Sonochemical synthesis of nanophase metals, alloys and carbides

Abstract

Sonochemistry arises from acoustic cavitation; the formation, growth, and implosive collapse of bubbles in a liquid. The implosive collapse of bubble generates localized hot spot; temperature of similar to 5000 K and pressure of similar to 1800 atm, with heating and cooling rates that exceed 10(7) K/s. Using these extreme conditions, we have developed a new synthetic technique for the synthesis of amorphous and nanostructured inorganic materials. When irradiated with high intensity ultrasound in low volatility solvents under argon, volatile organometallic precursors produce high surface area, amorphous solids that consist of agglomerates of nanometer clusters. For Fe and Co, nanostructured metals and alloys are formed that are non-crystalline by x-ray, neutron, and e-beam diffraction. For Mo and W, metal semicarbides, e.g., Mo2C are produced. These nanostructured solids are active heterogeneous catalysts for hydrocarbon reforming and CO hydrogenation. Using polymeric ligands (e.g., polyvinylpyrrolidone) or oxide supports (alumina or silica), the initially formed nanoscale clusters can be trapped as colloids or supported catalysts.