X-Ray Diffraction Phase Analysis Using Microcomputers

X-ray diffraction to determine the phases present in complex specimens generally proceeds by acquiring a pattern of D-spacings and intensities from the sample, which is then compared to patterns from a series of known or standard phases. The process of searching through large data bases to identify matches is too time consuming for manual methods, and so computerised search/match programs have come into use. The magnitude of the general problem, in which perhaps 40,000 known patterns (corresponding to the present size of the JCPDS powder diffraction file) are involved, places it in the realm of large nainframe computers, which are often accessible on a time-share basis by many laboratories or researchers using XRD. On the other hand, in many practical applications, the search need only be carried out over a limited range of compounds which are expected or may possibly be present based on the known history of the material, or on its independently determined composition. In this case, the data base becomes much smaller, and can be accommodated In micro- and minicomputers. The system we report here utilizes a 64K-byte 8 -bit microcomputer (Apple 11+) with dual floppy disk drives. One 5-1/4 inch disk can hold the pattern information for fifty compounds, and can be searched for possible matches in a few minutes. The same computer can control the scanning diffractometer to acquire the pattern data, and can act as an intelligent terminal to larger time-share machines when it is necessary to access the large data bases.