X-ray Diffraction Line-broadening Research Articles

A study of the texture and structure of Raney nickel

The texture of Raney nickel was simultaneously approached by nitrogen adsorption, magnetic measurements, X-ray diffraction line-broadening, X-ray small angle scattering and electron microscopy. The grain of Raney nickel, with a size larger than 1000 Å, takes the form of a collection of crystallites ranging in size from 25 to 150 Å, held together in the shape of a sponge. The average pore radius is 34 Å, but individual elements possessing an average radius of 7 to 8 Å also appear. Electron and X-ray diffraction patterns correspond to face-centered cubic nickel.

Conversion of Monetite, CaHPO4, To Apatites: Effect of Carbonate on the Crystallinity and the Morphology of the Apatite Crystallites

AbstractThe incorporation of carbonate in the apatite causes a decrease in crystallite size as demonstrated in precipitated apatites prepared at 37°C. Carbonate disturbs the crystallization of the growing apatite crystallites to such an extent that materials with more than 15 wt% CO3 gives an ‘amorphous’ x-ray diffraction pattern. The incorporation of carbonate in precipitates prepared at 100°C. causes a shortening of the a-axis and a lengthening of the c-axis which is proportional to the carbonate content, supporting the concept that in these apatites, CO3 substitutes for PO4 (11). X-ray diffraction linebroadening studies of CO3-apatites precipitated at 100°C and electron micrographs show that the size and shape of the crystallites change from long needles to smaller rods to tiny spheroids, depending upon the amount of CO3. Carbonate causes the bonding in the apatite to become weaker and more isotropic, which results in the small spheroidal crystals.This paper reports the effect of carbonate on lattice parameters and morphology of carbonate-apatites which have been prepared by the conversion of rnonetite, CaHPO4 in hot carbonate solutions. The structural effects of CO3 on the apatite is further reflected by the modification of the vibrations of the PO4 groups in the infrared absorption spectra. The morphology of ‘amorphous’ CO3- containing apatitic precipitates and that of CO3∼apatite with high CO3 content (prepared at 100°C) is similar, i.e., spheroidal in shape, but greatly differing in crystallite size.

Correlation of Magnetic Permeability and X-Ray Diffraction Line Broadening in Cold-Worked Iron

The permeability of annealed and cold-worked iron (0%–3.8% plastic tensile strain) was measured at field levels up to 0.8 Oe. and found to obey the Rayleigh relationship, μ=μ0+vH. The results show that the reciprocal of either Rayleigh constant, μ0 or v, varies linearly with the square root of the plastic strain value and that their ratio (μ0/v) is essentially independent of the degree of plastic strain. X-ray diffraction lines were also recorded for each sample and the line width was found to vary linearly with the square root of the plastic strain. The x-ray line broadening produced by cold work is ascribed to small particle size, caused by dislocations with an average spacing of D. The constant μ0, taken as a measure of reversible domain wall motion, is shown to be directly proportional to D, in support of certain models which have been proposed for hindrances to wall motion.

An X-ray absorption edge study of zeolite-supported platinum

Platinum in a large pore zeolite (Linde SK-200: 0.5% Pt Ca Y zeolite) was characterized by X-ray absorption edge spectroscopy, acid solubility studies, X-ray diffraction line-broadening, and hydrogen adsorption measurements. The absorption edge data show that, all the platinum was reduced to a zero-valent state, and that on the average this platinum is smaller in size than that found in conventional reforming catalysts. Sixty percent of the reduced platinum is small enough in size to dissolve in acid; X-ray diffraction shows the remaining 40% is present as 60 Å metal crystals. These data in conjunction with hydrogen adsorption data showing an uptake of 0.5 hydrogen atom per platinum atom lead to an estimate of 10 Å for the size of the acid-soluble platinum, small enough to fit inside the zeolite cages. The exposure of zero-valent platinum to hydrogen leaves the platinum with a negative charge. The exposure of zeolite-supported platinum to hydrogen at 300 °C and 1 atm pressure for 1–2 hr produces a larger change in the platinum X-ray absorption edge spectrum than does a similar exposure at 100 °C. This has been interpreted to mean that a stronger platinum-hydrogen bond is formed at 300 °C. For every platinum atom in the sample 0.5 hydrogen atom is adsorbed after a 1-hr exposure at either 100 ° or 300 °C and 1 atm pressure. This hydrogen affects the X-ray absorption edge spectrum. Therefore, it is this hydrogen that is bonded to platinum and serves as a measure of its size. An additional 1.2 hydrogen atoms can be adsorbed per sample platinum atom at 300 °C under 1 atm pressure by waiting 20 or more hours. This additional hydrogen does not affect the platinum absorption edge spectrum and is therefore interpreted to be not adsorbed by the catalyst platinum.

