Contact Points Of Particles Research Articles

Burn-out of Binder and Sintering Behavior of Powder Compacts of Bimodally Distributed Alumina Powders with Stearic Acid and Polyethleneglycol

In order to achieve high green density of alumina powder compacts of particles with bimodal size distribution, stearic acid and polyethleneglycol were used as forming aids. Burn-out of binder and sintering behavior of these powder compacts were investigated. The forming aids melted at 50°C and concentrated on contact points of particles where large capillary force acts and became difficult to burn out. Therefore, the forming aids in compacts containing a large amount of fine particles tended to burn out at higher temperature. Powder compacts containing 40-100% fine particles expanded prior to burn-out of forming aids and began to contract simultaneously with burn-out of forming aids at 170°C. Powder compacts containing 0-30% fine particles did not expand but began to contract at 300°C. As forming aids burn-out, small pores in compacts shrank, whereas large pores grew. The sintered densities of compacts that were high green density with forming aids were also higher than those of compacts that were low green density without forming aids, until the relative density reached 95%. However, the effect of green density on the densification decreased when the relative density exceeded 95% due to remarkable grain growth.

Rapid consolidation of YBa2Cu3O7 powder

Electrical current in a powder transits particle contact points, whose high resistance localizesI2R heating. The occurrence of sintering at particle contact points suggests an efficient means of consolidating the difficult-to-sinter ceramic superconductor YBa2Cu3O7.

ＮａＣｌ‐ＫＣｌ混合粒子の液相焼結体を用いる海綿状鋳造アルミニウムの製造法の検討

Sponge cast aluminum alloy (SCA) can be produced by a new process where NaCl particles are sintered first, molten aluminum is forced to fill the pores of the sinter, and then NaCl is dissolved away from the NaCl-Aluminum composite in the water. The liquid phase sintering of NaCl particles covered with fine KCl powders has the advantages of lowering the sintering temperature and saving the sintering time, because KCl can decreases the melting temperature of NaCl through reaction and has a wide range of solid-liquid coexistance in its phase diagram. Another advantage of liquid phase sintering is the high permeability of the resulting SCA. The reason for this is thought that the liquid phase gets together at the contact points of NaCl particles leading to the wide connection of NaCl particles each other.

Ceramic gas sensors.

Relationship between microstructure and gas sensing characteristics of ceramic gas sensors was described, and highly functional gas sensors using ultrafine particles were reviewed.Using ultrafine particles brings about activation of particle-surface (for adsorption and redox reaction) as well as increases of surface area and contact-points of particles. As a result, a high sensitivity, rapid response and detection of inactive gas species become possible.

Theoretical analysis of the tensile strength of a powder bed

The authors have proposed an experimental equation which correlates the tensile strength of a powder bed measured by split cell methods with the porosity of a powder bed. In this report, the authors discuss the relationships between the porosity and the pre-compressive stress and also between the tensile strength and the pre-compressive stress. As the results of this discussion, the physical base of the proposed experimental equation is proved theoretically. Furthermore, it has also been proved that the pre-compression of a powder bed brings not only the decrease of the porosity but also the increase of compressive force at the contact point of particles, and therefore the increase of tensile strength by increasing the-compression force cannot be explained simply by the change of the porosity, and then another factor, such as the compressive force at the contact point, must be considered.

Kinetics of the Cubic → Hexagonal Transformation of Cadmium Sulfide

The kinetics of cubic→hexagonal transformation of conforms to a second‐order rate equation with an activation energy of ca. 67 kcal/mol. The transformation is enhanced by the addition of of 0.001–0.1 weight ratio with little change of the activation energy. The role of the added is considered to reside, in that makes the movement and rearrangement of atoms in easy as a flux, and that the contact points of particles with provide the starting points of the further phase transformation. The mechanism of this transformation is presumed to be a linear growth process where the cubic‐hexagonal interface moves progressively along the [111] direction of the cubic form.

ＮｉＯ‐ＭｏＯ３２成分系固相反応速度に対する単独および混合摩砕の効果

Reactants of NiO-MoO3 binary solid state reaction are preliminary ground either separately or together in air (dry) or in cyclohexane (wet) by a laboratory vibro-mill. Subsequently, the rate of nickel molybdate formation on heating at 600°C in air was determined by applying Dander rate equation. Dry grinding of NiO followed by an intimate mixing with MoO3 and by wet co-grinding brought the highest rate, due to the large amounts of lattice imperfections introduced into NiO. Preliminary grinding of MoO3, on the other hand, was effectiveless, because of high degree of agglomeration which hinders the intimate mixing on subsequent wet vibromilling. Dry co-grinding was also effective, although less amounts of lattice im-perfections are introduced, compared with dry separate grinding, presumably because of originating precursory products at the contact points of foreign reactant particles during grinding.

