Ceramic oxide electrodes, their method of manufacture and a cell and processes for molten salt electrolysis using such electrodes

Claim 2

A process of electrolysis in a molten salt electrolyte using an anode comprising a body consisting essentially of a ceramic oxide material of spinel structure, characterized in that said material has the formula: where: M, is one or more divalent metals from the group Ni, Co, Mg, Mn, Cu and Zn; x is 0.5-1.0; M il is one or more divalent/trivalent metals from the group Ni, Co, Mn and Fe, but excluding the case where M, and M,, are both the same single metal; M III n+ is one of more metals from the group Ti4+, Zr 4+ , Sn 4+ , Fe 4+ , Hf 4+ , Mn 4+ , Fe 3+ , Ni 3+ , Co3+, Mn 3+ , A1 3+ and Cr 3+ , Fe 2+ , Ni 2+ , Co2+, Mg 2+ , Mn 2+ , Cu2+ and Zn 2+ , and Li +; and the value of y is compatible with the solubility of M III n+ O n/2 in the spinel lattice, providing that y≠0 when (a) x=1, (b) there is only one metal M,, and (c) there is only one metal M II or there are two metals M II in an equal whole atom ratio.

Claim 3

The process of claim 1, wherein M II is Fe.

Claim 4

The process of claim 2, wherein M III n+ is a metal from the group Ti4+, Zr 4+ , Hf 4+ , AI 3+ , Co3+, C r 3+ and Li + and y=0-0.1.

Claim 5

The process of claim 1, wherein the metal or metals M III n+ is the same as the metal or metals M, and/or M II .

Claim 6

The process of claim 4, wherein y=0-0.2.

Claim 7

The process of claim 1, wherein M,, is predominantly Fe with up to 0.2 atoms of Ni, Co or Mn.

Claim 8

The process of claim 1, 2, 3, 4, 5 or 6, wherein x=0.8-0.99.

Claim 9

The process of claim 1, 2, 3, 4, 5 or 6, wherein the spinel material contains at least two metals from the group.

Claim 10

The process of claim 2 or 3, wherein the anode body is a self-sustaining body sintered from a mixture of xMol , (1-x) Mol Fe 3 0 4 , xMol Fe 2 O 3 and yMol M III n O n/2 .

Claim 11

The process of claim 1, wherein the anode body is a sintered self-sustaining body containing up to 10% of other materials in a separate phase from the spinel material according to the given formula.

Claim 12

The process of claim 9 or 10, wherein the sintered anode body has an open porosity of less than 1%.

Claim 13

The process of any preceding claim wherein oxygen is evolved at the anode.

Claim 14

The process of claim 12, wherein the electrolyte is a cryolite-based fused bath containing alumina.

Claim 15

A substantially non-consumable anode for molten salt electrolysis, in particular the production of aluminium from a cryolite-based fused bath containing alumina, comprising a body consisting essentially of a ceramic oxide material of spinel structure, characterized in that said material has the formula: where: M, is one or more divalent metals from the group Ni, Co, Mg, Mn, Cu and Zn; x is 0.5-1.0; M II is one or more divalent/trivalent metals from the group Ni, Co, Mn and Fe, but excluding the case where M I and M II are both the same single metal; M III n+ is one or more metals from the group Ti4+, Zr 4+ , Sn 4+ , Fe 4+ , Hf 4+ , Mn 4+ , Fe 3+ , Ni 3+ , Co 3+ , Mn 3+ , A1 3+ and Cr 3+ , Fe 2+ , Ni 2+ , C 0 2+ , Mg 2+ , Mn2+, Cu2+ and Zn 2+ , and Li + ; and the value of y is compatible with the solubility of M III n+ O n/2 in the spinel lattice, providing that y≠0 when (a) x=1, (b) there is only one metal M,, and (c) there is only one metal M,, or there are two metals M,, in an equal whole atom ratio.

Claim 16

A substantially non-consumable anode for molten salt electrolysis, in particular the production of aluminium from a cryolite-based fused bath containing alumina, comprising a body consisting essentially of a ceramic oxide material of spinel structure, characterized in that said material has the formula: where: M, is one or more divalent metals from the group Ni, Co, Mg, Mn, Cu and Zn; x is 0.5-1.0; M II is one or more divalent/trivalent metals from the group Ni, Co, Mn and Fe, but excluding the case where M I and M II are both the same single metal; M III n+ is one or more metals from the group Ti4+, Zr 4+ , Sn 4+ , Fe 4+ , Hf 4+ , Mn 4+ , Fe 3+ , Ni 3+ , Co 3+ , Mn 3+ , A1 3+ and Cr 3+ , Fe 2+ , Ni 2+ , C 0 2+ , Mg 2+ , Mn2+, Cu2+ and Zn 2+ , and Li + ; and the value of y is compatible with the solubility of M III n+ O n/2 in the spinel lattice, providing that y≠0 when (a) x=1, (b) there is only one metal M,, and (c) there is only one metal M,, or there are two metals M,, in an equal whole atom ratio.

Claim 17

The anode of claim 14, wherein M,, is Fe.

Claim 18

The anode of claim 14, wherein M III n+ is a metal from the group Ti4+, Zr 4+ , Hf 4+ , AI 3+ , Co3+, Cr 3+ and Li + , and y=0-0.1.

Claim 19

The anode of claim 14, wherein the metal or metals M III n+ is the same as the metal or metals M I and/or M II .

Claim 20

The anode of claim 17, wherein y=0-0.2.

Claim 21

The anode of claim 14, wherein M,, is predominantly Fe with up to 0.2 atoms of Ni, Co or Mn.

Claim 22

The anode of claim 14, 15, 16, 17, 18 or 19, wherein x=0.8-0.99.

Claim 23

The anode of claim 14, 15, 16, 17, 18 or 19, wherein the spinel material contains at least two metals from the group.

Claim 24

The anode of claim 15, wherein the anode body is a self-sustaining body sintered from a mixture of xMol , (1-x) Mol Fe 3 O 4 , xMol Fe 2 O 3 and yMol M III n+ O n/2 .

Claim 25

The anode of claim 14, wherein the anode body is a sintered self-sustaining body containing up to 10% of other materials in a separate phase from the spinel material according to the given formula.

Claim 26

The anode of claim 22 or 23, wherein the sintered anode body has an open porosity of less than 1%.

Claim 27

A cell for the electrolytic production of aluminium comprising a cryolite-based fused bath containing alumina into which dips an anode as claimed in any one of claims 14 to 24.

Claim 28

A method of manufacturing the anode of claim 22 or 23, wherein powders of said oxides with a diameter from 0.01 to 20 µm are sintered under pressure.