A new process for preparing particles of superconducting oxides was developed by using an aerosol flow reactor in which aqueous solutions of corresponding metal nitrates are atomized and their droplets are evaporated and thermally decomposed. The particles obtained from this process are spherical and their size can be controlled by changing the concentration of the aqueous solutions. For the Y-Ba-Cu-O system, the particles having an orthorhombic YBa2Cu3O7-x phase can be formed directly at the decomposition temperatures from 900 to 1000ºC. The bodies sintered from these particles show the offset temperature of the superconducting transition at 87 K. For the Bi-Ca-Sr-Cu-O system, the superconducting particles of the Bi2Ca2Sr2Cu3Ox and Bi1.8Pb0.2Ca2Sr2Cu3Ox compounds were prepared directly. The crystalline phases of the particles were found to be very sensitive to oxygen pressure in the carrier gas as well as to the decomposition temperature. The sintered bodies from the powders of Bi1.8Pb0.2Ca2Sr2Cu3Ox had onset temperature of 110 K and offset temperature of 80K.
†This report was originally printed in J. Soc. Powder Technology, Japan. 26(3), 146-150 (1989) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
A new method for forming a ceramic membrane was devised. Ultra-fine particles synthesized by thermally activated CVD (Chemical Vapor Deposition) were deposited on the surface of a porous ceramic supporter by electrostatic force and sintered in an inert gas atmosphere. The ceramic membrane made by this method is available for ultrafiltration because it has very fine pores of about 0.04 micro-meter in diameter but a large porosity.
†This report was originally printed in J. Soc. Powder Technology, Japan. 26(3), 169-173 (1989) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
Generally a slip-casting process is closely related to the flocculation state of particles. The present investigation was undertaken in order to understand the relationship between the flocculation state of the particles and the packing structure on the surface of gypsum mold. The flocculation state of particles in an Al2O3 -slurry was discussed on the basis of rheological and sedimentation behavior as a function of dispersant concentration. It was found that these properties could be classified into three modes. On the slurries, the rate and pressure in the absorption of water, the increase in the packing layer thickness, and the porosity and permeability of the packing layer were measured in order to explain the packing structure on the surface of mold. From these measurements, the relationship between the flocculation state of the particles and the packing structure could be modelled.
†This report was originally printed in J. Soc. Powder Technology, Japan. 25(9), 585-590 (1988) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
Contamination during fine grinding is an important problem for a raw powder of newly developed materials. Wear behaviors of grinding media, which were made of steel, alumina and zirconia, were examined during fine grinding using a vibration ball mill. Ball wear was nearly proportional to a specific surface area of ground products. It was supposed that the wear in wet grinding is more than in dry grinding, because wet grinding is more effective for fine grinding. Wear was effected by the materials of the grinding media. Ball wear, which was made of zirconia, was the least of three kinds of balls, that were used. Linear wear was not as much as ball wear.
†This report was originally printed in J. Soc. Powder Technology, Japan. 26(6), 411-416 (1989) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
Baker's yeast suspended in pure water was disintegrated by the agitator bead mill using glass beads having a diameter of 0.5 to 2.0 mm. ADH (alcohol dehydrogenase) was released faster than protein and G-6-PDH (glucose-6-phosphate dehydrogenase), and a concept of the selective release of enzyme was defined. The final weight of the protein released and the activities of enzymes, the release rate constant for protein and ADH, and the release selectivity between the protein and ADH were dependent on the bead size, the weight of beads and the agitation speed. The optimum condition for release existed for each operation parameter. The electrical conductivity of the yeast slurry had good correlation with the amount of G-6-PDH and protein released. This result indicated that the degree of release for these substances could be estimated from the measurement of electric conductivity.