Measurement of the state of metal dispersion on supported nickel catalysts by gas chemisorption

Gas chemisorption has been investigated as a technique for the estimation of the state state of nickel dispersion on supported nickel hydrocarbon conversion catalysts. Published chemisorption studies on nickel catalysts are critically reviewed. Catalysts which were examined included nickel on alumina and nickel zeolites. Gas chemisorption measurements were supplemented by X-ray diffraction line-broadening determinations to establish the average nickel crystallite sizes. Nickel areas estimated from hydrogen chemisorption at 250°C at a hydrogen vapor pressure of 100 mm mercury and from average nickel crystallite size determined by X-ray diffraction line-broadening were in good agreement. These results provide strong evidence that dissociative hydrogen adsorption occurs only on nickel crystallites of sufficient size to offer adjacent hydrogen adsorption sites. Carbon monoxide chemisorption at room temperature at a carbon monoxide vapor pressure of 100 mm mercury, after correction for carbon monoxide adsorption on the support, provides the more accurate measure of total nickel area including nickel in an atomic state of dispersion. A combination of hydrogen chemisorption or X-ray diffraction line-broadening measurement, plus carbon monoxide chemisorption, can be used to estimate the relative amounts of nickel in comparatively large crystallites (∼50 Å) and in an essentially atomic state of dispersion, as well as the specific surface area of the nickel in these two size ranges.

Applicability of Routine Methods of Crystallite Size Analysis*

AbstractSeveral methods for the routine determination of crystallite size by means of X-ray diffraction line-broadening have previously been reported. Although these techniques have proven useful and reliable when utilized with the single X-ray diffractometer and instrumental geometry used to originally develop the methods, it was not known whether other instruments would provide similar reliability. Therefore a study was performed to evaluate the applicability of routine methods of crystallite size analysis to other X-ray diffraction units. A series of six beryllium oxide powder specimens, whose average crystallite sizes ranged stepwise from about 35 to nearly 3000 Å, were used to test a number of X-ray diffractometers. By using a predetermined diffraction geometry for each instrument tested, measured crystallite sizes were found to be quite reproducible and well within the limits of experimental error. The testing procedure, instrumental conditions, and individual performance results are presented in this paper.

Routine Crystallite-Size Determination by X-Ray Diffraction Line Broadening

AbstractIncreasing interest in the sintering characteristics of various ceramic materials has resulted in the need for a knowledge of the crystallite sizes of many constituent ceramic powders. Standard X-ray diffraction line-broadening techniques have been utilized to determine these crystallite sizes. This paper presents a general review of the theory of line broadening as a means of measuring crystallite size and gives the methods and modifications used to perform this type of analysis rapidly and on a routine basis.Four modifications have been used in the determination of crystallite size routinely by X-ray line broadening. These methods are (1) a graded set of powder photographs, (2) a computer program to calculate sizes from diffractometer data, (3) a set of crystallite-size curves for a given material for use with diffractometer data, and (4) a standard set of curves to use with diffractometer data for any strain-free materials. The preparation, use, and limitations of each of these methods is presented.

X-Ray Diffraction Line Broadening and Strain Hardening

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