Materials Science Forum Vol. 814

Abstract: The thermal stability of molten salts, operating temperature range and latent heat of melting for the molten salts at high temperature have been studied in the present investigation. The multi-component molten salts composed of purified potassium nitrate, purified sodium nitrate were prepared by statical mixing method [1]. The stability experiments were carried out at 500 to 600°C, and the experimental result showed that the purified nitrate molten salts performed better high-temperature thermal stability and its optimum operating temperature was increased from 500°C to 550°C. DSC analysis indicated that the purified nitrate molten had a lower melting point and a higher phase change latent heat. The melting point of purified binary nitrate molten salts was sharp decreased to 225.2°C and latent heat of melting for molten salts was also reduced from 78.41J/g to 81.15J/g compared with unpurified nitrate salts. Besides, the change in the concentration of impurities by analyzing in the binary molten salts, and combination of XRD test results can be found that the degree of degradation reduce and improve the thermal efficiency of the storage of binary molten salts by purified sodium nitrate and potassium nitrate.

Abstract: The sintering properties of appetite-type lanthanum silicate La₁₀Si₆O₂₇prepared by sol-gel process were studied. The precursor powder was sintered by one-step sintering (OSS) process, two-step sintering (TSS) process and spark-plasma sintering (SPS) process. The phase structure, microstructure, relative density, thermal expansion properties, electrochemical properties of the samples were investigated by means of the techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), Archimedes method, dilatometer, and AC impedance spectroscopy. The experimental results show that the samples sintered by SPS process can decrease the sintering temperature, shorten the sintering time, increase the density, and reduce the particle size. The appetite-type lanthanum silicate La₁₀Si₆O₂₇ sintered by SPS process shows better sintering properties than of sintered by OSS process and TSS process, which can beneficial to the thermal expansion properties and conductivity.

Abstract: Graphite is the widely used material as anode materials for Li-ion cells with a low theoretical capacity of 372 mAhg^-1. Silicon has a high theoretical capacity of 4212 mAhg^-1, but has a low intrinsic conductivity and its lower cycling life makes it unpractical. In this paper, silicon/artificial graphite composite was prepared by mechanical alloying to improve the cycle property of Si. On one hand, a new kind of alloy SiC was composited and composed as a coacervate, and the particle sizes of the silicon was reduced settled by mechanical alloying but the size of the new material become larger and larger with the proportion of artificial graphite increasing. On the other hand, the new material exhibits a better electrochemical performance, with the rate of its cyclic discharge capacity decreasing slowly.

Abstract: This paper provides a novel route to prepare silica monoliths with hierarchical porous structure via freeze drying. In this method, macroporous silica monoliths were first produced by freeze-drying and calcination. By adjusting the concentration of cetyltrimethylammonium bromide in ethylsilicate, a layer of mesoporous thin film was attached on the macroporous silica monolith. The structural characterization of the hierarchical porous monoliths were studied by field emission scanning electron microscopy, mercury porosimeter and nitrogen adsorption-desorption techniques (BET). It turned out that the pore distribution of the obtained monoliths was ranged from 3.72 nm to 23.21nm and the maximum specific surface area calculated from BET was about 288 m^2/g, which indicated the existence of hierarchical structure in the obtained material.

Abstract: The precursor Ni (OH)₂ was synthesized by a simple hydrothermal method with hexamethylenetetramine ((CH₂)₆N₄) as precipitant and template, and then NiO was gained after calcination. The phase and morphology of the synthesized product were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM), and the electrochemical capacitive characterization was performed using cyclic voltammetry (CV), chronopotentiometry and electrochemical impedance spectroscopy (EIS) in a 6mol/L KOH aqueous solution electrolyte. The result shows that spherical NiO without impurity was synthesized, the average diameter of the spheres is 5 um and these spheres were constructed by the interactive arrangement of many nanoflakes in three dimensions. This kind of NiO shows the typical electrochemical characteristics of pseudo capacitance with high specific capacity and excellent rate capability. The specific capacity can reach 515F/g at the current density of 1A/g

Abstract: The precursor nickel and manganese carbonates were synthesized by co-precipitation with sodium carbonate as precipitant, and then nickel and manganese oxides were gained after calcination. The phase and morphology of the synthesized product were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM), and the electrochemical characterization was performed using cyclic voltammetry (CV), galvanostatic charge–discharge tests (GCD) and electrochemical impedance spectroscopy (EIS) in a 6mol/L KOH aqueous solution electrolyte. The result showed that the products were the mixture of nickel and manganese oxides and solid solution. nanoparticles and spherical particles were gained by controlling the molar ratio of nickel and manganese. All of the samples exhibited typical Faradic redox capacitance. The specific capacitance was different with the change of nickel and manganese molar ratio. The specific capacitance (Cs) reached 130F/g at 1A/g when the ratio was 2:1.

Abstract: Triboelectric nanogenerators have recently been used to harvest mechanical energy from surrounding environment which is of great significance in the field of energy conversion. Electrospinning provides a simple, low cost and versatile method for the generation of 1D nanostrucutures. Nanofiber membranes have many advantages over the commonly used dense film for designing the riboelectric nanogenerators, such as the low wear resistance caused from the internal and excellent external consistency of the electrospinning membranes. In this paper, we produce a variety of polymer films by electro-spinning, and fabricate Polyvinylidene Fluoride (PVDF) triboelectric nanogenerators with different polymer films afterwards. We except to explore the TEG power generation effect, and influencing factors, and then determine the best combination of the results of TEG (PVDF-PHBV). Such a flexible polymer TEG generates output voltage of up to 112 V at a power of 0.045W.

Abstract: In this study, a model based on bond number calculation in a system was developed to predict size-dependent evaporation temperature of nanoparticles. This model, free of any adjustable parameters, can be utilized to predict the thermal stability for low dimensional materials. If the atomic structure of a nanoparticle is known, the size and shape-dependent bond number can be obtained. The cubooctahedral structure was taken as the shape of nanoparticles for simplicity. According to the established model, the evaporation temperature of nanoparticles is dependent not only on their size, but also on their atomic diameter. The results indicated that the evaporation temperature decreased with the decreasing size of free-standing nanoparticle. The theoretical predictions are consistent with the evidences of the experiments or molecular dynamic simulations for Au and Ag nanoparticles.

Abstract: In this study, electrical properties of multi-walled carbon nanotubes (MWCNTs) reinforced epoxy resin composites were investigated, with respect to the method of dispersion, surfactants, content and chemical groups of CNTs. Experimental results show that chemical functionalization and surfactants improved the dispersion of CNTs in epoxy resin. Electrical conductivity of epoxy increased by two orders of magnitude with 0.5 wt% MWCNTs, while seven orders of magnitude with 2.0 wt% MWCNTs-NH₂. The results also indicated that an effective electron transport channels formed in the composites with 0.5 wt% CNTs approximately.

Abstract: Super-aligned carbon nanotube films are carbon nanotube macrostructures which have excellent orientations. The bending actuator based on super-aligned carbon nanotube/polymer composites can make a significant controllable bending deformation under a very low DC voltage (< 700 V/m). In this paper, we explored how to make the thermal induced actuator reach maximal deformation. By theoretical modeling and simulation through Mathematica software, the relationship between free-end displacement of the actuator and actuator length, thickness (or thickness ratio) of two layers, difference of coefficient of thermal expansion between two layers, temperature variation and other parameters were studied. Simulation results showed that the deformation is greatly influenced by the thickness ratio of the two layers of the actuator. The deformation displacement reaches a maximum value with a specified thickness ratio. This study may provide valuable theoretical references for the experimental design of carbon nanotube composite actuators.