Advanced photochemical processes for the manufacture of nanopowders: an evaluation of long-term pilot plant operation

In this study, a UV light-based technology for the syntheses of nano-dimensional metal oxides feasible in an industrial scale is proposed, based on our long term experience with the operation of a photochemical pilot plant. We demonstrate the synthesis, properties and manufacturing costs with a case study for ZnO, Y3Al5O12 and Gd3Ga2Al3O12 materials that are comparable with laboratory-scale yields and purity. The process relies on irradiation of aqueous solutions containing dissolved precursors, typically formate anions and soluble metal salts, with 254 nm UV light. Depending on the solution composition, UV irradiation leads to the formation of nanocrystalline or amorphous products of particulate or gel-like character. These materials can be either used as is, or further processed, usually by drying in air and heat-treating at elevated temperatures (200-1200 degrees C), leading to a fine powder suitable for a subsequent use in different applications. A number of syntheses were developed during the past few years to provide an evaluation of various aspects influencing the manufacturing process such as solution composition or character of the product. The observed yields were correlated with both the concentration of the salts in solutions and the irradiation time; then, photochemical production rates were determined, and the potential of this method for up-scaling was evaluated. X-ray diffraction results and radioluminescence measurements prove that the phase purity and emission spectra of the produced materials are fully comparable to those from laboratory-scale preparations. Realistic assumptions and considerations were then used for a comprehensive estimation of manufacturing costs in the described photochemical pilot plant and the parameters leading to lower manufacturing costs were identified.