Thermophoresis in dense gases: A study by Born-Green-Yvon equation

Thermophoresis in dense gases is studied by using a multi-scale approach and Born-Yvon-Green (BYG) equation. The problem of a particle movement in an ambient dense gas under temperature gradient is divided into inter and outer ones. The pressure gradient in the inner region is obtained from the solutions of BYG equation. The velocity profile is derived from the conservation equations and calculated using the pressure gradient, which provides the particle velocity in the outer problem. It is shown that the temperature gradient applied to the quiescent ambient gas induces some pressure gradient and thus flow tangential to the particle surface in the interfacial region. The mechanism that induces the flow may be the dominant source of the thermophretic particle movement in dense gases. It is also shown that the particle velocity has a nonlinear relationship with the applied temperature gradient and decreases with increasing temperature.     

Evaluation of the particle-particle interactions in a toner by colloid probe AFM

In order to evaluate the particle-particle interactions in a toner particle with a high accuracy, the changes in the adhesion force between a toner particle glued to an AFM cantilever tip and a particle in a compressed layer of toner powder was measured by colloid probe atomic force microscopy. Toner particle layers compressed by a pressure of 54.9 MPa were used as the substrate in this study. The effects of the scan rate, particle diameter, humidity, and surface coating of silica nanoparticles on the adhesion force were discussed on the base of measurement results. The adhesion force between the toner surfaces decreased with an increase in the AFM scan rate; it then reduced to a constant value at 1.95 Hz. The adhesion force between the toner particles increased proportionally with approximately the second power law of the particle diameter; it exhibited a change that differs from the force characteristic that was directly proportional to the first power law of the particle diameter, as given in van der Waals expression. Next, the additives that consisted of SiO₂ were glued on to the surface of the toner particle, and the influence of the surface coverage of SiO₂ on the particle-particle interactions was examined. The particle-particle interactions consequently decreased in inverse proportion with a surface coverage of SiO₂ 26% or less. Moreover, when the SiO₂ surface coverage was 26%, almost no changes were observed in the particle-particle interactions at 80% R.H. It was confirmed that the influence of humidity reduced by coating the toner particle with SiO₂. The relationships between the particle-particle interactions and the flow properties were examined by using a rotary shear tester with a conical rotor. When the mean particle diameters were identical, a first strong positive correlation between the particle-particle interaction and the shearing torque that crossed the zero point was observed. When the shearing force H was calculated from the torque of the conical rotor method by using Rumpf's equation, a first strong positive correlation between the particle-particle interaction Fa and the shearing force H that crossed the zero point was observed.     

Adhesion force measurement of a DPI size pharmaceutical particle by colloid probe atomic force microscopy

The method to determine the adhesion characteristics of fine drug particles for dry powder inhalation (DPI) was established using a colloid probe which mounted a 1-3 μm drug particle on a commercial atomic force microscope (AFM) cantilever. A new preparation system of colloid probes for fine particles smaller than 2.5 μm in diameter was developed with the aid of a micromanipulator and a video microscope. Using this colloid probe, adhesion force distribution between a spherical polycrystalline drug particle and a plate of lactose monohydrate representing for DPI carrier materials or stainless steel for device wall materials was measured. Atmospheric humidity as well as the material and surface roughness of a target plate affected the determined adhesion force. With increasing surface roughness of a lactose plate, the adhesion force between a drug particle and the plate distributed more widely and their mean value decreased. Adhesion force increased meaningfully with atmospheric humidity. Adhesion force for stainless steel was higher than that for lactose.     

低温蜡-硅溶胶型壳的应用实践

分析了水玻璃型壳、复合型壳、中温蜡-硅溶胶型壳和低温蜡-硅溶胶型壳4种制壳工艺的优缺点,指出低温蜡-硅溶胶型壳工艺适用于质量要求一般的铸件,中温蜡-硅溶胶型壳工艺适用于高质量要求的小件、特小件。介绍了低温蜡-硅溶胶型壳的生产工艺要点。     

Film Formation by Colloidal Overbased Detergents in Lubricated Contacts

It has been reported in the literature that overbased detergents can possess good antifriction and antiwear properties although the origins of these properties are not fully clear. In practice, over-based detergents are colloidal dispersions and this may be important in determining their properties and mechanism of action.

