Titanium(IV) oxide phase stability in alkaline sodium phosphate solutions at elevated temperatures

摘要

Titanium(IV) oxide is shown to transform to a sodium titanium hydroxphosphate compound in concentrated sodium phosphate solutions at elevated temperatures via TiO(sub 2)(s) + 4Na(sup +) + 2HPO(sub 4)(sup =) (r reversible) Na(sub 4)T(OH)(sub 2)(PO(sub 4))(sub 2)(S). The thermodynamic equilibrium for this reaction was investigated in the system TiO(sub 2)Na(sub 2)O-P(sub 2)O(sub 5)-H(sub 2)O for Na/P atom ratios between 2 and 3. Based on observed reaction threshold values for sodium phosphate concentration and temperature, the respective standard entropy and free energy of formation for Na(sub 4)Ti(OH)(sub 2)(PO(sub 4))(sub 2) were calculated to be 823. 1 J/mol-K and -4025.1 kJ/mol at 298 K.