Jau-Ho Jean

Liquid-phase sintering in the glass-cordierite system

Densification mechanisms and kinetics of liquid-phase sintering were studied using borosilicate glass-cordierite as a model system. It is shown that the sintering behaviour can be represented predominantly by a non-reactive liquid-phase sintering and that the densification is achieved mainly in the initial stage of sintering. From the activation energy estimates of densification, it is concluded that the predominant mechanism of densification is the viscous flow of glass with contribution arising from both viscous sintering of glass and glass redistribution kinetics. The latter evidence stems from the microstructural observation that as the sintering proceeds, the glass undergoes a time-dependent wetting behaviour. Based on this observation, and calculated infiltration times of melt into the porous compact, it is found that the time-dependent contact angle between the melt and the solid particles plays a significant role in the glass redistribution process.

Isothermal and nonisothermal sintering kinetics of glass-filled ceramics

Isothermal and nonisothermal sintering behaviors of glass-filled ceramics are compared in this paper. Equations developed to describe the kinetics of shrinkage for both techniques can be readily used to interpret the experimental data. It is shown that the kinetics of linear shrinkage of powder compacts during isothermal and nonisothermal constant rate of heating are consistent and can be described by the viscous flow of glass.

Liquid-phase sintering in the glass-cordierite system: particle size effect

The effect of particle sizes of glass and ceramic filler on the densification kinetics of glassfilled ceramics has been studied using borosilicate glass-cordierite as the model system. Within the particle size range investigated, the densification is found to be significantly enhanced by increasing the cordierite size, reducing the glass size and increasing the green density. These results are attributed to both the increased driving force of densification by reducing the glass particle size and the decreased glass redistribution distance by either increasing the green density of compacts or increasing the particle size ratio between the cordierite and glass powders. In addition, a large cordierite-to-glass size ratio gives a dense, uniform microstructure of sintered body as a result of forming a homogeneous close packing of the low-melting glass phase around the refractory cordierite particles.

Cristobalite growth inhibitor in Pyrex borosilicate glass—gallium oxide

The effect of gallium oxide on cristobalite formation in Pyrex borosilicate glass has been studied. XRD results show that with 20 vol% gallium oxide, the precipitation of cristobalite at 800°C is completely prevented. This result is further evidenced by the linear thermal expansion measurement, in which, in contrast to the system without a sufficient amount of gallium oxide (0-10 vol%), the thermal expansion coefficient of the composite with 20 vol% gallium oxide remains unchanged with sintering time at the temperature investigated and, moreover, is very close to the theoretically calculated value

Origin of cristobalite formation during sintering of a binary mixture of borosilicate glass and high silica glass

It was shown previously 1 that cristobalite precipitates out of a mixture of borosilicate glass (BSG) and high silica glass (HSG) when sintered at temperatures ranging from 800 to 1200 °C. In this paper, both direct and indirect evidences are presented to conclude that the formation of cristobalite originates in HSG. It is proposed that the cristobalite is formed as a result of dissolution of HSG in BSG and precipitation at heterogeneously nucleated sites. The process of dissolution and precipitation continues until the whole HSG particle is consumed.

Liquid Phase Sintering in the Glass-Cordierite System - Effect of Melt Infiltration Distance

Effect of glass infiltration distance, controlled by particle sizes of glass and ceramic filler, and green density, on densification kinetics of glass-filled ceramics has been studied using borosilicate glass-cordierite as the model system. Within the particle size range investigated, the densification is found to be significantly enhanced by increasing cordierite size, reducing glass size and increasing green density. The above results are attributed to both increased driving force of densification by reducing glass particle size, and decreased glass redistribution distance by either increasing green density of compacts or increasing the particle size ratio between cordierite and glass powders.