Showing papers by "Wuhan University of Technology published in 2000"

Preparation, microstructure and photocatalytic activity of the porous TiO2 anatase coating by sol-gel processing

Abstract: In this study the porous TiO2 anatase coatings are prepared from alkoxide solutions containing polyethylene glycol (PEG) by a dip-coating technique. The effects of PEG addition to the precursor solution on the photocatalytic activity and microstructure of the resultant coatings are studied. The larger amount and the larger molecular weight of PEG, the larger size and more pores produced in the resultant coatings on the decomposition of PEG during heat-treatment. The adsorbed hydroxyl content of such porous coatings is found to increase due to the larger size and more pores in the coatings. However, the transmittance of the coatings decreases due to the scattering by the larger size and more pores. Photocatalytic degradation experiments show that organophosphorous insecticide, dimethyl-2,2-dichlorovinyl phosphate (DDVP), was efficiently degraded in the presence of the porous TiO2 coatings by exposing the DDVP solution to sunlight. Photocatalytic degradation rate was related to the adsorbed hydroxyl content, transmittance and morphology of the resultant coatings.

Seismic response control of frame structures using magnetorheological/electrorheological dampers

Abstract: Semi-active control of buildings and structures for earthquake hazard mitigation represents a relatively new research area. Two optimal displacement control strategies for semi-active control of seismic response of frame structures using magnetorheological (MR) dampers or electrorheological (ER) dampers are proposed in this study. The efficacy of these displacement control strategies is compared with the optimal force control strategy. The stiffness of brace system supporting the smart damper is also taken into consideration. An extensive parameter study is carried out to find the optimal parameters of MR or ER fluids, by which the maximum reduction of seismic response may be achieved, and to assess the effects of earthquake intensity and brace stiffness on damper performance. The work on example buildings showed that the installation of the smart dampers with proper parameters and proper control strategy could significantly reduce seismic responses of structures, and the performance of the smart damper is better than that of the common brace or the passive devices. The optimal parameters of the damper and the proper control strategy could be identified through a parameter study. Copyright © 2000 John Wiley & Sons, Ltd.

Design of steering mechanism and control of nonholonomic trailer systems

Abstract: A wheeled mobile robot with trailers has been studied as a class of nonholonomic systems. It is proved that a system of a tractor and trailers with an appropriate connecting mechanism can be stabilized to desired positions via nonholonomic motion control. Trailers, on the other hand, have been developed and widely used in the industry. The main focus of industrial design is set on reducing tracking error from a reference trajectory. This paper attempts to bridge over the gap between these two approaches. We develop a design theory of trailer systems with passive steering. The designed systems show a good performance in practical path following, and accept the chained form transformation and nonlinear control strategies for nonholonomic systems.

Novel Nanoparticles Formed via Self-Assembly of Poly(ethylene glycol-b-sebacic anhydride) and Their Degradation in Water

Abstract: A novel diblock copolymer, poly(ethylene oxide-b-sebacic acid) (PEO-b-PSA), was prepared by polycondensation. Its self-assembly in water via a microphase inversion resulted in narrowly distributed stable polymeric nanoparticles with a size of ∼70 nm. Such formed nanoparticles had a core−shell nanostructure with the insoluble hydrophobic PSA blocks as the core and the soluble hydrophilic PEO blocks as the protective shell. The core was degradable, and its degradation led to the disintegration of the nanoparticle. The structure of the nanostructure and the degradation kinetics were investigated by a combination of static and dynamic laser light scattering. Our results indicated that the degradation was a first-order reaction, and the degradation rate increases with the dispersion temperature.

Effect on ionic conductivity with modification of polymethylmethacrylate in poly(ethylene oxide)-layered silicate nanocomposites (PLSN)

Abstract: The polymer-layered silicate nanocomposites (PLSN) are prepared by the polymer (polyethylene oxide (PEO) or PEO-polymethylmethacrylate (PMMA)) melt intercalation in layered silicate. Experimental results show that polymers can intercalate in silicate interlayer by melt intercalation and thus ionic conduction can be improved. The modification of polymethylmethacrylate (PMMA) can enhance the ionic conductivity at room temperature and decrease the apparent conductive activation energy in PLSN, which reach 1.2×10 −4 S cm −1 and 0.14 eV, respectively. The nanocomposites exhibit better ionic conduction at high temperature. The modification of PMMA can be used to improve ionic conductivity for PLSN.

