Boron carbon vapor

The selected value is an average based on the equilibrium data summarized below. Drowart and co-workers have used the Knudsen effusion-mass spectrometric technique to determine the vapor equilibria over the systems SiC-graphite ( ), SiC-silison (2 ) and boron-carbon-silicon (3). 3rd law analysis of the partial pressures of C Si and Si lead to the concordant values -1 ... 

Golda E M, Gallios B (1992) Chemical vapor deposition of multiphase boron-carbon-sihcon ceramics. In Besmann TM, Gallois BM, Warren JW (eds) Chemical vapor deposition of refractory metals and ceramics II. Materials Research Society, Pittsburgh, PA, ppl67-172... 

Figure D.l is reprinted from Journal de Physique IV, Vol. 5, L Vandenbulke and M Leparoux, Silicon and boron containing components by CVD and CVI for high temperature ceramic composites, C5-735-751,1995, with permission from EDP Science. Figure D.2 is reprinted from Materials Research Society, E M Golda and B Gallios, Chemical vapor deposition of multiphase boron-carbon-silicon ceramics, in T M Besmann, B M Gallois and J W Warren eds, Chemical vapor deposition of refractory metals and ceramics II, pp. 167-172, 1992, with permission from Materials Research Society.

However, the cocondensation of boron halides and carbon vapor yields only < 0.05 g per pass, and no continuous process is available. 

Kouvetakis J., McElfresh M.W and Beach D.B. Chemical Vapor Deposition of Highly Conductive Boron-Doped Graphite from Triphenyl Boron // Carbon. 1994. V. 32. No 6. P. 1129-1132. 

Real-time solid-state neutron detectors were fabricated from semiconducting boron-carbon alloys deposited by plasma-enhanced chemical vapor deposition (Robertson et al. 2002). Single neutrons... 

Boron-carbon-nitride ceramic is deposited on iron-based sliding parts by chemical vapor deposition (CVD) it is used as rotary compressor shafts, in order to improve the wear resistance [1 to 5]. Such B-C-N coatings have also been applied to dynamic pressure air bearings [6]. In gas-cooled nuclear reactors, °B-enriched B-C-N can be deposited by CVD in the fluid channels of the fuel elements for permanent deactivation in case of an emergency [7]. Radiofrequency or microwave-enhanced CVD is employed in order to deposit a diamond carbon and (3-BN superlattice structure [8]. 

As opposed to oxides, carbides such as silicon carbide (SiC) and boron carbide (B4C) are compatible with carbon fibers, and satisfactory composites are produced with these matrices and PAN-based yarn by chemical vapor infiltration (CVI).l l A boron-carbon intermediate coating provides optimum strength and toughness as it prevents fiber degradation. 

Preparation. The simplest method of preparation is a combination of the elements at a suitable temperature, usually ia the range of 1100—2000°C. On a commercial scale, borides are prepared by the reduction of mixtures of metallic and boron oxides usiag aluminum, magnesium, carbon, boron, or boron carbide, followed by purification. Borides can also be synthesized by vapor-phase reaction or electrolysis. 

Of these three diatomic moiecuies, only N2 exists under normal conditions. Boron and carbon form soiid networks rather than isolated diatomic molecules. However, molecular orbital theory predicts that B2 and C2 are stable molecules under the right conditions, and in fact both molecules can be generated in the gas phase by vaporizing solid boron or soiid carbon in the form of graphite. 

In certain respects, the combustion of boron is different from that of carbon because, under normal temperature and pressure conditions, the product oxide, B203, is not a gas. Thus, a boron particle normally has an oxide coat that thickens as the particle is heated in an oxidizing atmosphere. This condition is characteristic of most metals, even those that will bum in the vapor phase. For the efficient combustion of the boron particle, the oxide coat must be removed. The practical means for removing the coat is to undertake the oxidation at temperatures greater than the saturation temperature of the boron oxide B203. This temperature is about 2300 K at 1 atm. 

Boron-doped chemical-vapor-deposited diamond is an exceptionally inert carbon electrode with a very wide potential window and very low voltammetric background current. [A. E. Fischer, Y. Show, and G. M. Swain, Electrochemical Performance of Diamond Thin-Film Electrodes from Different Commercial Sources, Anal. Chem. 2004, 76, 2553.]... 

Substances that are ordinarily deliquescent are sulfuric add (concentrated), glycerol, calcium chloride crystals, sodium hydroxide (solid), and 100% ethyl alcohol. In an enclosed space, these substances deplete the water vapor present to a definite degree. Other substances are used to accomplish this end by chemical reaction, e.g.. phosphorus pentoxide (forming phosphoric acid), and boron trioxide (forming boric acid). Water is absorbed from nonmiscible liquids by addition of such substances as anhydrous sodium sulfate, potassium carbonate, anhydrous calcium chloride. and solid sodium hydroxide. The converse phenomenon is known as efflorescence. 

Nonmetals. Boron reacts violently with concentrated HN03. Phosphorus vapor may ignite. Silicon, arsenic, and finely divided carbon react violently.40... 

Hach CT, Jones LE, Crossland C, Thrower PA. An investigation of vapor deposited boron rich carbon—a novel graphite-like material—part I The structure of BCj (C6B) thin films. Carbon 1999 37 221-230. 

Nishimura K, Kim YA, Matushita T, Hayashi T, Endo M, Dresselhaus MS. Structural characterization of boron-doped submicron vapor-grown carbon fibers and their anode performance. J Mater Res 2000 15 1303-1313. 

Boron-doped diamond electrodes — Electrode material made from synthetic diamond (- diamond electrode) for example via vapor deposition techniques. In an atmosphere of methane (as a carbon source) and hydrogen (as etchant) at ca. 600 °C diamond seeds tend to grow whereas graphitic carbon deposits are etched... 

---