The compaction of powder has been simulated on two-dimensional numerical model by employing a digital computer. In the process of formation of the initial bed, 400 discs of equal size were dropped one by one into a container, introducing the probabillity P to make each two discs cohere in contact. The successive packing of beds by subjecting them to vibratory or tapping treatment has also been simulated by using the above mentioned bed generated. Each disc is shifted in turn to the hole which existed in the lower layer. In this process the cohesion probability P' was taken into consideration. For the data of porosity and tapping number we followed Kawakita's and Kuno's empirical equations, and it was indicated that the cohesion probability P' is closely related to the rate constant in those equations.
Kaolin minerals are used as filler and coater in paper manufacturing. In recent years the natural resources of kaolin of good quality have diminished in this country, thus necessitating the import of raw materials and products from Soviet Russia, the United States of America and some other countries. It is considered desirable that filler and coater should contain 35∼65% of -2μ particles and 70∼90% of -2μ particles, respectively. It is also desirable that the whiteness degree should be high, the suspension viscosity be low, and the abrasiveness of the screen and the cutter for paper manufacturing be low. We conducted the wet attrition-grinding of coarse kaolin minerals of low quality by making a tentative attrition-grinding machine in order to make use of the effectiveness of domestic kaolin resources, and investigated the nature of the ground material in terms of particle size distribution. In other words, we conducted the wet attrition-grinding of domestic coarse kaolin materials and studied its effects on particle size distribution of the ground material of attrition-grinding time, initial concentration, rotor's rotating numbers, and the quantity of the medium. As a result, d50≈1.5μ kaolin minerals were obtained by increasing the rotating numbers of the rotor and the quantity of the medium, and decreasing the quantity of raw materials. The observation by the use of an electron microscope shows that coarse kaolin minerals are stacked, and that they seem to get detached by attrition-grinding. We studied also the abrasiveness of the material of an attrition-grinding machine and the consuming power. In this experiment it became evident that stainless steel (SUS 27), nitriding steel, vinyl chloride, rubber, nylon and polypropylene as metallic and organic materials were resistant to abrasion, respectively. The abrasiveness of spherical glass particles used as medium is extremely low. The power needed for the attrition-grinding from 6.2μ kaolin to 1.5μ is about 400watt/kg kaolin. From the above results, we conclude that the wet attrition-grinding of kaolin minerals are industrially feasible.
The rate of decrease of mean molecular weight and the change in molecular weight distribution of PVP by ball-milling in an atmosphere of nitrogen, air or oxygen were investigated. The influence of an atmosphere on the probability of the degradation of a PVP molecule in a unit time and molecular size distribution of the polymers formed by the degradation was then discussed. If the function representing the probability a PVP molecule to be cut off in a unit time, S(M), was proportional to (M-M∞)α, α was considered to be between 1.0 and 1.5, and to be 1.0 for the case of ball-milling in nitrogen or air and to be larger than 1.0 for the case of ball-milling in oxygen. It is considered to be probable that a PVP molecule with molecular weight of 1.6×106 is broken both at the center and at the molecular weight between 6.0×103 and 1.1×104 from the end of a main chain by ball-milling in nitrogen, and at the molecular weight of 3.6×104 from the end by ball-milling in air or oxygen. It seems to be possible that the PVP molecule is broken at the molecular weight between 5.0×104 and 3.7×105 from the end by ball-milling in oxygen.
The crystallite dimension and the lattice distortion of the ground NiO and ZnO powder were measured by X-ray diffraction method, and the effects of dry ballmilling on the catalytic decomposition of H2O2 and apparent density and angle of repose were studied and excess oxygen were measured by iodometry. The following results have been obtaind (1) In the early stage of grinding process, the catalytic activation energy of the NiO powder increases by removal of the oxygen rich surface layer, and decreases as it formes, but the rate of grinding process, other active center would be increased as lattice distortion increases, and it appears that activation energy increases as excess oxygen increases. The changing of activation energy of ZnO powder with the change of excess oxygen shows symmetric behavior as that of NiO powder. (2) The frequency factor of the catalytic reaction with NiO and ZnO powder changed as activation energy changes. It shows compensation effect. (3) Excess oxygen of the NiO and ZnO powder changed as lattice distortion increases. (4) It seems that the coagulate force of the NiO powder changes as the excess oxygen changes.