Theoretical approach to effective electrostriction in inhomogeneous materials

Abstract: An analytical approach is developed for the effective electrostriction, a nonlinearly coupled electromechanical effect, in inhomogeneous materials based on Green's-function method. For an isotropic composite containing randomly oriented ferroelectric crystallites with cubic symmetry, we derive the first effective-medium-like formulas for calculating its effective electrostrictive coefficients. The effects of microstructural features (such as volume fraction, crystallite shape and orientation, and connectivity of phases) on the effective electrostrictive coefficients are illustrated numerically and discussed. The calculations show that it is possible to develop new electrostrictors combining large electrostriction with mechanical flexibility by choosing the best combination of ferroelectric ceramics and polymer.

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

Abstract: 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

Fabrication of W-Mo-Ti system flier-plate with graded impedance for generating quasi-isentropic compression

Abstract: A fully dense W-Mo-Ti system flier-plate with graded impedance in its thickness direction was successfully fabricated by the method of powder metallurgy. The result of the impact experiment on a light gas gun showed that dynamic quasi-isentropic compression has been created.

Design and fabrication of W-Mo-Ti-TiAl-Al system functionally graded material

Abstract: To obtain a kind of functionally graded material (FGM) with a density gradient, the W-Mo-Ti-TiAl-Al system graded material was designed, and the powder metallurgy method was chosen for its fabrication. The sintering of W, W-Mo, and Mo-Ti alloys at low temperature was studied, and then the approximately wholly dense W-Mo-Ti-TiAl system FGM was achieved by one-step sintering at 1473 K for 1 hour under a pressure of 30 MPa. It was found that through sintering at 1473 K, mainly the mechanical mixtures of W and Mo were formed in W-Mo alloys. In Mo-Ti alloys, the newly designed Fe-Al sintering aids not only have an important effect on the densification of the alloys, but also contribute to the formation of the (Mo, Ti) solid solution. However, the solid-solution reaction that occurred in Mo-Ti alloys was still insufficient. During the sintering of Ti + TiAl, the chemical reaction of Ti + TiAl → AlTi2 was induced within the sintered body. The W-Mo-Ti-TiAl-Al system FGM was finally fabricated by joining of the TiAl side of the sintered W-Mo-Ti-TiAl system FGM to metal Al with an Al-based brazing filler metal, and its density changed quasi-continuously within the large range from 17.15 to 2.70 g/cm3.

Structures of Liquid Al-Si Alloy Modified by Sr

Abstract: The structures of liquid Al-Si alloys modified by Sr were measured by using a high temperature x-ray diffractometer. The structure factor and the coordination numbers of liquid Al-Si alloys with different Si content have been obtained by Radial distribution functions, the nearest atomic distance and the coordination numbers of eutectic Al-Si alloys were studied, before and after being modified with Sr. The radial distribution functions of the liquid alloys were decomposed by 5 Gaussian peaks. These results show that Si-Si covalent bond exists in the liquid eutectic and hypereutectic alloys. Sr in the liquid Al-Si has a capability to weaken the covalent bonds of Si-Si, suppressing the nucleation of eutectic silicon phase.

Microcalorimetric study of the toxic effect of sodium selenite on the mitochondria metabolism of Carassius auratus liver

Abstract: The fundamental thermogenesis curves of the metabolic process of liver mitochondria from Carassius auratus and the toxic effect of Na2SeO3 on it were studied by using an LKB-2277 bioactivity monitor, ampoule method, at 28°C. From the thermogenesis curves, the thermokinetic equations were established under different conditions. The kinetics show that a low concentration of Na2SeO3 (1–4 mg/L) had promoting action on the metabolism process of Carassius auratus liver mitochondria, but that a high concentration of Na2SeO3 (8–16 mg/L) inhibited the mitochondria metabolism.

