Thermal diffusion of magnetic nanoparticles in ferrocolloids: Experiments on particle separation in vertical columns

Experiments on nonstationary separation of nanometer-sized Fe₃O₄ particles of hydrocarbon-based ferrocolloids in a flat vertical thermal diffusion column are performed. By using a modified separation theory which accounts for an one-dimensional mixed (thermal and concentration) convection in the column, the Soret coefficient of magnetic nanoparticles are calculated. It is shown that particles are transferred in the direction of decreasing temperature. The thermal diffusion ratio α_T for magnetite particles suspended in tetradecane reaches the value α_T ≈ - 20. Neither a dependence of ≈_T on temperature nor any changes in particle-size distribution curves during the separation are observed.