Evaluation of the possibility to use powders of polymineral silica-containing sands as a hydrophobizing coating

Introduction. An important performance characteristic of many building materials is one related to water. Therefore, hydrophobization of the surface of the material is an important task, which at the current level is solved by applying special means. It has been found that it is possible to impart water repellent properties to the surface by using polydisperse mineral materials capable of forming a rough surface. Fine powder from polymineral sand is proposed to be used as a hydrophobisate. The revealed functional relationship between the specific surface and the value of the average particle diameter of the powders, having a linear character, allows assessing their morphological structure and predicting the powder's ability to form a rough layer that enhances the water repellent properties of the surface. Methods and Materials. Four deposits of polymineral construction sands are selected as raw materials. The samples were washed and dried. Then their size modulus and true density were determined. To obtain finely dispersed powders, the raw material was ground by dry dispersion. Particle dimensional characteristics were determined by photon-correlation spectroscopy. The visual characteristic of the shape and size of the particles is determined on a laser analyzer. The specific surface area of highly dispersed rock systems was determined by gas sorption, according to BET theory. Measurement of the edge stationary wetting angle was carried out by applying a drop of distilled water to the powder surface. Results and Discussion. The dimensional characteristics of the obtained fractions showed that with a milling time (30 min) for the sands of all deposits, the average particle size (d) is 360±45 nm. At the same time, the sands of the Kenitsy and Nekhtskoye deposits have the highest values of specific surface area (Ssp). The functional relationship between the Ssp of the powders tested and 1/d was determined. The resulting linear dependencies were characterized by mathematical expressions of the form Ssp = (a/d)+b, a where reflects the rate of change in the specific surface value as the average particle diameter of the samples changes; b – is the regression line shift associated with the asymmetric shape of the particles and the non-uniformity (roughness) of the surface. It has been found that as the value of b increases, the degree of inhomogeneity of the surface formed by these particles also increases. Determination of the edge wetting angle of the surface of the powders under study showed that as the grinding time increased, the wetting angle (surface hydrophobicity) increased. So, for the surface of the fine powder of the Nekhtskoye deposit, the wetting edge angle reaches a value (114о) close in magnitude to superhydrophobicity (120о). Conclusion. The experiments showed the validity of the proposed working hypothesis related to the possible assessment of surface hydrophobicity by the experimentally determined dependence of Ssp = f (1/d). This technique can be used to select mineral powders whose fine systems are capable of hydrophobizing (if necessary hydrophilizing) the surface of the material.