X-ray measurements of strain and mosaic particle size in annealed tungsten powder

X-ray line profiles of annealed tungsten powder of 99.9% purity were measured with a high resolution of the order of 0.01° (2θ). A primary beam of Mo Kα₁ radiation which had a divergence of less than 0.01° in the plane of the diffractometer was used. After elimination of all instrumental effects, the mosaic particle-size broadening and the strain broadening were obtained. With the approximation of spherical particles a generalized Maxwellian mass distribution with a mean particle radius of 2500 Å and a poly dispersity of 25% was found. A strain of 3.6 × 10⁻⁴ in the mosaic particles was observed. The results are compared with various theories of X-ray scattering from dislocation arrangements. Two interpretations of the strains are discussed. The strains originate either from dislocations in the walls of the mosaics or from dislocations inside the mosaics. In the latter case less than two dislocations are present in the mosaic particles. The strain broadening function was found to be Gaussian for strains less than 2 × 10⁻⁴ and to be above the Gaussian function for larger strains.