The Microstructure of Silica Brick

The microstructure of silica brick is a multiphase non-uniform type of structure composed of tridymite, cristobalite, residual quartz, silicates, and glass phase. 

During the transformation of the high-temperature type and the low-temperature type, cristobalite has the intense volume change, followed by quartz and tridymite has the weakest volume changes. The silica brick is required to have a large amount of tridymite, but as little cristobalite, residual quartz as possible. 

 

Tridymite, cristobalite, silicates, and glass phase form the matrix structural unit. The volume ratio of tridymite and direct binding rate are the indicators of the amount of tridymite and the network continuity. 

 

False wollastonite, hedenbergite, calcium iron olivine and dicalcium form the silicate phase and disperse or are enriched in the gaps of the tridymite network. Iron oxides unevenly distributed are still capable of existing in the matrix in the form of α-F2O3. 

 

Metastable or steady cristobalite and residual quartz form the particle structural unit. Metastable cristobalite is the merastable phase of the α cristobalite between 870-1470 ℃. In the early stage of the transformation from α quartz to metastable cristobalite and cristobalite, the metastable cristobalite forms a continuous network which separates the residual quartz into isolated islands. The volume ratio of the residual quartz decreases if continued to be heated or disappears from the particle structural unit. 

 

The brown reaction layer in the grain edges is composed of the glass phase, tridymite and metastable cristobalite and is the product formed by the reaction of the mineralizing agent and the particles. 

 

In order to obtain stable dense structure, there should be as much tridymite and as little cristobalite as possible in the microstructure of silica brick.