Showing papers by "Wuhan University of Technology published in 2003"

Effects of alcohol content and calcination temperature on the textural properties of bimodally mesoporous titania

Abstract: Bimodally mesoporous titania was prepared by hydrolysis of titanium tetraisopropoxide in pure water or the EtOH–H2O mixed solution under ultrasonic irradiation. Effects of alcohol content and calcination temperature on the phase composition and porosity of bimodally mesoporous titania was investigated by thermogravimetric and differential thermal analysis (TG–DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) surface areas. The results showed that for all TiO2 powders calcined from 400 to 600 ◦ C, the pore size distribution is bimodal with fine intra-particle pore diameter at maximum pore diameters of ca. 2–4 nm and larger inter-particle pore diameter at maximum pore diameters of ca. 18–50 nm. The EtOH/H2O molar ratios obviously influenced the crystallization, crystallite size, BET surface areas, porosity and morphology of the prepared TiO2 powders. © 2003 Elsevier B.V. All rights reserved.

Hybridization of the multi-objective evolutionary algorithms and the gradient-based algorithms

Abstract: It is known from single-objective optimization that hybrid variants of local search algorithms and evolutionary algorithms can outperform their pure counterparts. This holds, in particular, in continuous search spaces and for differentiable fitness functions. The same should be true in multiobjective optimization. An efficient gradient-based local algorithm, sequential quadratic programming (SQP) is combined with two well-known multiobjective evolutionary algorithms, strength Pareto evolutionary algorithm (SPEA) and nondominated sorting genetic algorithm (NSGA-II) respectively, by means of a modified /spl epsiv/-constraint method. The resulting two hybrid algorithms demonstrate great success over two sets of well-chosen functions regarding the convergence rate. In addition, from the simulation studies, the hybridization approach also enhances, at least does not ruin, the diversity of the solutions.

Morphology and formation mechanism of hydroxyapatite whiskers from moderately acid solution

Abstract: Hydroxyapatite (HA) whiskers with uniform morphology and good crystallinity were successfully prepared by a precipitation-hydrolysis method in moderately acid solution at 85-95 °C for 48-120 h, their lengths were in the range of 50-150 mm and aspect ratios (length/diameter) in the range of 40-100. The precipitates formed at each stage of the synthesis were characterized by XRD, FTIR, TEM and SEM. The morphology and crystallinity of the precipitates depended on the synthesis temperature and time as well as the concentrations of soluble calcium and phosphate ions. The HA whiskers were formed by the hydrolysis of precursors produced during the reactions and took over the morphology of fibrous octacalcium phosphate (OCP). The stoichiometric HA whiskers were improved with the increase of pH value of solution, the synthetic temperature and the duration.

Synthesis and thermoelectric properties of (NaxCa1−x)3Co4O9 ceramics

Abstract: (NaxCa1� x)3Co4O9 (x=0.05� 0.2) ceramics with a layered crystal structure were prepared by a sol–gel method followed by a lowtemperature sintering procedure. The electrical conductivity and Seebeck coefficient of the complex oxide ceramics were measured from 400 to 900 � C. Their electrical conductivity and power factor increase with increasing temperature, while the thermal conductivity is very weakly dependant on the temperature. Na dopant amount has a remarkable effect on electrical and thermal transport properties. The figure of merit in the ceramic samples is smaller than that of traditional thermoelectric alloys. # 2002 Elsevier Science Ltd. All rights reserved.

Morphology and properties of soy protein plastics modified with chitin

Abstract: A series of bioplastics from isolated soy protein (SPI) and chitin (CH) was prepared with glycerol as a plasticizer by blending and compression molding. Their morphology and properties were investigated by wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), dynamical mechanical thermal analysis (DMTA), scanning electron microscopy (SEM), and tensile and water-absorption tests. The added CH as a filler cannot strongly interact with SPI molecules and, hence, this results in phase separation in blends. However, the rigid nature of the CH molecules enhanced the tensile strength and Young's modulus, but decreased the breaking elongation of the materials. When the CH content was higher than 10 wt %, the water absorption of the blends were obviously lower than that of the sheets without CH, resulting from the formation of a CH framework in the blends. Both soy protein and CH exhibit good biodegradability, biocompatibility, and bioactivity, and their composites may become a promising biomaterial. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3676–3682, 2003

Finite element analysis of cyclic indentation of an elastic-perfectly plastic half-space by a rigid sphere

Abstract: This paper presents a numerical study on the cyclic indentation of an elastic-perfectly plastic half-space by a rigid sphere. The study is performed using non-linear finite element methods....

