Showing papers in "Journal of The Society of Powder Technology, Japan in 2012"

Effects of Polyelectrolyte Dispersant Conformation and Magnesium Ion on Adsorption to Slurry Particles

Abstract: In wet shaping, the amount of dispersant added to the slurry is a crucial factor in producing high-quality ceramic products. Many researchers have investigated the amount of dispersant that adsorbs to slurry particles. However, few studies have examined how the solid concentration of slurry affects the amount of adsorbed dispersant. In our previous work, we measured the amount of adsorbed dispersant at various solid concentrations and addition amounts of dispersant. In the present work, alumina particles containing magnesium as a sintering aid were used. The conformation of polyelectrolyte dispersant was changed by magnesium ions, and the adsorption isotherm showed a local maximum. In the case of laurate, some molecules remained in solution and did not adsorb to particles because of its thermal motion and few adsorbing sites. Consequently, the amount of adsorbed dispersant was affected by the diffusion of magnesium from the particles, the molecular weight of the dispersant, and the solid concentration of the slurry.

Redispersion Property of TiO2 Nanoparticles Modified with Oleyl-group

Abstract: The effect of post-synthesis process, such as washing and drying of nanoparticles, on their redispersion behavior in solvents were investigated by using TiO2 nanoparticles (c.a.5 nm) modified with oleyl phosphate (TiO2-OP). The washing process conducted in this article was dispersion of TiO2-OP in toluene and collection by centrifugation after flocculating the particles by adding poor solvent. When TiO2-OP cake was simply vacuum dried after washing, the average size after their redispersion with ultra-sonication in toluene was c.a. 40 nm. It was found that this average size gradually reduces to 20 nm by settling the suspension. Contrary, when TiO2-OP was dried by evaporating the solvent after dispersing the cake in toluene, their average size in toluene easily reduced to 20 nm just after treating ultra-sonication. The behavior of these differently dried TiO2-OP during redispersion process in toluene is discussed based on the structure of ligands and particle interactions in toluene.

Carbamazepine-dicarboxylic Acid Cocrystal Formation Induced by Multicomponent Cogrinding and Exchange Reaction of Dicarboxylic Acids

Abstract: Effect of dicarboxylic acids : malonic acid (MA), succinic acid (SUA), and glutaric acid (GA), on the preferential cocrystal formation with carbamazepine (CBZ) was investigated. Stoichiometries of CBZ / MA, CBZ / SUA and CBZ / GA cocrystals formed were 2 / 1, 2 / 1 and 1 / 1. When CBZ / SUA ground mixture (GM) was coground with MA, CBZ / SUA cocrystal still remained, i.e., no exchange reaction occurred. On the other hand, exchange reaction occurred when CBZ / MA GM was coground with SUA. CBZ / SUA cocrystal was formed by ternary cogrinding of CBZ, MA and SUA. In CBZ, MA and GA system, preferential cocrystal formation was observed for CBZ / GA. The results of cryogenic cogrinding suggested that preferential CBZ / GA cocrystal formation was due to the stable and rapid crystallization. Preferential CBZ /GA cocrystal formation was assumed when CBZ, SUA and GA ternary cogrinding was performed. Structure and stability of cocrystal, mechanism of cocrystal formation and grinding energy affected the preferential cocrystal former exchange reactions.

Investigation and DEM Simulation for Part Detachment Process of Printed Circuit Board in a Drum-type Impact Mill

Abstract: The mechanism of part detachment and board breakage process in a drum-typed impact mill to recover valuable metals by removing components from printed circuit boards (PCBs) was investigated. Experimental results using test PCBs showed that parts detachment was enhanced by the increase of input number of PCBs in the mill and board breakage was enhanced by the increase of rotational speed of the agitator. DEM simulation results using spherical particles model showed that board breakage was achieved by the collision of boards with drum wall and agitator, and part detachment was achieved by the interaction between PCBs. To simulate part detachment and board breakage process more briefly, particle-based rigid body model, in which model PCB geometry was constructed consisting of bonded particulates, was included to DEM simulation. Simulation results showed that board breakage was obtained from the impact of boards with the drum wall and part detachment was obtained from the collision of the boards with each other. These simulation results were successfully corresponded to experimental observations.

Adsorption and Desorption Mechanism of Carboxylate to Alumina Particles

Abstract: The particle assembling state in a slurry affects the production quality or performance in ceramic industry and so on. Generally, to control the assembling state dispersants are added However, it is difficult to control it precisely because the adsorbing mechanism of dispersants has not been clarified enough. We have tried to make clear the adsorption mechanism of dispersant mainly through the observation of desorption behavior of the adsorbed dispersant. A mono-carboxylate and a polycarboxylate were used as dispersant, and two kinds of pure alumina powder were used : one contains Mg as sintering aid and the other one doesn't. It was found that the hydrophilic carboxyl groups in dispersants adsorbs on alumina particles electrostatically. In addition it was shown that polycarboxylate strongly adsorbs on alumina powder since it has a lot of carboxyl groups in a molecule. Furthermore, when containing Mg into alumina powder, dispersants should associate to Mg on the particle surface, resulting in much stronger adsorption.

