|
International
Tables for Crystallography Volume C Mathematical, physical and chemical tables Edited by E. Prince © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. C. ch. 2.3, p. 71
|
The symmetrical back-reflection camera, Fig. 2.3.4.1(e)![[link]](/graphics/greenarr.gif)
, is mainly used for lattice-parameter and solid-solution studies because the high reflection angles can be recorded. The specimen can be mounted on a curved holder matching the film curvature to obtain sharp lines and is oscillated during exposure.
The flat-plate camera, Fig. 2.3.4.1(f), can be used for forward- or back-reflection. The angular range is small and varies inversely with the specimen-to-film distance. Polaroid film is frequently used. The same method is used for Laue photographs, usually in back-reflection with a goniometer to orient the crystal. The method is often used for fibre and polymer specimens because the entire cone can be recorded (Alexander, 1969).
The Gandolfi (1967) camera produces a powder-like pattern from a tiny single crystal by simultaneous rotation of the crystal around two inclined axes. It is often made as a modification to the cylindrical camera. The crystal may be very small but the pattern is greatly improved by using several crystals. The smoothness of the lines depends on the chance orientation of the crystal with respect to the rotation axes, and the multiplicity of the reflection. The centring of the specimen and the rotation axes must be done precisely. Anderson, Zolensky, Smith, Freeborn & Scheetz (1981) obtained patterns routinely from 5 μm particles in 2–4 d exposure at 40 keV, 20 mA in an evacuated camera; see also Sussieck-Fornefeld & Schmetzer (1987) and Rendle (1983). A high-brilliance microfocus X-ray tube can greatly increase the intensity.
Another type of camera for the same purpose was developed by Parrish & Vajda (1971). The small crystal is mounted on a glass fibre at the end of a vertical shaft that rotates continuously and simultaneously scans about 90°. The film is mounted in a half-cylinder with about 20 mm radius. A microscope is used for precise alignment and centring.
A camera with a wide film cassette has been used for high-temperature diffraction patterns. The cassette can be translated synchronously with the change in temperature, or held in fixed positions during exposure at selected temperatures. The advantage is that all the patterns are recorded on a single film showing the phase changes and thermal expansion as a function of temperature. A Weissenberg camera can be adapted for this purpose.
References
Alexander, L. E. (1969). X-ray diffraction methods in polymer science. New York: John Wiley. [Reprint 1979; Huntington, New York: Krieger.]Google Scholar
Anderson, C. A. F., Zolensky, M. E., Smith, D. K., Freeborn, W. P. & Scheetz, B. E. (1981). Applications of Gandolfi X-ray diffraction to the characterization of reaction products from the alteration of simulated nuclear wastes. Adv. X-ray Anal. 24, 265–269.Google Scholar
Gandolfi, G. (1967). Discussion upon methods to obtain X-ray `powder patterns' from a single crystal. Mineral. Petrogr. Acta, 13, 67–74.Google Scholar
Parrish, W. & Vajda, I. (1971). X-ray camera having a semicylindrical film holder and means to simultaneously rotate a specimen about two mutually perpendicular axes. US patent No. 3 626 185, 7 December 1971.Google Scholar
Rendle, D. F. (1983). A simple Gandolfi attachment for a Debye–Scherrer camera and its use in a forensic science laboratory. J. Appl. Cryst. 16, 428–429.Google Scholar
Sussieck-Fornefeld, C. & Schmetzer, K. (1987). A modified Gandolfi camera with improved adjustment facilities. Powder Diffr. 2, 82–83.Google Scholar
