英文原文Dispersion of nanoparticles by novel wet-type pulverizer utilized supersonic jet flowAbstract.We have examined the dispersion of barium titanate nanoparticles (BT-NPs) andhave discussed the effect of air pressure supplied to the nozzle on the dispersion by using novelwet-type pulverizer utilized supersonic jet flow (SSJM). The aggregated particle size wasdecreased with increasing the air pressure and the collision times. In the optimized condition,almost the BT-NPs were dispersed with the primary particles, however, further excessivecollision had caused reaggregations. The degree of dispersion has been affected by the airpressure. The injected droplets had formed almost the same diameter regardless of air pressureand the velocity was increased with increasing of the air pressure and reached 300 m/s. Wehave speculated that the shockwave dominates the dispersion of BT-NPs.1. IntroductionNanoparticles are required highly in many applications such as dielectric materials for electronicdevices, electrode materials for secondary batteries, etc. The nanoparticles have been frequentlyproduced by the so-called build up processes such as hydrothermal process, coprecipitation process,and sol-gel method. For exploiting size effect of nanoparticles, it is crucial to control the dispersion and aggregation of the nanoparticles in suspension. However, nanoparticles aggregate more easily and strongly than submicron sized particles, and aggregated nanoparticles do not fragment easily.Therefore, it is quite difficult to disperse nanoparticles perfectly, and the dispersion of nanoparticles has become a fundamental technique for handling nanoparticles in industries. It has been reported that he nanoparticles were well-dispersed by using beads mill 1.Bead milling with balls several tens of micrometers in diameter has recently been developed as anew method to disperse nanoparticles to almost primary particle size 1. However, the contamination caused by the grinded ball in bead milling was ten times higher than that caused by dry grinding 2.For providing nanoparticles dispersing method that can solve the above problem, we have developed novel wet-type pulverizer utilized supersonic jet flow (hereafter referred to as supersonic wet jet mill;SSJM). In this study, we have reported the dispersing result of barium titanate nanoparticles (BT-NPs) and have discussed the effect of air pressure on the dispersion by using the SSJM.2. Experimental apparatus and procedure2.1. Experimental apparatusFigure1 shows schematic diagram of the SSJM (left). The right part of describes shows the internal configuration of the nozzle part. The compressed air (maximum air pressure was 0.6 MPa) was supplied at the top part of the nozzle. The Laval nozzle, which was used for the SSJM as shown in Figure1, is used to accelerate a compressed air passing through it to a supersonic speed, and upon expansion, to form the exhaust flow so that the heat energy propelling the flow is maximally converted into kinetic energy. As a result, the injected droplets passing through the nozzle were accelerated to supersonic and were naturally cooled. The suspension in the feed tank was supplied to the throat of the nozzle, while controlling the volume flow through the pump tubing. The supplied suspension had been formed droplets by jet flow and had been accelerated inside the nozzle. The accelerated droplets had collided with the SiC plate. Most of the processed suspension was collected at the bottom tank, and some of the processed suspension was evacuated along with the jet flow, therefore, the solvent recovery tank unit attached to the exhaust line. Figure 1. Schematic diagrams of supersonic wet jet mill (left) and the nozzle part (right), showing approximate flow velocity (V), together with the effect on temperature (T) and pressure (P). 2.2. Experimental procedureTwo kinds of BT-NP were used in this work. BT-NPs with the average particle size of 30 nm weresynthesized by the sol-gel method 3 (referred to as sol-gel BT). Commercially available BT-NPs(BT-01, Sakai Chemical Industry, Japan) with the average particle size of 100 nm were manufactured by hydrothermal method (referred to as hydrothermal BT). A dispersant used in this study was an ammonium salt of poly (acrylic acid) (PAA-NH4+ , Mw 8000, Touagousei, Japan). The sol-gel BT was added to ethylene glycol monomethyl ether in 2 volume % (referred to as sol-gel BT suspension). PAA-NH4+ was added to distilled water in 5 wt% against powder weight and then the hydrothermal BT was added in 20 volume percents against distilled water (referred to as hydrothermal BT suspension). Each suspension was injected under various air pressures from 0.3 to 0.6 MPa. An aggregated particle size was evaluated by dynamic light scattering method (DLS, Nano-ZS, Malvern,UK). A shape and microstructure of the BT-NPs we