Dispersion State Of Particles Research Articles

Effect of particle size of graphites on electrical conductivity of graphite/polymer composite

The effect of particle size of graphite particles on the dispersion state of graphite particles and electrical conductivity of graphite/low-density polyethylene (LDPE) composites is investigated. Graphite particles which have plate-like and spherical shapes and mean particle sizes of 2.1 to 82.6 μm are used. Scanning electron microscopy observation showed that graphite particles are not aggregated and ordered along the direction of mixing-roll in the polymer matrix. X-ray diffraction measurements show that crystallite size of the (110) plane of polyethylene crystal and the crystallinity are significantly affected by the particle size of graphite particles. These results were interpreted as due to the orientation of PE crystallites. The electrical conductivity of composites changes discontinuously at the critical volume fraction of particles, Øc. The Øc values given by the percolation equation increase with decreasing of the particle size of graphites. The plate-like graphite particles with a mean particle size of 2.1 μm could induce conductivity at Øc of 0.135. The values of Øc increased linearly with increasing of the mean particle sizes of the plate-like graphites. The value of Øc of spherical graphite particle is the largest value, 0.292, in all specimens.

Synthesis of gold particles in organized molecular assembly films

Gold particles were produced by photoreduction of AuCl 4 − ions incorporated as counter anions in dioctadecyldimethylammonium (DODMA) multi-bilayer and Langmuir-Blodgett (LB) films. AuCl 4 − ions could be reintroduced into the films by immersing them in aqueous HAuCl 4 without loss of gold particles. The size of gold particles in the LB film was significantly smaller than in the multi-bilayer film. By repeating the photoreduction-intercalation cycle, Au 0 particles in the films grew in both size and concentration. In the LB films the isolated dispersion state of gold particles was maintained while in the multi-bilayer films the particles aggregated.

Electrochemical activity enhancement of a LaNi 4.7Al 0.3 electrode treated with an alkaline solution containing H 2O 2

Enhancement of the electrochemical activity of a LaNi 4.7Al 0.3 electrode was observed subsequent to some charge–discharge cycles in a KOH solution containing hydrogen peroxide. Metallic nickel is enriched at the alloy surface after the treatment, and the concentration of lanthanum decreased during the treatment. The change in the distribution of elements at the alloy surface is expected to lead to a different dispersion state of nickel particles in the region, resulting in improvement of the catalytic activity for the charge-transfer process on the alloy surface.

Effect of dispersion state of SnO2 particles in a glass matrix on the densification behaviour and the electrical properties of SnO2-glass composites

The present work was undertaken as part of a study to clarify the relationship between the electrical properties and the microstructure of the SnO2-glass composite. The glass composites with different particle dispersions of SnO2 were prepared under various mixing conditions of the starting powder. The densification behaviour and the electrical properties of the glass composites were discussed from quantitative analysis of the dispersion of SnO2 particles in glass matrices. As a result, the glass composite having homogeneous particle dispersion densified and showed an abrupt increase in conductivity (κ) and the temperature coefficient of resistance (TCR) at a low firing temperature. But after the completion of densification, the glass composite with the inhomogeneous dispersion of SnO2 particles showed a high κ and a TCR close to zero because the highly aggregated SnO2 particles connect with each other to form highly electrically conductive networks.

Microrheological Study of Magnetic Particle Suspensions

Two different microrheological characterization techniques for the microstructure of complex fluids (i.e. rheomagnetic and rheooptic measurements) were adopted to study the microstructural state of magnetic particle suspensions. These two techniques measure the dispersion state of various single-domain magnetic particles (rodlike γ-Fe2O3 or CrO2 and platelike Ba-ferrite). The techniques complement one other by measuring the order parameter for the magnetic particles in suspension over different concentration ranges. The rheomagnetic measurement is good for on-line characterization of microrheological properties of magnetic particle suspensions. The rheooptical measurement is useful for off-line dispersion microstates and rheological properties of the suspensions.

Effect of interfacial energy and viscosity on percolation time of carbon black-filled poly(methyl methacrylate)

The dispersion state of carbon black (CB) particles in a polymeric matrix was found to be affected by such factors as interfacial energy of the CB-polymer interface and the melt viscosity of matrix polymers. At a given CB volume fraction, the electrical conductivity of CB-filled poly(methyl methacrylate) (PMMA) was measured as a function of time at a temperature higher than the glass transition temperature (Tg ). At a characteristic time, as a result of the aggregation of CB, networks facilitating electrical conduction were formed and a percolation-like transition was observed. We defined this characteristic time as the percolation time (t p) and estimated the dispersion state of particles by the tp . The effects of interfacial energy of the CB-polymer interface and melt viscosity of the matrix were estimated quantitatively by changing the surface energy of CB and the temperature. The experimental values of tp were compared to the calculated values using a simple model. The percolation time decreased with increase of interfacial energy and CB content, and increased with the matrix viscosity. The model well explains the dependency as long as the volume fraction of CB is not large and matrix viscosity is neither very small nor very large.

