The success of a diffraction experiment often depends on the proper preparation of the sample under study. Many different methods of sample preparation have been devised for many different purposes. A survey was conducted to collect together many of these methods, and the results are reported in this paper.

There are three factors which may influence the method by which a piece of evidence is analyzed in a forensic laboratory. The first stems from the definition of the word forensic. It means ”… pertaining to, connected with, or used in the courts of law…” The major areas of forensic analysis are criminal, regulatory, and civil. The purpose of an analysis may be to aid in the prosecution or defense of criminal charges, to determine if a product meets its statutory requirements, to satisfy a consumer complaint, or to determine liability. For these reasons the legal aspects of an analysis may often put constraints upon the analyst. These may require special handling or documentation procedures.

Studies of changes in the flexural strength and phase composition of castable refractories are being carried out in simulated coal gasification reactor environments. This paper describes a pressure vessel in which x-ray powder diffraction measurements can be made by an energy dispersive method while the specimen is being heated to temperatures as high as 1000°C in atmospheres containing H2O, CO2, CO, H2, CH4, NH3 , and H2S at pressures up to 7 MPa (1000 psig).

X-ray diffraction studies on radioactive materials are reviewed. Considerable emphasis is placed on the safe handling and loading of not-too-exotic samples. Special considerations such as the problems of film blackening by the gamma rays and changes induced by the self-irradiation of the sample are covered. Some modifications of common diffraction techniques are presented. Finally, diffraction studies on radioactive samples under extreme conditions are discussed, with primary emphasis on high-pressure studies involving diamond-anvil cells.

This paper presents a comprehensive study of various applications of x-ray fluorescence and diffraction techniques for the characterization of thin films. With the proper use of x-ray instruments and techniques, a fairly complete understanding of the chemical and physical structure of thin films was obtained. The x-ray fluorescence (XRF) method was used for the determination of composition, mass-thickness, and density. The x-ray diffraction (XRD) method was used for structural characterization, including: local atomic arrangements of amorphous materials; phase identification, preferred orientation, crystallite size, stacking faults, microstrain, the annealing behaviors of polycrystalline films; and lattice mismatch between the epitaxial film and its single-crystal substrate.

In order to obtain a clear picture of the capabilities of the x-ray method and the properties of thin films, a series of carefully selected specimens representing a wide range of compositions and thicknesses was used. A number of practical x-ray techniques, which are valuable for this type of analysis, are also introduced.

To assure an adequate supply of such critical metals as nickel and chromium, extraction procedures must be developed to process low grade domestic sources. In optimizing these procedures it is essential to use suitable analytical procedures to characterize the materials, identify phase transformations, and determine metal and mineral association of the critical metallic elements through all stages of the process. Evaluation of complex sources such as laterites requires special material handling techniques coupled with X-ray diffraction and with optical and SEM analyses of many individual particles. A joint study by the Bureau of Mines and the Denver Research Institute using these procedures has resulted in optimizing a new modification of an extraction process.

The spray drying of powders is a method of forming spherical or torroidal shaped agglomerates. A relatively simple method is given for preparing spray dried samples of the quantities used in x-ray diffraction analysis. This technique is shown to minimize preferred orientation effects on diffraction intensities from materials of widely differing symmetry and crystallite habit.

An assembly consisting of an X-ray tube, a quartz crystal monochromator, and a vertical X-ray goniometer with proportional counter was mounted in a glove box for work with actinide metals and compounds. An evacuated camera containing the expander tube of a closed-cycle cryogenic system was fitted onto the goniometer. A thin layer of the powdered sample was fixed on the end-plate of the expander tube. Beryllium windows were provided in the camera wall for the incident and for the diffracted beam.

The cooling camera is suitable for use with thin powder layers or metallic foils. Thicker layers can be studied, but a strong thermal gradient perpendicular to the specimen surface is expected. The camera has been applied to the study of lattice contraction and phase transformation at low temperature In actinide metals and compounds .

X-ray powder diffraction (XRPD) analysis has proven to be extremely valuable in the study of the transplutonium elements. The high specific activity and the thermal energy associated with the radioactive decay of einsteinium isotopes make XRPD analysis of einsteinium samples very difficult. The major problems are destruction of the samples crystallinity and alteration of their chemical composition. Blackening of the X-ray film also compromises the analyses. By applying certain guidelines given here, a limited amount of success has been achieved in obtaining diffraction data on einsteinium and some of its compounds.

Three variables in the identification of crystalline multiphase unknowns by computer search/match methods were examined: presence or absence of chemical information; varying quality of d-I diffraction data; use of a large data base vs a data base having about 10% as many entries--both contain the unknown phases. The results showed that the search/match using average quality d-I data with chemical information was quite successful, while that obtained using higher quality d-I data alone missed one of four phases. It took only half the time to obtain the average d-I data plus chemistry as it did to obtain the higher quality data. Searching the smaller data base with the higher quality data alone resulted in an identification of all phases with high reliability.

