Quartz inversion
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The alpha to beta quartz inversion is one of the most important factors to be considered in the production of vitreous sanitary ware. [1] Between 575 and 600 degrees celsius, there's a 2% expansion and 2% contraction on cooling. In this phase, alpha quartz turns to beta quartz and reverses during the cooling phase. It's recommended to fire slowly through quartz inversion as to avoid cracking.[2] Quartz inversion is an important silica reaction in firing clay bodies. The size of the silica particles is important in determining how easily the alpha and beta quartz contracts. Fine-grained silica will more easily change into non-contracting silica glass or sudden-contracting cristobalite, and thus not providing the proper contraction for a glaze. If the thermal expansion rates and contraction rates for the clay and glaze are different it will result in crazing and/or "shivering".[3]
Raw material samples, which have proven beneficial to decreasing the A to B quartz inversion "hump":
Talc- 1.The formation of cristobalite and cordierite 2.Fluxing of the silica
Nephaline Syenite-1.Taking the silica into solution
Petalite-1.Formation of cristobalite 2.Fluxing of the silica
Alumina- 1.Possible formation of mullite with the free silica 2.The effect on the quartz inversion "hump" was not as evident in this material
Maguire studied the use of talc as a means to lower the maturing temperature of sanitary ware bodies. It would bring the body to quartz inversion earlier.[4]
