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

用两种鼓泡塔对碱性Fe(OH)2悬浮液进行空气氧化，生成针铁矿颗粒。针铁矿粒子的形成由HFeO_2氧化生成氢氧化铁络合物、氢氧化铁络合物水解生成针铁矿和针铁矿粒子沉积三个步骤组成。发现氧化反应在气泡周围的液丝中完成，而针铁矿的形成主要发生在体液相中。氧化反应对Fe(II)为零级反应，对溶解氧为一级反应。所制备的针铁矿颗粒呈针状，尺寸在0.15~0.30微米之间。随着氧化反应速率的增加，针状颗粒的平均尺寸变小，粒度分布变得更清晰。正硅酸乙酯(TEOS；Si(OC_2H_5)_4在乙醇中的水解生成p-…使用串接容器进行了更多的球形二氧化硅颗粒的制备。之所以选择该反应体系，是因为反应动力学信息对于建立颗粒大小和形状控制方法至关重要。球形二氧化硅颗粒的形成由水解和缩聚两部分组成。在正硅酸乙酯、碱性催化剂NH_3和水中，聚合反应均为一级反应。在反应的早期阶段，正硅酸乙酯发生了水解，并沉积了尺寸几乎均匀的非常细的颗粒(主体颗粒)。随后，在保持基质颗粒数量不变的情况下，通过在基质颗粒表面进一步沉积硅酸盐单体来生长球形颗粒。平均粒径可控制在0.03~0.30微米之间，通过改变NH_3的浓度，可使ISZE分布变窄。在丙酮、二氧六环等不同的溶剂中均可制得较大的球形粒子。Ti(OC_2H_5)_4的受控水解也得到了球形的二氧化钛微粒，其机理和动力学与此相似。较少

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