Quantitative Determination of the Development of Mullite in Fired Clays by an X‐ray Method 1

Firing clays alone or with fluxes to high temperatures results in the formation of mullite crystals in a highly siliceous vitreous mass. Quantitatively, the extent to which mullite in clays is developed by firing to cone 10 has been determined for Ivory Fat English ball clay, Great Beam ball clay, Jernigan Tennessee ball clay, M. & M. English ball clay and A‐1 English china clay. The method consisted in procuring X‐ray patterns by the powder method of the clays fired with feldspar as a flux, using mullite as a reference material. The intensities of the lines in these photographic films were then compared with the intensities of lines obtained from a series of mullite and feldspar mixtures, fired to vitrify the flux. The results given in Table II indicate that each clay develops the maximum quantity of mullite in crystalline form, which the chemical composition of the clay allows.