Cameras for x-ray diffraction

Figure 5.8 A Debye-Scherrer powder camera for X-ray diffraction. The camera (a) consists of a long strip of photographic film fitted inside a disk. The sample (usually contained within a quartz capillary tube) is mounted vertically at the center of the camera and rotated slowly around its vertical axis. X-rays enter from the left, are scattered by the sample, and the undeflected part of the beam exits at the right. After about 24 hours the film is removed (b), and, following development, shows the diffraction pattern as a series of pairs of dark lines, symmetric about the exit slit. The diffraction angle (20) is measured from the film, and used to calculate the d spacings of the crystal from Bragg s law.

Fig. 20. Vacuum camera for x-ray diffraction studies of thin evaporated metal films. [After Rhodin, Metals Transactions 185, 371 (1950).]...

Weissenberg Camera. A camera for X-ray diffraction analysis of crystal structures. The crystal is rotated, in the X-ray beam. The film is rotated and moved parallel to the axis of rotation. Weissenberg Rheogoniometer. In essence a cone and plate viscometer (q.v.), but with accessories and control systems to allow it to measure, as well as viscosity, elasticity and a wide range of flow properties such as dilatancy, thixotrophy, relaxation phenomena, etc in steady rotation or in torsional oscillation, over wide but controlled ranges of temperature and shear. 

For X-ray diffraction, the effect of the absorption on the PID is normally negligible for the purpose of polytype identification, if a sufficient number (e.g., four or more) of periods along the same row are considered and the corresponding PIDs are weighted. The LP factors are critical, however, if the diffraction pattern is taken with a precession camera, because the Lorentz-polarization effect in the precession motion is severe. 

A) Schematic of the Debye-Scherrer method, developed in 1916, for X-ray diffraction of powders (polycrystdlline samples). Each characteristic interplanar spacing in the crystal gives rise to a cone of diffracted X-rays, segments of which are captured on the film strip placed inside the camera. 

Part of the crystals were allowed to dry and were then inserted into thin wall capillaries for x-ray diffraction studies which were made using a Wahrus flat-film camera mounted on a Siemens Kristalloflex X-ray generator. 

A Siemens Kratky camera system was utilized for small angle x-ray scattering (SAXS) measurements in conjunction with an M. Braun position sensitive detector from Innovative Technology Inc.. Wide angle x-ray diffraction was obtained utilizing a Philips table-top x-ray generator. 

X-ray diffraction pictures taken with a flat-film camera show that crosslinked SE-BR samples crystallize on stretching. Sharp reflections are observed at an extension ratio of 4 1 (Figure 4). With samples having different degrees of stereoregularity the order for increasing strain-induced crystallization is the same as the order for the rate of low temperature crystallization. 

The crystal is placed in an X-ray diffraction apparatus (camera or diffractometer) where the X-ray pattern is recorded photographically or by measuring the intensity of the X-rays electronically. The resulting intensity values are used to obtain the observed structure factors which constitute the fundamental experimental data from which the crystal and molecular structures are derived. The structure derived is used for calculating structure factors that are compared with the experimental structure factors during the period when the derived structure is being modified to fit the experimental data. 

The preceding setup allows both X-ray diffraction (32) and absorption experiments (33, 34). The capillary geometry was used until about 30 years ago for ex situ XRD studies in connection with the placement of Lindemann tubes in powder Debye-Scherrer cameras. At that time, films were used to detect the diffracted X-rays. Today, this cumbersome technique has been almost completely replaced as modern detectors are used. 

Cameras in which powder photographs of substances maintained at high temperatures may be taken are much used, especially in metal-lurgy other special cameras have been designed for low temperatures. For reviews of high and low temperature cameras, see the chapters by Goldschmidt and Steward in X-ray Diffraction by Polycrystalline Materials, ed, Peiser, Rooksby, and Wilson (1955). A powder camera for high pressures is described by Frevel (1935). 

X-ray and calorimetric data show that structural changes can occur in TNT on heating and that different forms can be prepared by crystallization and sublimation (Ref 36). Differences in the X-ray diffraction patterns of TNT were shown to be based on the method of preparation of TNT (Ref 35), Post-expin debris were examined by a Gandolfi camera, requiring but a single crystal of TNT of micron size for identification purposes (Ref 149). The X-ray diffraction patterns of TNT are included, together with those of Hexanitrostilbene (Ref 94)... 

Samples of purified EuC12 were analysed for europium and chlorine by conventional analytical methods. Calc for EuC12 Eu, 68.18%. Found Eu, 68.1 x +0.2i Cl, 31.80+0.02. X-Ray diffraction patterns of the polycrystalline samples and residues from the vaporization experiments, to which an internal Pt standard (a = 3.9238 +0.0003 A) had been added, were obtained with a Haegg-type Guinier camera and Cu Ka radiation. The lattice parameters and intensities of the diffraction lines were in agreement with those reported (1) for orthorhombic EuC12 (PbCl2 structure). 

Three analytical tools were used to characterize the compounds. The first is powder x-ray diffraction methods using a 114.6-mm. diameter camera. The photographs were in general poor for germanium telluride and, as a result, the parameters were determined from low-angle reflections only. The second procedure involved room temperature Seebeck coefficient data (taken versus copper and converted to absolute values) which qualitatively vary inversely as the log of the carrier concentration. Finally, Hall measurements were taken on 1.6 X 0.5 X 0.1 cm. plates in a manner already described (6). 

This study is concerned with four different mixtures, including kaolinite and calcite (kc) kaolinite and dolomite (kd) montmorillonite and calcite (me) and montmorillonite and dolomite (md). All the mixtures, by weight, were 95% clay and 5% carbonate mineral. The minerals were first ground to a fine powder and thoroughly mixed by hand before heating in a muffle furnace (temperature controlled to within 20 °C). Each mixture was heated for 1 h, air quenched at room temperature, and analyzed by X-ray diffraction. X-ray films were made in cameras of 11.46-cm diameter with filtered copper radiation and exposure times of 6 h. Several wet mixtures that simulated ceramic paste before firing were heated and studied in like manner, but they showed no differences from the dry mixtures. 

Selected stretched films were Investigated using wide angle X-ray diffraction (UAXD). Sandwiches from the SAXS experiments were also used for WAXD. Samples were Irradiated for 12 hours using a flat plate film camera. A Philips Cu Ra radiation source was used, with power settings of 20 kV and 30 mA. 

X-ray powder diffraction photographs. The quartz capillaries used for X-ray powder diffraction studies were dried under vacuum (10 Torr) at 1070 K for 24 h before being transferred to the dry Ar atmosphere of a Vacuum Atmospheres Corporation DRILAB. X-ray powder samples were prepared as previously described (17). Photographs were taken using a 45-cm-circumference G.E. camera with Straumanis loading, the radiation being CuKa with a nickel filter. 

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