Heat boron compounds

Heating triacetylboron at temperatures above its melting poiat, 123°C, causes a rearrangement to B20(0CCH2)4 (15). An explosive hazard is also generated by dissolving BF ia anhydride (see Boron compounds). 

Boron trifluoride [7637-07-2] (trifluoroborane), BF, was first reported in 1809 by Gay-Lussac and Thenard (1) who prepared it by the reaction of boric acid and fluorspar at duU red heat. It is a colorless gas when dry, but fumes in the presence of moisture yielding a dense white smoke of irritating, pungent odor. It is widely used as an acid catalyst (2) for many types of organic reactions, especially for the production of polymer and petroleum (qv) products. The gas was first produced commercially in 1936 by the Harshaw Chemical Co. (see also Boron COMPOUNDS). 

Next to Cr C2, TiC is the principal component for heat and oxidation-resistant cemented carbides. TiC-based boats, containing aluminum nitride, AIN, boron nitride, BN, and titanium boride, TiB2, have been found satisfactory for the evaporation of metals (see Boron compounds, refractory boron compounds Nitrides). 

For a large number of applications involving ceramic materials, electrical conduction behavior is dorninant. In certain oxides, borides (see Boron compounds), nitrides (qv), and carbides (qv), metallic or fast ionic conduction may occur, making these materials useful in thick-film pastes, in fuel cell apphcations (see Fuel cells), or as electrodes for use over a wide temperature range. Superconductivity is also found in special ceramic oxides, and these materials are undergoing intensive research. Other classes of ceramic materials may behave as semiconductors (qv). These materials are used in many specialized apphcations including resistance heating elements and in devices such as rectifiers, photocells, varistors, and thermistors. 

A product of higher purity is obtained by reducing a volatile boron compound, such as BCli or BBr3, with hydrogen on a heated filament (tantalum is used for the filament because it has a very high melting point) ... 

Fuel, oxygen, and high temperature are essential for the combustion process. Thus, polyfluorocarbons, phosphazenes, and some composites are flame-resistant because they are not good fuels. Fillers such as alumina trihydrate (ATH) release water when heated and hence reduce the temperature of the combustion process. Compounds such as sodium carbonate, which releases carbon dioxide when heated, shield the reactants from oxygen. Char, formed in some combustion processes, also shields the reactants from a ready source of oxygen and retards the outward diffusion of volatile combustible products. Aromatic polymers, such as PS, tend to char and some phosphorus and boron compounds catalyze char formation aiding in controlling the combustion process. 

Figure IV. A. 3. is a heat of combustion plot of the elements with fluorine as the oxidizer. One can carry through the same arguments as those made for the oxygen plot except it is well to remember that many of the metal fluorides are gaseous under the combustion chamber conditions that prevail. Since BF is a gas, the significance of boron compounds as fuels with fluorine oxidizers particularly changes for the better. Comparison of figures IV. A. 1. and IV. A. 3. will show that H2 -02 and H2 - F2 have the same standard state heat release. Yet above it was stated that the specific impulse with hydrogen-fluorine was the greater. This comparison again points out the limitations of the plots, which do not take into account the diss-...

Boron Carbide. Boron carbide [12069-32-87, B4C, is produced by the reaction of boron oxide and coke in an electric arc furnace (70% B4C) or by that of carbon and boric anhydride in a carbon resistance furnace (80% B4C) (see Boron compounds, refractory BORON compounds). It is primarily used as a loose abrasive for grinding and lapping hard metals, gems, and optics (18).. Although B4C is oxidation-prone, the slow speed of lapping does not generate enough heat to oxidize the abrasive. 

SAFETY PROFILE A poison and strong irritant. See also FLUORIDES and BORON COMPOUNDS. When heated to decomposition it emits very toxic fumes of F", NOx, and NH3. 

SAFETY PROFILE Confirmed carcinogen. It will ignite in contact with ait or water. When heated to decomposition it emits toxic fumes of BeO, BOx, and NOx. See also BERYLLIUM COMPOUNDS and BORON COMPOUNDS. 

SAFETY PROFILE A severe eye irritant. See also BORON COMPOUNDS and ESTERS. Dangerous fire ha2ard when exposed to heat or flame will react with water or steam to produce flammable vapors. Incompatible with oxidi2ers, heat, and open flame. To fight fire, use CO2, dry chemical. 

SAFETY PROFILE A poison. Corrosive. A skin, eye, and mucous membrane irritant. Dangerous may explode when heated. This and other boron halides react with water or steam to produce toxic and corrosive fumes and may explode. Incompatible with K Na. When heated to decomposition it emits toxic fumes of Br . See also BORON COMPOUNDS and HYDROBROMIC ACID. 

SAFETY PROFILE A poison by inhalation. A strong irritant. See also BORON COMPOUNDS and FLUORIDES. A nonflammable gas. Dangerous when heated to decomposition or upon contact with water or steam, will produce toxic and corrosive fumes of F". Incompatible with... 

DOT CLASSIFICATION 4.1 Label Flammable Solid, Poison SAFETY PROFILE Poison by inhalation, ingestion, skin contact, and intraperitoneal routes. Ignites in O2 at 100°C. Forms impact-sensitive explosive mixtures with ethers (e.g., dioxane) and halocarbons (e.g., carbon tetrachloride). Incompatible with dimethyl sulfoxide. When heated to decomposition it emits toxic fumes of boron oxides. See also BORON COMPOUNDS and BORANES. 

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