Precise Determination of the 3CaO·SiO2 Cells and Interpretation of Their X‐Ray Diffraction Patterns

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Abstract
The cell dimensions of pure triclinic 3CaO·SiO2 and monoclinic 3CaO·SiO2 solid solution (54CaO·16SiO2·Al2O3·MgO) were determined and the powder diffraction patterns were indexed by the method of precise measurement of the spacings. The lattice constants are expressed in terms of triclinic or monoclinic cells corresponding to pseudo‐orthorhombic cells derived from Jeffery's trigonal cell. The apparent lattice constants for pure 3CaO·SiO2 are a= 12.195 a.u., b = 7.104 au., c = 25.096 a.u., α= 90°, β= 89°44’γ= 89°44′; for 54CaO·16SiO2.‐Al2O3MgO, a= 12.246 a.u., b = 7.045 a.u., c = 24.985 a.u., β= 90°04′. Precise lattice constants of Jeffery's monoclinic lattice for 54CaO.‐16SiO2‐Al2O3·MgO are derived as a = 33.091 a.u., b = 7.045 a.u., c = 18.546 a.u., β= 94°08′. High‐temperature X‐ray patterns showed that pure triclinic 3CaO·SiO2 transformed to a monoclinic form at about 920°C. and then to a trigonal form at about 970°C. Monoclinic 54CaO.16SiO2·Al2O3–MgO transformed to trigonal at about 830°C. These transitions were reversible and reproducible and were accompanied by only slight deformation of the structure forms.

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