1. Athmospheric Surface Treatments of Niobium A. Camacho*^, A.A. Rossi* and V. Palmieri*^, * INFN – Legnaro National Laboratories ^ University of Padua

2. Material Study or Cavity construction? Samples or Cavities?

3. Low research budget  Large amount of cavities 6 GHz

4. Resistive Samples Real cavities Inductive H c1 Measurement Calorimetric methods R S Differential measurements Microstrip Resonators 6 GHz cavities 1,5 /1,3 GHz monocells 1,3 GHz 3-cell cavity 1,3 GHz 9-cell cavities Pillbox cavities, etc

5. No electron beam welding, neither for flanges Obtained by spinning from Nb scraps Short fabrication time Fast and low cost BCP and EP treatments Inexpensive Cryogenics Quick RF Measurements 6 GHz CAVITY MINILAB

6. 6 Ghz Cavity Geometry 20 mm 36 mm Seamless flanges [mm] Flange Area = 7 cm 2

8. Mini Mechanical Tumbling SiCZrO 2 Al 2 O 3 + SiO 2

9. Mini EP

10. 6 GHz CAVITY MINI-furnace

11. 6 GHz CAVITY MINI-Camera

12. Ready for the RF measurement

13. 6 GHz CAVITY: MINI-Kapton gasket

14. Quick RF Measurements The insert has been conceived to even enter into a 450 lt Helium dewar INSERT DEWAR RF measuring system

15. High Temperature Rapid Metathesis (Nitriding in Mushy State)

18. The Homologous Temperature 0 1 T [K]  = = T m [K] for Nb 2467 °C

19. T [K]  = = T m [K] 0,98 0,9 1 2467 °C 2196 °C Mushy State 0,96 2357 °C2412 °C Premelting

20. 6 Ghz @4,2K Bulk Nb

21. Fast ( takes only few sec) Cheap (Vacuum Technology Free) Simple (No need of special expertise) High Temperature Rapid Metathesis (Nitriding in Mushy State) The Process is:

22. Premelting (also Surface melting) Even below its melting point (T m ), quasi-liquid films can be observed on crystalline surfaces

23. The thickness of the quasi-liquid film is T - dependent This effect is common for all crystalline materials Premelting (also Surface melting)

24. Nb NbN 3 mm Nb NbN

25.  Nb 5 N 6 ; N 4 N 3 Over-Stoichiometric  -NbN 1-x ;  -Nb 4 N 3-x Under-Stoichiometric  -Nb (N) (bcc solid solution)  Niobium

26. Nb 5 N 6 ; N 4 N 3  NbN 1-x ;  -NbN (hexagonal);  ’  NbN (hexagonal);  -Nb2N (hexagonal);  -Nb 4 N 3-x  -Nb (N) (bcc solid solution) Niobium

27. Surface layers

28. Temperature Time T m of Nb 3 – 30 sec

29.  -Nb N  -Nb N

30. As the  -NbN   -Nb 4 N 3-x phase transformation is a very fast, quasi-continuous Transition, it cannot be avoided by quenching

31. The good layer is t he most external one

32. BCP 3 ’ Pure Nb NbN

34. NbN @4,2K T = 4,2 K Bulk Nb

35. High Temperatures for Nb Purification

36. IL - EP Classical – EP 5 min at 2300°C

37. Conclusions 1 6 Ghz cavities allow a fast and dense statistics

38. Conclusions 2 No vacuum required! 5min @ 2300°C seem to purify Nb Nitriding performed at Atmospheric pressure At 4,2 K the Q-value at low field increases of even a factor 5