title: Potential use of only Yb2O3in producing dense Si3N4ceramics with high thermal conductivity by gas pressure sintering.
abstract: Yb2O3is an efficient sintering additive for enhancing not only thermal conductivity but also the high-temperature mechanical properties of Si3N4ceramics. Here we report the fabrication of dense Si3N4ceramics with high thermal conductivity by the gas pressure sintering of α-Si3N4powder compacts, using only Yb2O3as an additive, at 1900 °C under a nitrogen pressure of 1 MPa. The effects of Yb2O3content, sample packing condition and sintering time on the densification, microstructure and thermal conductivity were investigated. Curves of the density plotted against the Yb2O3content exhibited a characteristic 'N' shape with a local minimum at 3 mol% Yb2O3and nearly complete densification below and above this concentration. The effects of the sample packing condition on the densification, microstructure and thermal conductivity strongly depended on the Yb2O3content. The embedded condition led to more complete densification but also to a decrease in thermal conductivity from 119 to 94 W m-1K-1upon 1 mol% Yb2O3addition. The sample packing condition had little effect on the density and thermal conductivity (102-106 W m-1K-1) at 7 mol% Yb2O3. The thermal conductivity value was strongly related to the microstructure.
authors.affiliation: Institute for Sustainability Research and Education, Hosei University, 2-17-1 Fujimi, Chiyoda-ku, Tokyo 102-8160, Japan.
authors.forename: Xinwen
authors.initials: X
authors.lastname: Zhu
authors.affiliation: Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Science and Technology, 2266-98 Anagahora, Shimo-Shidami, Moriyama-ku, Nagoya 463-8560, Japan.
authors.forename: You
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Science and Technology, 2266-98 Anagahora, Shimo-Shidami, Moriyama-ku, Nagoya 463-8560, Japan.
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Hirao
authors.affiliation: Institute for Sustainability Research and Education, Hosei University, 2-17-1 Fujimi, Chiyoda-ku, Tokyo 102-8160, Japan; Department of Chemical Science and Engineering, Hosei University, 3-7-2 Kajino-cho, Koganei, Tokyo 184-8584, Japan.
authors.forename: Takamasa
authors.initials: T
authors.lastname: Ishigaki
authors.affiliation: Nano Ceramics Center, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan.
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Sakka
keywords: Si3N4, Yb2O3; gas pressure sintering; grain growth; thermal conductivity