Development of Continuous Apparatus using Microreactor for Production of Nanoparticles in Supercritical Water

近十年来，为在亚临界和超临界水中制备微米级或纳米级金属氧化物，建立了一种采用微反水热合成法连续生产金属氧化物的方法。这种方法保证了启动溶液快速加热到给定的温度，并准确控制反应时间。当水处于近临界或超临界状态时，水热反应速率和金属氧化物的溶解度可以通过改变温度和压力来控制，因为反应溶剂的性质强烈依赖于这些区域的条件。因此，该方法在制备纳米金属氧化物微粒方面具有很大的潜力。用这种方法制备纳米粒子的报道很多。然而，目前还没有从金属氧化物的溶解度和过饱和度来探讨其粒度可控性的报道。在这项工作中，要将此方法开发为泛型…更多的纳米晶制备技术我们着重于定量阐明用该方法制备单一纳米金属氧化物的实验条件以及在估计金属氧化物溶解度的基础上其结晶度。我们利用该方法在673K和30 Mpa的条件下从金属硝酸盐的水溶液中合成了金属氧化物(AlO(OH)、CuO、Fe2O、NiO、ZrO2)纳米颗粒。用透射电子显微镜、X射线衍射仪和热重分析等手段对所制得的纳米粒子的粒度、物相和结晶度进行了表征。在过饱和度的基础上分析了原料中金属的不同对颗粒大小、转化率和结晶度的影响，并通过估算金属氧化物的溶解度来评价过饱和度。结果表明，若要获得单一纳米尺度的颗粒，过饱和度应设置为高于104。此外，通过热重分析对所得粒子的结晶度进行了评价。此外，反应时间越长，结晶度越高，过饱和度越小，结晶度越高。这一结果可以解释为大的过饱和度导致在形成颗粒的过程中包含水分子。较少

Over the past ten years, a flow-through hydrothermal synthesis method with microreactor for continuous production of metal oxides have been established for forming micro or nano size metal oxide fine particles in subcritical and supercritical water. This method promises to heat starting solutions rapidly to the given temperature and to control reaction time exactly. When water in its near-critical or supercritical state is used, the hydrothermal reaction rate and metal oxide solubility can be controlled by changing temperature and pressure since the reaction solvent properties are strongly dependent on the conditions in these regions. Therefore, this method has great potential for producing nano-size metal oxide fine particles. There are many reports for producing nanoparticle by this method. However, there is no report that the controllability of the particle size is discussed on the basis of metal oxide solubility and supersaturation. In this work, to develop this method as a generic … More technology for producing nanocrystals we focus on the quantitative clarification of experimental conditions for producing single nano-sized metal oxide particles by this method and also its crystallinity on the basis of estimated metal oxide solubilities.We carried out hydrothermal synthesis of metal oxides (AlO(OH), CuO, Fe2O3, NiO, ZrO2) nanoparticles from metal nitrates aqueous solution at 673 K and 30 MPa by this method. Particle size, phase and crystallinity of the obtained particles were characterized by TEM, XRD and TG, respectively. Effect of the difference of the metals in starting materials on particle size, conversion and crystallinity was analyzed on the basis of supersaturation, which was evaluated by estimated metal oxide solubilities. The result suggests that supersaturation should be set to higher than 104 in this method to obtain particles in single nanoscale. Further, crystallinity of the obtained particles was evaluated as weight loss through TG analysis. In addition that longer reaction time increased the crystallinity, it was found that smaller supersaturation also increased the crystallinity. This result can be explained that large supersaturation lead to include water molecule on the way to formation of particles. Less