A Mechanical Model of Particulate Material Based on Stochastic Process

In this paper the probability theory is applied to analyse the motions of particles in a particulate material and the mechanical model for particulate material is established. In modelling, the motions of particles are regarded as the Markov process which is one of the well-known stochastic processes. In this model the contact angles formed at contact points of particles are adopted as random variable. The basic equation of the two dimensional Markov process is derived and applied to the mechanical behaviours of particulate material. Furthermore, the strains are defined for particulate material and derived by using probability density function of contact angles and the discontinuous motions of particles at contact points.

Erosion Control of Granular Soils Using PVA

One of a number of methods used to arrest soil erosion is by chemical means. Within this category is polyvinyl alcohol (PVA), a commercially available polymer. When applied to a highly erodable granular soil in the amount of 48g/m² (400 lb/acre) erosion was resisted during a 120 min duration rainfall of an intensity of 3.8 cm/hr (1.5 in/hr). Subsequent laboratory tests showed that the mechanism involved in the success of the PVA treated soil to resist erosion allowed for rainfall to penetrate into the soil rather than running off of the soil’s surface. The PVA bonding was seen via micrographs to occur at the particle contact points but the resulting soil structure was still porous enough to allow for water infiltration. This situation was also seen to promote plant growth thereby further retarding soil erosion. A small field study on a micaceous sandy soil confirmed the laboratory findings in that the ratio of eroded soil from an untreated site adjacent to a PVA treated site was 28 to 1.

Contact recrystallization of silver halide microcrystals in solution

An extremely rapid recrystallization was found in silver halide microcrystals which were in contact with each other in solution. It appears to be characteristic of some microcrystals in coagulated suspension, which are in clear contrast with those in stable colloidal suspension whose recrystallization is due to Ostwald ripening. The direct contacts of the microcrystals were achieved by filtration, flocculation, and centrifugation. This recrystallization as well as Ostwald ripening was inhibited by some adsorptives, such as 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene or 1,1'-diethyl-2,2'-cyanine. The experimental results are described mainly for silver chloride, but identical behaviors were also found in suspensions of silver bromide, silver iodide, and their mixtures. This recrystallization is accounted for by the mechanism that the contact points of particles, acting as active centers of crystal growth, are supplied with silver and halide ions via solution by the particles apart from them as well as by parts of themselves other than the contact points. Concerning the role of the contact points, some thermodynamical interpretation is attempted in comparison with the mechanism of Ostwald ripening. Finally, the difference between the so-called contact nucleation and the above contact recrystallization is discussed.

Improving efficiency of electrostatic precipitation by physicochemical modification of the electrical resistivity of flyash

AbstractTheory and experiment show that lowered resistivity of fly ash, frequently caused by adding conditioning agents to flue gas to improve efficiency of electrostatic precipitation, is caused by capillary condensation of liquid at the contact points of ash particles, thereby providing additional pathways for flow of electrical current.

粉粒体の水中沈積物の機械的性質について

In the previous reports it was shown that the structure of sediments of solid particles in water depends upon bonding force at the contact points of particles and the bonding force consists ofadhesion and friction.In this report the relations between rheological properties and structure of sediment are described.As solid particles in water are enveloped by thin hydrated layer, the sediment is not fixed at contact points of particles but the particles can mutually be rotated and moved.The rheological properties depend on only a bonding force. The sediment is called “quasi-solid” by Rehbinder, while the agglomerate such as concrete or pellet is fixed at contact points of particles, so the rheological properties depend on both the strengthof solid and the bonding force at contact points. These agglomerate is regarded as true solid.Generally the rheological properties of solid particles settled in water shows structural viscosity and viscosity decreases on increasing shear rate.

粉粒体の水中沈積物の粒子間結合力について

粉粒体の水中沈積物の粒子間結合力について

Measurement of Adhesion Force of Powder Particles by Powder Bed Tensile Strength Method

The adhesion force of silica sand, limestone and copper powder beds were measured with the split cell type tensile strength measurement method, which had been developed by Ashton, Farley and Valentin4), and later modified by the authors. The effect of porosity change on the strength of powder bed, σz, was measured and correlated with the function of porosity, (1-e) k, which had been proposed by Rumpf5)6) in Eq. (1).These results reveal that the relation between σz and (1-e) k does not follow the proportionality which is shown in Eq. (1), and so the adhesion force at a contact point, H, is also affected quite severely by the compacting conditions as are shown in Figs. 4, 5, 6.The effect of compression force was investigated with two different compacting methods, compression and tapping. The results show that the adhesion force of the powder bed by compression is usually larger than that by tapping at same porosity as are shown in Figs. 4, 5.From these results and another consideration which the authors made4), it is suggested that the adhesion force of powder is affected not only by the factors which Rumpf analysed but also by the change of contacting condition, perhaps contact area, at the contact point of particles.