Enhanced solubility Ag-Cu nanoparticles and their thermal transport properties
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ALLOYING of metals with a different metal is a way of developing new materials that have better technological usefulness than their parent metals. Additionally, nanoscale materials show different structural and physical properties compared to the bulk samples, such as lower melting point[1] with decreasing particle size, etc. Studies on alloy nanoparticles also revealed that physical properties differ from what is observed in bulk samples.[2] Enhancement of solid solubility of alloy components with decreasing particle size is one of the prominent effects. It has been theoretically and experimentally shown that the enhancement of solid solubility in nanoparticles is possible in systems where equilibrium bulk solid solubility limit is very small.[2,3] Ag-Cu is one of the alloy systems that are naturally immiscible at room temperature. Under equilibrium conditions at room temperature, the mutual solid solubilities approach zero. The maximum solubility limit of Cu in Ag is 13.5 vol pct at the eutectic temperature of 779 °C, and rapidly decreases as the temperature decreases.[4] Nanofluids, consisting of nanoparticles suspended in a heat-transfer liquid, may offer significant enhancement of thermal conductivity, which is technologically important for cooling applications that rely on the efficient transfer of heat. This is a problem that affects such diverse facets of industry as ventilation systems, automotives, cooling towers, and chemical process plants. It has been previously demonstrated that nanofluids consisting of CuO or Al2O3 in water or ethylene glycol enhanced the thermal conductivity of the fluids.[5] Additionally, thermal conductivity of nanofluids has been associated with strong temperature ABDULLAH CEYLAN, Student, is with the Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, and the Physics Engineering Department, Hacettepe University, Ankara 06800, Turkey. KATIE JASTRZEMBSKI, Student, is with the Chemical Engineering Department, University of Delaware. S. ISMAT SHAH, Professor, is with the Department of Physics and Astronomy and the Department of Materials Science and Engineering, University of Delaware. Contact e-mail: [email protected] Manuscript submitted July 20, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS A
dependence[6,7] and a significantly higher critical heat flux than that of the pure fluid.[8] The present work is focused on the synthesis of Ag-Cu alloy nanoparticles by using the inert gas condensation (IGC) technique in which metal vapor flux is obtained and rapidly condensed by a carrier gas, which has high thermal conductivity. The evaporation method depends on the material to be evaporated and includes resistive evaporation, laser ablation, etc. Rapid condensation of atomic vapor limits the possibility of phase separation and also restricts chemical diffusion. Such metastable environment leads to the deviation from chemical equilibrium and supersaturated alloys can be formed. Evaporation temperature, carrier gas pressure, and flow rate are the main parameters th
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