Aerogel for Highly Thermally Insulative Coatings

By James Pidhurney, Peter F. Pescatore

Recognizing the advantages of a high performance insulative coating, some advanced coatings manufacturers are exploring the use of silica aerogel as an additive to paint to achieve significantly lower thermal conductivities. These coatings, a new class of materials called highly thermally insulative coatings (HiTICs), are designed to offer energy savings along with burn protection. Within the insulative coatings space, there traditionally have been two main additives promoted as providing an insulation benefit: glass and ceramic spheres.

These mysterious little balls are hollow in nature, and trap a small amount of air inside. This trapped air can be considered “still” in nature, and contribute an impressive thermal conductivity of 0.015 BTU/ft.hr.°F (26mW/mK). Factoring in the glass or ceramic shell that holds the air, individual spheres in the range of 0.029–0.115 BTU/ft.hr.°F (50–200 mW/mK) are easily produced in a variety of sizes and wall thicknesses. When mixed with paints at high loadings, they can achieve an overall thermal conductivity of 0.046+ BTU/ft.hr.°F (80+ mW/mK).

This performance, though far from the still air value of 0.0015(26), is still significantly better than paint alone with a typical thermal conductivity of 0.115 BTU/ft.hr.°F (200+ mW/mK) (lower is better for reducing heat transfer). If shear forces can be controlled well enough during mixing and spraying, it is possible to eventually build up (with 20–50 coats) enough thickness to have a meaningful R-value of approximately 1.7 per in. of dry coating. Unfortunately, if the control is insufficient, spheres break down, creating 0.517 BTU/ft.hr.°F (1000 mW/mK) thermal shorts in the coating.