S.M. Deambrosis*^, G. Keppel*, N. Pretto^, V. Rampazzo*, R.G. Sharma°, D. Tonini * and V. Palmieri*^

Padova University, Material Science Dept

* INFN - Legnaro National Labs ^ Padua University, Science faculty, Material Science Dept

° Interuniversity Accelerator Center, New Delhi

Nb3Sn by Liquid TinDiffusion

Nb3Sn by liquid Sn diffusion

1) Theory

2) Literature review

3) Technique choice reasons

4) Method

5) Work in progress

6) Conclusions

Vapor Sndiffusion

Liquid Sn

diffusion

Usedsystem

“1 Step”

process

“2 Steps”process

“Hybrid”

process

TOeAR

R TKn

n

nBCS

B ,,12

12

3

RBCS

If T < Tc / 2

Empirically, Rres is found to be dependent on n too.

Theory

For low rf losses, a high TC value is not sufficient

A metallic behaviour in the normal state is mandatory

18Tc (K)

ρn

(μΩ

cm)

Nomogram

Theory

RBCS IdealR BCS ~ 1 nΩ

At T = 4.2 K,

f = 500 MHz,

s = 4,

RBCS depends

on Δ and ρn

~ 10 μΩcm

Literature review

Literature

Many papers of different authors with different aims:

• Nb3Sn by CVD and PVD techniques to compare bulk and film properties

• Nb3Sn by bronze process for high field Superconducting Magnets

• Nb3Sn RF application: Wuppertal

Q vs. Epeak of the first two Nb3Sn-coated 1.5 GHz single-cell cavities in comparison to pure Nb at 4.2 K and 2 K f romCEBAF

Wuppertal: Nb3Sn cavity (1.5 GHz) obtained trough Sn vapour phase diffusion (’90s)

Literature

Vapor Sn Diffusion

Technique Choice Reasons

1) Cavity manufactoring

2) Formation of nucleation centers

of Nb3Sn (Nb Surface

Anodization + SnCl2 Treatment)

3) Nb3Sn film growth in a Sn

atmosphere (T = 1050-1250°C,

t = dozens of h, p(Sn) ~ 10-

3mbar)

4) Cool down and unwanted

phases Chemical removal

(anodizaton + HF 48%)

Laboratory Procedure Heating system

Accelerating structure

Sn source

Sn source heater

Pumping system

Liquid solute diffusion technique

Cu

Sn

Nb3Sn

Nb

Technique Choice Reasons

Liquid Sn Diffusion?

Bulk Nb substrate dipping

in a liquid Tin bath

Sample

Annealing

• No nucleation sites on Nb are required

• Fast growth of Nb3Sn layer

• Deasirable uniform thickness

Technique Choice Reasons

Linearfeedtrough

Cooling water jacket

Furnace

Liquid Sn

Furnace

Used System

Method: used system

Nb3Sn: Phase Diagram

Nb3Sn

<Tc

phases

930°C

Method: used system

To Summarise

●Liquid solute diffusion technique choice

●Working T > 930 °C

Linearfeedtrough

Cooling water jacket

Furnace

Liquid Sn

Furnace

1) Bulk Nb Substrate chemical cleaning (10 min in a 1:1:2

solution)

2) Substarte fixing to feedtrough, vacuum and T reaching (1 day)

3) Substrate thermalization (30 min - 1 h)

4) Dipping (few min - 2 h)

5) Annealing above the Sn bath without opening the chamber

(some h)

6) Residual Sn Chemical removal trials

Laboratory Procedure

“1 Step” Process

Method: “1 step” process

Nb3Sn photo

Residual Sn

Sn drop

Method: “1 step” process

SEM Image

10 m

Nb

Nb3Sn

Method: “1 step” process

Process T = 1000°C

Dipping t = 120’

Annealing t = 14h

Post annealing:

5h at 500°C

XRD spectrum

Method: “1 step” process

Dipping T = 1000 °CDipping t = 30 min

Annealing T = 1000 °CAnnealing t = 10 h

Dipping T = 1000 °CDipping t = 30 min

Annealing T = 1000 °CAnnealing t = 10 h

Angle 2θ (degrees)

Rel

ativ

e In

tens

ity

Process T = 1000°C, Dipping t = 30’, Annealing t

= 10h

EMPA Analysis

Distance (m)

Sn

at.%

Distance (m)

Sn

at.%

Nb3Sn n°16

Dipping T = 1000 °C

Dipping t = 120 min

Annealing T = 1000 °C

Annealing t = 14 h

Post annealing T = 500

°C

Post annelaing t = 5 h

Method: “1 step” process

A Superconductive Transition Curve

Temperature (K)

M’ (

emu)

Nb3Sn 16: 970°C; 120’+14h. Post annealing: 500°Cx5hNb3Sn 16: 970°C; 120’+14h. Post annealing: 500°Cx5h

Nb3Sn (Tc = 17,7 K)

Nb (Tc = 9,3 K)

Sn (Tc = 3,6 K)

