Enhancing the spark-plasma sinterability of B4C nanopowders via room-temperature methylation induced purification

B4C nanopowders were subjected to room-temperature methylation to assess its possible beneficial effect on single-step cycle spark-plasma sinterability. It was found that methylation removes the oxidic impurities, thus chemically purifying the B4C nanopowders without nanoparticle growth. Next, it was determined that the temperature of spark-plasma sintering optimizing the microstructure and mechanical properties is similar to 1500 degrees C, below which there is insufficient densification and above which there is marked grain growth, scenarios both detrimental for the hardness of these B4C ceramics. It was also found that the so-purified nanopowders are more sinterable than the as-received nanopowders, and also than the same nanopowders purified by annealing under an inert atmosphere. This greater sinterability resulting from the elimination of the oxidic impurities is attributable to the enhanced grain-boundary diffusion favouring the densification. Thanks to the methylation, dense, nano-grained, superhard B4C ceramics can thus be fabricated with greater energy efficiency. Implications of interest for the ceramics community are discussed. (C) 2016 Elsevier Ltd. All rights reserved.