X-ray diffraction camera

Assembly of the mounted crystal onto the X-ray diffraction camera... 

The x-ray studies were made with a high-temperature x-ray diffraction camera of Hume-Rothery design. This camera had a 9-cm. diameter and employed the Straumanis film setting. A fine Chromel-Alumel thermocouple within the furnace cavity and adjacent to the sample served to measure and control temperature. The sample temperature was calibrated against the thermocouple e.m.f. through a series of lattice-constant measurements on pure silver. 

INTERLOCKS ON - Equipment with internal hazards, such as X-ray diffraction cameras, or areas in which the space is rendered unsafe to enter by the presence of a hazard, are often provided with a fail safe circuit, or interlock, which will turn off the equipment representing the problem if the circuit is broken. The sign provides a warning that the interlock is on to prevent access to the hazard. 

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. 

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.

Considering the fact that the X-ray diffraction pattern of a crystal depends on its lattice structure, pigment powders can be analyzed with a Debye-Scherrer diffraction camera to establish a correlation between X-ray diffraction and crystal modification. It is synthetically not possible to produce a defined crystal modification of a new pigment. Attempts to modify the preparative procedure or to apply different aftertreatment may result in a pigment of two or more crystalline forms, different not only in lattice structure, but also in color and performance. 

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). 

Figure 3. X-ray diffraction diagram of an oriented bundle of complex crystals in a fine glass capillary. Needle axis is vertical, and pattern was recorded with flat plate camera...

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)... 

It will be assumed here that the X-ray diffraction data were collected on flat films with a point focus camera. This simplifies the theoretical presentation. The TMV data analyzed in the results section were collected on cylindrical films with Guinier cameras, but positions on the cylindrical films can be mapped onto positions on a flat film by a simple geometric transformation. In general, the form of the optical density, D(r,), in a fiber diffraction pattern can be expressed in film coordinates as the sum of contributions from all reflections, I (r,iJ> ), plus a background term, B(r,) ... 

X-ray diffraction photographs were recorded on flat film using a camera with pinhole collination (250 ym diam.) and Ni-filtered Cu Ko radiation. Calcite (characteristic spacing 0.3035 nm) was used as an internal diffraction calibration. Interplanar spacings were measured off the original photographs and the unit cell dimensions were refined, where possible, by a least-squares procedure. 

X-ray diffraction (XRD) patterns of small portions of the solids were periodically obtained with a Gandolfi camera using CuK radiation (10) to monitor crystallinity. 

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). 

X-ray diffraction patterns of vitamin Bg and other vitamins by a precision x-ray camera, have been determined. Elementary cell-dimension studies have been reported (11). 

---