TITANIUM OXIDE

Chemical Properties

Ti₃O₅: (1) Rel.molar mass (Mr ): 223.0070; (2) wt.% Ti: 64.1; (3) Color: Dark blue; (4) crystal lattice structure: dimorphic (120°C) Low T: Anasovite-type I Monoclinic, C2/m, Z = 4 a = 975.2 pm; b = 380.2 pm; c = 944.2 pm; β = 91.55° High T: Pseudobrookite (orthorhombic); (5) ρcalc. = 4900 kg.m^–3, m.p. = 1777°C

Physical properties

Dark blue crystals. Anasovite Type II is similar to that identified in titania slags. Can be stabilized at room temperature with a small amount of iron.

Uses

Nanocrystalline titanium oxide electrodes is useful for photo voltaic applications. It plays an important role as photocatalyst under visible light radiation. Treated titanium oxide nanotubes play a significant part in the development of nano-scale hydroxy apatite. It is too utilized as catalysts.

Preparation

Anosovite can be prepared in the following ways:
(i) By the hydrogen reduction of solid TiO₂ at temperature around 1300°C16 according to the following reaction scheme: 3TiO₂(s) + H₂(g) —> T₃O₅(s) + H₂O(g) (1300°C).
(ii) By mixing intimately stoichiometric quantities of titanium metal and titanium dioxide in an electric-arc furnace under an argon atmosphere according to the following reaction scheme:
5TiO₂(s) + Ti(s) —> 2Ti₃O₅(s) (1150°C)
followed by annealing in a vacuum of the crushed material for 2 weeks at 1150°C in a sealed silica tube. This oxide is dimorphic with a rapid phase transition from semiconductor to metal occurring at roughly 120°C. α-Ti₃O₅—> β-Ti₃O₅ (120°C).
The low-temperature form (α-Ti₃O₅), also called anosovite type I, crystallizes with a monoclinic unit cell with the Ti-O bond distances ranging from 178 to 221 pm. The structure can be described in terms of TiO6 8– octahedra joined by sharing the edge and corners to form an infinite three-dimensional network. Anosovite I is obtained by the hydrogen reduction of pure rutile at 1300°C. The high-temperature form (β-Ti₃O₅), also called anosovite type II, is a slightly deformed pseudobrookite structure (AB₂O₅) with the Ti-O bond distances ranging from 191 to 210 pm. The type II is obtained by hydrogen reduction at 1500°C with magnesia as a catalyst. The anasovite type II is similar to that identified in titanium slags. It can be stabilized at room temperature with a small amount of iron.