铁氧化物纳米晶自组装空心微球的制备、表征及其应用

铁氧化物纳米材料和纳米结构空心微球分别代表了材料研究中组分和结构的研究热点. 而由铁氧化物纳米晶自组装形成的空心微球的研究则是二者相结合, 具有重要的科学意义和良好的应用前景. 虽然已发展了多种方法制备各种单质及化合物的空心微球, 但铁氧化物纳米晶自组装空心微球的制备方法报道较少. 本文简要介绍了近几年发展起来的多种铁氧化物纳米晶自组装空心微球的一些制备方法, 利用上述方法, 制备出了多种不同组成单元、不同尺寸、不同空心程度的铁氧化物纳米晶自组装空心微球, 对所制备的铁氧化物纳米晶自组装空心微球进行了表征, 并初步介绍了所制备的铁氧化物纳米晶自组装空心微球在药物缓释和环境领域中的应用.     

纳米结构太阳能电池材料的研究进展

纳米结构材料是当今科学研究的热点,它应用于太阳能电池具有成本低、稳定性好、光电转化率高等特点.介绍了纳米结构材料,如自组装纳米结构的有机盘状液晶太阳能电池和无机纳米晶太阳能电池材料(主要包括敏化TiO2纳米晶、CdSe和CdTe纳米晶、Si基纳米结构)的研究和应用进展,并展望了这些纳米结构材料作为太阳能电池材料的未来发展.     

复合分子筛的合成及应用研究新进展

综述了近年来复合分子筛合成及应用方面的最新研究进展。系统地介绍了复合分子筛的各种合成方法,包括原位合成法、二次合成法、分子筛硅铝源法、预置晶种法、纳米组装法,以及气相转移法和预先负载原料法两种新方法,并分析比较了各种方法的特点;简单介绍了复合分子筛在催化和吸附方面的应用研究。     

MCM-41介孔分子筛和纳米TiO2/MCM-41的合成与结构表征

以工业水玻璃为硅源,表面活性剂十六烷基三甲基溴化铵为结构模板剂,利用室温晶化法合成出MCM-41介孔分子筛,并以钛酸丁酯为前驱体,通过溶胶凝胶法及液相沉积法对介孔分子筛MCM-41进行纳米TiO2的组装。运用XRD、FT-IR、N2吸附-脱附等表征手段对其结构特征和氧化钛分散状态进行了研究,结果表明：TiO2与MCM-41端基硅氧键反应形成Ti-O-Si键;纳米TiO2不仅进入孔道,较均匀地修饰了介孔分子筛MCM-41的孔壁,而且使介孔分子筛MCM-41仍保持有序的孔道结构。     

两步晶化法制备MCM-48/ZSM-5复合分子筛

利用两步晶化法制备了高水热稳定性的MCM48/ZSM-5介微孔复合分子筛.通过SEM、TEM、XRD、IR和N₂吸附脱附进行表征,结果显示,该材料的结构不同于简单的机械混合,而是具有微孔孔壁和三维立方介孔孔道的复合材料,其孔道尺寸为2.6nm左右.该复合分子筛在沸水中处理6h后,介孔结构仍保留完好.通过考察晶化时间对复合分子筛的影响,证明了介孔和微孔的组装是一个竞争的过程,复合分子筛中介孔与微孔结构的比例随晶化时间的变化而变化,且具有介孔孔道和微孔孔壁的复合分子筛150℃的最优晶化时间为8h.     

三维块体纳米晶材料的制备及应用

综合评述了三维块体纳米晶材料的最新研究进展.概述了三维块体纳米晶材料的常用制备方法及新颖制备技术,并对各种制备方法进行了综合比较,指出其优缺点及已有实际应用的材料体系;介绍了三维块体纳米晶材料的性能表现;展望了三维块体纳米晶材料的未来研究发展方向及其在新领域的应用前景.     

纳米晶金属材料塑性变形及超塑性行为研究进展

纳米晶块体材料有望改善金属材料传统的加工工艺并且在应用方面有很广阔的前景.结合近年来实验研究、计算机模拟及理论计算等各方面的分析结果对纳米晶金属块体材料在塑性和超塑性方面的研究进展情况进行了评述,分析了影响纳米晶金属块体材料力学性能的因素,并对其变形机理进行了初步探讨.     

