Phan Ngoc Hong

Enhanced thermal conductivity of nanofluid-based ethylene glycol containing Cu nanoparticles decorated on a Gr–MWCNT hybrid material

In this study, nanofluid based ethylene glycol (EG) containing Cu nanoparticles decorated on a Gr–MWCNT hybrid material (Gr–MWCNT/Cu) was synthesized successfully for the first time via a chemical reduction method. The SEM, HRTEM, FTIR and XRD studies revealed that Cu nanoparticles with an average diameter of 18 nm were well decorated on the surface of both MWCNTs and graphene sheets. The nanofluids containing Gr–MWCNT/Cu material showed good stability and a maximum thermal conductivity enhancement of 41% at 60 °C for the nanofluid containing 0.035 vol% material compared to EG alone. The enhancement is due to the combination of the high thermal conductivity of graphene, CNT and Cu nanoparticles as well as the higher surface area of the Gr–MWCNT/Cu hybrid structure. Experimental results of thermal conductivity were evaluated using different theoretical models, amongst which the Hamilton–Crosser model was found suitable for predicting the thermal conductivity of the nanofluid.

Application of multiwall carbon nanotubes for thermal dissipation in a micro-processor

One of the most valuable properties of the carbon nanotubes materials is its high thermal conductivity with 2000 W/m.K (compared to thermal conductivity of Ag 419 W/m.K). It suggested an approach in applying the CNTs in thermal dissipation media to improve the performance of computer processors and other high power electronic devices. In this research, the multiwall carbon nanotubes (MWCNTs) made by thermal chemical vapour deposition (CVD) at our laboratory was employed as the heat dissipation media in a microprocessor a Personal Computer with configuration: Intel Pentium IV 3.066 GHz, 512Mb of RAM and Windows XP Service Pack 2 Operating System. We directly measured the temperature of the microprocessor during the operation of the computer in two modes: 100% usage CPU mode and over-clocking mode. The measured results showed that when using our thermal dissipation media (a mixture of the mentioned commercial thermal compound and 2 wt.%. MWCNTs), the temperature of the microprocessor decreased 5°C, and the time for increasing the temperature of the microprocessor was three times longer than that when using commercial thermal compound. In over-clocking mode, the processor speed reached 3.8 GHz with 165 MHz of system bus clock speed; it was 1.24 times higher than that in non over-clocking mode. The results confirmed a promising way of using MWCNTs as the thermal dissipation media for microprocessor and high power electronic devices.

Influence of defects induced by chemical treatment on the electrical and thermal conductivity of nanofluids containing carboxyl-functionalized multi-walled carbon nanotubes

In this paper, we present the results on the influence of chemical treatment time on the structure of carboxyl-functionalized MWCNTs (MWCNT–COOH) and their nanofluids. The morphological and structural studies investigated by FTIR, HRTEM and Raman scattering demonstrated that the structural defects of MWCNT–COOH increase with increasing chemical treatment time. Nanofluids containing MWCNT–COOH treated for a longer time showed better stability due to the increasing of COOH functional groups attached to the surface of MWCNTs. The electrical conductivity of the nanofluids increases with increasing CNT concentration and decreases with increasing chemical treatment time. The thermal conductivity of the nanofluids enhanced when increasing CNT concentration and reached the highest value for MWCNT–COOH with 5 h chemical treatment. By using the effective medium theory (EMT) and experimental data fitting, the thermal boundary resistance (TBR) and the thermal boundary conductance (TBC) of MWCNT–COOH/water were found to be 90 × 10−8 m2 K W−1 and 1.1 MW m−2 K−1, respectively. The interfacial layer thermal conductivity (Ki) between CNTs and base fluid was estimated by using Mursheds model. The highest Ki was obtained to be 2.6 W m−1 K−1 for a nanofluid with 5 h chemical treatment. The results implied that the thermal conductivity of CNT based nanofluids could be improved by increasing the Ki via optimizing of the chemical treatment conditions.

Electron field emission characteristics of carbon nanotube on tungsten tip

Electron field emission characteristic of carbon nanotubes on tungsten tip was investigated in 2?10-6 Torr vacuum. The measurement results showed that the CNTs/W tip could emit electron at 0.7 V/?m (nearly 10 times lower than that of the W tip itself) and reach up to 26 ?A at the electric field of 1 V/?m. The emission characteristic follows the Fowler-Nordheim mechanism. Analysis of the emission characteristic showed that the CNTs/W tip has a very high value of field enhancement factor (? = 4.1 ? 104 cm-1) that is much higher than that of the tungsten tip itself. The results confirmed the excellent field emission behavior of the CNTs materials and the CNTs/W tip is a prospective candidate for advanced electron field emitter.

Effect of Surface Morphology and Dispersion Media on the Properties of PEDOT:PSS/n-Si Hybrid Solar Cell Containing Functionalized Graphene

We present the results on the effect of surface morphology and dispersion media on the properties of PEDOT:PSS/n-Si hybrid solar cell containing functionalized graphene (Gr). The hybrid solar cells based on SiNWs showed higher power conversion efficiency (PCE) compared to the planar based cells due to suppressing the carrier recombination and improving carrier transport efficiency. The PCE of hybrid solar cells could be improved by adding Gr into PEDOT:PSS. Different solvents including deionized (DI) water, ethylene glycol (EG), and isopropyl alcohol (IPA) were used as media for Gr dispersion. The best performance was obtained for the cell containing Gr dispersed in EG with a measured PCE of 7.33% and nearly 13% and 16% enhancement in comparison with the cells using Gr dispersed in IPA and DI water, respectively. The increase in PCE is attributed to improving the carrier-mobility, electrical conductivity, PEDOT crystallinity, and ordering.

