Mechanical seal arrangement having sliding surfaces of different hardness

1. Mechanical seal arrangement comprising:

a rotating slide ring having a first slide surface and a stationary slide ring having a second slide surface which define a sealing gap between them;

wherein the first and second slide surfaces have different hardnesses;

wherein the harder slide surface has a diamond coating and the softer slide surface is produced from carbon composite material, wherein the carbon composite material is a silicon carbide graphite composite material comprising silicon carbide, graphite and free silicon; and

wherein an average initial roughness (Ra 1 ) of the first slide surface of the diamond coating is smaller than an average initial roughness (Ra 2 ) of the second slide surface made from carbon composite material, wherein the diamond coating of the slide ring is additionally provided on a non-sliding surface on an outer peripheral region of the slide ring.

2. Mechanical seal arrangement as claimed in claim 1 , wherein the average initial roughness (Ra 1 ) of the slide ring with the diamond coating is 50% less than the average initial roughness (Ra 2 ) of the slide ring made from carbon composite material.

3. Mechanical seal arrangement as claimed in claim 2 , wherein the average initial roughness (Ra 1 ) of the diamond coating is in a range of 0.01 μm to 0.06 μm and/or that the average initial roughness (Ra 2 ) of the slide surface made from carbon composite material is in a range of 0.1 μm to 0.2 μm.

4. Mechanical seal arrangement as claimed in claim 1 , wherein the diamond coating has doping such that the diamond coating is electrically conductive.

5. Mechanical seal arrangement as claimed in claim 4 , wherein the doping is boron doping.

6. Mechanical seal arrangement as claimed in claim 1 , wherein the diamond coating is provided only partially on the outer peripheral region of the slide ring and in particular the diamond coating on the outer peripheral region has a tapering region.

7. Mechanical seal arrangement as claimed in claim 1 , wherein a support ring at least partially covers the diamond coating provided on the outer peripheral region of the slide ring.

8. Mechanical seal arrangement as claimed in claim 1 , wherein the diamond coating of the slide ring is additionally provided on an inner peripheral region of the slide ring.

9. Mechanical seal arrangement as claimed in claim 1 , wherein the first slide surface of the diamond coating is polished.

10. Mechanical seal arrangement as claimed in claim 1 , wherein the rotating slide ring comprises the diamond coating.

11. Mechanical seal arrangement as claimed in claim 1 , wherein the first slide surface of the diamond coating has a support portion of ≧50%.

12. Mechanical seal arrangement as claimed in claim 1 , wherein the carbon composite material comprises 60 to 75% by weight silicon carbide, 15 to 40% by weight carbon and 0.5 to 10% by weight free silicon.

13. Mechanical seal arrangement as claimed in claim 1 , wherein on the second slide surface made from carbon composite material are formed graphite-containing regions, in particular with a Rockwell hardness of 50 to 100 HR15T, which are arranged to receive free particles.

14. Power station feed pump comprising a mechanical seal arrangement as claimed in claim 1 .

15. Mechanical seal arrangement comprising:

a rotating slide ring having a first slide surface and a stationary slide ring having a second slide surface which define a sealing gap between them;

wherein the first and second slide surfaces have different hardnesses;

wherein the harder slide surface has a diamond coating and the softer slide surface is produced from carbon composite material, wherein the carbon composite material is a silicon carbide graphite composite material comprising silicon carbide, graphite and free silicon; and

wherein an average initial roughness (Ra 1 ) of the first slide surface of the diamond coating is smaller than an average initial roughness (Ra 2 ) of the second slide surface made from carbon composite material.

16. Mechanical seal arrangement as claimed in claim 15 , wherein the average initial roughness (Ra 1 ) of the slide ring with the diamond coating is 50% less than the average initial roughness (Ra 2 ) of the slide ring made from carbon composite material.

17. Mechanical seal arrangement as claimed in claim 15 , wherein the diamond coating has doping such that the diamond coating is electrically conductive.

18. Mechanical seal arrangement as claimed in claim 15 , wherein the rotating slide ring comprises the diamond coating.

19. Mechanical seal arrangement as claimed in claim 15 , wherein the first slide surface of the diamond coating has a support portion of ≧50%.

20. Mechanical seal arrangement comprising:

a rotating slide ring having a first slide surface and a stationary slide ring having a second slide surface which define a sealing gap between them;

wherein the first and second slide surfaces have different hardnesses;

wherein the harder slide surface has a diamond coating and the softer slide surface is produced from carbon composite material, wherein the carbon composite material is a silicon carbide graphite composite material comprising silicon carbide, graphite and free silicon; and

wherein an average initial roughness (Ra 1 ) of the first slide surface of the diamond coating is smaller than an average initial roughness (Ra 2 ) of the second slide surface made from carbon composite material, wherein the diamond coating of the slide ring is additionally provided on an outer peripheral region of the slide ring.