Optical transforms are of particular value In the earlier stages of crystal-structure determination; they enable trial structures to be tested rapidly and may indicate the nature of changes which will improve a postulated structure. The optical transforms are produced in a simple instrument called an optical diffractometer. The projected positions of the atoms in a postulated structure are represented by a set of holes punched in a mask, and the diffractometer produces the Fraunhofer diffraction pattern of the mask. The distribution of intensity in the optical transform is comparable, when sampled at suitable Intervals, with the distribution of intensity among the observed intensities in a particular zone of X-ray reflections. The use of optical transforms in the determination of crystal structures and in the study of imperfect structures will be illustrated by examples.

To aid in the study of the preparation and properties at BeO, X-ray diffraction investigations were performed to determine the various phases and transformation temperatures occurring in the different BeO calcination processes and to determine the theoretical density of the final BeO product.

The hydroxide, sulfate, and oxalate of beryllium were the starting materials in the three calcination series. The samples studied were prepared by heating small portions of the starting materials for 1 hr at various temperatures and slow cooling. Analysis of the hydroxide series showed a direct conversion from Be(OH)a to BeO by simple loss of water. However, both the sulfate series and the oxalate series go through a series of intermediate phases in transforming to BeO. X-ray data and structure information have been obtained for most of these phases, and temperature ranges of their occurrence have been established.

Wherever possible, the X-ray results have been compared with results of stereoscopic and polarizing microscope examinations, and temperature range of occurrence have been compared with thermal balance curves.

As part of a study on the fundamental properties of BeO, the surface area, particle size, and crystallite size of BeO powders prepared from different source materials were measured. The results obtained by means of small-angle X-ray scattering and X-ray line-broadening have been compared with electron micrographs and surface area values by air permeability, nitrogen adsorption, and water-vapor adsorption.

Small-angle scattering data were analyzed to yield particle size distribution curves as well as surface areas for various calcined BeO samples. Line-broadening measurements were made to determine mean crystallite dimensions of these same materials. By using both photographic film and automatic recording techniques, crystallite sizes from about 50 to over 5000 A were estimated. The rate of growth of BeO crystals from beryllium hydroxide, beryllium sulfate, and beryllium oxalate source materials has been followed by these complementary techniques.

In the course of work on the vacuum deposition of metallic films, a series of X-ray diffraction investigations was run on the effects of base material orientation, heat treatment, and angle of deposition, on the structure of the deposed films. Results show that the film structure can be altered by changing several parameters during and after the deposition process. An attempt is made to correlate this structure with film adhesion and protective characteristics.

A method has been derived and is currently being used to plot normalized pole figures by computer techniques. As the pole distribution traces, i.e., intensity of the diffracted X-ray beam, versus angular position of the specimen are not an acceptable input for the computer, the data required from such traces are entered onto IBM punch cards. Corrections for defocusing effects may be readily made as the data are transferred from the Brown recorder traces to IBM punch cards. It is possible to program other correction factors into the computer operations providing that these correction factors or curves can be established accurately. The computer translates angular position of the specimen into reactiiinear coordinates which are an identical representation of stereographic coordinates. This computer method has been used in conjunction with the Schulz reflection technique, but modification of the computer program permits its use with other quantitative X-ray techniques for determining preferred orientation.

The feasibility of using computer techniques to plot inverse pole figures has been considered.

The new value determined for the parameter was y= 0.1025 ± 0.0003 compared to a previous value of y= 0.105 ± 0.005 deduced by Jacob and Warren. The absorption errors and preferred orientation effects were eliminated and the statistical precision of the measurements was increased by employing a single-crystal diffractometrlc technique.

The cell dimensions were also refined by using the diffractometric technique for high-purity annealed polycrystalllne uranium. Cell dimensions were ao= 2.854 A, bo=5.869 A, and co=4.955 A, all ±0.002 A. Interatomic distances of the twelve nearest neighbors were two atoms at 2.754 and 2.854 A andfour atoms at 3,263 and 3,342 A. The bond lengths were only slightly affected by the changes in y. The main effects of the new parameter are to alter the component of the bond along the b direction by 0.015 A and to change appreciably the calculated relative diffraction intensities.

