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In this paper, ultrasonic dispersion and surface chemical modification were used to prepare the modified multi-walled carbon nanotubes (MWNTs)/paraffin composite phase-change materials (PCMs). The surface modification of MWNTs was developed via coating MWNTs with silica dioxide. The modified MWNTs were marked as SiO2@MWNTs. The phase-change properties, thermal stability and chemical functional groups of the MWNTs/paraffin composite PCMs were measured by differential scanning calorimetry, thermogravimetric analysis (TG) and Fourier transform infrared spectroscopy, respectively. The results indicated that paraffin and MWNTs were compound physically. The diameter and content of MWNTs had influence on the phase-change temperature and the latent heat of the MWNTs/paraffin composite PCMs. The smaller the diameter or larger content of the SiO2@MWNTs, the greater the influence was. The reduction degree of PCM1(the diameter of the SiO2@MWNTs is 20–30 nm) in latent heat is about 4.5 times of that of PCM3(the diameter of the SiO2@MWNTs is larger than 50 nm). The thermal stability and the thermal conductivity of the composite PCMs were improved with the addition of the SiO2@MWNTs. When the content of SiO2@MWNTs is 5 mass%, the thermal conductivity of the paraffin PCMs is 0.383 W m−1 K−1). [ABSTRACT FROM AUTHOR]

Hybrid nanofluid can be considered as a new generation of nanofluids. Despite the success of the researchers in the field of hybrid nanofluids, no acceptable model has been proposed yet that can accurately predict the thermal conductivity of these nanofluids. The nanofluids, containing carbon nanotubes, are not excluded. This research to provide a model based on previous models to predict the thermal conductivity of hybrid nanofluids containing carbon nanotubes. For this reason, the thermal conductivity of MWCNT-MgO/water-EG nanofluids was experimentally measured. The experimental data were in seven solid volume fractions from 0.015 to 0.96%, in which the tests have been done at the temperature range 30-50 °C. A modified conventional model (as a proposed correlation in present study) can produce better results in forecasting the experimental data. The predicted data error by modified Jang-Choi model as proposed correlation was less than 3%. In addition, the price-performance analysis of the thermal conductivity data shows that hybrid nanofluids are better than single particle nanofluids. [ABSTRACT FROM AUTHOR]

Silica has been non-covalently coated on multi-walled carbon nanotubes (MWCNTs) using the sol-gel chemistry, where tetraethoxy silane (TEOS) was used to form an inorganic silica layer immediately next to surface of MWCNTs and octyl triethoxy silane was coated over the TEOS. Transmission electron microscopy (TEM) measurements show that the diameter of MWCNTs increases with increasing the number of coating layer, indicating that the silica has been coated on MWCNTs. Quantitative analysis from thermogravimetric analysis (TG) also indicates that the inorganic and organic silica has been successfully coated on MWCNTs. Further, quantitative analysis found that the amount of silica measured by TG agrees well with the increase of thickness of coated MWCNTs obtained from TEM, indicating that little or no free silica exists in the system. The thermal conductivity of epoxy/MWCNTs composite was studied and the results show that the thermal conductivity of the composite is improved by coating MWCNTs in this manner and increases with increasing the number of coatings. [ABSTRACT FROM AUTHOR]

The paper concerns thermal properties of epoxy/nanotubes composites for aircraft application. In this work, influence of carbon nanotubes on thermal stability, thermal conductivity, and crosslinking density of epoxy matrix was determined. Three kinds of nanotubes were used: non-modified with 1- and 1.5-μm length, and 1-μm length modified with amino groups. Scanning electron microscopy observations were done for examining dispersion of nanotubes in the epoxy matrix. Glass transition temperature ( T) was readout from differential scanning calorimetry. From dynamic mechanical analysis, crosslinking density was calculated for epoxy and its composites. Also, thermogravimetric analysis was done to determine influence of nanotubes addition on thermal stability and decomposition process of composites. Activation energy was calculated from TGA curves by Flynn-Wall-Ozawa method. Thermal diffusivity was also measured. SEM images proved the uniform dispersion of carbon nanotubes without any agglomerates. It was found that nanotubes modified with amino groups lead to the increase of epoxy matrix crosslinking density. The significant increase in T was also observed. On the other hand, addition of carbon nanotubes leads to the decrease of thermal stability of polymer due to the increase of thermal diffusivity. [ABSTRACT FROM AUTHOR]

A series of fatty acids/carbon nanotubes (CNTs) composite shape-stabilized PCMs were prepared through infiltration method by using the eutectic mixture of capric acid, lauric acid, and palmitic acid as phase change materials, multi-walled CNTs as a supporting material. Nitrogen adsorption-desorption curves and SEM images of composite shape-stabilized PCMs indicate that the eutectic mixture was effectively absorbed into the porous structure of the CNTs. DSC thermograms show that the composite fatty acids/CNTs possess good phase change behavior. And the latent heat of the sample absorbed with 80 wt% fatty acids can achieve 101.6 J g in the melting process and its phase change temperatures and latent heat almost remain unchanged in 30 times of thermal cycling. Moreover, the thermal conductivity of the composite materials are significantly improved (up to 0.6661 W m k) due to the addition of the highly thermal conductive CNTs. [ABSTRACT FROM AUTHOR]

In the present study, the MWNT/epoxy composites are prepared with three weight percentages (0.0, 0.3, and 0.5%) of multiwall carbon nanotube (MWNT). The temporal response of multi-wall carbon nanotube (MWNT)/epoxy composite with different wt% of multi-wall carbon nanotube (MWNT) is measured by experiment. Also, a cavity-type measuring system is designed to experimentally measure the surface temperatures and obtain the thermal conductivity of these composites at different heating rates. It is found that the responses of the 0.3 and 0.5% weight percentage of multi-wall carbon nanotube (MWNT)/epoxy composites are found to be about 25 and 47.8%, respectively, faster than that of the pure epoxy resin. Both the responding characteristics and the variation trends of the measured surface temperatures of these composites can be well predicted by the lumped-heat capacity model. Besides, the higher the weight percentage (wt%) of multi-wall carbon nanotube (MWNT) in the composite, the larger is the thermal conductivity. Relative to the pure epoxy, the thermal conductivities for the composites with 0.3 and 0.5% of multi-wall carbon nanotube (MWNT) increase by 15.9 and 44.9%, respectively. For the weight percentages studied, the thermal conductivity of these composites is found to increase mildly at low heating rates; however, it remains nearly constant at high heating rates. [ABSTRACT FROM AUTHOR]

Thermoanalytical and electron microscopic methods were used as characterisation tools for the determination of the composition of single walled carbon nanotube samples. Acid purification method of single-walled carbon nanotubes (SWCN) proved to be effective, resulting in a three fold increase in the percentage of SWNTs present in the purified product as determined by thermogravimetric analysis. In this work we report the thermogravimetric analysis by conventional and high resolution methods of the raw SWNTs and purified SWNTs. [ABSTRACT FROM AUTHOR]