银纳米材料制备与生长规律的同步辐射研究

发布时间：2018-03-06 15:07

本文选题：银纳米颗粒　切入点：银镍合金颗粒　出处：《北京科技大学》2017年博士论文　论文类型：学位论文

【摘要】：纳米材料具有十分独特和优异的性能,目前纳米材料在各领域的应用都取得令人瞩目的成就,关于纳米材料的性能开发与应用拓展受到了十分广泛的关注。纳米材料的性能主要是由其成分和结构决定的,而纳米材料的成分和结构是由其制备工艺决定的。因此,想要获得各种优异性能的纳米材料就要对其制备过程进行精确地设计与控制,其主要前提是深入了解纳米颗粒的形成机制。目前这一方面的研究面临着诸多困难,其中捕获纳米颗粒形成早期的尺寸与结构的动态信息是难点中的难点。同步辐射光源具有高亮度、高穿透性、高准直性和高的时间空间分辨率等诸多优点,对纳米材料的研究有着得天独厚的优势,特别是在实现动态研究和提高时间分辨率等方面效果显著。近些年来,同步辐射理论与技术都有了迅速的发展,同时与同步辐射技术配套的探测器和原位实验装置大量涌现,这些条件使得对纳米颗粒早期形成过程的观察成为可能。本课题以合成方法较为简单、完善、成本相对较低且性能优异的银纳米颗粒为主要研究对象,通过结合常规的实验室表征手段与先进的同步辐射技术分别研究了溶液中银纳米颗粒的生长过程;加热过程中银纳米粉体的尺寸与结构变化过程;溶液中银镍二元合金颗粒的制备与结构变化过程。针对溶液会对X射线产生较强的吸收作用而导致时间分辨率降低的问题,以空间换时间的思路,设计了流速可控、混合均匀的连续流原位反应装置。采用该装置结合北京同步辐射光源开展了原位小角X射线散射实验并实现了毫秒量级的时间分辨率,获得了 2 mM、4 mM、6 mM和8 mM四种初始银离子浓度合成银纳米颗粒的生长曲线。实验表明,不同初始银离子浓度溶液有着不同的临界形核半径,初始银离子浓度从2 mM、4 mM到6 mM,溶液的临界形核半径随浓度逐渐增加,当银离子浓度升高到8mM时,临界形核半径有所下降。颗粒最终尺寸随初始银离子浓度的变化和临界形核半径随初始银离子浓度的变化趋势是一致的。根据不同浓度溶液的临界形核半径和最终尺寸的变化建立了扩散团聚模型来描述颗粒的生长过程,该模型很好的拟合了颗粒的生长曲线。从实验结果得出临界形核半径、颗粒的生长速率以及生长速率的变化对颗粒的最终尺寸有十分明显的影响,是控制颗粒尺寸的主要因素。根据加热过程中银纳米粉体的形貌、尺寸和结构变化规律,首次提出了银纳米颗粒在高温下的定向合并机制,描述了不同阶段加热过程中银纳米颗粒的行为。具体为:从形貌上讲,室温到600℃颗粒均为准球形,700℃时颗粒呈花生形;从尺寸上讲,室温到400℃的过程中,纳米颗粒尺寸增长缓慢,400℃到700℃的过程中颗粒尺寸增长较快;从晶体结构上讲,从室温到500℃,一个纳米颗粒只包含单个晶粒,500 ℃到600 ℃ 一个颗粒包含多个晶粒,600℃到700℃时一个颗粒包含一个晶粒。根据颗粒生长机制可将整个加热过程分为四个阶段:第一阶段为颗粒缓慢生长的奥斯特瓦尔德机制;第二阶段为颗粒快速生长的奥斯特瓦尔德机制,第三阶段为颗粒随机团聚合并的生长机制;第四阶段为定向合并生长机制。纳米颗粒的生长导致小颗粒具有的较高的表面能和界面能转化为颗粒内能,最终导致纳米颗粒的热膨胀系数比块体银样品大30%左右。实验结果详细的描述了银纳米颗粒的热行为,为银纳米颗粒在高温环境的应用提供了实验和理论基础。采用液相还原法制备了银-镍二元合金颗粒,这种合金颗粒是由镍原子掺杂到银基底上形成的。通过对不同银镍比例获得的颗粒进行表征,确定了镍元素对颗粒尺寸的影响。不同银镍比例的纳米颗粒主要包含两种晶体结构,一种是单晶颗粒,一种是五折孪晶颗粒。热力学计算表明,颗粒尺寸较大时两种结构的自由能差别很小,这为两种结构的颗粒能够在同一体系中共存提供了依据。颗粒最终结构的形成是由动力学过程以及反应最初阶段溶液中的晶核结构共同决定的。通过上述这些研究,对不同条件下银/银镍合金纳米颗粒的形成机制有了更深入的了解,为可控制备提供了理论依据;提出了银纳米颗粒在高温环境下的定向合并机制,为银纳米颗粒在高温领域的应用提供了实验和理论依据。希望这些研究结果能为其他纳米颗粒的相关过程研究提供实验和理论帮助。
[Abstract]:Nano materials have unique and excellent performance, the application of nano materials in various fields have made remarkable achievements, expand the performance of development and application of nanomaterials have been widely concerned. The performance of nano materials is mainly determined by its composition and structure, and the composition and structure of nano materials is prepared decided by its system. Therefore, nano materials to obtain excellent performance on the preparation process of precise design and control, the main premise is to understand the formation mechanism of nano particles. At present, the research of this aspect is facing many difficulties, the formation of the nanoparticles capture the dynamic information of the size and structure of early is the most difficult. High brightness synchrotron radiation light source, high penetration, high accurate and high time straightness has many advantages such as spatial resolution, nanometer material The study on the richly endowed by nature, especially the effect in realizing the dynamic research and improve the time resolution significantly. In recent years, synchrotron radiation theory and technology are developing rapidly, at the same time and in situ experimental device of large volume detector and synchrotron radiation technology supporting the emergence of these conditions make the observation of the early formation of nanoparticles possible. The synthetic method is simple, perfect, silver nanoparticles with relatively low cost and excellent performance as the main object of study, through a combination of laboratory characterization of conventional and advanced synchrotron radiation were studied during the growth of silver nanoparticles in solution; process size and structure change of silver nano powder heating process; preparation and structural changes of silver nickel solution two element alloy nanoparticles. The solution will have strong absorption for X ray With the resulting time resolution is reduced to the problem of space for time idea, design flow control, mixed continuous uniform in-situ reaction device. The device combined with Beijing synchrotron radiation source was carried out in situ small angle X ray scattering experiment and realizes the millisecond time resolution, obtained 2 mM, 4 mM, growth curve 6 mM and 8 mM four initial concentration of silver ions synthesis