Journal of the Japan Society of Powder and Powder Metallurgy
Online ISSN : 1880-9014
Print ISSN : 0532-8799
ISSN-L : 0532-8799
Volume 66 , Issue 9
September
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  • Akihiro MATSUMOTO, Toshihiko SUGIURA, Makoto KOBASHI, Shinpei YAMAMOTO
    2019 Volume 66 Issue 9 Pages 429-433
    Published: September 15, 2019
    Released: September 15, 2019
    JOURNALS RESTRICTED ACCESS

    Well-defined SiO2-coated Fe nanoparticles with various SiO2 thickness from 1.2 to 27.8 nm have been successfully prepared by controlling the amount of tetraethyl orthosilicate and by the subsequent reduction of SiO2-coated Fe3O4 nanoparticles with CaH2. The saturated magnetization of the SiO2-coated Fe nanoparticles increased with decreasing SiO2 thickness. The saturated magnetization of the SiO2-coated Fe nanoparticles with SiO2 thickness of 2.7 nm or more have slightly decreased by 192 hr and did not change above 192 hr throughout atmospheric exposure, whereas that with SiO2 thickness of 1.2 nm steeply decreased in 24 hr and continued to decrease above 24 hr.

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  • Thi Minh Phuong NGUYEN, Ken HIROTA, Masaki KATO, Kazuhiko TSUKAGOSHI, ...
    2019 Volume 66 Issue 9 Pages 434-441
    Published: September 15, 2019
    Released: September 15, 2019
    JOURNALS RESTRICTED ACCESS

    Recently, bio-safe germicidal ZnO has been attracting much attention because of the interaction with various biomolecules chemically as well as physically. As its antibacterial activity is related to reactive oxygen species (ROS), the ROS have been investigated in terms of luminol chemiluminescence (CL) emitted from the ZnO surface. In this study, the relationship between the disinfect activity of four kinds of ZnO powders and their physico-chemical properties has been studied using XRD (X-Ray Diffraction), SEM (Scanning Electron Microscope), BET (Brunauer–Emmett–Teller), CL, ESR (Electron Spin Resonance), and XPS (X-ray Photoelectron Spectroscopy) and bio-test using E. coli. Four ZnO powders tested were as following; No. 1 is newly developed ZnO, prepared via hydrothermal treatment in aqueous Zn(NO3)2 solution and then re-oxidized, which reveal a strong antimicrobial activity under dark conditions; No. 2 starting material for No. 1, derived from zinc acetate; No. 3 fine ZnO prepared at low-temperature heating of basic zinc carbonate; No. 4 conventional fine ZnO synthesized from vaporized metal Zn in air. All powders revealed antimicrobial activity in the dark; different amounts and kinds of ROS have been emitted from each ZnO powder, however, it has been cleared that its sustainability depends significantly on the contents of interstitial Zn contained in ZnO particles.

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  • Hiroshi KIMURA
    2019 Volume 66 Issue 9 Pages 442-448
    Published: September 15, 2019
    Released: September 15, 2019
    JOURNALS RESTRICTED ACCESS

    The millimeter wave pressure sintering featuring power output (Wm) control of amorphous B4C powders is proposed without the need for any additive, in order to reveal definitely divided densification far below a glass transition. With the constant-rate heating technique, amorphous B4C containing nanocrystalline rhombohedra can be consolidated without sub-μm sized pore at 50 MPa. The heating rate used is found to be a dominating variable; with an increase from 10 to 20 K·min-1, it leads to a decrease from 510 to 444 K in full-density temperature. Its second-stage densification is expressed by the constitutive equation of consolidating strain rate ε˙n via non-Newtonian flow: ε˙n=ε˙osinh(Cσeff/RT)exp(-Q/RT) with a decreasing apparent activation energy Q from 42.5 to 35.4 kJ·mol-1 under an increased Wm. The constant-power output technique with a maximum Wm of 2 kW enables one to obtain a considerable initial abrupt shrinkage and subsequently full consolidation at the lowest temperature of 386 K under 98 MPa. The process control of the first-stage densification is then characterized by a neck formation law based on the first order chemical reaction d(Af-A)/dt = -kp(Af-A) where A is the fraction of a contacted area between particles, having an increasing kp with Wm.

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