Structure Formation in Concentrated Disperse Systems under Dynamic Conditions
Regularities of combination of mechanical (vibration) effects and surface-active additives of various chemical nature and structure in the processes of formation and destruction of structures in concentrated disperse systems have been studied: in highly dispersed powders (such as SiO2, CaCO3, CaF2 and others) and also in systems with a liquid dispersion medium (in aqueous dispersions of calcium aluminates and silicates, of calcium bentonite and in non-aqueous dispersions, such as graphite in vaseline oil and others).
It is shown that the formation of a saturated absorption layer of surface-active substances (for instance, octadecylamine for quartz powder, stearic acid for calcium carbonate), while substantially weakening the strength of adhesion in contacts, at the same time, as a result of a reduction in the liophobic-liophilic mosaicity of the surface or particles, drastically diminishes the scatter in the strength of these elementary atomic and coagulation contacts. There has been found an effect of mutual strengthening of the action of mechanical factors (vibration) and adsorptionactive medium, characterized by a continuous growth of the relationship D = I0/I1 with an increase in the degree of destruction of the structure, i.e. of the decrease of effective viscosity from its maximum value ηv0 to the minimum viscosity of the ultimately destroyed structure ηvmin (I0 being specific power of mechanical (vibration) actions without the Introduction of surface-active additives and I1, in combination with such additives). A concept is introduced concerning the dynamic criterion of the action of surface-active substances, which is determined by this relationship Dm = Io/I1 with the extreme destruction of the structure ηv = ηvmin. The maximum value Dm is shown to be reached with the Introduction into concentrated disperse systems of chemically adsorbing surface-active substances with a developed hydrocarbon chain, which form a saturated adsorption layer on the surface of the particles. The results of investigations in the regularities of combination of mechanical (vibration) actions and surface-active additives have found wide practical application in various technological processes, including the technology of blending multi-component disperse systems; in heterogeneous mass transfer processes used in chemical engineering and carried out in a fluidized bed; in the technology of producing various kinds of dispersed materials rich in solid phase.