Preparation of Metal-Oxide Composites using Solid-State Displacement Reaction

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Preparation of metal-and oxide composites was examined for the solid-state displacement reactions between powders of NiO, CoO Cu_2O and Ti and between Cu_2O and Fe, using pellets obtained by die-pressing their mixed powders. In the both reactions of NiO and CoO with Ti, TiO_2 phases and metallic phases were finely combined after annealing at 1000ﾟC for 25 h. Diameter of Ti powder used was ranging form 50 to 100mum, but, after displacement reaction, TiO_2 phases and metallic phases were interwoven in micron size. In the reaction of Cu_2O with Ti, pellets were explosively fused at temperatures of 600 to 800ﾟC by thermit reaction. The powder of ZrO_2 was added to the mixtures as an inert substance, which had only a kinetic influence to a reaction. The addition of very fine powder by at least 2 wt.% pevented the thermit reaction the increase of ZrO_2 lead to bad sinterability ; samples containing ZrO_2 above 30 wt.% were not sintered. Sintered sample had interwove n structures of Cu and TiO_2 phases ; ZrO_2 was distributed at grain boundaries of Cu phases. In the reaction of Cu_2O and Fe, both the reactions Cu_2O + Fe = 2Cu + FeO and 4Cu_2O + 3Fe = 8Cu + Fe_3O_4 proceeded and the former reaction was predominant at higher mixing ratios of Fe/Cu_2O.Composites obtained by the displacement reaction had porosities of 20 to 40 vol.%. The increase of the pressure applied to a die and of the annealing temperature were lowered porosity.