An index for microcarrier dispersion inside a horizontally rotating bioreactor for animal cell culture

An index of particle dispersion is used to quantify the degree of particle dispersion inside the horizontally rotating bioreactor. Resin particles were suspended inside a horizontally rotating cylinder. The states of particle dispersion were observed and recorded on video, from which data the index of particle dispersion was calculated. The effect of the operating parameters particle concentration and cylinder rotational speed on the state of particle dispersion were described using the index. By comparing the quantitative and qualitative classifications of particle dispersion it was confirmed that the new index does reflect the degree of particle dispersion. From the comparison it can also be concluded that if the index is greater than 0.96, the particle distribution can be considered uniform.

粉末プロセスの制御と製品評価 Ｉ 複合粒子表面上における微粒子の微視的な分散状態の評価

In this study, composite particles were prepared by dispersing fine powder particles (mean diameter 0.2μm) on core particles (mean diameter 12μm) by dry coating. This paper shows a new method of quantitatively evaluating the state of fine powder particle dispersion on the surface of each core particle by image analysis. The findings are summarized as follows:The state of fine powder particle dispersion on the surface of each core particle was successfully evaluated by degree of dispersion.Evaluation of the dispersion state by degree of dispersion was verified by the coefficient of variance for the relative intensity of the characteristic X-ray from fine powder particles and powder layer brightness on each composite particle.Image analysis makes it possible to obtain the diameter of each fine powder particle dispersed on the surface of a composite particle. The process in which fine powder particles are dispersed in the form of primary particles was thus clarified. Optimum operation time for obtaining composite particles having fine powder particles dispersed thereon was found on the degree of dispersion and the measurement of the diameters of fine powder particles.

Characterization of dispersion and percolation of filled polymers: Molding time and temperature dependence of percolation time in carbon black filled low density polyethylene

The degree of dispersion of fillers such as carbon black (CB) particles in a polymeric matrix is known to be a determining factor of the physical properties of composites. The dispersion state of particles in the polymeric matrix was found to be affected not only by the volume fraction of particles but also by the preparation conditions of the composite such as press time and temperature. At a given CB volume fraction, we measured the electrical conductivity of the composite films, which were molded at a temperature higher than Tm of polyethylene (LDPE), as a function of press time. As a result of aggregation of CB, the networks-facilitating electrical conduction were formed and percolation-like transition was observed at a characteristic time. We have defined the characteristic time as a percolation time (t P ). It was found that the t P decreased with increasing CB volume fraction and increasing molding temperature. The change of the dispersion state of CB in a polymeric matrix was characterized by a di...

Performance evaluation of dry dispersers

Several kinds of powders were dispersed into air by use of a mixer type or a nozzle-jet type dry disperser and the size distributions of the dispersed aerosol particles were measured. In the data analysis, a newly defined dispersion efficiency was introduced in order to represent the dispersion state of aerosol particles, independently of the sort of tested powders. On the other hand, the adhesive characteristic value representing the inter-particle adhesive force was obtained through a particle re-entrainment test developed in our laboratory. The data expressed by use of the dispersion efficiency and the adhesive characteristic value made it possible to evaluate quantitatively the disperser performance for different kinds of powders. It was found that the dispersion efficiency was well correlated with the adhesive characteristic value as far as the mass flow ratio between particles and air was kept constant. Therefore, the dispersion efficiency of any powder can be estimated by the particle re-entrainment test.

A method for measuring two-dimensional dispersed state of particles

The Voronoi polygonal analysis has been available for evaluating the dispersed state of particles, where the coordinates of particle positions are measured and the Voronoi tessellation is conducted to obtain the distribution of cell areas. Although the method can provide precise data concerning particle dispersion, it has the demerit of being time consuming. Hence a simple method is proposed in this paper to obtain the distribution of Voronoi cell areas from the measurement of variation in local particle concentrations by a probe of adjustable size. Evaluation of the state of particle dispersion therefore becomes faster for TV monitoring systems.

Ｎｉ‐ＴｉＯ２分散めっき皮膜の光電気化学的挙動

Photoelectrochemical technique was applied to characterize the dispersion state of TiO2 particles in Ni-TiO2 composite films. Ni-TiO2 composite films were prepared by dispersion plating under various conditions, and when they were used as the photoelectrode in sulfuric acid solution, the differences in the dispersion of the TiO2 particles in the films modified the photocurrent-potential curve. The photocurrent obtained showed one peak (A) in the region of less noble potential and an ordinal increase (B) in the noble potential region. The increased exposure of TiO2 particles on the surface as a result of chemical etching caused an increase in photocurrent (B), and the thicker the film grew, the smaller its photocurrent (B) became. This is due to the fact that the TiO2 particles in the film acted as an electrical resistance. When composite films were formed under high plating current density, codeposition of TiO2 particles was suppressed and the corresponding photocurrent (A) was relatively small. The condensation of TiO2 particles in the film reduced the photocurrent park (A), but increased photocurrent (B). This behavior suggests that the first photocurrent peak (A) located in the less noble potential region corresponds to the photoelectrochemical dissolution of the nickel matrix, and that the second increase (B) located in the noble potential region corresponds to the photoelectrochemical oxidation (probably O2 evolution) on the TiO2 particles.