Fine powdery polyethylene with extremely high specific surface area can be produced by polymerization of ethylene induced by radiation at a lower temperatures than the melting point of the polymer in bulk or in the presence of aqueous tert-butanol. The specific surface area of the polymer is mainly determined by the polymerization temperature. The polymerization temperature of 30°C, the specific surface area exceeds 100m2/g, while at 90°C the specific surface area is decreases down to 20m2/g. When the polyethylene slurry is obtained by the polymerization in the presence of tert-butanol, and is dried up as it is, the polymer has small surface area. When the drying is carried out after substitution of butanol for water, the surface area of the polymer increases to the above described values. In connection with these facts, highly defective nature of fine structure of the polymer has been reported based on X-ray diffraction and NMR measurement. The fine structure must be closely connected with the large specific surface area. The measurement of pore distribution of the polymer by isothermal capillary condensation of liquid nitrogen has indicated the presence of pores at having a peak radius of less than 100Å. The pore easily disappeared by annealing at a moderate temperature. The presence of hexane vapor remarkably accelerates the annealing. The specific surface area measured by nitrogen adsorption by the use of BET equation coincides well with the value calculated from the pore volume distribution by assuming that the pore is cylindrical capillary. These kinds of polymer are easily tend to be deformed by external stress, and they are useful materials for cold forging.
The surface of silica gels was treated by the following procedure; the silica gels were soaked into hexane solution of various kinds of alcohols, i. c. saturated and unsaturated, both of linear and branched chains, phenyl alcohols, etc. Several diols were made to be reacted upon by the respective alcohols in autoclave under high pressure and temperature, and then the solution vapours were blown out at or near the critical point of hexane. The silica gels were then washed by alcohol or benzene and hexane. The following results were confirmed. (1) These surface-treated silica gels were organophilic, except those which were treated by diol in the test of the preferable property of dispersion into the mixed media like water∼hexane. (2) The surface group of treated silica gels were assigned as the alcohoxy group through the elemental analysis and argon surface area and also the silica gel treated by the unsaturated alcohol still held the double bond in the surface group. (3) The silica gel showed the hydrophilicity after treatment with diol, since a hydroxyl group of diols are reacted upon by a silanol of the silica gel. (4) Silanols of the silica gel were not reacted upon by tertiary alcohols like tert-butanol or tert-pentanol. (5) The decrease of argon surface area after surface treatment was interpreted by the existence of the micropores covered by the surface group.
The surface properties of the organophilic silica gels were investigated by the adsorption of argon at 77°K, of water vapour at 288°K and of n-heptane at 273°K and the heat of immegions of water and n-heptane, respectively, on the samples which the native silica gels were treated by methanol, ethanol, butanol, pentanol, hexanol, octanol, decanol, dodecanol and tetradecanol. The following results were confirmed: (1) Since the BET surface area of argon and of water on the native silica gel showed good agreement, and the one of argon on the activated carbon agreed with the one of n-heptane, the argon molecule could be adsorbed on both the organophilic and the hydrophilic surface. (2) The argon surface areas on the surface-treated samples showed remarkable decrease, increasing the carbon chain of alcohol. The water surface area showed remarkable decrease in comparison with the argon surface area on each sample. (3) The surface area from argon adsorption on the surface-treated silica gels showed the sum of the surface areas from water and from n-heptane, respectively. (4) The heat of immersion in water and n-heptane on the surface-treated silica gels were well-explained by using the respective surface areas from water and n-heptane.
In the preparation of impregnated catalyst composed of alumina carrier and cobalt salt the mixture of alumina or alumina hydrate and cobalt salt is calcined at the temperature between 500°and 800°C. From the theoretical and practical viewpoints it is important to clarify the state of cobalt compounds in the prepared catalysts. In the present study it is shown that the formation of cobalt aluminate begins at temperature higher than 850°C, while at lower temperature the oxidation or reduction of cobalt oxide occur, as in the case Without alumina. DTA or TGA measurement and high temperature X-ray analysis were carried out during the heating process for the mixture of α-Al2O3, γ-Al2O3 or Al2O3·3H2O and CoO, Co3O4 or Co(CH3COO)2·4H2O. The heated mixtures were chemically analysed to determine the amounts of Co2+ and Co3+. From the results obtained it will be concluded that the main reaction is the oxidation below 800°C, the oxidation and the reduction are in equilibrium between 700°and 900°C, and the reduction and the solid-state reaction occur in parallel between 900°and 1100°C, then the latter reaction becomes predominant above 1050°C. The beginning temperature of the solid-sate reaction has been affected by the presence of water vapor, while the rate of reaction would be affected by the diameter of reactant particle formed at the reaction temperature by the decomposition of the starting materials.
