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Because the agglomerated silica fume can’t realize its filling effect, hydration nucleation effect and pozzolanic effect in cement-based composites, a new dispersing method on silica fume aiming to dispersing it fully is introduced. The influence of physical and chemical properties of the modified silica fume on performance of cement-based materials was investigated. In view of the presence of silanol groups and negative charges of silica fume surface, the zeta potential of silica fume surface becomes positive after reaction of silanol groups on silica fume surface and calcium ions in modification solution. The change of zeta potential generates stronger adsorption force to anionic polycarboxylate copolymer. This paper discusses in detail the effect of the modified solution with different concentrations and pH values on adsorption amount of calcium ions on the surface of silica fume, thereby the optimal modified system was determined. The optimized dispersion of the modified silica fume was characterized by infrared spectra and comparing with the result of the commercial silica fume. The performance of modified silica fume in the simulated cement pore solution was evaluated by zeta potential and adsorption amount of polycarboxylate copolymers on silica fume particles surface. Besides, laser particle distribution and SEM photos help us clarify the difference between the particle size distribution and microstructure of the modified silica fume and the commercial silica fume. Results show that zeta potential, adsorption amount of polycarboxylate copolymers on modified silica fume surface increases obviously, the homogeneous dispersion fraction of the modified silica fume in the simulated cement pore solution increases significantly. Furthermore, influence of modified silica fume on the performance of cement-based materials was evaluated. Results showed that the effects of modified silica fume on fluidity, mechanical properties, hydration heat, non-evaporable water, hydration products, pore structure and morphology of cement-based materials are optimizer than the commercial silica fume. And the Ca/Si ratio of the C-S-H gel of cement-based material containing modified silica fume is lower than that of cement-based material containing commercial silica fume.

As a new method, liquid-metal cooling (LMC) process is used in manufacturing industrial gas turbines (IGT) blades. Numerical simulation is an effective way to investigate the grain’s growth and morphology, and optimize the process. In this paper, mathematical models for heat dynamic radiation and convection boundary of LMC process is established to simulate the temperature fields. Cellular Automaton (CA) method and KGT growth model are used to describe the nucleation and growth. Simulation results and experimental results are compared. The mushy zone and microstructure evolution are studied in detail. This study indicates that simulation and experimental results agree very well with each other. The withdrawal rate has an important influence on the shape of mushy zone and growth rate of the grain directly. A concave mushy zone is formed and the grain tends to convergent under an excessive high of withdrawal rate. But, the mushy zone has a convex shape and the grain is divergent under a smaller withdrawal rate. A variation withdrawal rate (from 2mm/min to 9mm/min) is found to obtain smooth mushy zone, which improves the parallelism of grain and produces high quality IGT blades.

The effect of Ca(2+) ions on the hydration shell of sodium dodecyl carboxylate (SDC) and sodium dodecyl sulfonate (SDSn) monolayer at vapor/liquid interfaces was studied using molecular dynamics simulations. For each surfactant, two different surface concentrations were used to perform the simulations, and the aggregation morphologies and structural details have been reported. The results showed that the aggregation structures relate to both the surface coverage and the calcium ions. The divalent ions can screen the interaction between the polar head and Na(+) ions. Thus, Ca(2+) ions locate near the vapor/liquid interface to bind to the headgroup, making the aggregations much more compact via the salt bridge. The potential of mean force (PMF) between Ca(2+) and the headgroups shows that the interaction is decided by a stabilizing solvent-separated minimum in the PMF. To bind to the headgroup, Ca(2+) should overcome the energy barrier. Among contributions to the PMF, the major repulsive interaction was due to the rearrangement of the hydration shell after the calcium ions entered into the hydration shell of the headgroup. The PMFs between the headgroup and Ca(2+) in the SDSn systems showed higher energy barriers than those in the SDC systems. This result indicated that SDSn binds the divalent ions with more difficulty compared with SDC, so the ions have a strong effect on the hydration shell of SDC. That is why sulfonate surfactants have better efficiency in salt solutions with Ca(2+) ions for enhanced oil recovery.

