The influence of methods of suspension preparation on the redispersion degree of titanium dioxide powder

Abstract

The redispersion of titanium dioxide powder during the preparation of its aqueous suspensions by mechanical stirring has been considered. The model of the destruction of the spatial structure of powders, which exists in the air, during the preparation of its [titanium dioxide] aqueous suspensions is based on the process of gradual withdrawal of the peripheral particles from the compositional parts most closely associated with it and the establishment of the equilibrium: aggregates <=> primary particles. Following the introduction of air-aggregated powders into the liquid environment, the following physicochemical processes occur, namely: a) the redispersion of the powder particles due to the action of mechanical forces during the stirring of suspensions (destruction of aggregates existing in air); b) the interaction of the components of the liquid medium, in particular hydrogen ions, ions of low molecular weight electrolytes, surfactant molecules with the surface groups of solid particles and the establishment of a new interfacial equilibrium; c) interparticle interaction related to the change in the balance of far-reaching surface forces due to the establishment of a new interphase equilibrium. Five methods for preparing suspensions of titanium dioxide have been used to show that during their preparation, agglomerates of primary particles containing regions of closed air, the size of which depends on the ratio of the intensity of successive processes of fluid flow over the surface of the powder and the formation of areas of closed air and fluid percolation in the formed area of closed air, may occur. The appearance of such agglomerates complicates interparticle interaction and affects the degree of redispersion of powders in liquids. It has been revealed that the presence of surfactants in suspensions causes changes both in the interparticle interaction and in the occurrence of regions of closed air in the intermediate particle agglomerates. Thus, the equilibrium dispersive characteristics of the obtained highly dispersed systems depend on the ratio of the intensity of such processes as the fluid flowing over the surface of the powders and the formation of areas of closed air and subsequent percolation of fluid in the area of closed air. However, it should be borne in mind that the role of these processes depends on the dispersion of the primary particles and their spatial structure in the air, i.e. the whole pre-history of how these powders have been manufactured. Keywords : water suspension, interparticle interaction, powders aggregation, titanium dioxide.