Nb3Sn n°16: 1000°C; 120’+14h+post annealing 500°Cx5h

Method: “1 step” process

• Mechanical polishing

• Chemical polishing

3. Q Factor Measurement

• Nb3Sn film obtainment

6 GHz Cavities

1. Spinning Technique

2. Surface Treatments

Method: “1 step” process

T = 1025°C

tdipping = 15 min, tannealing = 15 h

HCl 37%,

t = 10 min, T = 85°C

Nb3Sn film obtainment

Film production:

Chemical treatment:

Method: “1 step” process

Q Factor Measurement

Nb3Sn

Method: “1 step” process

A Nb3Sn 6 GHz Cavity

Nb3Sn 1

1) As obtained

2) HCl

3) HCl + us

Method: “1 step” process

Nb3Sn with good superconductive properties

Residual Sn traces on the sample surface

To Summarise

+Tc = 16,9 K Tc= 0,2 K

-

Sn rich Phases Presence-

Method: “1 step” process

“2 Steps” Process

Method: “2 steps” process

1) Bulk Nb Substrate chemical cleaning (10 min in a 1:1:2

solution)

2) Substarte fixing to the feedtrough, vacuum and T reaching (1

day)

3) Substrate thermalization (30 min - 1 h)

4) Dipping (few min - 2 h)

5) System opening to remove Sn bath, vacuum and T reaching (1

day)

6) Sample annealing without Sn vapor (some h)

7) Growth film chemical treatment

Linearfeedtrough

Cooling water jacket

Furnace

Liquid Sn

Furnace

Laboratory Procedure

Nb3Sn photo

Method: “2 steps” process

SEM Images

Method: “2 steps” process

Proc T = 1025°C, Dipp t = 15’, Ann t = 15h

Proc T = 1025°C, Dipp t = 5’, Ann t =

20h

XRD spectra

Angle 2θ (degrees)

Rel

ativ

e In

tens

ity

Angle 2θ (degrees)

Rel

ativ

e In

tens

ity

Method: “2 steps” process

Proc T = 1025°C,

Dipp t = 5’,

Ann t = 20h

Proc T =

1025°C, Dipp t

= 5’,

Ann t = 10h

A Superconductive Transition Curve

Method: “2 steps” process

-0,028

-0,026

-0,024

-0,022

-0,02

-0,018

-0,016

-0,014

-0,012

1 3 5 7 9 11 13 15 17 19

Temperature (K)

M' (

em

u)

Proc T = 1025°C, Dipp t = 5’, Ann t =

20h

Tc (Nb3Sn) = 14,9 K

Tc (Nb3Sn) = 0,43 K

Growth film chemical treatment (HCl)

Method: “2 steps” process

Tc and Tc vs THCl

T HCl (°C)

T HCl (°C)

Method: “2 steps” process

Worst Nb3Sn film superconductive properties

+

-

To Summarise

No Residual Sn traces on the sample surface

Tc = 15,2 K, Tc = 0,5 K

Sn rich Phases Presence-

Method: “2 steps” process

HCl chemical treatment deteriorates the growth film-

“Hybrid” Process

Method: “Hybrid” process

Laboratory Procedure

1) Bulk Nb Substrate chemical cleaning (10 min in a 1:1:2

solution)

2) Substarte fixing to the feedtrough, vacuum and T reaching (1

day)

3) Substrate thermalization (30 min - 1 h)

4) Dipping (few min - 2 h)

5) Sample annealing with Sn vapor (some h)

6) System opening to remove Sn bath, vacuum and T reaching (1

day)

7) Sample annealing without Sn vapor (some h)

Linearfeedtrough

Cooling water jacket

Furnace

Liquid Sn

Furnace

Method: “Hybrid” process

Nb3Sn photo

XRD spectrum

Angle 2θ (degrees)

Rel

ativ

e In

tens

ity

Method: “Hybrid” process

Proc T = 975°C, Dipp t = 30’, Ann (Sn) t = 2h, Ann t

= 5h

A Superconductive Transition Curve

Method: “Hybrid” process

Proc T = 975°C, Dipp t = 30’, Ann (Sn) t = 2h, Ann t

= 5h

-0,028

-0,026

-0,024

-0,022

-0,02

-0,018

-0,016

-0,014

-0,012

1 3 5 7 9 11 13 15 17 19

Temperature (K)

M' (

emu)

Tc (Nb3Sn) = 16,6 K

Tc (Nb3Sn) = 0,28 K

Good Nb3Sn film superconductive properties

+No Residual Sn traces on the sample surface

Tc = 16,5 K, Tc = 0,3 K

No Sn rich Phases

To Summarise

+

+

Method: “Hybrid” process

Work in progress

• Two furnaces system to avoid air contamination of the

superconducting thin film while opening the vacuum

system

• Use of the best results to coat 6 GHz Nb cavities for a

Nb3Sn RF properties sistematic testing

• Use of a different experimental method to prepare

Nb3Sn:

multilayer obtained altermatively depositing Nb and Sn

Conclusions

• Liquid solute diffusion technique (working T > 930 °C)

• Three different processes:

“1 step”

“2 steps”

“Hybrid”

trying to optimize T and t

• Finally:

◊ Good superconducting properties

◊ No Sn

◊ No Sn rich Phases

End