Materials Science Forum Vol. 999

Abstract: SiC/B₄C composite was obtained using the reaction sintering method with Si infiltration, which exhibited excellent mechanical properties. The dynamic compressive response was investigated using a Split Hopkinson pressure bar at high strain rates ranging from 0.4×10³ to 1.2×10³ s^-1. The results show that the dynamic strength of the SiC/B₄C composite obtains a peak value at a strain rate of 1000/s, while its strain increased continuously with increasing strain rate. The dynamic loading mode of SiC/B₄C composite exhibited three deformation regions, including an inelastic deformation region, rapid loading region and failure region. The dynamic failure mode of SiC/B₄C composite depended upon the strain rate.

Abstract: The multilayer composite films consisting of poly (diallyldimethylammonium chloride) functionalized graphene (PDDA-rGO) and phosphomolybdic acid functionalized graphene (PMo₁₂-rGO) were prepared by layer-by-layer self-assembly method. The {PDDA-rGO/PMo₁₂-rGO}_n multilayer composite films were used as a support for electro-deposition of Pt particles in situ. Cyclic voltammetry (CV), X-ray photoelectron spectroscopy and scanning electron microscopy were employed for examining the composition, structure, and morphology of the catalyst. Results revealed that the Pt/{PDDA-rGO/PMo₁₂-rGO}_n catalyst is successfully prepared and that the multilayer composite films support improves the dispersion of the Pt particles. CV and chronoamperometry were employed to evaluate the electrocatalytic performance for methanol oxidation. Results revealed that the electrocatalytic activity and stability of the Pt/{PDDA-rGO/PMo₁₂-rGO}₃ catalyst for methanol oxidation are considerably improved in comparison with that of the Pt/GCE catalyst. The current density for the oxidation of methanol increased from 0.66 mA/cm² to 1.21 mA/cm². In addition, the ratio of the forward current density to the backward current density (I_f/I_b) was 1.92 for Pt/{PDDA-rGO/PMo₁₂-rGO}₃ catalyst, corresponding to 1.3 times that of the Pt/GCE catalyst. This result indicated that the multilayer composite films remarkably enhanced the electrocatalytic activity regarding methanol oxidation.

Abstract: The objective of the present investigation is to study the oxidation resistance of SiO₂/SiC coating on carbon fiber by electrolytic plasma spraying. The SiO₂/SiC coating can be easily prepared within several tens seconds through this approach. The effect of spraying parameters (fixed point 5s and spray 5 times at the speed of 20mm/s) on the microstructure and oxidation resistance properties of coatings was discussed in this paper. Scanning electronmicroscopy (SEM), energy dispersive spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS), thermogravimetric (TG) and DTG have been used to characterize the SiO2/SiC coatings. It was demonstrated that fixed-point spray 5s has better density and oxidation resistance coating, and the oxidation resistance increased by 12% compared with spray 5 times at the speed of 20mm/s. The fixed-point spray 5s coating was mainly composed of SiO₂ and SiC. The SiO₂ relative content was 72.6% and the SiC relative content was 27.4%.

Abstract: As a potential functional material in the perovskite family, the KCaF₃ on electronic structure, elasticity, Debye temperature and anisotropy are studied based on density functional theory (DFT). Above all, the structural parameters of KCaF₃ crystal are optimized. Then the elastic constants and Debye temperature are calculated. The results show that: (1) KCaF₃ is composed of covalent bonds, in which the Ca-F bond is stronger than K-F. (2) Ca atom mainly contributes for the electronic properties of KCaF₃. (3) The structural parameters of KCaF₃ is in fair agreement with the experimental data. (4) The anisotropy of KCaF₃ was analyzed from the pure and quasi waves, of which the longitudinal wave velocity in the direction of [100] is the larger than the others two directions ([110] and [111]). Finally, The homogenized elastic moduli (bulk modulus B, shear modulus G, Young's modulus E), Pugh and Poisson ratio, are obtained. This research is meaningful and thus to provides a good theoretical guidance for the design the new ABX₃-type material with better performance.

Abstract: Lithium ion battery is a key component of energy storage system. Accurate and scientific prediction of its Remaining Useful Life (RUL) is an important factor to check the operation of energy storage system is whether reliable. ARIMA is an effective time series prediction processing method, which can be used to calculate battery RUL and its confidence interval. And the more predicted samples, the higher the prediction accuracy. Compared with the empirical model and support vector machine algorithm, the analysis results show that the support vector machine is over-fitting. For two sets of the experimental data, the absolute predictive error of ARIMA algorithm is approximately 1.2%, that of linear model is approximately 1.4%, and that of Verhulst model is approximately 7.5%, which verifies the accuracy of ARIMA time series model in predicting the RUL in long interval.

Abstract: The three-dimensional growth chamber model was established by GAMBIT software, and the FLUENT software was used to simulate the Vapor Phase Epitaxy ( VPE ) growth AlN material. By changing parameters, results of simulation were obtained, in turn described the effect of uniformity and concentration of AlN. The study mainly focuses on the research of flow velocities of nitrogen and argon gas, the distance from the substrate to the inner tube mouth, the substrate front-back angular height difference, the inner tube diameter, and the substrate thickness. It is discovered through the research: above parameters play a very important role in the crystal growth of AlN film, and there are optimal parameter values. The structure of growth chamber is designed and optimized according to the simulation result. By using the simulation software, experimental costs can be greatly saved, which provides a theoretical basis for the optimal growth process of high quality AlN film, and has a certain guiding role for the actual growth process.

