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Title:
Large Errors in Electron Microprobe Analysis of Laphamite due to Uncertainties in ZAF Correction Parameters
Authors:
Kracher, A.; Bindi, L.; Bonazzi, P.; Fournelle, J.; Frahm, E.; Spry, P. G.
Affiliation:
AA(Ames Laboratory, Iowa State University, Ames, IA 50011, United States ; ), AB(Museo di Storia Naturale, Università degli Studi di Firenze, Firenze, I- 50121, Italy ; ), AC(Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Firenze, I- 50121, Italy ; ), AD(Dept. of Geology & Geophysics, University of Wisconsin-Madison, Madison, WI 53706, United States ; ), AE(Dept. of Geology & Geophysics, University of Minnesota, Minneapolis, MN 55455, United States ; ), AF(Dept. of Geological and Atmospheric Sciences, Iowa State University, Ames, IA 50011, United States ; )
Publication:
American Geophysical Union, Fall Meeting 2007, abstract #V51A-0327
Publication Date:
12/2007
Origin:
AGU
AGU Keywords:
1094 Instruments and techniques, 3694 Instruments and techniques
Abstract Copyright:
(c) 2007: American Geophysical Union
Bibliographic Code:
2007AGUFM.V51A0327K

Abstract

Laphamite, As2Se3-xSx (x~0.75), was analyzed by electron microprobe in three different laboratories, using different acceleration voltages (15kV and 20kV) and a number of different standards for As (As2S3, GaAs) and Se (Se, PtSe2, Bi2Se3). Lines used were Kα for S and Lα for As and Se. All analyses resulted in totals between 104 and 109 weight-%. Satisfactory results were obtained, however, by using As2Se3 as standard for both As and Se, giving totals between 100.1 and 100.8 weight-% Since all three laboratories used JEOL instruments with similar manufacturer-supplied software, a problem with ZAF parameters was suspected. One set of analyses was recalculated with different mass absorption coefficients (MACs), substituting the FFAST set derived from data by Chantler [1] for the Heinrich-Henke set in the instrument software. This resulted in changes of ZAF factors of -4.2% for As, -11.1% for Se, and -8.1% for S, reducing the analysis total from 107.9% to 99.3% (average of 6 analyses). The recalculated result as well as the analyses obtained with As2Se3 as standard were also close to the composition inferred from the X-ray diffraction study. To further elucidate the source of the discrepancy we are also performing calculations using the Monte Carlo program PENEPMA for comparing theoretical K-ratios to the ones obtained by electron microprobe. The theoretical K-ratios will then be processed with the same ZAF correction procedures as the microprobe data. [1] Chantler, C.T., J. Phys. Chem. Ref. Data 29, 597-1048 (2000).
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