介晶半导体材料的合成及应用研究进展

传统半导体纳米材料大部分为多晶结构或单晶结构。而介晶是一类由初级纳米颗粒以结晶学有序的方式自组装而成的纳米粒子超结构,具有类似单晶的原子结构和散射特征,既保留着初级纳米颗粒的晶界,又表现出强烈的各向异性,从而具有与多晶和单晶均不同的独特结构与性能。例如,介晶结构中的初级纳米颗粒以一定的方式相互连接,与无序堆积的多晶相比,具有极高的结晶性,甚至接近单晶,能够有效减小载流子在材料内部的复合概率;初级纳米颗粒之间的晶界并未完全消失,存在一定的空隙,具有较高的空隙率和比表面积以提供更多的活性位点;初级纳米颗粒在定向吸附过程中有序地取向排列,暴露出高能晶面,显著提高了其反应活性。金属氧化物半导体材料在光催化、电化学和气敏等领域应用广泛,其反应机理均是发生在材料表面的气-液、气-气、气-固反应,因而均需要材料具有大的比表面积和较高的表面活性。而介晶结构是以纳米颗粒作为基本构筑单元的非经典结晶产物,具有比表面积大、孔隙率高、表面活性高等优点,有望获得远超过传统材料的优异性能,因此近年来介晶结构金属氧化物半导体的制备成为了研究热点。研究者们基于物理或者化学驱动的纳米架构自组装过程,通过改进传统制备工艺,如水热法、溶剂热法、离子热法等,成功调控纳米材料成核、生长的方式,制备出具有介晶结构的TiO_2、ZnO、CuO、SnO_2等半导体材料,并且通过优化制备工艺,可以调节材料的比表面积、孔隙率和表面活性。进一步分析介晶结构与性能的构效关系,对推广介晶结构材料的应用具有重大的指导意义。但是目前介晶的研究还处于起步阶段,各种组分、形貌和结构的介晶的合成、结晶理论的基础研究以及材料的应用开发都还有待进一步探索。本文归纳了介晶半导体材料的研究进展,包括制备方法及不同制备方法所获得材料的特征及优缺点;介绍了半导体介晶材料在光催化性能、电化学性能和气敏性能等领域的应用现状,总结了介晶结构与性能的构效关系,对介晶结构的发展方向进行了展望并指出了其面临的问题。     

稀土纳米材料的研究进展

稀土纳米材料的研究与应用将有助于发现新性质,开拓新材料,已成为当前的研究热点.本文简述了稀土纳米粉体、稀土纳米薄膜、稀土纳米陶瓷和纳米复合与组装的研究进展,介绍了在磁性材料、发光材料、催化剂、光学材料等领域稀土纳米材料的应用和进展.     

纳米晶材料热力学函数及其在相变热力学中的应用

在应用界面膨胀模型和普适状态研究纳米晶界面热力学特性的基础上,发展了纳米晶整体材料热力学函数的计算模型,给出了以纳米晶界面上的原子分数作为权重的纳米晶体单相材料的焓、熵、自由能随界面过剩体积、温度以及晶粒尺寸发生变化的明确表达式.由此可以定量预测纳米晶材料发生相变的特征温度和临界尺寸.并以Co纳米晶为计算实例,对其相变参量进行了预测,计算结果全面证实了已有文献报道中的实验结果.由此,可以预测晶粒尺寸降低到几十纳米以下时,材料高温相的热稳定性将会增强.     

Structural nanocrystalline materials: an overview

This paper presents a brief overview of the field of structural nanocrystalline materials. These are materials in either bulk, coating, or thin film form whose function is for structural applications. The major processing methods for production of bulk nanocrystalline materials are reviewed. These methods include inert gas condensation, chemical reaction methods, electrodeposition, mechanical attrition, and severe plastic deformation. The stability of the nanocrystalline microstructure is discussed in terms of strategies for retardation of grain growth. Selected mechanical properties of nanocrystalline materials are described; specifically strength and ductility. Corrosion resistance is briefly addressed. Examples of present or potential applications for structural nanocrystalline materials are given.     

