The torsion-effusion method, with simultaneous torque angle and weight loss measurements, was used to study the thermal decomposition of MgSO4 and CaSO4. The initial step in the decomposition/vaporization process appears to be the evolution of an SO3 molecule from the lattice, followed by conversion to SO2 and O2 on the surface. Measurements of decomposition pressure as a function of orifice area show that both steps are kinetically hindered. The experimental results can be correlated very satisfactorily by the Whitman–Motzfeldt model, so that reliable equilibrium data can be derived despite large degrees of undersaturation of the vapors. With MgSO4 it was possible to evaluate both the SO3 and SO2+O2 equilibrium pressures, the latter by addition of a small amount of Fe2O3 catalyst to the sample. Analysis of the derived equilibrium pressures yields values of −310.3±0.5 and −344.8±0.5 kcal/mol for the standard enthalpies of formation of MgSO4(s) and CaSO4(s), respectively, at 298 K.

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The oxidation of NC 132 hot‐pressed silicon nitride in dry oxygen was studied at 1521 to 1731K. The rate of O2 uptake and N2 release, as a function of time, was measured volumetrically. The ratio of N2 released to O2 consumed was smaller than expected from the stoichiometry of the oxidation reaction for Si3N4. The low value was attributed to impurities in the material. The oxidation rate followed the parabolic law with an activation energy of 440 kJ/mol. The corrosion scales (examined by microsurface techniques) were porous due to bubbles of released N2. The scales consisted of a mixture of unoxidized silicon nitride grains, crystalline oxides (SiO2 and MgSiO3containing other elements), and a glass phase. Reoxidation showed that the oxide scale was not protective. The magnesium profile in the subsurface layers indicated that the diffusion of magnesium in the unoxidized material was the rate‐limiting step in the oxidation.