Reaction mechanism of the hydrothermally treated CaO-SiO2-Al2O3and CaO-SiO2-Al2O3-CaSO4systems

✍ Scribed by E. I. Al-Wakeel; S. A. El-Korashy

• Publisher: Springer
• Year: 1996
• Tongue: English
• Weight: 444 KB
• Volume: 31
• Category: Article
• ISSN: 0022-2461
• DOI: 10.1007/bf00372207

✦ Synopsis

Mixtures of CaO, amorphous SiO2 and kaolinite in the presence or absence of SO~-ions (added as CaSO4.2H20) were treated in suspension under hydrothermal conditions at temperatures of 80-200 ~ Kaolinite was added to replace 3 and 10% of the total weight of the dry mix with the overall CaO/SiO2 mole ratio being 0.83. The hydration products were investigated by XRD, IR spectroscopy and DTA techniques in order to elucidate their phase compositions. The results indicate that the presence of SO~-ions leads to a marked increase in the reaction rate at all temperatures investigated. In the C-S-A* system, the detected hydration products are calcium silicate hydrate which is then transformed into 1.13 nm aluminium-substituted tobermorite and =-C2SH by increasing the autoclaving temperature. In the C-S-A-C~ system the hydrated products are calcium silicate hydrate, ettringite and monosulpho-alumirtate. On increasing the hydrothermal temperature they decompose, recrystallize and 1.13 nm aluminium-substituted tobermorite, r and anhydrite II are formed. In both systems the excess AI203 appeared as a hydrogarnet phase, CaASH4.