Ca2SiO4 Phase Research Articles

Phase diagram study for the CaO-SiO2-Cr2O3-5 mass.%MgO-10 mass.%MnO system

The phase diagram of the CaO-SiO2-CrOx-MgO-MnO system at moderately reducing oxygen partial pressure was calculated using a commercial thermochemical program and compared with the phase analysis for converter slags taken from the stainless steelmaking process. It was found that a (Mn,Mg)Cr2O4 solid solution and Ca2SiO4 phase are in equilibrium with the oxidation slags after the oxygen blowing period, which is consistent with thermodynamic calculations. Furthermore, it could be proposed that the thermodynamic properties of a MgCr2O4-MnCr2O4 binary spinel make it close to an ideal solution.

Dissolution of Dense Lime in Molten Slags under Static Conditions

Static dissolution of CaO into a CaO–SiO2–Al2O3 slag with fluxing agents (fluorspar, ilmenite and nepheline syenite) was studied using two experimental techniques. In one method, the slag was packed into dense CaO crucibles, and heated to 1500°C/1600°C. After reaction, the crucible was air cooled and cross-sectioned. In the second technique, slag with a piece of lime was heated in a platinum capsule. The development of the Ca2SiO4 phase at the lime/slag interface and the CaO dissolved in the slag from the lime specimen were examined by Electron Probe Micro Analysis and Scanning Electron Microscopy. Ilmenite and nepheline syenite were found to be effective substitutes for fluorspar, increasing the CaO dissolution rate in the slag.

Dissolution Behavior of Al2O3 and MgO Inclusions in the CaO–Al2O3–SiO2 Slags: Formation of Ring-like Structure of MgAl2O4 and Ca2SiO4 around MgO Inclusions

The dissolution behavior of Al2O3 and MgO particles in various CaO–Al2O3–SiO2 slags was investigated using a confocal scanning laser microscope at 1 550°C. The dissolution paths of Al2O3 and MgO particles varied depending on slag compositions. Reaction products such as CaO·6Al2O3, CaO·2Al2O3 and Ca2Al2SiO7 formed on the surface of Al2O3 particle. Surprisingly, however, in the case where reaction products were MgAl2O4 and Ca2SiO4 phases, these reaction products formed ring-like structure around MgO particles. Inside of the ring-like structure, liquid phases of which compositions correspond to the co-saturation compositions with MgO and MgAl2O4 (Ca2SiO4) phases. In addition, this unique dissolution phenomenon retarded the dissolution rate of MgO particle in molten slags. In the present study, the dissolution mechanism of this unique dissolution phenomenon is proposed.

High‐Temperature, High‐Pressure X‐ray Investigation of Dicalcium Silicate

Energy‐dispersive X‐ray powder diffraction experiments have been investigated at high temperature and room pressure, and at high pressure and room temperature, starting from either γ‐ or β‐Ca2SiO4. High‐temperature studies were performed up to 1980 K, using a versatile heating cell. The high‐temperature phase transformations previously described were reexamined. Volume and linear thermal expansions were measured for each Ca2SiO4 polymorph, γ, β, α′;L,α′;H, and α. Volume thermal expansion increases with increasing temperature except for α′;H, whose thermal expansion tends to decrease at elevated temperature. High‐pressure investigations were performed in the 0–15 GPa pressure range, using a diamond anvil cell, with silicon oil as the pressure‐transmitting medium. The value of the room‐pressure bulk modulus K0, assuming a second‐order BirchMurnaghan equation of state with K'0= 4, is 140(8) GPa for γ‐Ca2SiO4. The γ olivine form exhibits anisotropic compression, with the c axis as the most compressible. From such in situ high‐pressure X‐ray investigations, the γ‐→Ca2SiO4 phase transformation induced by cold compression is clearly evidenced and extends from 2 to about 5 GPa.