Fundamental structural study of hexagonal boron nitride (h-BN) and boron nitride nanotube (BNNT) at low and high temperatures

The molecular structure stability at low and high temperature is important for an industrial application. The boron nitride-based materials, such as hexagonal boron nitride (h-BN) and boron nitride nanotubes (BNNTs), have been interested due to their high oxidation resistance and thermal stability. In this study, ex-situ and in-situ characterization techniques (e.g., Raman spectroscopy, X-ray Diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR)) were applied to investigate the structural change of BNNT and h-BN at high (up to 800 °C) and low (down to -50 °C) temperatures. The Raman spectroscopy results showed that at high temperatures (800 °C), h-BN exhibited a significant red shift under both inert and oxidizing conditions, while BNNT showed no peak shift, indicating its more stable structural resistance compared to h-BN. Both h-BN and BNNT showed no peak shift after cooling to low temperatures (-50 °C). Stability of h-BN and BNNT up to a high temperature of 800 °C was revealed from the thermogravimetric analysis (TGA) and FTIR spectroscopy results. The FTIR results also indicate that under oxidizing conditions, heating h-BN results in the formation of more hydroxyl groups compared to BNNT. The in-situ XRD results showed a greater magnitude of lower 2θ shift with increasing temperatures for h-BN compared to BNNT. Additionally, there was a more significant increase in FWHM values with respect to temperatures for h-BN than BNNT regardless of the sample under inert or oxidizing conditions. The characterization results from this study indicate that BN-based materials, especially BNNT, are suitable candidates for high temperature chemical reaction applications.