Carbon nanotubes based lubricating oils for engines

Carbon nanotubes (CNTs) are well-known nanomaterials with many excellent properties such as high hardness, high strength, and excellent thermal conductivity. Owing to their very high thermal conductivity (2000 W/m.K compared to thermal conductivity of Ag 419 W/m.K), CNTs become ones of the most suitable nano additives for fabricating the lubricating oils in order to increase the thermal conductivity of lubricating oils, to enhance the efficiency of heat dissipation for the engine, and to improve the performance efficiency of engine. In this work, we present the obtained results on application of the CNTs in lubricating oils for some engines. The results showed that with the addition of CNTs, the thermal conductivity of lubricating oils increase about 15%, this helps improve the efficiency of heat dissipation for the engine. Experimental results show that when using the lubricating oils containing carbon nanotubes, the temperature of engine dropped about 10°C, fuel saving was upto 15% and longevity of lubricating oil increased upto 20,000 km.

Synthesis of vertically aligned carbon nanotubes and diamond films on Cu substrates for use in high-power electronic devices

Currently, most of the vertically aligned carbon nanotubes (VA-CNTs) and diamond films are mainly synthesised on flat silicon (Si) substrate. However, to achieve thermal dissipation in high-power electronic devices (HPEDs), the VA-CNTs and diamond films need to be attached to thermal dissipation metal substrates (like Cu, Ag, Al, etc.). In this paper, the fabrication process of the VA-CNTs and diamond films on Cu substrate is reported in detail. The VA-CNTs were synthesised by the thermal chemical vapour deposition (CVD) method. The VA-CNTs on Cu substrates were fabricated by two different methods: directly growing the VA-CNTs using thin catalytic metal layers such as Fe/Al or Cr/Al as a catalyst; transferring the VA-CNTs film that was pre-grown on Si substrate to Cu substrate. The diamond films were also directly grown on the Cu substrate by microwave plasma chemical vapour deposition (MPCVD). The grown VA-CNTs and diamond films were tested as the thermal dissipation media on a 0.5W InGaN LED chip. The VA-CNTs and diamond films greatly increased input current of the LED by more than 500 mA and 350 mA without reaching saturation. This is higher compared with that of the device packaged using normal commercial silver thermal paste. Initial experiment results on the LED demonstrated that the VA-CNTs and diamond films greatly improve the lights output power and that they are optimal choices for the thermal dissipation of HPED.

Thermal Dissipation Efficiency in a Micro‐Processor Using Carbon Nanotubes Based Composite

Modern electronic and optoelectronic devices such as μ‐processor, light emitting diode, semiconductor laser issued a challenge in the thermal dissipation problem. Finding an effective way for thermal dissipation therefore becomes a very important issue. It is known that carbon nanotubes (CNTs) is one of the most valuable materials with high thermal conductivity (2000 W/m.K compared to thermal conductivity of Ag 419 W/m.K). This suggested an approach in applying the CNTs as an essential component for thermal dissipation media to improve the performance of computer processor and other high power electronic devices. In this work multi walled carbon nanotubes (MWCNTs) based composites were utilized as the thermal dissipation media in a micro processor of a personal computer. The MWCNTs of different concentrations were added into polyaniline, commercial silicon thermal paste and commercial silver thermal paste by mechanical methods. A personal computer with configuration: Intel Pentium IV 3.066 GHz, 512 MB of ...

Removal of arsenic from water using crumpled graphite oxide

Abstract In this work, we fabricated crumpled graphite oxides (CGOs) from discharged electrodes of waste batteries by the cathodic plasma electrolysis process and applied it for arsenic (As) removal from water solutions. Several factors that affect the removal efficiency of As(III) were investigated, including pH, initial concentrations, and contact time. After 120 min of experiment [10 mg of CGO in 40 ml of 1 mg/l As(III) solution], the removal efficiency reached to as high as 98.6%. From the Langmuir isotherm model, the calculated maximum adsorption capacity (qmax) was found to be 47.39 mg/g. The results from this study showed that CGOs could be an effective adsorbent for As(III) removal from the water environment and acts as a promising adsorbent for other heavy metals from contaminated water.

Effect of Annealing Time on the Power Conversion Efficiency of Silicon Nanowire Based Solar Cell Prepared by Wet Diffusion Technique

1 Institute of Materials Science, Vietnam Academy of Science and Technology, 18, Hoang Quoc Viet Str., Cau Giay Distr., Hanoi, Vietnam 2 Graduate University of Science and Technology, Vietnam Academy of Science and Technology, 18, Hoang Quoc Viet Str., Cau Giay Distr., Hanoi, Vietnam 3 Center for High Technology Development, Vietnam Academy of Science and Technology, 18, Hoang Quoc Viet Str., Cau Giay Distr., Hanoi, Vietnam