Thermal Analysis of CNT-Based Nano-Composites by Element Free Galerkin Method

This paper deals with the thermal analysis of carbon nanotube (CNT) based composites by meshless element free Galerkin method. Cylindrical representative volume element (cylindrical RVE) has been chosen to evaluate the thermal properties of nano-composites using multi-domain and simplified approaches. The values of temperature have been calculated at different points and plotted against RVE length and RVE radius. A sensitivity analysis of RVE as well as CNT dimensions has been carried out in detail. The present computations show that the equivalent thermal conductivity is a function of CNT length, CNT radius, RVE length and RVE radius. Based on present numerical simulations, an approximate formula is proposed to calculate the equivalent thermal conductivity of nano-composites. The results obtained by simplified approach have been found in good agreement with those obtained by multi-domain approach.     

Application of silica-containing nano-composite emulsion to wall paint: A new environmentally safe paint of high performance

A new emulsion-type paint was prepared by utilizing a nano-composite emulsion (NCE), which contained nano-size particles (ca. 60 nm in diameter) consisting of silica (inorganic core, ca. 30 nm in diameter) and polyacrylate (organic shell), and evaluated as wall paint. By applying NCE for the wall paint, about 35 wt.% of the organic content in the paint could be reduced in comparison with the commodity emulsion-type paint, which is highly effective to save the petroleum resources. The basic properties of the white NCE paint film on gloss, surface hardness, adhesion, and solvent resistance were evaluated and compared with those of acrylic emulsion-type paints as well as those of silica-containing paints which were prepared simply by blending the acrylic emulsion with silica sol. The NCE paint was especially excellent in solvent resistance. Then the practical tests were performed to evaluate its appropriateness as wall paint, which clarified the excellent antipollution property and the high flame resistance of the NCE paint.     

纳米In2O3／TiO2介孔复合体的制备及其光致发光性能研究

本论文利用尿素水解均匀沉淀法制备锐钛矿型纳米TiO2介孔粉体，然后在硫酸铟溶液中浸泡一周，并在650℃下退火处理5h，制得纳米In2O3／TiO2介孔复合体。采用X射线衍射（XRD）和光致发光（PL）谱表征In2O3／TiO2介孔复合体的组成结构和发光性能，并对相同温度退火处理下的介孔TiO2粉体进行比较，结果表明：经过650℃退火后，在激发波长380nm，发射波长570nm附近，纳米In2O3／TiO2介孔复合体产生荧光增强效应。     

The effects of surface elasticity and surface tension on the transverse overall elastic behavior of unidirectional nano-composites

The effects of surface elasticity and surface tension on the transverse overall behavior of unidirectional nano-scale fiber-reinforced composites are studied. The interfaces between the nano-fibers and the matrix are regarded as material surfaces described by the Gurtin and Murdoch model. The analysis is based on the equivalent inhomogeneity technique. In this technique, the effective elastic properties of the material are deduced from the analysis of a small cluster of fibers embedded into an infinite plane. All interactions between the inhomogeneities in the cluster are precisely accounted for. The results related to the effects of surface elasticity are compared with those provided by the modified generalized self-consistent method, which only indirectly accounts for the interactions between the inhomogeneities. New results related to the effects of surface tension are presented. Although the approach employed is applicable to all transversely isotropic composites, in this paper we consider only a hexagonal arrangement of circular cylindrical fibers.     

Spark plasma sintering and in vitro study of ultra-fine HA and ZrO2–HA powders

Spark plasma sintering (SPS) was employed to sinter RF suspension plasma sprayed HA ultra-fine powders and ZrO₂–HA nano-composite powders. The powders were sintered at 1000 °C for 5 min at 11.1 MPa and 1100 °C for 5 min at 11.1 MPa, respectively. After sintering, the samples were ground and polished for subsequent indentation and microscopy studies. The as-sintered compacts of the HA–CaP powders were studied in vitro by immersion in simulated body fluid (SBF). The in vitro studies indicated that a bio-active apatitic layer was formed as early as 1 week after immersion. Optical microscopy and SEM investigation revealed negligible porosity and dense microstructure suggesting liquid phase sintering to have taken place. Phase composition was calculated with the aid of XRD and the Rietveld method. The results indicated that the mechanical properties of the as-sintered compacts were improved in the presence of nano-ZrO₂. The Young’s modulus increased to 130 MPa and the fracture toughness was 1.6 MPa m^1/2 for ZrO₂ loading lower than 3 vol.% indicating greater enhancement of properties than that suggested by the rule of mixtures.     

