The high temperature powder X-ray diffraction methods and the differential thermal analysis were applied in studying the modifications, α, α′, β of 2CaO⋅SiO2, which covered the temperature range 25°-1550°C.
These methods have proved to be able to determine distinctly the inversion temperatures during both in the heating as well as in the cooling processes with the following results:
A. Heating process.
1) γ-form was stable in the temperatures from 25° to 740°C, giving the X-ray pattern similar to that of 2MgO⋅SiO2.
2) α′-form was stable in the temperatures from 900° to 1450°C, giving the X-ray pattern similar to that of β-K2SO4, and the cell dimensions a=6.883, b=5.605, and c=9.543 a. u. at 1300°C.
3) α-form was stable above 1490°C, giving X-ray pattern similar to that of α-K2SO4 (glaserite), and the cell dimensions a=5.27, and c=5.11 a. u. at 1500°C.
B. Cooling process.
4) Inversion α→α′-form occured between 1450° and 1390°C. The intensity of X-ray diffraction of α′-form produced by the inversion of α was slightly different from that produced by heating γ-form. The difference, however, faded away when passing 1190°-1150°C.
5) The inversion from α to β-form occured at 690°C. The X-ray pattern of β-form is the same with that stabilized to room temperature by adding stabilizers, Cr2O3, B2O3. The cell dimensions at 550°C were a=5.558, b=6.823 and c=11.261 a. u., ∠β=123° 11′.
6) The change from β- to γ-form occured at 450°C accompanying the dusting. The unit cells of α, α′ and β shown in this paper were P3ml, Pnma and P21/c, respectively following the International Tables for X-ray Crystallography (1952).