Abstract
Hexagonal boron nitride (h-BN) is a well-known material whose use is almost restricted to lubricating applications in domains ranging from metallurgy to cosmetics. Howover, h-BN displays many other interesting properties, opening new perspectives for other engineering applications, such as as a solid lubricant in aeronautics, as the perfect substrate to graphene for electronic devices, etc. However, all these promising developments require tailored h-BN shapes displaying a high level of crystallization, ensuring its properties for the long term. Here, we developed three strategies, all associated with the Polymer Derived Ceramics (PDCs) route, to prepare highly crystallized supported thick coatings and self-standing nanosheets. The first strategy concerns the innovative implementation of a Rapid Thermal Annealing to prepare micrometric h-BN coatings on thermal sensitive substrates. Compared to conventional treatment the crystallization of h-BN has successfully lowered to about 300 °C. The second strategy consists of an additivation of the used polymer precursor. Effect of lithium nitride as a crystallization promoter was investigated lowering the onset crystallization temperature from 1400 °C (traditionally) to 1000 °C. This novel synthetic route allows preparing self-standing highly crystallized h-BN nanolayers. Finally, the third strategy is based on a unique combination of the PDCs route with Spark Plasma Sintering to profit of both approaches. This original method leads to large and well-crystallized flakes available for a subsequent exfoliation.
Highlights
Hexagonal boron nitride (h-BN) is a famous non oxide ceramic known and appreciated for its numerous interesting properties, such as a high thermal conductivity, an excellent thermal chock resistance, a high resistance against oxidation (850 ̋ C under air), a good chemical inertness [1,2], etc.Based on this non exhaustive list of important properties, it is easy to understand the key role of h-BN for real or potential applications
Keeping these issues in mind, the second way, involving exfoliation of single crystals, is relevant if an accessible source of pure and highly crystallized crystals becomes available [76]. It is well-known that the group of Watanabe at the National Institute for Materials Science (NIMS) [77,78] can prepare this kind of high quality single crystals using the High Pressure High Temperature (HPHT) process, but the whole procedure runs through severe production conditions and long treatment time [76] making its widespread restricted
This review reports several strategies to synthesis highly crystallized hexagonal boron nitride using the Polymer Derived Ceramics (PDCs) route
Summary
Hexagonal boron nitride (h-BN) is a famous non oxide ceramic known and appreciated for its numerous interesting properties, such as a high thermal conductivity, an excellent thermal chock resistance, a high resistance against oxidation (850 ̋ C under air), a good chemical inertness [1,2], etc. Keeping these issues in mind, the second way, involving exfoliation of single crystals, is relevant if an accessible source of pure and highly crystallized crystals becomes available [76] It is well-known that the group of Watanabe at the National Institute for Materials Science (NIMS) [77,78] can prepare this kind of high quality single crystals using the High Pressure High Temperature (HPHT) process, but the whole procedure runs through severe production conditions and long treatment time [76] making its widespread restricted. We focused our attention on three main strategies developed insize theof group in order domains, this route needs heavy equipment and reproducibility is strongly dependent on the used to increase the h-BN crystallization foritssupported coatings and self-standing nanosheets prepared apparatus, which really limits development.thick. The second strategy is directly linked toAnnealing the chemistry, (RTA)
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