Boron carbonitride

Boron-containing nonoxide amorphous or crystalline advanced ceramics, including boron nitride (BN), boron carbide (B4C), boron carbonitride (B/C/N), and boron silicon carbonitride Si/B/C/N, can be prepared via the preceramic polymers route called the polymer-derived ceramics (PDCs) route, using convenient thermal and chemical processes. Because the preparation of BN has been the most in demand and widespread boron-based material during the past two decades, this chapter provides an overview of the conversion of boron- and nitrogen-containing polymers into advanced BN materials. 

The third approach, this one by Seyferth, is based on the coordinative linkage of borane cage structures by diamines or phosphines to form soluble oligomers (9.21), followed by pyrolysis (reaction (20)).66-68 Pyrolysis in an inert atmosphere gives a 70-90% ceramic yield of a black boron carbonitride, but pyrolysis in ammonia yields white BN in 70% yield. A disadvantage of a process based on a borane starting material is its high cost. 

Theoretical Investigation of Structure of Boron Carbonitride Nanotubes... 

These novel microstructures have extraordinary combination of physical and chemical properties [11-13], for this reason they become an important scheme of actually science work. One example of such nanomaterials is boron carbonitride (BNC) with graphite-like structure. Based on theoretical calculations, the existence of nanotube structures of BN was predicted in 1994, which was soon verified by the first synthesis of BN nanotubes in 1995. 

The synthesis of a range of silicon boron carbonitride ceramics can conveniently be carried out by thermal treatment of suitable amorphous precursor molecules in which the desired atomic linkages are already in place. A series of new amorphous precursor molecules has been investigated by "B MAS NMR and double resonance techniques such as Si- B) Rotational Echo Adiabatic Passage DOuble Resonance (REAP-DOR) and B-j Si) Rotational Echo DOuble Resonance (REDOR) (van Wiillen and Jansen 2001). The results indicate the presence of hexagonal BN and (3-Si3N4 in some... 

Kosinova ML, Fainer NI, Rumyantsev YM, Golubenko AN, Kuznetsov FA (1999) LPCVD boron carbonitride films from triethylamine borane. J de Physique IV, 9, Pr8-915-921... 

Amineboranes were thermally decomposed at 1273 K in Ar to boron carbonitrides [262]. These materials were reported to show a turbostratic structure where atoms in a carbon-like structure are partially substituted by boron and nitrogen, respectively. At temperatures higher than 2073 K (Ar-atmosphere) the single phase material of compositions BC4N and BC2N, respectively, started to crystallize and a-BN, B4C and elemental C (graphite) were observed. 

Sauter (2000) [266] investigated the structure of amorphous boron carbonitride of composition B31C37N32 by X-ray and neutron diffraction as well as by NMR spectroscopy. It was shown that annealed precursor-derived B-C-N ceramics (1200 K < T < 1600 K) contain predominantly tricoordinated boron, carbon and nitrogen atoms arranged in hexagonal rings, or fragments of them, as structural units. No phase separation occurred. 

As precise as possible a knowledge of the chemical composition is a crucial pre-requisite to any serious attempt to determine the geometric and topological structure of a multi-component random network. However, chemical analyses of refractive materials like the silicon boron carbonitrides discussed here is a difficult task. In general, there exist two different classes of procedures, destructive ones, such as wet chemical digestion, and non-destructive (physical) ones. 

AlSb—GaSb solid solutions were obtained by melting the appropriate amounts of aluminum (AVOOO), antimony (SuOOO), and gallium (GIO), there beii a constant 10 at.% excess of antimony. Melting was carried out in boron carbonitride crucibles in evacuated and sealed quartz ampoules at temperatures 100 deg above the liquidus the temperature was then slowly reduced below the solidus, and the samples were annealed for 15 h. There were no traces of evaporated material on the ampoule walls. A further anneal was carried out in the measuring cell itself. 

Because fonnation of cubic boron carbonitride is of great fundamental interest with respect to superhard materials much additional effort is needed to succeed in the preferential synthesis of the cubic B-C-N phase. As follows from the above results the most promising way would be synthesis under nonequilibrium conditions such as flash-heating at static pressures or shock-wave compression [140]. Successful synthesis of cubic BC2.5N solid solution in 18% yield by shock-compression of hexagonal BC2.5N has been reported [143]. The material obtained was a single cubic BC2.5N phase with a diamond-like structure and crystals between 5 and 20 nm in size. 

Non-oxide preceramic polymers which are expected to yield, under convenient thermal and chemical conditions, boron-containing amorphous or crystallized ceramics including boron nitride (BN), boron carbide (B C), boron carbonitride (B-C-N), and boron silicon carbonitride Si-B-C-N. 

Polymer derived ceramics have been known for the last four decades and are prepared via solid-state thermolysis of preceramic polymers. They exhibit a unique combination of remarkable properties due to their covalent bonding and amorphous nature. Thus, silicon oxycarbide (SiOC) and silicon carbonitride (SiCN) based ternary PDCs have been shown to possess outstanding high-temperature properties such as stability with respect to crystallization and decomposition, oxidation and corrosion resistance as well as excellent thermomechanical properties (e.g., near zero steady state creep resistance up to temperatures far beyond 1000 °C). Their properties are directly influenced by the chemistry and the architecture of the preceramic precursors, thus there is an enormous potential in tuning the microstructure and properties of the PDCs by using tailored polymers. Furthermore, suitable chemical modification of the preceramic precursors leads to quaternary and multinary ceramics, as it has been shown for instance for silicon boron carbonitride ceramics in the last 25 years, which in some cases exhibit improved properties as compared to those of the ternary materials. 

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