GB833107A - Zirconia rods for coating articles by flame spraying - Google Patents

Abstract

Porous sintered zirconia rods consisting to a major extent of cubic and tetragonal crystals, having 8-40% by volume of voids constituted by open and interconnected pores, a breaking stress of more than 2000 lbs./sq. in. and comprising, apart from hafnia and lime, magnesia, ceria or titanium monoxide present as stabilizer, at least 96% ZrO2, are suitable for flame spraying to coat articles, e.g. as described in Specification 745,257. Preferably more than 50 volume % of the pores are more than 20 microns in diameter. The rods are preferably produced from zirconia particles, 30% by weight of which are coarser than 100 microns and substantially all of which are finer than 500 microns by mixing said zirconia particles with water together with dextrine and corn starch, extruding the mixture to form rods, drying and firing at Orton cone 20-42 to effect sintering. If desired, other substances which burn out on firing (such as sawdust, walnut shells, coffee or organic resins) or sublime (e.g. p-dichlorobenzene) may be added to produce pores in the product; when such substances are used, the size of the zirconia particles may be reduced, e.g. to 25 microns or less, and the firing may be less intense, e.g. to Orton cone 14. The zirconia particles used for the production of the rod may consist of zirconia consisting wholly of or comprising a major proportion of cubic or tetragonal crystals; lime, magnesia, ceria or titanium monoxide, by fusion with the zirconia, produce the required crystal form. Hafnia may also be present but does not affect the nature of the product. Impurities such as iron oxide, silica and titania may be present in amounts up to 4% of the zirconia. U.S.A. Specification 2,535,526 is referred to.ALSO:Porous sintered zirconia rods consisting to a major extent of cubic and hexagonal crystals, having 8 to 40% by volume of voids constituted by open and interconnected pores, a breaking stress of more than 2,000 lbs. per square inch and comprising, apart from hafnia and lime, magnesia, ceria or titanium monoxide present as stabilizer, at least 96% ZrO2, are suitable for flame spraying to coat articles, e.g. as described in Specification 745,257. Preferably more than 50 volume per cent of the pores are more than 20 microns in diameter. The rods are preferably produced from zirconia particles, 30% by weight of which are coarser than 100 microns substantially all of which are finer than 500 microns by mixing said zirconia particles with water together with dextrine and corn starch, extruding the mixture to form rods, drying and firing an Orton cone 20 to 42 to effect sintering. If desired other substances which burn out on firing (such as sawdust, walnut shells, coffee or organic resins) or sublime (e.g. 1-p-dichlorobenzene) may be added to produce pores in the product; when such substances are used, the size of the zirconia particles may be reduced e.g. into 25 microns or less, and firing may be less intense, e.g. to Orton cone 14. The zirconia particles used for the production of the rod may consist of zirconia consisting wholly of or comprising a major proportion of cubic or tetragonal crystals; lime, magnesia, ceria or titanium monoxide by fusion with zirconia, produce the required crystal forms. Hafnia may also be present but does not affect the nature of the product. Impurities such as iron oxide, silica and titania may be present in amounts up to 4% of the zirconia. U.S.A. Specification 2,535,526 is referred to.