Examination of Metallic Materials by X-ray Emission Spectrography

Abstract

The examination of metallic materials by X-ray emission spectrography is reviewed from the viewpoint of the analytical chemist. Reasons are cited to show why X-ray emission spectrography is particularly suited to these applications and why it should prove a welcome complement to other analytical methods including emission spectrography at ordinary wavelengths. A recent successful application of X-ray spectrography (the routine determination of molybdenum, nickel, chromium, cobalt, and iron in a complex alloy developed for high-temperature applications) is described. In addition, a fragmentary comparison of results by X-ray and ordinary emission spectrography is given. Discussed in a practical way are precision, range of standards, resolution, types of excitation, counting errors, depth of penetration, and deviations caused by absorption. In this discussion, the method has been looked at through the eyes of the analytical chemist who wants his samples analyzed rapidly, as completely as possible, and with good precision (standard deviations smaller than 1 part per 100). Finally, a few nonroutine applications of X-ray emission spectrography are mentioned, the most striking of which is the modification of an electron microscope to excite the characteristic lines in volumes as small as that of a micron cube.

X-Ray Absorption and Emission

“…It is interesting to compare this account in detail with earlier work (37) both as regards precision attained and the rapid progress being made.…”

Effects Due to Chemical State of Samples in X-Ray Emission and Absorption

“…In these cases, disregard of the wave length shift, and of a change in efficiency of emission, can result in serious errors in analytical results, (1,3,6) for the radiochemical determination of cerium in fission product mixtures depend either in part, or entirely, on precipitation for separating cerium from other fission products. If precipitation alone is used, as many as nine precipitations (two as the fluoride, three as the hydroxide, two as the iodate, and twro as the oxalate) may be required to ensure a radiochemically pure product.…”

“…Manual shaking of hydrocarbon samples with distilled water for as long as 15 minutes was unsatisfactory, giving incomplete extraction and generally erratic sodium analyses. However, a 30-minute vigorous mechanical shaking (1) proved sufficient, a second 30minute extraction yielding only a minute trace of sodium.…”

“…The valence state of an element in a series of compounds has a relatively small effect on both wave length (6) and intensity in x-ray absorption and emission. These effects are so small that it was possible to neglect them in the early work on x-ray methods for chemical analysis (1,5). Several years ago, when this conclusion was first reached, it probably would not have been possible to demonstrate these chemical effects.…”

Quantitative Analyses by Fluorescent X-Ray Spectrography. Determination of Germanium in Coal and Coal Ash

“…When the background is negligible-e.g., line-background ratios exceeding 10 to 1-the standard deviation approximates the square root of the number of counts collected. However, in trace analysis, the ratio of line height to background is a very important factor (3,14). With a 1% standard deviation on both measurements, the analytical line can be determined within ± 5% when the ratio of analytical line to background is unity.…”