疲劳短裂纹扩展速率的电测技术

木文研究了间接直流电位法(IDC法)和交流电位法(AC法)用于监测疲劳短裂纹扩展速率的有关技术问题。文中提出了一种用电磁场边界元法对电位法进行标定的理论标定方法。研究了有关的试验标定方法。并对IDC法和AC法的适用范围、灵敏度和稳定性等做了详细的比较分析。     

Nanoscale Surface Modification of Lithium‐Rich Layered‐Oxide Composite Cathodes for Suppressing Voltage Fade

Lithium‐rich layered oxides are promising cathode materials for lithium‐ion batteries and exhibit a high reversible capacity exceeding 250 mAh g⁻¹. However, voltage fade is the major problem that needs to be overcome before they can find practical applications. Here, Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (LLMO) oxides are subjected to nanoscale LiFePO₄ (LFP) surface modification. The resulting materials combine the advantages of both bulk doping and surface coating as the LLMO crystal structure is stabilized through cationic doping, and the LLMO cathode materials are protected from corrosion induced by organic electrolytes. An LLMO cathode modified with 5 wt % LFP (LLMO–LFP5) demonstrated suppressed voltage fade and a discharge capacity of 282.8 mAh g⁻¹ at 0.1 C with a capacity retention of 98.1 % after 120 cycles. Moreover, the nanoscale LFP layers incorporated into the LLMO surfaces can effectively maintain the lithium‐ion and charge transport channels, and the LLMO–LFP5 cathode demonstrated an excellent rate capacity.     

Thermodynamics and kinetics of evaporative crystallization of sodium gluconate

Thermodynamic properties of sodium gluconate (SG) aqueous solution have been measured over the 303.15–343.15 K temperature range including solubility, density, and viscosity. For proper crystallization of SG, the kinetics of evaporative crystallization with spontaneous nucleation was subsequently investigated in a semi-batch mode. The crystals present a size-dependent growth rate, and the number particle size distribution (PSD) data were well fitted with the MJ2 model. The effects of supersaturation, suspension density, and agitation intensity were carefully analyzed to contribute to a better understanding for the control of crystal size of SG.     

Phase retrieval of optical fringe patterns from the ridge of a wavelet transform

A new method for phase retrieval of optical fringe patterns is presented. This method is based on a wavelet transform and is capable of extracting the full 2D phase distribution from a single fringe pattern. An important conclusion that the phase of the optical fringe pattern is equal to the phase of its wavelet transform on the ridge of the wavelet transform is theoretically clarified. The method is compared with the Fourier transform and the integration methods. A numerical simulation and an experimental example of phase retrieval are shown.     

通过物理化学研讨课培养学生的研究能力——以两个连通气泡的变化为例

在物理化学的"界面与胶体化学"部分,表面张力、表面自由能和拉普拉斯公式是非常基础的内容,如何让学生深刻理解、灵活掌握至为重要,也是该章后续学习的关键。本文以分析两个连通气泡的变化为例,结合演示实验,实施研讨式教学,通过多角度(力学、能量等)、多层次(变化的方向、变化的限度)分析,巩固学生对表面张力、表面自由能及拉普拉斯公式的理解,进而与两个连通气球的变化进行类比,分析两个体系的异同点。通过启发引导,培养学生运用知识、分析问题的能力,提高学生综合素质。在物理化学课堂中,以学生为中心实施基于问题的研讨式教学,为相关课程的教学提供了参考。     

Application of PAC to study equilibrium point defects in intermetallic compounds

A new method has been developed to measure properties of equilibrium, or thermal, defects in intermetallics using the technique of perturbed angular correlations of gamma rays (PAC). After quenching, thermal defects are detected microscopically by distinctive nuclear hyperfine interaction signals produced when they localize next to probe atoms present in high dilution. Using a Schottky defect model and applying the law of mass action to defect equilibria, a linear Arrhenius temperature dependence is predicted for a normalized monovacancy site fraction. We have observed such linear dependences in PAC experiments on NiAl, CoAl and TiAl using the¹¹¹In probe. Features of the method are summarized, of which the most important are the abilities to discriminate between different defects and to determine absolute vacancy concentrations, formation enthalpies and entropies. Extremely large formation entropies have been obtained for NiAl, CoAl and TiAl, suggesting vacancy concentrations of 15% at the melting temperatures.     

A simple, universal theory and method for computer plotting of stable equilibrium phase diagrams of a multisystem—SFM method

A new easy method has been presented to calculate the variable intervals corresponding to the stable univariant curves and to discriminate the stabilities of invariant points. This method and the one reported previously constitute a simple and universal theory for the computer-plotting of the equilibrium phase diagrams of a multisystem—sign function matrix (SFM) discrimination method. Its main steps are: determining the stable univariant scheme according to the derivative (or difference) of A_IG _m ; grouping the univariant curves by comparisons of the mutual relations among them; determining the existing intervals of the variables for the stable curves by comparisons of coordinate values of the curves about the invariant point; determining the stabilities of invariant points by comparisons of relations between the common curves and the invariant points. This method is suitable for any kind of phase diagram of closed or open systems in a phase diagram “space” with either 2 or more than 2 dimensions.     

Loading of Vesicles into Soft Amphiphilic Nanotubes using Osmosis

The facile assembly of higher‐order nanoarchitectures from simple building blocks is demonstrated by the loading of vesicles into soft amphiphilic nanotubes using osmosis. The nanotubes are constructed from rigid interdigitated bilayers which are capped with vesicles comprising phospholipid‐based flexible bilayers. When a hyperosmotic gradient is applied to these vesicle‐capped nanotubes, the closed system loses water and the more flexible vesicle bilayer is pulled inwards. This leads to inclusion of vesicles inside the nanotubes without affecting the tube structure, showing controlled reorganization of the self‐assembled multicomponent system upon a simple osmotic stimulus.     

Morphology and composition on Al surface irradiated by femtosecond laser pulses

We study the surface chemicals and structures of aluminum plates irradiated by scanning femtosecond laser pulses in air for a wide range of laser fluence from 0.38 to 33.6 J/cm². X-ray photoelectron spectroscopy and X-ray diffraction analyses indicate clearly that crystalline anorthic Al(OH)₃ is formed under femtosecond laser pulse irradiation. Besides aluminum hydroxide, crystalline Al₂O₃ is also found in the samples irradiated at high laser fluence. Field emission scanning electron microscopy demonstrates that the surfaces of the samples irradiated with low laser fluence are colloidal-like and that nanoparticles with a few nanometers in size are embedded in glue-like substances. For high laser fluence irradiated samples, the surfaces are highly porous and covered by nanoparticles with uniform size of less than 20 nm.     

Investigation of a novel hybrid process of laser drilling assisted with jet electrochemical machining

Recast layer and spatter are two inherent defects commonly associated with holes produced with laser drilling. This paper reports a novel hybrid process of laser drilling assisted with jet electrochemical machining (JECM-LD) that aims to minimize such defects and improve the quality of laser-drilled holes. The process based on the application of a jet electrolyte, being aligned coaxially with the focused laser beam, on the workpiece surface during laser drilling. The effect of the jet electrolyte mainly is an electrochemical reaction with materials. The jet electrolyte also cools the workpiece and transports debris during the process. On the basis of a measurement of laser attenuation in electrolyte, an experimental apparatus system is made and JECM-LD experiments have been performed on 0.5-mm-thick 321S20 stainless steel with two lasers at wavelength of 1064 and 532 nm. It is shown that recast layer and spatter have been effectively reduced during the JECM-LD compared with laser drilling in ambient atmosphere conditions.