Epitaxial ZnO films with high crystallinity and smooth surface were fabricated on a (1 1 2 0)Al 2 O 3 substrate using a technique of electron cyclotron resonance (ECR) N 2 O plasma-enhanced pulsed laser reactive deposition. The electric properties were measured by four-probe Van der Pauw method. The results indicate that the doped N created in ECR N 2 O plasma strongly influence the electrical properties and the ZnO film shows a trend toward p-type conduction under optimized deposition condition. A sharp band-edge emission at 3.3eV irradiated using a 325 nm He-Cd laser at 77 K on ZnO films was clearly observed.

p-Type conduction in transparent ZnO films grown by electron cyclotron resonance (ECR) N2O plasma-enhanced pulsed laser reactive deposition has been induced by incorporating active N radical species created in N2O plasma within the ZnO films. N impurity has been shown experimentally to be an effective acceptor for producing shallow ptype dopant in ZnO films, which is consistent with previously published conclusions [1]. The room-temperature resistivity and carrier density of the as-grown p-type ZnO films are in the range 2–5 X cm and 4–6 � 10 18 cm � 3 , respectively. These properties provide the practical basis for potential applications of ZnO films in LEDs. The p-type conduction properties may be improved by further increasing the emitting proportion of active N radical species from a plasma source. 2002 Elsevier Science B.V. All rights reserved.

An optimized approach is applied to realize the transfer printing of an In0.2Ga0.8As/GaAs/In0.2Ga0.8As trilayer nanomembrane (NM) onto a plastic substrate with high quality. Bendable metal-oxide-semiconductor capacitors (MOSCAPs) are fabricated on the transferred NM. A detailed COMSOL simulation study is conducted to investigate the mechanical bending behavior induced tri-principle stress of the NM on flexible substrates. The electrical characteristics of the fabricated MOSCAPs exhibit almost no hysteresis voltage of only 0.03 V, an extremely low gate leakage of 10-6 to 10-7 A/cm2, and low accumulation frequency dispersion, thus indicating the possibility of achieving high performance III-V MOS transistor operation. The impact of mechanical strains on the flatband voltages has been carefully investigated from the capacitance-voltage (C-V) measurements. The corresponding accumulation capacitance shows good robustness under tensile bending conditions. The results indicate an important step toward the realiz...

P-type ZnO films with carrier density 3‐610 18 cm ˇ3 , resistivity 2‐5Ocm and Hall mobility=0.1‐0.4cm 2 V ˇ1 s ˇ1 have been grown on fused silica and glass substrate by pulsed laser reactive deposition using a pure metal Zn target in N2O plasma. The N acceptor doping was eectively enhanced using the active N formed by N2O gas passing through an electron resonance source during the pulsed laser reactive deposition process. P-type conduction was achieved by optimizing the microwave-input power (E) and deposition pressure (PN2O). These electrical properties are suAcient for some practical applications. We expect this result to facilitate the fabrication of transparent p‐n homojunctions suitable for light-emitting diodes. # 2001 Elsevier Science B.V. All rights reserved.

A series of three dimensional (3D) porous TiO2–graphene (TGR) hydrogel samples with different mass ratio of graphene to TiO2 were obtained using a one-step hydrothermal method. Their microstructure, mechanical properties, and photocatalytic activity were investigated. The TGR samples exhibited well defined interconnected 3D porous network microstructure and good mechanical strength. Moreover, the pore size and the compressive strength could be easily adjusted by changing the content of TiO2, showing a decreasing tendency with the increase of the relative content of TiO2. The results of the photodegradation of methylene blue indicated that the photocatalytic activity of the TGR samples can be significantly enhanced, compared to the pure TiO2 nanoparticles. The TGR sample also showed good durability and reusability. The mechanisms resulting in the improvement of photocatalytic activity were investigated with DRS, PL spectra, and adsorption experiment under dark conditions. It was found that adsorption is the dominant factor for the enhanced photocatalytic activity.

A transparent ZnO homostructural light-emitting diode (LED) with a structure of Au electrode/p(i)-ZnO film/n-ZnO single crystal/In electrode was fabricated using the technique of N2O plasma-enhanced pulsed laser reactive deposition. The contact between the p(i)-ZnO layer and n-ZnO wafer was found to exhibit nonlinear and rectifying current–voltage (I–V) characteristics. A current injection emission with bluish-white light was clearly observed at room temperature, and its intensity increased with increases in the injected electric current.