Lianmeng Zhang

Facile fabrication and enhanced photocatalytic performance of Ag/AgCl/rGO heterostructure photocatalyst.

Graphene/reduced graphene oxide (rGO) modification has been demonstrated to be an efficient route to improve the photocatalytic performance of various photocatalysts by promoting the effective separation of photogenerated electrons and holes. It is highly required to develop facile and environmental-friendly methods for the preparation of graphene-based photocatalytic materials. In this study, the Ag/AgCl/rGO heterostructure photocatalyst was fabricated by a mild oxidization reaction of hydrothermally prepared Ag/rGO in FeCl3 solution. It was found that the reduction of graphene oxide (GO) was accompanied with the in situ formation of metallic Ag in a Ag[(NH3)2](+)-immobilized GO solution during hydrothermal treatment, while the following in situ oxidation of metallic Ag by FeCl3 solution resulted in the formation of strongly coupled Ag/AgCl/rGO heterostructure photocatalyst. The photocatalytic experimental results indicated that all the resultant Ag/AgCl/rGO nanocomposite photocatalysts exhibited a much higher photocatalytic activity than the Ag/AgCl and physically mixed Ag/AgCl/rGO composite, and the Ag/AgCl/rGO (3.2 wt % rGO) showed the highest photocatalytic performance. The enhanced photocatalytic performance of Ag/AgCl/rGO heterostructures can be attributed to the cooperation effect of the effective separation of photogenerated carriers via strongly coupled rGO cocatalyst and the enrichment of organic molecules on the rGO nanosheets. Considering the facile preparation and its high photocatalytic activity, it is possible for the present Ag/AgCl/rGO nanocomposites to be widely applied in various fields such as air purification and wastewater treatment.

Preparation of zirconium pyrophosphate bonded silicon nitride porous ceramics

Abstract A new method for preparing high bending strength porous silicon nitride ceramics with controlled porosity was developed using a pressureless sintering technique, using zirconium pyrophosphate as a binder. The fabrication process was described in detail and the sintering mechanism of porous ceramics was analysed by an X-ray diffraction method. The microstructure and mechanical properties of the porous Si3N4 ceramics were investigated, as a function of the content of ZrP2O7. The resultant porous silicon nitride ceramics sintered at low temperature (1000 and 1100°C) showed fine micropore structure and a high bending strength. Porous silicon nitride ceramics with porosity of 34–47%, a bending strength of 40–114 MPa and a Youngs modulus of 20–50 GPa were obtained.

High-temperature thermoelectric properties of n-type BayNixCo4-xSb12.

(x 4 0–0.1, y 4 0–0.4) were investigated at temperature range of300 to 900 K. Thermal conductivity decreased with increasing Ba filling fraction andtemperature. When y was fixed at 0.3, thermal conductivity decreased with increasingNi content and reached a minimum value at about x 4 0.05. Lattice thermalconductivity decreased with increasing Ni content, monotonously (y l 0.1). Electronconcentration and electrical conductivity increased with increasing Ba filling fractionand Ni content. Seebeck coefficient increased with increasing temperature anddecreased with increasing Ba filling fraction and Ni content. The maximum ZT valueof 1.25 was obtained at about 900 K for n-type Ba

Degradation of yttria stabilized zirconia at 370 K under a low applied stress

Abstract The tetragonal-to-monoclinic phase transformation in ZrO 2 –3mol.%Y 2 O 3 containing 0–5% A1 2 O 3 during aging in hot water (370 K) under 100 MPa stress is investigated. It is found that while a small tensile stress accelerates the degradation, a compressive stress has little affect on the degradation. The degradation of PSZ under tensile stress is considered to be caused by the reaction between Y 2 O 3 and H 2 O. Small amount of A1 2 O 3 addition does not change the degradation mechanism of PSZ, but it prevents further continuation of degradation when the transformed volume reaches a certain value.

Properties of TiCNi3Al composites and structural optimization of TiCNi3Al functionally gradient materials

Abstract The thermomechanical properties of TiCNi 3 Al composites with various TiC:Ni 3 Al ratios were measured. The relationship between the properties and the material microstructures was discussed. By using an axisymmetric finite element method, the fabricated thermal stress in a disc-shaped TiCNi 3 Al functionally gradient material (FGM) was calculated. According to a comprehensive examination of the relationship between the maximum thermal stress and the FGM composition, the stress at the FGM interlayers and the stress state at the pure TiC side, an optimum composition of the FGM was obtained.

