Chemical Engineering Aspects of Production of Extremely Fine Particles by Liquid-Phase Reactions

用两种鼓泡塔对Fe（OH）_2碱性悬浮液进行空气氧化制备针铁矿的研究。针铁矿颗粒的形成过程包括HFeO_2氧化生成铁羟基络合物、铁羟基络合物水解生成针铁矿和针铁矿颗粒的沉积三个步骤。氧化反应在气泡周围的液膜中完成，而针铁矿的形成主要发生在液相中。氧化反应显然是零级相对于Fe（II）和一级相对于溶解氧。所制备的针铁矿颗粒为针状，其尺寸范围为0.15 - 0.30 <micrn>μ m。随着氧化反应速率的增加，针状颗粒的平均尺寸变小，尺寸分布变窄，正硅酸乙酯（TEOS; Si（OC_2H_5）_4）在乙醇中水解生成针状颗粒的过程中，由于氧化反应速率的增加，针状颗粒的平均尺寸变小，尺寸分布变窄 ...更多信息 生产球形二氧化硅颗粒。选择该反应体系是因为反应动力学的信息对于建立颗粒尺寸和形状控制的方法是必不可少的。球形二氧化硅粒子的形成是由水解和缩聚组成的。在正硅酸乙酯（TEOS）、氨水（NH_3）和水（H_2O）中，聚合反应均为一级反应。在反应的早期阶段，发生TEOS的水解，并且沉积几乎均匀尺寸的非常细的颗粒（主体颗粒）。接着，球形颗粒通过在主体颗粒的表面上进一步沉积硅酸盐单体而生长，同时主体颗粒的数量保持恒定。通过改变NH_3的浓度，可以将平均粒径控制在0.03 ~ 0.30 <micrn>μ m之间，使粒径分布窄。较大的球形颗粒可以在不同的溶剂如丙酮和二氧六环中制备。Ti（OC_2H_5）_4的控制水解反应也可生成球形二氧化钛微粒，其机理和动力学与Ti（OC_2H_5）_4相似。少

The formation of goethite particles by air oxidation of alkaline suspensions of Fe(OH)_2 was carried out using two types of bubble columns. The formation of goethite particles is composed of the formation step of ferric hydroxo-complex by oxidation of HFeO_2,the formation step of goethite by hydrolysis of the ferric hydroxo-complex, and the deposition step of goethite particles. The oxidation reaction has been found to complete in the liquid filmaround the gas bubble, while the formation of goethite has been found to mainlyoccur in the bulk liquid phase. The oxidation reaction was apparently zero-order with respect to Fe(II) and first-order with respect to dissolved oxygen. The prepared goethite particles are needle-like shapes whose size ranges from 0.15 to 0.30 <micrn>m. As the oxidation reaction rate increases, the meansize of the needle-like particles becomes small and the size distribution becomes sharp.The hydrolysis of teraethyl orthosilicate (TEOS; Si(OC_2H_5)_4 in ethanol to p … More roduce spherical silica particles, was performed using a strred vessel. This reaction system was selected because the information on reaction kinetics was essential to establishment of the methodology of particle size and shape control. The formation of spherical silica particles is composed of hydrolysis and polycondensation. The polymerization reaction was found to be first-order in TEOS, NH_3 as a basic catalyst and H_2O, respectively. In the earlier stage of reaction, hydrolysis of TEOS takes place and very fine particles of nearly uniform size (host particles) are deposited. Successively, spherical particles are grown by further deposition of silicate monomer on the surface of the host particles while the number of the host particles is kept constant. The mean particle diameter can be controlled in the range of 0.03 to 0.30 <micrn>m, keeping the isze distribution narrow by changing the concentration of NH_3. Larger sperical particles can be prepared in different solvents such as acetone and dioxane. Spherical titania fine particles are also formed by controlled hyddrolysis of Ti(OC_2H_5)_4 in the similar mechanism and kinetics. Less