Key Engineering Materials Vol. 519

Abstract: This paper deals with the synthesis of ultralow density silica aerogels using tetramethyl orthosilicate (TMOS) as the precursor via sol-gel process followed by supercritical drying using acetonitrile solvent extraction. Ultralow density silica aerogels with 6 mg/cc of density was made for the molar ratio by this method. The microstructure and morphology of the ultralow density silica aerogels was characterized by the specific surface area, SBET, SEM, and the pore size distribution techniques. The results show that the ultralow density silica aerogel has the high specific surface area of 812m²/g. Thermal conductivities at desired temperatures were analyzed by the transient plane heat source method. Thermal conductivity coefficients of silica aerogel monoliths changed from 0.024 to 0.043W/ (m K) as temperature increased to 400°C, revealed an excellent heat insulation effect during thermal process.

Abstract: In the present investigation, the Al-C-KCl composite powders were prepared by a ball milling processing in an attempt to improve the hydrogen evolution capacity of aluminum in water. The results showed that the hydrogen generation reaction is affected by KCl amount, preparation processing, initial aluminum particle size and reaction temperature. Increasing KCl amount led to an increased hydrogen generation volume. The use of aluminum powder with a fine particle size could promote the aluminum hydrolysis reaction and get an increased hydrogen generation rate. The reaction temperature played an important role in hydrogen generation rate and the maximum hydrogen generation rate of 44.8 cm3 min-1g-1of Al was obtained at 75oC. The XRD results identified that the hydrolysis byproducts are bayerite (Al(OH)3) and boehmite (AlOOH).

Abstract: Ammonia borane (AB) hydrides have been employed as disposable hydrogen (H2) sources for fuel cell applications, due to their high hydrogen capacity. In this paper, ammonia borane (AB) complex with high purity was synthesized by chemical method, using the low cost raw materials of NaBH4, CO2, and NH3. The thermal dynamic for the synthesis process is analyzed. The phase composition for the obtained ammonia borane (AB) complex powders was detected by X-ray diffraction (XRD) characterization. The results suggest that, very high purity ammonia borane (AB) complex powders were obtained, which was quite in agreement with the standard index of ammonia borane.

Abstract: In this paper, LaNi4.7Al0.3 alloy samples were obtained via melting in middle frequency influence fire .In addition, The alloy pellets were milled for absorbing and desorbing Hydrogen ability study, The P-V-T measurement provided us with poisonous effect on the oxidation of LaNi4.7Al0.3.To understand the poisoning mechanism of O2 on LaNi4.7Al0.3, the X-ray photoelectron spectroscopy (XPS) was introduced to analyzed the process of poisoning of LaNi4.7Al0.3 alloy, Which revealed the changes of the valence of the elements of the alloy LaNi4.7Al0.3 poisoned by O2.

Abstract: Converting biomass into fuel is becoming increasingly important owing to the desirability of finding substitutes for fossil fuels and to the need to address the problem of global warming. Cellulose, one of the main constituents of biomass, is the most abundant bio-renewable material on the planet. Considerable effort has been devoted to the hydrolysis of cellulose in order to convert it into fuel. In this paper, both two-dimensional electrode electrochemical degradation of cellulose and the use of biological degradation of cellulose were investigated, which provides a detailed study of cellulose activity and stability in various ionic liquids. In the two-dimensional electrode reaction system, after 5 hours at the voltage of 8 V under the conditions of electrolysis, the degradation of cellulose reached 43.7%, BOD5/COD also significantly improved with biological treatment to the combination of electrochemical techniques. As the result, HEMA is a promising, novel, green medium for performing cellulose hydrolysis reactions to convert biomass into bio-fuels.