THE MICROSTRUCTURE DESIGN OPTIMIZATION OF NEGATIVE INDEX METAMATERIALS USING GENETIC ALGORITHM

In recent years, metamaterials have been the subject of research interest for many investigators worldwide. However, most of reported metamaterial microstructures are obtained based on human intuition, experience or large numbers of simulation experiments which were time-consuming, inefiective or expensive. In this paper, we propose a novel negative index metamaterial microstructure design methodology that uses a FDTD solver optimized by genetic algorithm (GA) technique in order to achieve a simultaneously negative permeability and permittivity. Firstly, an novel genetic algorithm optimization model for wide frequency band of negative refraction was proposed. Then the efiectiveness of the new technique was demonstrated by a microstructure design example that was optimized by GA. By using numerical simulations techniques and S-parameter

Residual and working stresses of a TiC/Ni3Al FGM and its structure optimization

Metal/ceramic type functionally gradient materials [1 ] (FGMs) are new-generation composite materials for future use in aerospaee, nuclear engineering, etc. The key problem for their practical use is how to ensure no damage is caused by the thermal stresses in the preparation and working processes. In analysing the residual and working stresses of ceramic/metal FGMs, Kawasaki [2], Kato [3], and Yuan et al. [4] have done some interesting work. However, work which optimizes the composition and structure by comprehensively surveying the residual and working stresses has not been done until now. In fact, these studies are very important to the thermal stress relaxation design of FGM. I n this paper, a TiC/Ni3A1 FGM is studie& As a ceramic phase, TiC has a high electronic expansion coefficient and high-temperamre strength; as a metal phase, the intermetallic Ni3A1 has a fine creepresistance at elevated temperature, and an excellent interface bondability with TiC [5, 6]. The thermomechanical properties of TiC/Ni3A1 composites with different TiC-Ni3A1 ratios are first tested. The tested properties are then used as a basis of axisyrnmetric finite element calculation for the two different types of stresses. For a disc-like TiC/Ni3A1 FGM, by surveying the stresses, the stress sites, and the stress state at the pure ceramic side, the second optimization for the FGM compositional distribution and structure is obtained. TiC/Ni3A1 composites with Ni3A1 volume fraction of 0, 20%, 40%, 60%, 80% and 100% were sintered by the HP method for 2 h at 1300 °C and.300 MPa under Ar gas protection. These sintering conditions are the same as the conditions for sintering TiC/ Ni3A1 FGM. The sintered composites were cut and ground into 36 x 4 x 3 m m strip samples; the properties were then tested with a four-point bending test method in a materials test system. In the test, the top span of the samples was 3 0 m m and the underpart span 20 mm. Strain ganges were fixed at the centre of the samples. Youngs modulus E was calculated through the tested load-defiection curve; t h e Poisson ratio /z was determined by the ratio of the tested cross-strain to the longitudinal strain; and the fracture strength of the samples was indicated as the four-point bending strength o-. The average values of E and /z were obtained from 30 samples and the average ofrom seven samples. In addition, the thermal expansion coefficient was tested by a nonloaded thermal dilatometer and the thermal diffusion coefficient ff and specific heat Cp were tested by a laser perturbation method (SHINKO RIKO TC-700). The samples were 10 mm long and 2 mm wide; they were tested at 25 °C, 300 °C, 600 °C, 800 °C and 1200 °C, respectively. The thermal conductivity A was calculated from A = ff x Cp x d, where d is the sample density. The tested properties are indicated in Table I. F ig . 1 is a finite element model for the thermal stress calculation of a disc-like TiC/Ni3A1 FGM. The material is 30 mm in diameter, 6 mm in thickness, and has 1 l gradient layers. The top side is the metal phase, the bottom is the ceramic phase, and between the two sides are the FGM interlayers. Due to the

Optimizing low loss negative index metamaterial for visible spectrum using differential evolution: reply

A novel negative index metamaterial design methodology for the visible spectrum with low losses was presented in this paper. A robust differential evolution (DE) was employed to optimize the metamaterial design to achieve a desired set of values for the index of refraction. By using numerical simulation of a wedge-shaped model and S-parameter retrieval method, we found that the DE-designed optimal solution can exhibit a low loss LH frequency band with simultaneously negative values of effective permittivity and permeability at the violet-light wavelength of 408 nm, and the figure of merit is 15.2, that means it may have practical applications because of its low loss and high transmission. Therefore, the design methodology presented in this paper is a very convenient and efficient way to pursue a novel metamaterial with desired electromagnetic characteristics in the visible spectrum.

