Patent GB-1286952-A (GB)
Title: Method of preparing finely-divided solids
Inventor: EVEREST DAVID ANTHONY
IPC: C01B31/36
Filed: 1968-08-13
Abstract: 1286952 Oxides; finely-divided solids NATIONAL RESEARCH DEVELOPMENT CORP 7 Aug 1969 [13 Aug 1968] 38647/68 Headings C1A and C1N [Also in Division F4] A finely divided solid is made by heating, using a high-temperature and high-enthalpy gas stream, a melt containing a non-volatile inorganic oxide or a precursor thereof centrifugally distributed on the inner surface of a hollow rotating body, so as to produce a non- volatile inorganic oxide in the vapour phase and then condensing the oxide, or a species derived therefrom, by chemical and/or physical modification, in a finely divided form. A precursor is defined as a material from which the oxide is readily derived, e.g. an oxalate or nitrate. The hot gas may be a plasma jet or an electricallyaugmented chemical flame. The melt may contain an additive designed to aid volatilization, e.g. carbon or a free metal. The process may be conducted in a so-called centrifugal liquid-wall furnace. In one embodiment, a water-cooled steel tube 1 contains a rotatable core 2 of the material to be melted and vaporized. The core is heated by gas from plasma jet 3 provided with nozzles 4 for injection of further raw material if continuous operation is desired. Water-cooled quenching section 6 is provided with radially-directed tubes 8 for inlet of quenching gas. The outlet 9 of the quenching section feeds tangentially into electrostatic precipitator 10 comprising a tube 11 and electrostatically charged tungsten wave 12. The size of the particles, e.g. less than 2000 , is determined by the rate of gas flow and the positioning of the gas jets. The oxide may be a refractory such as alumina, zirconia, titania, chromium oxides, thoria, magnesia, silica, manganese oxide, zinc oxide or eerie oxide. Modification may be effected by introducing a reactive gas into the oxide vapour. For example, a carbon-containing gas, e.g. methane, may be fed into SiO or SiO 2  vapour to produce SiC, and NH 3  or N 2 /H 2  mixture may be fed in to form nitrides. A lower oxide may be converted to a higher oxide by reaction with Al 2  or O 2 . Further modification may be effected during quenching. By introducing H 2 O vapour (as such, or produced in situ by oxidation of H 2  derived from the plasma jet), a product with a hydroxylated surface may be obtained. Alternatively an organic vapour, e.g. methanol, may be used to impart hydrophobic properties. Hydroxylated SiO 2  may be further modified by reaction with methyl chloride or trimethyl silyl chloride. In examples: (1) fibres of 70% SiO, 30% SiO 2  are made from a furnace core of an equimolecular mixture of fused quartz and coke; (2) spherical alumina particles are made from a coke: alumina (1 : 2) core, the lower oxides evaporated being oxidized to Al 2 O 3  by a stream of air; (3) spherical TiO 2  particles (rutile) are made from a TiO 2  : coke core, the TiO vaporized being oxidized to TiO 2  by a stream of air; (4) cubic MgO particles are made from a core of mag nesia and coke; (5) surface-hydroxylated magnesia is made by quenching vaporized MgO in water vapour; (6) silicon carbide is made by evaporating SiO from a SiO 2  : coke core, and reacting in the vapour phase with methane.