RI 3888 Routine Quantitative Analysis by X-Ray Diffraction,1. Photometric 2. Analytical Method

"The X-ray method of quantitative determination is advantageous because it permits determination of compounds rather -than ions or elements; for example, the direct determination of quartz in silicates,4/,5/,6/ The method also takes into account the finest particles of a sample, which may be lost in wet chemical methods because of solubility or in petrographic methods because of limitation of the microscope. The sample is usually reduced to a powder and is easily prepared,7/ only a few milligrams of material being necessary. The sample and its chemical composition are not destroyed and may be used for further analysis by X-ray diffraction or by other methods.This paper presents in detail some of the more essential problems that arise in the application of X-ray diffraction to quantitative chemical analysis, Photometric measurements are discussed in connection with line intensities and the choice of X-ray film. The internal standard method, successfully used in spectrographic analysis, is applied.Copper K-alpha X-rays from a demountable research-type X-ray tube were used with a camera of 20 centimeters radius with a cast-lead-slit collimating system. A combination of a tilted wedge and a lead-slit collimating system permitted irradiation of a large amount of sample with X-rays. This tended to minimize errors due to possible inhonogeneity of the sample, to decrease the time of exposure, and to keep the lines on the X-ray film to a minimum width. There was sufficient dispersion of the lines for satisfactory analysis of most samples. Power was furnished the tube by a. source of constant high potential consisting of a synchronous motor generator furnishing 500-cycle power to a 100-kv. transformer, rectifying valves, and a condenser filter circuit. The X-ray tube was operated as a gas-type tube at 35 kv, and 20 ma,, the exposure times varying from 1 to 2 hours. The constant output of X-rays from the tube, indicated bar an exposure meter built for the purpose, was satisfactory.The recording microphotometer8/has been described. It was found preferable to a nonrecording instrument for measuring blackening of lines above a background on X-ray films. This background, which usually occurs, is sometimes complicated by numerous peaks from lines of complex diffraction patterns. is microphotometer record of the pattern, therefore, facilitates the location of the background 'and the measurement of the heights of the peaks and thus contributes to the accuracy of a determination."