Thermodynamic modeling and characterizations of Al nanoparticles produced by electrical wire explosion process
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R. Sarathi Department of Engineering Design, IIT Madras, Chennai-600036, India
R. Jayaganthana) Department of Electrical Engineering, IIT Madras, Chennai-600036, India (Received 27 July 2016; accepted 12 December 2016)
Aluminum (Al) nanoparticles are synthesized by wire explosion process (WEP) in an inert ambience of argon. Thermodynamic analysis and structural characterization of nano Al particles are made in the present work. Transmission electron microscopy (TEM) characterization has shown that the Al nanoparticles produced are spherical in shape and it follows a lognormal distribution. A unimodal size dependent thermodynamic model is formulated to understand the size dependent thermal behavior of aluminum nanoparticles. Three different melting modes such as, homogeneous melting mode (HMM), liquid skin melting (LSM) and liquid nucleation and growth (LNG) are assumed to understand the melting behavior of aluminum nanoparticles synthesized by the WEP process. The effect of saturation ratio on the nucleation rate and the impingement factor is also discussed. The size dependent melting and enthalpy of fusion of Al nanoparticles predicted by thermodynamic model are in tandem with the DSC results.
I. INTRODUCTION
Nanoparticles exhibit excellent chemical, physical, mechanical and thermodynamic properties by the virtue of their surface atoms. Various synthesizing routes are available to produce nanoparticles.1 One of the common synthesizing routes is top-down approach, wherein a bulk grain is broken down in to nanosized grains. The electrical wire explosion process (WEP) is a top-down technique for synthesizing nanoparticles, which is well proven for producing ultrafine particles of high purity. It is an inert gas pyrolytic technique in which a thin conducting metal wire is evaporated by passing a high current through it, in an inert gas ambience.1–6 The electrical wire explosion enhances the energy contained in the crystal owing to the high density of crystal defects.7 In comparison with the other synthesizing techniques, the nanoparticles synthesized by this method exhibit unique properties such as8: (i) lower sintering and melting temperatures (ii) high density of point, linear, surface and volume defects (iii) increased chemical activity and (iv) more stored enthalpy. It is possible to control the electrical energy density in WEP and it is highly efficient.9 The particle size and shape can be controlled by providing an appropriate energy to the thin conductor during explosion.10,11 Contributing Editor: Susan B. Sinnott a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.507
It is possible to synthesize the nanoparticles of nitrides, carbides and oxides through judicious choice of the ambient gas in the explosion chamber. The synthesis of oxide, carbide and nitride nanoparticles by electrical explosion technique has been reported in the literature.12–19 Aluminum nanoparticles are one of the ultrafine powders produced by this technique. The wide range of applications of alum
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