Synthesis ofHeatResistance Wall Material fconi Sliirasu in the Kagoshima Prefecture

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The Shirasu, a volcanic ash is distributed widely in southern Kyushu, Japan. The SiO_2/Al_2O_3 mole ratio in shirasu (SiO_2 : 72.20 %, Al_2O_3 : 12.41, K_2O : 3.44, CaO : 1.29) and 11-tobermorite(10CaO・Al_2O_3・10SiOa・10H_2O) with heat-resistance are almost equal. 11-Tobermorite was synthesized from shirasu by the two methods.1. The first method with alkali (KOH).2. The Second method by alkali-freeBy the first method : 11-Tobermorite was synthesized from shirasu by two steps hydrothermal reaction in an autoclave. At the first step, the materials were mixed at suitable amount (CaO/SiO_2=1.0, K_2O/SiO_2=0.32), and is pretreated in the autoclave at 60℃ for 5 hours to prereact. At the next step, 11-tobermorite was obtained by the way of increasing temperature to 150℃. In the first step, Si-O in shirasu is thought to be decomposed with alkali, and Ca adsorbed, and then 11-tobermorite nucleation place. But under condition of above 60℃ for 5 hours, alkali dissolved Ca and 11-tobermorite nuclea. In the next step, 11-tobermorite, crystal seed grows immediately.But the second method of alkali-free the materials are only shirasu, Ca(OH)_2, and water. The langer reaction time was necessary in compared with method by alkali, but the pretreatment was not necessary.