Electron Optical and X-ray Studies on the Formation of Porcelain; Formation and Microstructure of the Mullite Phase

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Abstract
Using X-ray diffraction, optical and electron optical methods, it is possible to make reliable observations and measurements on the phase composition and phase distribution in fired kaolins and whiteware bodies. The methods are briefly discussed and it is then demonstrated that mullite in fired kaolins, contrary to the prevailing opinion, is formed between 1 000° C and 1 200° C and completely developed even after only a short time at 1 200° C. The chemical mullite analysis fails here completely. The use of the replica method for studying the microstructure in the optical and the electron optical microscope is also demonstrated with examples from electrical porcelains. The distribution of the mullite phase in the poreclain body is determined by the original composition with respect to clay, feldspar and quartz. The appearance of the mullite crystals formed in the clay fields is quite different from the mullite crystals in the feldspar fields. Only part of the mullite phase is visible in the ordinary light microscope.

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