A new quantitative X-ray powder diffraction (QXRPD) method has been developed to analyze polyphase crystalline mixtures. The unique approach employed in this method is the utilization of the full diffraction pattern of a mixture and its reconstruction as a weighted sum of diffraction patterns of the component phases. To facilitate the use of the new method, menu-driven interactive computer programs with graphics have been developed for the VAX* series of computers. The analyst builds a reference database of component diffraction patterns, corrects the patterns for background effects, and determines the appropriate reference intensity ratios. This database is used to calculate the weight fraction of each phase in a mixture by fitting its diffraction pattern with a least-squares best-fit weighted sum of selected database reference patterns.The new QXRPD method was evaluated using oxides found in ceramics, corrosion products, and other materials encountered in the laboratory. Experimental procedures have been developed for sample preparation and data collection for reference samples and unknowns. Prepared mixtures have been used to demonstrate the very good results that can be obtained with this method.

information on the hydrocarbon-type composltion of gasoline is required for continued research on Internal combustion engines, including efforts to Improve efficiency and reduce emissions. The standard method for obtainlng thls Information Is based on liquid chromatography and has been used for many years. An Improved technlque of greater precision was sought that would require less analysis time, whfle serving as an independent method of anaiysls. A nuclear magnetic resonance (NMR) technique has been developed for determlnlng the composltion (aromatlc, parafflnic, and oleflnlc) and hydrogenharbon ratio of gasoline. The equations requlred for the caiculatlons are derived. Results from the NMR method on 36 commerclai gasoiines are presented along with the results from the more familiar fluorescent indicator adsorption (FIA) method and the combustion method. The absolute standard devlations between the NMR and FIA methods are l.Q%, 3.2%, and 2.4% for the aromatics, paraffins, and olefins, respectively. A standard deviation of 0.055 is obtained on hydrogen/carbon ratios, Gasolines, which are complex mixtures of several hundred compounds, are usually characterized by hydrocarbon type rather than by complete analysis. Hydrocarbon types are usually determined by the fluorescent indicator adsorption (FIA) method. This method is a liquid chromatographic technique which separates the sample on silica gel into aromatic, paraffinic, and olefinic components. The FIA method is described fully in ASTM Method D-1319 ( 1 ) . The need for a rapid, independent technique of greater precision has been recognized for some time.High resolution NMR is a potentially useful tool f?r the analysis of petroleum mixtures, such as gasoline (2-4), because they are rich in hydrogen atoms which provide Ztrong ' proton NMR signals. The principles of NMR spectrometry utilized in such an analysis are described (5-7).As the FIA method provides a chromatographic separation of the three hydrocarbon types, the NMR method provides the spectrometric measurement of the three hydrocarbon types without separations. One purpose of this paper is to describe how to interpret the NMR spectrum of a gasoline to obtain a quantitative measure of the three hydrocarbon types (aromatic, paraffinic, and olefinic) present in the sample. The second purpose of this paper is to show how the equations derived for the hydrocarbon-type distribution can be easily rearranged to yield the hydrogen/carbon ratio.

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Accurate values for x-ray relative intensity factors, which are the fraction of intensity measured, are important for quantitative calculation procedures used in scanning transmission electron microscope thin 6lm x-ray microanalysis. We have developed equations for calculating these parameters for the K, L and M shells and have applied them to a thin film quantitative analysis procedure. The K shell values were obtained from experimental and theoretical data in the literature and show a constant region between atomic numbers 20 and 30. To obtain L shell values measurements were made with an electron probe and an energy dispersive system on a 200 kV scanning transmission electron microscope. These data were combined with values calculated from Coster-Kronig and flnorescence yield data in the literature. The result was two curves with a step at atom number 51 and a significantly different magnitude than values used in other thin fiIm methods. The following equations for use in a computer program were developed from these curves; uLn,,,(z = 27-50) = 1.617 -0.03982+ 3.766 x ~O -~Z~; sin [0.161(2-51)].