In the manufacture of materials of different natures, it is very common for suspensions of solid particles to be used at some stage of the processing, also known in some sectors, such as slurries or slips. Unlike solutions, where solids are dissolved in water or another solvent, in suspensions the particles are only dispersed. In order for these suspensions to be stable over time and not present excessive sedimentation or viscosities incompatible with transport operations, as a rule, additives called dispersants (or deflocculants) are used in industrial processes.
These chemical additives (generally made up of polyelectrolytes) hinder the formation of agglomerates of particles in suspensions through different mechanisms, such as electrostatic repulsion, sterile repulsion or the formation of complexes with certain ions present in the suspension. Consequently, the viscosity and thixotropy of suspensions decrease, often allowing the formation of suspensions with very high solids concentrations.
Dentre os dispersantes The most commonly used are sodium silicate, phosphates and sodium polyacrylates, which can present very different performances depending on the characteristics of the suspensions in which they are used. In order for the effectiveness of a dispersant to be analyzed and the ideal content for application in a given suspension to be determined, deflocculation curves are generally used. This tool consists of a laboratory analysis, where the relationship between the apparent viscosity of suspensions and the addition content of dispersants is determined.
In many cases, the aim is to seek the point of maximum dispersion of the suspensions, where the apparent viscosity and thixotropy of the suspensions are minimized. In other processes, a certain degree of thixotropy is sought, so that the addition of dispersant is controlled, so as to produce only partial dispersion of the particles.
Deflocculation curves can also help evaluate the combined use of different dispersant families, since in many cases the combination of two or more deflocculants is more effective, as they may have different and complementary mechanisms of action. In this context, it is essential to know the dispersants available on the market and their operating principles.
To obtain good results in the laboratory, which are then successfully transferred to industrial processes, it is essential to establish meticulous laboratory procedures, bearing in mind that the rheological behavior of suspensions is affected by a series of factors, such as temperature, stirring speed, suspension preparation history, etc.
Interessado no tema? O CRC realiza estas analyses making use of rotational viscometers and can also contribute to technical training courses ou consultorias sobre o assunto.