De röntgendiffractie-analyse. Deel 2. Ontwikkeling van technieken

The development of XRD analysis was initiated directly after the discovery of X rays by W.C. Röntgen. The first experimens were conducted under the supervision of M. von Laue, who directed a continuous X ray at a crystal and documented the deflected rays on photographic film. This method, commonly referred to as the Laue method, has now become obsolete. Much research was carried out, following upon von Laue's experiments, by father and son, W.H. Bragg and W.L. Bragg. Not only did the Braggs build a spectrometer which they used to study deflection effects, they also conducted the first real structural analyses. An important step was the powder method of P. Debije and P. Scherrer. Here, instead of a single crystal, a certain amount of powder is used, with the assumption that within a larger amount of crystalline particles there is always a particle in such a position that there is compliance with Braggs equation (see Part 1). For a long time, the deflected X rays were documented on photographic film; nowadays, counters are used which send the data directly to computers which plot them as graphics (the diffractogram) on screen or supply a print-out for visualisation. The huge amount of structural data obtained over the years is contained in data bases. The largest of these is the PDF (Powder Diffraction File) of the International Centre for Diffraction Data, with currently 131,000 phases. With this data base at hand, unknown phases resulting from analyses may be comparatively rapidly identified by comparison.