Fabrication and effective thermal conductivity of multi-walled carbon nanotubes reinforced Cu matrix composites for heat sink applications
A novel particles-compositing method was used for the first time to disperse different contents of multi-walled carbon nanotubes (CNTs) in micron sized copper powders, which were subsequently consolidated into CNT/Cu composites by spark plasma sintering (SPS). Microstructural observations showed that the homogeneous distribution of CNTs and dense composites could be obtained for 0–10 vol.% CNT contents. The CNT clusters were appeared in the powder mixture with 15 vol.% CNTs, which resulted in an insufficient densification of the composites. The effective thermal conductivity of the composites was analyzed both theoretically and experimentally. The addition of CNTs showed no enhancement in overall thermal conductivity of the composites due to the interface thermal resistance associated with the low phase contrast of CNT to copper and the random tube orientation. Besides, the composite containing 15 vol.% CNTs led to a rather low thermal conductivity due possiblely to the combined effect of unfavorable factors induced by the presence of CNT clusters, i.e. large porosity, lower effective conductivity of CNT clusters themselves and reduction of SPS cleaning effect. The CNT/Cu composites may be a promising thermal management material for heat sink applications.
[Show abstract] [Hide abstract] ABSTRACT: For high sensitivity in micro bio-analysis devices (MBD), the fabrication of the micro-structured reaction field using vertically aligned carbon nanotubes (VACNTs) which is pillar-structured by two methods was performed. The first method is the combination of photolithography and thermal chemical vapor deposition (CVD). The second method is the molding process of polydimethylsiloxane (PDMS) substrate with micro-pillars array and the transfer press of VACNTs synthesized by thermal CVD on PDMS substrate for lower cost in mass production compared with photolithography process. In the first method, circular-pattered metal film on silicon (Si) substrate as the catalyst for VACNTs synthesis was fabricated by photolithography and VACNTs-pillars array was successfully fabricated using the substrate with circular-pattered metal film by thermal CVD. Furthermore, the protein adsorption property of these structures was evaluated as the reaction field of MBD by ultraviolet (UV) spectroscopy. The results show that the protein adsorption property was improved considering the design of micro pattern in VACNTs structures. On the other hand, in the second method, pillar-structured PDMS substrate was molded using a photoresist mold by photolithography and VACNTs was transferred on PDMS substrate by transfer-press equipment. The results indicate that VACNTs can be transferred on the top of micro pillar of PDMS substrate controlling the load of transfer press. Furthermore, it is indicated that micro-pillar VACNTs structures can be fabricated by molding and transfer press with lower cost than the combination of photolithography and thermal CVD.0Comments 0Citations
- "Therefore, the combination of top-down process and bottom-up process is important to fabricate micro structures with the desired shape and size effectively. This combination technique using the synthesis of vertically aligned carbon nanotubes (VA CNTs) as bottom-up process has been attracting attention for the fabrication of micro structures due to the fact that CNTs are one of the nanomaterials with chemical stability and high aspect ratio which brings in high specific surface area (Hu, et al., 2009, Chu, et al., 2010). In this work, we performed the fabrication of the reaction field with micro structures which form is a pillar shape for high sensitivity of MBD by the combination of top-down process and the VACNTs synthesis. "
[Show abstract] [Hide abstract] ABSTRACT: Multi-walled carbon nanotube (MWCNT) reinforced titanium matrix composites were synthesized using a spark plasma sintering method at a low sintering temperature of 550 °C. The effects of the weight fraction of MWCNTs on the microstructures and the mechanical and thermal properties of the composites were investigated. No reaction products were detected in the composites, indicating that the MWCNTs in the composites maintained their structural integrity after sintering, and thus, because of their advantageous properties, could reinforce the titanium matrix. As a result, the compressive strength of the composite containing 0.4 wt.% MWCNTs reached 1106 MPa, which was an increase of 61.5% compared to that of pure titanium under at the same conditions. In addition, the results revealed that compressive strength of the bulk compacts increased initially and then decreased with an increase in weight fraction of MWCNTs. However, compressive strain of the sintered composites continued to fall at a slow rate. The microhardness and thermal diffusivity of the composites rose steadily with an increasing content of MWCNTs. When the weight fraction of MWCNTs in the composites exceeded 0.8%, the compressive strength of the composites declined significantly due to the increasing aggregation of the MWCNTs.0Comments 0Citations
- "The pores among the tubes can efficiently spread the heat flow and simultaneously the pores at the interfaces can lead to extra thermal barriers ; thus, the thermal diffusivity of the composites is reduced. Third, the MWCNT clusters can reduce the cleaning effect involved in SPS by weakening the spark discharge effect . Because the cleaning effect in SPS process can not only reduce the kinks or twists of MWCNTs , but also remove contaminations and impurities from MWCNTs , the weakening of the cleaning effect in SPS may result in a decrease in the thermal diffusivity of the MWCNTs/Ti composites. "
[Show abstract] [Hide abstract] ABSTRACT: In this present work, two methods for dispersing carbon nanotubes into the copper matrix were tested: a Solid Route process where CNTs are simply mixed with the copper powder and a Liquid Route process where CNTs are dispersed in a copper salt solution and then mixed with the metallic copper powder. Powders are sintered by uni-axial hot pressing process under vacuum atmosphere at 650°C and thermal conductivities of composite materials were measured using the laser flash method. Results are compared with a theoretical model of Nan et al. which enables to predict the thermal conductivity of materials containing CNTs. Comparison of experimental and theoretical results tends to prove that CNTs are 2D-randomly dispersed in a plane perpendicular to the pressing direction during uni-axial hot pressing process. Moreover, an increase of +7% of the thermal conductivity is shown for the composite material containing 1 vol. % of CNTs into the copper matrix.0Comments 0Citations
- "Cho et al.  prepared materials containing Multi Wall Carbon Nanotubes (MWCNT) by spark plasma sintering and shows a 3% increase of the thermal conductivity of the composite materials, compared with pure copper, for a volume fraction of 1% nanotubes. Chu et al   fabricated Cu-CNTs materials with a novel technique for dispersing carbon nanotubes into the matrix. Despite a relative good dispersion of the reinforcement, the thermal conductivity of the composite materials was lower than the copper reference. "