溶解度法研究粒度对纳米颗粒表面热力学性质的影响

发布时间：2018-03-19 15:03

本文选题：纳米颗粒　切入点：表面热力学性质　出处：《太原理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：纳米颗粒由于其突出的表面效应和尺寸效应,使得其化学反应、相变、吸附、电化学、溶解等化学过程与其块状物质有很大差别,而这些差别皆归因于纳米颗粒的表面热力学性质。目前关于粒度对纳米颗粒表面热力学性质影响的规律还不清楚,而且还缺乏纳米颗粒表面热力学性质的测定方法。本文首先在经典热力学理论的基础上,通过引入表面变量,首次从理论上分别导出了纳米颗粒摩尔表面热力学性质和偏摩尔表面热力学性质与粒度的关系式,讨论了粒度对它们的影响规律；并且在过渡态理论的基础上,导出了纳米颗粒溶解的动力学参数与表面热力学性质的关系式,完善了纳米颗粒溶解的动力学理论。其次,在实验上分别采用水热均匀沉淀法和复分解法制备了不同平均粒径的纳米氧化镁和纳米碳酸钙,用X射线衍射仪、扫描电镜和透射电镜对所制备的样品的粒径大小和形貌进行了表征。然后,利用电导率仪,测定了不同温度下不同粒度的纳米氧化镁和纳米碳酸钙在水中溶解的瞬时浓度和平衡浓度,进而得到了它们的溶解标准平衡常数Ko、溶解热力学函数和溶解动力学参数(k、Ea和A)；并根据溶解热力学和动力学数据,分别计算出了纳米颗粒的表面热力学性质；讨论了粒度对纳米氧化镁和纳米碳酸钙溶解热力学函数、动力学参数以及表面热力学性质的影响规律,并将实验结果与理论进行了对比分析。研究结果表明: (1)采用水热均匀沉淀法和复分解法，，通过改变制备条件，可以分别制备出高纯度的平均粒径为14~55nm的纳米方镁石型氧化镁颗粒和17~71nm的纳米球霰石型碳酸钙颗粒。 (2)纳米颗粒的粒度对溶解热力学有很大的影响：随着纳米颗粒粒径的减小，溶解的ln Ko增大，而G o m、 H om、 S o m均减小；且它们与粒径的倒数之间均存在较好的线性关系，这些实验规律与纳米溶解热力学理论一致。 (3)纳米颗粒的粒度对溶解的动力学有显著的影响：随着粒径的减小，溶解的lnk逐渐增大，而Ea和lnA却逐渐减小；并且lnk、Ea和均与1/d呈现良好的线性关系，这些实验规律与纳米溶解动力学理论一致。 (4)纳米颗粒的粒度对纳米颗粒的表面热力学性质有显著的影响：随着纳米颗粒粒径的减小，其摩尔表面吉布斯能、摩尔表面焓和摩尔表面熵均增大，且均与粒径的倒数呈线性关系；这些影响规律与表面热力学性质的关系式一致。 (5)采用溶解度法，利用不同粒度纳米颗粒的溶解热力学数据和动力学数据均可得到其表面热力学性质，但由溶解热力学数据得到的表面热力学性质更可靠。
[Abstract]:Because of its outstanding surface effect and size effect, nanoparticles have different chemical processes such as chemical reaction, phase transition, adsorption, electrochemistry and dissolution from their bulk materials. However, these differences are attributed to the surface thermodynamic properties of nanoparticles. At present, the influence of particle size on the surface thermodynamic properties of nanoparticles is not clear, and there is a lack of methods for the determination of surface thermodynamic properties of nanoparticles. On the basis of classical thermodynamic theory and by introducing surface variables, the relations between surface thermodynamic properties of nanoparticles and partial moles and particle size are derived theoretically for the first time in this paper. The influence of particle size on them is discussed, and based on the transition state theory, the relationship between the kinetic parameters of the dissolution of nanoparticles and the thermodynamic properties of the surface is derived, and the kinetic theory of the dissolution of nanoparticles is improved. Secondly, nanocrystalline magnesium oxide and calcium carbonate with different average particle sizes were prepared by hydrothermal homogeneous precipitation method and double decomposition method respectively. The particle size and morphology of the prepared samples were characterized by SEM and TEM. The instantaneous concentration and equilibrium concentration of nano-magnesium oxide and nano-calcium carbonate dissolved in water at different temperatures were determined. Then their dissolution standard equilibrium constants Ko, dissolution thermodynamics function and dissolution kinetics parameters, such as Ku EA and An, were obtained, and the surface thermodynamic properties of the nanoparticles were calculated according to the dissolution thermodynamics and kinetic data, respectively. The effects of particle size on the dissolution thermodynamic function, kinetic parameters and surface thermodynamic properties of nano-MgO and nano-CaCO3 were discussed, and the experimental results were compared with the theoretical analysis. The results show that:. 1) by means of hydrothermal homogeneous precipitation method and double decomposition method, high purity nano-periclase magnesium oxide particles with average particle size of 145nm and nano-spheroidal calcium carbonate particles of 1771nm can be prepared by changing the preparation conditions. (2) the particle size of nanoparticles has a great influence on dissolution thermodynamics: with the decrease of particle size, the dissolved ln Ko increases, while G om, H omand Som decrease, and there is a good linear relationship between them and the reciprocal of particle size. These experimental rules are consistent with the thermodynamics theory of nano-dissolution. (3) the particle size of nanocrystalline particles has a significant effect on the kinetics of dissolution: with the decrease of particle size, the dissolved lnk increases gradually, while EA and lnA decrease gradually, and the sum of Ln Ku EA shows a good linear relationship with 1 / d. These experimental rules are consistent with the theory of nano-dissolution kinetics. (4) the particle size has a significant effect on the surface thermodynamic properties of nanoparticles: with the decrease of particle size, the molar surface Gibbs energy, molar surface enthalpy and molar surface entropy increase. All of them are linearly related to the reciprocal of particle size, and these effects are consistent with the thermodynamic properties of the surface. 5) the surface thermodynamic properties can be obtained by using the dissolution thermodynamic data and kinetic data of different particle sizes, but the surface thermodynamic properties obtained from the dissolution thermodynamics data are more reliable.
【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

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