KINETICS AND MECHANISM OF COARSENING FOR NANOPARTICLES OF SULFUR AND ALKALINE EARTH METAL SULFATES COPRECIPITATED FROM TRUE POLYSULFIDE SOLUTIONS

Alkaline-earth metal sulfate nanoparticles (ALMS) and nanocomposites of ALMS with sulfur nanoparticles (nanosulfur) are synthesized from aqueous solutions of polysulfides (ASP) of alkaline-earth metals (AEM) of calcium, strontium, and barium (CaSn, SrSn, BaSn; n>1). AEM ASP are obtained in the aqueous medium at temperatures of 70 and 90°C as a result of the reaction between metal hydroxide and sulfur. It is found that the use of sulfur mechanically activated in the disintegrator for synthesis allows obtaining higher concentrations of AEM ASP in shorter times. To establish possible mechanisms of mechanochemical recrystallization in liquid media, the method of static light scattering is used to determine the kinetics of particle aggregation as a result of reversible aggregation of sulfur and AEM sulfate nanoparticles. It is found that at first particles with sizes about 30 nm are formed, which are enlarged to tens of microns with time. The values of the rate constant of particle aggregation (agglomeration) (Q) increase with the concentration of acids, and their optimal value for the realization of the Q-mechanism is 10%. It is found that applying a surfactant (neonol; concentration 5%) reduces Q by multiple times. It is also found that the value of Q grows with the temperature, and the activation energies of S/MeSO4 particle aggregation processes are determined for the optimum interval 300÷350 K. Practical aspects of the results of the work are considered by the example of using the obtained samples to germinate wheat grains, as well as hydrophobicity of S/MeSO4 samples due to the presence of sulfur in them.