A new technique particularly suitable for fabricating uniform, hollow silica spheres of controlled size and porosity is described. The technique, which combines sol-gel processing with a hollow-drop generation technique, consists of producing a continuous stream of uniform, hollow drops of a tetraethyl orthosilicate solution and then converting the drops into a rigid form by exposing them to an ammoniated vapor gelation medium. The parameters controlling the properties of the resulting silica spheres are the detailed chemical makeup of the reactant solution and the gelation medium, and the dimensions and relative positions of the nozzles used for drop generation. [

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