The selection of an adhesive for bonding the VPTs to the PbWO4 crystals in the end cap electromagnet

1
The selection of an adhesive for bonding the
VPTs to the PbWO4 crystals in the end cap
electromagnetic calorimeters

• P.S.Flower RAL

2
Contents Dow Corning RTV 3145

• Adhesive Requirements
• Refractive index
• Transmission
• Radiation damage
• Gluing
• Drying of glue
• Handling
• Unbonding
• Conclusion

3
Requirements

• Refractive index between 1.5 and 2.18
• Transmits UV
• Does not darken under radiation
• Does not embrittle under radiation
• Bonds well

• Does not impose stresses on crystal
• Stable for life of experiment
• Does not form bubbles
• Dries quickly
• Easy to use
• Can be unbonded

4
The effect of µ of adhesive
5
Refractive index of RTV

• a 12.79 b 115.38c -11.92 d -74.69

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Sample preparation

• 1 mm quartz or glass plates
• Clean Ethyl alcohol Distilled water
  2.5 solution Decon 90
  Distilled water Distilled water
• Adhesive 157 µ 898 µ
  1586 µ

7
Calculation of transmission

• Use different thicknesses of adhesive
• Eliminate refractive index and glass absorption
  terms

8
Sample measurement

• ? 20 Dual beam spectrophotometer

• Collimate beam
• Sample must be perpendicular to beam
• accurately positioned 10 µ
• Reproducibly positioned

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Results
10
Absorption of DOW RTV3145
RTV3145

• Comparison of results with published data,
  M.Montecchi

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? Irradiation of samples

• Brunel 15 Gy/h
• 1.7 Ci 60Co

• P Bonner MRC3.16 kGy/h
• 2 off 2000Ci 60Co

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? Irradiation, results

• 205 kGy in 64 hours, adhesive 1155 µ thick

• 205 kGy in 64 hours, adhesive 66 µ thick

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Gluing procedure

• Fill syringe with RTV Dow 3145
• Centrifuge for 1 min at app. 3800 rpm, (2000 g)
• Dispense resin. Settings Gas 80 psi, Grey, taper
  tip nozzle, time 1.35 sec

• Press VPT on to crystal, allow meniscus to form.
• Hold in position for 2 hours
• EFD 1500XL Dispenser

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Tests on resins
22 mm discs on 26 mm squares, cleaned 0.9mm
microscope slides

• 5 samples DOW RTV 3145, high viscosity
• Resin thickness 0.119 0.010 mm
• Skew mean 3.9 m rad.
• One part resin, constant viscosity, long usable
  time

• 4 samples DOW Sylgard, low viscosity
• Resin thickness 0.023 0.003 mm
• Skew mean 0.7 m rad.
• Two part resin, variable viscosity, short usable
  time

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Curing, Manufacturers Spec.

• Cures by neutral alkoxy reaction with moisture in
  the air.
• Releases methanol on curing
• 98 Non volatile
• 50 humidity at 23 ºC taken as normal
• At less than 30 humidity, curing slowed

• Manufacturers spec
• Skin over time 50 min (25)
• Tack free time 1.5 hrs
• Cure, 0.5 mm 24 hours
• Cure 3.2 mm 72 hours
• Full cure 3.2 mm 7 days

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Curing measurements

• Student, C Pattison, noticed adhesive in syringe
  picked up colour from rubber plunger
• This colour disappeared when adhesive dried

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Drying tests

• Initially all thicknesses dry at same speed
• Curing is moisture diffusion process
• After 48 hours, when the glue has dried about 4
  mm 100 micron glue dries at about 1 mm/day500
  micron glue dries at about 1.4 mm/day

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Handling Tests on Dow Corning RTV 3145

• After 5 min no slip observed
• After 30 min 100 g supported
• After 35 min 200 g supported
• After 40 min 225 g broke free

weight
32 mm dia glass bottle
Glass plate
19
Unbonding

• Literature suggests acidulated dichloromethane
  dissolves RTV3145.
• Nitromorse paint stripper contains
  dichloromethane.
• Unstuck bottle, 24 hours after gluing with 20
  hours soaking in nitromorse.
• RAL resin rotter is dichloromethane, phenol and
  formic acid.

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ConclusionDow Corning RTV3145

• Refractive index
• UV Transmission
• Radiation darkening
• Radiation embrittlement
• Adhesive bonding
• Stresses on crystal
• Long term stability
• Bubbles
• Drying
• Ease of use
• Can be unbonded

• OK
• OK
• OK
• OK
• OK
• OK
• Not tested
• OK
• OK
• OK
• Not yet solved