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Volume 6, Issue 1
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Henry H. Hausner1959 Volume 6 Issue 1 Pages 1-18
Published: February 20, 1959
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSPowder metallurgy proves to be a most useful metallurgical technique for the fabrication of nuclear reactor components, especially for fuel elements. The variables which control the powder metallurgy of uranium, thorium, beryllium and zirconium and the oxides of some of these materials, are well under control. Powder metallurgy is the only technique which permits fabrication of the so.called matrix-type fuel elements, the core of which consists of a cermet material, usually with UO2 particles dispersed in a metallic matrix.
The advantages which powder metallurgy has to offer in nuclear engineering are especially the small grain structure of some of the sintered products and the random distribution of point defects in the crystal lattices. The ability of powder metallurgical products to bond well to other metals is also superior to that of metals made by a more conventional technique-a fact which is of importance with respect to the heat transfer problems occurring in nuclear reactors.
New powder metallurgy methods, such as powder densification by the rolling technique or metal powder slip casting, offer many advantages in nuclear engineering.View full abstractDownload PDF (11401K) -
[in Japanese]1959 Volume 6 Issue 1 Pages 19-24
Published: February 20, 1959
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESS1. 2. Study on the sintering process with the reducing reaction of oxide or slightly preoxidized powder compacts. Recent years, it was pointed out that the sintering process of powder compacts were promoted through some chemical reaction i. e. evaporation and condensation, oxidation and reduction among powder particles. Generally speaking, while the decomposion of metal oxide to metal and oxygen is the endothermic reaction, the combustion of hydrogen gas or that of carbon monoxide gas is the exothermic reaction. Then as the case may be, the reducing reaction of some metal oxide by hydrogen or by carbon monoxide is endothermic or exothermic. Above estimations were given to be sure experimentally by the anther as the temperature difference between metal and preoxidized powder compacts.
In the last parts of this paper, studies were carried on the relation between the microstructure and heating conditions of oxide or slightly preoxidized powder compacts. Whether heating up rapidly or slowly under reducing atmosphere, corresponded to whether higher or lower in the sintering temperature and longer or shorter in the sintering time. Then it was revealed that conditions of the flow rate, gas pressure, the sort of furnace atmosphere and the content of CO2 in CO, or H2O in H2 influenced on microstructures as the factors of reaction rate, reaction heat and repetition of reversible reaction among capillaries of powder particles. Also suspension of vapour produced by reaction, accumulation of reaction heats in some parts of capillaries and heterogeneous crystal grain growth were influenced by the factors above mentioned. Then the chemical reaction among powder particles did not always mean to promote the densification of sintered compacts.View full abstractDownload PDF (5643K) -
[in Japanese], [in Japanese]1959 Volume 6 Issue 1 Pages 25-29
Published: February 20, 1959
Released on J-STAGE: November 19, 2010
JOURNAL FREE ACCESSThermal dilatometric curves of OP magnets, Co-Fe ferrite, were measured in the temperature range from room temperature to 800°C. Measurement was made in air and also in low pressure on OP magnets which were sintered in air and in low pressure.
In this measurement an anomalous curve was obtained. When OP magnet which was field-cooled in low pressure of about 0.5mm Hg was heated in air, it showed a remarkable shrinkage in the temperatures from 300° to 400°C. This shrinkage is explained as follows ; In the temperatures between 300° and 400°C, Fe304 contained in OP magnet becomes γ-Fe2O3 by oxidation. In this case, increase in volume of the specimen seems to happen by increase of the number of mols due to combination of oxygen with Fe2O4, but actually only the volume of pores in sintered body decreases and the length of specimen is almost the same. This is because oxygen is thought to combine with Fe2O4 only on the surface of particles. When Fe2O4 become γ-Fe2O3 by oxidation, its lattice constant becomes from 8.37 to 8.30 Å, i. e. the specimen shrinks in length to 99.2%. When Fe2O4 which is about 1/4 of OP magnet shrinks to 99.2% in its length, OP magnet shrinks to 99.8% (Δl/l≅2×10-3).
Such assumption has been supported by dilatometric measurement and at the same time by thermal analysis.View full abstractDownload PDF (350K) -
[in Japanese]1959 Volume 6 Issue 1 Pages 30-34
Published: February 20, 1959
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSDownload PDF (6199K)
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