Phase diagram of the system Ca-Ti-O at 1200 K

Abstract

Phase relations in the system Ca-Ti-O have been established by equilibration of several samples at 1200 K for prolonged periods and identification of phases in quenched samples by optical and scanning electron microscopy, XRD and EDS. Samples representing 20 compositions in the ternary system were analyzed. There was negligible solid solubility of Ca in the phases along the binary Ti-O, and of Ti in CaO. Four ternary oxides were identified: CaTiO 3 , Ca 4 Ti 3 O 10 and Ca 3 Ti 2 O 7 containing tetravalent titanium, and CaTi 2 O 4 containing trivalent titanium. Tie-lines link calcium titanite (CaTi 2 O 4 ) with the three calcium titanates (CaTiO 3 , Ca 4 Ti 3 O 10 and Ca 3 Ti 2 O 7 ), CaO, oxygen excess TiO 1+δ and stoichiometric TiO. Tie-lines connect CaTiO 3 with TiO 2-x , Magneli phases Ti n O 2n-1 (28 ≥ n ≥ 4), Ti 3 O 5 , Ti 2 O 3 and TiO 1+δ . CaO was found to coexist with TiO, and Ti-O solid solutions α and β. The phase diagram is useful for understanding the mechanisms and kinetics of direct calciothermic reduction of TiO 2 to metal and electrochemical reduction of TiO 2 using graphite anode and molten CaCl 2 electrolyte.

The phase stability of Ca2TiO4 and related Ruddlesden–Popper phases

“…For the Sr-Ti-O system, R-P phases with n ¼1-3 are known to be thermodynamically stable in agreement with lattice simulation studies [6,7], although n ¼1-5 have been grown by means of molecular beam epitaxy [11]. For the Ca-Ti-O R-P system only the phases n¼ 2 and 3 have been reported [9]: there are no reports in the literature of the n ¼1 phase, Ca 2 TiO 4 , and it is unclear why this phase cannot be synthesized [12,13]. There is also some disagreement in the literature regarding the crystallographic structures of the n ¼2 and 3 phases: x-ray powder diffraction studies suggest that the cells are tetragonal [14,15], whereas a neutron powder diffraction study concludes that the cells are orthorhombic [9].…”

Reduction of CaTiO₃ in Molten CaCl₂ - as Basic Understanding of Electrolysis

“…The ternary phase equilibrium of Ca-Ti-O system at 1273 K was reported 29) , but it contained some discrepancy with various experimental conditions 29,30) . As shown in Fig.…”

Solid–Solid Phase Transformation During the Reduction of Titanium Dioxide (Anatase) to Produce High‐Grade Titanium Powder

“…In an attempt to isolate the solid titanium phase from titanium dioxide powder, the Ca‐Ti‐O phase diagram constructed by Jacob and Gupta, shown in Figure , was used as reference. The phase equilibrium of Ca–Ti–O established at 1200 K shows the presence of Ti(α) + CaO at an average composition of 0.2 calcium:0.4 titanium:0.4 oxygen.…”

“…An isothermal section of the phase diagram for the system Ca–Ti–O at 1200 K. Reproduced with permissionfrom.…”

“…As a result the activity of TiO 2 decreases with decrease in oxygen content whilst forming the Ti–O bond. Further reduction by Ca results in the formation of CaTi 2 O 4 where all the titanium is in the trivalent state . This is the critical stage in the de‐oxidation process.…”