The destruction time of the sediment column structure as a method for studying the dispersion system

In our laboratory, in the 1960s, a simple device was used to measure the destruction time of the sediment column structure that is proportional to the attachment forces between mineral grains. Using this simple device, measurements of the destruction time of the sediment column structure of coal grains precovered with n-alkane and n-alcohol films of different thickness were carried out. The measurements were conducted for different size fractions of coal grains precovered with a film which thickness was changed from 0 to 8 statistical monolayers. It was found that the destruction time of the sediment column structure of coal grains increased with increasing film thickness, reaching constant values for films whose thickness was bigger than 3–4 statistical monolayers. The destruction time also increased as the number of carbon atoms in the hydrocarbon chain of the liquids increased. The dependences of the reciprocal of the destruction time as a function of the diameter of the coal grains were linear, and by extrapolating these linear dependences to time equal infinity we determined the critical diameter of coal grains. The critical diameter was also calculated from linear equation of these dependences. The obtained results showed that the critical diameter values do not depend on the length of the hydrocarbon chains and the thickness of the films. To explain the influence of the film thickness and kind of the used liquid on the destruction time, the free energy of the interactions between coal grains covered with liquid film through water was determined, and comparison of the constants a and b in the equation expressing the reciprocal destruction time as a function of the diameter of coal grains to surface tension, density and molecular weight was made. On this basis, it was stated that the destruction time depends on the free energy of the interaction in the coal/film–water–coal/film system, and the contact plane results from the bulk and surface properties of the studied liquids.