Synthesis of Silica Particles from Sugarcane Bagasse Ash for Its Application in Hydrophobic Coatings ^†

: Wastes such as sugarcane bagasse ash (SCBA) can be used as raw material in ceramics by the elaboration of bricks and tiles and the glass industry, due the high amount of silica in its composition (>70%). Another application for SCBA is the synthesis of metallic silicates. In this work, we study the synthesis of sodium silicate with SCBA as the main raw material and the future application of sodium silicate for the preparation of silica particles in order to create hydrophobic surfaces for ceramic materials to prevent their erosion. The sodium silicate synthesis was carried out by the thermochemical method with batches of ash and sodium carbonate in a 1:1 sodium oxide–silicon oxide molar ratio. The thermal treatment was in an electric furnace at 800 °C for 8 h. Then, for the synthesis of the silica particles, the sodium silicate was dissolved in water, and then we added methanol in a 3:2 water methanol volume ratio. The solution was left to age for an hour to create the Si-OH bond. Finally, tetraethylorthosilicate (TEOS) was added and the solution was stirred for 2 h to create a hydrophobic and hydrolytically resistant siloxane by the displacement of H in the Si-OH bond. The application of the solution was by the spray-coating method over substrates of concrete and red clay with the application of 10, 15, and 20 layers. The hydrophobicity was evaluated with the water contact angle test, with the results of contact angles above the 110°, thus demonstrating the capacity of a waste for the generation of coatings to prolong the useful life of building materials.