Position sensitive proportional counters (PSPCs) increase the scope of X-ray diffraction analyses. High pressure flow through type PSPCs can significantly reduce data collecting times due to She ability for simultaneous data collection over large two-theta ranges. This inherent characteristic allows the diffraction user broad capabilities such as scanning very rapidly over large two- theta ranges or collecting data in real time over shorter two-theta ranges without scanning. Thus, we have been able to perform detailed high- temperature experiments in relatively short time frames, observe phase transitions and reactions as they occur, and perform unusual experiments such as observing the crystallization of a plasma spray in-situ.

The advent of intense synchrotron radiation sources for X-ray diffraction has made many otherwise difficult experiments feasible. The increased intensity will not he fully utilized, however, unless there are farther developments in detector technology. Improvement in detector characteristics will, of course, aid those using laboratory sources as well. For instance, construction of low noise, high, quantum efficiency detectors will reduce integration times and enable one to detect weak signals.

The traditional medium for collecting two-dimensional x-ray scattering patterns is photographic film. While x-ray film has excellent resolution, several factors make it a poor choice as a detection device: slow speed, limited dynamic range, the “human factor” (developing, fixing, film handling), and the lack of a commercial scanning system designed for reading two-dimensional x-ray films. Until recently, there were no practical alternatives to the use of photographic film for obtaining two-dimensional x-ray scattering data using a conventional x-ray source. In the past few years, two different detection systems have become available for collecting high quality two-dimensional x-ray scattering data: (1) the Siemens (Xentronics) area detector system, which is a gas filled, wire grid detector, and (2) the Fuji imaging-plate system, which utilizes a phosphor storage plate for imaging the x-ray scattering and a laser scanner to process the image.

Procedures and tools for evaluation of reference x-ray powder patterns in the JCPDSICDD Powder Diffraction File are illustrated by a review of air-stable binary oxides. The reference patterns are evaluated using an available microcomputer version of the NBS*A1DS83 editorial program and PDF patterns retrieved directly from the CD-ROM in the program's input format. The patterns are compared to calculated and experimental diffractograms. The majority of the oxide patterns have been found to be in good agreement with the calculated and observed diffractograms, but are often missing some weak reflections routinely observed with a modern diffractometer. These weak reflections are added to the PDF pattern. For the remainder of the phases, patterns are redetermined.

The availability of automated powder diffractometers, APD, has revolutionized the collection of diffraction data and allowed many improvements in the analysis of these data. The biggest change is the ease of digitizing the diffraction trace rather than preparing it as a strip chart on paper from an analog recorder. When the data are collected properly, the trace is a digitized record of intensity versus 2θ. The trace is an accurate representation of the diffraction pattern containing the sample information along with the spectral and instrument aberrations.

A protocol for semi-quantitative XRD analysis of fly ash has been applied to 178 ashes in studies of the typical mineralogy of high-calcium and iow-calcium fly ash, the consistency of fly ash mineralogy from a typical power station, the partitioning of chemical constituents into crystalline phases, and the crystalline phases relevant to the use of fly ash in concrete.

X-ray powder diffraction (XPD) is an important tool for the chemical characterization of atmospheric aerosol samples particularly when combined with elemental analysis obtained from X-ray fluorescence (XRF) measurements of the same specimen. Aerosol samples obtained in typical monitoring studies consist of thin, uniform deposits of particles corresponding to a known size distribution with aerodynamic equivalent diameters of less than 10 microns.This is an ideal form for X-ray fluorescence analysis since absorption and matrix enhancement effects are minimized. However, the ability to perform quantitative X-ray powder diffraction without the use of internal standards is restricted by several factors which affect the linearity of response between diffracted intensity and sample concentration. In addition to the normal photoelectric absorption due to passage of the X-rays through the sample, XPD intensities can be affected by primary and secondary extinction due to diffraction of the incident beam, particle size effects and preferred orientation of particles.

Li et al (1990) reported experiments with gibbsite powder specimens on the use of Rietveld pattern-fitting, involving the March preferred orientation model, to characterise preferred orientation according to the March r parameter. It was shown that intensity corrections may be applied with the March r parameter derived from Rietveld analysis or with the related line intensity ratio MR which is sensitive to preferred orientation. The present paper reports an analytic expression involving r and MR which has proved highly reliable for the correction of preferred orientation bias in quantitative phase analysis of gibbsite. Similar expressions may be readily derived for other materials for which the March model is appropriate. Therefore the line ratio approach has considerable potential for rapid correction of intensities for preferred orientation.

A powder x-ray diffraction technique has been developed for the quantification of carbamazepine in tablets. The other tablet ingredients were microcrystalline cellulose, starch, stearic acid and silicon dioxide. The tablets were ground in a ball mill and the powder mixed with lithium fluoride (20% w/w) which was the internal standard. Five lines of carbamazepine with d-spacings of 3.38, 3.34, 3.28, 3.26 and 3.23 Å and the 2.01 Å line of lithium fluoride were used for the quantitative analysis. A plot of the intensity ratio (sum of the intensities of the lines of carbamazepine/intensity of die lithium fluoride line) as a function of the weight fraction of carbamazepine in the tablets resulted in a straight line. Using this standard curve, the carbamazepine content in “unknown” tablets was determined and ranged between 98.6 and 101.6% of the actual drug content. The coefficient of variation in the determinations ranged between 0.28 and 2.1%.

