An indirect model for sintering thermodynamics

摘要

A model was proposed and used to calculated the changes in enthalpy $(Delta H^{o})$, entropy $(Delta S^{o}),$ and Gibbs energy $(Delta G^{o})$, as well as equilibrium constant $(K)$ relating to the sintering of alumina compacts. Specific nanopore volume $(V)$ of the compacts was assumed as a thermodynamic variable. A hypothetical equilibrium constant $(K_{h})$ and corresponding Gibbs energy $(Delta G_{h}^{o})$ were calculated depending on the $V$ value measured after each sintering. The thermodynamic relationships with the SI units were respectively evaluated for the initial-stage $(i)$ sintering between 1000 and 1200 $^{circ}$C and final-stage $(f)$ sintering between 1200 and 1600 $^{circ}$C in the following form: $, Delta G_{i}^{o}=-RTln K_{i}=Delta H_{i}^{o}-TDelta S_{i}^{o}=$161,042$-$110.5$T$ and $Delta G_{f}^{o}=-RTln K_{f}=Delta H_{f}^{o}-TDelta S_{f}^{o}=$39,000$-$47.5$T$.