Several examples of time-resolved X-ray powder diffraction studies with linear position-sensitive proportional counters (PSPC) are described. The changing patterns are recorded by spectrum multiplexing in a multichannel counter device. The time resolution for single processes is limited to seconds or tenths of seconds mainly because of the counting statistics of the observed peaks. Repetitive processes, however, where the interesting peaks can be accumulated over a large number of periods, permit much higher time resolution. It is finally determined by the timing of a detected X-ray quantum. Using a continuous beam source like a conventional X-ray tube the incidence of a photon into the PSPC can be timed with an accuracy of 20 ns (fwhm). A pulsed synchrotron radiation source, like a storage ring, will be able to define this resolution to its pulse duration, which is less than 200 ps.

Before approaching those limits this paper presents the high temperature phase transformations in iron for different steel specimens as an example of single processes. It also discusses domain-wall effects and electrostriction in ferroelectric perovskites as a function of polarization at frequencies of up to 10 Hz, and elastic lattice distortions of a steel sheet vibrating at about 200 Hz. The timing limit of 20 ns for the PSPC detection system was measured at the storage ring DORIS at DESY, Hamburg.