The influence of absorption effects in measuring elements in petroleum oil by X-ray fluorescence can, under certain circumstances, be predicted approximately from theory. Exact information on specific systems and instrumental conditions must practically be provided by experiment, however. The influence of absorption on fluorescent intensity under specific conditions of interest has been studied from three viewpoints; varying the depth through oil of a solid elemental specimen, varying the depth of a solution containing the element dissolved in oil, and varying the amount of the dissolved element in oil over a broad range in concentration. The group of elements selected for study illustrate characteristic fluorescent radiations often1 measured from oil. The experimental results are expressed graphically and are compared between elements as well as with theory. The results have analytical implications which pertain to the quantitative determination of elements in oil by X-ray fluorescence.

X-ray fluorescence methods for the direct determination of aluminum, chlorine, titanium, and iron in polyolefins have been developed. The procedures require no preconccntration of elements, are satisfactory for any polyolefin, and are free from matrix effects. The accuracy and precision are generally comparable with or better than chemical procedures. In addition, the speed of the analysis is six to eight times faster.

Finely divided iron oxide is used as a burning-rate catalyst in several solid rocket propellants. The concentration is critical and must be accurately determined as a quality control point before the propeltant is cast in the motor case and cured, in addition to the iron oxide, the propellant used for ignition of the Air Force Minuteman first stage contains a polymeric binder system, a solid oxidizer, and a metal powder. This composition makes it difficult to determine accurately the iron content by wet methods in the time available daring the propellant processing cycle. The use of X-ray fluorescence has been investigated as a means of satisfying the analysis time requirements while meeting the prescribed accuracy of ±1% of the amount of iron oxide present. Procedures for preparing test specimens have been developed and instrument operation conditions chosen which yield satisfactory precision. When ten specimens from each of three premixes were analyzed for iron content, the observed within-mix mean relative standard deviation was 0.28%; for propellant analyzed under the same conditions, the mean relative standard deviation was 0.35%. Factors affecting mix-to-mix accuracy, such as particle size and shape and interelement absorption and enhancement effects, have been investigated. Accuracy is adequate for in-process control of the iron oxide level in the premix, but further work is required before satisfactory control of propellant is achieved.

Several design concepts were evaluated for on-stream X-ray analysis, chief among which were: (1) sample presentation, (2) X-ray spectrograph and (3) data handling. The sample is presented to the X-ray spectrograph through a vertical cell having a mylar window and a device to measure variations in sample density. The X-ray spectrograph is of fixed-channel, modular design, with a capacity of up to six channels, and is designed for use in industrial environments. The complete spectrograph can be translated in a horizontal plane to position itself and determine the elemental composition in a series of sample cells. The data handling uses digital circuitry to permit normal use of analog readouts or digital data logging systems. Operational data are given for on-stream analysis.

A relationship is derived between X-ray intensity and particle size for a minor constituent in a powder sample. Theoretical and experimental curves are compared for several elements which are of importance in mining applications. Based upon these curves, some general guides are established relating to a method of predicting the particle size required for a given application. It is also shown that the relative intensity of a minor constituent is independent of the absorption coefficient of the matrix, if the particle size of the matrix is constant. Mineralogical effects, which relate to the occurrence of an element in two or more forms of chemical combination, are discussed and several examples in mining applications are cited.

The X-ray analysis of the materials associated with the mining and mineral processing industries offers a wide variety of potential applications and a challenge to the X-ray analyst. X-ray methods are rapid, reproducible and, when suitably applied, accurate for elements of atomic number 12 or greater. These characteristics make it an ideal process control system. In general, the materials for each type of process require individual analytical techniques to provide reliable analytical data. A wide variety of materials have been studied on the ARL Vacuum X-ray Quantometer and their performances evaluated. An evaluation of the sample preparation and analytical methods required are given.