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Densification of carbon-rich boron carbide nanopowder compacts

机译：富碳碳化硼纳米粉体的致密化

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The densification behavior of 20-40-nm graphite-coated B_4C 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℃); remnant B_2O_3 kept particles separated until B_2O_3 volatilization, and the graphite coatings imposed particle-to-particle contact of a substance more refractory than B_4C. Solid-state sintering (1500-1850℃) was followed by a substantial slowing of contraction rate attributed to the formation of eutectic liquid droplets more than 10x the size of the original nano-particles. These droplets were induced to form well below the B_4C-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℃, a permanent and interconnected liquid phase formed, which facilitated rapid contraction by liquid phase sintering and/or compact slumping.
机译：使用膨胀计，X射线衍射和电子显微镜研究了20-40 nm石墨包覆的B_4C纳米粒子的致密化行为。烧结起始温度高于纳米粉末的预期温度（〜1500℃）。残留的B_2O_3保持颗粒分离，直到B_2O_3挥发为止，并且石墨涂层使难燃物质比B_4C更加坚硬。固态烧结（1500-1850℃）后，收缩率显着降低，这归因于形成的共晶液滴超过原始纳米颗粒尺寸的10倍。由于纳米粒子的高表面能，这些液滴被诱导在远低于B_4C石墨共晶温度下形成。它们被认为已经迅速固化，在颗粒堆积中形成大量空隙，从而阻碍了对连续固态烧结的检测。在2200℃开始，形成了永久的，相互连接的液相，通过液相烧结和/或致密塌陷促进了快速收缩。

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