Kinetic Studies of Eutectoid Decomposition of CuFe5O8

The kinetics and mechanism of eutectoid decomposition of CuFe₅O₈ were studied by X-ray diffractometer, electron probe microanalyzer, and reflecting-light microscope techniques. The isothermal decomposition curves were sigmoidal and the maximum rate of decomposition occurred at ∼600°C. Sigmoidal-type curves indicated that the decomposition proceeded by a process of nucleation and growth. Kinetic data were best expressed by Avrami's equation with n≃2 and n≃4 below and above 850°C, respectively. A "site saturation" mechanism is suggested. Bainite-type and pearlite-type microstructures were observed below and above 800°C, respectively. Grain boundaries were active sites in the nucleation process.     

类金刚石纤维砂轮的开发及其磨削特性

为了获得高精度加工表面，最近磨具市场上有一种Al2O3纤维砂轮问世^[1]。该砂轮克服了磨粒砂轮中磨粒易于脱落的缺点，但其硬度仍受到一定限制。近十年来，由于类金刚石薄膜具有接近金刚石的硬度、高耐磨性和很低的摩擦系数等优良的机械、物理、化学和光电特性，因而被广泛地应用于精密零部件和涂附刃具的制造^[2]。如果能将类金刚石薄膜形成类金刚石纤维，然后将其代替Al2O3纤维作为磨料，就可以满足纤维砂轮的硬度要求。因此，1999年以来，日本山口胜美教授和中国魏源迁教授成功地将类金刚石纤维植入基体并与树脂结合剂结合，开发了一种类金刚石纤维砂轮^[3-5]。该砂轮中的类金刚石纤维按同一方向排列且与砂轮磨削面相垂直，纤维的端部可用作为切削刃。为了考察这种新型砂轮的磨削特性，本文作者对难加工材料如模具钢SKD11及硬脆材料如硅片、光学玻璃、石英和大理石进行了大量的磨削试验。试验结果表明能获得纳米级加工表面，例如被磨硅片和模具钢的表面粗糙度分别为Ra2nm(Ryl5nm)和Ra2nm(Ry23nm)。     

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.     

A series of discrete-time models of a continuous-time system based on fluency signal approximation

A discrete-time system model based on the discretization of a continuous-time system has been called a sampled-data system. But, in such discretization of the continuous-time system, it has been assumed that input signal u(t) is a staircase signal, that is, u(τ) has a constant value of u(kh) = u_k over the integration interval. The present paper derives a series of discrete-time models of a continuous-time system based on m-order fluency signal approximation. It is revealed that the series of models includes and generalizes the conventional system model based on the assumption of staircase signal input (m = 1). Furthermore, the adaptive discretization is obtained by selecting the appropriate order m according to the characteristic (continuous differentiability) of the input signal of the continuous-time system we are dealing with. Thus, this concept provides a better family of the relationship between the discrete-time system model and the continuous-time system     

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.