Spinodal decomposition of Ag-Cu nanoparticles
| Authors | |
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| Year of publication | 2014 |
| Type | Conference abstract |
| MU Faculty or unit | |
| Citation | |
| Description | Ag-Cu nanoparticles (NPs) of near-eutectic composition were prepared by solvothermal synthesis at 230C from metallo-organic precursors in organic solvent. The nanoparticle size was measured by both dynamic light scattering (DLS) and small angle X-ray scattering (SAXS) method. The size and shape were evaluated by electron microscopy (SEM, TEM and HRTEM), the thermal properties were investigated by differential scanning calorimetry (DSC) and temperature controlled Xray diffraction method (XRD). HRTEM results show that AgCu nanoparticles with face centered cube (fcc) crystal lattice exist as a substitutional solid solution in contrast to bulk AgCu system, which reveals spinodal decomposition under eutectic temperature. The phase diagram respecting size of the AgCu NPs was calculated by the CALPHAD method using surface tension of the bulk Ag-Cu alloy in liquid and solid (fcc) states. The predicted eutectic melting point depression was not experimentally observed when the nanoparticles were melted by DSC. The samples melt at eutectic temperature exactly as bulk AgCu alloy. The microparticles consisting of the eutectic copper and silver rich phases were observed by SEM after melting. A spontaneous separation of copper and silver atoms was observed by temperature controlled X-ray diffraction method (XRD). The temperature treatment of the AgCu NPs showed that a spinodal decomposition and crystallinity changes (size evaluation using Scherrer equation) occur at a narrow range of temperature. The reason for the phenomenon observed can be the metastable state of the nanoparticles but there are also other unknown effects at the nano-scale level that hinder the Cu- and Ag-rich phase separation at low temperatures. The open question is also if the general equilibrium thermodynamics can be used to describe the AgCu NPs system under view. |
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