Director Standard Reference Materials : Homogeneity Characterization of NBS Spectrometric Standards IV : Preparation and Microprobe Characterization of W-20 % Mo Alloy Fabricated by Powder Metallurgical Methods
A significant problem of the National Bureau of Standards Standard Reference Materials program is the provision of standards suitable in homogeneity for use with microanalytical techniques such as the spark source mass spectrograph and the electron probe microanalyzer. An interim approach to the problem has been the extended homogeneity characterization of selected existing standards. This paper describes the preparation and evaluation of the first NBS standard tested specifically from the beginning for application to electron probe microanalyzers. The standard designated SRM 480 is a tungsten-20 weight percent molybdenum alloy prepared by a powder metallurgy process. Based on the results of about 1500 determinations for both tungsten and molybdenum by electron probe microanalysis, the material was found to be of high homogeneity at about the micrometer level of spatial resolution. The coefficient of variation for molybdenum was 2.5% and that for tungsten 1.5%. Correction of relative intensity ratios to obtain concentrations is discussed in terms of input parameter uncertainties such as mass absorption coefficients, and electron backscatter factors. The result of studies for atomic number correction and effects on operating voltage on the microprobe absorption correction., will be given. It is concluded that SRM 480 should be a valuable addition to any microprobe laboratory doing quantitative analysts.
Quantitative electron probe microanalysis: Absorption correction uncertainty
ZusammenfassungDie Genauigkeit der Röntgenstrahl-Absorptionskorrektur für die quantitative Mikrosondenanalyse ist von Fehlern der benützten Parameter (Massenabschwächungskoeffizienten, Austrittswinkel und Arbeitsspannung) und auch von Ungenauigkeiten in der Form der Korrektur beeinflußt. Wenn der Abschwächungskoeffizient mit 5% Genauigkeit bekannt ist, so muß die Absorptionsfunktion,f(χ), 0,8 oder größer sein, um den Korrekturfehler unter 1% zu halten. Die zur Verminderung der Absorptionskorrektur nötigen Arbeitsbedingungen werden angegeben und die Vorteile eines großen Austrittswinkels nachgewiesen. Die theoretische und experimentelle Analyse von Aluminium-Magnesium-Legierungen wird als Erläuterungsbeispiel verwendet.RésuméL'exactitude de la correction d'absorption dans l'analyse quantitative par sonde électronique est disminuée á conséquence des erreurs des paramétres utilisés (coefficients d'absorption massique, angle d'émergence du rayonnement analysé, et tension d'accélération des électrons) et du modéle de correction. Si le coefficient d'absorption est connu á 5% prés, pour éviter des erreurs plus grandes que 1%, il faut que la fonction d'absorptionf(χ) soit 0,8. On indique les conditions expérimentales conduisant á une faible correction d'absorption et on démontre les vantages d'un angle d'émergence élevé. L'analyse théoretique et expérimentale des alliages aluminium-magnésium est utilisée á maniére d'example.
Preparation of electron probe microanalyzer standards using a rapid quench method
A modified Duwez method of splat cooling in which a small quantity of molten alloy is accelerated and made t o strike a cold substrate havlng a high thermal conductivity was investigated as a means for preparing several cubic centimeters of standard materials suitable for quantitative electron probe microanalysis. T h e major requirements for such standards are that the spatial its composition suggested analysis procedure when using splat cooled standards is also outlined. The electron probe microanalyzer results for the Au-Si and Al-big systems are evaluated.