Mitsumasa Kimata

Preparation of monodisperse magnetic particles by hydrolysis of iron alkoxide

Abstract The synthesis of iron oxide particles was carried out by the hydrolysis of iron tri-n-butoxide in an octanol/acetonitrile solution. The morphology of the particles formed was found to depend on composition of the mixture of solvents used and also on the method of its addition, i.e. either instantaneous or continuous. The data of apparent reaction rate revealed that the selection of reaction conditions controlling the reaction rate was the most important factor for achieving formation of monodispersed particles. These particles were subsequently used for preparation of magnetic particles by de-oxidation process. With respect to the relationships between the reduction condition and magnetic characteristics of the particles formed in this process, it was found that the particles synthesized showed a saturation magnetization magnetic susceptibility greater than that of commercial magnetite when they were reduced at a temperature higher than 573 K under a hydrogen atmosphere. The particles obtained after reduction treatment at 523 K for 3 h were identified as γ-Fe2O3 and those at temperature higher than 623 K for 3 h as α-Fe types, respectively, by using powder X-ray diffraction technique. A suspension obtained using the monodisperse magnetic particles in silicone oil was prepared and its rheological characteristic was determined using a parallel-plate rheometer and was found to have an apparent magnetorheological (MR) effect. It is believed that the monodisperse magnetic particles obtained in this work can be used as a component of a model MR fluid to elucidate the general mechanism of cluster formation of particles in such fluids.

The Effect of Liquid Additives on Dry Ultrafine Grinding of Quartz

The dry ultrafine grinding of quartz with liquid additives was carried out using a vibration rod mill with a laboratory scale. Liquid additives used were mainly seven alcohols and three glycols with different alkyl groups. All of the experiments were carried out by batch operation, and the variations of specific surface areas of products with grinding time were measured by BET adsorption method. The results showed that alcohol and glycol additives were satisfactorily effective for the ultrafine grinding of quartz. The maximum specific surface area of quartz obtained with an additive was found to increase in proportion to the amount of the additive. The additive molecules of multimolecular layers were supposed to adsorb on the quartz surface when the specific surface area reached the maximum value. The principal effect of additives in ultrafine grinding is considered to be the increase in flowability and the control of reagglomeration of quartz powder due to the alkoxylation of hydroxyl groups on the quartz surface.

Mechanochemical polymerization of styrene initiated by the grinding of layered clay minerals

The polymerization of styrene mechanochemically initiated by the grinding of talc was performed by using a vibrating ball mill. Talc used was one of layered clay minerals as well as montmorillonite. The effect of the grinding of talc on the polymerization of the styrene was investigated by characterizing the polymer formed and talc ground. The results revealed that of all the experiments we have performed thus far, styrene most abundantly polymerized by grinding of talc. The polymerization of styrene was closely related to the total surface area of the ground talc. The products obtained were the composites of talc particles and resulting polymer attached to the particle surface. From the analysis of the molecular weight distribution of the polymer, it was suggested that the polymerization of the styrene proceeded with two types of cationic active species which were produced by the grinding of layered clay minerals. Mechanochemical polymerization is expected to be one of the more promising production processes of polymeric nanocomposites when layered clay minerals can be ground to finer nanometer sized-particles.

Microstructure of iron particles reduced from silica-coated hematite in hydrogen

Poly- and nearly monocrystalline hematite particles having diameters of around 2 and 0.1 μm, respectively, were prepared by the gel-sol method and coated with a uniform silica layer by the sol-gel method. The core in the silica shell was reduced to iron without agglomerate formation between the particles by using a hydrogen stream. The microstructure and morphology of these cores and the silica layers were examined by high-resolution transmission electron microscopy, and electron and X-ray diffraction analysis. In hematite particles, around 2 μm in diameter, the reduced products were mostly α-Fe, but partially magnetite. In hematite particles, around 0.1 μm in diameter, only α-Fe was observed. Most of the raw hematite and iron particles produced were monocrystalline, and part of core grew hexagonal prism-shaped monocrystalline particles. In the case of the growth of a crystal to a hexagonal prism, a nanometer-scaled space at the interface between the iron crystal core and the silica layer was discovered.