PREPARATION OF ZnS NANOPARTICLES BY ELECTROSPRAY PYROLYSIS

Zinc sulfide particles 20-40nm in diameter were prepared by electrically driven spray pyrolysis. Solutions of ethyl alcohol with zinc nitrate (Zn(NO3)2) and thiourea (SC (NH2)2) at concentrations from 0.0025 to 0.2moll-1 and electrical conductivities between 10-4 and 10-1Sm-1 were electrosprayed from steady cone-jets at flow rates from 0.05 to 0.25mlh-1, with positive and negative polarity. The initially highly charged drops formed were neutralized by bipolar ions from a radioactive source to increase the overall transmission efficiency through a reactor furnace. This process was made particularly effective by the innovation of placing the ion source directly within the electrospray chamber. The diameters of the final ZnS particles were measured on-line by a differential mobility analyzer and a condensation nucleus counter. In spite of ambiguities in the flow rate of liquid through the cone-jet (associated to solvent evaporation from the meniscus), these diameters agree approximately with values expected from available scaling laws. Transmission electron micrographs also confirmed these results. Electrospray pyrolysis is hence able to generate nonagglomerated and spherical ZnS nanoparticles with geometrical standard deviation (sigma)g of about 1.3.