关键词： concretes   corrosion   durability   microstructure   reinforcing steel  

摘要： Corrosion of steel in concrete is a complex phenomenon. The corrosion performance of reinforcing steel embedded in concrete is dependent on many variables. These variables include differences in materials constituents, microstructure, processing procedures, concrete mixture proportions, structural design, construction methods, loadings, cracks, and environmental conditions. Reinforced concrete structures are often expected to have relatively long service lives under severe loading and exposure conditions. Often, the primary governing factor affecting the service life of the structure is the corrosion performance of the steel reinforcement. For many systems, concrete is often the only protective cover that prevents the ingress of aggressive ions and eventual corrosion of the reinforcing steel. Significant advances in state of the practice have been exhibited with the use of high-performance concrete materials. Due to the high cost associated with deteriorating reinforced concrete structures, however, other approaches need to be investigated to ensure long-term serviceability of these structures. A complementary approach to improving the quality and corrosion performance of reinforced concrete structures is to utilize reinforcement that has been microstructurally designed to resist corrosion. This approach can increase the redundancy of the protective system, decrease corrosion activity, and increase the service life of reinforced concrete structures. To properly evaluate the corrosion performance and to better predict the service life of reinforced concrete structures, it is necessary to evaluate the characteristics of the bulk concrete, the steel-concrete interface, the steel mill scale, the passive film, and the steel microstructure. This research program investigated the performance of microstructurally designed reinforcing steel for improved corrosion resistance when embedded in concrete and exposed to accelerated chloride environments. Reinforced concrete specim

关键词： 离子辐照   微结构   土壤结构  

关键词： 纳米粉   添加剂   陶瓷   烧结性能   微结构  

关键词： microstructure-final   mechanical properties   abrasion   zirconia-flyash  

摘要： The addition of zirconia in different proportions to one type of Indian flyash has been studied. The study is concentrated on mechanical properties of the materials like MOR, MOE and hardness, the sand abrasion resistance and the microstructural investigation by scanning electron microscope. It is observed that MOR of the material increases upto 10 vol% of ZrO2 in flyash and then starts decreasing. On the other hand, both MOE and the Vickers hardness increase with the increase in ZrO2 content in the matrix. The abrasion volume loss of the material decreases upto 15 vol% ZrO2 in flyash which further increase with increase in ZrO2 content. It has been pointed out from the microstructural investigation that, with the increase in addition of ZrO2 in flyash, the needle shaped mullite phases are being replaced by the near spherical shaped zircon grains. This paper correlates these data along with the physical properties and phase identification studies, which were reported earlier. (C) 1999 Elsevier Science Ltd and Techna S.r.l. All rights reserved.

关键词： ferrous materials   sintered blank   compacting force   Conductivity measurement   dewaxing   application methods   Test Method   MECHANICAL STRENGTH   Microstructure   Mechanical properties   Electric conductivity   Percent  

摘要： The role of microstructure on mechanical properties of sintered ferrous materials was studied using a method based on electrical conductivity measurement. The method was accompanied by quantitative fractography to evaluate the dewaxing and sintering process in iron compacts. The effects of manufacturing parameters, such as compacting pressure in the range of 150-800 MPa, sintering temperature from 400 to 1300 degreesC, sintering time up to 8 h, and lubrication mode were investigated. Several mathematical models were checked to obtain the best one for prediction of electrical conductivity changes as a function of manufacturing parameters. The mechanical properties of the sintered compacts were also evaluated to establish a relationship between conductivity, total porosity, pore morphology, and mechanical behaviour. The results show that the electrical conductivity/resistivity of sintered materials is closely related to its microstructure, so that measuring these properties can replace destructive test methods for prediction of mechanical strength of sintered materials with homogeneous matrix microstructure. The application of the method is shown for sintered Fe, Fe-0.8%C, and Fe-1.5%Mo-0.7%C compacts. PM/0877. (C) 2000 IoM Communications Ltd.