The effects of grinding and heat treatment on the structure of CuFe2O4 have been investigated by X-ray diffraction analysis. The sample of tetragonal CuFe2O4 was ground in water in a ball mill at room temperature for varying times up to 190hr, and cubic CuFe2O4, up to 70hr. From the results of the X-ray diffraction analysis, it has been observed that the tetragonal structure was gradually transformed into the cubic one with increasing grinding time, and that the reverse transformation did not occur. In both cases, the strain in the lattice increased and crystallite size decreased with grinding time. This fact indicates that lattice imperfections such as dislocation and stacking fault increase with grinding. It can be considered that a cooperative alignment in the tetragonal CuFe2O4 is gradually destroyed with an increase in the lattice imperfections, and that the tetragonal structure has consequently been transformed into a cubic one. When each of the samples of the ground cubic CuFe2O4 was heated for 4hr at 350°C, what was ground for a short time has been transformed into the tetragonal structure, while those samples which have been ground for a long time have not been transformed. When each sample of the CuFe2O4, which had been substantially transformed from the tetragonal into the cubic structure by grinding for a long time, was heated at varying temperatures up to 800°C for 2hr and then cooled slowly, the reflection line (311) of the cubic structure remained unchanged below 500°C. At the heating temperatures above 600°, the transformation from the cubic into the tetragonal structure progressed with rising temperature. The heating temperatures above 600°C closely corresponded to those of the recovery process of the induced strain and the reduced crystallite size.
The authors discuss in the present paper on the following facts. (1) The passing phase of size distribution has been investigated concerning the impact crushing and the static compressive crushing. In the region of grinding limit, the behavior of size distribution is discussed. (2) The remarkable tendency of specific surface increase is recognized between the impact crushing and the static compressive crushing. (3) The aparent difference is recognized between the specific surface increase measured by means of size distribution method and that measured by means of air permeability method. (4) We obtained Eq. (10) from the specific surface increase by those two methods of measurement.
The aqueous slurries of salicylic acid and sodium salicylate containing various kinds of binder, e.g. gum arabic, gelatin, polyvinyl alcohol, carboxymethylcellulose, methylcellulose, polyvinylpyrrolidone, tragacanth and sodium alginate, were spray-dried using a centrifugal wheel atomizer. Almost all of the agglomerated products are fine granules having a diameter of 15-100μ, compared with 1-8μ for the original salicylic acid, and are fairly free flowing. It is the case with polyvinylpyrrolidone and gum arabic products. The particle properties, such as diameter, true density, sphericity and surface area were measured, all of these being strongly influenced by the concentrations of sodium salicylate and binder. The surface topography of the products was studied with a scanning electron mciroscope. Gum arabic and polyvinylpyrrolidone products had smooth surfaces without holes or craters. Granules borne with other binders showed characteristic surfaces having craters of 5-10μ. The analysis of the X-ray diffraction patterns and the infrared absorption spectrum of products showed that gum arabic and polyvinylpyrrolidone granules still contained both salicylic acid and sodium salicylate, in contrast to the cases where other binders were used, where only sodium salicylate remained, the salicylic acid having sublimed. Gum arabic and polyvinylpyrrolidone products are microcapsules containing salicylic acid and sodium salicylate of grain size of about 200-800Å, amorphous contents of about 50-80% and grain size of about 130-170Å, polymorphism including original crystalline form of 3-20% respectively. The thickness of the encapsulating film is 1-3μ. Finally, the change in appearance of a drying slurry droplet is discussed and two typical drying processes, namely agglomerated crust and encapsulating film formation, are described.
