低电压氧化锌压敏电阻器的研究

研究了一种制造低电电压氧化锌压敏电阻器的方法。在基本成分的基础上适当加入二氧化钛可降低梯度电压（Ｖ１ｍＡ／ｍｍ），适量掺硼和改进热处理工艺可减小元件的漏电流和提高其稳定性。     

Pd/Mg(OH)2 Heterogeneous Nanocatalysts Synthesized by a Facile One-Pot Hydrothermal Method for CO Direct Esterification to Dimethyl Oxalate

Catalysis Letters - Pd-based heterogeneous nanocatalysts have wide application in chemical industry. However, the traditional synthesis process contains multi-steps such as impregnation, dry,...     

Facile synthesis of nitrogen and oxygen co-doped hierarchical porous carbon materials for high performance super capacitors

Journal of Porous Materials - Nitrogen and oxygen co-doped hierarchical porous carbons (NOPCs) is prepared by the pyrolysis of polyethylene glycol-200 (PEG) and triazine carbon forming agent (CFA)...     

Adsorption characteristics of hexadecyl ammonium with different numbers of carbon chains in montmorillonite and the structure of the prepared composites

Journal of Porous Materials - The dynamics and thermodynamics of adsorption of hexadecyl ammonium with different numbers of carbon chains in montmorillonite (Mt) with different layer charge density...     

Modulation on the electrical and optical properties of Na and Rh co-doped Ruddlesden-Popper layered Ca3Ti2O7

Layered perovskite Ca_2.91Na_0.09Ti_2-xRh_xO₇ (x?=?0.00, 0.02, 0.04, 0.06) were synthesized by a conventional solid-state reaction. Room temperature ferroelectricity has been confirmed. The remanent polarization increases with an increase of Rh content, which is due to a larger oxygen octahedral distortion by Rh doping. The coercive field increases with Rh doping as the pinning effect of oxygen vacancies reduce the mobility of domain wall. Remanent polarization and coercive field are caused by different mechanisms, so it is possible to modulate them independently to meet the requirement of application in ferroelectric field. The concentration of oxygen vacancy increased with Rh doping, leading to the significant increase of leakage current density. The bandgap of samples doped with Rh drastically decrease and the visible light response of the sample was improved by Rh doping due to the formation of impurity energy levels within the band gap.

     

Effects of Ultrasonic Vibration on Material Flow and Thermal Cycles in Friction Stir Welding of Dissimilar Al/Mg Alloys

Comparative experiments are performed in friction stir welding (FSW) of dissimilar Al/Mg alloys with and without assistance of ultrasonic vibration. Metallographic characterization of the welds at transverse cross sections reveals that ultrasonic vibration induces differences in plastic material flow in two conditions. In FSW, the plastic material in the peripheral area of shoulder-affected zone (SAZ) tends to flow downward because of the weakening of the driving force of the shoulder, and a plastic material insulation layer is formed at the SAZ edge. When ultrasonic vibration is exerted, the stirred zone is divided into the inner and outer shear layers, the downward material flow trend of the inner shear layer disappears and tends to flow upward, and the onion-ring structure caused by the swirl motion is avoided in the pin-affected zone. By improving the flow behavior of plastic materials in the stirred zone, ultrasonic vibration reduces the heat generation, accelerates the heat dissipation in nugget zone and changes the thermal cycles, thus inhibiting the formation of intermetallic compound layers.

     

Mold-filling characteristics of AZ91 magnesium alloy in the low-pressure expendable pattern casting process

The magnesium (Mg) alloy low-pressure expendable pattern casting (EPC) process is a newly developed casting technique combining the advantages of both EPC and low-pressure casting. In this article, metal filling and the effect of the flow quantity of inert gas on the filling rate in the low-pressure EPC process are investigated. The results showed that the molten Mg alloy filled the mold cavity with a convex front laminar flow and the metal-filling rate increased significantly with increasing flow quantity when flow quantity was below a critical value. However, once the flow quantity exceeded a critical value, the filling rate increased slightly. The influence of the flow quantity of inert gas on melt-filling rate reveals that the mold fill is controlled by flow quantity for a lower filling rate, and, subsequently, controlled by the evaporation of polystyrene and the evaporation products for higher metal velocity. Meanwhile, the experimental results showed that the melt-filling rate significantly affected the flow profile, and the filling procedure for the Mg alloy in the low-pressure EPC process. A slower melt-filling rate could lead to misrun defects, whereas a higher filling rate results in folds, blisters, and porosity. The optimized filling rate with Mg alloy casting is 140 to 170 mm/s in low-pressure EPC.     

Analysis of the central cavity of axisymmetric forward extrusion by the upper bound approach

In this paper, the use of a kinematically admissible velocity field to predict the presence of a central cavity in the final stage of axisymmetric forward extrusion is advanced, in accordance with the results of Moire experiments. On the basis of the velocity field, the critical condition for central cavity formation is obtained by the upper bound approach. Furthermore, the quantitative relationships between central cavity formation and process parameters (reduction in area, frictional factors on the ram and chamber wall, relative residual thickness of the of the billet) are studied. The results show that (1) the critical relative residual thickness of the billet used for the central cavity formation is affected primarily by the reduction in area and the frictional factors on the ram, and slightly by the frictional factor on the chamber wall; (2) the relative dimensions of the central cavity increase with a decrease in the relative residual thickness of the billet; (3) the growth rate of the central cavity decreases with an increase in the frictional factors on the ram, but is affected by the frictional factors on the chamber wall only slightly. Good correlation is found between the analytical and experimental results.     

超滤在明胶生产中的应用

本文研究了超滤在明胶生产中的应用,超滤作为初级浓缩是可行的。同时,对超滤设备、超滤膜与工艺条件作了讨论。