Celsian–fluorophlogopite porcelain based on Egyptian talc

Celsian and fluorophlogopite phases have been developed in porcelain using Egyptian talc. Well developed fluorophlogopite with randomly oriented crystals within the glassy phase acts as a reinforcing aid. Hexacelsian crystallises at or below 900°C and then transforms into monoclinic celsian by epitaxial growth. Formation of fluorophlogopite enhances the transformation of hexacelsian to monocelsian. The best conditions for simultaneous crystallisation of a fluorophlogopite and celsian phase mixture are a heating rate of 5 K min−1 and cooling rate of 10 K min−1 between 700 and 930°C. A marked shift in the positions of XRD peaks for celsian occurs as a result of the substitutional solid solution between Ba2+ and K+. Crystallisation of forsterite disappears in the mix with highest silica content. Microhardness decreases at temperatures above 950°C because of transformation of hexacelsian into celsian and the decrease in fluorophlogopite content.