Effect of calcium oxide addition on carbothermic formation of hexagonal boron nitride

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2009

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Özkenter, Ali Arda

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Hexagonal boron nitride (h-BN) formation by carbothermic reduction of B2O3 under nitrogen atmosphere at 1500°C and effect of CaO addition into the initial B2O3 – active C mixture were investigated during this study. Reaction products were characterized by powder X-ray diffraction, scanning electron microscopy (SEM) and quantitative chemical analysis. Main aim of this study was to investigate the presence of a second reaction mechanism that catalytically affects h-BN formation during CaO or CaCO3 addition into the initial mixture. It was found that similar to CaCO3 addition, CaO addition has a catalytic effect on carbothermic formation h-BN. In order to investigate the reaction mechanism experiments with B2O3 – CaO mixtures without active carbon addition into the mixture were conducted. Furthermore nucleation of h-BN from calcium borate melts had been investigated and experiments were conducted with h-BN addition into CaO – B2O3 mixtures. It was concluded that nucleation of h-BN in calcium borate slags under experimental conditions is not possible. Hexagonal BN should be present in the system in order to activate the second nitrogen dissolution followed by h-BN precipitation mechanism. Highest efficiency was achieved in the experiment conducted with CaCO3 addition and largest particle size was observed during the experiment conducted to investigate the effect of nucleation.

Subject Keywords

Metallurgical and materials engineering.

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http://etd.lib.metu.edu.tr/upload/12610740/index.pdf
https://hdl.handle.net/11511/18556

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

A. A. Özkenter, “Effect of calcium oxide addition on carbothermic formation of hexagonal boron nitride,” M.S. - Master of Science, Middle East Technical University, 2009.