Stability analysis and experimental evaluation of a matrix converter drive system

Abstract: The interest in using the matrix converter (MC) technology for motor drive applications is steadily increasing due to its advantages: high quality of the input currents, regeneration capability and high power density but a few unsolved issues delays its industrial use. This paper deals with one of them: the stability of a MC drive caused by using the voltage across the input filter capacitor in the control scheme. First, a small-signal model of the matrix converter is carried out for two load types: a passive RL-load and an induction motor, which is helping to assess the stability of the whole system. Based on this model, the factors that influence the stability are analyzed and design guidelines to improve the system stability are given and verified by simulations. Experimental results are carried out on an 8.5 kVA MC prototype, which show some disagreements with the theory but reasons for these are identified.

The Preparation and Characterization of 3D-Silica Fiber Reinforced Silica Composites

Abstract: The Preparation process of fused silica matrix composites reinforced with threedimensional (3-D) braid via liquid phase infiltration deposition was investigated. The results indicate that the densification is significantly enhanced by using infiltration process with suspension of silica and the addition of a non-ionic surfactant. The 3D SiO2f/ SiO2 specimens have density of 1.65g/cm, flexural strength of 75MPa. Flexural testing and scanning electron microscopy of fracture surface were used to determine mechanical properties and fracture mechanisms. Fractography reveals that the fiber and matrix interface debonding and fiber pulling-out absorb the majority of fracture energy, which is regarded as the principal reason for resulting in the pseudo ductility and toughening mechanisms of the composites.

Theoretical study on two sedimentation processes used to form functionally graded materials

Abstract: Functionally graded materials (FGMs), which feature a continuous variation in microstructure and properties, have potential applications in engineering. Much interest has been shown in the processing methods that can be employed to produce such FGMs. One interesting method is that reported by T. Jungling et al. at the FGM’94 [1]. In this work, a compositional gradient was produced by the settling of particles under gravity in a vessel. Subsequently, J. Huang et al. and G. Kapelski et al. also used this method to produce SUS316/3Y-PSZ and Al2O3/C FGM with smoothly-varying composition, respectively [2, 3]. Based on these researches, another settling process has been proposed to form FGMs [4, 5], as shown in Fig. 1. The significant feature of the latter process is that an additional settling distance is added below the suspension. For convenience, the latter process is called the “process 2” and the former process the “process 1” in the following description. Until now few people have noticed that there are great differences between the above two processes in forming FGMs. In the present investigation, an attempt has been made to theoretically analyze the characteristics of the above two settling processes. Under the influence of gravity, particles in a dilute suspension often fall and stack at the bottom of a stationary vessel. The particle-depositing mass fraction is a function of time t and frequency mass distribution f (D) of the powder. It was given by Oden [6] as follows,

Piezoresistivity of Graphite Modified Asphalt-Based Composites

Abstract: Asphalt and its composites are electrical insulating materia ls, whose resitivity ranges from 10~10 . The conductive performance of the asphalt-based composite can be mark dly improved with the addition of conductive materials such as graphite. The electrically modified asphalt composites exhibit self-sensing ability to strain, defects , and temperature. Conductive asphalt-based composite would have a profound effect on pavement deicing, dam age testing, highway traffic monitoring and so on. Materials such as Koch AH-70, basalt aggregate, limestone powder and graphite particles were used to prepare a conductive aspha lt-based composite in this study. Special attention was placed to its conductive behavior and piezor esistivity. The results show that when the graphite content in asphalt-based composite increases to a critical content, the resistivity declines rapidly. Beyond the critical content, the r ate of resistivity varying with the graphite content becomes smooth. Temperature has a remarkable eff ect on the electrical conduction of the asphalt-based composites. There is a turning point of resisti vity with the increase of temperature. Dynamic and static compressive loadings also affec t the resistance obviously. The reasons may involve the proximity effect, microcracks and the sta ggered arrangements of conductive pass-ways.

