Evaluation of Optical Properties of Silicate White Thermal Control Paints Employed in Spacecraft by Taguchi Method

Thermal control paints are coatings with special thermo-optical properties that carried out on the outer surface of spacecraft to control the input and output heat. In the present study, to evaluate the effects of different factors on these coatings, ZnO, TiO2 and synthesized pigments and two different compositions of potassium silicate binder with three pigment to binder ratios were used to produce different coatings. The fabricated coatings were applied on the grounded and anodized Al substrates. The design of experiment was performed by Taguchi method including nine experiments. The results of solar absorption and thermal emission indicated that the pigment type was the most important processing parameter and the type of substrate preparation had also a significant effect. In fact, the ZnO pigment had the higher thermal emission and the anodized substrate had the lower solar absorption. The binder composition and pigment to binder ratio had no significant effects on thermo-optical properties. The morphological analyses were carried out by FE-SEM, indicated that all pigments had the similar morphologies and suitable distribution in applied coatings. It can be concluded from the obtained results that the sample consisted of ZnO pigment, the resin with 44.25 solid percentage and SiO2/K2O equal to 1.925, pigment to resin ratio of 4:1 and anodized substrate, can be considered as a optimum specimen.