Fig. 1 FESEM micrograph of Cu/10vol% CNTs sintered at 1050°C for 150 min. under argon atmosphere (From paper ‘Effects of Sintering Parameters on the Microstructural Characteristics of Cu/CNTs Nanocomposites’, by A.S. Muhsan, etal. ARPN Journal of Engineering and Applied Sciences, Vol 11, No. 24 , December 2016, 14294-14298).

High powered electronics are increasingly being integrated into devices and the excessive heat generated by the next generation of microelectronic chips is not likely to be removed efficiently or economically by conventional copper heat sinks.

The University of Technology Petronas in Perak, Malaysia, has developed a unique nanocomposite material based on copper reinforced with carbon nanotubes (CNTs) which can be processed into high thermal conductivity material using Powder Injection Moulding (PIM). Ali Samer Muhsan and co-researchers the University of Technology Petronas recently reported the results of their work into producing the fully dense PIM Cu/CNTs nanocomposites in the December 2016 issue of the ARPN Journal of Engineering and Applied Sciences (Vol 11, No. 24, 2016, pp14294-14298). The authors stated that the most attractive features of using the PIM route to produce the metal matrix nanocomposite material is that it allows the combination of ingredient materials such as copper and carbon nanotubes that would not be compatible in the molten state and which would be difficult to produce into complex shapes via conventional techniques. They therefore undertook to study the effect of different PIM sintering parameters on the thermal properties and microstructural characteristics of the unique Cu-carbon nanotubes reinforced nanocomposites.

The copper powder used had a particle size of 15-20 µm and the purified multiwalled carbon nanotubes have diameter of 60-80 nm and are 5-15 µm in length. To produce a homogeneous injection moulding feedstock the CNTs were first mixed with a paraffin wax solution diluted with heptane and using sonication and magnetic stirring. The CNTs/diluted paraffin wax mixture was dried and then mixed with the other binder components – polyethylene and stearic acid – to produce a molten binder system with uniformly dispersed CNTs to which copper powder was added gradually to form the Cu-10 vol.%CNTs+binder feedstock having a solids loading of 59%.

Following solvent and thermal debinding to completely remove the binder from the green samples, the PIM Cu-10vol.%CNTs nanocomposites were sintered under argon at different temperatures (900, 950, 1000, 1050°C) for 2.5 hrs. It was found that sintering temperature had a significant effect on the microstructure of the nanocomposites where at a low temperature of 900 and 950°C Cu particles were hardly diffused in small contact spots due to insufficient kinetic energy required for the densification step. However, in the case of sintering at 1050°C the Cu/CNTs nanocomposites showed near full density microstructures with obvious elimination of the formed pores and with stable reinforcement phase of CNTs penetrated in the Cu. Thus 1050°C and a dwell time of 2.5 hrs was selected as the optimal sintering condition.

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