Precipitation of Barium Sulphate Nanoparticles in Microemulsion: Experiments and Modelling Fällung von Bariumsulfat Nanopartikeln in Mikroemulsionen: Experimente und Modellierung

Today, the scenario of a well-controlled large-scale production of nanoparticles is a very important aspect in nanotechnology. The present work aims at the investigation of different engineering aspects on the production of nanoparticles using microemulsions, which lead to possible process control. Prior to the precipitation process, this study explains that the phase behaviour of the ternary as well as of the quaternary mixture (with reactants) has to be analysed to identify microemulsion regions being suitable for nanoparticle precipitation. Dynamic light scattering had been used for determining the droplet size and viscosity measurements had been undertaken to predict the internal structure of the fluid. Bulk phase precipitation of BaSO4 was also conducted at different operating conditions in order to get basic understanding of the process itself. Generally a microemulsion made out of water, cyclohexane and surfactant is loaded with two reactants, BaCl2 and K2SO4, to carry out BaSO4 precipitation. A non-ionic technical surfactant, Marlipal O13/40 is employed, as this surfactant is cheap and available in big quantities and therefore preferred for a scale-up approach. The influence of suitable process control parameters like the feeding rate, the stirring rate, the feeding sequence, or the initial concentrations of the reactants on the particle size has been studied to gain a deeper understanding of the process formation of nanoparticles in a non-ionic water/oil microemulsion. The particle precipitation was carried out in a semibatch reactor. Transmission electron microscopy was used to analyse the size, the size distribution, and shape of precipitated nanoparticles. A measurable influence on particle size was found for different initial concentration ratios of the two reactants. It was also found that with increasing particle size the shape changed from spherical to cubic. A corresponding simplified mathematical model based on mass balances qualitatively confirms the observed changes in particle size. Argumentations based on the droplet occupancy number, the critical nucleation number and the corresponding number of nucleated particles are given to explain the change in the mean particle size.