†This report was originally printed in J. Soc. Powder Technology, Japan. 26(6), 424-429 (1989) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
Experimental and theoretical studies of particle deposition on a surface composed of different materials (copper and polyethylene) were conducted. Deposition of charged aerosol particles was affected by a localized electrostatic field created by the contact potential difference between the metal (copper) and the dielectric material (polyethylene), and the particles charged with positive polarity deposited mainly on the polyethylene surface, which was charged with negative polarity. This fact suggests that the deposition is caused by the Coulombic force between the surface and the particles. The deposition flux was larger for smaller particles because of the larger effect of the electrostatic field. Aerosol particles with negative polarity do not deposit on the polyethylene surface because the surface charge is negative. The deposition is, however, enhanced on the neighboring copper surface. This is explained by the fact that the electrostatic field vector directs to the main stream. It is found that the agreement between calculated results and experimental data is better for the case of assuming intrusion of the electric charge into the polyethylene than for that of assuming fixed interface charge.
†This report was originally printed in KAGAKU KOGAKU RONBUNSHU, 14(5), 655-662 (1988) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Chemical Engineers, Japan.
The control characteristics of the moisture content within a product (dried sardine powder called "fish meal") are investigated for an in-direct heating continuous dryer. The system is described by a state space model, and the controller is designed based on the discrete I-PD control scheme. State variable is estimated by applying the steady or extended Kalman filter because the moisture content measured by an infra-red hygrometer contains a large amount of random noise due to the rough surface of the powdery product. Satisfactory control performance is achieved for a pilot-scale continuous dryer.
†This report was originally printed in J. Soc. Powder Technology, Japan. 25(10), 654-659 (1988) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
To study the shape separation mechanism of solid particles of differing shapes on a rotating conical disk with a spiral scraper, the behaviors of particles travelling along the scraper wall were discussed by using some cylindroid particles differing in cross-sectional shape. In this paper, for the simulation of the particle's motion along the scraper, three types of the motion were proposed and combined each other. Simulations were carried out under various operating conditions, and the values of θs (: the vectorial angle at which a particle leaves the scraper wall) were calculated for each particle. The following results were obtained. (1)θs decreases with increase in the shape index k over a comparatively wide range of k, where k is the ratio of the semi-minor axis b to semi-major axis a of an ellipse at cross section of a cylindroid. The correlation between θs and k is considerably affected by the rotating speed of the disk n and inclination angle of the disk surface β. (2) The particles of differing shapes could be effectively sorted along the scraper on the disk. (3) θs values estimated by the simulation agree approximately with the ones observed for various cylindroid particles.
†This report was originally printed in J. Soc. Powder Technology, Japan. 26(1), 12-22 (1989) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
A vibrational tester for measuring the dynamic physical properties of powders has been developed. The tester system consists of an electromagnetic vibrator with a controller for frequency and acceleration, a solid sphere sensor attached to a load transducer, and a microcomputer. It has been shown that the characteristic curves, when measured as the relationship between the frequency and the vertically transmitted force through the powder bed, are sensitive to changes in the physical properties of the powders. The mixing effect of a small amount of fine powder on the change in the peaks of the characteristic frequency has been measured using two different mixers.
†This report was originally printed in J. Soc. Powder Technology, Japan. 25(9), 609-614 (1988) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
The media motion in a ball mill is simulated using a numerical algorithm known as the Discrete Element Method. The motion of the charge is modelling by considering the forces acting at each contact point during a collision and following the movement of individual balls as per Newton's law. First, experimental verification of the model is shown. Then a few simulated results are shown for some interesting cases. For the first time it is possible to get information about the distribution of energy in the collision between balls. Also the cataracting and cascading motion of charge in large mills can be simulated accurately with this simulation program.
Hydrothermal and commercial barium titanate powders were examined for undesirable impurity phases. Compositional differences in the powder were evaluated using x-ray diffraction (XRD), x-ray fluorescence (XRF), and x-ray photoelectron spectroscopy (XPS). A barium-rich impurity phase, virtually undetectable by XRD, was detected via XPS. Barium impurity phase peaks were detected at binding energies @1.5 eV higher than those characteristic of barium in a barium titanate bonding state for both the Ba 3d and Ba 4d transitions. Simple curve-fitting techniques were used to quantify the percentage of barium in a barium titanate bonding state versus another barium bonding state for each set of doublets. The barium impurity bonding state accounted for 20-50 mol% of the barium detected by XPS.
