|Description:||Quartz inversion (alpha-beta)|
NotesThis term refers to an abrupt change in volume that occurs in quartz crystals when they are heated from the room temperature stable alpha phase to the beta crystal phase that exists above a theoretical temperature of 573C. It is referred to as an inversion because the process is reversed when the temperature falls back below 573C (although the reversal expansion curve is not identical to the heatup one). Since the change occurs across a narrow range of temperatures, ware will crack if there are significant temperature gradients within it. For example, if one side of a piece is at 573 and the other at 600, then as the piece cools further the volume change will move horizontally across it and could start a crack at the first weakness it encounters. The range we indicate for quartz inversion recognizes the fact that kiln gradients almost always exist and that quartz inversion does not happen at one specific temperature as is often suggested (the curve of temperature vs expansion is simply much steeper across a narrow range than it is outside that range, about 50 degrees).
Quartz inversion can be beneficial because it can put the glaze under compression and thus prevent crazing.
Out Bound Links
Wikipedia quartz inversion
Quartz - SiO2
Cristobalite is a crystalline form of silica (SiO2). Silica has the rather amazing ability to exist in different crystalline forms (called polymorphs) each of which has subforms (e.g. alpha, beta). Each form has different physical properties. Quartz in the preferred most stable form, the one found i...
Cristobalite inversion (alpha/beta) (210C-280C)
Occurs in cooling clay bodies at around 225C (and on heat-up for vitreous ware being refired). It is accompanied by a sudden volume change. Cristobali...
In Bound Links
#1 Q-Rok - 30 mesh silica
The term "quartz inversion" is used in two ways. Often, people are simply referring to the temperature 573C. More likely they are referring the phenomena that occurs there: The sudden volume change that particles experience as they pass up and down (thus it is called an inversion) through 573C. Actu...
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