Oxygen-resistant electroconductive carbon bodies

Claim 2

An electroconductive body for use in the electrolysis of fused metal salts characterized by improved resistance to oxidation agents at elevated temperatures comprising in combination: (a) a carbon body; (b) a first protective oxide coating disposed on said carbon body, said first protective oxide coating being characterized by minute pores and discontinuities; and (c) a second electrodeposited protective oxide coating disposed within said pores and discontinuities, said second protective oxide coating comprising an oxidation agent impermeable metal salt having a boiling point in excess of 400° C.

Claim 3

An electroconductive body according to claim 1, wherein the carbon body is graphite.

Claim 4

An electroconductive body according to claim 1, wherein said oxidation agent-impermeable coating covers substantially all of the surface thereof.

Claim 5

An electroconductive body according to claim 1, wherein said oxide is alumina.

Claim 6

An electroconductive body according to claim 1, wherein said oxide is chromic oxide.

Claim 7

An electroconductive body according to claim 1, wherein said oxide is silica.

Claim 8

An electroconductive body according to claim 1, wherein the refractory metal salt in said protective coating is cryolite.

Claim 9

An electroconductive body according to claim 7, wherein said cryolite contains alumina in about 85-95:15-5 weight ratio.

Claim 10

An electroconductive body according to claim 1, wherein the refractory metal salt in said coating is an alkaline metal chloride.

Claim 11

An electroconductive body according to claim 1, wherein the refractory metal salt in said coating is a mixture of an alkaline metal chloride and aluminum chloride in 55-95:45-5 weight ratio.

Claim 12

An electroconductive body possessing improved resistance to oxidation agents at 400° C. comprising in combination: (a) a carbon body having a first porous oxide coating; and (b) a protective refractory, oxidation agent impermeable electrodeposited second coating disposed in said pores of said first coating and composed essentially of (1) a metal oxide and (2) a refractory metal salt which in the molten state is a solvent for at least a part of said second coating.

Claim 13

An electroconductive body possessing improved resistance to oxidation agents at 400° C. comprising in combination: (a) a carbon body having a first porous oxide coating; and (b) a protective refractory, oxidation agent impermeable electrodeposited second coating disposed in said pores of said first coating and composed essentially of (1) a metal oxide and (2) a refractory metal salt which in the molten state is a solvent for at least a part of said second coating.

Claim 14

A process for improving the resistance of the surface of an electroconductive carbon body against attack by oxidation agents at 400° C., said surface having surface pore openings and carrying an adherent discontinuous coating composed of refractory oxide particles, which comprises: (a) immersing said body into a non-oxidizable refractory metal salt melt, having a boiling point in excess of 400° C.; (b) applying a continuous voltage, said voltage being below the disassociation voltage of the non-oxidizable refractory metal salt, using said carbon body as cathode; (c) electrodepositing said metal salt melt on said body thereby closing substantially all of said pore openings and discontinuities with said metal salt melt; and (d) removing said body from said metal salt melt before said oxide has completely disintegrated or dissolved.

Claim 15

A process for improving the resistance of the surface of an electroconductive carbon body against attack by oxidation agents at 400° C., said surface having surface pore openings and carrying an adherent discontinuous coating composed of refractory oxide particles, which comprises: (a) immersing said body into a non-oxidizable refractory metal salt melt, having a boiling point in excess of 400° C.; (b) applying a continuous voltage, said voltage being below the disassociation voltage of the non-oxidizable refractory metal salt, using said carbon body as cathode; (c) electrodepositing said metal salt melt on said body thereby closing substantially all of said pore openings and discontinuities with said metal salt melt; and (d) removing said body from said metal salt melt before said oxide has completely disintegrated or dissolved.

Claim 16

A process according to claim 12, wherein said body is immersed in said melt sufficiently deeply to contact substantially all of said refractory oxide coating with said melt.

Claim 17

A process according to claim 12, wherein said electrode is substantially completely covered by said porous coating and said electrode is substantially completely immersed in said melt.

Claim 18

A process according to claim 12, wherein said melt is non-oxidizable.

Claim 19

A process according to claim 12, wherein electrodeposition of said melt on said body is continuous until substantially all of said pore openings and discontinuities have been closed.

Claim 20

A process according to claim 12, wherein electrodeposition of said melt on said body is commenced as soon as said body is immersed in said melt.

Claim 21

A process according to claim 12, wherein said melt is a metal halide.

Claim 22

A process according to claim 18, wherein said melt is a metal fluoride.

