1. PREPARATION OF PROTECTIVE/REFLECTIVE COATINGS FOR CsI(Tl) SCINTILLATORS BASED ON BaSO4 PARTICLES DISPERSED IN THERMOSETS
G. Carotenuto
CaloCube Meeting, 12/11/2015

2. WHITE REFLECTANCE COATING FORMULATION
Aim: development of a white reflectance coating for ionic crystal substrates. The formulation was prepared by combining together an optical-grade epoxy resin with barium sulfate powders.
Epoxy ionic structure
CsI
Cure and epoxy/CdS adhesion mechanism.
The Technovit Epox® (Heraeus Kuzler) perfectly adheres to ionic substrates (CsI) and it does not absorb visible and UV-A light.
Commercial barium sulfate powders (Alfa Aesar) used as composite filler.

3. MORPHOLOGY OF BARIUM SULFATE ‘’PRECIPITATED’’ (99%)
EDS-Composition
Cu:
Ba: 35.95 S: O:
Average size: 431nm
Barium sulfate, precipitated, 99% - Alfa Aesar (price: 19.60euro/500g).

4. MORPHOLOGY OF BARIUM SULFATE ‘’PURATRONIC’’ (99.998%)
EDS-Composition
Cu:
Ba: 25.84 S: O:
Average size: 487nm
Barium sulfate powder, Puratronic, % (metals basis) Alfa Aesar (price: 29.70euro/5g)

5. COMMERCIAL WHITE REFLECTANCE COATING
(LABSPHERE 6080)
Oblong and spherical BaSO4 crystals with a size of nm
PVA/BaSO4/ethanol

6. FILLER DISPERSION BY MAGNETIC STIRRING
Properties compromised by the aggregation in thin coatings:
- Diffusion barrier (prevention of surface oxidation, Tl toxicity limitation, etc.)
Shock absorption. O2 +
H2O
BaSO4/epoxy sample (27.6% by weight of BaSO4).
Aggregates of BaSO4 grains present into the resin
When the BaSO4 powder is dispersed into the epoxy resin simply by using magnetic stirring, the obtained composite is not very homogeneous and some aggregates are present inside the material. The presence of such aggregates must be avoided in the deposition of thin reflective coatings. In order to scatter uniformly BaSO4 grains into the epoxy, an ultrasound treatment has been conveniently adopted. Stable (colloidal) dispersions are generated by such approach.

7. FILLER DISAGGREGATION BY ULTRASOUND TREATMENT
Base-resin
Filler
Hardner
Plastic mould
The base-epoxy/BaSO4 mixture after a sonication treatment of 30’
Glass vial with
base-resin + BaSO4
Epoxy/BaSO4 sample (21.3% by weight of “Precipitated” BaSO4) cured in oven at 80°C.
BaSO4 dispersion into the base-resin component by using a sonicator bath (350W, 40°C)

8. BaSO4 DISPERSION BY USING A HORN SONICATOR
Alternatively, a horn sonicator can be used to achieve very good and stable dispersions of the BaSO4 powder into the base-resin component.
Cooling bath
(H2O)
Glass vial
Sonicator probe
Base-resin + BaSO4
White reflectance increases with the amount of dispersed BaSO4.

9. Dip coating technology
CONCLUSIONS
• Commercial white reflectance powders (barium sulfate, BaSO4) can be finely dispersed into the epoxy resin (Technovit Epox®) by using a sono-acoustic treatment.
• The filled epoxy resin can be perfectly cured by using the fast-curing hardner (2h in a oven at 80°C).
• The reflectivity of the composite material increases with the resin filling by BaSO4.
FUTURE ACTIVITIES
Optical characterization of epoxy/BaSO4 samples by diffuse-reflectance measurements and best composition evaluation (reflectance/adhesion balance).
Identify the best technology for a large-scale application of these formulations to the CsI crystals.
Dip coating technology