Boron compounds thermal properties

Up to the early 1990s, the only rare earth boride known with RB (n > 12) was RB66. These compounds have been primarily studied for their interesting structure and structurally derived features like the amorphous behavior of thermal properties. However, in a recent development, new higher borides have been discovered like the RB25 and RB50 compounds. Furthermore, with addition of small amounts of 3rd elements like C, N, Si, the boron cluster framework was found to arrange... 

The examination of structure/property relations of molecular educts and resulting ceramics required the synthesis of stoichiometrically and stmcturally different precursors. A variety of synthesis routes for Si-B-N-C precursors fiom organosilanes, silazanes, and boron compounds have been reported in recent years [3 - 5]. As an example, Riedel obtained a polymeric precursor via hydroboration of methylvinyldichlorosilane and subsequent condensation of the hydroboration product with ammonia (Eq. 1). Pyrolysis led to silicoboron carbonitride ceramics exhibiting thermal stability up to 2000 °C [6]. 

Gd, Gd, and Hf. The properties of B are favorable, and boron compounds have been tested clinically (for over 20 years in Japan) for the treatment of melanomas, bone marrow and malignant brain tumors (82). The isotope B undergoes fission on bombardment with thermal or epithermal neutrons, giving rise to a particles that are destructive to local tissue (within 10 p,m) ... 

CHEMICAL PROPERTIES thermally unstable water reactive hydrolyzes in water to hydrogen and boric acid reacts with ammonia to form diborane diammoniate reacts slowly with bromine to form boron bromides reacts with hydrocarbons or organoboron compounds to give alkyl- or aryl-boron compounds reacts with metal alkyls to form metal borohydrides reacts with strong electron pair donors to form borane addition compounds FP (-90°C, -130°F) LFL/UFL (0.9%, 98%) AT (40-50°C, 104-122°F) HF (35.6 kJ/mol gas at 25°C). 

Cosset, D., Query, M., and Kryger, B., Thermal Properties of Some Boron-rich Compounds, in Boron-Rich Solids, AIP Conf. Proc. 140 (D. Aselage, et al., eds), Am Inst, of Physics, New York (1986)... 

M Bougoin, R Fillit, F Thevenot, H Bruyas. Determination of free graphite in textured samples of boron carbide and boron-carbide-silicon carbide composites. J Less Common Met 117 215, 1986. D Gosset, M Query, B Kryger. Thermal properties of some boron-rich compounds B C and AIB12 . In D Emin, T Aselage, AC Switendick, B Morosin, CL Beckel, eds. Boron-Rich Solids, AIP Conference Proceedings 231. Albuquerque AIP, 1990, p 380. 

There are a number of papers in the open literature explicitly reporting on the properties of boron cluster compounds for potential neutron capture applications.1 Such applications make full use of the 10B isotope and its relatively high thermal neutron capture cross section of 3.840 X 10 28 m2 (barns). Composites of natural rubber incorporating 10B-enriched boron carbide filler have been investigated by Gwaily et al. as thermal neutron radiation shields.29 Their studies show that thermal neutron attenuation properties increased with boron carbide content to a critical concentration, after which there was no further change. 

Cubic BC2N. Hetero-diamond B C—N compounds have recently received a great interest because of their possible applications as mechanical and optical devices. The similar properties and structures of carbon and boron nitrides (graphite and hexagonal BN, diamond, and cubic BN) suggested the possible synthesis of dense compounds with all the three elements. Such new materials are expected to combine the best properties of diamond (hardness) and of c-BN (thermal stability and chemical inertness). Several low-density hexagonal phases of B,C, and N have been synthesized [534] while with respect to the high-density phases, different authors report contradictory data [535-538], but the final products are probably solid mixtures of c-BN and dispersed diamonds [539]. 

There is obviously a particular need to develop materials which can function at high temperatures. Due to their strong covalent bonding, boron cluster compounds generally possess attractive mechanical properties as materials, e.g. stability under high temperature due to their high melting points (typically >2300 K), chemical stability, resistance to acidic conditions, and small compressibility. Furthermore, importantly, the B12 icosahedra compounds have also been found to have intrinsic low thermal conductivity, as will be discussed in detail in later sections, and which is desirable for thermoelectric applications. 

The formation of borophosphate partially explains the good performance when APP and boric acid are mixed together in the epoxy resin. Indeed, in that case good mechanical resistance of the intumescent char is observed as borophosphate is a hard material, which also shows a good thermal stability. As a conclusion, the boron containing compounds provide the good structural properties of the char, whereas the phosphorus ensures the adhesion of the char to the steel. 

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