纳米颗粒相变热力学和电化学热力学的理论和实验研究

发布时间：2018-01-11 21:08

本文关键词：纳米颗粒相变热力学和电化学热力学的理论和实验研究　出处：《太原理工大学》2017年博士论文　论文类型：学位论文

【摘要】：在纳米材料的制备、研究和应用中会经常涉及到纳米颗粒的相变和电化学问题。与相应的块状物质相比,当颗粒的尺寸减小到纳米级时,其相变热力学和电化学热力学呈现出显著的差别,而这种差别取决于纳米颗粒的粒度和形貌。目前,不同相变热力学模型的合理性和适用范围以及形貌对纳米颗粒相变温度的影响规律和影响机理还不清楚,核壳结构纳米电极(双分散相)的电化学热力学研究还未见报道。因此,本论文将从理论和实验两方面研究这些问题。(1)纳米颗粒的相变热力学的理论和实验研究在理论研究方面,根据不同的相变模型,导出了相应的描述相变热力学性质与粒度和形貌之间的精确关系式。然后,通过纯理论计算值与文献值的比较,讨论了不同相变模型的合理性和适用范围以及形貌对纳米颗粒相变温度的影响规律。结果表明:三个模型中,Reiss和Rie模型都是合理的熔化热力学模型,其中Reiss模型适用于纳米颗粒熔化的前期,而Rie模型适用于熔化后期。对于较小粒度的纳米颗粒(r10 nm),表面张力和比表面积共同影响其相变热力学性质,且粒度越小,相变热力学性质随粒度的减小而降低的越显著;而对于较大粒度的纳米颗粒,表面张力近似为常数,其相变热力学性质主要由比表面积影响,且分别与粒径的倒数成线性关系。对于体积相同形貌不同的纳米颗粒,比表面积是影响相变热力学性质的主要因素;形貌越偏离球形,其相变热力学性质就越小。在实验研究方面,以纳米铜的熔化和纳米钛酸铅的晶型转变为研究体系。分别采用微波法、溶胶凝胶法制备了不同粒度的纳米铜、纳米钛酸铅颗粒,并通过x-射线衍射仪(xrd)和扫描电子显微镜(sem)表征了纳米颗粒的粒度和形貌,分析并总结了影响纳米铜和纳米钛酸铅颗粒粒度的因素及其影响规律。然后,通过差示扫描量热仪(dsc)测定了纳米颗粒的相变热力学性质,得到了粒度对其相变热力学性质的影响规律。结果表明:随着纳米颗粒粒度的减小,其相变热力学性质减小,且随粒径的倒数线性变化。纳米颗粒的相变实验结果与上述的相变理论关系式一致。(2)纳米颗粒的电化学热力学的理论和实验研究在理论研究方面,首次提出了核壳结构的纳米电极模型,即电极的反应物和产物都是纳米级的,且反应物包覆产物构成复合纳米颗粒。通过引入表面化学势,首次推导出了核壳结构纳米电极的摩尔反应吉布斯能随分散相粒度变化的关系式,然后结合摩尔反应吉布斯能与电极电势的关系及热力学基本方程,得到了核壳结构纳米电极的电极电势、电极电势的温度系数、摩尔反应焓、摩尔反应熵和可逆反应热分别随分散相粒度变化的关系式。结果表明:复合纳米颗粒内核的粒度和壳厚度对核壳结构纳米电极的电化学热力学均有影响;在一定条件下,如果内核的粒度不变而壳厚度减小,则电极电势和平衡常数减小,而温度系数、摩尔反应吉布斯能、摩尔反应熵、摩尔反应焓和可逆反应热增大;反之,则影响规律相反。在实验研究方面,以核壳结构纳米氧化银电极为研究体系,研究了复合纳米颗粒的粒度和壳厚度对核壳结构纳米电极的电化学热力学的影响规律。首先,采用液相化学还原法制备了不同粒度的纳米银,并通过xrd和SEM表征了其粒度和形貌。分析和总结了纳米颗粒粒度的影响因素及其影响规律。然后,通过对纳米银颗粒表面进行电化学氧化的方法,首次制备出以纳米银为核、纳米氧化银为壳的核壳结构纳米电极,测其不同温度下的电极电势,进而得到了粒度和壳厚度对其电化学热力学的影响规律。结果表明:核壳结构纳米电极的电化学性质与粒度和壳厚度均有关;随着粒度的减小,电极电势和反应平衡常数增大,而温度系数、摩尔反应吉布斯能、摩尔反应焓、摩尔反应熵和可逆反应热均减小;并且,电极电势、电极电势的温度系数、摩尔反应吉布斯能、反应平衡常数的对数、摩尔反应熵、摩尔反应焓和可逆反应热均分别与粒径的倒数呈线性关系。当复合纳米颗粒的粒径基本不变时,壳厚度越大(内核越小),核壳结构纳米电极的电极电势就越高。纳米颗粒的电化学实验结果与上述所推导的核壳结构纳米电极的理论关系式一致。本文导出的纳米相变热力学性质与颗粒粒度和形貌的关系式能够定量地预测和解释不同粒度、不同形貌纳米颗粒的相变热力学性质,描述纳米颗粒的相变行为,从而为纳米材料在设计、制备以及应用过程中涉及到的相变热力学问题提供理论依据和指导。核壳结构纳米电极的电化学热力学关系式能够定量地描述核壳结构纳米电极的颗粒粒度和壳厚度对其电化学热力学的影响规律,可解释涉及核壳结构复合纳米颗粒的相关电化学现象,对于制备高灵敏的电化学传感器具有重要的指导作用。
[Abstract]:In the preparation of nano materials, research and application often involves transformation and electrochemical problems of nanoparticles. Compared with the corresponding bulk material, while reducing the size of the particles at the nanometer level, the thermodynamics and electrochemical thermodynamics showed significant difference, and this difference depends on the particle size and morphology. At present, the different thermodynamics model is reasonable and applicable scope as well as the influence of morphology and influence mechanism of nano particle phase transition temperature is not clear, the core-shell structure nano electrode (double dispersed phase) electrochemical thermodynamic studies have not been reported. Therefore, this paper will study these problems from two aspects of theory and experiment. (1) theoretical and experimental study on thermodynamics of nanoparticles in the aspect of theory research, according to the different phase change model, the corresponding description of the thermodynamics properties and particle size and shape are derived The precise relationship between appearance. Then, by pure theoretical value compared with the literature value, the influence law of different transformation model is reasonable and applicable scope and morphology of nano particle phase transition temperature discussed. The results show that the three model, Reiss model and Rie model is melting thermodynamic model of the pre the Reiss model is suitable for nano particles melt, while the Rie model is suitable for melting period. For nanoparticles with smaller size (R10 nm), the surface tension and the surface area of the common effect of the phase transition and thermodynamic properties, the smaller the particle size, the thermodynamic properties of phase change decreases with the decrease of the particle size of the nano and for more effective; larger particle size, the surface tension is approximately constant, the thermodynamics properties are dominated by surface area effect, and the particle size of the inverse linear relationship. The nanoparticles morphology with the same volume The specific surface area, are the main factors influencing the thermodynamic properties of the phase transition; morphology deviate from spherical, the thermodynamic properties of phase change is small. In the experiment, the crystal type of nano copper melting and nano titanate transformation system was studied respectively. By microwave method, nano copper with different particle size were prepared by sol gel method lead titanate nano particles, and by means of x- ray diffraction (XRD) and scanning electron microscopy (SEM) characterization of the particle size and morphology of nanoparticles, analyzed and summarized