Electrolytic cell

1. An electrolytic cell for the production of aluminum by reduction of alumina, said cell containing an electrolyte bath and having a side wall that comprises at least one side block, said side block comprising an aluminous material having

an open porosity of less than 10%, and

a composition, as a weight percentage on the basis of the aluminous material and for a total of 100%, such that:

Al 2 O 3 >50%, beta-alumina representing less than 20% of the weight of the aluminous material,

oxides that are less reducible than alumina at 1000° C.: <46%,

Na 2 O <3.9%,

other constituents <2%,

said composition of the aluminous material being such that: Al 2 O 3 +MgO +CaO >95%.

2. The cell as claimed in claim 1 , the electrolyte bath comprising AlF 3 and at least one alkali metal fluoride NaF or KF at an (NaF+KF)/AlF 3 molar ratio of less than 3.

3. The cell as claimed in claim 1 , the electrolyte bath comprising a molar content of AlF 3 of greater than 30%.

4. The cell as claimed in claim 1 , the electrolyte bath comprising a molar content of AlF 3 of greater than 37%.

5. The cell as claimed in claim 1 , said side block having a minimum thickness of greater than 40 mm.

6. The cell as claimed in claim 1 , said side block having a total porosity of less than 5%.

7. The cell as claimed in claim 1 , a content of oxides that are less reducible than alumina at 1000° C. being less than 10%.

8. The cell as claimed in claim 1 , a content of oxides that are less reducible than alumina at 1000° C. being less than 5%.

9. The cell as claimed in claim 1 , said composition of the aluminous material being such that: SiO 2 <1.5%.

10. The cell as claimed in claim 1 , the aluminous material comprising at least a corundum and/or magnesium spinel crystalline phase and/or a hibonite (CaO.6Al 2 O 3 ) phase.

11. The cell as claimed in claim 1 , said composition of the aluminous material being such that: Al 2 O 3 >92%.

12. The cell as claimed in claim 1 , the composition of the aluminous material being such that: Na 2 O <3%.

13. The cell as claimed in claim 1 , said composition of the aluminous material being such that: Na 2 O <1%.

14. The cell as claimed in claim 13 , said composition of the aluminous material being such that: Na 2 O <0.1%.

15. The cell as claimed in claim 1 , a thermal conductivity of the aluminous material at 600° C. being less than 10 W/m·K.

16. The cell as claimed in claim 1 , an electrical resistivity of the aluminous material at 700° C. being greater than 2000 ohm·cm.

17. The cell as claimed in claim 1 , the electrolyte bath being a cryolite bath or a potassium bath.

18. The cell as claimed in claim 1 , a temperature of the electrolyte bath being below 950° C. and/or above 800° C.

19. The cell as claimed in claim 1 , a total content of other constituents being less than 4.5%.

20. The cell as claimed in claim 1 , said side block being obtained by a fusion process or by a sintering process comprising a compaction step and/or comprising a sintering step at a temperature above or equal to 1300° C.

21. The cell as claimed in claim 1 , said side block being in contact with the electrolyte bath.

22. The cell as claimed in claim 1 , comprising an insulating material placed so as to limit heat losses through said side block.

23. A process for producing aluminum by passing an electric current into the electrolyte bath of a cell as claimed in claim 1 .

24. The process as claimed in claim 23 , wherein, under steady-state operation, the aluminous material is in contact with the electrolyte bath.

25. The process as claimed in claim 23 , wherein, under steady-state operation, the electrolyte bath is at a temperature below 950° C.

26. The process as claimed in claim 23 , wherein the electrolyte bath is passed through by an electric current having an intensity of greater than 100 kA.

27. A process for purifying aluminum by passing an electric current into an electrolyte bath by means of a cell as claimed in claim 1 .

28. An electrolytic cell for the production of aluminum by reduction of alumina, said cell containing an electrolyte bath and having a side wall that comprises at least one side block, said side block comprising an aluminous material having

an open porosity of less than 10%, and

a composition, as a weight percentage on the basis of the aluminous material and for a total of 100%, such that:

Al 2 O 3 >50%, beta alumina representing less than 20% of the weight of the aluminous material,

oxides that are less reducible than alumina at 1000° C.: <46%,

Na 2 O <3.9%,

other constituents <5%,

wherein MgO >28%.

29. The cell as claimed in claim 28 , said side block having a total porosity of less than 5%.

30. The cell as claimed in claim 28 , a content of oxides that are less reducible than alumina at 1000° C. being less than 10%.

