Search

Thermally conductive and electrically insulating polyamide 6 (PA6) matrix quaternary composites were prepared by hot press molding and injection molding, respectively. The quaternary composites were composed of zero-dimensional aluminum oxide particle, one-dimensional silicon carbide whisker, two-dimensional flake graphite, and PA6 resin matrix. Morphology, structure, density, thermal conductivity, volume electrical resistivity, and tensile strength of two types of composites were characterized by scanning electron microscopy, X-ray diffractometer, thermal conductivity tester, high resistance micro-current tester, and tensile tester. The results showed that crystallinity, thermal conductivity, density, and tensile strength of hot press molding samples were superior to those of samples made by injection molding method. This is due to that hot press molding method can provide higher molding pressure and longer annealing time than injection molding. The mechanism could be explained that the performances of the composites were promoted by increasing molding pressure and annealing time. [ABSTRACT FROM AUTHOR]

Abstract A series of paraffin/expanded graphite (EG) composites with various mass fraction were prepared. The microscopic geometry configuration, thermal conductivity and saturation sorption capacity of EG were obtained. In this paper, a method based on the experiments of EG pores was proposed for constructing geometric models. The geometric model constructed by this method has obvious anisotropy and has been employed in the calculation. Furthermore, the numerical results of thermal conductivity indicate anisotropy of a single-pore. Moreover, it had been observed by experiment that the anisotropy is weakened and transformed to isotropy in the process of combining geometric models with a large number of single pores. The final numerical results agree well with the experiments, which validates the precision and reliability of the proposed model. The increasement of thermal conductivity is also calculated and discussed during the phase change process of paraffin/EG. Highlights • A method of EG pores was proposed for constructing geometric models which has obvious anisotropy. • The SEM micrograph and saturation sorption capacity are employed to build the geometric models of EG pores. • Effective thermal conductivity during non-phase change process and the phase change process was calculated. • The numerical results agree well with the experiments. [ABSTRACT FROM AUTHOR]

A novel kind of paraffin-based shape-stable phase change materials (SSPCMs) was prepared by introducing paraffin into reduced graphene oxide (rGO)/carbon nanotubes (CNTs) aerogel via vacuum-assisted impregnation method. The effects of ratio of rGO to CNTs in 3D network structure on morphology, structure and property of paraffin-based SSPCMs were investigated. The rGO/CNTs 3D network structure with high thermal conductivity, served as thermally conductive skeleton together. In particular, CNTs was used as a secondary heat conductive filler, which could be well dispered in the SSPCMs to conduct heat synergistically. The SSPCMs exhibited high thermal conductivity and excellent shape-stability. And the thermal conductivity of SSPCMs can be regulated by adjusting the ratio of rGO to CNTs in aerogels. These results indicate that 3D rGO/CNTs aerogels have advantages as thermally conductive skeleton, and can endow phase transition materials with stable shape, so as to realize the application of phase change materials in the field of heat dissipation. [ABSTRACT FROM AUTHOR]

Graphene encapsulating paraffin (paraffin@graphene) microcapsules were fabricated by electrostatic interaction-based self-assembly. An aqueous dispersion of graphene sheets charged with cation, were mixed with a water-based emulsion containning negatively charged paraffin droplet spheres to form self-assembled microcapsules. The morphology of the microcapsules was characterized by scanning electron microscope (SEM). Results show that the microcapsules with a well-defined spherical structure were prepared successfully. Differential scanning calorimeter (DSC) results indicate that the phase change latent heat are all above 200 J g−1. With a graphene mass fraction of 8 wt%, the thermal conductivity of the fabricated composites can reach 1.73 W m−1 K−1. Attributing to the interlocking of graphene with each other, the microcapsules enable lock the paraffin in the shell thus successfully avoiding its leakage during phase change process. The prepared phase change microcapsules are expected to apply in energy storage field. [ABSTRACT FROM AUTHOR]

