Oxidation kinetics of copper nanowires synthesized by AC electrodeposition of copper into porous aluminum oxide template
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Uttandaraman Sundararaja) Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, Alberta T2N 1N4, Canada
Jing-Li Luo Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2G6, Canada (Received 4 January 2012; accepted 3 May 2012)
Oxidation kinetics of copper nanowires (CuNWs) with diameter 25 6 4 nm were studied. The dry powder of CuNWs before oxidation comprises 73.2 wt% Cu and 26.8 wt% Cu2O. The oxidation reaction can be divided into two stages at weight of 111.2%. Oxidized CuNWs after Stage 1 consist of Cu2O and CuO. Oxidized CuNWs after Stage 2 comprise CuO only. The activation energies for both stages are determined by Kissinger method and other five isoconversional methods: Flynn–Wall–Osawa, Starink, Kissinger–Akahira–Sunose, Boswell and Friedman differential methods. The isoconversional activation energies determined by Starink method are used to fit different master plots. The Johnson–Mehl–Avrami equation gives the best fit. Surface atoms are the sites for the random nucleation, and the crystallite strain in CuNWs is the driving force for the growth of nuclei during the oxidation process.
I. INTRODUCTION
Copper nanowires (CuNWs) with one-dimensional nanostructure have potential applications in many fields such as electronics, optoelectronics, and photonics1–3 due to their high electrical and thermal conductivity. The specific properties of CuNWs make them excellent candidates for nanofillers in multifunctional polymer composites. AC electrodeposition of copper into anodized porous aluminum oxide (PAO) templates is one of the most efficient methods to produce CuNWs.4 CuNWs with diameters less than 100 nm have much higher surface area and thus are subject to much higher oxidation rate than bulk copper due to crystallite strain and more surface area. It is very important to study the oxidation kinetics of CuNWs to know their corrosion and activity loss so as to understand their long-term performance and durability. Oxidation kinetics of bulk copper have been extensively studied. The conclusion has been reached that the oxidation rate increases with temperature, while O2 partial pressure makes no difference on the rate when it is above the equilibrium potential for Cu/CuO.5 Regarding oxidation kinetics, parabolic law has been reported most frequently, while logarithmic and inverse logarithmic laws were also a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.168 J. Mater. Res., Vol. 27, No. 13, Jul 14, 2012
observed at low temperatures as well as cubic law at moderate temperatures 600–850 °C.6 The reported activation energies of bulk copper oxidation in air/O2 between 300 and 1050 °C vary from 39 to 223 kJ/mol.7 Although the kinetics and mechanism of bulk copper oxidation are widely studied and well understood, very little is known about nanoscale copper particles like CuNWs. In this study, oxidation kinetics of CuNWs synthesized by AC electrodeposition of Cu into PAO templates was studied. The ac
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