31. The cell as claimed in claim 28 , a content of oxides that are less reducible than alumina at 1000° C. being less than 5%.

32. The cell as claimed in claim 28 , said composition of the aluminous material being such that: SiO 2 <1.5%.

33. The cell as claimed in claim 28 , the aluminous material comprising at least a corundum and/or magnesium spinel crystalline phase and/or a hibonite (CaO.6Al 2 O 3 ) phase.

34. The cell as claimed in claim 28 , the composition of the aluminous material being such that: Na 2 O <3%.

35. The cell as claimed in claim 28 , said composition of the aluminous material being such that: Na 2 O <1%.

36. The cell as claimed in claim 28 , said composition of the aluminous material being such that: Na 2 O <0.1%.

37. An electrolytic cell for the production of aluminum by reduction of alumina, said cell containing an electrolyte bath and having a side wall that comprises at least one side block, said side block comprising an aluminous material having

an open porosity of less than 10%, and

a composition, as a weight percentage on the basis of the aluminous material and for a total of 100%, such that:

Al 2 O 3 >50%, beta alumina representing less than 20% of the weight of the aluminous material,

oxides that are less reducible than alumina at 1000° C.: <46%,

Na 2 O <3.9%,

other constituents <5%,

wherein CaO >1%.

38. The cell as claimed in claim 37 , said side block having a total porosity of less than 5%.

39. The cell as claimed in claim 37 , a content of oxides that are less reducible than alumina at 1000° C. being less than 10%.

40. The cell as claimed in claim 37 , a content of oxides that are less reducible than alumina at 1000° C. being less than 5%.

41. The cell as claimed in claim 37 , said composition of the aluminous material being such that: SiO 2 <1.5%.

42. The cell as claimed in claim 37 , the aluminous material comprising at least a corundum and/or magnesium spinel crystalline phase and/or a hibonite (CaO.6Al 2 O 3 ) phase.

43. The cell as claimed in claim 37 , the composition of the aluminous material being such that: Na 2 O <3%.

44. The cell as claimed in claim 37 , said composition of the aluminous material being such that: Na 2 O <1%.

45. The cell as claimed in claim 37 , said composition of the aluminous material being such that: Na 2 O <0.1%.

46. The cell as claimed in claim 1 , the composition of the aluminous material being such that Al 2 O 3 >85%.

47. An electrolytic cell for the production of aluminum by reduction of alumina, said cell containing an electrolyte bath and having a side wall that comprises at least one side block, said side block comprising an aluminous material having

an open porosity of less than 10%, and

a composition, as a weight percentage on the basis of the aluminous material and for a total of 100%, such that:

Al 2 O 3 >50%, beta-alumina representing less than 20% of the weight of the aluminous material,

oxides that are less reducible than alumina at 1000° C.: <46%,

Na 2 O <3.9%,

other constituents <1%,

said composition of the aluminous material being such that: Al 2 O 3 +MgO +CaO >95%.

48. An electrolytic cell for the production of aluminum by reduction of alumina, said cell containing an electrolyte bath and having a side wall that comprises at least one side block, said side block comprising an aluminous material having

an open porosity of less than 10%, and

a composition, as a weight percentage on the basis of the aluminous material and for a total of 100%, such that:

Al 2 O 3 >50%, beta-alumina representing less than 20% of the weight of the aluminous material,

oxides that are less reducible than alumina at 1000° C.: <46%,

Na 2 O <3.9%,

other constituents <5%,

said composition of the aluminous material being such that: Al 2 O 3 +MgO+CaO>95%,

wherein the total content of copper, tin, boron, phosphorus, chromium and zinc oxides is less than 2%.

49. The electrolytic cell according to claim 48 , wherein the total content of tin, boron, phosphorus, iron, titanium, chromium and zinc oxides is less than 2%.

50. The electrolytic cell according to claim 48 , wherein the total content of tin, boron, phosphorus, iron, titanium, chromium and zinc oxides is less than 1%.

51. An electrolytic cell for the production of aluminum by reduction of alumina, said cell containing an electrolyte bath and having a side wall that comprises at least one fused side block, said side block comprising an aluminous material having

an open porosity of less than 10%, and

a composition, as a weight percentage on the basis of the aluminous material and for a total of 100%, such that:

Al 2 O 3 >50%, beta-alumina representing less than 20% of the weight of the aluminous material,

oxides that are less reducible than alumina at 1000° C.: <46%,

Na 2 O <3.9%,

other constituents <5%,

said composition of the aluminous material being such that: Al 2 O 3 +MgO +CaO >95%.