Crystallization of fluorcanasite-fluorrichterite glasses

The crystallization behavior of alkali-modified glasses in. the fluorcanasite-fluorrichterite system was investigated using DTA, XRD, SEM, dilatometry and other techniques. The coefficient of thermal expansion, density, Vickers' microhardness and chemical durability of the obtained products were also evaluated. Limestone, magnesite, and quartz sand together with potassium and sodium carbonates, calcium and magnesium fluorides served as starting materials for glass preparation. The main crystalline phases formed after different heat-treatments were fluorcanasite, fluorrichterite, agrellite, fluorite and diopside ss. The microstructures of the crystalline products consisted of interlocking blade-like and acicular crystals with increasing degrees of fineness as the nominal fluorrichterite content was increased. The coefficient of thermal expansion of the obtained glass-ceramic materials ranged between 79 x 10(-7) and 109 x 10(-7) degrees C(-1); and the density between 2.55 and 2.93 gm/cm(3). The crystalline products attained Vickers' hardness values of 508-743 kg/mm(2). The chemical durability of the materials was better in acidic than in alkaline solutions. (C) 2007 Elsevier Ltd and Techna Group S.r.l. All rights reserved.