HR: 0800h
AN: V51A-0327    [Abstracts]
TI: Large Errors in Electron Microprobe Analysis of Laphamite due to Uncertainties in ZAF Correction Parameters
AU: Kracher, A
EM: akracher@iastate.edu
AF: Ames Laboratory, Iowa State University, Ames, IA 50011, United States
AU: Bindi, L
AF: Museo di Storia Naturale, Università degli Studi di Firenze, Firenze, I- 50121, Italy
AU: Bonazzi, P
AF: Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Firenze, I- 50121, Italy
AU: * Fournelle, J
AF: Dept. of Geology & Geophysics, University of Wisconsin-Madison, Madison, WI 53706, United States
AU: Frahm, E
AF: Dept. of Geology & Geophysics, University of Minnesota, Minneapolis, MN 55455, United States
AU: Spry, P G
AF: Dept. of Geological and Atmospheric Sciences, Iowa State University, Ames, IA 50011, United States
AB: Laphamite, As₂Se_3-xS_x (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).
DE: 1094 Instruments and techniques
DE: 3694 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting