Vaporization Thermodynamics of Yttrium Dicarbide–Carbon System and Dissociation Energy of Yttrium Dicarbide and Tetracarbide

The Knudsen effusion method was used in conjunction with a double‐focusing mass spectrometer to study the vaporization of the yttrium dicarbide–carbon system. Over the temperature range from 2270 to 2550°K the measured vapor pressures for yttrium, yttrium dicarbide, and yttrium tetracarbide were found to be ${\log }_{10}P\mathrm{Y}{\text{\hspace{0.17em}=\hspace{0.17em}(−\hspace{0.17em}2.423\hspace{0.17em}×\hspace{0.17em}10}}^4\text{\hspace{0.17em}/\hspace{0.17em}T)\hspace{0.17em}+\hspace{0.17em}9.45,}{\log }_{10}{P}_{{\mathrm{YC}}_2}{\text{\hspace{0.17em}=\hspace{0.17em}(−\hspace{0.17em}3.286\hspace{0.17em}×\hspace{0.17em}10}}^4\text{\hspace{0.17em}/\hspace{0.17em}T)\hspace{0.17em}+\hspace{0.17em}11.95,}{\log }_{10}{P}_{{\mathrm{YC}}_4}{\text{\hspace{0.17em}=\hspace{0.17em}(−\hspace{0.17em}4.456\hspace{0.17em}×\hspace{0.17em}10}}^4\text{\hspace{0.17em}/\hspace{0.17em}T)\hspace{0.17em}+\hspace{0.17em}14.72}$ , where the units of pressure are newtons per square meter. Experimentally determined enthalpies were combined with published thermodynamic data to yield the atomization energy of yttrium dicarbide and yttrium tetracarbide: $${\mathrm{YC}}_2\mathrm{(g)\hspace{0.17em}=\hspace{0.17em}}\mathrm{Y}{\text{(g)\hspace{0.17em}+\hspace{0.17em}2C(g)D°}}_{\text{0,atom}}\text{\hspace{0.17em}=\hspace{0.17em}1229\hspace{0.17em}±\hspace{0.17em}17}{\mathrm{kJ\; mole}}^{\text{−1}},$$ $${\mathrm{YC}}_4\mathrm{(g)\hspace{0.17em}=\hspace{0.17em}}\mathrm{Y}{\text{(g)\hspace{0.17em}+\hspace{0.17em}4C(g)D°}}_{\text{0,atom}}\text{\hspace{0.17em}=\hspace{0.17em}2461\hspace{0.17em}±\hspace{0.17em}18}{\mathrm{kJ\; mole}}^{\text{−1}}.$$ The heat of formation of solid yttrium dicarbide was calculated as $\text{ΔH°298,f\hspace{0.17em}=\hspace{0.17em}−91\hspace{0.17em}±\hspace{0.17em}17}\mathrm{kJ\; mole}\text{−1}$ .