It is an important concern to explore the properties and principles of lubrication at nano or molecularscale. For a long time, measurement apparatus for filmthickness of thin film lubrication (TFL) at nano scale havebeen devised on the basis of superthin interferometry technique. Many experiments were carried out to study the lubrication principles of TFL by taking advantages of aforementioned techniques, in an attempt to unveil the mechanism of TFL. Comprehensive experiments were conducted to explore the distinctive characteristics of TFL. Results show that TFL is a distinctive lubrication state other than any known lubrication ones, and serves as a bridge between elastohydrodynamic lubrication (EHL) and boundary lubrication (BL). Two main influence factors of TFL are the solid surface effects and the molecular properties of the lubricant, whose combination effects result in alignment of liquid molecules near the solid surfaces and subsequently lubrication with ordered film emerged. Results of theoretical analysis considering microstructure are consistent with experimental outcomes, thus validating the proposed mechanism....
The effect of sintering process (especially the sintering temperature) on the magnetic property and microstructure of sintered sample of nanosized soft magnetic MnZn ferrite powder was investigated. The sintered sample of MnZn ferrite was prepared by both traditional pressing and cool isostatic pressing on MnZn ferrite nanoparticals. The sintering process of which was segmented. Thedensity, microstructure and phase composition of sintered sample were analyzed by Archimedes'law, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The grain growth and densification in sintering process of MnZn ferrite were investigated. The magnetic property was measured by vibrating sample magnetometer (VSM) and Nim2000 magnetic material testing system. The results show that the better sintering temperature is 850 ℃, at which the better magnetic property and microstructure of sintered compact were obtained....
Despite the great achievements made in improvement of wear resistance properties of aluminum alloys,their applications in heavy surface load-bearing are limited. Single coating is insufficient to produce the desired combination of surface properties. These problems can be solved through the duplex coatings. The aim of the present study is to overview the research advances on processes of duplex coatings on aluminum alloys combined with micro plasma oxidation process and with other modern processes such as physical vapour deposition and plasma assisted chemical vapour deposition and also to evaluate the performance of micro plasma oxidation coatings in improving the load-bearing, friction and wear resistance properties of aluminum alloys in comparison with other coatings. Wherein, a more detailed presentation of the processes and their performances and disadvantages are given as well....
Semisolid metal forming by a novel sloping plate process was studied. A sloping plate with wavelike surface was used to prepare semisolid alloy. Semisolid billets and slurries with good microstructures and excellent property were prepared by cooling or preheating the sloping plate. During preparing semisolid alloy by the proposed process, the co-action of burst nucleation and dendrite fragmentation causes fine spherical microstructure formation, and casting temperature, cooling strength and sloping angle are the main factors influencing the alloy microstructure. Under the current experimental conditions, in order to prepare good quality semisolid billets, proper casting temperature ranges of 660-690 ℃ for AlMg3 alloy and 660-680 ℃ for AlSi6Mg2 alloy are suggested. A small car hub wheel of AlSi6Mg2 alloy was thixoformed, and its pattern and inner microstructure are fine. The reasonable technological conditions for preparing AlSi6Mg2 slurry are also proposed: the sloping plate preheating temperature is 300 ℃, and the casting temperature is 680 ℃....
This investigation deals with the observations pertaining to the effects of specimen and slurry compositions as well as traversal distance on the slurry wear response of a zinc-based alloy. The composition of the alloy was altered by adding 4% silicon to it. The slurry composition was varied through changing the concentration of the sand particles in the range of 0-60% that were suspended in the (liquid) electrolyte. The electrolyte contained 4 g sodium chloride and 5 mL concentrated sulphuric acid dissolved in 10 L of water. The slurry wear tests were conducted at a speed of 7.02 m/s over the traversal distance range of 15-500 km. The wear rate increased initially with traversal distance, attained a maximum and decreased thereafter irrespective of the specimen and test environment. However, the wear rate peaks were less prominent in the liquid plus sand environments than the liquid-only medium. Further, the wear rate peak in the liquid-only medium appeared at a shorter traversal distance than the one in the sand containing slurries. Addition of sand particles to the electrolyte reduced the wear rate of the samples to 5%-15% depending on the sand concentration of the slurry. Moreover, intermediate (40%) sand content led to a maximum wear rate when compared with in the liquid plus sand media. However, this maximum was still less than in the liquid-only medium. The silicon containing alloy suffered from higher wear rates than the silicon free alloy samples when tested in the liquid-only medium. On the contrary, the trend reversed in liquid plus 20% and 40% sand environments whereas a mixed response was noted in the slurry containing 60% sand. In the latter case, the presence of silicon proved deleterious initially while an opposite trend was observed at longer traversal distances. The wear response of the samples was discussed in terms of specific features of their microconstituents like silicon and the predominant material removal mechanism in a given set of experimental conditions. The observed behaviour of the alloys was also substantiated further through the characteristics of their affected surface and subsurface regions....
We report the structural characterization and proposed formation mechanism of honeycomb-like ZnO conglomerationsfabricated by direct precipitation method. X-ray diffraction (XRD), energy-disperse X-ray spectrometry (EDS), scanning electronmicroscopy (SEM) showed that the as-prepared ZnO calcined at 700℃ were micron sphere particles with honeycomb-likestructure. In the UV-vis absorbing spectrum, it was observed that there is a new additional absorption band at 260 nm, and it wasspeculated that the absorption may be caused by defects on the surface and interface of honeycomb-like ZnO. The as-productsshowed high sensitivity and short response time to sulfured hydrogen gas. These results demonstrate that honeycomb-like ZnOconglomerations are very promising materials for fabricating H2S gas sensors.2008 Chao Li. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved....
A new continuous casting mold repairing method-cold gas dynamic spraying(CGDS)is introduced.The study investigates the advantages of the CGDS process regarding repairing operation,such as convenient,in-situ repairation,little heat delivery,microstructural and dimensional stability and other special applications.Microstructure and mechanical properties of the copper alloy coating,nickel coating,ceramic composite coating,and their interface to the substrates,which are usually used in repairing operation have been researched by means of optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and micro-hardness tests.Experimental results have demonstrated the relative density of the copper alloy coating is as high as 98.7%,and that no obvious diflference Can be observed between the CrZrCu substrate and the Cu alloy coating in terms of microstmctures;thus the interface is quite difficult to be identified.The bonding strength and micro-hardness of the Cu alloy coating reach up to 37 MPa and 310 HV0. 2,respectively.The interface between the copper alloy coating and the nickel coating is either zigzag or wave shaped,and the cohesion is relatively good.As-sprayed nickel coating is dominated by severely deformed particles,and the relative density is up to 98.5%.Complete recrystallization occurred after annealing at 900℃ for one hour,while its micro-hardness remains as high as 124.1HV0.2. All these results have indicated that CGDS is a promising technology for repairing the continuous casting mold and that its future development is prosperous as well....
在系统动力学模型中将城市商品住宅价格系统划分为宏观经济、城市人口、市场需求、市场供给、房屋租赁和土地价值六个子系统，并引入了住宅开发投资及其比例、供求比影响因子、住宅销售面积中成交比例、开发利润率和基建投资等影响因子。通过仿真比较了桂林市商品住宅价格与人均可支配收入、住宅开发投资、 GDP 等主要因素的变动情况，分析了长期和短期各主要因素对商品住宅价格影响程度和时序，以此确定政府在不同时期以控制商品住宅价格为目的所应采取的宏观调控措施和手段，同时为消费者和房地产开发商择机购房和投资提供相应的决策依据。...