纳米晶体材料腐蚀行为的研究进展

抗腐蚀能力是实现纳米材料广泛应用的关键.综述了近几年国内外在这一领域的研究进展,重点介绍了表面纳米化金属和纳米软磁材料的耐腐蚀性能,针对不同方法制备纳米材料的腐蚀行为进行了讨论和比较.并分析了纳米晶体材料腐蚀研究中存在的问题,提出了进一步研究的思路.     

Structure and thermal stability of nanocrystalline materials

Nanocrystalline materials, which are expected to play a key role in the next generation of human civilization, are assembled with nanometre-sized “building blocks” consisting of the crystalline and large volume fractions of intercrystalline components. In order to predict the unique properties of nanocrystalline materials, which are a combination of the properties of the crystalline and intercrystalline regions, it is essential to understand precisely how the structures of crystalline and intercrystalline regions vary with decrease in crystallite size. In addition, study of the thermal stability of nanocrystalline materials against significant grain growth is both scientific and technological interest. A sharp increase in grain size (to micron levels) during consolidation of nanocrystalline powders to obtain fully dense materials may consequently result in the loss of some unique properties of nanocrystalline materials. Therefore, extensive interest has been generated in exploring the size effects on the structure of crystalline and intercrystalline region of nanocrystalline materials, and the thermal stability of nanocrystalline materials against significant grain growth. The present article is aimed at understanding the structure and stability of nanocrystalline materials.     

Review on the fracture processes in nanocrystalline materials

An overview of experimental study, computer simulations and theoretical models of fracture of nanocrystalline materials is presented. The key experimentally detected facts on ductile and brittle fracture processes are discussed. Special attention is paid to computer simulations and theoretical models of nucleation and growth of nanocracks and nanopores in deformed nanocrystalline materials. Also, we discuss mechanisms for fracture suppression in such materials showing good ductility or superplasticity.     

Enhanced activity of hierarchical zeolitic material with ZSM-5 structure for the tert-butylation of phenol

Nanocrytsalline phase of hierarchical zeolite structure with ZSM-5 was successfully synthesised via a facile and new method using NR latex as a polymer macrotemplate for the liquid phase alkylation of phenol with tert-butanol. X-ray diffraction pattern, FT-IR spectrum and TEM observations confirm the formation of pure and nanocrystalline zeolite ZSM-5 phase. Catalysis measurements show that the prepared zeolite ZSM-5 phase leads to high phenol conversion and 2,4-di-TBP selectivity which is mainly due to the presence of the hierarchical porosity within the zeolite ZSM-5 phase as confirmed by FESEM and pore size analyses.     

Structure and properties of nanocrystalline materials

The present article reviews the current status of research and development on the structure and properties of nanocrystalline materials. Nanocrystalline materials are polycrystalline materials with grain sizes of up to about 100 nm. Because of the extremely small dimensions, a large fraction of the atoms in these materials is located at the grain boundaries, and this confers special attributes. Nanocrystalline materials can be prepared by inert gas-condensation, mechanical alloying, plasma deposition, spray conversion processing, and many other methods. These have been briefly reviewed. A clear picture of the structure of nanocrystalline materials is emerging only now. Whereas the earlier studies reasoned out that the structure of grain boundaries in nanocrystalline materials was quite different from that in coarse-grained materials, recent studies using spectroscopy, high-resolution electron microscopy, and computer simulation techniques showed unambiguously that the structure of the grain boundaries is the same in both nanocrystalline and coarse-grained materials. A critical analysis of this aspect and grain growth is presented. The properties of nanocrystalline materials are very often superior to those of conventional polycrystalline coarse-grained materials. Nanocrystalline materials exhibit increased strength/hardness, enhanced diffusivity, improved ductility/toughness, reduced density, reduced elastic modulus, higher electrical resistivity, increased specific heat, higher thermal expansion coefficient, lower thermal conductivity, and superior soft magnetic properties in comparison to conventional coarse-grained materials. Recent results on these properties, with special emphasis on mechanical properties, have been discussed. New concepts of nanocomposites and nanoglasses are also being investigated with special emphasis on ceramic composites to increase their strength and toughness. Even though no components made of nanocrystalline materials are in use in any application now, there appears to be a great potential for applications in the near future. The extensive investigations in recent years on structure-property correlations in nanocrystalline materials have begun to unravel the complexities of these materials, and paved the way for successful exploitation of the alloy design principles to synthesize better materials than hitherto available.     

