Temperature Dependency on Crystallinity and Durability of Mineral Dolomite Doped Nanocrystalline Hexagonal Boron Nitride

Abstract

In this study, Nanocrystalline Hexagonal Boron Nitride powders (n-hBN) were synthesized from boron oxide and urea in the presence of very cheap mineral of dolomite (chemical compound of calcium magnesium carbonate, CaMg(CO3)2) followed by a catalytic annealing method and subsequent heat treatment under the ammonia reactive gas atmosphere at different reaction temperatures. Experiments were performed in a tube furnace with controlled atmosphere at 1000 °C, 1150 °C, 1300 °C and 1450 °C for 3 h as the weight ratios of 2.5/5.0/3.0 for B2O3/urea/dolomite. Furthermore, the powder n-hBN samples produced were experimentally investigated by means of Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Thermal Gravimetric Analysis (TGA) and High-Resolution Transmission Electron Microscopy (HR-TEM). Instrumental methods pointed out that the samples indicate the boron nitride formation founded on the phase (crystal structure) transition from irregular turbostratic nature to highly crystalline hexagonal morphology. Additionally, it was observed from the results of FTIR and XRD analyses that the optimum reaction temperature was found to be 1450 °C for the high crystalline n-hBN structure. In fact, the formation temperature for the boron nitride material was also found to be relatively lower such a value of 1000 °C as compared to that of O’Connor method (1600 °C). The TGA and DSC examinations also displayed that the thermal dependence of BN in the hexagonal crystal structure was obtained to be stable up to the temperature of 1200 °C in the open atmosphere, and the exothermic peak reaching its top point at 1160 °C took place at a temperature range of 1050–1300 °C.