Processing of nano-sized boron carbide powder
Silver, Kathleen G.
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Recent studies indicate B4C nanopowder may provide additional advantages without loss of established properties. In this study, preliminary forms of graphite-coated B4C nanopowders on the order of 20-40 nm with various additives were sintered and analyzed. Methanol washing was performed on the powders to remove most of the B2O3 impurity usually present. XRD analysis of the powders verified the nanograined nature and, to some extent, the amount of amorphous material within the powders. A dilatometer furnace was used to track the dimensional changes during sintering, and densities of sintered samples were compared to green compact densities. The onset of sintering occurred at various temperatures depending on the dopant and its amount, most often occurring at higher temperatures than expected. This was likely due first to volatilization of residual B2O3 and then to the graphite coatings of the powders preventing direct B4C-B4C contact. Double-stage sintering, where sintering is either slowed, arrested or reversed and then re-accelerated, occurred in all but one sample. Samples with sintered densities greater than 93% theoretical density were hot isostatically pressed (HIP) with the expectation that the post-HIP density would be 100% theoretical density. Ultimately, post-HIP densities increased less than 2% compared to sintered densities.