High-Temperature Reaction Between Cemented Tungsten Carbide and Copper

Interdiffusion in the system cemented tungsten carbide-molten copper has been studied in the range ≤1120°C with special emphasis on the effects of WC grain size and Co content. Techniques used for analyzing the diffusion layers obtained are EPMA, optical microscopy, and microhardness measurement. A Cu-bonded WC layer develops with simultaneous diffusion of Co from the cemented carbide into the bulk copper. The Cu-bonded WC layer grows until a Co-rich layer forms at the Cu/WC-Co interface; further heating pushes the Cu-bonded WC layer deep into the bulk cemented carbide without any significant change in layer thickness. When the WC grain size is reduced and the cobalt content increased, the penetration of copper into cemented carbides increases. A tentative mechanism of interdiffusion has been proposed based on the experimental results.     

Crystallization of Hexagonal BaNb2O6

Pure hexagonal BaNb₂O₆ crystallizes at 640° to 700°C from an amorphous material prepared by simultaneous hydrolysis of barium and niobium alkoxides. The structure is characterized by layer networks of NbO₆ octahedra. Crystallization isotherms are described by the Avrami equation In (1—f) = -ktⁿ with n=2; the activation energy is 268 kJ-mol-'. Hexagonal BaNb₂O₆ transforms to the ortho-rhombic modification one at 12.50° to 1310°C.     

On the estimation of noise covariances in linear discrete-time systems

This paper is concerned with an approach for estimating or tracking the time-varying input and measurement noise covariances in time-varying discrete-time linear systems. The approach is firstly to introduce the estimators for the case where the noise co-variances are unknown constants. (The estimators are defined as the mean squares of the estimators of noises based on all the available measurement data.) They arc then transformed in sequential form, and are subsequently modified by incorporating a fading memory to yield estimates for time-varying noise covariances. The time-varying noise covariance estimates are evaluated as the fading mean squares of the estimates of noises based on all the measurement data up to present time. A numerical example for a simple system indicates acceptable performance of the proposed method.     

Visible light responsive photocatalysts developed by substitution with metal cations aiming at artificial photosynthesis

To solve resource, energy, and environmental issues, development of sustainable clean energy system is strongly required. In recent years, hydrogen has been paid much attention to as a clean energy. Solar hydrogen production by water splitting using a photocatalyst as artificial photosynthesis is a promising method to solve these issues. Efficient utilization of visible light comprised of solar light is essential for practical use. Three strategies, i.e., doping, control of valence band, and formation of solid solution are often utilized as the useful methods to develop visible light responsive photocatalysts. This mini-review introduces the recent work on visible-light-driven photocatalysts developed by substitution with metal cations of those strategies.     

Effects of AIN Additions and Atmosphere on the Synthesis of Cubic Boron Nitride

Aluminum nitride was found to act as the catalyst for the synthesis of cubic BN by sealing the mixture of hexagonal BN and AIN in a pressure cell under the inert or reducing atmosphere. No conversion of hexagonal BN to cubic BN was observed under pressures below 7×10⁹ Pa (7 GPa, 70 kbar) without AIN addition. All hexagonal BN could be completely converted to cubic BN under 6.5 GPa at 1600°C by the addition of 20 mol% AIN. The cubic BN thus synthesized was a typical tetrahedron (grain size ≅2 μm). The pressure-temperature diagram for the synthesis of cubic BN was determined at >7 GPa and T <1700°C.     

基于自然对流PCR与毛细管电泳技术的牙周病原菌检测

细菌种类的快速识别在牙病防治中具有重要的应用价值。以牙周病原菌为研究对象,建立了DNA快速扩增的自然对流聚合酶链式反应(PCR)方法及毛细管电泳荧光光学检测系统。研究表明,当毛细管有效长度为8cm、电场强度为100V/cm时,50bp DNA ladder在筛分介质为0.5%HEC(羟乙基纤维素)(1 300K)中的分离效果最佳。毛细管电泳结果表明,采用自然对流法可以在25min内在圆柱腔体中实现牙周病原菌的快速PCR。     

Characteristics and Problem of Chrome-containing Refractory

One of characteristics of Cr2O3-containing refractory is excellent corrosion resistance. However, there is a problem of hexavalent chromium, which is noxious to the human body, and easily formed by the reactions among the refractory and CaO, Na2O and/or K2O in slag. In this article, the reason why the Cr2O3-containing refractory has excellent corrosion resistance, the forming conditions of hexavalent compounds, and the methods for suppressing generation of the compound, are described as a base of further development of excellent refractories.     

层片状双相TiAl合金拉伸与压缩变形行为差异

本文研究了层片状双相TiAl合金的室温拉伸压缩变形行为与断裂行为,发现在拉压变形条件下,其室温塑性有显著差异.并且这种差异与裂纹扩展路径有关.在室温拉伸与压缩变形时,该合金的拉压屈服应力随外载与层片界面间的夹角φ的变化趋势一致,而拉压断裂应变εf随夹角φ的变化趋势正好相反.外载与层片界面垂直时(φ=90°),拉伸断裂应变最小(εf≈0);压缩断裂应变最大(εf≈38%).夹角φ减小时,拉伸断裂应变增加,压缩断裂应变减小.在拉、压变形时裂纹的扩展路径不同.