关键词： composite   polycrystall   ferroelectrics   finite element modeling   microstructure  

摘要： A new concept of microstructural designing of polymer-free polycrystalline composite materials is offered. The concept based on controllable substitution during composite formation of separate crystallites making a polycrystal by pores, crystallites with other composition and/or structure or amorphous substances with preliminary FEM modeling of polycrystalline composite properties. A line of precursor small-scale production technologies and polycrystalline composites with unique and reproducible properties (micro- and nano-porous ferroelectric ceramics, ferroelectric ceramics/ceramics and ceramic/crystal composites etc.) have been developed and systematically studied.

关键词： electrophoretic deposition   functionally graded materials   ceramic composites  

摘要： An important challenge in the design and processing of engineering materials is to combine irreconcilable properties of materials, such as hardness and toughness, in the same component. A possible concept to meet this demand is that of functionally graded materials (FGMs). The main feature of a graded material is the position-dependant composition and related mechanical properties. Electrophoretic deposition (EPD) is a fairly rapid low cost process, capable of producing such FGMs with complex geometry. This paper reports on processing of homogeneous as well as continuously graded ceramic-ceramic (ZrO2-Al2O3) and ceramic-metal composites (WC-Co) by means of EPD. The EPD characteristics of the constituent powders, such as the point of zero charge (pzc), the natural pH, the electrophoretic mobility, the effective particle charge and the resistance of the suspension are experimentally determined. The EPD processing parameters are described and the mechanical properties of the densified FGM composites are reported and evaluated. A model for the EPD process has been developed which enables to calculate the composition gradient in the FGM material from the starting composition of the suspensions, the EPD operating parameters and the powder-specific EPD characteristics. (C) 2003 Elsevier Science B.V. All rights reserved.

关键词： 氧化硅   金红石   纳米TiO2   微结构   晶粒尺寸   氧化钛   原始粒径   比表面积   孔径   光催化剂  

摘要： 通过硅酸钠水解生成的无定形氧化硅对金红石相纳米TiO2进行修饰,利用红外光谱、紫外-可见漫反射光谱、X射线衍射、透射电镜和比表面仪对纳米TiO2进行了表征。结果表明,氧化硅沉积在纳米TiO2的表面和颗粒之间形成一个空间网络体系,有效地抑制了TiO2晶粒尺寸和原始粒径的长大。当热处理温度低于700℃时,经氧化硅处理的纳米TiO2的晶粒尺寸、原始粒径和比表面积几乎不变;当热处理温度高于700℃时,经氧化硅处理的纳米TiO2的晶粒尺寸和原始粒径开始缓慢变大,比表面积快速下降,在900℃下煅烧2h,经氧化硅处理的纳米TiO2原始粒径仍为20～40nm。氧化硅的存在使纳米TiO2吸收紫外线的能力增强并使其平均孔径变小。

关键词： 铅基压电薄膜材料   微观结构   性能   制备方法   脉冲激光法   溶胶凝胶法  

摘要： 随着微电子技术的发展和高度集成化的趋势,压电薄膜材料愈来愈受到人们的重视.本文对铅基类压电薄膜材料的研究进展进行了评述,主要讨论了: (1)两种主要制备方法:脉冲激光熔融法(PLD)和溶胶凝胶法(Sol—Gel);(2)压电薄膜微观结构的表征,如畴结构,薄膜材料与大块材料的差别等;(3)压电薄膜材料力学、电学及相互耦合性能的评价参数,薄膜处理过程的相变和残余应力和破坏特征.最后提出了人们可能关注的一些问题.

关键词： Casting   Magnsium alloys   Microstructures  

摘要： The low pressure and gravity casting processing techniques offer the component designer an opportunity to produce pieces with increased complexity over those able to be fabricated via the high pressure die casting route. The design of appropriate microstructures for the enhancement of elevated temperature properties is dependent on the chosen processing route, with the low pressure and gravity techniques allowing for post-cast manipulation of the microstructure through heat treatment. There are competing microstructural requirements for strength and, creep resistance in casting alloys, and the optimised microstructure must, of necessity, be a compromise., The contributions from solid solution strengthening, grain boundaries and precipitation processes are described, with particular reference to elevated temperature magnesium alloys.

