Cladding of metals

Claim 2

An article according to claim 1 wherein the barrier layer comprises magnesia.

Claim 3

An article intended to be used at high operating temperatures above 1,000* C. comprising a core of a metal selected from the group consisting of niobium, tantalum, niobium-tantalum alloy, niobium-chromium alloy, tantalum-chromium alloy and niobium-tantalum-chromium alloy, a getter for oxygen on the core consisting essentially of a refractory coating, a sheath of a material selected from the groUp consisting of a platinum group metal and an alloy having at least one platinum group metal, and a barrier layer interposed between said core and said sheath comprising a refractory compound compatible with said core and said sheath at the operating temperature, whereby volatilization of oxides of said core material is reduced and said core material is prevented from forming with said sheath an alloy having a melting point below said operating temperature.

Claim 4

An article according to claim 4 further having an interfacial space between the core and the sheath wherein the said space has a partial pressure of not more than 2 mm. of mercury.

Claim 5

An article intended to be used at high operating temperatures above 1,000* C. comprising: (a) a core consisting essentially of a refractory metal selected from the group consisting of molybdenum, tungsten and a refractory alloy based on at least one of said metals; (b) a getter for oxygen on the core consisting essentially of a refractory coating; (c) a barrier layer on the getter consisting essentially of a refractory compound selected from the group consisting of refractory carbides, silicides, borides, sulphides, nitrides and oxides, and (d) an outer sheath enclosing the core, getter and barrier layers and consisting essentially of a material selected from the group consisting of the platinum group metals and a platinum group metal alloy, volatilization of the oxides of said core material thereby being prevented from forming with said outer sheath an alloy of lower melting point than that of the sheath.

Claim 6

An article according to claim 6 having an interfacial space between the core and the sheath wherein the said space has a partial pressure of not more than 2 mm. of mercury.

Claim 7

An article according to claim 7 wherein the getter is a material selected from the group consisting of zirconium, tantalum, niobium, titanium, vanadium and hafnium.

Claim 8

An article according to claim 8 wherein the getter material is present in relatively small quantities as dilute alloys of molybdenum or platinum.

Claim 9

An article according to claim 6 wherein the getter is in the form of a plasma or flame sprayed coating.

Claim 10

An article according to claim 6 wherein the getter is concentrated in an area which, in use, is not subject to temperatures greater than 1,200* C. so that the getter absorbs oxygen without contact with the barrier layer, thereby avoiding decomposition of the sheath material.

Claim 11

An article according to claim 6 wherein the core material is molybdenum alloyed with minor quantities of at least one of the materials of the group consisting of titanium and zirconium.

Claim 12

An article according to claim 6 wherein the core material is alloyed with at least one of the metals selected from the group consisting of titanium, zirconium, niobium, tantalum and hafnium.

Claim 13

An article according to claim 6 wherein the getter material comprises zirconium metal and the barrier layer is zirconia.

Claim 14

An article according to claim 6 wherein the getter material is zirconium and the barrier layer is magnesia.

Claim 15

An article according to claim 15 wherein the barrier layer of magnesia includes a minor amount of silica.

Claim 16

An article intended to be used at high operating temperatures above 1,000* C. having a core of the class consisting of molybdenum, tungsten, an alloy of molybdenum, and an alloy of tungsten, and a flame-sprayed coating on said core of zirconium, a further flame-sprayed coating thereon selected from the group consisting of zirconia and magnesia, and a sheath enclosing said coated core and comprising a material selected from the group consisting of a platinum group metal and an alloy of at least one platinum group metal.