Corrosion of a Silica-Bearing Ceramic in Sulfur-Oxygen Atmospheres

Experimental observations and thermodynamic calculations are described which show that formation of SiS vapor from SiO₂ in a high-sulfur, low-oxygen atmosphere is a viable corrosion mechanism. This mechanism will become more important than the well-known decomposition of SiO₂ to SiO in those sulfur-bearing atmospheres where the oxygen activity is close to the Si/SiO₂ phase boundary on a volatility diagram.     

Sintering,thermal stability and mechanical properties of ZrO2-WC composites obtained by pulsed electric current sintering

ZrO₂-WC composites exhibit comparable mechanical properties as traditional WC-Co materials, which provides an opportunity to partially replace WC-Co for some applications. In this study, 2 mol.% Y₂O₃ stabilized ZrO₂ composites with 40 vol.% WC were consolidated in the 1150°C–1850°C range under a pressure of 60 MPa by pulsed electric current sintering (PECS). The densification behavior, microstructure and phase constitution of the composites were investigated to clarify the role of the sintering temperature on the grain growth, mechanical properties and thermal stability of ZrO₂ and WC components. Analysis results indicated that the composites sintered at 1350°C and 1450°C exhibited the highest tetragonal ZrO₂ phase transformability, maximum toughness, and hardness and an optimal flexural strength. Chemical reaction of ZrO₂ and C, originating from the graphite die, was detected in the composite PECS for 20 min at 1850°C in vacuum.     

Material Loss and High Temperature Phase Transition in Lithium Ferrite

The morphology and kinetics of the phase transformations accompanying oxygen and lithium loss in LiFe₅O₈ were studied at 1200°C in air, in oxygen ( P O₂ = 760 torr), and in vacuum ( P = 5×10⁻⁵torr), using high-voltage electron microscopy. LiFeO₂ nucleated and grew in the LiFe₅O₈ matrix and finally transformed to spinel in all three atmospheres; however, the kinetics of the transformation depended on the atmobphere. The dependence of these phase transformations on material loss is discussed.