Enhanced Solubility of Cu in Ag Nanoparticles Synthesized by Inert Gas Condensation
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Enhanced Solubility of Cu in Ag Nanoparticles Synthesized by Inert Gas Condensation Abdullah Ceylan a, b, C. Ni c, and S. Ismat Shah a, c a Department of Physics and Astronomy, University Delaware, 305A Sharp Lab, Newark, DE 19716, USA b
Physics Engineering Department, Hacettepe University, Beytepe, Ankara 06800, TURKEY
c
Department of Materials Science and Engineering, University of Delaware, Newark, DE 19716, USA ABSTRACT Ag-Cu alloy nanoparticles were prepared by rapid condensation of metal flux obtained by the simultaneous evaporation of high purity Cu and Ag wires on a tungsten boat in the presence of circulating He gas. Structural properties of the samples prepared at different conditions were investigated by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area diffraction (SAD) patterns. X-ray diffraction patterns showed that particles were phase separated. The particle size obtained either from Scherer’s formula or the TEM images show no systematic change on the size of either Cu or Ag particles in the evaporation temperature range between 800 and 1400 oC. By using lattice constant values and Vegard’s law, the composition of the particles was calculated to be 6.6 vol% Cu in Ag. Electron diffraction images revealed that particles were softly agglomerated; these electron diffraction results were also consistent with XRD results regarding phase separation. Individual diffraction rings of the Cu and Ag were observed in the SAD patterns. INTRODUCTION Alloying of metals with a different metal is a way of developing new materials that have better technological usefulness than the 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 reveal that physical properties differ from what is observed in bulk samples. Enhancement of solid solubility of alloy components with decreasing particle size is one of the pronounced effects. It has theoretically and experimentally been shown that the enhancement of solid solubility is possible in systems where equilibrium solid solubility is very small [2, 3]. Ag-Cu alloys are one of those materials
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that are naturally immiscible at room temperature, i.e., under equilibrium conditions at room temperature the mutual solid solubilities approach zero. The maximum solubility of Cu in Ag is 13.5 vol% at the eutectic temperature, 779 oC, and it rapidly decreases as the temperature decreases [4]. The present work is focused on the synthesis of Ag-Cu alloy nanoparticles by using inert gas condensation (IGC) technique in which atomic metal vapor 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 diffusi
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