Special Cases, Problems, and New Frontiers Non-destructive analysis? Heat Deposition of charge Beam sensitive materials: Sample temperature rises during exposure to the electron beam Leads to: Loss of water from hydrous phases (clays, micas, etc.) Loss of CO 2 from carbonates Damage to halides, phosphates, glasses Migration of alkalis in silicates
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Special Cases, Problems, and New Frontiers Non-destructive analysis? Heat Deposition of charge Beam sensitive materials: Sample temperature rises during.
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Special Cases, Problems, and New Frontiers
Non-destructive analysis?
Heat
Deposition of charge
Beam sensitive materials:
Sample temperature rises during exposure to the electron beam
Leads to: Loss of water from hydrous phases (clays, micas, etc.)
Comparison of Osmic - Ovonyx LSMs to STE, MYR, CER
Problems:
Interferences from low energy X-rays from heavy elements
High order interferences
Coating thickness variation
Bonding – coordination effects
Carbon contamination
Reduction / oxidation effects
High absorption
Interference of Til on NK
And TiLβ3 on OK
Coating thickness and Carbon contamination
Bonding – coordination effects
Absorption
CK in Fe3C
For best results:
Samples and standards should be similar in composition and physical properties
Try to ensure constant coating thickness
Can coat samples and standards at the same time to help
Use multilayers whenever possible to minimize high order interferences and maximize count rates
Peak distortions due to bonding effects can be accounted for by using integrated peak intensities rather than peak heights
Minimize carbon contamination by
Use of oil-free vacuum pumps
can use vapor trap on backing line
Use O2 gas jet and / or cold plate to remove carbon
If possible, use lower kV to decrease depth of interaction volume
minimize absorption corrections
maximize count production near surface
Using peak shape and position effects…Fe oxidation state
Examine shape of
Fe-L emission
Fe electronic structure = Ar + 3d64S2
N-I
Using peak shape and position effects…Fe oxidation state
Examine shape of Fe-L emission
Flank Method…
Almandine:Fe3
2+Al2Si3O12
Andradite:Ca3(Fe3+ ,Ti)2Si3O12
A=8 B=6
B=6 A=8
cps L cps L
LLratio
Peak energy with increasing Fe3+
Low energy analysis
LEXES (Low Energy X-Ray Emission Spectrometry)
Excitation volume
Sample
Low energy beam
5 – 100 μm
1 – 500 nm
detector
Some other applications:
Particle analysis
Thin films
Rough surfaces
Garnet - Moretown Formation, MA CaKα
S-shaped trails of minerals in the inner part of the garnet were trapped as the mineral grew, and were part of an earlier fabric. A higher Ca internal zone ends at the edge of the zone of inclusions defining the older fabric. Subsequent growth of inclusion –free garnet occurred first, with little Ca, then much more, then little again.
Records either:
1) smooth single-stage metamorphic history (excursion in P and T) or;
2) A multi-stage history
Chemical equilibria involving the outermost rim and the matrix minerals (biotite, muscovite, paragonite, chlorite, plag, ilmenite, and quartz) records final equilibration at ca. 5200 C and 7kb, or about 23 km depth.
Garnet - Italy MgKα
Lago di Cignana locality, Valtournenche, Italy
Very high pressure metamorphism (>25kb and 6000C) and uplift of coesite-bearing metasediments from the Zermatt-Saas zone, Western Alps.
The matrix assemblage includes quartz (after coesite), phengite (Si ~ 3.4pfu), Mn-rich phlogopite, piemontite, and Mn-rich calcite. Inclusions in garnet are piemontite and quartz.
Note the angular unconformity between core and overgrowth
Originalopx
Cpx + qtz
opx
plag
opx+plag+ mt
garnet
matrixplag
Corona texture - CaKα Saskatchewan
Orthopyroxene core and surrounding mantle from 2.6 Ga East Athabaska mylonite triangle
Multi-stage coronitic overgrowths on OPX in mafic granulite
Sequence:
original opx core (lower-right)→
Mantle of cpx+qtz→
2nd generation opx→
Moat of plagioclase→
Symplectitic intergrowth of opx+plag+magnetite→
Outer shell of garnet →
Matrix plagioclase (upper left)
Proposed reaction history:
Prograde growth of a cpx+garnet+qtz assemblage at the expense of opx+plag,
and retrograde growth of opx+plag+oxide from the peak assemblage