The key to production of silica bricks is to select the raw materials and the firing process in which the degree of quartz transformation is suitable for the intended application.

The raw material for silica brick is quartz which must meet certain requirements. If refractoriness or thermal expansion are the main requirements, a quartz of high chemical purity must be selected. If volume stability is the main requirement, raw materials should have good transformation properties.

The chemical composition of quartz is important in its evaluation as a raw material, in particular the content of alumina and alkali, as these lower the melting point and considerably reduce the possibilities of application. In addition the firing behavior of the quartz must be taken into account.

After the raw materials have been crushed, ground and screened to the various grain fractions, they are mixed in predetermined proportions according to the required application properties. In most cases, mixers are used for mixing and special bonding agents. Generally around 2% lime water and some sulphite solution as a temporary binder, are added at the same time. The mixture is then processed on friction presses or hydraulic presses. Complicated shapes or those where short runs are required, are still rammed by hand.

After drying, silica bricks are fired at temperature of about 1450-1500℃. Because the transformation of the silica takes place suddenly, cooling must be carried out slowly, or the brick will crack. It is necessary to maintain a carefully planned time temperature cycle during firing. A strong, well bonded high quality silica brick can be obtained only after passing through critical temperature ranges. During firing, silica brick will have about 4% linear growth.

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