A program system design which will facilitate the exchange of automated diffractometer control programs is presented. The various procedures for collecting data and finding peaks, not involving profile fitting, were programmed, tested and evaluated. The optimum strategy evolving from this work involves a decision making algorithim which locates and removes the experimental threshold from the digital diffraction data, removes the Kα2 component, smooths and locates diffraction peaks via a second derivative procedure.

Six computer synthesized data sets, each representing a mixture, and one physical mixture were prepared and widely distributed in order to study the various search/match methods and factors which affect their success. A total of 67 returns were received representing eight countries and three search methods. The participants were primarily from industrial laboratories. The average score exceeded 90%. The Hanawalt search method yielded the best overall score. Use of the Frequently Encountered Phases subfile decreased the search time by about 40% and marginally increased the success rate. For the physical mixture the Δd/d and ΔI/I values were measured to about 2/1000 and 40% respectively. Use of an internal standard improved the d-values by a factor of 2 and resulted in better search/match performance.

In most routine chemical analyses, a trade-off is made between quality of data and time required to obtain and analyze the data.In X-ray powder diffraction, identifications are normally made by Debye-Scherrer film methods or by medium speed (1-2°20/min.) diffractometry, with or without an internal standard. With one notable exception, the inherent precision of the Guinier camera geometry has been virtually ignored as too expensive or time consuming for routine work, or relegated to special projects. The accessibility of microcomputers, however, not only makes it economically and realistically feasible to automate the equipment previously used for special Guinier projects, but to extend the overall precision of observed d-spacings into the area of routine analysis. Search-match procedures benefit from the increased data precision to such an extent that they can be used routinely to propose the identity of major pure phases and release the analyst to concentrate on minor components and impure phases which may be subject to lattice constant shifts.

The interfacing of a Hewlett-Packard 9825 calculator to an Enraf-Nonius microdensitometer and a Philips powder diffractometer provides automated data collection and manipulation on a routine basis. Data is acquired and stored on a floppy disk; background corrections are made; diffraction peak maxima are found, normalized and plotted; a table of approximate d-spacing (±0.0lÅ) is printed. The analyst designates the internal standard peaks. Corrected d-spacings are then computed, tabulated and printed above the appropriate peak. An accurate d-spacing scale is drawn on the plot. The total time for a scan is approximately twenty minutes with only about five minutes of operator time required. The program is conversational and requires little prior knowledge of the software by the operator. Data interpretation is further aided by supporting programs to calculate patterns from literature, determine lattice constants for observed phases, help index patterns, deconvolute overlapping peaks, carry out crystalline size determinations and perform search/match procedures. Such supporting programs are possible because, even though the system can be used in a “dedicated” manner, it is still a stand-alone computer. Thus, the desired degree of automation in data collection has been obtained without sacrificing flexibility.

Automated powder diffractometers are beginning to come into general use. The principal reason for automating or purchasing an automated powder diffractometer is to increase the speed and accuracy of the analysis. Three principal methods are used. The first is that a multisample changer increases the through-put on the instrument since the unit can be operated unattended during the evening. The second is the diffractometer can be scanned at faster rates when digital data are collected, as opposed to the analog method of using a strip chart recorder. The third is the elimination of reading the peak positions and intensities from the strip charts. These readings would typically have to be tabulated manually for later interpretation. Another reason for having an automated powder diffractometer is for experiments where digital data are necessary to make the analysis practical. These experiments include routine quantitative analysis, radial distribution functions, Fourier profile analysis, and signal averaging to bring out very weak diffraction peaks.

The Castel dell'Ovo on the Bay of Naples, Italy, is an important historic structure dating from the 12th century. It is composed of a soft, volcanic tuff that was employed because it was locally available and easy to quarry and work. The exposed stone of this monument shows extensive decay, principally in the form of the crumbling away of the surface, and this has progressed to the greatest extent in the lower parts of the structure. Restoration and preservative intervention are now being considered. The essential prerequisites to the formulation of a safe and effective strategy of treatment of the monument are the understanding of the nature and properties of the stone, and of the factors responsible for its decay. The present investigation was undertaken to provide that information. In the course of these studies certain novel and significant features of the crystal chemistry of one of the common zeolite minerals have been observed, and are reported here.

Spray drying is shown to be an effective and rapid method for preparing samples for quantitative analysis by x-ray powder diffraction. Previously intractable problems like the simultaneous analysis of multiple phases in orientation prone systems can be carried out. Using this method, and a computer controlled diffractometer, five and six phase analyses of Devonian shales can be accomplished in approximately forty minutes. A rapid and convenient method for using the absorption diffraction technique for x-ray quantitative analysis is described.

Natural zeolite 1010A, mostly clinoptilolite, was found to be stable to prolonged heat treatment up to 600° C. Stability to treatment by acids and bases is dependent on solution strength, treatment time and temperature. Variations in intensities of diffraction lines correlate well with changes in exchange capacities for ammonium ions and other observed physico-chemical changes.