Nucleation and crystallization studies of some glasses in the CaO-MgO-Al₂O₃-SiO₂ system

Abstract

SUMMARY. Glass-ceramics based on the mineral cordierite have good mechanical and thermal properties. They can be easily prepared from glasses whose compositions lie in the primary phase field of cordierite on the 5 % CaO plane of the CaO-MgO-SiO2-A1208 system. For uniform crystallization in the bulk, addition of a suitable nucleating agent is essential. The addition of to-~2 wt % of TiO~ is considered to be suitable for both ternary and quaternary glasses. During controlled heat treatment of these glasses extensive phase separation occurs. The nucleation and crystallization processes that follow have been studied by differential thermal analysis, X-ray diffraction, and light and electron microscopy. Some of the physical and mechanical properties of these glass-ceramics have been measured. THE high melting point and the very low thermal expansion coefficient of the mineral cordierite are two important properties that have been utilized in the development of industrial ceramic materials in which this phase is a major constituent. Although cordierite ceramics are commonly manufactured by a sintering process, the possibility of producing glass-ceramic materials based on cordierite has already been explored in several laboratories (e.g. British Patent 829,447). The thermal, electrical, and mechanical properties of such a material are considered to be satisfactory, but there are production limitations due to the high melting points and the high viscosity of ternary MgO-A1203-SiO~ glasses even after the addition of suitable nucleating agents. The present work, of which this report is a preliminary account, is aimed at examining several quaternary glasses with compositions in the primary phase field of cordierite in the CaO-MgO-AI.~Oa-SiO2 system with a view to studying their crystallization behaviour. Previous work.Cordierite is an incongruently melting compound having a stable primary phase field in the MgO-A120~-SiO2 system (see Osborn and Muan, I96o). Its mineralogy and polymorphism have been extensively studied (Deer, Howie, and Zussman, I962). The form stable at all temperatures and called low-cordierite is orthorhombic. High-(or ~-) cordierite is hexagonal and is considered to be metastable at all temperatures. Cordierite crystal structures provide typical examples of orderdisorder in aluminosilicates.Crystallization of cordierite from glasses of widely different compositions in the system MgO-A120~-SiO2 has been recently studied in great detail by Schreyer and Schairer (I96I a and b). One important discovery in these studies was the observation that quartz solid solutions previously described as t~-cordierite by Karkhanavala and Hummel (I953) and silica O by Roy (I959) form metastably on devitrification of these glasses at relatively low sub-solidus temperatures and are usually the first crystalline 9 Copyright Building Research Station, Ministry of Public Building and Works.

Glass-ceramics materials from basaltic rocks and some industrial waste

“…The DTA curves show small dips in the temperature ranging between 665 and 700°C due to the transition temperature of the glass Tg, or corresponding approximately, in accordance with Devekey and Majumdar [27], to the temperature range defined by Tg and Ts. An increase in the DTA-Tg could be observed as the nominal content of ceramic waste was increased from G0 (665°C, ceramic waste = 0%) to G40 (700°C, ceramic waste = 40%).…”

Effect of Excess MgO on the Properties of Cordierite Ceramic Sintered by Solid‐State Method

“…, sapphirine instead of μ‐cordierite appeared at a low temperature. It is similar to the phenomenon that de Vekey and Majumdar found in their study . They indicated that there may be at least two other phases present at the temperature range from 1090 to 1180°C, when the cordierite began to appear and increase.…”

“…It is similar to the phenomenon that de Vekey and Majumdar found in their study. 22 They indicated that there may be at least two other phases present at the temperature range from 1090 to 1180°C, when the cordierite began to appear and increase. One was sapphirine and the other was a crystalline quartz solution.…”

Kinetic thermal analysis of glass ceramics from industrial wastes

“…This family has been selected because it fits well with the chemical composition of the industrial wastes used in this work and because of its excellent mechanical properties and chemical stability. It is thought that the level of impurities present in wastes used could promote bulk crystallization as reported for Fe 2 O 3 [2] and for alkaline oxides [3]. Furthermore, a kinetic study could provide information on the crystallization mechanism and knowledge needed to prepare glass ceramics.…”