Applications boron carbide

The doping of semiconductors is important for tailoring their electronic properties in applications. Boron carbide is p-type because of its high concentration of largely... 

Carbide-based cermets have particles of carbides of tungsten, chromium, and titanium. Tungsten carbide in a cobalt matrix is used in machine parts requiring very high hardness such as wire-drawing dies, valves, etc. Chromium carbide in a cobalt matrix has high corrosion and abrasion resistance it also has a coefficient of thermal expansion close to that of steel, so is well-suited for use in valves. Titanium carbide in either a nickel or a cobalt matrix is often used in high-temperature applications such as turbine parts. Cermets are also used as nuclear reactor fuel elements and control rods. Fuel elements can be uranium oxide particles in stainless steel ceramic, whereas boron carbide in stainless steel is used for control rods. 

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. 

Small single crystals, such as those of potassium titanatc, are being used at an annual rate of over 10,000 tons for the reinforcement of nylon and other thermoplastics. These composites are replacing die-cast metals in many applications. Another microfiber, sodium hydroxycarbonate (Dawsonite), also improves the physical properties and flame resistance of many polymers. Many other single crystals, called whiskers, such as alumina, chromia, and boron carbide, have been used for making high-performance composites. 

Uses. Applications for boron carbide relate either to its hardness or its high neutron absorptivity (10B isotope). Hot-pressed boron carbide finds use as wear parts, sandblast nozzles, seals, and ceramic armor plates but in spite of its hardness, it finds litde use as an abrasive. However, this property makes it particulady useful for dressing grinding wheels. 

Boron carbide is used in the shielding and control of nuclear reactors (qv) because of its neutron absorptivity, chemical inertness, and radiation stability. For this application it may be molded, bonded, or the granular material may be packed by vibration. 

B4C boron carbide has a melting point of 2450 °C and a hardness somewhere between those of SiC and diamond. This makes the material a suitable abrasive. It is used in heads of sand blasting equipment, in mortars and in armour plating. For the latter application a B4C plate is provided on both sides with a plastic which has been reinforced with glass fibre. This is done to reduce the risk of splintering. Boron carbide is also used as the raw material for many other boron compounds ... 

Although few applications have so far been found for ceramic matrix composites, they have shown considerable promise for certain military applications, especially in the manufacture of armor for personnel protection and military vehicles. Historically, monolithic ("pure") ceramics such as aluminum oxide (Al203), boron carbide (B4C), silicon carbide (SiC), tungsten carbide (WC), and titanium diboride (TiB2) have been used as basic components of armor systems. Research has now shown that embedding some type of reinforcement, such as silicon boride (SiBg) or silicon carbide (SiC), can improve the mechanical properties of any of these ceramics. 

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. 

Analytical Applications of Boron Carbide Electrodes. Anal. Chim. Acta 23,467 (1960). 

Most borides are chemically inert in bulk form, which has led to industrial applications as engineering materials, principally at high temperature. The transition metal borides display a considerable resistance to oxidation in air. A few examples of applications are given here. Titanium and zirconium diborides, alone or in admixture with chromium diboride, can endure temperatures of 1500 to 1700 K without extensive attack. In this case, a surface layer of the parent oxides is formed at a relatively low temperature, which prevents further oxidation up to temperatures where the volatility of boron oxide becomes appreciable. In other cases the oxidation is retarded by the formation of some other type of protective layer, for instance, a chromium borate. This behavior is favorable and in contrast to that of the refractory carbides and nitrides, which form gaseous products (carbon oxides and nitrogen) in air at high temperatures. Boron carbide is less resistant to oxidation than the metallic borides. 

The determination of quartz dust in the air samples in industrial workplace is an established procedure. Although capable of collecting the particulates, organic polymer membranes can not be employed as an XRD substrate since the diffuse diffraction lines at or near the 10 angle of quaru makes polymeric membtanes not suitable for this application [Minneci and Paulson, 1988]. It is possible to quantify as low as 0.005 mg quartz under well controlled conditions (Bumsted, 1973]. Similarly, silver membranes can also be used as a collecting medium and XRD substrate for measuring crystalline and amorphous silica, lead sulfide, boron carbide and chrysotile asbestos [Leroux and Powers. 1970]. 

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

A. Lipp, Boron Carbide Production, Properties, Application, Technische Rundschau Nos. 14, 28, and 33 (1965) and 7 (1966), Elektroschmelzwerk Kempten GmbH, Munich, 1966. 

Reviews are concerned with structures, properties, preparations ° and applications.The boron carbide phase is a complex solid solution." ... 

Starting from fine boron and carbon powders, the direct synthesis of stoichiometric boron carbide is possible -, either under vacuum at 2073K in an electric furnace, or at 2273 K by hot pressing under Ar. This method is inefficient economically and finds no practical application. The compositions in the phase homogeneity range B10.4C-B4C can be obtained by hot pressing mixtures of B C with boron . The diffusion diagram between B and C is established. ... 

Sodium borohydride is marketed in powdered or pellet form, and in solution, for use in fuel cells. Boron nitride can withstand temperatures of up to 650°C (1,202°E) when subjected to high pressures and temperatures, it forms cubic crystals whose hardness rivals that of diamond. Boron carbide, produced by reacting coke and boric acid at 2,600°C (4,712°E), is a highly refractory material and one of the hardest substances known. It has both abrasive and abrasion-resistant applications, and is used in nuclear shielding, see ALSO Davy, Humphry Gay-Lussac, Joseph-Louis Nuclear Chemistry. 

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