The percolation of fine particles through packed bed of coarse powder was studied in the vibrating state. CaCO3, α-Al2O3, glass beads, nylon powder, graphite and potato starch were used as sample powders. The percolation curves seemed to consist of two parts. In the initial stage, the percolation weight increased rapidly. This is considered to show the process where fine particles tend to drain through every hole of the packing structure of coarse particles without mutual interactions between them. Then, in this region, the percolation rate increased as the particle size ratio of fine powder to coarse powder decreased. However, the percolation behaviors are dependent upon the kinds of materials and the properties of particle surface. In the latter region where the increasing rate of percolation weight is very slow, it is considered that the movement of the fine particles through the packed bed is affected by the adhesion of fine particles to the surfaces of coarse powders. With combination of fine and coase powders, the percolation curves are measured in various amplitudes of vibration. There are critical points at which the percolation weight in the initial region decrease rapidly with the decreasing amplitude. It is considered that the kinetic energy of fine particles at this critical point corresponds to the adhesive force between the fine particles and the coarse particles. This technique is considered to be available for the measurement of interaction force between the particles of different materials.
An experimental study was carried out on the flow pattern of particles at the cross section of a horizontally rotating cylinder with twenty-three kinds of particulate systems of different characteristics. The following relations were obtained as the experimental results. (1) The width of the static zone was expressed with the volumetric charge ratio of particles F/V(-) and the mixing Froude number N2R/g(-) in the following equation. (h/R)=[a-b(N2R/g)](F/V) where, h is the width of the static zone (cm), R is the inner radius of the cylinder (cm), N is the rotating speed of the cylinder (1/min), F is the total volume of particles charged in the cylinder (cm3), V is the inner volume of the cylinder (cm3) and g is the acceleration of gravity (cm/min2) respectively, and a and b are the experimental constants. (2) The following relation was obtained between the mean circulation time of particles T(sec) and the rotating speed N'(1/sec) for the range of rotating speed less than one revolution per second or so. N'T=0.77(F/V)1/2
In order to discuss the axial segregation of solid mixture in a horizontal rotary vessel, the experiments were carried out by using a horizontal conical vessel of 12.5cm inside diameter of one end, where the diameter of the vessel is a minimum, 24.5cm in i. d. of the other end, where the diameter is the maximum, and 30cm in length. As materials, three kinds of mixtures were prepared. As the result of the experiments, the larger particles of silica sand mixture having size distribution move to the point of the maximum inside diameter, and the smaller particles segregate near the end of the maximum diameter of the conical vessel at lower speed of rotation (at 20≤n<80 r.p.m.). The smaller particles migrate toward the point of smaller diameter at 80<n≤100 r.p.m., and this tendency of the segregation is contrary to the result of the segregation at n<80 r.p.m.. Most of spherical silicagel particles of the binary solid mixture which consists of spherical and irregular silica gel of nearly the same size are segregated near the end of the minimum diameter at 15≤n<80 r.p.m. and the irregular particles are collected at the point of smaller diameter at 80<n≤100 r.p.m.. The irregular particles of the binary solid mixture, whose diameter is larger than that of the spherical particles in Weigels diameter, are segregated near the end of the minimum diameter of the vessel at n=15 r.p.m.. At about 80 r.p.m., the degree of these axial segregations decreases. These experimental results are discussed on the basis of a few characteristics of cascading particles in a rotary cylinder and the shape of the conical vessel.
Hereunder is presented a report of studies made of the table feeder, particularly in respect of the mass flow rate, step response, and fluctuation. The mass flow rate is found to be in proportion to the angular velocity of the table when the centrifugal effect Z is smaller than 0.005. However, for Z beyond this value, the shape of the powder bed must be taken into consideration for accurate prediction of the mass flow rate. This problem has been studied based on our previously published theory. As to the dynamics, it has been found that, under certain operating conditions, the response of the mass flow rate to the step change in angular velocity of the table is of derivative nature, similar to that obtained with the scraper position as input. The fluctuation in mass flow rate is attributable to the inclined installation of the table. However, this fact suggests that the feeder may be used as a sine-wave generator for powder flow rate studies. From this standpoint, the experimental relationship between its amplitude and the angular velocity has been studied analytically.
