Effect of crystal, grain, and particle size on X-ray power diffracted from powders

Abstract

A theoretical and experimental investigation has been made on diffraction of X-rays from crystalline powders in which the diffracted power is modified by the powder coarseness and absorption inhomo- geneities in the sample. Compared with previous theories, the present theory is more extensive and has been found to fit the experimental data better. The magnitude of the diffracted power is related theoretically to particle diameter, linear absorption coefficient, degree of compaction of the powder, crystal size, primary extinction coefficient, crystal-chemical composition and grain size for polyphased particles. It is shown theoretically and experimentally that these variables can cause the diffracted power to be significantly different from that for an ideal case. For a powder of a single substance (iron), excellent agreement between theory and experiment has been obtained for the effects due to particle size, absorption coeffieient and degree of compaction. Theoretical predictions of diffracted power from an iron-tungsten mixture have been substantiated experi- mentally. Measurements on heat-treated iron samples show that the diffracted power decreases with increasing crystal size, and indicate that the equation for this effect might be useful in determining crystal sizes in the range 10 -5 to 10 -8 cm.