Michael Shaffer INCO Innovation Centre Memorial University St. John’s, Newfoundland [email protected]Advanced Techniques in EPMA Seminar August 7, 2010 University of Oregon Eugene, Oregon A brief introduction to the FEI Mineral Liberation Analyzer ™ : the technique & results
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Advanced Techniques in EPMA Seminar August 7, 2010 University of Oregon Eugene, Oregon
A brief introduction to the FEI Mineral Liberation Analyzer ™ : the technique & results. Michael Shaffer INCO Innovation Centre Memorial University St. John’s, [email protected]. Advanced Techniques in EPMA Seminar August 7, 2010 University of Oregon Eugene, Oregon. - PowerPoint PPT Presentation
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Michael ShafferINCO Innovation CentreMemorial UniversitySt. John’s, Newfoundland [email protected]
Advanced Techniques in EPMA Seminar
August 7, 2010University of Oregon
Eugene, Oregon
A brief introduction to theFEI Mineral Liberation Analyzer™:
the technique & results
MLA:points of interest
Particle analysis Rocks crushed, sized and representative Most accurate E.G, iron ore from Labrador
DensityWt%Area%Area (microns)Area (pixels)PerimeterMax SpanLength (MBR)Breadth (MBR)Hull AreaHull PerimeterEE Minor AxisHull EE Minor AxisEE Major Axis (P&A)EE Minor Axis (P&A)EE PerimeterEC DiameterAngularityEnclosed Length DeltaForm Factor
Hull AreaHull PerimeterEE Minor AxisHull EE Minor AxisHull EE PerimeterEE Major Axis (P&A)EE Minor Axis (P&A)EC DiameterAspect RatioAngularityEnclosed Length DeltaForm FactorBoundaries with other mineralse.g., Quartz (%)
Sources of instrumental error:electron beam illumination
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195 = Hm198 = Mt
192 = Hm195 = Mt
Sources of instrumental error:varying e-beam current
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195 = Hm198 = Mt
192 = Hm195 = Mt
3rd frame 143rd frame
2 hoursLater …
Remedying BSE problemsNon-uniform illumination
No remedy if the SEM manufacturer did not anticipate applications in quantitative BSE
Except to use high magnification Difficult to remedy if the SEM
manufacturer did not provide alignment tools for uniformity
FEI Quanta SEMs: Centering the illumination provided by e-
gun tilt Tetrode & gun alignment should be
accurate Illumination gradients worse for large spot
sizes
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Remedying BEI problems
Varying beam current Very common depending on age of
filament … Stability generally monotonic, i.e., not
erratic … allows for breaking the BSE JKF file into 2
to 4 files, thereby creating more reliable histograms that represent time periods during analysis.
Note also that this method is quite dependent on a significant amount of Hm-Mt in the sample, which builds a more accurate reliable histogram
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Anticipating problems we haven’t yet encountered, and possible
improvements MUN IIC has not yet applied this method to
mineral assemblages other than the minerals discussed here I.E., a severe complication would arise for
significant amounts of titano-magnetite, thereby blurring the distinction of Hm in the reliable histogram
A very helpful improvement, which would allow the same tools to be applied to other applications, would be for the spectra-classified result to mask the minerals of interest to be classified with BSE 39
MLA Mode BSE conclusions
Hm – Mt BSE discrimination works … And Hm-Mt associations are possible
… but not specifically with other minerals
and, by itself, cannot discriminate most other minerals because of average atomic number (i.e., BSE ambiguity)
However, it presents a suitable solution for augmenting spectral classification (mode XBSE)
How to augment with spectral classification? …
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SummaryHm–Mt BEI discrimination is possible
… Hm-Mt associations are possible, and with all minerals Mineral modes and associations can be reproduced with
acceptable accuracy A comparison with quantitative XRD is within errors
associated with the difficulty associated with representative down-sampling (XRD sampling independent of MLA sampling)
However, a well-aligned and stable SEM is necessary … Electron beam illumination must be uniform over 1 – 2mm Beam current must be stable over the 2 – 3hr analytical time
(although data processing can accommodate a monotonic variation)
This technique is more generally applicable, even to more complex mineral assemblages when chemistry (x-ray spectra) aids in masking the minerals of interest
41
Consider an independent approach …
42
Exported BEI frames into 3rd-party software
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The masked & cleaned frames
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A clean histogram allows for automatic thresholding