Synthesis and characterization of copper nanofluid by a novel one-step method

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Abstract

This paper presents a novel one-step method for the preparation of stable, non-agglomerated copper nanofluids by reducing copper sulphate pentahydrate with sodium hypophosphite as reducing agent in ethylene glycol as base fluid by means of conventional heating. This is an in situ, one-step method which gives high yield of product with less time consumption. The characterization of the nanofluid is done by particle size analyzer, X-ray diffraction topography, UV–vis analysis and Fourier transform infrared spectroscopy (FT-IR) followed by the study of thermal conductivity of nanofluid by the transient hot wire method.

Introduction

Cooling has become one of the top technical challenges faced by hi-tech industries such as microelectronics, transportation, manufacturing and metrology. There is a strong need in these industrial fields to develop heat transfer fluid [1], [2] with significantly higher thermal conductivity than pure fluids. It is a well-known fact that crystalline solids have a higher thermal conductivity by one to three orders of magnitude than traditional fluids like water, ethylene glycol, oil, etc. Therefore fluids containing suspended solid particles are reasonably expected to have a higher thermal conductivity than pure fluids. Nanofluids [3], containing metallic or non-metallic particles have attracted a great deal of research attention due to their higher heat transfer efficiency.

Nanofluids having suspensions [4], [5] of nanometer sized particles have been proposed as a route for surpassing the performance of heat transfer liquids that are currently available [6]. Recent experiments on nanofluids have indicated that a significant increase in thermal conductivity could be achieved when compared with liquids without nanoparticles or larger particles [7], [8], [9], [10]. For example 0.3 vol.% copper nanoparticles dispersed in ethylene glycol is reported to increase its inherent poor thermal conductivity by 40% [7].

At present copper nanofluids are prepared by dispersing copper nanoparticles in the base fluid [8]. This is a step-by-step method, which involves agglomeration that takes place during the process of drying, storage and transportation of nanoparticles. Agglomeration will result in settlement and clogging of the microchannels and hence the thermal conductivity of the nanofluids will be decreased. There are several other methods that are similar to one-step physical method, in which copper vapour is directly condensed into nanoparticles by contact with a flowing low vapour pressure liquid [7] but this method appears to be cost ineffective. By polyol process [11], monodispersed, non-agglomerated copper nanoparticles are obtained since polyol acts as solvent and reducing agent. However, the major drawback of this method is that solution of the copper salt should be heated to its boiling point and kept under refluxing conditions for a long time [12]. In the aqueous chemical reduction method, though the rate of the reaction is high, the agglomeration problem exists, as a consequence, a decrease in the thermal conductivity of the nanofluid is observed in most cases [13]. Hence the development of a new and novel method for the preparation of a copper nanofluid is inevitable. With all these ideas in mind, an attempt has been made in the present investigation to synthesize copper nanofluid by a novel one-step method using copper sulphate as a source for copper nanoparticles, ethylene glycol as base fluid and sodium hypophosphite as reducing agent by means of conventional heating.

In the one-step synthesis method, copper nanofluids of metallic copper dispersed in ethylene glycol are prepared using sodium hypophosphite as the reducing agent and conventional heating is carried out. The method is a unique one, where preparation of nanoparticles is combined with the preparation of nanofluids and hence the process of drying, storage, transportation and redispersion of copper nanoparticles is avoided and ultimately it reduces the production cost as well. These aspects of this work are novel.

Section snippets

Preparation of copper nanofluids

All the reagents used in our experiments were of analytical purity and were used without further purification. The beakers used in this procedure were cleaned by an ultrasonic cleaner in an ultrasonic bath. In this procedure, 25 ml of ethylene glycol solution was taken in a 500 ml beaker. To this 15 ml of (0.1 M) copper sulphate pentahydrate, 50 ml of sodium lauryl sulphate (SLS) surfactant and 100 ml water was added. Further few drops of kerosene were added to prevent oxidation of the copper

Results and discussion

The effect of copper sulphate concentration on the formation copper nanoparticles is shown in Table 1. From the table it is evident that copper nanofluid of 0.1 M concentration seems to be quite effective for obtaining copper nanoparticle of desired particle size. This is mainly due to the fact that the growth and nucleation process take place independently. That takes place separately, and as a result, the distribution range of copper nanoparticle is narrow. But at higher concentrations, of 0.3 

Conclusion

A novel one-step method was developed for preparing copper nanofluids by reducing copper sulphate pentahydrate using sodium hypophosphite as reducing agent and ethylene glycol as base fluid by means of conventional heating. This novel one-step method for preparing copper nanofluids is advantageous over other more conventional methods due to the following reasons:

  • It is an in situ, one-step method.

  • Non-agglomerated and stably suspended copper nanofluids are obtained.

  • Copper nanofluids can be

Acknowledgements

One of the authors K. Shree Meenakshi is thankful to NML Madras Centre for having provided the facility to carry out this work. Furthermore, she is grateful to Dr. S. Nanjundan, professor and head, Department of Chemistry, Anna University for granting her permission to carryout the work in NML, Madras Centre.

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