The effects of strain rate and grain size on nanocrystalline materials: A theoretical prediction

The article describes a dislocation-based model for the coupling effects of strain rate and grain size on the mechanical behavior of nanocrystalline materials. Two important experimental findings about nanocrystalline materials are explained by the model: 1. the difference of the dependencies of strain rate sensitivity (SRS) on grain size between FCC and BCC nanocrystalline materials and 2. the abnormal dependency of activation volume on thermally activated stress. Our analysis shows that the strain rate-dependent behavior of nanocrystalline materials is mainly determined by the ratio between the activation volumes in grain and grain boundary regions.     

Phase transformations and phase stability in nanocrystalline materials

The current state of the researches on diffusionless phase transformations, including allotropic, polymorphous and martensitic transformations, and phase stability are reviewed. The behaviors of phase transformation and phase stability in nanocrystalline materials are markedly affected by the non-equilibrium conditions involved in their preparation, as a result, in this review an ideal demonstrating method of critical size for the stability of a high-temperature phase at low-temperatures is suggested, and the intrinsic conditions of the phase stability are clarified. Our recent experiments exhibit that the reversal transformation temperatures of low-temperature phases in nanocrystalline Co bulk metal and Fe–30Ni wt% alloy are significantly raised up over 800 °C when their grain sizes are smaller than about 15 nm, while in the reported experiments of nanocrystalline particles or films the reversal transformation temperature lowers with decreasing grain size or is independent of grain size. Therefore, the author suggests that more experiments and theories for phase stability in reversal transformation should be performed. The study of grain growth kinetics of nanocrystalline materials, as a basic of investigating phase stability, is another attention aspect.     

Nanomechanics of Hall-Petch relationship in nanocrystalline materials

Classical Hall-Petch relation for large grained polycrystals is usually derived using the model of dislocation pile-up first investigated mathematically by Nabarro and coworkers. In this paper the mechanical properties of nanocrystalline materials are reviewed, with emphasis on the fundamental physical mechanisms involved in determining yield stress. Special attention is paid to the abnormal or ‘inverse’ Hall-Petch relationship, which manifests itself as the softening of nanocrystalline materials of very small (less than 12 nm) mean grain sizes. It is emphasized that modeling the strength of nanocrystalline materials needs consideration of both dislocation interactions and grain-boundary sliding (presumably due to Coble creep) acting simultaneously. Such a model appears to be successful in explaining experimental results provided a realistic grain size distribution is incorporated into the analysis. Masumura et al. [Masumura RA, Hazzledine PM, Pande CS. Acta Mater 1998;46:4527] were the first to show that the Hall-Petch plot for a wide range of materials and mean grain sizes could be divided into three distinct regimes and also the first to provide a detailed mathematical model of Hall-Petch relation of plastic deformation processes for any material including fine-grained nanocrystalline materials. Later developments of this and related models are briefly reviewed.Prof. Frank Nabarro was a physicist by training, a metallurgist by profession and a genius by nature, blessed with a unique ability to treat everyone as his equal. During his later years he was very much interested in the mechanical properties of nanocrystalline materials. This review on that topic is our contribution to the special issue of Progress in Materials Science honoring him.     

电沉积法制备块体纳米晶材料的研究进展

综述了电沉积法制备块体纳米晶材料的原理;阐述了电流密度、电流波形、有机添加剂等工艺参数对沉积层晶粒尺寸的影响;介绍了直流电沉积、脉冲电沉积、喷射电沉积和复合电沉积等几种常见的电沉积方法;概述了电沉积法制备块体纳米晶材料的国内外研究现状;探讨了电沉积块体纳米晶材料的力学性能、磁学性能、耐蚀性能、热稳定性及其应用前景.