The electro-deoxidation of dense titanium dioxide precursors in molten calcium chloride giving a new reaction pathway

• Published in: Electrochimica acta 2011-03, Vol.56 (9), p.3286-3295
• Main Authors: Alexander, D.T.L., Schwandt, C., Fray, D.J.
• Format: Article
• Language: English
• Subjects: Calcium chloride; Chemistry; Electrochemical reduction; Electrochemistry; Electrolytes; Exact sciences and technology; General and physical chemistry; High temperature electrochemistry (including molten salts); Optimization; Pathways; Porosity; Precursors; Titanium; Titanium dioxide; Transformations
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2011.01.027

► Electro-deoxidation of dense TiO 2 precursors creates new reaction pathway. ► Insufficient free volume of the precursors blocks calcium incorporation reactions. ► Effective reaction pathway for dense precursors is: TiO 2 → Ti 2O 3 → TiO → Ti metal. ► CaTiO 3 from limited calcium-incorporation reactions is also reduced to Ti metal. A new study is presented on the electro-deoxidation of porous TiO 2 precursors in molten calcium chloride electrolytes. It is shown that by reducing precursor open porosity from standard values of ≥25% to ∼11–12%, such that there is insufficient free volume to permit substantial incorporation of calcium, a new reaction pathway for electro-deoxidation is created. Kinetically and microstructurally it is more direct, with an effective pathway of TiO 2 → Ti 2O 3 → TiO → Ti metal at an inward-moving transformation front. CaTiO 3, from limited calcium-incorporation reactions occurring at the beginning of the process, is shunted inwards and eventually reduced to Ti metal. The results indicate that there is greater freedom for precursor design and process optimisation than previously recognised.