Development of Mo(Si,Al)<Subscript>2</Subscript>-base oxidation-resistant coating on Nb-base structural materials

Mo(Si,Al)₂-base oxidation-resistant coatings for Nb-base structural materials have been studied. The coating is composed of a Mo(Si,Al)₂-base Al reservoir and Al₂O₃ interlayer to suppress interface reactions between the Al reservoir and the substrate. To develop a suitable Al-reservoir material, some Mo(Si_0.6,Al_0.4)₂-HfB₂ composites were prepared. Their oxidation resistance and coefficients of thermal expansion were investigated, in addition to their chemical reactivity with the Nb substrate at high temperatures. As a result, Mo(Si_0.6,Al_0.4)₂-20 vol pct HfB₂ was selected as one of the satisfactory Al reservoirs. The introduction of a stable Al₂O₃ interlayer was attempted using a novel powder metallurgical process to overlay the Nb substrates with the Al reservoir, where the Nb substrates were subjected to a slight surface oxidation prior to the coating process. The Nb specimens, which are thoroughly coated with the Al reservoir and Al₂O₃ interlayer, can be successfully fabricated by this method. The coated Nb specimens are not damaged at all after prolonged exposure in flowing Ar-20 pct O₂ at 1673 K for 120 hours. Furthermore, the Al₂O₃ interlayer is very effective and no reactions occur at the interface. Thus, this Mo(Si,Al)₂-base oxidation-resistant coating is applicable to Nb. The utility of the coating system is also confirmed for a Nb_SS/Nb₅Si₃ composite. This article is based on a presentation made in the symposium entitled “Beyond Nickel-Base Superalloys,” which took place March 14–18, 2004, at the TMS Spring meeting in Charlotte, NC, under the auspices of the SMD-Corrosion and Environmental Effects Committee, the SMD-High Temperature Alloys Committee, the SMD-Mechanical Behavior of Materials Committee, and the SMD-Refractory Metals Committee.     

An explicit application of partition of unity approach to XFEM approximation for precise reproduction of a priori knowledge of solution

The application of the XFEM to fracture mechanics is effective, because a crack can be modeled independently from the meshes and a complex remeshing procedure can be avoided. However, the classical XFEM has an essential problem in the approximation of partially enriched elements, that is, blending elements, which causes a lack of accuracy. For the weighted XFEM, although the numerical results show the effective improvements, it was found that the issue of blending elements still remains upon detailed examination. In the present paper, the PU‐XFEM is formulated as an explicit application of the partition of unity (PU) approach to the XFEM, in order to precisely reproduce a priori knowledge of the solution by enrichment. The PU‐XFEM is applied to two‐dimensional linear fracture mechanics, and its effectiveness is verified. It is consequently found out that the PU‐XFEM precisely reproduces a priori knowledge of the solution and is therefore effective to completely solve the problem of the blending elements. Copyright © 2013 John Wiley & Sons, Ltd.     

帘线钢表面氧化优化工艺及控制机理研究

采用OM和SEM分析方法研究了帘线钢空气气氛下连续氧化行为以及高线精轧、吐丝温度对热轧盘条表面氧化铁皮厚度和相组成的影响,同时采用热模拟方法分析了FeO层发生先共析、共析转变生成Fe3O4的条件.实验结果表明,945℃是帘线钢快速氧化起点温度,随着温度升高,氧化速率急剧增加;而当温度降低到700℃时,氧化过程极其缓慢.控制700~945℃范围内的冷速是控制氧化铁皮厚度及相组成的关键工艺.高线生产控制精轧和吐丝温度在900~940℃,氧化铁皮厚度7~20μm,FeO质量分数为65%~80%,具有最佳除鳞性能.热模拟分析表明,400~500℃是FeO层发生共析转变的"鼻尖"温度,孕育期最短.提高400~500℃区间冷速可抑制FeO层发生共析转变,使机械除鳞率提高3%左右.     

地面塌陷因素重要度分析

通过收集大量文献,总结已有的研究工作,将地面塌陷因素概括为水、采矿、工程活动、地质四个方面,简述各因素的作用机理,建立相应的评价体系,在此基础上通过收集已有塌陷事故,运用数理统计方法及极差与方差分析,相互验证得出塌陷因素的重要性排序,对塌陷面积影响显著的因素为工程活动,水与地质的交互影响。     

Theoretical models and experimental results on the temperature dependence of polyfluorene solar cells

The temperature dependence of device parameters of polymer solar cells based on alternating copolyfluorene incorporating dioctyl-fluorene and di-thienyl-benzothiadiazole (APFO-3) mixed with [6,6]-phenyl-C61-butyric acid methylester (PCBM) was modeled theoretically by simulation and investigated experimentally under illumination of AM1.5 (100 mW/cm²). Both simulation and experimental results show photocurrent, fill factor and power conversion efficiency all increase, and the open-circuit voltages monotonically decrease with temperature increase from room temperature (RT) to 120 °C. These results can be explained by taking into account the temperature dependence of the mobility, and the thermal activation of the injection current from the electrodes. The increase of PCE with temperature is a distinguishing feature of polymer solar cells.     