聚丙烯/BA原位聚合改性MMT纳米复合材料的微观结构

通过原位聚合制备了聚丙烯酸丁酯（PBA）改性蒙脱土（MMT），再与PP熔融复合，制成PP／MMT复合材料，利用X射线衍射（XRD）、扫描电子显微镜（SEM）和电子探直表征了复合材料的微观结构。结果表明：PP／MMT复合材料为纳米复合材料，MMT的加入诱导了β－晶型PP的形成。     

Real-time investigation of crystallization in poly(vinylidene fluoride)-based nano-composites probed by infrared spectroscopy

Via time-resolved Fourier transform infrared spectroscopy (FTIR), we examined the real-time investigation of the conformational changes of poly(vinylidene fluoride) (PVDF) chain segment during crystallization of neat PVDF and the corresponding nano-composites having intercalated structure. It was shown that in the following crystallization processes the crystal growth was virtually the same in both nano-composites and neat PVDF. We have examined an annealing at an infinitely long time at 200 °C (∼20 min) to erase the thermal history in the nano-composites. The dispersed titanate nano-filler particles exhibited strong contribution to enhance the heterogeneous nucleation for the formation of both γ- and β-phase crystals.     

Thermal shock behavior of Si3N4-TiN nano-composites

Si₃N₄-TiN nano-composites were fabricated by hot press sintering nano-sized Si₃N₄ and TiN powders. The microstructure, mechanical properties and thermal shock behavior of Si₃N₄-TiN nano-composites were investigated. The addition of proper amount TiN particles can significantly increase the flexural strength and the fracture toughness. Si₃N₄-TiN nano-composites showed both higher critical temperature difference and higher residual strength compared with those of monolithic silicon nitride nano-ceramic when the amount of TiN is less than 15 wt.%. But a further increase in the amount of TiN leaded to a decrease in the thermal shock resistance.     

Effect of fluid–particle-interactions on dispersing nano-particles in epoxy resins using stirred-media-mills and three-roll-mills

Fibre reinforced composites are indispensable in the field of modern lightweight structures, such as used in aerospace, automotive industry or in wind power plants. Those materials provide high weight savings and increase the efficiency of a structure significantly. Therefore, various efforts are made to continuously improve the quality of the matrix and the fibres. By embedding nano-particles into the epoxy matrix, the mechanical properties as well as the electrical and thermal characteristics can significantly be improved [1]. In most cases these nano-sized particles are produced as dry powders not as single primary particles but rather as particle collectives consisting out of several primary particles. For the application in reinforced composites the particles must be suspended in epoxy resin as separately dispersed primary particles or in a certain aggregate size. Generally, the influencing parameters to break up the aggregates in a dispersion process can be divided into the stress mechanism, the intensity and the frequency of the dispersing machine itself, the properties of the dispersed particles (e.g. the particle–particle interactions) the properties of the homogenous phase and the particle–resin-interactions. Besides the effect of the chosen dispersing machine the optimization of the dispersing process was investigated by applying modified particle surfaces and varying the fluid properties. The results show that the surface properties of the particles must fit to the epoxy resin properties and the attractive forces between the primary particles must be reduced or the stabilization improved, respectively. An indication for an improved stabilization and adjustment of the particles surface properties to the fluid properties can be obtained by measurements of the contact angle and the rheological properties. Generally, an increase of viscosity and mass fraction of the product leads to a higher energetic efficiency of the dispersion process in the stirred media mill and three-roll-mill.     

Magnetically recoverable CoFe1.9Gd0.1O4 ferrite/polyaniline nanocomposite synthesized via green approach for radar band absorption

The gadolinium substituted cobalt ferrite (CoFe_1.9Gd_0.1O₄) nanoparticles and CoFe_1.9Gd_0.1O₄/Polyaniline (PANI) microwave absorber were synthesized by sol-gel auto combustion technique using lemon juice and in-situ polymerization method respectively. X-ray patterns confirmed the formation of single phase cubic structure. The crystallite size of the synthesized CoFe_1.9Gd_0.1O₄ nanoparticles are within the range of 15–68 nm. The saturation magnetization of CoFe_1.9Gd_0.1O₄ ferrite/Polyaniline (PANI) composite was reduced due to nonmagnetic PANI. The reflection loss for microwave absorbing properties of CoFe_1.9Gd_0.1O₄ ferrite nanoparticles and CoFe_1.9Gd_0.1O₄/PANI nanocomposite were investigated and minimum value of reflection loss was found to be −16.85 dB at 13.52 GHz for nanoparticles of thickness 2.5 mm and −25.59 dB at 11.92 GHz for CoFe_1.9Gd_0.1O₄/PANI nanocomposite of thickness 2.0 mm) respectively. The prepared samples have low density, high surface resistivity and enhanced attenuation constant. The nanocomposite exhibits excellent absorption performance over a broad band range in the radar band.