The Debye characteristic temperature, θ, of carbonyl iron has been determined as being between 433 and 445°K at an ambient temperature of 310°K from an X-ray diffraction study utilizing both monochromatlzed and filtered radiation by both stationary and scanning slit methods.

In computing θ, several factors have been taken into consideration; the diffracted integrated intensities have been corrected for temperature diffuse scattering (TDS); the temperature gradient through the specimen was found to be critical and given as 160°K/in. at 95°K; corrections for the temperature dependence of θ have been made; and extinction effects were investigated, and results contrary to those of U'lna, Krltskaya, and Kurdyumov have been found.

The TDS corrected values for static and dynamic atomic displacements are also given.

Previous radial distribution work which we have found reported in the literature has invariably been based on film technique. Our work is entirely based on X-ray spectrometer intensity measurements, Radial distribution (RD) patterns for silica gel and η-aluinina are presented and the correlation with accepted structures for these materials demonstrated. The advantages of spectrometer over film technique are discussed. The entire calculation problem has been programed for the IBM 650 computer, A difference technique which appears very sensitive to small structure changes is described and demonstrated for silica-alumina cracking catalysts. A procedure for identifying systematic errors in the RD pattern is presented.

A diffractometer equipped with a gas proportional counter and pulse-height analyzer provides a very satisfactory means of recording the X-ray diffraction patterns of chromium-containing materials with Cu Kα radiation. The fluorescent chromium K radiation can be rejected along with much of the white background radiation without appreciable loss of Cu Kα intensity, and the advantages of copper over chromium or molybdenum radiation can be fully utilized. This is illustrated by an X-ray diffraction study of coprecipitated chromia-alumina catalysts, in which the chromium concentration varies between 0 and 37 w, %. At each chromium concentration the precipitate was studied in the washed and dried state, as well as after calcination at 500, 750, and 1400°C. X-ray diffraction patterns are presented to show the phase transformations and sample inhomogenelties that were observed.

Basic lead azides are obtained by the slow thermal decomposition of PbN6 at temperatures up to 200°C in oxygen, argon, and air containing varying amounts of moisture. The decomposition diagrams show several stages due to the formation of different phases, two of which have been separated. One phase can be identified as a tetragonal deformed cubic lattice. Further slow decompositions of the basic lead azide at 250°C lead to tetragonal lead oxide. The structure of the other isolated phase Is of lower symmetry and has not yet been classified. The results of this investigation are also compared with the work of previous investigators.

Urea complexes consist of a channel made up of hydrogen-bonded urea host molecules into which a variety of guest molecules can fit to form a crystalline complex. The urea host can accommodate, one at a time, a variety of guests having the requisite size and shape. The stability of the resulting complex is a function of the properties of the guest molecule. A procedure has been devised which produces pure complex free of any uncomplexed urea or host molecules in solution. The insoluble crystalline complexes formed from the solution of urea and guest molecule in methanol established a dynamic equilibrium. When the crystals of complex are removed from the solution, dissociation to urea and guest occurs to an extent, depending upon the dissociation constant of the complex. If the dissociation constant, KD, is very low, undetectable quantities of uncomplexed urea form along with complex. If the dlissoclation constant is high, extensive amounts of urea form in the presence of complex. Characteristic interplanar spacing s are obtained for a urea complex irrespective of the guest molecule present. The pattern obtained for the hexagonal complex is completely different from the pattern obtained for tetragonal urea. X-ray examination of a homologous series of compounds gives, for each partially dissociated complex, spacings for both urea and complex. The relative intensities of urea and complex spacings permit the estimation of the stability of such a complex compared to that of other homologues.

Pure cobalt and cobalt-nickel alloys have been plated from simple electrolytic baths with and without additive and with and without ac superimposed upon the dc plating current.

X-ray analysis reveals preferred orientation in the polycrystalline deposits generally and extreme preferred orientation (characterized by [00.2] and [11.0] fiber axes) in the case of those samples obtained with additive-free electrolyte. It is shown that a change in the pH of the bath or the addition of an ac component are equally effective in determining the type of fiber axis in the deposit. The effects on plating texture owing to the use of additive KCNS in the bath are described. Finally, the correlation between the texture and the magnetic properties of the plating Is discussed.

