Effect of borates on the synthesis of nanoscale hexagonal boron nitride by a solid‐state method

• Published in: Microscopy research and technique 2021-11, Vol.84 (11), p.2677-2684
• Main Authors: Öz, Muhammed, Bozkurt, Çetin, Kanbur Yılmaz, Binnur, Yıldırım, Gürcan
• Format: Article
• Language: English
• Subjects: Ammonium; Ammonium pentaborate; Bonding strength; Borates; Boron; Boron nitride; Boron oxides; Chemical bonds; Chemical synthesis; Crystal structure; electron microscopy; Fourier transforms; Heat treatment; Heat treatments; hexagonal boron nitride; Infrared spectroscopy; Lithium; Lithium borates; Measurement methods; nanocrystalline materials; Nanorods; Nanotechnology; Nanotubes; Sodium; Sodium tetraborate; Spectrum analysis; Transmission electron microscopy; Urea; Vibrations; X-ray diffraction; X‐ray techniques
• ISSN: 1059-910X; 1097-0029
• DOI: 10.1002/jemt.23817

This study delves deeply into the effect of different borates (lithium tetraborate, sodium tetraborate, calcium metaborate, ammonium pentaborate) on the production and fundamental characteristic features of nanoscale hexagonal boron nitride (hBN) structure with the assistant of standard characteristic measurement methods, namely, Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM). The hBN samples are synthesized by reaction of powder urea, boron oxide, and different kinds of borates via the modified O'Connor method (performed at a relatively lower main heat treatment temperature of 1,100°C). All the results obtained show that the usage of borates affects positively the formation of nanoscale hBN structure. In more detail, the FTIR experiment results reveal that the presence of two strong c peaks appeared at ~1,380 and ~780 cm−1 in the spectra points out the conventional BN in‐plane and out‐of‐plane vibrations, respectively. The XRD patterns also confirm the production of high‐ordered hBN as the existence of the main peaks of the corresponding hexagonal system. As for the SEM examination, it is found that all the hBN materials exhibit totally different crystallinity quality and microstructural characteristics. The hBN compound prepared by the sodium tetraborate content shows the most uniform surface appearance with the smoothest/densest crystal structure, best grain orientations, and finest grain interactions. Hence, the material with strong stretching of interatomic bonds shows the highest material (fracture) strength. Moreover, the TEM images illustrate that all the products are composed of uniform multi‐walled nanotubes and nanorods with an average length of ~250 nm. The main finding of this study was that the grain size of the hBN samples mainly influenced by the type of the borate salt that was determined by XRD, SEM, and TEM analysis methods. Lithium tetraborate had the best contribution to the highly crystalline hBN formation while sodium tetraborate affected the crystallinity moderately. The electron microscopy pictures display that each hBN material prepared possesses wholly different crystallinity quality and microstructural characteristics. According to the results obtained, the sodium tetraborate content plays more superior role in the formation of nanoscale hBN structure while ammonium pentaborate has the least among these salts.