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Understanding of crystal growth and reaction mechanism in hydrothermal synthesis at supercritical conditions

了解超临界条件水热合成中的晶体生长和反应机理

基本信息

批准号：
11450287
负责人：
ARAI Kunio
金额：
$ 8.26万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2001
项目状态：
已结题

项目摘要

We have conducted hydrothermal synthesis of metal oxide fine particles in supercritical water. To establish these new technologies, it is necessary to clarify characteristic and function of supercritical water as the reaction solvent. In this study, firstly, we developed the simple estimation model of equilibrium constant (dissolution and dissociation reaction) and the flow-through apparatus for measuring pH and metal oxide solubility at supercritical conditions. Secondary, we conducted the experiment of hydrothermal synthesis of several metal oxides with flow-through experimental apparatus and considered the relationship between experimental condition and generation region of nano size fine particle.The hydrothermal reaction rate in supercritical water is higher, and the solubility of metal oxides is much lower than that in subcritical water. Both facts lead to the generation of higher super-saturation degree. The nucleation rate is expressed by the function of super-saturation degree and the surface energy according to the nucleation theory. Thus, extremely high nucleation rate can be expected at supercritical conditions. Simulation of reaction kinetics, nucleation, and crystal growth would provide quantitative explanation for the temperature dependence of the particle size. In spite of the lack of such quantitative information, the results shown in this study suggests the specific features of supercritical water hydrothermal synthesis method for the production of nanocrystals.

我们在超临界水中进行了金属氧化物微粒的水热合成。为了建立这些新技术，有必要阐明超临界水作为反应溶剂的特点和作用。在这项研究中，我们首先建立了简单的平衡常数(溶解和解离反应)估算模型和超临界条件下测定pH值和金属氧化物溶解度的流动装置。其次，利用流通式实验装置进行了几种金属氧化物的水热合成实验，考虑了实验条件与纳米微粒生成区域的关系，发现超临界水中的水热反应速率较高，金属氧化物的溶解度远低于亚临界水中。这两个因素都导致了较高的过饱和度的产生。根据成核理论，用过饱和度和表面能的函数来表示成核速率。因此，在超临界条件下，可以预期极高的成核率。对反应动力学、成核和晶体生长的模拟将为颗粒尺寸的温度依赖性提供定量的解释。尽管缺乏这样的定量信息，但本研究的结果表明了超临界水热合成法制备纳米晶体的特殊性。