Carbon Nanotube (CNT) Metallic Composite with Focus on Processing and the Resultant Properties

Metal-carbon nanotubes (CNTs) composites are the promising advanced materials that are being developed to take the advantage of the exceptional properties of CNTs. Because of the intrinsically strong in-plane atomic SP2 bonding CNTs offer high young\u27s modulus (1.0–1.8 TPa), high tensile strength (30–200 GPa) and high elongation at break (10–30%). The thermal conductivity of individual single-walled carbon nanotube (SWCNT) and multi-walled carbon nanotube (MWCNT) are about 6000 W/m-K and 3000 W/m-K, respectively. Therefore it is expected that by incorporation of CNTs in metal matrices multi-functional composites can be used ideally as thermal interface materials, light-weight high-strength structural materials, electric components, optical devices, electromagnetic absorption materials etc. However, so far results are far from satisfied for CNT composites, mainly due to the fact that there are two main key issues remained without good solutions for CNT composites: the poor uniformity in CNT dispersion and the weak interfacial bonding between CNTs and the matrices. In this study, MWCNTs were functionalized and coated with metals like Cu and Ni by electroless deposition methods prior to their application. Metal coatings result in strong interfacial bonding at CNT-metal interfaces and uniform dispersion. During metal coating processes CNTs are physically separated in electrolyte and after coating they get physically retain the separation by the coated metal layer that they are not allowed to aggregate to form bundles. Moreover, after metal coating, the resultant density of Ni-coated MWCNTs is close to that of molten metal matrix. This prevent separation of CNTs due to buoyancy effects and results in uniform dispersion. Metal coating on CNTs surfaces also allows to form strong interfacial bonding with the metal matrices. SnBi alloy has been identified as novel lead-free thermal interface material (TIM) for electronics packaging. However the thermal conductivity and the mechanical strength of pure SnBi alloy are not sufficient to withstand harsh environment imposed by powder electronics. Therefor how to increase the thermal conductivity and the mechanical strength of SnBi solders becomes important. In this study, MWCNTs have been added into SnBi alloy to form SnBi/CNT composite solders by different material processing methods. First, in sandwich method Cu-coated CNTs were added to the 70Sn-30Bi alloy and mixed mechanically. UTS was increased by 47.6% for 3 wt. % Cu/CNTs addition. Second. Ni-coated CNTs were added by sonication assisted melting method in fabricating 70Sn-30Bi solder. For 3 wt. % Ni-coated MWCNTs, equivalent to 0.6 wt. % pure MWCNTs, UTS and YS were increased by 88.8 % and 112.3% respectively. In addition the thermal conductivity was also increased by more than 70%. Ni-coated CNTs were also added to pure Al by powder metallurgy method. For 7 wt. % Ni/CNTs having diameter 30-50 nm, UTS and YS were increased by 92.7% and 101.6% respectively. For CNTs having diameter 8-15 nm, UTS and YS were increased by 108.9% and 128.2% respectively for 7 wt. % addition. All these results are first time obtained that are much greater than published data on CNT/metal composites. Results discussion and mechanism in reinforcement were also presented

Thermal Conductivity Of Ni-Coated Mwcnt Reinforced 70Sn-30Bi Alloy

The high thermal conductivity of thermal interface material (TIM) is essential since the heat dissipation of electronic chips in an integrated circuit is solely achieved through TIM, which forms the bottleneck of the heat conduction. In the current study, the efficiency of utilizing multi-walled carbon nanotubes (MWCNTs) to increase the thermal conductivity of a typical TIM 70Sn-30Bi alloy has been investigated. Encapsulation of carbon nanotubes (CNTs) with nickel by electroless deposition was used to prevent aggregation of CNTs and to enhance the interfacial bonding between CNTs and the metal matrix. The nickel encapsulation also allows avoiding the separation of CNTs from the molten metal due to the buoyancy effect. The dispersion of Ni-encapsulated CNTs was assisted by sonication. The thermal conductivity of 3 wt % Ni/MWCNTs reinforced 70Sn-30Bi alloy was found to be more than 170% greater than that of the base alloy

Micro Hardness Of Mwcnt Reinforced 70Sn-30Bi Solder Alloys

In this study different weight percentages of copper coated multi-walled carbon nanotubes (MWCNTs) have been incorporated into 70Sn-30Bi solder alloy to form nanocomposite solder. Pure tin and bismuth were melted together in argon gas atmosphere to make 70Sn-30Bi alloy. Copper coated MWCNTs were produced by electroless copper deposition method. Pre-activated, activated and copper coated MWCNTs were characterized using SEM and EDS. MWCNTs reinforced SnBi composites were made by cold rolling process followed by the hot pressing. Micro hardness of the both the pure alloy and composites with different percentages of Cu/MWCNTs was measured using QV-1000 Vickers hardness tester at room temperature. Characterization results revealed a linear trend of increase in micro hardness with the addition of coated MWCNTs. The enhanced micro hardness is believed due to the improved interfacial bonding between matrix and CNT as well as better dispersion to efficiently utilize the potential of high strength reinforcements inside the composites and increased fracture toughness that arises from bridging mechanism of the coated MWCNTs as the crack propagates

Effect Of Activation Site Density On Copper Encapsulation Of Mwcnts By Electroless Deposition

Importance of the activation site density on final encapsulation of multi-walled carbon nanotubes (MWCNTs) with copper was investigated in this study. MWCNTs, sensitized with tin and activated with silver, were used as precursors to prepare copper-decorated nanotubes. The effect of activation bath pH was found to be critical to control the density of silver-activation sites and to produce uniform encapsulation of carbon nanotubes (CNTs) with copper in the subsequent electroless deposition method. The morphology of the copper decorated nanotubes was studied using Field Emission Gun Scanning Electron Microscope (FEG SEM) and Energy Dispersive Spectroscopy (EDS)

Sn/Mwcnt Nanocomposites Fabricated By Ultrasonic Dispersion Of Ni-Coated Mwcnts In Molten Tin

Carbon nanotubes (CNTs) are regarded as a desirable filler to develop advanced composites including advanced solders due to their exceptional mechanical properties. However, some issues remain unsolved for metallic composites owing to “wetting” and nonuniform dispersion of CNTs. In this study, electroless nickel coating onto CNTs was used to overcome these issues. Multiwalled carbon nanotubes (MWCNTs) were used for this study, and Ni-coated MWCNTs were dispersed in molten Sn assisted by sonication and compared with MWCNTs without Ni coating. Adding 3 wt.% Ni-coated MWCNTs, which corresponds to 0.6 wt.% pure CNTs, resulted in an increase in tensile strength by 95% and hardness by 123%. Nickel coating also prevented separation of the CNTs from the molten metal due to buoyancy effects, leading to more uniform dispersion