GB986289A - A material produced by devitrification of a glass made from a metallurgical slag - Google Patents

Abstract

A material is produced by devitrification of a glass made from a metallurgical slag, the glass and material consisting essentially of: SiO2, 45-65%; CaO, 15-45%; Al2O3, 5-30%; MgO, up to 10%; and a nucleating agent. The nucleating agent may be an oxide of a transision element, e.g. V, Mn, Cr, Ti, Fe; a fluoride, e.g. of Ca or Na; a phosphate, e.g. apatite; or mixtures or compounds thereof, e.g. cryolite, ilmenite, chromite; open hearth, V, or Mn slags, bone ash or fuel ash. The proportion of nucleating agent may be less than 5% by weight. Other substances which may be present in the material in small quantities include oxides of Na, K, Mn, Fe, Ti. The material may be coloured by additions to the melt, e.g. of cobalt oxide. The initial slag composition may require modification, e.g. by adding e.g. sand, clay, gangue or slag. The principal glass component, e.g. blast furnace slag, may be admitted to the glass-making furnace as a liquid. Two or more glass-making furnaces may be employed. Suitable types of furnace include an open-hearth furnace, or a cyclone, rotary, top-blown or bottom-blown furnace in combination with a conventional glass tank. A part or all of the charge may be fed through the flame. If a fuel is used for firing, the ash therefrom may provide nucleating agents. O2 with or without air may be used for combustion and this or other gases may be injected into the melt. Added solids may be injected into a flame directed on to or into the bath; they may be preheated, e.g. in a fluidized bed; waste heat from the melting furnace may be used. The bath may be stirred, e.g. mechanically or by bubbling or by submerged combustion. Iron shot contained in blast furnace slag will accumulate at the bottom of the glass-melting furnace and may be tapped periodically or continuously. The melt is devitrified by (i) cooling below annealing point, i.e. to 630 DEG -750 DEG C., thereafter optionally cooling to room temperature, and then (ii) reheating to above softening point, i.e. to 800 DEG -950 DEG C., after which the temperature may be maintained or increased until the desired degree of crystallization is attained. The heat treatment is performed by conventional means, e.g. in a tunnel kiln or lehr, or heat for stage (ii) may be obtained from a coolant material employed in stage (i). Waste gases from melting furnaces may provide heat, or dielectric or microwave heating may be used. During heat-treatment, the vessel may be of e.g. plumbago or sillimanite. The glass may be shaped before, during or after devitrification by conventional glass-forming techniques, or by foundry casting or by other metal-shaping methods, e.g. spinning, pressing, rolling, tube-making by welding skelp longitudinally or spirally, or piercing billets. During shaping, further particles, e.g. of fully crystallized material, may be added. Alternatively, the material may be granulated, and then sintered and shaped before, during or after devitrification, or bubbles may be introduced into the viscous melt, e.g. by injection of air, by chemical action, e.g. oxidation of sulphur in the melt, or by reduction of the external pressure. The product may be reinforced with metal mesh or nylon, or with fibres of metal. The product may be laminated with metals, and may be used to cover rubber. It may be impregnated with e.g. metal, or chips of the product may be pressed into a hot steel surface. The non-crystalline glass component of the product may be preferentially dissolved or grit-blasted. For constructional purposes the product may be cast with channels therein. Metal piping or bolts may be cast into the product. Fibres of the product may be incorporated into other materials. Articles of the material may be welded together, or particles of the product may be used to coat the uncrystallized glass, followed by heat treatment to produce crystallization. A long list of applications is given, including pipes, tiles, paving, railway sleepers, chemical stoneware, sanitary ware, tanks, bottles, abrasive grit, breakwaters, electrical insulators, cylinder blocks, firebars, cyclone fan blades, fluidized bed components, ingot moulds.ALSO:A composition may comprise fibres of a material, referred to as "slagceram," produced by devitrification of a glass made from a metallurgical slag.