atroshchenko - presence of residual tin drops in thermally diffused nb3sn
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http://www.surfacetreatments.it/thinfilms Presence of Residual Tin drops on Thermally Diffused Nb3Sn (Atroschenko Konstantin - 10') Speaker: Atroschenko Konstantin - INFN-LNL | Duration: 10 min.TRANSCRIPT
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Authors: Konstantin Atroshchenko Antonio Alessandro Rossi
Supervisor: prof. Enzo Palmieri
"Presence of residual Tin drops in Thermally diffused Nb3Sn"
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Advantages of the liquid Tin diffusion method
relatively cheap technique; uniformity of the film (stoichiometrically); can be used for covering surface of wide and complex shaped substrates (!). we don't need to manipulate dangerous substances as SnCl2 to create a nucleation centers, and the diffusion process is considerably faster
Liquid tin diffusion is a method of obtaining the superconductive A15 Nb3Sn coating over the 6 GHz cavities or other substrates. A bulk Nb 6 GHz cavity is introduced into molten Sn (dipping step) and after it follows the heat treatment (annealing step).
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6 GHz cavities ready for treatments
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Experimental stand
Inconel chamber: (chosen because of its stability at the high process temperature).
Alumina (Al2O3) crucible contains the Sn inside (99.99% nominal purity);
top chamber
upper furnace
lower furnace
linear feedthrough
cooling water
pumping
cavity
flanges
crucible with liquid Tin
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cavity
droplets of Tin
Problem: • The residual droplets of
Tin on the banded parts (planes, which is horizontal) of the cavity
Problems of the methodProblem: • external furnace. Maximum temperature 1200OC,
but it’s hard to transmit it inside the chamber, so the temperature inside is not high enough to evaporate the residual Tin droplets
• Diffusion of contaminations through the wall of the chamber at high temperatures
external furnace
vacuum chamber
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Residual Tin drops on the internal and external surface of the cavity
Nb3Sn
Sn
Sn
External surface Internal surface
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The L - samples
For the experiment was designed the L-samples, which imitates the shape of the cavity. Samples is made of Niobium.
50
10
153
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Basic surface treatment (for all samples)
washing in Rodaclean with ultrasonic (60 min) washing in deionized water with ultrasonic washing with deionized water drying with nitrogen BCP in the solution: HF/HNO3/H3PO4 = 1/1/2 washing with deionized water drying with nitrogen
All samples have been lapped using abrasive papers to reduce the residual roughness after machining.
1. Mechanical treatment
2. Basic chemical treatments
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Preparing the surface. Glow Discharge
voltage connector
feedthrough with the sample inside
chamber
coil
baking time: 16 hours;baking temperature 120oC ;GD pressure: 10-3 mBar;
Cathode Parameters:current: 0,04 A
Coil Parameters:Current : 8 AMagnetic field 525 Gauss
Procedure:
Ultrasonic + Rodaclean 60 min
Clean with acetone
Clean with alcohol
Glow Discharge 1 min
Annealing. 4 hours. T = 1000OC
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Ceramic tube
Sample
Nb wire
Flange
Glow Discharge. Results.
Horizontally fixed sample
Glow discharge. View from the bottom window
After glow discharge
After dipping
and annealing@ 1000oC
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Preparing the surface. Anodization
Procedure:
BCP 10 min
Ultrasonic + Rodaclean 60 min
Clean with acetone
Clean with alcohol
Anodization inammonium citrate. V = 20V
Annealing. 4 hours. T = 1000OC
Ammonium citrate
sample
To the power supply
After anodization
After dipping
and annealing@ 1000oC
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Ultrasonic + Rodaclean 60 min
Clean with acetone
Clean with alcohol
Chemical etchingHNO3 : HF = 1 : 1
Procedure:
Preparing the surface. Chemical etching
After annealing
After etching
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Comparison of external resistive and internal heaters
Parameter Internal furnace External furnace
Maximum temperature < 2000OC 1200OC
Diffusion of the contaminations
through the wall of the chamber
No (chamber is cold) Yes (chamber is hot)
Chamber Could be used stainless steel chamber
Requires Inconel chamber
Time of heating to 1000OC < 5 min 3 hours
Cooling Doesn’t requires cooling Requires cooling the pumping zone
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Linear feedthrough
Hot zone
Cold zoneVacuum chamber
heater
Pumping out
L - samples
Internal heater high temperature annealing
The cross-section of the system:
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Vacuum Chamber
Vacuum chamber
Temperature control unit
baking control unit
Gate switch
Pumping control unit
Whole – metal valve
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Comparison of annealing at 1000OC and 1300OC
annealing at 1300OCfor 5 minutes
annealing at 1000OCfor 4 hours
etching glow dischargeanodizationJust BSP
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Outlook
Definition of optimal parameters of high temperature annealing: temperature and time of annealing, ets.
SEM measurements
Profilometric measurements
Covering of the Nb 6 GHz cavities;
RF – measurements
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Thank you for attention!