Phase transformations in sodium zinc silicate glasses containing PbS nanocrystals

The phase composition and the kinetics of formation of the lead sulfide crystalline phase at the late stages of heat treatments of sodium zinc silicate glasses have been investigated using small-angle X-ray scattering and X-ray powder diffraction. It has been established that, after the completion of the precipitation of the PbS crystalline phase, the reaction PbS + ZnO = PbO + ZnS begins to proceed on the surface of nanocrystals. This reaction results in a decrease in the volume of the PbS phase and the precipitation of ZnS nanocrystals. The size effect has been revealed: PbS nanocrystals with a radius larger than approximately Å are stable, whereas nanocrystals with smaller sizes initiate the reaction PbS + ZnO = PbO + ZnS.