Constraint of Oxygen Fugacity During Field‐Assisted Sintering: TiO₂ as a Test Case

Abstract

Field‐assisted sintering exposes samples in a graphite die to reducing conditions. Using TiO2 as a test case, this work shows that internal redox equlibria in the sample, rather than the graphite–CO–O2 equilibrium, appear to control the oxygen fugacity. Samples sintered at 1160°C for 20 min are homogeneous in oxygen content and have an average composition of TiO1.983±0.001. The oxygen fugacity during these sintering experiments is calculated to be about 10−16 atm, which is higher than the value obtained from thermodynamic equilibrium of graphite–CO–O2 at the given temperature. The oxygen fugacity is similar to that for the quasi‐two‐phase region, or hysteresis loop, representing the coexistence of reduced rutile with random crystallographic shear (CS) planes and the first ordered CS phase.