Synthetic Effects of Frequency and Duty Ratio on Growth Characteristics,Energy Consumption and Corrosion Properties of Microarc Oxidized Coating Formed on Ti6Al4V

The synthetic effects of frequency and duty ratio on growth characteristics and corrosion properties of coating on Ti6 Al4 V fabricated by microarc oxidation are investigated comprehensively. Under the condition of uniform cumulating time of positive impulse width, the essence of altering frequency and duty ratio to determine the formation of coating is to vary the duration and interval time of positive pulse. The growth of coating is mainly controlled by duration time of positive pulse and hardly correlated to the interval time of positive pulse, while both duration and interval time of positive pulse have few influences on the morphology and phase structures of coating. The dynamic current is related to positive impulse width and the ratio of positive pulse on-time to pulse off-time. Regardless of uniform duration or interval time of positive pulse, the energy dissipation presents a descending tendency. The relationship between energy consumption and anticorrosion performance is contradictory, and obtaining excellent corrosion resistance is bound to sacrifice lots of energy. The duty ratio and frequency can be designed purposefully to realize the optimal process.     

Experimental Study of Sub-critical Velocity in Longitudinally Ventilated Tunnels

Fire Technology - The critical velocity is the minimum velocity blowing towards the fire seat in tunnels to reduce the length of back-layering to zero, and it has been extensively adopted in the...     

Influences of gap pressure on machining performance in radial ultrasonic rolling electrochemical micromachining

Microdimples as a typical surface texture has been widely used for improving the properties in tribology and heat transfer fields. Ultrasonically assisted     

定子分段式永磁直线同步电机速度波动抑制方法研究

为了解决定子分段式永磁直线同步电机(PMLSM)存在的因磁阻效应、负载阻力、摩擦力、参数摄动以及动子进出定子时耦合面积变化所造成的控制性能下降的难题,根据动子和定子的耦合状态,提出一种在完全耦合阶段和动子退出定子阶段的分段式控制方法。首先,在动子与定子完全耦合阶段采用改进滑模控制器减小推力波动导致的速度波动,再通过加入扰动观测器降低滑模切换项所带来的抖振现象;在动子退出定子阶段,建立相关电磁参数与动子位置的函数关系,实时补偿由耦合面积变化引起的动子失速,使动子速度在退出时接近给定值。仿真及实验结果表明动定子完全耦合过程中的速度稳态误差为0.005 m/s,收敛时间为0.3 s,动子退出定子阶段的速度波动不超过0.04 m/s,满足定子分段式PMLSM用于长行程自动运输系统对平稳性及快速性的需求。     

童寯1930年旅欧日记(选登)

我国第一代建筑学家、设计大师、建筑学教授童寯先生(1900—1983)于1928年在美国宾夕法尼亚大学获建筑学硕士后,先后在费城科尔建筑师事务所和纽约伊莱·康建筑师事务所从事建筑设计工作,于1930年4 月回国。从4月26日登船并于5月1日在英国南安普顿上岸,至8月26日抵达中苏边境,在英国、法国、德国、意大利、瑞士、比利时、荷兰、捷克、波兰和前苏联等10个国家参观考察达4个月之久,并用英文写下了近7万字(中文译文)的日记。童寯先生的这些日记弥足珍贵,经他孙子童文整理英文原稿并经童明翻译成中文, 已编入《童寯文集》(四卷本)第四卷。该书将于2006年五、六月份由中国建筑工业出版社出版发行。现征得该文集编者童明、杨永生两位先生同意,本刊特选出若干篇日记先期发表, 以飨读者。     

对市政工程造价管理的探讨

通过了解发达国家对市政工程的造价管理模式,结合当前我们所处的状况,分析原因,找出差距,阐明了理顺造价管理体制的重要性及政府在市政工程造价管理中应起的作用。     

道桥用SBS改性沥青防水卷材的研制

在生产普通SBS改性沥青防水卷材的基础上运用正交实验的方法对所选原材料进行优化组合，成功研制出道桥用SBS改性沥青防水卷材。经检验，其各项指标均达到或超过国家建材行业标准JC/T974--2005的要求。     

Friction behavior of Al-Cu-Fe-B polycrystalline quasicrystals

Dry sliding friction between the polycrystalline Al59Cu25.5Fe12.5B3 quasicrystals(QCs) and coating of the diamond-like carbon(DLC) was carried out by self-made tribometer under different conditions. The influences of four parameters(temperature, sliding velocity, applied load, atmosphere) on friction of quasicrystal surface were studied. Microstructure of quasicrystal, morphology of worn surface, and wear debris were observed by scanning e-lectron microscope(SEM). The results show that for QCs, the friction coefficient and the roughness of worn surface is influenced by the parameters, especially greatly by the temperature. With increasing the applied load and sliding velocity, the friction coefficient decreases. The dominant wear mechanism at 350℃ is delamination for QCs. The cracks forms on the worn surface during friction. Moreover, phase transformation is not observed on worn surface of QCs at 350℃.     

Recovery of gallium from phosphorus industry flue

The flue dust generated during electric furnace production of elemental phosphorus was investigated for the recovery of gallium. Then the flue dust was slurried with water and blended with concentrated sulfuric acid, followed by ageing. The gallium in the dust was thereby converted to soluble sulfate. The factors affecting the dust curing were investigated to understand the process chemistry of the pretreatment. The optimal curing conditions are determined as follows: the mass ratio of dust to water and acid is 1 : 1 : 1, ageing temperature and time are 200℃ and 2h, respectively. Almost all the gallium available to acid dissolution in the dust, about 90% gallium, can be extracted by leaching the cured dust at 80℃ for 1h.     

S,Fe共掺杂纳米TiO_2的制备及其光催化性能

以水热法制得了S,Fe共掺杂的纳米TiO2光催化剂(TiO2-S-Fe),XRD分析表明,其为锐钛矿晶型,S,Fe掺杂能抑制TiO2粒径的生长;UV-vis漫反射表明,TiO2-S-Fe对可见光吸收增强,吸收带边明显红移;XPS显示S,Fe共掺杂,使得TiO2表面羟基氧含量提高,从而提高催化剂活性;可见光降解甲基橙溶液结果表明,共掺杂样品光催化效果优于单掺样品,S和Fe共掺杂对提高TiO2可见光活性具有协同效应。当Fe3+∶S∶Ti(摩尔比)=0.005∶1∶1,180℃下水热反应3 h时,制得的TiO2-S-Fe可见光催化活性比纯TiO2的活性提高了约10倍。