. Sohm, Oxydation anodique du zinc en milieu faiblement basique, Corrosion Science, 12 (1972) 713-724.
[197] J.W. Schultze, M.M. Lohrengel, Stability, reactivity and breakdown of passive films. Problems of recent and future research, Electrochimica Acta, 45 (2000) 2499-2513.
[198] A.D. Keitelman, S.M. Gravano, J.R. Galvele, Localized Acidification as the Cause of Passivity Breakdown of High-Purity Zinc, Corrosion Science, 24 (1984) 535-&.
[199] M. Suchea, S. Christoulakis, N. Katsarakis, T. Kitsopoulos, G. Kiriakidis, Comparative study of zinc oxide and aluminum doped zinc oxide transparent thin films grown by direct current magnetron sputtering, Thin Solid Films, 515 (2007) 6562-6566.
[200] Y. Matsumoto, T. Yoshikawa, E. Sato, Dependence of the Band Bending of the Oxide Semiconductors on Ph, Journal of the Electrochemical Society, 136 (1989) 1389-1391.
[201] J.F. Dewald, The Charge and Potential Distributions at the Zinc Oxide Electrode, Bell System Technical Journal, 39 (1960) 615-639.
[202] D.G. Yoo, S.H. Nam, M.H. Kim, S.H. Jeong, H.G. Jee, H.J. Lee, N.E. Lee, B.Y. Hong, Y.J. Kim, D. Jung, J.H. Boo, Fabrication of the ZnO thin films using wet-chemical etching processes on application for organic light emitting diode (OLED) devices, Surface & Coatings Technology, 202 (2008) 5476-5479.
[203] W. Jo, S.-J. Kim, D.-Y. Kim, Analysis of the etching behavior of ZnO ceramics, Acta Materialia, 53 (2005) 4185-4188.
[204] Y. Sato, T. Yamamoto, Y. Ikuhara, Atomic structures and electrical properties of ZnO grain boundaries, Journal of the American Ceramic Society, 90 (2007) 337-357.
[205] S.E. Pust, J. Worbs, J. Hüpkes, S.O. Klemm, K.J. Mayrhofer, Electrochemical Etching of Zinc Oxide for Silicon Thin Film Solar Cell Applications, ECS Transactions, 33 (2011) 41-55.
[207] H.L. Tuller, ZnO grain boundaries: Electrical activity and diffusion, Journal of Electroceramics, 4 (1999) 33-40.
[208] S.E. Pust, J.-P. Becker, J. Worbs, S.O. Klemm, K.J.J. Mayrhofer, J. Hüpkes, Electrochemical Etching of Zinc Oxide for Silicon Thin Film Solar Cell Applications, Journal of the Electrochemical Society, 158 (2011) D413-D419.
Chapter 11: Bibliography
140
[209] D.M. Mattox, Handbook of Physical Vapor Deposition (PVD) Processing, Noyes Publications, New Jersey, 1998.
[210] C. Blawert, D. Manova, M. Störmer, J.W. Gerlach, W. Dietzel, S. Mändl, Correlation between texture and corrosion properties of magnesium coatings produced by PVD, Surface and Coatings Technology, 202 (2008) 2236-2240.
[211] E.R. Jette, F. Foote, Precision determination of lattice constants, Journal of Chemical Physics, 3 (1935) 605-616.
[212] T. Ohba, Y. Kitano, Y. Komura, The Charge-Density Study of the Laves Phases, MgZn2 and MgCu2, Acta Crystallographica Section C-Crystal Structure Communications, 40 (1984) 1-5.
[213] M.V. Akdeniz, J.V. Wood, Microstructures and phase selection in rapidly solidified Zn-Mg alloys, Journal of Materials Science, 31 (1996) 545-550.
[214] G. Garcés, M.C. Cristina, M. Torralba, P. Adeva, Texture of magnesium alloy films growth by physical vapour deposition (PVD), Journal of Alloys and Compounds, 309 (2000) 229-238.
Chapter 0: Appendix
141
Appendix Publications
S.O. Klemm, A.G. Martin, J. Lengsfeld, J.C. Schauer, B. Schuhmacher, A.W. Hassel,
Theoretical simulation and preparation of binary and ternary combinatorial libraries by thermal PVD,
Physica Status Solidi A-Applications and Materials Science, 207 (2010) 801-806.
S.O. Klemm, J.P. Kollender, A.W. Hassel, Combinatorial corrosion study of the passivation of