Advanced Materials Research Vol. 842

Abstract: Considering physical mechanisms, an electro-thermal effect model of GaAs pseudomorphic high electron mobility transistor (PHEMT) was proposed. The model included PAD capacitances, intrinsic elements and extrinsic elements, which represented the relationship of performance parameters to physical structure and temperature. By using this model, the effects of temperature to devices performance parameters could be analyzed, and the device's structure and materials' parameters could be optimized. A typical GaAs PHEMT was simulated in the EDA software. Thus, DC I-V characteristics and small-signal S parameters of PHEMT under varied temperatures could be given.

Abstract: The carbon nanotubes with its stable structure, excellent mechanical properties, become the ideal enhancement phase of composite materials. The enhancement effect is affected by various factors, interface is one of the key factors determine its enhancement effect, also is the research focus of metal matrix composites. Briefly introduced carbon nanotubes reinforced aluminum matrix (CNTs/Al) composite material interface bonding mechanism and interface effect on the properties of composite materials, thermal expansion coefficient and preparation methods were reviewed, purity of carbon nanotubes and other factors impact on CNTs/Alcomposites interface, and puts forward the way to improve interface.

Abstract: The creep properties and creep life estimation experiment was carried out on the P91 steel with low hardness (About 135HBHLD),and the creep life of P91 pipe was estimated.The result was that the ability for anti-plastic fracture, cracking and crack propagation of resistance to damage of high pressure steam conduit pipe with low hardness (About 135HBHLD) is very poor at 566°C and that the working life of low hardness zones (About 135HBHLD) from the creep crack propagation tests is about 5914 hours at 540°C.

Abstract: The Half-metallic and optical properties of wurtzite Cu and Cr codoped AlN were investigated by first-principles calculation based on density functional theory (DFT) using the generalized gradient approximation (GGA) for the exchange-correlation potential. It is shown that the Cu and Cr codoped AlN is a typical half-metallic material at the equilibrium lattice constant. As a p-type semiconductor, there exhibits higher hole concentration in Cu and Cr codoped AlN comparing with Cu doped AlN or Cr doped AlN, which indicates a significant increase in TC. This result suggests that it is possible to achieve high TC materials by Cu and Cr codoped AlN. In addition, the band gap of Cu and Cr codoped AlN is reduced and the absorption ability to ultraviolet light is expanded obviously, a noticeable red-shift of the absorption spectra edge is observed in the Cu and Cr codoped system and two new absorption peaks appear at around 28 nm and 225 nm.

Abstract: A simple, rapid and accurate method for the determination of fluoride in Antarctic krill has been developed. The fluoride content in Antarctic krill was determined by ion chromatography. The method requires a simple sample clean-up procedure to remove the interfering Cl^- from the hydrochloric acid extraction solution. The optimum extraction conditions of fluoride from Antarctic krill samples were obtained by adding 8mL of 1:11(v/v) hydrochloric acid solution and extracting for 60 min. Under these conditions, recoveries of fluoride from Euphausia superba and Penaeus vannamei were 97.9-105.6% and 95.1-101.9%, respectively. The limit of detection was 0.01mg/kg. The method was applied to the determination of fluoride in Antarctic krill. Key words: Fluoride, Antarctic krill, Ion chromatography

Abstract: The objective of this research was to introduce another kind of anti-biological activitiy group to xylan sulfate for improve performance in anti-biological activitiy. A novel double activity sulfate-gallate bagasse xylan was prepared by using bagasse xylan as raw material, sodium nitrilotriacetic sulfonate and gallic acid as esterifying agents. The structure of product was characterized by FT-IR and SEM. The results show that the bagasse xylan was modified successfully, and the final product is a novel double activity sulfate-gallate bagasse xylan.

Abstract: WC-8Co cemented carbide specimens were prepared via vacuum sintering. The influences of sintering time on phase composition, microstructure and mechanical properties of WC-8Co cemented carbide were investigated. The results show that dense specimens were obtained in the sintering time range of 15min~60min and the relative density reached over 95%. Only WC and Co₃W₃C (γ-phase) were detected by XRD without any else phases, even though Co. With the ascended sintering time, the transverse rupture strength (TRS) increased and hardness ascended to peak value and then descended. WC-Co cemented carbide with excellent mechanical properties (HRA>90, TRS~630MPa and K_IC>7MPa·m^1/2) were obtained. It would be a good candidate for applications of friction stir welding tool.

Abstract: A kind of double activity sulfate-gallate bagasse xylan was synthesized by grafting gallic acid onto bagasse xylan sulfate in the presence of catalyst via esterification. The bagasse xylan sulfate was synthesized by using sodium nitrilotriacetic sulfonate as esterifying agent in our previous work. The degree of substitution (DS) of product was determined with the method of acid-base titration. The influencing factors of the various conditions on the reaction of bagasse xylan sulfate with gallic acid was investigated, and the optimal conditions were obtained as follows:reaction temperature 45 °C, reaction time 5.0 h, mass ratio of xylan sulfate to catalyst 50:1, ratio of reaction solution to bagasse xylan 15:1 (mL/g).

Abstract: With the rapid development of magnesium alloys in electric industry, the more advanced requirement of decorative property is given. In recent years, Micro-arc oxidation (MAO) technique is the most favorable method in the surface treatment of magnesium alloys. In this paper, green ceramic coating was prepared on the surface of AZ91D magnesium alloy by micro-arc oxidation. The effects of electrolyte concentration, additive content, and reaction time of micro-arc oxidation on the formation of oxide ceramic coating were studied. The results show that the sample has micro-arc oxidation coloring reaction in the electrolyte added with colored salt KCr₂O₇ whose concentration is 1.2g/L. When the concentration of main salt Na₂SiO₃ is 13g/L, the concentration of KF is 12g/L, the concentration of additive sodium citrate is 1.0 g/L, and the reaction time of micro-arc oxidation is 20 minutes, smooth and dense ceramic layer of yellowish green oxide film can be generated.

Abstract: TiB₂ particulate reinforcing 7449 aluminum matrix composites were fabricated by in situ method. Their microstructure and impact properties were investigated. The impact toughness decreases with the increase of the weight fraction of the particulate whereas the hardness of the composites increases. The decrease of impact toughness could be accounted for the particulate cluster and brittle clusions. The increase of the hardness is due to fine grain size and high dislocation density.