Design and microstructures of Ti/TiAl/Al system functionally graded material

Since the concept of functionally graded materials (FGM) was proposed, a great deal of research work on such a kind of advanced material has been done worldwide for different applications. Recently, FGMs have come to show high potential for the application in dynamic high-pressure technology [1]. Shock wave techniques offer unique capabilities for the experimental characterization of material properties at very high pressures and strain rates [2]. But the usefulness of the shock wave experiments can be expanded by using a kind of material with a density gradient [1], from which extremely-high pressure can be offered at a much cooler temperature, and one can deduce some of the properties of different materials at the pressure and temperature. Recently, the application of graded-density layered materials in high-pressure technology has been reported [3]. However, they were only fabricated by bonding a series of thin plates such as Ta, Cu, Ti, Al, Mg and TPX-plastic, thus the density of the layered materials rises with great steps in the thickness direction. It is expected to achieve a better effect [1] by using a graded material with a continuous or quasi-continuous density change. Moreover, the graded material with a wide density range is desirable, namely, its density of one surface should be kept very low, while that of another surface should be kept as high as possible [1]. So far, many kinds of metal/metal [4, 5], metal/ ceramic [6, 7] or metal/polymer [8] FGMs have been reported. However, the density range is not wide enough to meet the demand in shock wave experiments. The authors designed the material system of W/Mo/Ti/Al/plastic to compose such a graded material. Only when high relative density of every transient layer of such a FGM is ensured can good performance be obtained in factual application. So, the densification of every part of the above graded material should be studied. According to the previous research results [9, 10], the W/Mo and Mo/Ti system FGMs can be densified by powder metallurgy method under the same sintering conditions of 1473 K—30 MPa—1 h. But, until now, the Ti/Al system FGM has not been specially studied. The purpose of this work is to design and fabricate this system graded material. It will be very difficult to directly densify the Ti/Al graded material because there exists a great difference in melting point between the metal Ti and Al. To solve this problem and to ensure that the density of Ti/Al system FGM changes quasi-continuously in the thickness direction, a transient phase of TiAl was introduced (Ti3Al and TiAl3 were not chosen, because the density of Ti3Al was too close to that of Ti, and because of great brittleness of TiAl3, respectively). That is, Ti/TiAl/Al system FGM is designed, in which Ti/TiAl part would be densified under the above sintering condition, while the TiAl side needs to be joined to metal Al with brazing method. The microstructures of this FGM are presented in this paper, and the formation mechanism of the graded microstructures as well as joining interface is also discussed. The TiAl was synthesized by thermal explosion reaction: First, high-purity Ti powders (−400 mesh) and Al powders (−300 mesh) were mixed mechanically in the atom ratio of 1 : 1. Then, the mixture was heated to 973 K at a heating rate of 25–30 K/min in a furnace with a flowing argon. Under this condition the thermal explosion reaction of Ti+Al=TiAl was occurred. Afterwards the reaction product was heated to 1473 K and held at that temperature for 30 min to improve its homogeneity. Finally, the cooled reaction product was smashed, ground and sieved through −400 mesh. Xray diffraction analysis (XRDA) method was applied to identify phases of the product, and the results show

Optimal design of light trapping in thin-film solar cells enhanced with graded SiN x and SiO x N y structure

In this paper, a graded SiNx and SiOxNy structure is proposed as antireflection coatings deposited on top of amorphous silicon (α-Si) thin-film solar cell. The structural parameters are optimized by differential evolution in order to enhance the optical absorption of solar cells to the greatest degree. The optimal design result demonstrates that the nonlinear profile of dielectric constant is superior to the linear profile, and discrete multilayer graded antireflection coatings can outperform near continuously graded antireflection coatings. Whats more, the electric field intensity distributions clearly demonstrate the proposed graded SiNx and SiOxNy structure can remarkably increase the magnitude of electric field of a-Si:H layer and hence, enhance the light trapping of a-Si:H thin-film solar cells in the whole visible and near-infrared spectrum. Finally, we have compared the optical absorption enhancements of proposed graded SiNx and SiOxNy structure with nanoparticles structure, and demonstrated that it can result in higher enhancements compared to the dielectric SiC and TiO2 nanoparticles. We have shown that the optimal graded SiNx and SiOxNy structure optimized by differential evolution can reach 33.31% enhancement which has exceeded the ideal limit of 32% of nanoparticles structure including plasmonic Ag nanoparticles, dielectric SiC and TiO2 nanoparticles.