The analysis of coal and the understanding of the combustion process is complex, due to the heterogeneous nature of the material and the myriad of high-temperature reactions inherent in this fossil fuel. The research presented below utilizes recently-developed x-ray diffraction methods to analyze the coal combustion products generated from a laboratory-scale entrained-flow reactor. The reactor was designed, constructed, and tested, as planned for the initial phase of a long-term project to evaluate the coals located in Mississippi. In this initial phase a well-characterized coal was used, supplied by The Pennsylvania State University. The proximate, ultimate, and sulfur analyses of the coal, PSOC 1368p, are outlined in the Appendix. X-ray diffraction techniques have been used In the past to characterize coals. An analysis of the mineral transformation during coal combustion has also been performed using x-ray diffraction instrumentation. The semi-quantitative results of the pyrite (FeS2) phase transformation at variable temperatures and the percent combustion of the coal, as determined by x-ray methods are reported below.

Recent advances in techniques to generate static ultra-high pressure (>100 GPa) in the diamond anvil cell have significantly enhanced our understanding of the properties of solids under these extreme conditions. In order to characterize the structure of solids at these pressures, X-ray diffraction using synchrotron radiation has become an invaluable tool. Since the highest pressures are attained at the expense of sample volume (~ 100 μm3) , it is best to use the intense radiation available from a synchrotron to study the very small samples used in ultra-high pressure studies. Even with the intense x-ray beams currently available, it is still often desirable to focus the x-ray beam to increase the available flux. We have developed a focusing system which uses multilayer coated spherical mirrors. With this system, intense x-ray beams with sizes smaller than 10 μm by 10 μm can be achieved at a synchrotron radiation beamline. Previously, we used the focusing system for x-ray microprobe experiments.

Pulsed neutron powder diffraction studies at IPNS have expanded our understanding of the phases present in Integral Fast Reactor (IFR) metal fuel alloys at temperatures in the range of reactor operating conditions. We report results from the binary alloy (U-10wt.%Zr) and ternary alloys (U-8%Pu-10%Zr) and (U-19%Pu-10%Zr). Determining the role and the location of Zr and Pu in these alloys is considered of fundamental importance for maximizing engineering efficiency.

Rietveld profile analysis was utilized to study the phase diagrams. Data were collected at temperatures ranging from 25-650°C. Although the expected U/Pu/Zr phases (α-U, β-U, γ-U, δ-U/Zr/Pu, ζ-U/Pu) were observed in appropriate temperature ranges, there were some unexpected results. Relative amounts of all phases at each temperature were calculated from Rietveld scale factors and inferences were made as to the location of zirconium and plutonium, i.e. amounts in each phase, from site occupancies and absorption characteristics of the phases present. Finally, we were able to identify ZrO and ZrO1-x inclusion phases in the U-Zr alloy present in very small (0.5-1.0%) amounts.

High-temperature x-ray diffraction has many applications. Applied to polymeric materials it is a useful tool for investigating changes in crystallinity, providing insight into molding and extrusion problems, and for examining solvent-resistancy problems. An example of the increasing crystailine character of a polymer as a function of temperature can be seen in figure 1. Diffraction scans at 25°C, 100°C, 150°C, and 200°C clearly show the increasing crystalline character of the potymer with an increase in temperature. Control of sample temperature for a polymer is very important, when analyzing under air, because a momentary overshoot in temperature may lead to the sample igniting. High-temperature investigations of polymers are also subject to the problem of the sample warping and bowing.

Residual strains in a hot-pressed α-Al2O3/25 wt % β-SiC (whisker) composite were determined at temperatures from 25 to 1000°C in 250°C increments. The data collected from the (146) reflections of Al2O3 and the (511+333) reflections of SiC whiskers indicates that residual strains in both phases decrease linearly with temperature; the composite's extrapolated zero-strain temperature is determined to be 1471°C and comparable to the value ~1350 °C obtained by Majumdar et al. from neutron data. The lattice thermal expansion of the whiskers agrees well with literature, data for the monolithic β-SiC form.

Recently, the remains of a giant Cretaceous Sauropod (~150 My old) were discovered in the Morrison Formation west of Albuquerque, New Mexico. This dinosaur, tentatively named Seismosaurus, was found in an exceptional state of preservation. Although it has been known since the 180Q's that fossilized bone is often composed of the mineral apatite, very few studies have been conducted to characterize farther the fossilized material. In an effort to gain insight into the state of preservation and Hie processes occurring in the bone since deposition, apatite in bone from Seismosaurus was compared with that from a contemporary elk from the Jemez Mountains, New Mexico, and with well-crystallized mineral apatite using X-ray powder diffraction and profile analysis techniques. Crystallite size/strain analyses were conducted using the Scherrer equation, the Warren-Averbaca and single-line methods, and the Rietveld method using the program GSAS. Heating the contemporary elk bone produced a decrease in the full-width-at-half-maximum (FWHM) of the reflections in the diffraction pattern. This decrease in FWHM is due to a decrease in microstrain along with a minor increase in crystallite size. Results from crystallite size/strain analysis show that both Seismosaurus and contemporary elk bone crystallites are elongate parallel to the c-axis. However, Seismosaurus bone crystallites are larger (-20-65 nm) with less strain than the contemporary elk bone crystallites (-8-20 nm), suggesting that if elk bone is an appropriate analog, then Seismosaurus bone must have undergone recrystallization.

