粒度对纳米钛酸铅和纳米钛酸钡晶型转变的影响

发布时间：2018-02-06 04:38

本文关键词： 纳米钛酸铅纳米钛酸钡晶型转变粒度效应相变热力学　出处：《太原理工大学》2016年硕士论文　论文类型：学位论文

【摘要】：在研究纳米材料的制备、性质及应用中常常涉及到晶型转变。由于纳米颗粒具有显著的纳米效应,在发生晶型转变的过程中,其晶型转变热力学性质(包括晶型转变温度、晶型转变焓和晶型转变熵)均与相应块状物质相比有很大的不同,而这些差异主要取决于纳米颗粒的粒度。因此研究粒度对纳米材料晶型转变热力学性质的影响规律具有重要的科学意义和实用价值。本文首先提出了纳米颗粒的晶型转变模型,推导出纳米颗粒晶型转变温度的普遍化方程,在此基础上,导出了不同形貌纳米颗粒晶型转变温度与粒径的热力学关系式,讨论了粒度和形貌对纳米颗粒晶型转变温度的影响规律。其次,在实验上选择纳米钛酸铅、纳米钛酸钡颗粒的晶型转变作为研究体系。采用溶胶-凝胶法制备了不同粒径的四方相纳米钛酸铅和纳米钛酸钡颗粒,并通过X射线衍射仪、傅里叶红外光谱仪以及扫描电子显微镜表征了样品的颗粒尺寸、晶型和形貌。然后采用矢量网络分析仪测定了纳米钛酸钡的复介电常数和复磁导率,讨论了粒径对纳米钛酸钡介电性能的影响规律;采用差示扫描量热仪测定了不同粒径纳米钛酸铅、纳米钛酸钡颗粒的DSC谱图,进而得到了不同粒径纳米钛酸铅、纳米钛酸钡颗粒的晶型转变温度、晶型转变焓和晶型转变熵;讨论了粒度对其晶型转变温度、晶型转变焓和晶型转变熵的影响规律,并与相应的理论关系式进行了比较。实验结果表明:(1)采用溶胶-凝胶法,通过控制实验条件,可制备出粒径分布均匀、纯度高的不同粒径的四方相纳米钛酸铅和纳米钛酸钡颗粒。在制备过程中,煅烧温度、反应物浓度和反应温度均对纳米钛酸铅和纳米钛酸钡颗粒的粒径有不同程度的影响,其中煅烧温度,反应物浓度对其粒径的影响较大,反应温度的影响则较小。(2)粒度对纳米钛酸钡的复磁导率的影响很小,在不同电磁波频率下,其实部均接近于1,虚部均接近于0,说明纳米钛酸钡为介电型损耗介质;随着钛酸钡纳米颗粒粒径的减小,其复介电常数和介电损耗均呈现减小的趋势。(3)粒度对纳米钛酸铅和纳米钛酸钡颗粒的晶型转变热力学性质有很大影响:随着粒径的减小,其晶型转变温度、晶型转变焓和晶型转变熵均随之减小,并且分别与半径的倒数呈良好的线性关系。关于粒径对纳米钛酸铅、纳米钛酸钡颗粒晶型转变温度的影响规律,实验结果与理论关系式一致。本文导出的纳米颗粒晶型转变温度的热力学关系式以及粒度对晶型转变热力学性质的影响规律,可用于解释和预测在纳米材料的制备及应用中所涉及到的晶型转变行为。
[Abstract]:The preparation, properties and application of nanocrystalline materials are often involved in crystal transformation. The thermodynamic properties of crystal transformation (including the transition temperature, enthalpy and entropy) are very different from the corresponding bulk materials. These differences mainly depend on the particle size of nanocrystalline particles. Therefore, it is of great scientific significance and practical value to study the influence of particle size on the thermodynamic properties of crystalline transformation of nanocrystalline materials. Crystal transformation model. Based on the generalized equation of the transition temperature of nanocrystalline particles, the thermodynamic relations between the transition temperature and the particle size of different morphologies of nanocrystalline particles are derived. The effect of particle size and morphology on the transition temperature of nanocrystalline particles was discussed. Secondly, nanometer lead titanate was selected in the experiment. The tetragonal nano-lead titanate and nano-barium titanate particles with different particle sizes were prepared by sol-gel method and were characterized by X-ray diffractometer. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to characterize the particle size, crystal shape and morphology of the samples. Then, the complex permittivity and complex permeability of nano-barium titanate were measured by vector network analyzer. The effect of particle size on dielectric properties of nanometer barium titanate was discussed. The DSC spectra of nanometer lead titanate and nanometer barium titanate with different particle sizes were measured by differential scanning calorimeter, and the crystal transition temperature of nanometer lead titanate and nanometer barium titanate were obtained. Enthalpy of crystal transformation and entropy of crystal transformation; The effects of particle size on the transition temperature, enthalpy and entropy of crystal transformation were discussed and compared with the corresponding theoretical formula. The experimental results show that the sol-gel method is used. By controlling the experimental conditions, tetragonal nanometer lead titanate and nanometer barium titanate particles with uniform particle size distribution and high purity can be prepared. The concentration of reactants and reaction temperature have different effects on the particle size of nano-lead titanate and nano-barium titanate, among which calcination temperature and reactant concentration have great influence on the particle size. The effect of reaction temperature on the complex permeability of nanocrystalline barium titanate is very small. Under different electromagnetic wave frequencies, the part is close to 1, and the imaginary part is close to 0. The results show that nanometer barium titanate is a dielectric loss medium. With the decrease of the particle size of barium titanate. The complex permittivity and dielectric loss show a decreasing trend. The particle size has a great influence on the thermodynamic properties of crystalline transformation of nanometer lead titanate and nanometer barium titanate: with the decrease of particle size. The transition temperature, enthalpy and entropy of crystal transformation are all decreased, and there is a good linear relationship with the reciprocal of radius. The particle size of nano-lead titanate is related to the particle size. The effect of crystal transition temperature of nanocrystalline barium titanate particles. The experimental results are in agreement with the theoretical formula. The thermodynamic relationship of the transition temperature of nanocrystalline grains and the influence of particle size on the thermodynamic properties of the crystal transformation are derived in this paper. It can be used to explain and predict the crystal transition behavior involved in the preparation and application of nanomaterials.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TB383.1

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