Ultrafine cobalt and cobalt alloy particles have been prepared by spontaneous autocatalytic reduction.
The influence of parameters such as protein structure, magnetic field applied for reduction and reduction reagent on particle growth was investigated. Ultrafine cobalt particles with the size ranging from 60 to 700Å can be easily obtained by using various kinds of proteins and thier particle sizes markedly depend on the structure of proteins used. The suggested explanation of protein effect is that the nuclei of cobalt particle are formed on each functional polypeptide group of the macromolecular protein. The strength of magnetic field, which is applied for reduction, should be more than twice as large coercive force of cobalt and cobalt alloy partticles. X-ray diffraction studies were carried out on the samples obtained by the reduction of hydrazine and hypophosphite. Cobalt particles obtained by the hydrazine reduction have almost fee crystal structure, and not in those containing phosphorous. However, in the case of hypophosphite reduction, the particles are crytalline hcp. This behavior may be explained by the increase of Co-P components.

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By means of adding an Fe-23Si alloy (Fe5Sia) into Fe powders and sintering them in the atmosphere of ordinary cylindered H2 gas, Fe-Si system sintered compacts which have excellent mechanical properties were obtained.
As a result of consideration of relations between aspects of alloying of Si and mechanical properties of sintered compacts, it was made clear that a large "expansion" based on alloying of Si into Fe and a large "shrinkage" based on a phase-sintering cause spheroidizing of residual porosity in the structure and an extreme improvement of mechanical properties.

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Producing Fe-P sintered alloy by means of master mix method was attemped.
The results obtained are follows;
1) The maximum point appears at the effect of P on the sintering vs. admixed weight of the master mix owing to complex of two factors; P content in the master mix and the interface area between Fe powders (matrix) and master mix.
2) In this master mix method, as the diffusion of P is very fast, eutectic liquid is not generated during sintering process, so that pores in the structures are extremely spherodized by solid a phase sintering.
3) Elongation of sintered compacts is extremely improved by this master mix method, and it is because of the pore structure that fine spherodized pores are homogeneously distributed.

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The transverse-rupture strength affected by carbon contents of the WC-Co alloys was investigated in the temperature range from 600 to 900°C in relation to fracture sources. The WC-(620)%Co high and low carbon two phase alloys with carbide grain size of 1.2 p. were used as specimens. The stress increasing rate was kept at 1 kg/mm2/sec.
The high temperature strength of the low carbon alloy was confirmed to be substantially superior to the high carbon alloy. However, actually, this relation due to the carbon content was not always observed over a wide range of temperatures up to 900°C, because in conventional alloys structural defects were apt to be fracture sources with decreasing temperature and Co content: That is, the above relation was usually held at temperatures higher than the specified one which was determined according to Co contents and defect dimensions. In this case, a specific fracture source (R-region) always appeared and was smaller in the low carbon alloy. Discussions concerning the influence of stress increasing rate on the strength have been made.

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It was previously reported by the present authors that anomalous phases [Ti_xS(x≥1) with the dimension of about 10-50 μm] developed generally in the microstructure of commercial TiC-Mo₂C base cermets, owing to a small amount of sulfur impurity contained in the starting titanium carbide (TiC) powder. Thus, the present study was undertaken to describe the influence of TixS phases on the strength of TiC-Mo₂C-Ni cermet at room temperature. A TiC powder especially produced from TiH₂ powder and two types of commercially available TiC powders were used as starting materials. The sulfur contents of these starting TiC powders were 0.001% and 0.0390-0.042%, respectively. Three types of TiC-20%Mo₂C-20%Ni or TiC-8%Mo₂C-17%Ni alloy systems depending on the starting powders were vacuum-sintered. The carbon contents of each alloy system were minutely varied.
It was found that the transverse-rupture strength of commercial cermets was always lower than that of the other cermet prepared from the special starting powder, independent of carbon contents. The lower strength of commercial cermets was due to the fact that Ti_xS phases or larger pores were apt to operate as a fracture source. It was concluded that a small amount of sulfur impurity contained in the starting powder was detrimental to the strength of TiC-Mo₂C base cermets.

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