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Densification of carbon-rich boron carbide nanopowder compacts

Published online by Cambridge University Press:  18 July 2011

Namtae Cho
Affiliation:
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332
Kathleen G. Silver
Affiliation:
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332
Yolande Berta
Affiliation:
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332
Robert F. Speyer
Affiliation:
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332
Noel Vanier
Affiliation:
PPG Industries, Inc., Allison Park, Pennsylvania 15101
Cheng-Hung Hung
Affiliation:
PPG Industries, Inc., Allison Park, Pennsylvania 15101
Corresponding
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Abstract

The densification behavior of 20–40-nm graphite-coated B4C nano-particles was studied using dilatometry, x-ray diffraction, and electron microscopy. The sintering onset temperature was higher than expected from a nanoscale powder (∼1500 °C); remnant B2O3 kept particles separated until B2O3 volatilization, and the graphite coatings imposed particle-to-particle contact of a substance more refractory than B4C. Solid-state sintering (1500–1850 °C) was followed by a substantial slowing of contraction rate attributed to the formation of eutectic liquid droplets more than 10× the size of the original nano-particles. These droplets were induced to form well below the B4C-graphite eutectic temperature by the high surface energy of nanoparticles. They were interpreted to have quickly solidified to form a vast number of voids in particle packing, which in turn, impeded detection of continued solid-state sintering. Starting at 2200 °C, a permanent and interconnected liquid phase formed, which facilitated rapid contraction by liquid phase sintering and/or compact slumping.

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Copyright © Materials Research Society 2007

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