Weather Resistance of Organosilicate Coatings in a Tropical Climate Depending on the Choice of the Pigment

The results of a study of the weather resistance of protective and decorative organosilicate coatings prepared using organosilicate compositions based on polydimethylphenylsiloxane as a binder and hydrosilicates as fillers are presented. The color of the coatings varies due to the use of pigments: natural FeO_x minerals of yellow, red-brown, and brown shades of flowers. Using X-ray phase and X-ray fluorescence (XRF) analysis, it is established that the composition of minerals is primarily determined by iron oxides in the crystalline modification of hematite (α-Fe₂O₃) and goethite (α-FeO(OH)). Pigments contain a small number of impurity compounds of a number of elements that contribute to the color range of the coatings. Organosilicate coatings are exposed for 11 months in the tropical climate of two climatic zones of Vietnam (in the suburbs of Nha Trang and Ho Chi Minh City). The high corrosion resistance and color stability of the coatings are established during the entire test period. According to slight changes in the color and gloss, revealed by spectrophotometric and photoelectric methods, it is shown that higher resistance to solar radiation and other adverse climatic factors is typical for coatings with a brown pigment based on hematite; and the lowest, with a yellow pigment based on goethite.