Some Studies on Matrix in Silica Brick, (I)

Abstract

In the first report, we have proposed “matrix brick” which is made of quartz flour through the 1600 hole/cm2 sieve mixed with abt. 5% of CaO. In mixing this “matrix” with varions amounts of coarer grains (400-1600 hole/cm2), we found that the sample cones containing less than 30% of “matrix” are more refractory, and therefore such bricks are good for use in open-hearth roof.In the second report, results of dilatometric experiments and microscopic observations of matrix bricks are given. There are two remarkable periods of mineral development during the sintering of matrix bricks; i.e.1000-1200°C cristobalite development1200-1400°C tridymite developmentThe formation of tridymite was detected byT1-inversson (α→β1 trid.) in samples fired at lower temperaturesT2-inversion (crist.→trid.) in samples fired at higher temperaturesBy comparing parmanent expansions at 1000°C in reheating the bricks, a minimum was found in samples fired at 900-1100°C, Milk of lime in green body gradully absorbs CO2 and is converted into CaCO3 at abt. 600°C, then it decomposes. At abt. 800-900°C, formation of calcium silicate was concluded from a marked shrinkage, and at abt. 1400°C it became visible under a microscope in forming ring-like shaped crystals. When fired at above 1400°C, calcium silicate diffused into the matrix, but when cooled, it recrystallized again.In the present (third) report, experimental results of parmanent expansion, porosity, apparent density and permeability are given.In the firing range of 1100°-1200°C, the apparent specific gravity of the matrix bricks has decreased from 2.60 to less than 2.40, but the porosity has also decreased and the crushing strength increased. Because there is no great change of porosity during firing, it is advisable to make quality control in green body. Increase of CaO content is good for crystal growth of Tridymite but rather decreases the it's amount, and makes expansion smaller.