Preparation and characterization of molybdenum oxide thin films by sol-gel process

Abstract: This paper presents a new sol-gel process to prepare molybdenum oxide thin films. A molybdenum acetylacetonate sol was prepared by employing the system CH3COCH2COCH3/MoO3/C6H5CH3/HOCH2CH2OCH3. A molybdenum acetylacetonate gel was prepared by addition of aqueous NH3. Thermal gravimetry (TG) and differential thermal analyses (DTA) of the gel suggested that crystallization of MoO3 occurs in a 140 K temperature range around 508°C. MoO3 films were prepared on fused silica, Si (111) and Al2O3 (012) substrates by annealing spin coating films of the sol in oxygen environment at 508°C. X-ray diffraction (XRD) showed that all films crystallize in α-MoO3 structure, and crystallites on fused silica substrate are arbitrarily oriented while those on Si (111) and Al2O3(012) substrates oriented in the (010) direction. SEM investigations showed that MoO3 grains of all films are randomly distributed, with a longitudinal dimension of about 1–5 μm and the film thickness is about 1 μm.

Study of self‐crosslinking acrylate latex containing fluorine

Abstract: Self-crosslinking acrylate latices containing fluorine were prepared by the batch method, with N-hydroxymethyl acrylamide (NMA) as a crosslinking agent. The structure and component of latex polymers were studied by FTIR, ion-selective electrode analysis, and DSC. The stabilities of latices, such as storage stability, centrifugal stability, and electrolyte-resistant stability, were examined. The morphology of the latex particles was characterized by TEM and the surface properties were determined by the Wilhelmy method. The effects of NMA on Tg of the latex polymers, the average particle size of the latices, and the surface properties of the latex films were discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3609–3616, 2003

Microstructural characteristics in plasma sprayed functionally graded ZrO2/NiCrAl coatings

Abstract: Different functionally graded 20 wt.% MgO-ZrO2/NiCrAl thermal barrier coatings were obtained through the plasma spraying process. The microstructures, chemical compositions and fractured surface were examined by means of electron probe microscopic analysis (EPMA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM and EPMA results showed that: (1) microstructures and compositions varied gradually in the coatings; (2) the elements Cr and Al were enriched along the sprayed lamellae boundaries and leaded to the formation of oxides. TEM observation enabled finding the formation of dense dislocations and deformation twins, and also the formation of the oxides Al2O3 and Cr2O3 between grain boundaries. The SEM observations of the fractured surface revealed that the intermediate graded layer had the compositive mechanical properties in strength and toughness, due to the microstructure improvement and relaxation of residual stress concentration.

An integrated on-line oil analysis method for condition monitoring

Abstract: An on-line oil monitoring system offers a suitable solution to the practical problems encountered in monitoring the conditions of machinery equipment. The objective of this paper is to present a systematic method for analysing wear particles in the lubricant used in a diesel engine, in a laboratory setting. An integrated on-line oil monitoring system, which combines an inductive transducer with a fibre optic transducer, was developed to primitive design stage and some experiments have been done. The inductance transducer, whose operation is based on an inductive measurement technique, can detect large ferrous and non-ferrous wear debris. A particle's material properties reflect its origin, and the frequency can be used for estimating wear particle size. The fibre optic transducer can detect small particles and is used for inspection of oil contamination levels. The integrated system combines the virtues of two measurement methods, extends the detection range and meaningfully improves the reliability of oil monitoring. So it has great promise and there are prospects for application as soon as the solutions to certain problems are found.

Novel soft solution synthesis and characterization of submicromic LiCoVO4

Abstract: A novel soft solution process has been used to prepare LiCoVO4 by reacting Co(CH3CH2COO)2, Li2CO3, NH4VO3 and citric acid. LiCoVO4 powders were successfully prepared at as low as 450 °C in 4 h. Compared to the solid-state reaction processes, the soft solution process greatly reduced the temperature and the time for preparing LiCoVO4. The inverse spinel structure and high crystallinity of the synthesized product has been confirmed by X-ray diffraction. Thermal analysis proves that the phase formation of the compound occurs at about 450 °C. The results of the IR investigations show that the band located at 820 cm−1 corresponds to the stretching vibration mode of VO4 tetrahedron with the A 1 symmetry. SEM examination reveals a spherical grain distribution, the average particle size being typically lower than 1 μm. The quantitative result from ICP-AES analysis is Li0.967Co0.994VO4.