X-ray diffraction studies have revealed that a titanium oxide with an NaCl-type structure is stable over a wide range of nonstoichiometric compositions, both above and below the 1:1 Ti/O atomic ratio. Attempts to prepare a strictly stoichiometric TiO as a single phase have revealed a marked tendency for such a composition to disproportionate into two nonstoichiometric “TiO”-type structures of variable composition, whereas nonstoichiometric compositions can be readily prepared under similar conditions as single, well-crystallized phases.

The oxide Ti3O5, which forms a constituent of the titanium-bearing slags produced in ilmenite smelting, has been prepared as a pure compound in two different crystalline forms, both monoclinic in structure, but one being very close to the orthorhombic pseudobrookite, Fe2O3 · TiO2, or ferrous dititanate, FeO · 2TiO2 structure. This “dititanate” form inverts to the other monoclinic form at high temperatures. Single crystals of the latter monoclinic form are readily made. The studies of the “dititanate” form have been restricted to powder diffraction work, since it inverts to the other form after melting. The two forms show different oxidation behaviors,

The Hilger & Watts microfocus X-ray diffraction instrument has been redesigned to provide a tube allowing up to three times the target loading of previous tubes. The line focus, 6 mm × 100 μ, increases the target loading to 50 kv dc, 10 ma. To accomplish this, a new high-power transformer is provided with a special demountable tube and anode assembly with suitable cooling provided. The original 40 μ and 100 μ tubes are interchangeable with the new tube. Considerable gains in performance with photographic methods are indicated, but more notable is the increase in resolution when the microfocus unit is used as a source of X-ray for a diffractometer. The diffractometer can now be operated under the same conditions as those required for a conventional tube but with the much higher resolution.

A design is described for a variable-temperature diffractometer specimen mount developed internally in the Physics Laboratory of Materials Central. Temperature capability of 1600°C is achieved using Indirect radiation heating. Higher temperatures may be obtained by directly heating the sample. An adaptation allows operation at temperatures as low as −196°C and is useful for studying low-temperature phase changes and examining materials normally liquid at room temperature. The mount operates in vacuum or inert atmosphere. A full 180° 2θ scanning range is possible through the use of curved beryllium- or aluminum-foil windows. Realignment of the sample at temperature and under vacuum may be accomplished from four points around the front plate of the mount. Only two vacuum seals are used In this mount in addition to the window seal and thermocouple seals. Power for the mount is high current, low voltage, and is controlled by an automatic temperature regulator and sensing device which maintains an accurate preset temperature.

Applications of variable temperature techniques on refractory metals, alloys, and compounds are shown, along with an example of low-temperature effects in materials normally liquid at room temperature.

A simple single-crystal goniostat has been built for the Norelco X-ray diffractometer using a modified eucentric goniometer head and the basic geometry of the Norelco pole-figure device.

The goniometer head was modified to provide interchangeable mounting tn the goniostat, a two-circle optical goniometer, or the sample holder of a flat-plate camera.

With this device one can orient and mount a. crystal along any desired direction in a fraction of the time required by conventional film techniques, thus reducing the mounting of a sample for intensity measure ment s for structure determinations or for measurements of anisotropic physical properties to a routine procedure.

A rugged and versatile counter adaptor for a Weissenberg camera is described. It has performed well in two years of daily use which has included collection of intensity vs. temperature data with conventional cold-stream techniques.

Advantage has recently been taken of the adaptor design to mount, directly on the Weissenberg base, a furnace device which blows hot air along the crystal mounting axis. Crystal temperature may be held constant or easily varied over the range up to about 700°C, with no obstruction of the X-ray beams and no readjustment of the furnace position, while the entire zero layer and close-in upper layers are explored.

An investigation of the phase changes in a complex aluminum-titanium-hardened nickel-base high-temperature alloy was carried out after solutioning at high temperatures and aging at lower temperatures. The physical distribution and size of the precipitated phases were studied by electron microscopy. X-ray diffraction and fluorescence analyses were carried out on chemically extracted residues. The results of the xtructure changes as well as correlation of some physical properties with the structural changes are presented.