Development of novel coatings to resist fireside corrosion in biomass-fired power plants Supervisors: Dr. Nigel Simms Prof. John Nicholls (Dr. Tanvir Hussain) Industrial Supervisor: Colin Davis, E.ON Technologies (Ratcliffe) Ltd 6 th of October 2015 Dominika Orlicka
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Development of novel coatings to resist fireside corrosion in biomass-fired
power plants
Supervisors:Dr. Nigel Simms
Prof. John Nicholls(Dr. Tanvir Hussain)
Industrial Supervisor:Colin Davis,
E.ON Technologies (Ratcliffe) Ltd
6th of October 2015
Dominika Orlicka
Aim
To develop a range of coating compositions resistant to fireside corrosion in biomass-fired power plants using a multi-target magnetron
sputtering technique
Objectives
Exposure conditions:• To understand stability of salts (KCl, NaCl, K2SO4, Na2SO4) at high
temperatures and chose a deposit for fireside corrosion testing
Coating development:• To use the combinatorial model alloy development methodology
by using two-target magnetron sputtering• To study the influence of Cr, Al and Fe on the coatings properties
and their role in chloride-based corrosion• To investigate the best coating compositions in the fireside
corrosion tests and to understand their behaviour in differentenvironments
• To evaluate the alternative methods of applying the best coatingcompositions on the boiler tubes
Experimental design
Mass Flow
Controller
(O2/SO2/N2/HCl/Air)
Vent
NaOH
scrubber
Alumina crucibles
with samplesAlumina
liner
Stainless steel
furnace tube
-5°C
+5°C
-5°C
H
o
t
z
o
n
e
Alumina tube
Safety gas
(N2) N2 vent
Schematic of a controlled atmosphere furnace (for salt stability and coating testing)
a) Test 1 (600ºC, HCl + SO2 environment, 22 mixtures, 50 hours)• conversion to sulphates• evaporation of chlorides• only chlorine left was in deposits that started with 50% at of Cl
b) Test 2 (550ºC, HCl + SO2 environment, 22 mixtures, 50 hours)• conversion to sulphates• evaporation of chlorides• only chlorine left was in 40% KCl+60% NaCl mixture and 100% NaCl
c) Test 3 (550ºC, HCl environment, mixtures (pure salts, KCl + NaCl, KCl + K2SO4), 50hours)• chlorides contaminated by sulphates• evaporation of chlorides• chlorine left was in each sample
d) Test 4 (550ºC, HCl environment, mixtures (pure chlorides, KCl + NaCl), 50 hours)• slight evaporation of chlorides• chlorine left was in each sample
Magnetron sputtering
Target 1
Target 2
Chromium target
Deposition chamber
Sample holder and substrates
Sample holder
Sapphire disc
Schematic of a controlled atmosphere furnace (1)
Mass Flow
Controller
(HCl/Air)
Vent
NaOH scrubber
Alumina crucibles
with samples Alumina liner
Stainless steel
furnace tube
-5°C
+5°C
-5°C
H
o
t
z
o
n
e
Alumina tube
Safety gas
(N2) N2 vent
Water pumpDeionised water
Coating compositions
Cr + Fe30Al
Fe50Cr + Fe20Al
Cr + Fe20Al
Experimental conditions
Test 1 Test 2 Test 3 Test 4
Temperature[°C]
550 550 550 550
Gas composition
Air315 ppm HCl,balance air
315 ppm HCl,balance air
344 ppm HCl, balance air,
10% H2O
Total flow rate[cc/min]
- 47 47 105
Duration[hour]
Up to 450 Up to 150 150 Up to 300
KCl - - + +
Techniques used
• SEM/EDX• XRD • FEG-SEM • Cross-section• FIB • IC • TGA• Mass change
Selected results
Mass change (Cr + Fe30Al)
Mass change graphs for the test Air + HCl without KCl (left) and with KCl (right) after 150 h
Lowest mass change E, F: 50-80 at.% Cr, 12-29 at.% Fe, 8-22 at.% Al
Lowest mass change F, G: 32-63 at.% Cr, 22-40 at.% Fe, 15-28 at.% Al
Mass change (Cr + Fe20Al)
Mass change graphs for the test in Air (left) and Air with HCl (right) after 150 h
Lowest mass change E, e, F: 39-68 at.% Cr, 22-42 at.% Fe, 10-19 at.% Al
Lowest mass change E, e, F: 39-68 at.% Cr, 22-42 at.% Fe, 10-19 at.% Al
Surface composition (Cr + Fe30Al)
Composition of unexposed coatings
Composition after the test in Air with HCl (with KCl)Composition after the test in Air with HCl (without KCl)
ESEM images (Cr + Fe30Al, Air with HCl and Air with HCl + KCl)
50 µm
Surface morphology of an as deposited coating (GSE)
Post-exposure surface
morphologies of the coatings (GSE). A4, D4, E4, F4, H4, K4 – without KCl; A3, D3, E3, F3, H3,
K3 – with KCl
Surface morphologies (Cr + Fe20Al and Fe50Cr + Fe20Al)
Post-exposure surface morphologies of the coating E (GSE) after 150 hours. First picture: Air exposure, followed by Air with HCl, Air with HCl + KCl and Air with HCl + KCl + 10% moisture (last picture)
Post-exposure surface morphologies of the coating A (GSE) after 50 hours. Left picture: Air exposure, right picture: Air with HCl
Cr + Fe20Al
Fe50Cr + Fe20Al
50 µm50 µm 50 µm50 µm
50 µm 50 µm
XRD analysis for Cr + Fe30Al
XRD spectra of Fe-Cr-Al coatings after 150 h exposure in Air with HCl (left) and Air with HCl (+ KCl) (right)
Cross-sections and FEG-SEM analysis
(Cr + Fe30Al)Test without KCl Test with KCl
1: low O content2: lower O and higher
Cr content than atthe top
1: high O and Cr content
2: depletion in O and Cr;higher KCl contentthan at the top(exception of sampleF)
• The magnetron sputtering was successfully used to producea range of Fe-Cr-Al coatings
• The presence of HCl in gas (and no KCl) did not result in any significantchanges compared to air alone
• KCl strongly accelerated the corrosion rate• The weight change data showed the smallest values for samples D – G with a composition range of 32-80 at.% Cr, 12-40 at.% Fe and 8-28
at.% Al for Cr + Fe30Al coatings E – F with a composition range of 39-68 at.% Cr, 22-42 at.% Fe, 10-19 at.%
Al For Cr + Fe20Al coatings• XRD analysis showed the presence of Cr2O3 and (Fe, Cr)2O3 oxides• No signs of chromates or chlorides were detected• The investigation of samples is still in progress