Controlling Self-Assembled Structure of Au Nanoparticles by Convective Self-Assembly with Liquid-Level Manipulation

Abstract: Microwire networks composed of noble metal particles are promising for the use of transparent conductive films. Bottom-up approaches can offer a route to establishing a fabrication technique that is robust and cost-effective, and template-assisted self-assembly techniques are widely used. However, they require additional processes to prepare templates and generally suffer from the difficulty in a large-scale fabrication. A template-free technique thus waits to be developed. In the present study, we explore a template free technique to fabricate colloidal networks of Au nanoparticles. We combine the convective self-assembly method with a liquid-level manipulation scheme in which the suspension is periodically pumped out. By using the technique, we successfully fabricate stripe, grid, and triangle patterns with controlled periodicity and examine the relationship between operation parameters and the resultant structures. We then measure the transparency and conductivity of a grid pattern to demonstrate the property as the transparent conductive film.

Effect of Nozzle Depth on Pneumatic Conveying Characteristics of Suction Nozzle with Injection Pipe

Abstract: In the vacuum system of pneumatic transport, the authors have proposed, that a suction nozzle equipped with an injection pipe at the center, would provide a highly-dense therefore a highly-efficient method of transporting a powder. In this paper, we examine the effect of nozzle length, the inserted depth of the suction nozzle into the powder bed. The resulting data show that the nozzle performance improved in a range of lower nozzle depths, but saturated in a range of higher nozzle depths with no insertion length of injection pipe. The powder behavior near the suction nozzle at different nozzle depths was observed with powder flow visualization.

Estimation of Adhesion and Aggregation of Acetate-utilizing Methanogens

Abstract: From the view point of fine particle technology, the effects of surface properties of methanogens, which are related to the rate-limiting step in the methane fermentation process, on their adhesion and aggregation were examined. As a result, Methanosarcina barkeri were found to be charged negatively and their isoelectric point was around pH 2. In contrast, Methanosaeta concilii was found to be non-charged and their isoelectric point was around pH 4.5. According to the ATR-FTIR analysis and acid-base titration, it was guessed that the difference of surface potential between two types of methanogens was due to the difference of the amount of carboxyl group and phosphate group on their microbial surface. Methanosarcina barkeri showed better adhesion to not the negatively-charged glass but to the positively-charged one. Percent aggregate of Methanosarcina barkeri increased with an increase in the ionic strength of the cell suspension. In contrast, percent aggregate of Methanosaeta concilii was almost constant regardless of the ionic strength. These adhesion and aggregation phenomena could be understood by the electrostatic interaction and the change of free energy of interaction between methanogen and slide glass.

Nanosized Particle Synthesis by Using Flash Boiling Atomization

Abstract: An innovative nanosized metal particle synthesis method by flash boiling atomization is proposed. Methane-oxygen premixed flame is utilized as the heat source and the precursor water solution is sprayed into the low-pressure field. Then, droplets are secondary-atomized by flash boiling phe-nomenon. The zinc acetate water solution is used as the precursor to synthesize ZnO nanosized metal particles. From the view point of industrial aspects, the size controlla-bility of nanosized metal particle, the inhibition of agglomeration and the inexpensive large production quantity are required for the particle synthesis method. The synthesis method, which is presented in this paper, is expected to achieve the above-mentioned characteristics. In this paper, firstly, the flashing spray is observed by using Mie scat-tering method. Secondly, ZnO nanosized metal particles are synthesized to investigate the effect of the flash boiling atomization on the synthesized particles. It was found that the droplets were well atomized and dispersed when the flash boiling phenomenon occurred. In addition, the higher the temperature of precursor solution became (above the saturated temperature), the smaller the synthesized particles were.

Effect of pH Change on the Shell Thickness of Calcium Carbonate Hollow Particles by CO2 Gas Bubbling Method

Abstract: Effect of pH change on the shell thickness of calcium carbonate hollow particles was investigated. Calcium carbonate hollow particles were synthesized at different pH change rates by Carbon dioxide bubbling into a solution. And influence of pH change rate on the shell thickness was estimated by observing SEM images of cross section of hollow particles. pH change curve could be divided into two stages, before and after the point where pH changes rapidly, and could express each stage with the approximated curve. Rate parameters of pH change rate were determined from these approximated curves, and the relation with shell thickness was investigated. As a result, it has become clear that thickness of hollow particles is expressible by the rate parameter of approximation curve corresponding to the first stage which is characterized as the process from start of bubbling to the point where shell is formed.

Direct Observation and Characterization of Effect of Preparing Condition on Particle Assembling State in Suspension

Abstract: Particle assembling state in suspensions prepared by different ways was numerically characterized by direct observation method. The aqueous suspensions of alumina powder were prepared by ultrasonication and ball milling. The particle assembling state was characterized by settling test and particle size measurement in addition to the direct observation. From the comparison, the particle images in a suspension getting by the direct observation method can much more distinguish coarse aggregates from primary particles than the other ways. And the black and whiteness of the particle images were classified into 256 steps. The mean values and standard deviations of the black and whiteness distributions were calculated. The variation coefficient determined by the standard deviation over the mean value can show the existence of coarse aggregates that were not ground or re-aggregated.