Metal oxide nanopowders play major roles in applications including recording media, catalysts, as fillers for plastics, or for forming ceramic prosthetics (hip replacements). Most commercial nanopowders are made by flame processing volatile, toxic and polluting metal chlorides. Researchers at the University of Michigan (UM) have developed a process that escapes metal chlorides furnishing the same products while greatly expanding the number and types of oxides accessible. This approach has generated metal oxide nanopowders that offer novel lasing behavior; act as new catalysts for auto and diesel exhaust cleanup as well as providing facile routes to prosthetic ceramics with exceptional control of final properties. The UM process uses turbulent flames to combust metal-organic complexes (not chlorides) dissolved in alcohols. Despite the unique materials made, the exact process(es) whereby combustion generates metal ions that condense to form nuclei, which coalesce to form particles primarily of kinetic products are unknown. Given the considerable potential of this process for creating novel nanomaterials, researchers at UM are conducting basic studies including computer modeling to delineate the steps involved in particle formation to identify the scientific principles whereby nanopowders form. These principles will then be used to design the synthesis of new nanopowders for applications including catalysts, ceramic materials with controlled/novel properties including for example transparent ceramics or lithium battery electrolytes.
TECHNICAL DETAILS: Liquid feed flame spray pyrolysis (LF-FSP), as developed at UM, provides a wide variety of single and mixed-metal oxide nanopowders that are often kinetic rather than the thermodynamic phases observed in most other nanoparticle syntheses. They have been shown to exhibit unique catalytic, photonic, electronic and ion conducting properties. LF-FSP uses a turbulent rather than a laminar flow flame. While laminar flow flames are easily modeled, turbulent flames are much less so. Consequently, most of the UM discoveries arise from empirical efforts. Researchers at UM believe that establishing a detailed understanding of the scientific underpinnings to LF-FSP processing will provide the basis for greatly expanding its utility in providing new nanopowders with novel properties especially for catalysts, photonic materials and in low temperature processing of dense, ceramic materials. The Laine and Violi groups have teamed together to develop a predictive model that identifies how specific processing parameters (e.g., temperature) contribute to the size and chemical composition of nanopowders. The model development is being guided and validated by the experimental techniques. In particular, they will explore the formation of spinel phase materials MOAl2O3 (M = Mg, Co, Ni, etc.) at compositions outside thermodynamic phase fields. The process variables that control the formation of these nanopowders are being assessed incisively to establish processing-property relationships of use in the modeling studies. The expected outcome entails controlled approaches to novel nanopowders for multiple practical applications. Research done in both groups is being used to train graduate and undergraduate students in the design, synthesis, characterization and processing (and handling) of nanopowders. At the undergraduate level, students from the undergraduate research opportunity program (UROP) are working with graduate students to learn how to characterize nanopowders using multiple spectroscopic tools, to map properties and to use the characterization data to develop theoretical models of the formation processes and methods of controlling what materials/nanopowders form.