摘要
This paper studies the low temperature synthesis of β-C2S from mixture of lime, BaCl2 and siliceous raw material (white sand, metakaolin and dealuminated kaolin) with the ratio (Ca + Ba)/Si = 2. The Mixtures were hydrothermally treated in stainless steel capsule at 180°C for 5 hours and calcined at 750°C for 3 hours. Raw materials, hydrothermally treated and calcined mixtures were analyzed by FTIR, XRD, TGA/DTA and SEM techniques. The reactivity siliceous raw materials towards lime under hydrothermal treatment increase in the following order: sand, metakaolin, dealuminated kaolin. Because sand composes of quartz crystals, metakaolin composes of amorphous metakaolin structure while dealuminated kaolin composes from enriched amorphous silicate. Calcium aluminate and aluminosilicate hydrate were observed in case of metakaolin which contains appreciable amount of Al2O3. Dicalcium silicate crystallizes into β-C2S in the temperature range 590°C - 760°C. Finally, β-C2S transforms to α’-C2S in the temperature range 790°C - 860°C. There is no sign for the formation of γ-C2S. This proves that Ba2+ ions stabilized β-C2S and retards its transformation to γ-C2S because Ba2+ions replace some of calcium atoms in the structure of β-C2S.
This paper studies the low temperature synthesis of β-C2S from mixture of lime, BaCl2 and siliceous raw material (white sand, metakaolin and dealuminated kaolin) with the ratio (Ca + Ba)/Si = 2. The Mixtures were hydrothermally treated in stainless steel capsule at 180°C for 5 hours and calcined at 750°C for 3 hours. Raw materials, hydrothermally treated and calcined mixtures were analyzed by FTIR, XRD, TGA/DTA and SEM techniques. The reactivity siliceous raw materials towards lime under hydrothermal treatment increase in the following order: sand, metakaolin, dealuminated kaolin. Because sand composes of quartz crystals, metakaolin composes of amorphous metakaolin structure while dealuminated kaolin composes from enriched amorphous silicate. Calcium aluminate and aluminosilicate hydrate were observed in case of metakaolin which contains appreciable amount of Al2O3. Dicalcium silicate crystallizes into β-C2S in the temperature range 590°C - 760°C. Finally, β-C2S transforms to α’-C2S in the temperature range 790°C - 860°C. There is no sign for the formation of γ-C2S. This proves that Ba2+ ions stabilized β-C2S and retards its transformation to γ-C2S because Ba2+ions replace some of calcium atoms in the structure of β-C2S.
