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Volume 28, Issue 1
Displaying 1-6 of 6 articles from this issue
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Tokuhiko Nishida1981 Volume 28 Issue 1 Pages 1-7
Published: January 25, 1981
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSIn order to produce low oxygen powders containing Cr, Mn and Si for hot formed P/M steel, a reduction of surface oxides by prealloyed carbon has been investigated. Gas analysis data showed that the reduction of the alloy steel powders was accomplished in two stages, the first was mainly the reduction of iron oxides by carbon at about 700°C, and the second was mainly that of oxides of alloyed elements over 1000°C. The process analysis studies indicated that the rate determining process of C-O reaction in powders was chemical reaction at the interface of metal and oxide layer at the initial step, and diffusion of carbon in particles at the later step.View full abstractDownload PDF (3080K) -
Katsushi Kusaka1981 Volume 28 Issue 1 Pages 8-14
Published: January 25, 1981
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSSome metallurgical studies were made on 15/17% Cr-Ni steel powder compacts bearing 0.19% or less of nitrogen and sintered materials under various sintering conditions.
The results were summarized as follows,
(1) Nitrogen in powder compacts was found to decrease the rate constant in vacuum-sintering and to deviate from Arrhenius' plots especially at lower temperature, but was outgassed to 100 ppm or less gradually during vacuum-sintering above 1100°C.
(2) Densification rate was accelerated with denitrogenization, especially for low Ni-15/17% Cr steel powder compacts because of γ-α/γ phase transformation. The singular point on densification curves was shifted to shorter time with an increase of sintering temperature and porosity in green compact.
(3) The residual amount of nitrogen was mainly related to sintering temperature under the influence of pore-closing, and also to specimen-size approximately in the form of rn(T) (r: radius of specimen).
(4) N-addition to original powders had no practical effect on sintered properties, tensile strength and corrosion resistance in 65% HNO3 and 5% H2SO4 solutions when the compacts were vacuum-sintered at 1100°C for 1 hr or more.View full abstractDownload PDF (4164K) -
Kazumasa Takatori, Masahiko Shimada, Mitsue Koizumi1981 Volume 28 Issue 1 Pages 15-19
Published: January 25, 1981
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSHigh pressure hot-pressing of pure silicon was examined as one of the fundamental studies on hot-pressing of the non-oxide ceramics, which are expected as new high temperature structural materials. Three kinds of silicon powders with different average particle size were used as starting materials and hot-pressed under various high pressure-temperature conditions. When the coarse powders were used, the relative densities of hot-pressed compacts were higher than those fabricated from the submicron fine powders at lower temperatures. The densification proceeded with increasing temperature and applied pressure, but no time dependence of densification was found. The results of the Vickers microhardness measurement of the hotpressed compacts showed the maximum and minimum values depending upon the hot-pressing time in a short run. This results was explained by considering the distribution state of strain within the grains and the strength of self-bonding between the grains. The interpretation could be supported by the results of the line width of X-ray diffraction peaks and also the microstructures of hot-pressed bodies.View full abstractDownload PDF (1601K) -
Kazuhiko Majima, Naoyuki Ishigaki, Koichiro Morimoto, Hiroyasu Mitani1981 Volume 28 Issue 1 Pages 20-27
Published: January 25, 1981
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSBy using mixed powder compacts of Sm-60.5wt%Co and Sm-62.5wt%Co, the reaction process which occurred between SmCo5 and 60wt%Sm-40wt%Co powders during liquid phase sintering was investigated mainly by means of EPMA and X-ray diffraction method.
The results obtained were as follows: The liquid produced by the peritectic reaction at 1075°C upon heating process, played an important role for the liquid phase sintering of the SmCo5 permanent magnet, and it was confirmed that this liquid penetrated to make a network along the grain boundaries and had the effect of restraining the grain growth. The considerably strong X-ray diffraction peak of Sm2Co7 phase observed in the Sm-60.5wt%Co specimen became weaker with increasing Sm content, and extremely weak peak of Sm2Co7 was recognized in the Sm-62.5wt%Co specimen. On the other hand, in the specimen containing higher amount of Sm than Sm-62.5wt%Co, the peak of Sm2Co17 was observed.View full abstractDownload PDF (9996K) -
Yoshiko Suwa, Yukihiro Kato, Shin-ichi Hirano, Shigeharu Naka1981 Volume 28 Issue 1 Pages 28-32
Published: January 25, 1981
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSLiTaO3 was prepared by hydrolyzing an ethanol solution of lithium ethoxide and tantalum ethoxide with H2O in N2 atmosphere. The samples with 25, 45, 46, ......, 54, 55 and 75 mole percent of Li2O (Li2O/Li2O+Ta2O5 mol%) were coprecipitated.
The as-prepared samples with 45 to 55 mol% Li2O were amorphous, but crystallized to LiTaO3 byheating at 500°C for 2 h. Stability range of LiTaO3 solid solution phase below 1100°C could be determined from change of the lattice constants of LiTaO3 ss in 45 to 55 mol% samples heated at temperatures up to 1100°C. The ranges of LiTaO3 ss phase were 49.9 to 51.2 mol% at 800°C, 49.1 to 51.6 mol% at 950°C and 48.0 to 52.0 mol% at 1100°C. The lattice constants of stoichiometric LiTaO3 heated at 1100°C for 20 h were ac=5.153+0.001 A, and co=13.78+0.01 A.
The as-prepared sample with 25 mol% Li2O was amorphous, and crystallized to LiTaO3 and fl-Ta2O5
at 700°C. Above 800°C, LiTa3O8 was formed by the reaction of LiTaO3 with β-Ta2O5. A disordered NaCl type of Li3TaO4 was formed from the as-prepared sample with 75 mol% Li2O which changed to ordered tetragonal phase above 800°C.View full abstractDownload PDF (338K) -
Kazumi Fujita, Isao Kayama1981 Volume 28 Issue 1 Pages 33-34
Published: January 25, 1981
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSDownload PDF (1003K)
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