Claim 23

A process according to claim 19, wherein said melt is predominantly cryolite.

Claim 24

A process according to claim 20, wherein said melt is composed of cryolite and alumina in 85-95:15-5 weight ratio.

Claim 25

A process according to claim 12, wherein said melt is magnesium fluoride.

Claim 26

A process according to claim 12, wherein said melt is a chloride.

Claim 27

A process according to claim 23, wherein said melt is an alkaline metal chloride.

Claim 28

A process according to claim 24, wherein said melt is a 55-95:45-5 by weight alkaline metal: AlCl 3 mixture.

Claim 29

A process according to claim 12, wherein the duration of immersion of said body in said melt is between 1 and 60 minutes.

Claim 30

A process according to claim 12, wherein said body on removal from said melt is allowed to cool to room temperature.

Claim 31

A process for providing a porous electroconductive carbon body with a coating which is oxidation agent impermeable at 400° C., which comprises: (a) coating at least a part of said body with a refractory oxide, said coating having discontinuities which expose pores of said body to the atmosphere; (b) immersing at least the thus coated part of said body in a salt melt for at least a part of said coating; (c) applying a continuous voltage said voltage being below the disassociation voltage of said salt melt, using said carbon body as cathode; (d) electrodepositing said salt melt on said body thereby closing substantially all of said pores and discontinuities; and (e) removing said body from said salt melt before said coating has completely dissolved or disintegrated.

Claim 32

A process for providing a porous electroconductive carbon body with a coating which is oxidation agent impermeable at 400° C., which comprises: (a) coating at least a part of said body with a refractory oxide, said coating having discontinuities which expose pores of said body to the atmosphere; (b) immersing at least the thus coated part of said body in a salt melt for at least a part of said coating; (c) applying a continuous voltage said voltage being below the disassociation voltage of said salt melt, using said carbon body as cathode; (d) electrodepositing said salt melt on said body thereby closing substantially all of said pores and discontinuities; and (e) removing said body from said salt melt before said coating has completely dissolved or disintegrated.

Claim 33

A process according to claim 28, wherein the oxide coated on said body includes particles that have a diameter between about 1μ and 200μ.

Claim 34

A process according to claim 29, wherein the oxide particles are alumina particles.

Claim 35

A process according to claim 29, wherein the entire body is coated with said oxide particles and said body is completely immersed in said melt.

Claim 36

A process according to claim 28, wherein said carbon body is coated to a thickness in the range of 200μ to 300μ.

Claim 37

A process according to claim 28, wherein said electrodeposition is continued until substantially all of said pores and discontinuities are filled.

Claim 38

A process according to claim 28, wherein said carbon body is sand-blasted prior to said coating step to provide said body with a clean, rough surface adapted to promote adhesion of said refractory oxide.

Claim 39

A process according to claim 28, wherein said coating is applied by brushing an aqueous suspension of oxide particles on the carbon, allowing the coating to dry, and then baking the coated carbon at elected temperature for several hours to cause said particles to adhere.

Claim 40

A process for providing a porous, electroconductive carbon body with a coating which is oxidation agent impermeable at 1000° C., which comprises: (a) plasma coating substantially all of said body with alumina particles to a thickness of 100μ to 1000μ thereby forming on said body an adherent fused coating of alumina particles, said coating having discontinuities which expose pores of said body to the atmosphere; (b) immersing said body in a electroconductive metal halide melt having a boiling point of at least 400° C.; (c) applying a continuous voltage, said voltage being below the disassociation voltage of the metal halide, using said carbon body as cathode; (d) electrodepositing said melt on said body thereby substantially filling all of said pores and said discontinuities; and (e) removing said body from said melt before said fused alumina coating has completely dissolved.

Claim 41

A process for providing a porous, electroconductive carbon body with a coating which is oxidation agent impermeable at 1000° C., which comprises: (a) plasma coating substantially all of said body with alumina particles to a thickness of 100μ to 1000μ thereby forming on said body an adherent fused coating of alumina particles, said coating having discontinuities which expose pores of said body to the atmosphere; (b) immersing said body in a electroconductive metal halide melt having a boiling point of at least 400° C.; (c) applying a continuous voltage, said voltage being below the disassociation voltage of the metal halide, using said carbon body as cathode; (d) electrodepositing said melt on said body thereby substantially filling all of said pores and said discontinuities; and (e) removing said body from said melt before said fused alumina coating has completely dissolved.