The complex relationships among composition, roartensite start and finish temperatures, morphology of the martensite, residual stress distribution, and quenching conditions produce significant microstructural changes through a carburized case. Variations in the amount of retained austenite, the diffracting-particle size, and hardness were measured every 50μm in depth through a one percent carbon case on AISI-SAE 4320 steel. Measurement were made to a total depth of 2 mm. The percent retained austenite decreases from a maximum of 26% near the surface to a few percent in the bulk. It is shown that the x-ray diffracting-particle size of the martenaite phase is a structure parameter that changes when the martensite morphology goes from plate to lath type. The austenite phase diffracting-particle size is controlled hy the deformatioxis induced by the martensite formation.

The lattice parameters and strain of ϒ'-phase particles in Nickel-base superalloys, which are duplex type alloys designed for turbine blades and widely called “Ni-base single crystal superalloys”; they are accurately determined by Synchrotron Radiation parallel-beam diffractometry. The superalloys have ϒ' precipitates, an ordered FCC structure based on Ni3Al, in a γ-matrix having disordered FCC structure.

In addition, the preparation method of stress-free ϒ'-phase particles, with no composition change in the preparation process, was newly developed to measure the coherency strain of ϒ'-particles due to lattice misfit. The prepared ϒ'-phase particles are similar in composition and form to ϒ'-phase particles in the γ-matrices. The method for determining of the lattice misfit between the γ and γ’ particles was previously reported.

We have been using crystallite size and strain data obtained from x-ray diffraction (XRD) peak profile analysis to predict the reactivity of solid calcium hydroxide sorbent with acid gases in combustion streams. The development of the method for relating reactivity to crystallite size and strain parameters obtained by the Warren-Averbach technique has been reported by Briden and Natschke and Briden.

The software used for the calculations requires that the XRD peak profile be corrected with a distribution function before application in the Warren-Averbach analysis. The reason for this according to the software developer, Gerhard Zorn, of the Siemens Munich Laboratory, is that he has shown that contributions to the profile from alien peaks and random noise can have serious effects on the Warren-Averbach analysis. The fitting of (he experimental XRD peak with a distribution function provides an effective means for filtering out both contributions.

Asymmetric crystal topography (ACT) in reflection and transmission electron microscopy (TEM) were used to investigate the crystal quality of both typical GaAs substrates and AIGaAs epitaxial layers grown on these substrates. ACT topographs of large sections of 75mm GaAs wafers revealed the presence of several types of crystal defects. All the GaAs wafers surveyed showed the presence of low angle grain boundaries which usually extended over a significant portion of the wafer. In addition, the well-known cell structure dislocation network was always observed in semi-insulating wafers. Less common but often present were inclusions and precipitates. The n-type (Si doped) substrates showed a typical cross-hatched pattern. ACT topography also easily revealed the crystal damage caused by wafer grinding.

Epitaxial layers of AIGaAs were grown by conventional molecular beam epitaxy on these characterized GaAs substrates. ACT topography was used to examine separately the epitaxial layers and substrate crystals. Layers which were grown below the pseudomorphic limit showed crystal features identical to the GaAs substrate on which they were grown and the substrate was unaffected by the presence of the epitaxial layer. AJAs layers which were grown above the pseudomorphic limit were severely dislocated: TEM confirmed the presence of misfit dislocations at the interface. The substrate in this case also showed the presence of crosshatching indicating the the extension of the dislocation strain field into the substrate.

Studies of the shapes of X-ray diffraction peaks from synthetic polymers are still rather uncommon. One probable cause of this situation is the small peak-to-background ratio in most polymer diffraction experiments; it is difficult to achieve precise line profiles for quantitative analysis. Increased utilization of automated data collection/analysis systems and more intense X-ray sources should alleviate this restriction. We suspect, furthermore, that confusion about nomenclature has impeded the acceptance of lineshape analysis for polymers. The peak broadening mechanisms which are generally considered are finite coherence length or crystal size, lattice parameter fluctuation, and displacement disorder of the second kind. Both latter mechanisms have, unfortunately, been referred to as “strains” or “microstrains”. Metallurgists have traditionally expressed displacement disorder as a (length dependent) “microstrain”, and this convention has been adopted in some studies of polymer diffraction. Other work on polymers, however, has termed lattice parameter fluctuation as “microstrain“. The inconsistent use of this term can imply a nonexistent relation between two distinct phenomena.