Abstract
Elemental boron and boron nitride powders were mixed and pressureless-sintered in nitrogen. The structure and mechanical parameters of the ceramics were investigated and compared with those obtained from boron nitride powder free of the elemental boron. A positive effect of the addition of boron was found in increasing density, mechanical strength and refractoriness, and in suppressing growth of boron nitride grains. The reason of these changes has been explained by the formation of a refractory suboxide with a formula B6O as a consequence of a boron-controlled extraction of boric oxide (B2O3). The extraction of the sesquioxide being originally adhered to the surface of boron nitride grains allowing a more effective formation of boron nitride ceramic skeleton. From the morphology of the ceramics, it has been suggested that the formation of volatile boron suboxide (B2O2) precedes to localization of oxygen in B6O grains.
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