Shape-controlled synthesis of Cu-based nanofluid using submerged arc nanoparticle synthesis system (SANSS)

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Abstract

The submerged arc nanosynthesis system for preparing Cu-based nanofluids with different morphologies and using various dielectric liquids has been developed. Pure copper is selected as the electrode as well as the workpiece material. Copper is heated and vaporized by arc sparking between two electrodes being immersed in dielectric liquids. The copper aerosol can be condensed to form nanoparticles immediately by the cooling media (dielectric liquids). The nanoparticles then dissolve in the dielectric liquids which become metal nanofluids. Various morphological Cu-based nanoparticles can be synthesized using different dielectric liquids. The effects of experimental parameters and dielectric liquids on the characteristics of final products have been investigated. The possible formation mechanism of Cu-based nanoparticles via the faster growing faces is suggested.

Introduction

Cu-based materials are becoming increasingly attractive for both fundamental research and practical purposes. They are industrially important materials that can be widely used in a variety of applications, such as gas sensors, magnetic storage, solar energy transformation, semiconductors and catalysis [1], [2], [3], [4]. Liquids with nanoparticle inclusions are of special interest. The effective thermal conductivities of nanoparticle suspensions can be much higher than those of normally used industrial heat transfer fluids. This kind of fluid has been termed as “nanofluid” by Choi [5], and is considered to be a novel enhanced heat transfer fluid.

Nanoparticles can be fabricated using different synthesis techniques and shaped into various structures, such as equal axis, layer and fiber. Current nanoparticle synthesis methods include chemical reduction, sputter deposition, spraying, oxidation–reduction and gas evaporation techniques. Gas-phase synthesis and sol–gel processing are traditional methods often applied for nanoparticles synthesis. Several methods for the preparation of CuO nanoparticles have been recently reported, such as the sonochemical method, sol–gel technique, one-step solid state reaction method, thermal decomposition of precursors and co-implantation of metal and oxygen ions [6], [7], [8], [9], [10], [11]. Copper nanoparticles have been fabricated using a top-down approach in which the properties of both physical arc-discharge and chemical solution reaction are combined. The method of preparing Cu and its oxide nanomaterials is based on a discharge in the liquid and self-assembly of nanoparticles into spindle-like or spherical nanostructures in selected solutions [12]. The morphology and size of nanomaterials prepared are significantly influenced by the processing parameters being deployed. Wu and Nancollas [13] have described ways to obtain interfacial free energies at particle surfaces via crystallization and dissolution data as well as provided new insights into the relationship between nanometer-size particles and the corresponding solubilities.

In this study, the submerged arc nanoparticle synthesis system (SANSS) has been developed to synthesize Cu-based nanofluids using various dielectric liquids, mainly including mixing solution of de-ionized water and ethylene glycol. We investigate the relationship between the type of dielectric liquid and the morphology of prepared Cu-based nanoparticles. The mechanisms of generating nanoparticles with dissimilar morphologies are also studied extensively.

Section snippets

Experimental methods

The schematic diagram of SANSS is shown in Fig. 1. This system consists of the heating source, a parameter control unit, a vacuum chamber unit, a pressure control unit and an isothermal unit. The heating source provides the experimental process with a stable arc for metal vaporization. The parameter control unit is used to modulate the process parameters, such as electric current, voltage, pulse-duration, off-time, feed speed, electrode gap and preparation time. The pressure control unit is

Results and discussion

A systematic study has been carried out in order to investigate the effects of current, voltage, pulse-duration time, pulse-off time, different dielectric liquids and dielectric liquid temperature on the quality of the final products. The effect of process parameters on the composition and morphology of particles obtained by the SANSS using the experimental conditions employed are summarized in Table 1. As can be seen, the sizes and shapes of nanoparticles change noticeably depending on the

Conclusions

The vacuum-SANSS method has been employed to prepare different nanofluids using different dielectric liquids: de-ionized water, 30%, 50%, 70% volume solutions of ethylene glycol and pure ethylene glycol as coolant. Five types of nanofluids with different particle morphologies and sizes have been synthesized. Nanoparticles prepared exhibit needle-like, polygonal, square and circular morphological shapes. The different morphologies are mainly influenced and determined by various thermal

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