粒度和形貌对纳米颗粒热力学性质影响的理论研究和量化计算

发布时间：2018-03-31 04:31

本文选题：粒度　切入点：形貌　出处：《太原理工大学》2015年硕士论文

【摘要】：众所周知，当材料的尺寸达到纳米级别时，由于表面效应和小尺寸效应，引起物质在化学反应平衡、反应动力学、相变、吸附、电化学和催化等方面产生了很大变化，而这些变化主要归因于其热力学性质的改变。因此，研究粒度和形貌对纳米材料热力学性质的影响是非常重要和必要的。目前，关于粒度对纳米颗粒热力学性质影响的研究报道较少，并且粒径对其热力学性质的影响规律还不清楚，球形纳米颗粒热力学性质的理论研究还不完善，，其它形貌纳米颗粒热力学性质的理论研究还未见报道。论文首先将界面变量引入到纳米颗粒的吉布斯函数中，系统地推导出不同形貌（球形、立方形、棒状和片状）纳米颗粒的表面热力学性质及其热力学性质分别与其粒度间的热力学关系式，包括摩尔表面吉布斯能、摩尔吉布斯能、摩尔表面焓、摩尔焓、摩尔表面熵、摩尔熵、恒压摩尔表面热容和恒压摩尔热容；将Young-Laplace方程首次应用于固体纳米粒子，导出了固体纳米颗粒的附加压力，进一步推导出固体纳米颗粒的摩尔表面能、摩尔内能、恒容摩尔表面热容、恒容摩尔热容。其次，编写出计算原子簇坐标的VB源程序，根据铁和银的单晶胞参数，构建出一系列不同粒度、不同形貌的纳米铁簇和纳米银簇模型；采用gaussian09软件中量子化学的半经验方法PM6分别对纳米铁簇和纳米银簇的热力学性质进行了计算，得到了不同粒度、不同形貌纳米团簇的摩尔吉布斯能、摩尔焓、摩尔熵、摩尔内能和恒容摩尔热容，并讨论了粒度和形貌对这些热力学性质的影响规律；还进一步估算出纳米铁的Tolman长度以及膨胀系数。研究结果表明：纳米颗粒的热力学性质主要与其粒度、表面张力、表面张力的温度系数和膨胀系数有关；关于粒度对纳米颗粒热力学性质的影响规律，量子化学的计算结果与纳米颗粒的热力学理论一致：纳米颗粒的摩尔吉布斯能、摩尔焓、摩尔熵和摩尔内能随着纳米颗粒粒度的减小而增大，恒容摩尔热容则变化不大，随着纳米颗粒粒度的减小而略有减小；不同形貌的纳米颗粒，如果原子数相同，则其各种热力性质差别不大。此外，还发现纳米Fe簇的Tolman长度大约为0.1，并且其膨胀系数为负值。纳米颗粒的热力学理论及其粒度对热力学性质的影响规律对于纳米颗粒在化学反应、相变、吸附、电化学及其催化中的研究和应用具有重要的指导作用。
[Abstract]:As we all know, when the size of the material reaches the nanometer level, because of the surface effect and the small size effect, the material changes greatly in the aspects of chemical reaction equilibrium, reaction kinetics, phase transition, adsorption, electrochemistry and catalysis, etc.These changes are mainly attributed to the changes in their thermodynamic properties.Therefore, it is very important and necessary to study the effect of particle size and morphology on the thermodynamic properties of nanomaterials.At present, there are few reports on the effect of particle size on the thermodynamic properties of nanoparticles, and the influence of particle size on the thermodynamic properties of nanoparticles is not clear, and the theoretical study of thermodynamic properties of spherical nanoparticles is not perfect.The thermodynamic properties of other morphology nanoparticles have not been reported.In this paper, the interface variables are introduced into the Gibbs function of nanoparticles, and the different morphologies (spherical, square, square) are deduced systematically.The surface thermodynamic properties of rod-shaped and flaky) nanoparticles and their thermodynamic relations with their particle size, including molar surface Gibbs energy, molar Gibbs energy, molar surface enthalpy, molar enthalpy, molar surface entropy, etc.Molar entropy, constant pressure molar surface heat capacity and constant pressure molar heat capacity. The Young-Laplace equation is applied to solid nanoparticles for the first time, the additional pressure of solid nanoparticles is derived, and the molar surface energy and intramolar energy of solid nanoparticles are further derived.Constant molar surface heat capacity, constant volume molar heat capacity.Secondly, a VB source program is written to calculate the coordinates of clusters. According to the unit cell parameters of iron and silver, a series of nano-iron clusters and nano-silver cluster models with different particle sizes and different morphologies are constructed.The thermodynamic properties of iron nanoclusters and silver nanoclusters were calculated by the semi-empirical method PM6 of quantum chemistry in gaussian09 software. The molar Gibbs energy, molar enthalpy and molar entropy of different particle sizes and morphologies of nanoclusters were obtained.The effects of particle size and morphology on these thermodynamic properties were discussed, and the Tolman length and expansion coefficient of nanocrystalline iron were also estimated.The results show that the thermodynamic properties of nanoparticles are mainly related to their particle size, surface tension, temperature coefficient of surface tension and coefficient of expansion.The calculated results of quantum chemistry are consistent with the thermodynamic theory of nanoparticles: the molar Gibbs energy, molar enthalpy, molar entropy and internal energy of nanoparticles increase with the decrease of particle size, but the constant volume molar heat capacity does not change much.With the decrease of the particle size, the thermal properties of the nanoparticles with different morphologies are not different if the number of atoms is the same.In addition, it is found that the Tolman length of Fe nanoclusters is about 0.1, and its expansion coefficient is negative.The thermodynamics theory of nanoparticles and the influence of particle size on thermodynamic properties have important guiding effects on the research and application of nanoparticles in chemical reaction, phase transition, adsorption, electrochemistry and their catalysis.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1

【参考文献】

中国期刊全文数据库前10条

1 薛永强,栾春晖,樊金串;粗糙表面对金属化学腐蚀的影响[J];材料导报;1998年02期

2 王岚,谭志诚,孟霜鹤,梁东白,高东升,孙志忠,刘振田;纳米晶体铁的低温热容和热稳定性(英文)[J];材料研究学报;2002年01期

3 储炜,尤金跨,杨勇,林祖赓;纳米科学技术在化学电源领域的新进展[J];电源技术;1998年06期

4 周广英,许馨予,李小丽;纳米吸附技术及其在环境保护中的应用[J];广东化工;2004年04期

5 范高超;黄在银;姜俊颖;李艳芬;孙丽;;野草状纳米氧化锌的制备及标准摩尔生成焓[J];高等学校化学学报;2011年05期

6 鲁圣国，张良莹，姚熹;纳米相铁电PbTiO_3超微粉的相变特性[J];硅酸盐学报;1995年01期

7 赵令豪;杨帆;余姗姗;王咪;吴新民;;两种形貌的纳米ZnO标准摩尔生成焓的测定[J];北京石油化工学院学报;2014年01期

8 范高超;马昭;黄在银;谭学才;姚先超;;花生状微/纳米CaMoO_4的表面热力学性质[J];高等学校化学学报;2014年05期

9 刘志平,黄世萍,汪文川;分子计算科学——化学工程新的生长点[J];化工学报;2003年04期

10 姜俊颖;黄在银;米艳;李艳芬;袁爱群;;纳米材料热力学的研究现状及展望[J];化学进展;2010年06期