Insulation materials, thermal weather resistance

The pottant is the vibration damping, elastomeric material that immediately surrounds both sides of the fragile solar cell wafers and their electrical contacts and interconnects. It must be soft, transparent, electrically insulating, weather resistant, chemically inert and form strong and stable adhesive bonds to the surfaces it touches. It protects the cells from stresses due to thermal expansion differences and external impact and isolates them electrically. The pottant also helps protect the circuit metallic contacts and interconnects from the corrosive effects of moisture, salt, smog, etc. 

The filler then contributes to reinforcement, thixotropy, and bulk. Since most of the fillers are mineral-like inorganic materials, they generally don t add or detract from the intrinsic silicone properties for which the sealants are most often sold, such as good electrical insulating properties, weather resistance, heat stability and low temperature serviceability. Organic fillers (polymers, resins, rubbers) have been added to some silicones and indeed enhance certain properties or reduce cost but always at the expense of another property. The property most often sacrificed is thermal stability. 

Asbestos cement materials are widely used due to their good mechanical properties, low thermal conductivity and resistance to weathering, frost and rotting. The slurry of asbestos and cement can also be processed directly using a spray process, as so-called asbestos spray for fire-retarding layers as well as for thermal (hot and cold) and sound insulation. 

The success of silicones adhesives is further due to a range of properties derived from the primary chemical structure. These include hydrophilicity/hydrophobicity balance, chemical resistance, electrical insulation, resistance to weathering, stability to extremes of temperature, resistance to thermal shocks, high elasticity, good tear strengths, capability to seal or bond materials of various natures, good electrical resistance, and so on. 

The highest resistance to heat flow comes from the air entrapped in the cell. Still air has one of the lowest thermal insulations, 25mW/mK (Table 4.4). Therefore, polymeric materials in the form of foam have more entrapped air and show improved thermal insulation, the As factor, which depends on the type of polymer itself and contributes approximately 30% of the total resistance to heat flow. Therefore, the type of polymer used in thermal insulators is the next major factor to be considered while designing a thermal insulator. The other two contributions, i.e. Aj, due to the radiation across the cell of the foam and due to the convection of the gas, is kept to optimum levels by proper design of the cell structure of the foam coating. Requirements for extreme cold weather are ... 

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