ABSTRACT
In the early 1970s we used a Gandolfi camera to collect diffraction patterns from single grains or very small amounts of powder. The Gandolfi camera used a method by which the sample is placed on the end of a fiber. Two axes of rotation (Jenkins and Snyder, 1996) were used to smooth out the effects from crystallite size and preferred orientation. Data was collected using 35-mm film just as with the Debye-Scherrer camera. The advantage this method has is that it allows collection of nearly the full possible range of two-theta values as opposed to the limited range in the microcamera, which is generally less than about 40° two-theta. Another important addition to MXRD equipment is the capillary optic. The refractive index for X-rays is slightly less than 1. Thus, total reflection occurs when
the beam is passing from a less dense medium to a denser medium. If the capillary is conical, the X-ray beam can be funneled down to a smaller size with a higher intensity compared to the primary beam. Hirsch and Kellar (1952) were one of the first to employ capillary optics for MXRD. They developed a precision-built camera designed for transmission and back reflection patterns on flat film. This camera used a glass capillary drawn down to a few micrometers. The X-ray source was a fine-focus rotating anode. Capillaries of different sizes were utilized in order to measure crystallite size by counting the spots contained in the Debye rings. This technique was capable of measuring crystallite sizes below I J1ffi The present use of glass capillaries as collimators and X-ray wave guides is described by Engstrom (1991). More discussion of capillary optics is given in the section on MXRF Diffractometer Methods In the early 1970s Rigaku Corporation started the process of developing a commercially available micro diffractometer. Previous to this development the incident beam was reduced into less than a millimeter or so by using collimators or crossed slits size on a standard diffractometer. These methods were marginally effective. When Rigaku started its endeavor the experimenters tried various detector configurations in order to obtain the best possible balance of two-theta range while minimizing the effects from orientation and crystallite size. The early Rigaku configurations are described by several authors (Araki, 1989, DeHaven, 1994; Goldsmith and Walter, 1987). DeHaven (1994) from the IBM Corporation used a diffractometer that employed a horizontal diffractometer and a scintillation detector. He and others (Goldsmith and Walter, 1987) from IBM also used an unusual design shown in Fig. 2, which used a scintillation detector to collect diffraction data in the front reflection region and a ring-shaped gas-filled proportional counter to collect data in the back reflection region. The detectors were moved along an axis to collect data from a large two-theta range. The detector configuration allowed for the collection of entire diffraction rings. Another advantage of this instrument was the ability to analyze samples in situ, and strain analyses could be done because of the ability to collect data from the higher two-theta regions. This method had the disadvantage of having to merge data from two different types of detectors. In addition, it was difficult to align and the data were difficult to interpret.