of silver nanoparticles. Experimental results show that the concentration of different initial silver ion with different critical nucleation radius, initial concentration of silver ions from the 2 mM, 4 mM to 6 mM, the critical nucleation radius of solution increased gradually with the concentration of silver ions, when the concentration increased to 8mM, the critical nucleation radius decreased. The particle size change with the initial concentration of silver ions and critical nucleation radius change with the initial concentration of silver ions is consistent. According to the different concentration of solution on Changes of nucleation radius and the final size of the established diffusion aggregation model to describe the growth process of particles, the model fit well the growth curve of particles. From the experimental results show that the critical nucleation radius significantly influences the particle growth rate and the change of the growth rate of particle size is in the end. The main factors controlling the particle size. According to the morphology of the heating process of silver nano powder, variation of size and structure, is proposed for the first time with silver nanoparticles in directional mechanism under high temperature, description of silver nanoparticles of different stages in the process of heating behavior. Specifically: from the morphology, room temperature to 600 DEG C particles for the quasi spherical 700 C particles with peanut shape; in terms of size, room temperature to 400 DEG C, nano particle size growth is slow, 400 DEG to 700 DEG C in the process of particle size is from fast growth; crystal structure The structure, from room temperature to 500 DEG C, a nanoparticle containing only a single grain, 500 to 600 DEG C. a particle comprising a plurality of grain, 600 to 700 DEG C. when a particle contains a grain. According to the particle growth mechanism can make the whole heating process is divided into four stages: the first stage is Ostwald particles slow growth mechanism; the second stage is the rapid growth of the Ostwald grain mechanism, the third stage is the growth mechanism of particle agglomeration with random; the fourth stage is the directional growth mechanism. Combined with nano particles to the growth of small particles with high surface energy and interface energy into particles can eventually lead to thermal expansion of nanoparticles ratio of bulk silver samples is about 30%. The experimental results of a detailed description of the thermal behavior of silver nanoparticles, silver nanoparticles used in high temperature environment and provide experimental and theoretical basis Basis. Two yuan of silver nickel alloy particles were prepared by liquid phase reduction, this alloy particles are composed of nickel atoms doped into the silver substrate. The formation was characterized by the different proportion of silver nickel particles, the effects of Ni on nano particles of different particle size. The proportion of silver nickel mainly contains two a crystal structure is a single crystal particles, a half off twin particles. Thermodynamic calculation shows that the larger particle size when the structure of the two kinds of free energy difference is small, which in the same system provides the basis for the coexistence of two kinds of particles can form the final structure. Particles are determined by nucleation the structure and dynamics of the initial stage of the reaction in solution. Through these studies, on different conditions of formation mechanism of silver / silver nickel alloy nanoparticles have a more thorough understanding, for controlled preparation provides a theoretical basis for; The directional combining mechanism of silver nanoparticles under high temperature is put forward, which provides experimental and theoretical basis for the application of silver nanoparticles in high temperature field. It is hoped that these research results can provide experimental and theoretical help for other nanoparticle related processes.

【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O614.122;TB383.1

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