Microcracking anisotropic thermal expansion

Heating or cooling of ceramics for which the thermal expansion is anisotropic. The magnitude of the stresses will depend on the thermal expansion anisotropy, and can cause polycrystalline bodies to spontaneously microcrack. This damage cannot be avoided by slow cooling, but can be avoided if the grain size is kept small. 

Particularly the thermal expansion of /3-eucryptite has been investigated by many authors. It appears that the expansion characteristics depend somewhat on the Al/Si order and possibly on other influences of thermal history, but the data given in Table 2.1 can be considered as typical. It should also be pointed out that coefficients of thermal expansion measured on polycrystalline aggregates by dilatometry can give different values due to internal stress and microcracking if the expansion of the crystals is highly anisotropic [2.27]. For / -eucryptite, several models have been proposed to explain the thermal expansion characteristics. 

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