SORET COEFFICIENT OF NANOPARTICLES IN FERROFLUIDS IN THE PRESENCE OF A MAGNETIC-FIELD

Experiments on a nonstationary separation of nanometer-sized Mn0.5Zn0. 5Fe2O particles of hydrocarbon-based ferrocolloids in a flat vertical thermal diffusion column are performed. By using a modified separation theory which accounts for a one-dimensional mixed (thermal and concen tration) convection in the column, the Soret coefficient of lyophilize d nanoparticles from the separation curves are calculated. It is shown that in a zero magnetic field particles are transferring toward decre asing temperatures. The thermal diffusion ratio a,reaches a value alph a(T)approximate to+20. A significant influence of a uniform magnetic f ield B on particle separation is observed. If B is oriented along the temperature gradient del T, a strong decrease in thermal diffusion coe fficient takes place whereas the transversal field B perpendicular to del T causes an intensification of particle thermophoretic transfer. B oth effects qualitatively well agree with theoretical predictions base d on a hydrodynamic theory of particle thermomagnetophoretic motion. ( C) 1998 American Institute of Physics.