Calciothermic reduction of electrically isolated oxide

Electric isolation of the oxide from the cathode was studied to emphasize the workability of calciothermic reduction mechanism. NiO was taken as the oxide example, and was reduced without any electric connection to the cathode [13]. NiO does not dissolve in the molten salt and it does not form any complex oxide with CaO, which are useful features to understand the basic mechanism. It was tried whether NiO can be reduced to Ni metal without serving any electron from the external field. This may demonstrate the role of Ca in the molten salt. 

The theoretical charge, Q, is defined as the charge to form the stoichiometric amount of Ca necessary for reduction of a filled amount of NiO. The supplied charge, Q, was evaluated by integrating current with respect to time. The ratio of QIQ can be used as an index for the supplied electric charge. Q/Qo was 366% for this electrolysis of NiO. 

In the case when QIQo was 120-150%, a small amount of NiO remained unreacted, but it was completely reduced when the sample basket was electrically connected to the cathode. This reflects that the Ca formed is diluted and its strong reactivity is weakened when the basket is apart from the cathode where Ca is generated. 

---