For clay-based aggregates, a liquid phase forms during firing, which infiltrates the pores between the particles; upon cooling, this liquid becomes a glass, which serves as the bonding phase. With cements, the bonding process Is a chemical, reaction between the water that has been added and the various cement constituents. The cement particles are bonded together by reactions that occur at the particle surfaces. 13. 15 (a) Explain why residual thermal stresses are introduced into a glass piece when it is cooled.
Residual thermal stresses are introduced into a glass piece when it is cooled because surface and interior regions cool at different rates, and, therefore, contract different amounts. (b). Are thermal stresses introduced upon heating? Why or why not? Yes, thermal stresses will be Introduced because of thermal expansion upon heating for the same reason as for thermal contraction upon cooling. 13. 18 Glass pieces may also be strengthened by chemical tampering. With this procedure, the glass surface is put in a state of compression by exchanging some of the actions ear the surface with other actions having a larger diameter.
Suggest one type of action that, be replacing, will induce chemical tempering in a soda-lime glass. Will do the degree to which beatification occurs in clay-based ceramic wares. Three factors are: the composition; the temperature of firing; and the time at the firing temperature. (b). Explain how density, firing distortion, strength, corrosion resistance, and thermal conductivity are affected by the extent of beatification. Density will increase with degree of beatification since the total remaining pore volume decreases.
Firing distortion will increase with degree of beatification since more liquid phase will be present at the firing temperature. Strength will also increase with degree of beatification because as more of the liquid phase forms it fills in a greater fraction of pore volume. Corrosion resistance normally increases at service temperatures below that at which the glass phase begins to soften. The rate of corrosion is dependent on the amount of surface area exposed to the corrosive medium. Thermal conductivity will increase since the glass phase has a higher conductivity than the pores that it has filled.