|Description:||Cristobalite inversion (alpha/beta)|
NotesOccurs in cooling clay bodies at around 225C (and on heat-up for vitreous ware being refired). It is accompanied by a sudden volume change. Cristobalite, a less stable form of crystalline quartz, can be present in the matrix of stoneware clays where sufficient fine quartz, time and temperature (above 1100C) are available during firing. The range of temperatures is given here because charts that plot the expansion against temperature vary with different sources. In addition variations in temperature in the cross section of ware changes in volume occur as waves across a piece and can crack it. Thus if one side of a piece is 250C and the other 200C, the inversion and associated volume change are happening in the center of the piece. Less cristobalite is formed in faster firings and in more vitreous clay bodies where the feldspar takes the small quartz grains into solution.
In Bound Links
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...
Quartz inversion (alpha-beta) (540C-600C)
This 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...
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