Low Emissivity Coating Options for the HET Enclosure 18 September 2002 John Good

Choices Available Aluminized Mylar (3M product #8437) –Emissivity = 0.03 –Solar Absorption = 0.15 Aluminum Foil (3M product #427, 2.8 mil. Thick, Compac #804 – Bron Tapes, Inc.) –Emissivity (new) = 0.03 –Emissivity (heavily oxidized) = 0.20 –Solar Absorption (new) = 0.15 LO/MIT I/II –Emissivity = 0.21 –Solar Absorption = 0.22 TiO 2 (White Paint) –Emissivity = 0.87 –Solar absorption = 0.25

Where they are in use (an incomplete list). Aluminized Mylar –SPIE technical papers. –Medical Imaging Equipment Aluminum Foil –WIYN, LBT, IRTF, Magellan, CTIO? LO/MIT I –Gemini, GTC

Method of application. Aluminum Foil –Clean surface with 50/50 alcohol/water solution and allow to dry. –Prime with 3M product #94 primer. Wet surface with rag and let dry for 5 minutes. –Cut to shape Paper linered acrylic adhesive. –Peel and stick. Smooth with squeegee. LO/MIT I –Water blast. –Dry. –Roll-on (2 coats).

Longevity and Maintenance Aluminum Foil –No problems reported from facilities using foil. WIYN – 8 years old. –Failure mode: Adhesive failure (de-lamination). –Replacement: Remove, Clean, & Re-apply. LO/MIT I –Company line: 6-7 Years “Coating on steel roof still good after 14 years.” –Failure mode: Abrasion. 100% silicone binder is very soft, flexible and thin (1/2 to 1 mil.). –Replacement: Light water blast, recoat with roller.

Cost (very preliminary) Dome, CSB roof, GTAG roof –Aluminum Tape: $58-60k $38,000 + Labor (~8-12 man-weeks) + $7k to $10k (125ft. Manlift) + $1,500 (Misc. Supplies). –LO/MIT I: $19-21k $5.5k (paint) + Labor (~6-8 man-weeks) + $7k (125ft. Manlift) + $1,500 (Misc. Supplies).

Test plan. Materials –Aluminum Tape Does the primer attack the present finish on the dome? Ease of Application. Day/Night thermal performance. –LO/MIT I Ease of application. Adhesion. Day/Night thermal performance. Location –Upper right hand corner of dome aperture (looking out of the dome).

Information Sources 1.Chas Cavedoni – Gemini 2.Bob Aresty – SOLEC (manufacturer of LO/MIT) 3.Dan Neff – M3 Engineering & Technology, Inc Don Ketchem (Chemical Engineer) - 3M Corporation 6.George Kuenig – Superintendent IRTF 7.Bron Tapes of Nevada, LLC 8.