Preparation of Synthetic Cordierite by Solide-State-Reaction with Addition of Dolomite
Cordierite was obtained from the mixture of aluminum hydroxide, sand, different magnesium compounds by a solid-state reaction method. The effect of dolomite doping on phase-transformation kinetics and microstructure has been investigated during thermal treatment by keeping a stoichiometric cordierite compound. Adding of dolomite has been used as a flux for preparation of a cordierite precursor by a coprecipitation process. Subsequently, DTA and XRD analyses were conducted to identify the phases formed in the sintered products. Morphological changes of the ground mixtures and sintered product were observed using SEM. The crystallization process of metastable quartz like μ-cordierite can be obtained at 1250…13000C. In this range of temperature form other compounds, such as spinel, quartz. Increase of sintering temperature and prolonged holding times promote the formation of only one phase – indialite or α-cordierite, the hexagonal form of cordierite. Experimental observation shows two steps in the solid-state reaction. First step – formation of volatiles compounds and pores, second – formation and growing of crystalline phases. Evolution of CO, CO2 and H2O that occurred during the thermal treatment of compositions is very important fact in the nucleation process. The intensity of crystallization depends on the gas volume and amount of pore in the sample. The experiments indicated that the intrinsic concentration of volatiles like CO, CO2, H2O influence the appearance of the cordierite phase. SEM photographs sowed that crystallization of cordierite start on the surface of pore. Growth of α-cordierite inside of pores is considerably affected by the time of thermal treatment and amount of adding of dolomite. A remarkable change in peak intensity of XRD patterns of the compositions was observed. Up to 20 wt. % addition of dolomite to the precursor allowed the fabrication of synthetic cordierite at lower temperature.
J. Setina "Preparation of Synthetic Cordierite by Solide-State-Reaction with Addition of Dolomite", Advances in Science and Technology, Vol. 45, pp. 77-82, 2006