Microencapsulated Cloud Seeding Materials

A process was developed for encapsulating hygroscopic, cloud-seeding agents, sodium chloride and urea. The encapsulation process involves depositing the coating polymer, ethylcellulose, onto finely divided powders using a phase separation-coacervation technique. The process produces small encapsulated aggregates, the size and distribution of which can be varied. Encapsulated materials prepared by the process are unique in that they are void, essentially, of powder fines. Laboratory tests of both encapsulated sodium chloride and urea proved the powders to be resistant to clumping and caking associated with premature moisture sorption occurring during storage and handling. The encapsulation coating polymer, ethylcellulose, is water insoluble, but is permeable to water vapor, water and solutes. Hence, water sorption and particle growth properties resulting from exposure of the encapsulated particles to humid atmospheres are effected by diffusion-mass transport processes. Laboratory testing of encapsulated sodium chloride and urea materials in simulated warm fog atmospheres revealed water sorption characteristics which were comparable to unencapsulated particles having equivalent dimension.