EARTH

[3801-11-06] Synthesizing α-cordierite powders using preheated raw materials

○Hsin-Wen - Fan¹, I-Ting - Liu¹, Fu Su - Yen¹ (1. Department of Resources Engineering, National Cheng Kung University, Taiwan)

Chairman: Chompunoot Wiraseranee （Mitsubishi Materials Corporation）, Liu Hui (Central South University)

Keywords:Cordierite, Kaolinite, Talc, Alumina

Industrial cordierite (composite) materials are mostly composed of α-cordierite mineral due to its characteristic lower thermal expansion coefficients. Synthesis of cordierite composites is normally fabricated using mineral powders of talc, kaolinite and synthetic alumina. The powders are mixed homogeneously in a stoichiometric composition of 2MgO·2Al₂O₃·5SiO₂, and then loaded in a high temperature furnace for thermal reaction, resulting in the formation of α-cordierite. As talc and kaolinite are phyllosilicates that containing Mg(OH)₂ and Al(OH)₃ layers, respectively in the structures, or simply, minerals with crystalline water. During thermal treatments, the water will be removed and the transition phase of proto-enstatite and mullite (and amorphous silica) will be generated. A series of thermal reaction among enstatite, mullite, alumina, and amorphous silica then encountered to form α-cordierite finally. Because the temperature for the reaction inevitably is higher than 1350 degrees Celsius. Measures of saving heat consumption are proposed to remove the crystalline water as well as hopefully ruin the crystal structure of the minerals in advance by preheat treatments at 700 C and 900 C using industrial waste heat. The thermal treated silicates then are used as the starting material to synthesize α-cordierite. It is found that the pre-heating stimulates a complete diminishment of alumina constitute at lower temperature accompanied with a narrowed temperature range for the presence of mullite. As a result, a relative large amount of spinel is formed that leading to the formation of α-cordierite instead of β-cordierite. The pre-heating of starting materials can be a heat saving procedure to synthesizing α-cordierite. And treated with 700 C can be more appropriate than that with 900 C.