Solid state reaction synthesis of filled skutterudite compounds (Ce or Y)yFexCo4-xSb12 and the effect of filling atoms Ce or Y on lattice thermal conductivity

Abstract: The synthesis of filled skutterudite compounds (Ce or Y)yFexCo4-xSb12, through a solid state reaction using chloride of Ce or Y, high purity powder of Co, Fe, and Sb as starting materials, was investigated (Ce or Y)yFexCo4-xSb12 (x = 0 10,y = 0 015) compounds were obtained at 850 1 123 K The results of Rietveld analysis demonstrate that (Ce or Y)yFexCo4-xSb12 synthesized by a solid state reaction possesses a filled skutterudite structure The filling fraction of Ce or Y obtained by Rietveld analysis agrees well with the composition obtained by chemical analysis The lattice constant of CeyFexCo4-xSb12 increases with increasing substitution of Fe at Co sites, and with an increasing Ce filling fraction in the Sb-dodecahedron voids The lattice thermal conductivity of (Ce or Y)yFexCo4-xSb12 decreases significantly with an increasing Ce or Y filling fraction in the voids and with substitution of Fe at Co sites

A simplified model for the dielectric function of three-component composite materials

Abstract: In three-component metal-dielectric composite materials, there are three kinds of metallic particles. Clausius-Mosotti equation is applied to a collection of the three kinds of metallic particles. A simple formula of effective dielectric function for the three-component composite system is derived. The optical absorptive coefficient of Au-Ag-SiO2 composite material is calculated with the derived formula. The calculation predicts the existence of double resonance absorptive peaks, which gives a satisfied explanation of the measured optical absorptive spectra of Au-Ag-SiO2 composite films. (C) 2000 Elsevier Science B.V. All rights reserved.

Surface-mediated absorption of (Au,Ag) alloy granular nano-composite films

Abstract: The nano-composite films consisting of (Au,Ag) alloy particles embedded in the fused quartz were prepared by the RF co-sputtering technique, and the optical properties of the samples heated in Ar atmosphere and in air atmosphere were investigated. The effective dielectric function for the three-component alloy-dielectric composite system was deduced from the Clausius-Mosotti equation. The calculations from this theory gave a proper explanation for the measured optical absorptive spectra of (Au,Ag)/SiO2 nano-composite films. (C) 2000 Elsevier Science B.V. All rights reserved.

The optical properties of Ag–Si nano-composite films prepared by sputtering

Abstract: Ag–Si nano-composite films were prepared with a co-sputtering technique and step-sputtering method, respectively. The step-sputtered sandwich Ag–Si samples with Ag islands of area fraction approximately 0.43 showed strong resonance absorption near 610 nm. In contrast, the resonance absorption was widened and weakened in the co-sputtered Ag–Si films with the Ag volume fraction at approximately 0.26. The effective dielectric function of the composite materials consisting of multi-stage nanosized metal particles (or clusters) was deduced based on the theory of Sheng. The calculated absorptive coefficients from this modified model coincides very well with the measured spectra of co-sputtered Ag–Si composite films.

Solid stae reaction synthesis of skutterudite compounds FexCo4-xSb12 and thermoelectric properties

Abstract: Skutterudite compounds Fe\- x Co\-\{4- x Sb\-\{12\} were synthesized by solid state reaction using high\|purity powders of Co,Fe,and Sb as starting materials.Fe\- x Co\-\{4- x Sb\-\{12\}( x =0—1 0) compounds were obtained at 900—1000?K.The lattice constant of Fe\- x Co\-\{4- x \}Sb\-\{12\} increased with increasing substitution of Fe for Co sites.Carrier concentration and electrical conductivity increased with increasing Fe content.Seebeck coefficient decreased and T opt of Seebeck coefficient shifted to higher temperature with increasing Fe content.Lattice conductivity was reduced significantly by substitution of Fe for Co sites.The maximum ZT value of 0\^5 was obtained for Fe\-\{0.92\}Co\-\{3.08\}Sb\-\{12\} at 750K.

The flexural strength and reinforcing mechanism of the top and-bottom layered steel fiber concrete

Abstract: The mix proportions and strength ofplain concrete, top-and-hottoim layered steel fiber concrete and common steel fiber concrete are camparatively researched in this article. The influence of the quantity and place of steel fiber layer on the concrete's strength is systematically researched and the simulated analysis is made by computer.