High-temperature interactions between solid ceramic grains and liquid glass result in final microstructures in which the grain-to-grain distance is governed by the specific equilibrium among the interfacial forces. Useful information for many practical applications is obtained by treating the system of interest as a high-temperature colloidal suspension and studying interactions among the constituents. Si3N4 and SiC silicate systems are investigated in the present study as dispersed suspensions, after liquid-penetration experiments and long oxidation treatment at high temperature. Dispersed systems by Si3N4 or SiC as solid particles and a silicate glass formed as a liquid phase are studied at high temperature. Particle interactions are described in terms of the surface tensions of the solid-liquid interface (gamma(sl)) of the grain boundary, both with an intergranular phase (gamma(gb)*) and without (Y(gb)degrees). Agglomerations of a few particles form In both systems as a result of attractive forces; the needlelike shape of beta-Si3N4 particles partially inhibits their mutual interaction. The specific equilibrium among the interfacial forces also drives microstructural evolution during penetration experiments of liquid silicates in dense Si3N4 and SiC at high temperature. In fact, at the original ceramic-glass interface, beta-Si3N4 grains move easily, and grain boundaries thicken; in contrast, a straight line between the ceramic and the glass characterizes the SiC-silicate interface, When the same dense materials are heat-treated in air, a glass layer forms on top of them, as a result of Si3N4 and SiC oxidation, The interface between the so-formed glass and the original ceramic is similar to those found after the penetration experiments. Finally, knowledge of the specific high-temperature behavior of these systems is used to produce Si3N4-Si3N4 and SiC-SiC joints both with and without a glass interlayer, Direct joints with an average strength of 716 MPa (76% of the strength of the as-sintered material) are obtained.
Interfacial forces in Si3N4- and SiC-based systems and their influence on the joining process
L Esposito;A Bellosi;
1999
Abstract
High-temperature interactions between solid ceramic grains and liquid glass result in final microstructures in which the grain-to-grain distance is governed by the specific equilibrium among the interfacial forces. Useful information for many practical applications is obtained by treating the system of interest as a high-temperature colloidal suspension and studying interactions among the constituents. Si3N4 and SiC silicate systems are investigated in the present study as dispersed suspensions, after liquid-penetration experiments and long oxidation treatment at high temperature. Dispersed systems by Si3N4 or SiC as solid particles and a silicate glass formed as a liquid phase are studied at high temperature. Particle interactions are described in terms of the surface tensions of the solid-liquid interface (gamma(sl)) of the grain boundary, both with an intergranular phase (gamma(gb)*) and without (Y(gb)degrees). Agglomerations of a few particles form In both systems as a result of attractive forces; the needlelike shape of beta-Si3N4 particles partially inhibits their mutual interaction. The specific equilibrium among the interfacial forces also drives microstructural evolution during penetration experiments of liquid silicates in dense Si3N4 and SiC at high temperature. In fact, at the original ceramic-glass interface, beta-Si3N4 grains move easily, and grain boundaries thicken; in contrast, a straight line between the ceramic and the glass characterizes the SiC-silicate interface, When the same dense materials are heat-treated in air, a glass layer forms on top of them, as a result of Si3N4 and SiC oxidation, The interface between the so-formed glass and the original ceramic is similar to those found after the penetration experiments. Finally, knowledge of the specific high-temperature behavior of these systems is used to produce Si3N4-Si3N4 and SiC-SiC joints both with and without a glass interlayer, Direct joints with an average strength of 716 MPa (76% of the strength of the as-sintered material) are obtained.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
