Quantitative phase analysis by XRD requires the attainment of (1) random crystallite orientation and (2) homogeneous and intimate mixing of the constituent phases in the samples. These two requirements must also be met in the preparation of random composite materials, particularly those containing randomly-oriented fibers or whiskers.

The two most common methods for producing random crystallite orientation are spray drying and the air suspension method. In the latter, an air suspension of the crystallites is rapidly collected onto a glass fiber filter. The crystallites then assume the random orientation of the filter fibers on which they are deposited.