Strengthening Silicate Coatings on Quartz Particles with the Addition of Aluminum Phosphate

Strengthening Silicate Coatings on Quartz Particles with the Addition of Aluminum Phosphate

For aesthetic purposes, quartz particles are coated to provide a wide array of colored sands. These colored sands are used extensively in roofing shingles and pool plasters. The coating is a proprietary mixture whose base is sodium silicate. Sodium silicate solutions are also referred to as water glass. Upon heating to remove water, a hard amorphous silicon dioxide coating is left behind. This coating is rugged but not a tough as crystalline quartz. This study investigates the use of Goldschmidt’s rules of substitution, a fundamental theory from geochemistry, to enhance the coating of the quartz particles. Aluminum phosphate was chosen as a potential hardener based on its ability to undergo coupled substitution in the silica lattice. Hardness was determined through scratch test and increased bond strength confirmed through FTIR. Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) was used to monitor the escape of toxic heavy metals from the coating into surrounding water. The increase in strength and durability as well as the modified coatings ability to inhibit the loss of toxic metals through solubilization are reported.