Paraffin, due to its linear chain and saturated hydrocarbons with low thermal conductivity, is difficult to transfer energy effectively. Using amphiphilicity of graphene oxide (GO), Pickering emulsion of paraffin@GO was obtained and then paraffin@graphene microencapsulated phase change materials (MEPCMs) were achieved by chemical reduction through adding hydrazine hydrate. Thermally conductive PCMs with segregated structure were constructed by hot compression of paraffin@graphene microencapsules. Scanning electronic microscopy, differential scanning calorimetry and thermal conductivity test were used to characterize microstructure and thermal properties of MEPCMs. Meanwhile, the effect of graphene on the phase change latent heat and phase transition temperature was investigated. Results indicated that GO did not react with paraffin during the process of chemical reduction and the obtained MEPCMs were regular spheres. These MEPCMs had paraffin content of 99% or even more. Graphene working as shell materials increased the phase change latent heat of paraffin from 227.6 to 232.4 J/g, without affecting the phase transition temperature. The hot-compress molding makes graphene shell form segregated structure with more thermal pathways, further enhancing thermal conductivity. The segregated-structure PCMs with high latent heat and thermal conductivity can be applied in energy storage field. [ABSTRACT FROM AUTHOR]

Two kinds of carbon aerogels, graphene aerogels (GA) and carbon nanotubes-graphene aerogels (CGA), were prepared by modified hydrothermal method. The form-stable phase change materials (PCMs) were fabricated by adsorbing paraffin into carbon aerogels. Morphology, structure, form stability and thermal property were characterized by scanning electron microscope (SEM),in situX-ray diffraction (in situXRD) and differential scanning calorimeter (DSC). The results showed that GA presented wrinkled surface textures with curling edges, and carbon nanotubes (CNTs) were interspersed or attached to GA sheets. The phase transition temperature and the phase change enthalpy of the GA/paraffin PCM composite were 48.7 °C and 223.2 J/g, respectively. Thermal and mechanical properties of PCM composites achieved a qualitative leap with the adding of carbon aerogels. The PCM composites had a thermal conductivity of about 2.182 W/m K at the carbon aerogels loading fraction of 2 wt%. The form-stable PCM composites with high thermal conductivity and high enthalpy could be promising for thermal energy storage applications in construction field. [ABSTRACT FROM PUBLISHER]

Thermally conductive form-stable phase change materials (FSPCMs) were prepared by using ethylene-vinyl acetate (EVA), paraffin, expanded graphite (EG) and carbon fiber (CF) as row materials. Two-dimensional EG and one-dimensional CF were used as thermally conductive fillers. Paraffin and EVA were phase change material (PCM) and supporting material, respectively. Differential scanning calorimetry (DSC) and leakage rate testing results indicated that FSPCMs owned the melting temperature of 45.63 °C and the latent heat of 167.4 J/g. The prepared material had a small leakage rate which was less than 2%. Scanning electron microscope (SEM) results shown that EG and CF possessed excellent compatibility in FSPCMs. In-situ X-ray diffraction (XRD) tests demonstrated that the crystal behaviors of paraffin and EVA were changed with the phase transformation. Thermal conductivity results shown that thermal conductivity of FSPCMs in horizontal orientation was higher than that in longitudinal orientation. EG and CF have synergistic enhancement to thermal conductivity of FSPCMs. [ABSTRACT FROM AUTHOR]

In this study, silica aerogel microspheres were prepared through sol–gel method with tetraethyl orthosilicate as the silicon source. Thermal insulation coatings were prepared by mixing silica aerogel and acrylic emulsion. The relationships between the thermal conductivity and volume fractions, densities, sizes, and interfaces of silica aerogel microspheres were investigated through scanning electron microscopy and thermal conductivity analysis. The thermal insulation mechanism of composite coating was discussed in detail. Results showed that the aggregations prevented the decrease of thermal conductivity in the coating when the volume fraction of silica aerogel microspheres was lower than 30 %. However, the pores in the coating reduced the thermal conductivity when the volume fraction was higher than 30 %. The porosity of silica aerogel increased with the declining density, which improved the thermal insulation performance of silica aerogel and reduced the thermal conductivity of the coating. The thermal conductivity of the coating with large microspheres was lower than that with small microspheres at low volume fractions. However, the thermal conductivity of the coating with small silica aerogel microspheres was low because of their large interfacial thermal resistance at high volume fractions. Wetting agents were beneficial in improving the compatibility of hydrophobic aerogel microspheres and polymer, improving the volume fractions of silica aerogel microspheres in the coating, and reducing the thermal conductivity of the coating. [ABSTRACT FROM AUTHOR]