GB824107A - Improvements relating to fire extinguishing powder compositions - Google Patents

Abstract

A fire-extinguishing powder comprises a mixture of finely-divided alkali metal bicarbonate, e.g. sodium or potassium bicarbonate, and a porous material having a porosity greater than 0.2 c.c./gm., an average pore diameter of not less than 5 Angstrom units, and a surface area of at least 100 sq. m/gm., coated with a cross-linked polysiloxane (see Group IV (a)). The coating is effected by mixing the finely-divided alkali metal bicarbonate and the porous material with a liquid or gaseous polymerizable polysiloxane-forming material, e.g. in a ball or ribbon mill, in the presence of water and allowing the material to polymerize either at room temperature or by heating, e.g. at 100 DEG C., the porous material acting as a catalyst. The porous material may be attapulgite, fuller's earth, heat-activated betonite, calcium or magnesium silicate, zeolite, or activated alumina, silica, silica-alumina, magnesia, silica magnesium, or carbon may be used in an amount of 0.5-50%, e.g. 5% and may have a particle size of 40-400 mesh. Various polymerizable silicon compounds are specified. The alkali metal bicarbonate to be coated preferably passes a 200-mesh sieve and has a moisture content of less than 1%. The alkali metal bicarbonate may constitute 76-99.5%, and the silicone 0.25-1.5%, of the total powder. The desired amount of water, e.g. 0.05-1.5%, may be ensured by adding water to one or more of the ingredients before mixing, or as a separate ingredient during mixing. Packing may be prevented by mixing in a micaceous material, e.g. muscovite mica, vermiculite, sericite or pyrophyllite having a particle size of 40-400 mesh, in an amount of 0.05-50%. e.g. up to 10% during or after the polymerization. Examples are given. Specification 675.940 is referred to.ALSO:Polysiloxane coatings on alkali metal bicarbonate, the polysiloxane preferably having the general formula (RxSiyOz)n, where R is a monlvalent hydrocarbon group or hydrogen and x, y, z and n are integers, x/z being between 2/3 and 2, are prepared by mixing the bicarbonate with a liquid or gaseous polysiloxane-forming material and polymerizing at room or elevated temperature in the presence of water and a porous material having a porosity greater than 0.2 cc/gm., an average pore diameter of not less than 5 Ängstroms, and a surface area of at least 100 sq. m/gm. Polysiloxane-forming materials specified are of the general formula (a) RSiX3, (b) mixtures of a RSiX3 + bR2SiX2, and (c) RxSiyOyX, where R is a monovalent hydrocarbon group or hydrogen, X is a reactive group, e.g. hydrogen, halogen, alkoxy or hydroxyl, and a, b, x and y are whole numbers. Examples of group (a) are methyltrichloro amyltrichloro-, octadecyltrichloro -, cyclohexyltrichloro -, allyltrichloro -, vinyltrichloro -, phenyltrichloro-, methyltriethoxy -, and vinyltriethoxysilane. Examples of group (b) are mixtures of any of the above examples of group (a) with any of dimethyldiethoxydimethyldichloro - and diphenyldihydroxysilane. The materials of group (c) are obtained by partial hydrolysis of di- or tri-functional silicones, e.g. any of the above examples of groups (a) or (b). The siloxane-forming material may be applied as an emulsion. Polymerization may be effected by heating at 100 DEG C. for 24 hours. The porous material may be attapulgite, fuller's earth, heat-activated bentonite, porous calcium and magnesium silicate, zeolite, or activated alumina, silica, silica-alumina, magnesia, silica-magnesia, or carbon, may have a particle size of 40-400 mesh, and may be used in an amount of 0.5-50% of the total composition. Examples are given. Specification 675,940, [Group III], is referred to.