Composite particles are applied in various industrial fields. In order to prepare higher function composite particles, it is often required to coat core particles with multi-component particles. In this paper, coating of polyethylene core particles with fine silica particles was investigated with particular attention to the effect of feeding procedures of fine particles on the coating ratio. Three types of silica particles with different sizes were used as coating particles. The feeding procedures investigated were (1) simultaneous feeding of all fine particles at once, (2) three-step coating started from the feed of the smallest particles followed by larger particles and (3) three-step coating started from the feed of the largest particles followed by smaller particles. It was found in (1) simultaneous coating and (2) three-step coating started from the smallest particles that the smallest particles obstructed the coating with the other fine particles, leading to a reduction in coating ratio, Among the three procedures, (3) three-step coating started from the largest particles was advantageous for the formation of densely packed coating surface. However, even in (3) three-step coating started from the largest particles, the effect of obstruction of coating in the second step was observed. The effect of the obstruction can be explained by a packing model of triangular units.

View full abstract

Spherical SiO₂ and Al₂O₃ fillers were synthesized by ultrasonic spray pyrolysis. The particles characteristics of these fillers were studied by SEM, TEM, XRD and a pycnometer. Crysalline state of both as-prepared fillers was amorphous. The morphology of SiO₂ fillers was maintained at up to 900°C . The morphology of SiO₂ fillers was changed to irregular shape after crystallization of cristobalite at 1100°C. On the other hand, the morphology of Al₂O₃ was retained after crystallization of α-alumina at 1100°C. By the surface modification of these fillers with a silane coupling agent, the composite materials of epoxy resin and fillers was successfully prepared. The Vickers hardness and thermal conductivity of composite materials were investigated. The use of fillers with a broad particle size distribution and spherical morphology led to an improvement in the packing fraction of fillers, Vickers hardness and thermal conductivity.

View full abstract

One of the methods to obtain inorganic phosphates is the chemical reaction by heating the mixtures of ammonium phosphate and target metal oxide, carbonate, and so on. The mixing condition is as important as heating temperature, time, atmosphere, and so on. In this report, the mixtures of raw materials were mechanically treated for syntheses of cerium, neodymium, copper, nickel, zinc, and manganese, ortho-, pyro-, poly-, cyclo-, and ultra- phosphates. By the mechanical treatment, cation exchange reactions took place in some system without heating. Furthermore, it not only altered the thermal products but also improved some of the functional properties of phosphates.

View full abstract

We propose a novel process to fabricate micropatterns of spherical particle assemblies. Hydrophilic regions of a patterned self-assembled monolayer (SAM) were covered with a methanol solution containing SiO₂ particles and then immersed in decalin to control the shape of droplets, where the methanol gradually dissolve into decalin. Particles were assembled to from spherical shapes in hydrophilic regions of SAM and, consequently, micropattems of spherical particle assemblies were successfully fabricated through the self-assembly. This patterned two-solution process possesses the advantages of a drying process with the meniscus force as well as the high controllability of a static solution process.

View full abstract

Monodisperse silica seed particles were coated with silica, titania and iron oxide by a seed growth method that employs the hydrolysis and condensation of the metal alkoxides (tetraethoxysilan (TEOS), titanium tetraisopropoxide (TTIP) and iron tri-n-butoxide (TNBI)). The resultant composite particles kept the characteristics of monodisperse particles. Electroconductive particles were prepared by nitriding the titania-coated particles. The nitriding of the composite particles were carried out with ammonia gas in a tube furnace at various temperatures. The surface of titania-coated particles changed to titanium nitride at a temperature higher than 700°C, and the electroconductivity of the composite particles was high enough for the practical usage. Magnetic particles were also prepared by reducing the iron oxide coated silica particles with hydrogen gas at 500°C. The particles could be used as the model particles such as an EMR fluid although the magnetic property was relatively poor.

View full abstract