950 keV, 3.95 MeV and 6 MeV X-band linacs for nondestructive evaluation and medicine

We are developing compact X-band linac X-ray sources for nondestructive evaluation and medicine. First, we develop a portable X-ray system by a 950 keV 9.4 GHz X-band linac to realize on-site inspection. We use a low power (250 kW) magnetron as an RF source for compactness of the whole system. Since the RF power source is quite small and the stored energy in the structure is also small, we faced the problem of beam loading and current/RF-power oscillation. We are analyzing the problem by the circuit model. We plan to use this system for erosion inspection of metal pipes of petrochemical complex. By adopting a side-coupling cavity design to avoid the oscillation, we have developed 6 MeV X-band (9.3 GHz) linac for pinpoint dynamic tracking cancer therapy. Furthermore, we are manufacturing 3.95 MeV X-band (9.3 GHz) linac X-ray source with flexible waveguides for on-site bridge inspection. Updated results and situations are presented.     

Negative faradaic resistance in extracellular electron transfer by anode-respiring Geobacter sulfurreducens cells

Geobacter sulfurreducens is a gram-negative δ-proteobacterium that is capable of transferring respiratory electrons to solid-state extracellular acceptors, including anodes, via abundant c-type cytochromes expressed in the outer membrane. As extracellular electron transfer (EET) to solid-state acceptors can proceed without the addition of exogenous mediators, this microbe has attracted significant attention with respect to energy conversion between electrical and chemical energy. Here, we revealed that clear redox peaks were present in the whole-cell cyclic voltammogram of G. sulfurreducens at around -0.15 V vs Ag|AgCl when tin-doped In(2)O(3) (ITO) glass was used as an anode. Interestingly, the EET current decreased in the potential region more positive than the midpoint potential (E(m)) of the redox peak. Thus, EET of anode-respiring G. sulfurreducens cells exhibited a negative Faradaic resistance (NFR) characteristic at the E(m) of the redox peak, in contrast to general electrochemical systems where the Faradaic current typically increases with increasing overpotential.     

Bubble behavior in vertical tube banks installed in a fluidized bed

Fluidized bed combustion is one of the advantageous technologies for coal and/or incineration firing especially with respect to the environmental protection of emissions, such as NO_x/SO_x. Bed material movement in such a fluidized bed has a prime importance in the heat transfer process. Thus, quantitative measurement of the bed material movement and the void fraction are indispensable for better understanding of the fluidized bed. In this investigation, neutron radiography is applied to visualize the bed material movement in a simulated fluidized bed heat exchanger installed with vertical tubes. Bubble behavior and void fraction profile are obtained by the image processing technique. Bubble movement is highly restrained by these vertical tubes, so that the bubbles rise up along the tube. The bubble diameter is well correlated by the modified Mori and Wen's correlation taking into account the pitch of the tube arrangement. The bubble rise velocity and void fraction are well correlated by applying the drift‐flux model. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(8): 727–739, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10127     

Feasibility study on 1.6 μm continuous-wave modulation laser absorption spectrometer system for measurement of global CO2 concentration from a satellite

A feasibility study is carried out on a 1.6 μm continuous-wave modulation laser absorption spectrometer system for measurement of global CO(2)concentration from a satellite. The studies are performed for wavelength selection and both systematic and random error analyses. The systematic error in the differential absorption optical depth (DAOD) is mainly caused by the temperature estimation error, surface pressure estimation error, altitude estimation error, and ON wavelength instability. The systematic errors caused by unwanted backscattering from background aerosols and dust aerosols can be reduced to less than 0.26% by using a modulation frequency of around 200 kHz, when backscatter coefficients of these unwanted backscattering have a simple profile on altitude. The influence of backscattering from cirrus clouds is much larger than that of dust aerosols. The transmission power required to reduce the random error in the DAOD to 0.26% is determined by the signal-to-noise ratio and the carrier-to-noise ratio calculations. For a satellite altitude of 400 km and receiving aperture diameter of 1 m, the required transmission power is approximately 18 W and 70 W when albedo is 0.31 and 0.08, respectively; the total measurement time in this case is 4 s, which corresponds to a horizontal resolution of 28 km.     

Oxidation behavior of copper nanoparticles at low temperature

A mass gain for copper nanoparticles with a mean diameter of 20 nm in a 20% oxygen-nitrogen atmosphere was measured at 150-300 °C using thermogravimetry (TG). The mass gain equilibrium of the copper particles differed at each temperature, and a threshold temperature was recorded. Oxide products, consisting mainly of Cu₂O, formed on the copper nanoparticles below the threshold temperature. Above the threshold temperature, there was an initial, and drastic, formation of Cu₂O, which then changed to CuO. The activation energy for the oxidation of the copper nanoparticles that could be calculated from the rate of the mass gain was an indication of the nano-effect of the copper nanoparticles.