Abstract: In this article, the Al/Ni reactive multilayer foils that can be used for joining materials in an efficient and energy-saving way were prepared by a hot rolling method, during which the Al/Ni multilayer foils were kept in furnace at a certain temperature for a period before the multilayer foils were rolled for each pass. After the cold rolling and hot rolling procedure at the temperature of 200 oC and 300 oC, no reaction between Al and Ni could be detected. The effect of rolling temperature on the self-propagating high temperature synthesis (SHS) reaction of the Al/Ni multilayer foils was investigated. As the rolling temperature rose to 300 oC, the SHS reaction of the Al/Ni multilayer was hard to be ignited and was even quenched before the SHS reaction completed. The XRD patterns and SEM images results demonstrated that the higher temperature increased the deformation of the samples during the rolling passes so the Ni particles increased, and thereby led to the decrease of the mix homogeneity of Al and Ni foils.

Abstract: A composite of reduced graphene oxide (r-GO) decorated densely with 20 nm Fe3O4 nanoparticles has been prepared by a facile solvothermal method. The Fe3O4/r-GO composites are used as the anode material for lithium ion batteries, which show an extremely high initial discharge specific capacity of 1702 mAh/g. Compared with the pure Fe3O4 nanoparticles, the composite anode exhibits a higher capacity retention capability since its specific capacity fades very slowly and retains a value of 711 mAh/g after 30 cycles. The r-GO sheets worked as an ultra-thin and conductive substrate can not only prevent the detachment and agglomeration of Fe3O4 nanoparticles, but also compensate for the volume change of Fe3O4 nanoparticles during the charge-discharge cycles, and thus extend the cycling life of the Fe3O4/r-GO composites electrode.

Abstract: Based on copper foil, this paper takes electrodeposition to prepare tin-nickel alloy based anode material, which is of Sn 81.23% (Mass Fraction, the same as below), and Ni 18.77% (Mass Fraction, the same as below). It also studies the plating state, and plating structures and its electrochemical properties under heat treatment at different temperatures. The X-ray diffraction analysis (XRD) shows that the plating structures are all Ni3Sn4 and unalloyed individual-phase Sn under plating state and 200 oC heat treatment, and are Ni3Sn2 , Sn, Ni3Sn2 , Ni3Sn4 under 300 oC and 450 oC heat treatment respectively. In a button cell, which was made up with lithium slice, the results of charge-discharge cycle test and cyclic voltammetric curves test indicate that tin-nickel alloy’s specific capacity and charge-discharge cycle performance are related to the heat treatment temperature and structure of lithium battery anode material. The plating under plating state and 200oC heat treatment has high specific capacity, and its charge-discharge stability is well above that of the plating under other temperatures. Under 200 oC heat treatment, the plating could crystallize better and increase its content of Ni3Sn4. Its charge-discharge stability would be well above that of the original plating state. The scanning electron microscope (SEM) shows that before discharging, the plating of tin-nickel alloy was made up of small spherical particles, which are uniform and dense. The plating began to swell and crack after 50 times charge-discharge, which may lead to rapidly attenuate the plating’s specific charging capacity.

Abstract: In this article, the structure and morphology of the carbon anode materials with different dimensions have been characterized through SEM and TEM. The performances of electrochemical intercalation and deintercalation of lithium-ions have been studied. The results show that graphene as the two dimensional nanomaterials possess more advantages of microstructure and better Li-ions intercalation performances than carbon nanotubes (CNTs) and graphite. The superior abilities of Li-ions intercalation and deintercalation are attributed to increasing lithium storage space, decreasing Li diffusion distance, and higher specific surface area for Li-ions.

Abstract: LiMn1-xFexPO4 cathode materials were synthesized by microwave hydrothermal using ascorbic acid as reducing agent. The crystal structure, microstructure, electrochemical properties were characterized by XRD and SEM, the discharge capacity and cycling performance were compared. The results show that the lattice parameters of LiMnPO4 decreased by doping Fe, and the doping amount is x = 0.4, the discharge capacity of the prepared material reaches to 145 mAh/g, which has improved of 76.8% compared with the undoped LiMnPO4 at 0.1C.