Postmortem analyses of salvaged conventional silica bricks from glass production furnaces

The microstructure, phase content, and thermal conductivity of salvaged conventional silica bricks from float glass and TV-panel glass production furnaces were examined as a function of position through the brick, and compared with the original, unaltered brick materials. The silica brick from the float glass furnace was in service for approximately 10 years while that for the TV-panel glass furnace was for approximately 6 1/2 years. The microstructure and phase content in both salvaged bricks showed gradients, from tridymite at the bricks' cold-face ends, to cristobalite at their hot-face and even though both bricks were an initial mixture of tridymite and cristobalite to begin with. The thermal conductivity of both bricks had increased as a consequence of these phase and microstructural changes. A thermal analysis model predicted that such changes would result in an increase in the bricks' cold-face temperature and heat content during service. The initially-produced temperature gradients and environment caused microstructural changes in the silica brick; however, the cause-and-effect relationship between temperature/environment and microstructural changes in the brick likely became mutually reversible once the microstructural changes initiated and the thermal conductivity of the brick started to change as a consequence.