Triaxial whiteware

Earthenware refers to products produced from unbeneficiated clays with no other additives. Earthenware clays are formed by incomplete conversion of the parent mineral formation and they contain substantial amounts of residual feldspar and quartz, giving a composition similar to a triaxial whiteware [3], Earthenware bodies are typically formed by throwing or modeling [22], Earthenwares are self-fluxing during firing due to the alkali content. Fired earthenware bodies typically have high absorption (10-15%) and are fired at moderate temperatures (cone 5-6) [22], Fired earthenware bodies are usually red and find use as decorative objects, as tiles, or as tableware [26],... 

Traditional ceramics are mainly made from mixtures of clays, silica (often extracted as flint) and feldspars (especially K2Al2Si60i6 and Na2Al2-SieOie). Low-quality structural products such as bricks and pipes are made directly from the appropriate clay. Higher-quality ceramics such as porcelain are made from carefully controlled amounts of specific clay, flint and feldspar. The use of these three major components has led to the name triaxial whitewares for these materials. 

When the ceramic contains more than one phase, each phase will have different thermal expansion coefficients. On heating and cooling, this difference can give rise to thermal stresses at the phase boundaries. These stresses can cause internal cracks. Such a crack is seen in the microstructure of a triaxial whiteware composition, shown in Figure 6.13. 

Microstructure of a triaxial whiteware composition. (From W. D. Kingery et al.. Introduction to Ceramics, 2nd Edn., John Wiley, 1976, pp. 783-812.)... 

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