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

Özkenter, Ali Arda
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.


Effect of calcium carbonate addition on carbothermic formation of hexagonal boron nitride
ÇAMURLU, HASAN ERDEM; SEVİNÇ, NACİ; Topkaya, Yavuz Ali (Elsevier BV, 2008-01-01)
Effect of CaCO3 on formation of hexagonal boron nitride (h-BN) was investigated by holding CaCO3 free and CaCO3 added activated carbon-boric oxide mixtures under nitrogen atmosphere at 1500 degrees C for 30-120 min. Amount of CaCO3 addition was varied in the range of 0-50 wt.% of the initial mixture. Products were characterized by powder X-ray diffractometry, FT-IR analysis, quantitative chemical analysis, scanning electron microscopy and BET specific surface area analysis. It was observed that calcium carb...
Role of boron carbide in carbothermic formation of hexagonal boron nitride
Camurlu, H. E.; Sevinc, N.; Topkaya, Yavuz Ali (Springer Science and Business Media LLC, 2006-08-01)
Formation of hexagonal boron nitride by carbothermic reduction of boric oxide under nitrogen atmosphere at 1500 degrees C was investigated. Experiments were performed for durations in the range of 15 min to 3 h. Reaction products were subjected to powder X-ray diffraction analysis, chemical analysis and were examined by scanning electron microscope. Formation of hexagonal boron nitride was found to be complete in 3 h with most forming in the initial 2 h. Boron carbide was found to exist in the reaction prod...
Investigations on bulk glass forming ability of titanium based multicomponent alloys
Süer, Sıla; Mekhrabov, Amdulla O.; Department of Metallurgical and Materials Engineering (2008)
The aim of this study is to investigate the bulk glass forming ability (BGFA) of Ti-based alloy systems. These investigations were carried out in two main parts that are complementary to each other: theoretical and experimental. For theoretical studies, which are based on electronic theory of alloys in pseudopotential approximation, Ti-Zr, Ti-Co and Ti-Cu alloys were chosen as the binary systems. Alloying element additions were performed to each binary for the investigation of the BGFA of multicomponent Ti-...
Ferroboron Production by Electrodeoxidation
Örs, Taylan; Öztürk, Tayfur; Department of Metallurgical and Materials Engineering (2008)
In this study ferroboron (Fe - 14 at %B) was synthesized in crystalline form (Fe + Fe2B) via electrodeoxidation. For this purpose, Fe2O3 and H3BO3 were mixed in suitable proportions via spex mill. The powder was cold pressed and sintered at 900 °C yielding a two phase structure Fe3BO6 and Fe2O3. The sintered pellets were electro-deoxidized in CaCl2 by applying 3.1 Volts at 850°C for 12 hours. This yielded Fe and Fe2B in proportions slightly deviating from the target composition. The chemical pathway of redu...
Effect of heat treatment on grindabilities of celestite and gypsum and separation of heated mixture by differential grinding
Sener, S; Bilgen, S; Ozbayoglu, G (Elsevier BV, 2004-03-01)
This study was conducted to determine thermal decomposition of gypsum (CaSO4 . 2H(2)O) and celestite (SrSO4), to examine the effect of heating on grindability and the possibility of celestite-gypsum separation by differential grinding after heating. The results indicated that no significant decomposition reaction was observed in celestite up to 900 degreesC whereas the decomposition of gypsum occurred within 100-450 degreesC.
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.