磁性塗膜形成とメタル粒子の表面改質効果

In this work, surface treatment of metal particles was performed by kneading with various solvent. The metal particles obtained from the surface treatment were kneaded, diluted and dispersed to make paint, and it was used to form paint films. The dispersion state and magnetic properties of metal particles were studied.Considering the results of SEM observation, glossiness and measurement by STM and XMA, the state of dispersion was clarified. It was found that surface treatment of metal particles obtained well-dispersed state of the particles, and magnetic tape with high magnetic property (magnetic retentivity) was formed. From the results, it was indicated that surface treatment of metal particles is effective on production of highgrade videotape.

Measurement of Particle Dispersion State in a Solid-Liquid Agitated Vessel using Multi-Points and a Real-Time Method of Measuring Slurry Concentration by Transmitted Light System Mode.

石炭液化, 晶析, 金属触媒などの操作において用いられている固液系撹伴では, 撹拌槽内における固体粒子の浮遊.分散状態を定量的に把握し, 評価することが装置の設計を行う際に極めて重要となる.本研究では, 著者らが先に開発したリアルタイム・ディジタル信号処理システムを応用し, スラリー濃度検出部の構成が容易にできる光透過方式による撹伴槽内における局所スラリー濃度を多点でしかも同時にリアルタイムで測定する手法について検討した.さらに本測定法では槽内の局所スラリー濃度を極めて微小な時間間隔で測定することが可能であるため, 液流の乱れ場におけるスラリーの濃度変動を測定することができる.したがって, 槽内局所のスラリーの濃度変動の測定結果に基づき, 固体粒子の浮遊・分散状態を定量的に表示する手法を検討した.

走査型トンネル顕微鏡による微粒子の分散状態の評価

Dispersion of magnetic powder was carried out by a wet type bead mill in order to evaluate a dispersion condition of fine particles. The three-dimensional surface condition of magnetic paint film was surveyed by a Scanning Tunneling Microscope (STM). Observation of film by a Scanning Electron Microscope (SEM) and measurement of glossity were also conducted. By applying the STM, the microscopic dispersion state of fine particles was able to be evaluated because the three dimensional surface condition of magnetic paint film could be obtained quantitatively. So, the evaluation method by STM is superior to that of the glossity or by SEM.From the experimental results of STM, the operational end-point of dispersion was found to be determind by the measurement of power consumption or viscosity of the paint. The STM evaluation method should be adoptable to other fine particles.

Effect of acrylonitrile content on the toughness of ABS materials

Styrene/acrylonitrile (SAN) copolymers were toughened by addition of several SAN emulsion grafted rubbers. The main variables of the study included the AN content of the SAN graft (14.2–37.5%) and the AN content of the SAN matrix (14.7–40%). The aim was to develop general principles underlying the properties of rubber toughened SAN or ABS materials. Rubber-matrix adhesion, state of rubber particle dispersion and the inherent ductility of matrix polymer were evaluated, and the trends found in the mechanical behaviour of the blends are reasonably well explained by these three factors. The concept of inherent ductility, in particular, is effectively utilized and its importance in the ultimate properties of rubber toughened SAN is emphasized.

Effect of Dispersion of ZrB<sub>2</sub> on Resistivity of SiC-ZrB<sub>2</sub> Electroconductive Ceramic Composites

Relationships between the resistivity and the dispersion state of ZrB2, particles and aggregates, in SiC-ZrB2 electroconductive ceramic composites were investigated by means of image analysis and other measurements. The resistivity decreases with increasing number of longer ZrB2 which has larger aspect ratio, length/average width. The aspect ratio of ZrB2 increases as the length and the content of ZrB2 increase, except for large ZrB2 aggregates which are formed due to insufficient mixing of SiC and ZrB2 powders.

粒子の分散・凝集と濃厚スラリーの挙動

粒子の分散・凝集と濃厚スラリーの挙動

微粉体スラリー中における粒子集合構造

This investigation is to study the aggregate process and the structure of particles in high concentration slurry using slip casting. The aggregate state of the particles in an alumina slurry were discussed on the basis of rheological and sedimentation behavior. From these properties, this slurry could be classified into three states of aggregated structure as a function of the dispersant concentration. The structure of these slurries was observed directly by the freeze drying technique. The behavior of spinability of these slurries was discussed on the basis of this structure.Simulation of the aggregate process of particles was done as a function of cohesion probability. Then, the relationship between the dispersion state of particles and the cohesion probability were showed.From the results of the measurments, the dispersion state of the particles in these slurries were determined.

Effect of Dispersion of ZrO<sub>2</sub> Particles on Creep of Fine-Grained Al<sub>2</sub>O<sub>3</sub>

The interface-reaction controlled diffusion creep in fine-grained Al2O3 polycrystals was affected by the dispersion state of ZrO2 particles. The ZrO2 particles at grain boundaries reduced the creep rate and increased the activation energy for creep. The stress exponents were two for both pure Al2O3 and ZrO2-containing Al2O3 polycrystals. The pure Al2O3 polycrystals deformed more rapidly than the superplastic ZrO2-toughened Al2O3 at 1250° and 1300°C.