4 sorts of silica bricks, made from high purity silica rock were investigated. The results of this investigation were as follows: (1) A little quartz remained in the brick A and D, which were cristobalite-rich bricks. But there were more amounts of tridymite than the conventional brick (Japanese silica brick, which we had adapted to hot blast stove before), and no quartz remained in the other 2 bricks. (2) The bricks, which had much cristobalite, had large expansion and increased apparent porosity after high temperature creep testing. Thus bricks transformed remarkably to cristobalite from tridymite, and it was presumed that strain and porosity were increased by the vacancies which were occurred in structure by this phase transformation. (3) Brick A was improved by CaO addition. It was possible to control brick A's phase transformation to cristobalite in unused bricks by CaO addition. After creep testing, these trial bricks were controlled by the transformation to cristobalite and brick's expansion decreased, but the deterioration of bending strength under high temperature was not confirmed.
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