Kinetic regularities of the precipitation of PbS nanocrystals in sodium zinc silicate glasses

The kinetics of formation of nanostructured glass-ceramic materials based on silicate glass doped with lead sulfide PbS is investigated using small-angle X-ray scattering and X-ray powder diffraction. The influence of two-stage heat treatment on the properties of the material is studied. It is established that, in the initial stages of the precipitation during secondary heat treatment, the volume of the lead sulfide phase increases proportionally with the cube of the nanocrystal size; i.e., the number of growing particles is constant and does not depend on the temperature of the secondary heat treatment. At high temperatures of the secondary heat treatment, an increase in the heat treatment time leads to a decrease in the volume of the crystalline phase. The inference is made that this effect is possibly caused by the reaction PbS + Na2O = PbO + Na2S, which should bring about a decrease in the lead sulfide concentration in the matrix and the dissolution of precipitated nanocrystals. The observed kinetics of crystal growth has defied description in terms of the known mechanisms. This is explained by the occurrence of a competing process of dissolution of the crystalline phase that is responsible for the absence of the Ostwald ripening stage, which is governed by the universal kinetics of diffusion phase decomposition at the late stages in supersaturated solid solutions.