MECHANISMS OF DEGRADATION OF POLYMERIC THERMAL CONTROL COATINGS. PART II: EFFECTS OF RADIATION ON SELECTED PIGMENTS

An investigation has been conducted on the mechanisms of degradation of pigments and polymeric coatings for thermal control applications exposed to ultraviolet (uv) and electron irradiation. The materials investigated were rutile (titanium dioxide) and strontium titanate (SrTiO3). The effects of treating the pigments by heating in various gas ambients at elevated temperatures were studied using gas chromatography and electrical conductivity measurements. Significant changes in the surface characteristics were found to result from these treatments. A comparison was made between the reflective degradation in binderless pigments and silicone-binder coatings exposed to uv light, to energetic electrons, and simultaneously to uv light and electrons. Evidence for stabilization of defect sites by charge capture was discovered in the binderless pigment experiments. This mechanism for defect stabilization does not appear as prevalent in the silicone-binder coatings, since the binder apparently passivates the pigment surface to some extent. The fluence dependence of the degradation and the recovery of the damage in vacuum and in the presence of various gas ambients was also studied. See also Part 1, AD686448. Prepared in cooperation with General Dynamics/Convair, San Diego, CA, Space Sciences Lab.