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.
NBS standard reference materials catalog 1988-89
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Chemical Analysis by X-Rays and Its Applications
FOR a long time the line spectrum of an element has been used as a means for its identification and, more recently, spectroscopic methods have been developed not only for qualitative but also for quantitative chemical analysis. If the optical spectrum has been found so useful in the practical problems of analysis, it is only to be expected that the X-ray spectrum should prove capable of being similarly employed. When the nature and method of excitation of the optical and the X-ray spectrum are compared, it becomes clear that the latter has much to commend it. In the first place, the X-ray spectrum is much less complex and remains practically unaltered by changes in external conditions. Again, all the elements have similar spectra which differ from one another only in a regular and continuous decrease in the wave-lengths of corresponding lines as the atomic number increases. It is thus possible to predict with accuracy the X-ray spectrum of an element. Further, in order to excite the optical line spectrum, it is necessary to vaporise the material, while the X-ray lines can be obtained without the destruction of the material under investigation.Chemical Analysis by X-Rays and Its Applications.By Prof. Georg von Hevesy. (The George Fisher Baker Non-Resident Lectureship in Chemistry at Cornell University.) Pp. xi + 333 + 28 plates. (New York: McGraw-Hill Book Co., Inc.; London: McGraw-Hill Publishing Co., Ltd., 1932.) 3 dollars.