The mechanical properties of powder beds were examined, with special attention paid to the movement of individual particles. The powder used was lactose, which was formed into a cylindrical green body, using compacting die. Direct and repeated compression tests were carried out using a triaxial compression apparatus. Some interesting results have been obtained as follows. (1) A concave type stress-strain curve to strain axis was obtained. (2) The virgin curve having remarkably different style from non-virgin relations was observed in the repetitious compression tests. (3) The deformation process could be divided into five typical stages depending on the movement of particles. The results (1) and (2) mentioned above seem to have been caused by the difference of stress distribution between the compaction state in the compacting die and the compression state in the triaxial cell, which causes sliding by the breaking of bridge-like weak structures in powder bed. These phenomena can not be explained fully by the common rheological model having spring, dashpot or slider elements. In order to describe these phenomena, a new mechanical model is presented by the authors based on the behavior of particles during these deformation process, which has new irrecoverable element as follows. ε=ε0(1-e-ασ) where α is experimental constant and σ, ε are stress and strain respectively.
In order to investigate the mechanism of binding silicate as additive, the tablets were measured with respect to its hardness, which had been compressed with several kinds of magnesium aluminosilicate, and the process of its compression was observed. As the result of this experiment it has been ascertained that the hardness of the tablet is related to the specific surface area and to the apparent specific volume of magnesium aluminosilicate, and that the tablet itself becomes higher in hardness as the additive becomes lower in particles size. In the process of compression the secondary aggregate particles are considered to be distracted and to get dispersed into the base. The scanned electron micrographs will substantially represent the mechanical action of the secondary aggregate particles. The magnesium aluminosilicate is considered to act as binder by its porous fine particles in fiber forms increasing the number of contact points, and making interparticle crosslinkage among the base particles, and forming the interparticle bridge after the occurrence of plastic deformation, and further making mechanical nets of finely divided magnesium alminosilicate itself.
The preparation of pelletized catalyst from the powdered raw materials is especially important in making solid catalysts for industrial use, and it is desirable from the practical point of view to elucidate the dependence of the mechanical strength of pellets on the pelletizing process. In the present study it is shown that the mechanical strength of zinc oxide-chromium oxide catalysts prepared by the extrusion process is dependent upon the water content in the paste and upon the amount of copper added to the paste, however the surface area and the pore size distribution of catalysts are dependent not so largely upon their strength as they might be in the case where alumina catalysts are prepared by the tabletting procedure. Zinc oxide was mixed with the 30% water solution of chromium trioxide and the paste thus obtained was extruded following the addition of copper compound. After drying to reduce the water content in the pellet below 1%, the mechanical strength of pellets was measured by compressing them in the direction of their cylindrical axis, and by compressing them in the direction of their radius, and by subjecting them to tensile test. From the results obtained it would be concluded that the measurements of the mechanical strength carried out by these three different methods show the deviations not to be so different from each other. It is clarified that the strength of ZnO-Cr2O3 catalysts depends upon the water content during the extrusion process, and that it is affected by the addition of copper and also by the reduction in the atmosphere where the catalysts are employed for industrial purposes.
The present paper is concerned with the effects upon the variation of plastic viscosity, of several properties of Kaolins. Six kinds of Kaolins were used. The plastic viscosity of Kaolin fluids increased in the order of the Kaolin A<the Kaolin B<the Kaolin C<the Kaolin E<the Kaolin F. The variation of the plastic viscosity of Kaolin fluids is considered to be connected with the apparent specific volume, the angle of repose, the specific surface area and the amount of oil absorption etc. of Kaolins. On the other hand, the authors paid attention to flow curves, yield values and solid fraction in limiting concentration, φvc, in Fig. 8, of Kaolin fluids. The variation from a Newtonian fluid increased in the order of the Kaolin A<the Kaolin (A+F) the Kaolin F.
Accurate classification of very fine powder is becoming a subject of wide interest in various fields of industry. In these days, water elutriator and batch settling classifier are used for this purpose. In order to make accurate classification by the use of these devices, it is necessary to understand the behavior of particles having wide size range in suspension. However, the great majority of works on sedimentation phenomena in suspension has hitherto dealt with particles of uniform size. In this investigation, classification of fine powder by batch settling classifier is undertaken to clarify the sedimentation phenomena of fine particles in suspension. On the basis of this experimental results, the following equation is proposed for the settling velocities of particles having wide size range in suspension. u=us·ε2·10-1.82(1-ε)·[Dc]-n where the exponent n is a function of Reynolds number of particles and size distribution.