Diffusion and Exchange of Zinc in Crystalline Zinc Sulfide

Abstract

The diffusion and exchange of zinc vapor with crystals of zinc sulfide has been measured from 925 to 1075°C. The measured exchange rate was observed to be controlled by the diffusion of Zn in ZnS. A critical examination of the log D versus 1/T plot reveals that three distinct diffusion processes are operative in the temperature range studied. At 1 atmos zinc pressure, the diffusion coefficients were calculated as $${\text{D=3×10}}^{\text{−4}}\exp \text{(−35\hspace{0.17em}}\mathrm{kcal}\mathrm{/RT)\hspace{0.17em}}{\mathrm{cm}}^2\hspace{0.17em}{\sec }^{\text{−1}}$$ below 940°C, ${\text{D=1.5×10}}^4\exp \text{(−75\hspace{0.17em}}\mathrm{kcal}\mathrm{/RT)}$ cm² sec^—1 between 940° and 1030°C, and $${\text{D=1×10}}^{16}\exp \text{(−150\hspace{0.17em}}\mathrm{kcal}\mathrm{/RT)\hspace{0.17em}}{\mathrm{cm}}^2{\sec }^{\text{−1}}$$ above 1030°C. Variation of zinc pressure from 0.25 to 2.0 atmos showed that D varies as P_Zn^1.5. Values of D were observed to increase with increasing penetration of Zn into the ZnS crystals. The kinetic and structural interpretations of these results are discussed.