the influencing factors of nano copper and nano titanate particle size and influence. Then, by differential scanning calorimetry (DSC) thermodynamics properties of nano particles were obtained, effects of particle sizes on the thermodynamics properties. The results show that with the decrease of the particle size, reduce the phase thermodynamic properties of reciprocal linear variation and with grain size. Theory of phase relationship between transformation results and the type of rice grains. (2) the theoretical and experimental study on electrochemical thermodynamics of nano particles in the aspect of theory, first proposed the nano electrode model of core-shell structure, the electrode of reactants and products are nanometer, and the reaction product of a composite coating nano particles. By introducing the surface chemical potential, we deduced a formula of molar reaction Gibbs core-shell structure nano electrode with dispersed phase size change, and then combined with the molar Gibbs energy and electrode potential and the thermodynamic basic equations, the electrode potential of core-shell structure nano electrode, temperature coefficient of electrode potential Moore, enthalpy of reaction between reaction entropy and reversible reaction heat respectively with the dispersed phase size changes. The results show that the particle size and shell thickness of composite nano particle core Electrochemical thermodynamics have influence of core-shell structure nano electrode; under certain conditions, if the kernel size is constant and the shell thickness decreases, while the electrode potential and the equilibrium constant decreased, and the temperature coefficient, molar Gibbs energy, reaction entropy, molar enthalpy and reversible reaction heat increase; conversely, it influences in the opposite. The experimental study, a core-shell structure nano silver oxide electrode as the research system, studied the influence of electrochemical thermodynamics size and shell thickness of composite nano particles of core-shell structure nano electrode. First of all, the silver nanoparticles with different particle size were prepared by chemical reduction in liquid phase, and through XRD and SEM characterization of the size and the morphology analysis and summarizes the influencing factors of nano particle size and influence. Then, by the method of electrochemical oxidation on the surface of silver nanoparticles, prepared for the first time in nano Silver nuclei, core-shell structure nano electrode shell nano silver oxide, measured under different temperature and electrode potential, and obtains the influence law of grain size and shell thickness on the electrochemical thermodynamics. The results showed that the core-shell structure nano electrode electrochemical properties and particle size and shell thickness were related; with the decrease of the particle size, electrode the potential and the reaction equilibrium constant increases, and the temperature coefficient, molar Gibbs energy, molar enthalpy, molar entropy and reversible reaction heat are reduced; and the electrode potential, the temperature coefficient of the electrode potential, molar Gibbs energy, the logarithm of the equilibrium constant of the reaction, reaction entropy, molar enthalpy of reaction and reversible reaction heat with the reciprocal of the particle size is linear. When the composite nano particle size unchanged, shell thickness greater (smaller kernel), the electrode potential of core-shell structure nano electrode of nano particles is higher. The theoretical relationship between uniform core-shell structure nano electrode electrochemical experiments and the derivation of the formula derived in this paper. The thermodynamic properties of nano phase and particle size and morphology can quantitatively predict and explain the different particle size, thermal and mechanical properties of particles with different morphologies, describe the phase transition behavior of nano particles, which is nano the material in the design, to provide theoretical basis and guidance for thermodynamics relates to the preparation and application process. Influence of particle size and shell thickness of the electrochemical thermodynamic relations of core-shell structure nano electrode can be described quantitatively by core-shell structure nano electrode on its electrochemical thermodynamics, electrochemistry phenomena can be explained involving nuclear shell structure composite nanoparticles, is of great importance for the preparation of highly sensitive electrochemical sensor.

【学位授予单位】：太原理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB383.1

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