A Comparison of Methods for Reducing Preferred Orientation

Abstract

Preferred orientations in powder diffraction specimens can cause large errors in measured intensities. An extreme case is shown in Figure 1, Smith and Barrett (1979) reviewed the various methods which have been proposed for reducing this effect. Subsequently, two methods which are used commercially for aggregating finely divided solids have been proposed for preparing powder diffraction specimens (Smith, Snyder, and Brownell, 1979; Calvert and Sirianni, 1980). In one of these, spray drying, a finely divided solid is suspended in a liquid together with small quantities of a deflocculent and a binder. This mixture is pulled by venturi action through a nozzle into a heated chamber. The spherically shaped aggregates dry before falling to a collection surface. The apparatus is fairly large (3 X 3 X 4 ft. at NBS), and operating parameters must be carefully chosen.