Barium titanate powders undergo a phase transition (PT) at a temperature of 125ºС; it is displaced toward lower temperatures when the powder is modified using different elements that replace barium or titanium cations [1]. These investigations of the temperature dependence of radiant emittance ε are important for practical application, since barium titanates with partly substituted cations can change the radiation power and stabilize the temperature of the objects on which they are deposited. In addition to ε, these coatings are characterized by the diffusion reflection spectra ρ λ that determine their color and solar radiation reflection coefficient. The spectra ρ λ of coatings and their stability under operating conditions depend on their granulometric composition determining the value of the specific surface and concentrations of unsaturated bonds and native defects [2].To modify the BaTiO 3 powders, they are heated with powders comprising substitution atoms. Therefore, it is of scientific and practical interest to study the influence of the modification conditions on the granulometric composition of the BaTiO 3 powders. The present work is aimed at investigations of changes in the granulometric composition of barium titanate powders subject to heating and grinding that are the integral parts of the modification processes.The BaTiO 3 powders were heated for 2 h at Т = 800ºС and grinded for 5 min. The granulometric composition was investigated for the initial powders, after their heating, grinding, and after joint subsequent heating and grinding. Photomicrographs of powders were recorded using a ТМ-1000 scanning electron microscope. They were processed to construct histograms and particle size distribution functions (Fig. 1) which were then decomposed into Gaussian curves. The decomposition demonstrated (see the insert in the figure) that all powders comprised particles of four sizes. The distribution maxima r max of the initial powder (curve 1) were at 1.06, 1.71, 2.77 and 5.17 μm, and their areas S were equal to 27.4, 46.1, 35.7, and 43.8 particles⋅μm, that is, the least number of the smallest particles and the numbers of particles of average and large sizes were approximately identical (see Table 1).The particle size distribution changed insignificantly after heating (curve 2), namely, the positions of maxima of distributions 1-4 were displaced to 1.03, 1.72, 2.82, and 4.88 μm, that is, by 0.03, 0.01, 0.05, and 0.29 μm, respectively. The areas of the first and second Gaussian curves increased by 7.3 and 4.6 particles⋅μm, whereas the areas of the third and fourth Gaussian curves decreased by 6.4 and 4.6 particles⋅μm, that is, the total increase of the areas of the first two Gaussian curves was approximately equal to the total decrease of the areas of the last two Gaussian curves.The number of small particles increased at the expense of fragmentation of large particles. Moreover, the number of the smallest particles increased faster, and the number of particles No. 3 with maximum at 2.77 μm decreased also fast...
