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A mold for metal casting contains a bonded refractory composition comprising hollow alumina-containing microspheres in which the alumina content is at least 40% by weight. The mold may be an ingot mold and the bonded refractory composition may be in the form of a sleeve or boards located in the top

A mold for metal casting contains a bonded refractory composition comprising hollow alumina-containing microspheres in which the alumina content is at least 40% by weight. The mold may be an ingot mold and the bonded refractory composition may be in the form of a sleeve or boards located in the top of the mold or in the head box thereto. The mold may be a sand mold and the bonded refractory composition may be in the form of a sleeve or boards located in a feeder cavity or in the form of a board or pad located so as to constitute a metal casting surface where it is desired to promote directional solidification in cast metal. The bonded refractory composition may also be in the form of a breaker core. In a preferred composition the microspheres contain alumina and silica and the composition may also contain one or more other particulate refractory materials, a readily oxidizable metal, an oxidizing metal, an oxidizing agent for the metal and a fluoride salt.

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A bonded refractory composition comprising hollow alumina- and silica-containing microspheres, and a binder, and wherein the microspheres have an alumina content of at least 40% by weight, and the quantity of alumina present in the composition expressed as a percentage of the total alumina plus sili

A bonded refractory composition comprising hollow alumina- and silica-containing microspheres, and a binder, and wherein the microspheres have an alumina content of at least 40% by weight, and the quantity of alumina present in the composition expressed as a percentage of the total alumina plus silica is less than about 55% by weight. A mold for metal casting having therein a bonded refractory composition comprising hollow alumina- and silica-containing microspheres and a binder, and wherein the microspheres have an alumina content of at least 40% by weight and the quantity of alumina present in the composition expressed as a percentage of the total alumina plus silica is less than about 55% by weight. A method of producing a casting in a mold having a mold cavity, comprising the steps of: (a) locating in operative association with the mold cavity a bonded refractory composition comprising hollow alumina- and silica-containing microspheres, and a binder, wherein the microspheres have an alumina content of at least 40% by weight, and the quantity of alumina present in the composition expressed as a percentage of the total alumina plus silica is less than about 55% by weight; (b) pouring molten metal into the mold so as to fill the mold cavity; and (c) allowing the molten metal to solidify.