The use of the contact angle as a criterion for the degree of hydrophobization of a solid surface and gypsum particles in suspensions containing surfactants showed that an increase in the concentrations of ethyl silicone oil and soap naphtha in the initial gypsum suspensions led to an increase in the contact angle of wetting of solid particles to 82.5° and 77.5°, respectively. However, on the surfaces of the formed solid samples containing ethyl silicone oil, a drop of water spreading and its rapid absorption were observed. Solid samples containing soap naphtha in an amount of 3% had a hydrophobic surface characterized by a contact angle of 82.2°. Probably, the hydrophilic and hydrophobic properties of the solid surface of the material are determined by its bulk structure at the stage of formation, including under wave action. In this case, the porous-capillary structure of the formed samples containing gypsum and surfactants affects the determination of the wetting criterion.

Keywords: contact angle, hydrophobization, gypsum, soap naphtha, ethyl silicone oil, ultrasonic treatment