• Dashwood, Richard
• Jackson, Martin
• Dye, David
• Inman, Douglas
• Jackson, Ben

Abstract

The FFC Cambridge process is a direct electrodeoxidation process used to reduce metal oxides to their constituent metals in a molten Ca Cl2 salt bath. NiTi O3 was used as a precursor (the first stable oxide to form upon blending and sintering NiO and Ti O2 powders) and was successfully reduced using the FFC Cambridge process at 1173 K and a constant cell voltage of -3.1 V to produce a NiTi alloy. This work builds on the literature work [Chinese Science Bulletin, 51, 2535 (2006)] through: (i) a predominance diagram calculated to show the regions of phase stability throughout the usable potential window of the Ca Cl2 salt; (ii) the investigation of a wide range of reduction times for a fixed cell voltage, elucidating several additional stable phases, to yield a complete and detailed reduction pathway. The reduction pathway for NiTi O3 was identified through the analysis of a series of partial reductions, with fully reduced NiTi formed after a period of 24 h. The first stage of the reaction involved the rapid formation of Ni and CaTi O3. The reduction then proceeded via the formation of the intermediate compounds Ni3 Ti and Ni2 Ti4O. All the NiTi O3 and Ni were consumed after a period of 6 h, while the intermediate compounds remained until the reaction was near completion. The experimental results related well to the thermodynamic predictions of the predominance diagram. A small variation in stoichiometry of the produced NiTi observed from the edge to the core of the samples was attributed to redeposition of Ti on the sample surface from the salt and a slightly Ti-rich NiTi O3 precursor material.

Topics

• impedance spectroscopy
• surface
• compound
• phase
• sintering
• phase stability