Premium
A COMPARISON OF THE THERMAL EXPANSION OF USED SILICA BRICK FROM AN INSULATED AND AN UNINSULATED OPEN‐HEARTH FURNACE ROOF *
Author(s) -
Pierce R. H. H.,
Austin J. B.
Publication year - 1936
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1936.tb19836.x
Subject(s) - thermal expansion , cristobalite , brick , spall , tridymite , materials science , eutectic system , mineralogy , metallurgy , tile , composite material , geology , quartz , microstructure
A bstract Measurements of the linear thermal expansion of different zones in the used silica roof brick whose composition and structure have been described by Harvey show that along the length of the brick there are two abrupt changes in expansion. The first, whose existencè was predicted by Harvey and by Miller, coincides with the limit of penetration of iron oxide and arises from the fact that in the presence of iron oxide the silica, originally present as cristobalite, has been largely converted to tridymite, which has a different expansion. The limit of penetration of iron oxide is taken as that level at which the average temperature is 1100°C (2010°F), the temperature of the ternary eutectic in the system CaO‐FeO‐SiO 2 ; consequently, the abrupt change in expansion, and therefore a zone of weakness, is to be expected after equilibrium has been established in any open‐hearth roof brick whose cold end is below 1100°C (2010°F). The second change, which is also due to a discontinuity in the distribution of cristobalite, occurs at that level in the brick at which the average temperature was 1470°C (2080°F), the lower limit of the stable range for cristobalite. In each case the change in expansion arises directly from a difference in the length‐change at the cristobalite inversion, which takes place at approximately 250°C (480°F), so that failure or spalling is most likely to occur when the roof is cooled below or heated through this temperature. The expansion data also show that the inversion temperature of cristobalite increases regularly with the temperature at which it was formed or at which it was brought to equilibrium. The data obtained enable the determination of the average distribution of tempera ture through the brick in service, which, combined with existing data on thermal conductivity of silica brick, permits an estimation of the mean thermal conductivity of that part of the brick into which iron oxide has penetrated. This conductivity is greater than that of the rest of the brick and has a negative temperature coefficient in contrast to the positive coefficient for the unaltered part.