CaO content in CaCl2 suitable for NiO reduction

A moderate concentration of CaO promotes a better reaction rate due to enhanced oxide ion transfer across the electrolyte [6]. The CaO content in the electrolyte is a key parameter to the process. The proper CaO concentration suitable for reduction has been rarely investigated, despite the fact that calcium oxide addition to molten calcium chloride yields positive results. Namely, in the purely calciothermic reduction of Ti02 without an external electrochemical potential [14], 0.5 mol% CaO in the CaCl2 melt resulted in a better deoxidation. 

Six hundred grams of CaCl2 were melted with CaO in the MgO crucible, and NiO powder in a Ni basket-type cathode and a graphite anode of 10 mm diameter were immersed at 1173 K. Electrolysis with a constant voltage of 3.1 V was terminated at 1.8ks and the electrodes were pulled up to cool in an Ar atmosphere. Further details will be reported separately [13]. 

Thus the current (reaction rate) depends on the CaO concentration in the molten salt, which supports the calciothermic reduction mechanism, as shown by other experimental evidence [1-3, 9,13,14], 

This work was financially supported in part by a Grand-in-Aid from the Japanese Ministry of Education, Science, Culture and Sports, Nos. 20360341 and 21656193, and by The Light Metal Educational Eoundation Inc. 

Suzuki, R.O., Teranuma, K. and Ono, K. (2003) Calciothermic reduction of titanium oxide and in-situ electrolysis in molten CaClj. Metall. Mater. Trans. B, 34, 287. 

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