Combustion synthesis of metal/metal oxide nanocomposite materials.

In the current work, a new method for the synthesis of nanocomposite materials is demonstrated. The technique is based on the hypothesis that staged decomposition and nucleation of multi-phase precursors and products can be used to create nanocomposite materials in a combustion system. As part of this work, a novel particle feed system (PFS) has been developed to inject solid-phase particle precursor materials into the reaction zone of a multi-element diffusion flame burner (a Hencken burner). Nanocomposite materials designed at the molecular level have considerable potential to improve numerous applications. In particular, tin dioxide (SnO 2) materials are excellent active materials for gas-sensing applications. Tin dioxide was selected for the demonstration studies because gas sensor applications utilizing SnO2 show strong sensitivity to nanocomposite properties, such as the dopant material and the size of the tin dioxide crystallites. In the study, several dopant materials (Au, Pd, CuxO, Alx Oy) were examined as well as multiple precursors for the same additive (e.g. gold acetate and metallic gold). The resulting materials were analyzed using a variety of techniques including: Transmission Electron Microscopy (TEM) imaging, TEM Energy Dispersive Spectroscopy (EDS), Scanning Electron Microscopy X-ray Energy Dispersive Spectroscopy (SEM XEDS), and X-ray Diffractometry (XRD). The results of the materials analyses provide valuable information on the composition, phase, size, and distribution of the additives in the SnO 2 matrix. A large range of control of the SnO2 crystallite size was demonstrated from the smallest dimension of 4 nm obtained using a high-temperature tetra-methyl tin (TMT)/gold acetate reactant precursor combination to the largest dimension of 11 nm using a TMT/pure metallic palladium reactant precursor combination. The results demonstrate the precursor properties and the burner operating conditions can be used to control the composite properties such as the additive loading and morphology. The nanocomposite morphology and other materials characteristics were also used to identify the physical and chemical pathways important in the mixed-phase combustion synthesis system. For example, the gold acetate precursor particles were irregular in shape and greater than 1 mum in size (approximate diameter). However, the gold particles identified in the nanocomposites using TEM imaging and elemental analyses indicate spherical gold particles with an average diameter of 83 nm. As evidenced by these results, significant particle restructuring occurs consistent with phase change and decomposition of the solid phase precursor.Ph.D.Applied SciencesMechanical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/124889/2/3163889.pd