The synthesis and characterization of solid-state materials produced by high shear-hydrodynamic cavitation
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A new method for the synthesis of complex metal oxides, based on hydrodynamic cavitation, was used to prepare pure phase, nanostructured solid-state materials. The continuous process afforded a wide variety of metal oxides in grain sizes of 1-10 nm. Catalysts, ceramics, superconductors, piezoelectrics, and zeolites were prepared by cavitational synthesis. The method enabled the synthesis of fine particles of metals and metal oxides supported on high surface area supports such as silica, and the synthesis of fine particles of cubic zirconia without ion modification.
I. INTRODUCTION We report a novel method for the general synthesis of complex metal oxides based on performing the synthesis under conditions of high shear and hydrodynamic cavitation generated by mechanical means. These studies resulted in the synthesis of a wide variety of metal oxide catalysts, ceramics, superconductors, electronic materials, and zeolites in most cases as single phase materials. In all cases the finished solid-state materials demonstrated much higher phase purities and smaller particle sizes as compared to identical formulations using classical, coprecipitation methods of synthesis. In most cases, the high temperatures generated by the cavitational synthesis resulted in the in situ calcination of the intermediate gel salt, resulting in the direct formation of the pure phase metal oxide or hydroxide without any postsynthesis calcination. The examination of a wide variety of representative metal oxides under conditions of the most forcing cavitational effect resulted in the synthesis of nanophase, crystalline materials.1 The cavitational method of synthesis is viewed as a general technique for the direct preparation of nanophasic materials in large quantities. Conventional methods of synthesis in several systems have resulted in the preparation of phase pure materials of a few nanometer grain sizes. This is usually accomplished through the application of a variety of chemical manipulations which is specific to each system. The advantage of this process is that one is required to do less chemistry on each system to achieve phase pure, nanostructured materials. The method of generation of mechanical cavitation in these studies used laboratory models M-110T and M-110EH Microfluidizers®,2 which enables the generation of a few kilograms per a) Author
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to whom correspondence should be addressed. J. Mater. Res., Vol. 10, No. 9, Sep 1995
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hour. Much larger equipment is currently available with capacities which are 400 kg/h to 2000 kg/h, depending on the desired intensity of the cavitational effect. This equipment is currently used for the large scale, commercial processing of solid slurries, and it has not yet been demonstrated to produce commercial size quantities of ceramic materials. Cavitation generated acoustically by ultrasound has been used in the processing of already formed metal oxides3 and in the destruction of chlorinated hydrocarbons.4 Suslick reported3 evidence for the
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