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in metallurgy, a material introduced into a liquid metal to change the composition and properties of the metal or slag. A distinction is made among slag-forming additives (lime, fluorspar, and bauxite and their combinations or substituents), carbonizing additives (ground coke, cast iron, and metal carbides), oxidizing additives (ores, clinker, and metal oxides), and alloying additives (ferroalloys, hardeners, and industrial-grade chemical elements). Additives are introduced into the melting unit, ladle, or casting mold.
in petrochemistry, a substance that is added in small amounts to fuels and industrial oils to improve their working properties. Liquid fuels and oils usually do not contain more than a few hundredths or tenths of a percent additives by weight, and only certain additives are used in concentrations of about 1-2 percent or greater.
Additives in fuels improve the efficiency of combustion processes, storage life, and the ability of a fuel to maintain its original properties during shipment and use. They also reduce the harmful effects of fuels on machinery and improve performance at low temperatures. The most common additives are antiknocks, for example, tetraethyllead, which reduce detonation of engine fuels. Other widely used additives act as antioxidants (para-oxydiphenylamine and naphthol), chemical inhibitors, modifiers, metal deactivators, stabilizers, and antifouling agents.
Additives for petroleum oils and synthetic oils are classified on the basis of their use. High-viscosity additives increase the viscosity and improve the viscothermal properties of oils, while pour-point depressants lower the pour point of oils. Antioxidants protect an oil from oxidation by atmospheric oxygen; anticorrosives reduce the decay of a metal in aggressive mediums; and antiwear and antiscuff agents improve the lubricating properties of oils. Antifoaming agents reduce foam, detergents prevent deposition of solids on mechanical parts, and multipurpose additives simultaneously improve several working properties of oils. Also used as additives for oils are various hydrocarbons and compounds that consist of organic molecules and certain elements, including low-molecular surfactants and polymers.
REFERENCESNefteprodukty: Svoistva, kachestvo, primenenie. Spravochnik Edited by B. V. Losikov. Moscow, 1966.
Kuliev, A. M. Khimiia i tekhnologiia prisadok k maslam i toplivam. Moscow, 1972.
L. A. SHITS