Thermische Zersetzung von Afwillit Ca3(SiO3OH)2 · 2 H2O

Thermal Decomposition of Afwillite Ca₃(SiO₃OH)₂ · 2 H₂O Using the molybdate method 1], infrared, Raman, and high resolution solid state ¹H and ²⁹Si NMR spectroscopy two intermediate phases can be identified in the process of dehydration of afwillite: At temperatures of 250 to 300°C a non-crystalline phase is formed mainly (about 80 to 90% referred to Si) with a structure similar to mineral killalaite Ca₃OH(Si₂O₆OH) 2] and phase F 3]. Between 300 and 500°C this compound is converted to a non-crystalline kilchoanite-like phase γ-Ca₂SiO₄ · Ca₄Si₃O₁₀ 4], consisting of ordered γ-Ca₂SiO₄ and disordered trisilicate layers. By a side reaction polysilicate (about 10 to 20% referred to Si) is formed.