Vaporization Kinetics and Thermodynamics of Antimony and the Vaporization Coefficient of Antimony Single Crystals

The vaporization rate of Sb₄ from Sb (111) single‐crystal cleavage faces has been measured over the temperature range 606–697°K using a recording vacuum microbalance. The results, expressed as Langmuir vapor pressures $P_L$ , yield $R\ln P_L(\mathrm{atm}\text{)\hspace{0.17em}=\hspace{0.17em}−[(49 740\hspace{0.17em}±\hspace{0.17em}2200))\hspace{0.17em}/\hspace{0.17em}T]\hspace{0.17em}+\hspace{0.17em}(35.67\hspace{0.17em}±\hspace{0.17em}3.4)}$ . At 650°K $P_L{\text{\hspace{0.17em}=\hspace{0.17em}1.2\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−9}}\mathrm{atm}$ . Comparison with equilibrium vapor pressures $P_E$ yields a vaporization coefficient ${\alpha }_{\upsilon }{\mathrm{\hspace{0.17em}=\hspace{0.17em}P}}_L{\mathrm{\hspace{0.17em}/\hspace{0.17em}P}}_E\text{\hspace{0.17em}=\hspace{0.17em}0.17\hspace{0.17em}±\hspace{0.17em}0.06}$ at 650°K which increases with temperature ${\alpha }_{\upsilon }\mathrm{\hspace{0.17em}=\hspace{0.17em}}\exp \text{(−2310\hspace{0.17em}/\hspace{0.17em}RT)}$ . The data are corrected for evaporated molecules which return to the sample. Vaporization rates of antimony powder and Kundsen effusion experiments in the same apparatus confirm the value of ${\alpha }_{\upsilon }$ . The apparent vaporization coefficient from the powder, 0.54, correlates well with the single‐crystal results. Kundsen‐effusion experiments at 683–819°K using a 0.4‐mm‐diam‐orifice aluminum cell give $R$ ln$P_E$ (atm) = − 223[(47600 ± 1330) / T] + (35.65 ± 1.79) and a third‐law enthalpy of sublimation ${\mathrm{\Delta H°}}_{298}\text{\hspace{0.17em}=\hspace{0.17em}49.67\hspace{0.17em}±\hspace{0.17em}0.32}\mathrm{kcal}/\mathrm{mole}$ in good agreement with other determinations. Averaging these results with those from other investigations leads to ${\mathrm{\Delta H°}}_{298}\text{\hspace{0.17em}=\hspace{0.17em}49.55\hspace{0.17em}±\hspace{0.17em}0.31}\mathrm{kcal}/\mathrm{mole}$ . The vaporization behavior of arsenic and antimony is compared and the differences in vaporization coefficient are rationalized as reflecting differences in atomization energies of the gaseous tetramers and in equilibrium enthalpies of vaporization.