Proceedings of The 4th International Conference on Applied Research in Science, Technology, and Knowledge
Effect of Synthesis Parameters on Thermal Behaviour and Crystalline Structures of Calcium Silicate Minerals
Buse Bozan and Suna Balcı
Calcium silicates are porous, large surface area ultra-light minerals, whose diversity comes from close Ca/Si ratios. Anhydrate calcium silicate (C-S) wollastonite and hydrate calcium silicates (C-S-H) xonotlite and tobermorite are common varieties. The structures whose economic production is limited are widely used as heat insulation and fire resistant especially in places that require special shaped passive fire protection (PFP) plate. In use as cement additive, in addition to its effects on the strength properties of concrete, it also creates serious effects especially on the hydration process. By using CaO as a calcium and silica fume as a silica sources, with different Ca/Si (0.83-1.00) and water/solid (10, 15) ratios in synthesis suspensions, directly or after the 4 hour pre-reaction under different temperature (40 oC < T <80 oC) synthesis of calcium silicate structures were carried out at an autogenous pressure of 200 oC applying or non-applying filtration after the pre-reaction. The products obtained were dried at room temperature, in oven at 60 oC and -110 oC freeze-drying techniques. Higher mass loss was observed with synthesis at 80 oC pre-reaction temperature and tobermorite phase synthesis condition. The removal of structural water and –OH which took place above 250 oC was found more tobermorite phase synthesis feed ratio sample. The decomposition of calcium hydrosilicate crystals in 320-600 oC and phase transforms between 800-875 oC had been observed Typical C-S-H crystal peaks were detected in XRD patterns. The increase in success of xonotlite synthesis with pre-reaction temperatures was seen in XRD peaks. The slight decreases in the descriptive peaks intensities were observed for samples synthesized at 40 and 80 oC pre-reaction temperatures and calcined at 300 oC, while even the most severe peak decreased significantly in samples calcined at 700 oC.
Keywords: xonotlite; tobermorite; thermal strength; mechanical strength; crystallinity.