Abstract: Based on the first-principles calculation and the quasi-harmonic Debye model, the electronic and thermodynamic properties of CuCl₂-type PbSe₂ compound of a promising thermoelectric (TE) material are studied. According to the analysis of the density of states (DOS) and the Mulliken electron population, it is found that the PbSe₂ compound possesses weak metallic characterization, where the covalent bonding exists in PbSe₂ compound and the ionic bonding exists between Pb and Se atoms. Besides, the Debye temperature decreases with increasing temperature at certain pressures, and it shows the increasing tendency under the elevated pressure at certain temperatures. The Grüneisen parameter increases with increasing temperature at the given pressures, and it also decreases with increasing pressure at the given temperatures. The density functional theory (DFT) is used to obtain the parameters of the Debye temperature, the Grüneisen constant and thermal expansion coefficient, which are about 319.76 K, 2.42, and 8.41×10^-5 K^-1 at 0 GPa, which provides useful parameters and contributes to explore new potential TE materials in future.

Abstract: Nano coir cellulose whiskersare materials abstracted from mesocarp of coconut shell which was modified by using KH570 as a coupling agent and modified nano coir cellulose whiskers need to be dispersed in chitosan/polyvinyl alcohol (CS/PVA) mixture solution. Because of regular structure and high crystallinity, nano coir cellulose whiskers could be applied in medical materials.In this paper, the results obtained with solution casting method by characterizing and analyzing structure, thermal properties, crystallization behavior and morphology of nano coir cellulose whiskers enhanced CS/PVA composite filmby FTIR, DSC, TG, XRD and SEM test. Different content of modified nano coir whiskers and CS/PVA composite film were preparedand themechanical properties of the composite film were also conducted. The results show that the tensile strength and Young's modulus of the CS/PVA composite film with modified nano coir whiskers are significantly improved, and Elongation break increases at first and then decreases, which indicates nano coir cellulose whiskers are good materials for medical purpose.

Abstract: Silylation, also known as silane grafting, is frequently used to organically modify montmorillonite (organo-Mt), which of properties were depended on the type of siloxane and intercalated interlayer structure of Mt, for construction of functional materials utilizing in a variety application of industry. We have synthesized organo-Mt using different siloxanes after Mt was firstly modified at three different surfactants of cationic cetyltrimethylammonium bromide (CTAB), anionic sodium oleate (So) and nonionic sorbitan monostearate (Span60) to identifying the effect of surfactants for silylation of Mt. The spectral and structural characters of the obtained products were characterized by a combination of X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetry (TG), and contact angle analysis. The basal spacing of the organo-Mt increased with surfactants loading. We found that CTAB can significantly increase the spacing between layers of Mt from 1.55nm to 1.90nm, load more siloxane on Mt. The average contact angles of CTAB-Mt-APTES and CTAB-Mt-PTES were 69.9±0.3° and 80.7±0.3°, which could be more prone to the interlayer locking effect. Our study showed that the charge of surfactants has significant influence for silylation of Mt, resulting in the loading amount of silane, interlayer structure, and the surface wetting properties.

Abstract: This study examined the co-pyrolysis characteristics of low-rank coal (SJC) and direct coal liquefaction residue (DCLR) through thermogravimetric analysis coupled with Fourier transform infrared spectrometry. It also investigated the influences of different mass fractions of DCLR to SJC on the co-pyrolysis characteristics and release regulation of gas phase components. Results showed that with increasing DCLR content, coke yield initially decreased and then increased, but tar and gas yield reversed. Different addition of DCLR changed the composition of the pyrolysis gas in various degrees, and reduced the content of-OH and nitrogen compounds in coke. The H₂ content in the gas gradually increased. When 40% DCLR was added, the maximum tar yield was 22.79%, and the maximum H₂ yield was 37.12%. At 60% DCLR, the lowest semi-coke yield was 65.01%, and the highest gas yield was 14.65%. The co-pyrolysis of SJC and DCLR can be divided into three stages. The first was the dry degassing stage, during which the adsorbed gas and small-molecule gas were removed on the coal surface at room temperature to 350 °C. The second stage (350 °C–650 °C) was the intense pyrolysis reaction stage, during which a large number of volatiles were obtained. The substantial weight loss rate peak appeared around 450 °C. The weight loss rate of pyrolysis gradually increased with increasing DCLR dosage. The co-pyrolysis of SJC and DCLR was not a simple sum between SJC and DCLR, which indicated a synergistic effect in the co-pyrolysis. The synergistic effect between SJC and DCLR enhances the interaction between free-radical fragments, thereby increasing the yield of pyrolysis tar. The third stage was the shrinkage of semi-coke from 650 °C to the end of the reaction. The polycondensation reaction between free-radical fragments to form solid coke with higher aromaticity, and H₂ released.