关键词： 混合导体透氧膜   Ba钙钛矿   颗粒复合   力学性能   氧渗透   电导率   NTC  

摘要： 该论文结合Ba钙钛矿(YBa<,2>Cu<,3>O<,7-δ>和Ba<,0.5>Sr<,0.5>Co<,0.8>Fe<,0.2>O<,3-δ>)透氧膜材料的组成特点,在保证输运性能的基础上,通过原位引入BaZrO<,3>基第二相颗粒,改变微结构和稳定相结构,提高氧离子-电子混合导体的力学性能和稳定输运性能.第一章详细阐述了混合导电陶瓷的氧离子-电子的输运原理,国内外研究现状及该材料在实际应用将会存在的一些问题;介绍了通过添加第二相颗粒对改善先进陶瓷微结构和力学性能的影响,及微结构对氧离子导体和混合导体输运性能的影响;最后给出了该论文确定的研究对象、目的和内容.第二章介绍了论文中所采用的试验方法、原理和设备,包括颗粒复合陶瓷基材料的设计原则、力学强度试验原理、O-TPD、氧渗透测量、碘滴定和电导率的测试.论文第三章对该实验室提出的单相双通道结构特征的YBa<,2>Cu<,3>O<,7-δ>,进行了原位引入BaZrO<,3>第二相颗粒的探索性研究.论文第四章同样采用通过加入ZrO<,2>和等摩尔过量的BaO,原位生成一定比例的BaZrO<,3>基第二相颗粒复合的制备方法,对具有较高氧渗透率的Ba<,0.5>Sr<,0.5>Co<,0.8>Fe<,0.2>O<,3-δ>(BSCF5582)进行了原位引入Ba(Sr)Zr(CoFe)O<,3>第二相颗粒的改性研究.

关键词： SHS   Al2O3-ZrO2纳米/微米复相陶瓷   原位结晶   共生共晶  

摘要： 通过在(CrO3+Al)燃烧体系添加ZrO2(4molY2O3)组元,利用SHS技术可以制备具有亚共晶、共晶和过共晶成分的Al2O3 ZrO2复相陶瓷。复相陶瓷基体组织主要由层片状和纤维状共晶组织所构成。在亚共晶成分复相陶瓷中,纤维状共晶组织体积分数较高,ZrO2纤维直径已达到纳米/微米尺度;在过共晶复相陶瓷中,层片状共晶组织体积分数较高,Al2O3 ZrO2两相层片间距基本在亚微米范围内。基于燃烧合成与凝固理论分析可认为,本试验所获得的复相陶瓷是通过SHS原位结晶及在大过冷条件下、熔体发生共生共晶反应生成的。所以在本试验条件下,只有亚共晶成分的复相陶瓷才易获得ZrO2相纤维直径在纳米/微米级尺度上的1 3复合的Al2O3 ZrO2纳米/微米晶内型复相陶瓷。

关键词： cross-linked polyamide   FT IR spectroscopy   positron annihilation spectroscopy   x-ray diffraction   transmission electron microscopy   electron diffraction  

摘要： A systematic investigation on the microstructural assay of aromatic polyamide membrane material has been presented. The study constitutes important aspects like critical micro-void size determination and the relative concentration of the same in the different samples synthesized using positron annihilation lifetime spectroscopy (PALS). Furthermore, assay of the partial crystallinity with the wide angle powder diffraction method and electron diffraction pattern along with the transmission electron micrograph (TEM) yields the micro-morphological description of the membrane material under investigation. The effect of ionizing radiation (Co-60 gamma-rays, similar to110 kGy) on the membrane material is found to have a significant increase in the relative population of the voids as examined through PALS. An FTIR spectroscopic analysis before and after irradiation of the sample is also presented. These a priori informations are expected to be useful in determining the efficacy of the desalination performance of this polyamide membrane material. (C) 2003 Elsevier B.V. All rights reserved.

关键词： 胶粒   SiO2凝胶   纳米SiO2   比表面积   显微结构   火山灰活性   粒子   稻壳灰   蜂窝   孔隙  

摘要： 对低温稻壳灰纳米尺度的显微结构进行了SEM、TEM(SAD)研究,首次发现稻壳灰由纳米尺度的SiO2凝胶粒子(～50nm)疏松地粘聚而成。稻壳灰结构中除了以往报道过的微米尺度的蜂窝孔(～10μm)外,还含有大量由SiO2凝胶粒子非紧密粘聚而形成的纳米尺度孔隙(<50nm)。纳米尺度的SiO2粒子和纳米尺度的大量孔隙是稻壳灰具有巨大的比表面积(50～100m2/g)和超高火山灰活性的根本原因。

关键词： friction materials   microstructure   microcrack   microvoid   wear mechanism  

摘要： In this study, a series of friction tests on semimetallic automotive friction materials were conducted on a friction test machine by pressing test samples against a rotating cast iron brake disc, thus simulating actual braking. After each friction test, the morphological changes of the wear surface and subsurface were investigated using scanning electron microscopy. Microstructural examinations showed that the major wear mechanisms in operation during braking are comprised of the following: (i) abrasive, (ii) adhesive, (iii) fatigue, (iv) delamination, and (v) thermal. The wear mechanism and wear transition are found to be influenced by the applied loads and braking times. In the study of the subsurface morphology, microcracks generated in the subsurface are thought to be due to the following phenomena;(i) growth of microvoids, (ii) coalescence of microvoids, (iii) coalescence of second phase particles, and (iv) coalescence of microvoids and second phase particles. The microcracks generated in the subsurface grew and propagated parallel to the sliding surface as the braking times as well as applied loads are increased. Finally, the microcracks grew and joined each other producing wear particles on subsequent braking. These mechanical and thermal failures manifested a complex wear mechanism, causing plastic collapse in the local region which subsequently produced wear particles in different shapes depending on the modes of failure. (C) 2003 Elsevier B.V. All rights reserved.