关键词： 气孔率   AK   电瓷材料   冲击弯曲强度   关系图   KIC   力学性能  

摘要： (上接《电瓷避雷器》2 0 0 0年第 3期第 33页 )3.2　瓷材料的力学性能3.2 .1　瓷材料的常规力学性能和 KIC为了进行统计处理 ,每组弯曲强度和冲击弯曲强度试样数不少于 2 0。断裂韧性试样数不少于 1 5。将试验数据统计处理得出平均结果和相应的 Weibull系数 m。弹性常数结果取每组四个样的平均值。结果列于表 6。表 6　瓷材料的常规力学性能和 KIC材料参量 σb(MPa) m(σb) KIC(MPa.m1 / 2 ) m (KIC) AK(k J/ m2 ) m(AK) E(GPa)G(GPa) v γ(J/ m2 )X 12 4.0 14.5 1.42 416 .12 .5 0 2 4.5 93.2 39.3 0 .18810 .9XX 10 8.2 15 .11.33933.5 1.82 8.5 0 83.2 34.5 0 .2 0 6 10 .8XXX 98.5 2 6 .6 1.31432 .6 1.45 15 .173.930 .70 .2 0 411.7X2 146 .3 16 .0 1.44 0 46 .72 .83 14.810 5 .5 42 .80 .2 0 2 ...

关键词： positive temperature coefficient of resistivity   microwave sintering   core-shell structure   domain arrangements  

摘要： Microstructural characteristics and the corresponding resistivity-temperature (rho-T) properties of microwave- and conventionalsintered Pb0.6Sr0.4TiO3 materials with positive temperature coefficient of resistivity (PTCR) were investigated in the present work. The specimens prepared by microwave sintering exhibited a single T-c, whereas those prepared using conventional sintering show double T-c behavior. During the microstructural investigations, sintering aids, SiO2 and TiO2, showed intriguing liquid phase sintering characteristics in the specimens. Large amounts of Pb-species dissolved in high Si regions, where a nonequilibrium core-shell structure was frequently observed, especially for microwave sintered specimens, which showed very complicated domain arrangements in the gain interiors.

关键词： 复合材料   烧结性能   结构   氮化铝   氮氧化铝   陶瓷  

摘要： 本文评价了在Al_2O_3和AlN粉末中加入少量的Y_2O_3置于1650℃～1900℃的1个大气压的N_2气中,用形成的烧结块所制备的粒状复合材料的显微结构和机械性能。用X射线衍射测定出氮氧化铝(AlON-5AlN·9Al_2O_3)、27R AlN假多型体和AlN是烧结材料中的主要物相。随着Al_2O_3含量的增加,在可比烧结条件下烧结体积密度也随之增加。AlON基质材料的烧结体积密度在1750℃时显示出最大值,而AlN基质材料的烧结密度随着烧结温度的增高而降低。在1850℃以上,主要由AlN与Al_2O_3的反应和Y_2O_3的协助而形成液相。AlON基质材料的致密化主要受所形成的液相和AlON晶粒生长的控制。在AlN基质材料中,在1650℃时形成液相,并随着烧结温度达到1900℃,只有少量的AlN晶粒生长。在烧结期间加入5mol％ Al_2O_3,在AlN晶粒边界析出AlON次生相。含分散的AlN颗粒的AlON材料在室温下的弯曲强度与断裂韧性高于AlON。含50mol％和64.3mol％Al_2O_3材料的高温弯曲强度,在1000℃时可分别稳定到～290MPa和420MPa,而在1200℃时则急剧下降。含5mol％和30mol％ Al_2O_3材料的弯曲强度,在1000℃时同室温值相比增长了～14％,但在1200℃又降到了室温值。

关键词： 多传感器信息融合   智能机器人   微型电子机械系统   不确定性   证据推理   分布式决 策融合  

摘要： 多传感器信息融合是传感器技术、模式识别、人工智能、模糊理论、概率统计等学科相交叉的一门兴学科,它研究如何充分发挥各个传感器的特点,利用其互补性、冗余性,提高测量信息的精度和可靠性,获得更加准确的识别、判断和决策.这是智能理论的重要的研究领域之一.该文以多传感器信息融合技术为研究重点,结合它在智能机器人中的应用的进行了理论和实践上的探讨.

关键词： 纳米二氧化钛粉体   溶胶-凝胶法   绿色化学   沉淀剂   催化  

摘要： 该论文以多种高分子物质作分散剂并以无机钛盐作前驱物质,利用溶胶-凝胶法制备纳米二氧化钛粉体.制备产物微结构控制的主要内容包括:颗粒尺寸、颗粒大小均匀性、晶体类型、颗粒的几何形状、颗粒的团聚程度和产品纯度等.其微结构控制的重要手段包括分散剂的选择、制备过程热处理手段的改进等.其微结构控制的重要手段包括分散剂的选择及分散剂的预先化学或共混改性、制备Ti(OH)<,4>所用碱性沉淀剂的选择、制备过程热处理手段的改进等.分散剂的结构及分散机理、目标产物制备过程及微结构的表征运用了电泳 、粘度测定、热分析、X射线衍射、红外、透射电子显微镜、比表面积测定等方法.