Boron carbide process

The boron carbide process can also start from blends of metal carbides, metal hydrides, boron oxide, boron carbide and carbon black ... 

Reactions of boron ttihalides that are of commercial importance are those of BCl, and to a lesser extent BBr, with gases in chemical vapor deposition (CVD). CVD of boron by reduction, of boron nitride using NH, and of boron carbide using CH on transition metals and alloys are all technically important processes (34—38). The CVD process is normally supported by heating or by plasma formed by an arc or discharge (39,40). 

Janson, U., Chemical Vapor Deposition of Boron Carbides, Materials and Manufacturing Processes, 6(3) 481-500 (1991)... 

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. 

Growth of anisofiopic silicon and boron carbide nanoparticles from powdered reagents was performed using a process of exothermic nanosynthesis [6,7] (Fig. 3.8). 

A preceramic, carrier polymer route to boron carbide has been reported via the pyrolysis of a polynorbomene that bears decaborane side groups.69 An important feature of this development is the ability to produce nanofibers of boron carbide in the following way. A solution of the poly(norbomenyldecaborane) in THF is subjected to the process of... 

Naturally occurring boron consists of two isotopes 10B, which comprises about 20%, and nB, which makes up the remaining 80%. This results in the average atomic mass being 10.8 amu. 10B has the ability to absorb slow neutrons to a great extent. Therefore, it finds application in reactors as control rods and protective shields. However, because boron itself is very brittle (and, therefore, nonmalleable), it must be combined or alloyed with a more workable material. Boron carbide is often mixed with aluminum and then processed into the desired shape. 

The influence of the laser and plasma parameters (such as wavelength, laser power density, pulse length, plasma temperature, electron and ion density and others) on the physical and chemical processes in a laser induced plasma with respect to the formation of polyatomic and cluster ions has been investigated for different materials (e.g. graphite, boron nitride, boron nitride/graphite mixture, boron carbide, tungsten oxide/graphite mixture and superconductors ). 

Boron carbide is also a very light and strong material. It can be prepared by reacting carbon yam with BClj and H2 at high temperatures, i.e. a CVD process (Economy and Lin, 1977). The chemical reaction involved is... 

The utilization of the outstanding mechanical and wear properties of cubic BN and related superhard materials has been demonstrated, although further process improvements are necessary before a more general use can be expected. Superhard cubic BN exhibits superb inertness to hot steel surfaces under conditions in which diamond would be severely attacked. Other tetrahedral structures, for instance, BCN and B2O, are anticipated to display similar attractive properties. The high-pressure phase B2O is a semiconductor with a band gap of 0.25 eV and a hardness between that of boron carbide and diamond. 

It is technically easier to manufacture a molded component from SiC-powder by slip casting or dry pressing, working it mechanically and then sintering pressureless at 1950 to 2000°C. Due to the low sintering activity of silicon carbides, such processes have only been recently successfully carried out with the advent of fine particulate SiC-powders (specific surface area > 5 m /g) with low oxygen-contents (< 0.2%). Boron or aluminum and free carbon or boron carbide are added as sintering aids. 

Finely divided boron carbide can be processed to ceramics. Applications ... 

W. B. Johnson, T. D. Claar, and G. H. Schiroky, Preparation and processing of platelet reinforced ceramics by the directed reaction by zirconium with boron carbide. Ceram. Eng. Sci. Proc. KK7-8), 588-598 (1989). 

The vaporization-cold-substrate condensation process of boron carbide melted by electron-gun heating and plasma torch deposition does not give a well-organized and crystalline B4C-type structure. In CH4 [1.33.10 Pa 1 torr)] an electron-gun evaporation of boron carbide contained in a graphite crucible, followed by a condensation on a water-cooled jacket, gives crystals. Sputtering by H is possible . 

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