For well mixed compacted powders such as those used in the Pharmaceutical and food industries, the assay variation in the composite particles is a bell shaped Gaussian curve with a mean assay of the bulk powder being compacted and a standard deviation proportional to the ratio of the powder to particle size raised to the 3/2 power divided by the volume fraction locked. With increasing compacted particle size, the standard deviation grows smaller. The Ferrara point, for these larger particles, becomes the peak of the Gaussian curve and differs in location from the Ferrara point of the smaller particles.
The influence of stirring speed, solids concentration, media density and size on grinding in a CoBall mill is described. The relationship between the product size and the process parameters was determined. It was observed that the product fineness is dependent on the balance between energy input and the ease with which the slurry-media (grinding bed) can be fluidized. It was found that the capacity and energy requirements are the decisive factors in optimizing the process parameters. Media colour, wear rate and separation problems would exert appreciable influence on the choice of grinding media. Very fine particles can be produced at a high throughput under optimal grinding conditions, but the associated rapid rise in temperature may be a hindrance in some applications.
With the data gathered from an experimental silo, operating with two different kinds of bulk solid (cohesive limestone powder and free-flowing plastic pellets), it is shown to what great extent the geometry of the transition from hopper to feeder influences flow profile and thus the stress pattern within the hopper. The optimal geometry for achieving mass flow and even withdrawal of a bulk solid over the entire outlet area depends on the bulk solid's flow properties and, in the case of the cohesive limestone powder, must be closely adhered to, as the flow pattern of this particular bulk solid is very sensitive to any deviations. Furthermore, it is shown how the load acting on the feeder can be ascertained. While the power required of the feeder for bulk solid removal in the discharging condition can be satisfactorily calculated from Jenike's theory, some well-known analytical methods available for the filled condition of the silo provide results which are too imprecise. The assumption of hydrostatic conditions in the hopper leads to stress values which are several times greater than those actually measured in the experimental silo. With the help of the empirically based equations, DIN1055, Part 6, one can find acceptable solutions for the order of magnitude and for the tendency of the stresses acting on the hopper walls. How one might determine the load on the feeder from these solutions needs further looking into. Through basic physical considerations, the dependency of the force required for removal of a bulk solid from under the outlet on the vertical load acting on the feeder, was found to be of a simple nature, from which an upper limit can be calculated. This was confirmed by measurements made on the experimental silo.
Abstract The Laser Chemical Vapour Precipitation (L-CVP) of Si3N4 powders from mixtures of halogenated silanes and NH3 has been studied. The reactant gases were mixed at varying position in the laser beam, thus preventing low temperature reactions. The Si3N4 was collected and separated from the waste product, NH4Cl, by electrostatic precipitation. A major problem in utilizing SiHCl3 and SiCl4 is their poor absorption of radiation from CO2-lasers. SF6 and SiF4 have been explored for possible use as an inert sensitizer. Silicon can be prepared from SiH2Cl2 without the use of a sensitizer. The diameter of the Si3N4 particles is typically between 15nm and 110nm dependent on the process conditions.
The combined collection of fine dusts and the sorption of gaseous pollutants at high temperatures have been experimentally and theoretically investigated. The results of the fractional separation efficiency measurements and the experimentally determined breakthrough curves have revealed that excellent SO2 and HCl sorption characteristics exist under conditions which also yield high particle collection efficiencies. New concepts have been developed to describe the measured fractional collection efficiency curves in the inertia dominated size range, which are based on particle trajectory calculations using a simple flow model. During the sorption, conversions of over 80% can be achieved when using a reactive bed consisting of pellets agglomerated from fine limestone particles. The application of such beds in a counter-current mode can even yield solid conversions of nearly 100%. The mathematical prediction of the conversion time behaviour under differential conditions and the breakthrough characteristics in a fixed bed are in reasonable agreement with the experimentally measured data.