| Abstract [eng] |
The influence of amorphous SiO2 additive on the formation of compounds in the CaO-Al2O3-H2O system during hydrothermal synthesis at a temperature of 130 °C was investigated and the properties of the obtained products were evaluated. It was found that both after 1 hour and after 72 hours of hydrothermal synthesis at different amounts of SiO2 additive, when the C/(S+A) ratio is equal to 2,8, X-ray diffraction analysis curves identify katoite, calcium monocarboaluminate, which could have formed during drying, unreacted portlandite and traces of calcium carbonate. Katoite with intercalated Si ions was also identified even at the lowest amount of additive. Simultaneous thermal analyzes were performed, which confirmed the X-ray diffraction analysis results. It was established that in the studied systems the main crystallization processes fully occur after 1 hour isothermal treatment at 130 °C. And the extension of the isothermal holding time affects only the transformations of the crystalline phases: katoite can partially recrystallize into calcium monocarboaluminate, so a large amount of material was synthesized to study the thermal stability of the obtained synthesis products. The products were burned for 1 hour at different temperatures. According to the obtained X-ray diffraction analysis curves, it can be said that at a temperature of 350 °C, katoite recrystallizes into a mixture of mayenite and portlandite, calcium monocarboaluminate is completely decomposed, and traces of calcium carbonate are observed. After heat treatment, calcium oxide and mayenite are identified in the X-ray diffraction analysis curves at 550 °C and 900 °C, since calcium hydroxide was completely decomposed already at 550 °C. The influence of SiO2 additive on the hydration kinetics has been determined after calcination of the obtained products, by using different amounts of the additive it is possible to change the start and mechanism of hydration and reduce or increase the amount of released heat. |