In the current study, the lubricating properties of commercial, overbased magnesium and calcium sulfonates were measured in thin film, lubricated conditions and compared to a neutral sulfonate additive. A range of techniques was employed to evaluate the tribological performance of solutions of these additives. Film thickness measurements were carried out using optical interferometry and in-contact visualization, while friction and wear measurements complemented the study.

It has been found that, when operating in thin film conditions, overbased detergents deposit solid-like boundary films on the rubbing surfaces. These films form in both rolling and mixed rolling/sliding conditions and, unlike many other colloidally-formed boundary films, are able to survive in high speed, thick film conditions. During formation, the film rapidly reaches a thickness corresponding to one colloid particle diameter, between 10 and 20 nm. After prolonged rubbing, however, the film thickness reaches the equivalent of three particle diameters. No such thick boundary films are observed with the neutral sulfonate.

The boundary films formed by overbased detergents produce a significant reduction in wear. However, for the very smooth surfaces used in this study, they also result in an effective roughening of the very smooth surfaces studied. This leads to an increase in friction in the intermediate speed region by promoting solid-solid contact in thin fluid film conditions.     

陶瓷胶态注射成型液固转变过程中内应力产生机制初探

陶瓷的胶态注射成型工艺适应了高性能陶瓷产业化的需要，其关键是要通过制备均匀性好的陶瓷坯体而保证部件的使用可靠性。本文提出在胶态注射成型液固转变过程中容易产生内应力，并且初步研究了陶瓷坯体中内应力的产生、遗传和变异的规律，并通过应力缓释的办法对内应力进行有效的调控。     

二维熔化的研究进展

晶体的熔化一直是凝聚态物理中广泛关注的研究方向,尽管有上百年的研究历史,但是仍然没有一个完整的基础层面上的理论。大量实验和计算模拟研究工作表明,熔化符合KTHNY理论。晶体在熔化过程中的结构和动力学也已成为大家关注的热点。     

Colloid stabilization by polyelectrolytes. Application to decontamination processes of nuclear reactors

The redeposition of colloidal magnetite particles can reduce the effectiveness of the chemical decontamination of nuclear reactors. Sodium salts of the following anionic polyelectrolytes were evaluated as particle stabilizers: polyacrylic acid, polymethacrylic acid, poly (methyl vinyl ether/maleic anhydride), sulfonated polymers. A cationic polyelectrolyte, a polyamine, was also evaluated. An active and an inactive oxidized carbon steel sample were treated in the same experimental set-up with the decontaminating reagent and with or without the polyelectrolyte. Activity pick-up by the inactive sample was measured. When no polyelectrolyte was added, 15% of the Co-60 activity was redeposited. With polyelectrolyte addition in the 5–450 mg kg^?1 range, the Co-60 activity redeposition ranged from 8.5 down to 0.8%. Polyacrylic acid was the most effective reagent. The transfer of the magnetite outer oxide crystals from the active to the inactive surfaces was identified on SEM micrographs.     

The sol-gel preparation of ZnO/silica core-shell composites and hollow silica structure

Three kinds of different ZnO colloid particles (flowerlike particles, nanoribbons and microspheres) and one kind of ZnO film have been coated with silica via a simple sol-gel method in the Stöber system and ZnO/silica core-shell microparticles or films have been obtained. The thickness of silica shell can be controlled by adjusting the concentration of TEOS added into the system. If the ZnO core is etched off by HCl, corresponding, hollow silica particles or film will be generated.     

胶体粒子扩散聚集过程的二维动态化模拟

简要地报道了用ＦＯＲＴＲＡＮ语言实现胶体粒子扩散聚集过程二维动态模拟的一种简单方法：将二维平面划分为网络,胶体粒子按一定的浓度和能量随机分布在网络格点上;调用着色子程度设定背景和绘图颜色;对某一时刻各胶体粒子所占位置进行屏幕点和着色操作;计算下一时刻各粒子的位置坐标;取消上一时刻各粒子,即置其位置为背景色;根据所计算出的新时刻的粒子坐标进行画点着色;重复上述过程至体系达某一状态或某一时刻。由于计算