Effects of Mechanical Milling of Raw Powders on Reaction Sequence of Thermite Combustion Synthesis of Tri-Nickel Aluminide

抄録

We investigated the effects of mechanical milling of the raw powders on the reaction sequence of thermite combustion synthesis (TCS) to produce fluid tri-nickel aluminide. The TCS reaction combines the ordinary combustion synthesis reaction and a modified thermite reaction which is more exothermic than the former reaction. The pre-milled mixture of nickel (Ni) and nickel oxide (NiO) was blended with aluminum powder manually in a mortar. The mixed powder with no NiO agglomerates was cold-pressed into a cylindrical precursor and then preheated to ignite the TCS reaction. The critical ratio of the modified thermite reaction for fluid product formation was 0.20 which was lower than the value (0.23) in the previous study in which all the raw powders were mixed in a mortar. On the other hand, additional mechanical milling of the pre-milled Ni+NiO mixture and aluminum powder suppressed the fluidized product formation. The reaction sequence of the pre-milled Ni+NiO mixture and aluminum powder was well explained by considering two competing mechanisms: reactive diffusion which is to produce relatively large liquid pools and reactive infiltration to produce composite material regions having fine alumina networks which support the shape of the specimen.