Patent GB-989005-A (GB)
Title: Refractory product and process for its manufacture
IPC: C22C32/00
Filed: 1962-01-11
Abstract: A crystalline refractory, having a porosity of from 20-90% is made up of either 4.6 to 99.95% of an oxide of a metal (A) formed by in situ oxidation or a composite of 4.6-99.95% of the air oxide of a metal (A), together with 0.02-20% of a fluxing agent (B) and contains no more than 85% of the residual metal (A) and when present no more than 95% of a filler refractory (C).  The product which comprises a rigid aggregate of metal oxide shapes having at least one dimension of from 0.5 to 125 units is formed by intimately contacting the surfaces of from 4-99.98% of particles of the metal (A) with 0.02-20% of the fluxing agent (B) and from 0-95% of a particulate, crystalline filler refractory (C), the contacted mass of (A), (B) and (C) having a porosity, after removal of volatile materials, of at least 20% and thereafter oxidizing the metal (A) in the contacted mass with gaseous oxygen at a temperature of at least 400 DEG  C. and if the filler refractory (C) is present, below that at which the filler refractory fuses for a period of time sufficient to give rise to a weight gain of at least 10% based on the weight of the metal (A) employed. Metals (A) are any yielding oxides that are refractory, i.e. having melting points above 1000 DEG  C. and possessing structural rigidity, e.g. aluminium, beryllium, calcium, chromium, niobium, copper, hafnium, iron, magnesium, nickel, silicon, tantalum, thorium, titanium and zirconium.  Suitable fluxing agents are an oxide or a salt which gives the oxide on heating, of a metal different from those quoted under (A) above from the class consisting of the alkali metals, the alkaline earth metals, vanadium, chromium, molybdenum, tungsten, copper, silver, zinc, antimony and bismuth. The oxides and hydroxides of the metals magnesium, strontium and barium are preferred. In addition trialkyl tin oxide and sodium and lead silicate are also useful as fluxing agents.  The filler retractories (C) may be any of the carbides of aluminium, boron, hafnium, niobium, silicon tantalum, thorium, titanium, tungsten, vanadium and zirconium, the nitrides of aluminium, boron, hafnium, niobium, tantalum, thorium, titanium, uranium, vanadium and zirconium; the borides of chromium, hafnium, molybdenum, niobium, tantalum, titanium, tungsten, vanadium and zirconium; or the oxides of aluminium, beryllium, corium, hafnium, lanthanum, magnesium, uranium, yttrium and the stabilized oxide of zirconium.  When in sufficient concentration and adequate size, many of the oxides used as fluxing agents can also serve as filler refractories. The fluxing agent is conveniently contacted with the metal particles using a concentrated aqueous solution or slurry. After the application of the fluxing agent the aggregate is compression moulded and dried until it has a porosity of between 20 and 70%.  The dried "green" moulded object is then heated in an oxidizing atmosphere at a temperature greater than 400 DEG  C.ALSO:A crystalline refractory having a porosity of from 20-90% is made up of either 4.6-99.95% of oxide of a metal (A) formed by in situ oxidation or a composite of 4.6-99.95% of an oxide of a metal (A) together with 0.02-20% of a fluxing agent (B), and contains no more than 85% of the residual metal (A) and when present no more than 95% of a filler refractory (C).  The product which comprises a rigid aggregate of metal oxide shapes having at least one dimension of from 0.5-125 mils is formed by intimately contacting the surfaces of from 4-99.98% of particles of the metal (A) with 0.02-20% of the fluxing agent (B) and from 0-95% of a particulate, crystalline filler refractory (C), the contacted mass of (A), (B) and (C) having a porosity, after removal of volatile materials, of at least 20%, and thereafter oxidizing the metal (A) in the contacted mass with gaseous oxygen at a temperature of at least 400 DEG C. and of the filler refractory (C) is present, below that at which the filler refractory fuses for a period of time sufficient to give rise to a weight gain of at least 10% based on the weight of the metal (A) employed.  Metals (A) are any yielding oxides that are refractory, i.e. having melting points above 1000  DEG C. and possessing structural regularity, e.g. aluminium, beryllium, calcium, chromium, niobium, copper, hafnium, iron, magnesium, nickel, silicon, tantalum, thorium, titanium and zirconium.  Suitable fluxing agents are an oxide or a salt which gives the oxide on heating of a metal different from those quoted under (A) above from the class consisting of the alkali metals, the alkaline earth metals, vanadium, chromium, molybdenum, tungsten, coper, silver, zinc, antimony and bismuth.  The oxides and hydroxides of the metals magnesium, strontium and barium are preferred.  In addition, trialkyl tin oxide and lead silicate (PbSiO3) are also useful as fluxing agents.  The filler refractories (C) may be any of the carbides of aluminium, boron, hafnium, nibium, silicon, tantalum, thorium, titanium, tungsten, vanadium and zirconium; the nitrides of aluminium, boron, hafnium, niobium, tantalum, thorium, titanium, uranium, vanadium and zirconium; the bonder of chromium, hafnium, molybdenum, niobium, tantalum, titanium, tungsten, vanadium and zirconium; or the oxides of aluminium, beryllium, cerium, hafnium, lanthanium, magnesium, uranium, yttrium and the stabilized oxide of zirconium. When in sufficient concentration and of adequate size, many of the oxides used as fluxing agents can also serve as filler refractories.  The fluxing agent is conveniently contacted with the metal particles using a concentrated aqueous solution or slurry.  After the application of the fluxing agent the aggregate is compression moulded and dried until it has a porosity of between 20% and 70%.  The dried "green" moulded object is then heated in an oxidizing atmosphere such as air, oxygen or mixtures of oxygen and inert gases at a temperature of at least 400  DEG C.