In handling powder materials it is necessary to pay attention to their internal friction as one of their most important properties. The direct shearing test is a simple and useful method to measure the internal friction. However, the behaviours of powder in the direct shearing test procedure are not yet certain, because of the complicated behaviour of particles arising from the shearing action in the powder bed. It must be admitted in any case that the correlation between the internal friction and the σ-τ relation has not yet been sufficiently understood. This research was undertaken to understand these behaviours of particles in the shearing procedure. For this purpose, these contributions to the σ-τ relation in the distribution of applied normal stress in the powder bed, the weight of the powder under the test, the shearing rate of the test, and the consolidation of powder, etc, were examined with the direct shearing test. It is concluded from the result of the examinations that the σ-τ relation has material contributions to the change of the particle arrangement in the powder bed in the shearing procedure, and that the deviation of the σ-τ relation from the Coulomb's law τ=μσ+c is due to the relaxation of stress in the shearing plane resulting from the rearrangement of particles in the powder bed. The σ-τ relation should be expressed with the decrease of effective normal stress in the shearing plane in the shearing procedure. τ=μσ(1-u/σ)+c where μ; Internal friction u; Decrease of effective normal stress c; Cohesive force Discussion on the correlation between the amount of u and the shapes of σ-τ relations has been made also.
In order to study fundamentally the nature of powder, the preparation of particles of uniform size is most important. But it is difficult to preparate the particles of uniform size. For the one of the methods to obtain the powder of uniform size the mixture of cadmium sulfide and various additives was heated. Cadmium sulfide prepared from cadmium nitrate solution by sodium sulfide solution was used as starting material. Halides of lithium, sodium, and potassium were used as the additive agents. Cadmium sulfide (The starting material) and alkali halide were mixed well and heated in a test tube at 350 to 500°C for 2 hours. The shape and size of cadmium sulfide particles were observed with an electronmicroscope, and the surface area was measured by BET method of nitrogen adsorption at boiling point of liquid nitrogen. The following results were obtained; The shape of cadmium sulfide particles tended to be affected by halogen, but slightly by alkali metal. Alkali halides had an effect on cadmium sulfide particles below their melting point. The spherical or nearspherical particles were obtained by heating the mixtures of the starting material and alkali iodide or bromide. The particle sizes that were calculated from the surface areas were nearly equal to the apparent sizes observed by electronmicrographs. And so, it is suggested that these particles had no pore, but smooth surface. The uniform and spherical particles of cadmium sulfide of particle size 100 to 2000mμ were obtained by the variation of the mixing ratio of the starting material to the additives, and by the adjustment of the heating temperature.
The mixtures of aluminum s-butoxide, titanium tetra-butoxide and tetraethyl orthosilicate in different molar ratio were hydrolyzed in aqueous alcohol. The precipitates were dried, and the growth and transformation of the crystals at calcination were estimated by means of an X-ray diffractometer. The surface properties of the oxide powders were studied by heat of immersion and adsorption of nitrogen and water vapor. The surface hydrophilicity was calculated as dependent on the ratio of the hydrophilic surface area determined by water vapor adsorption to the total area determined by nitrogen adsorption. The variation in the heat of immersion and in the surface hydrophilicity in accordance with the composition of the material has been discussed.
The oxidation processes of Fe(II) hydroxo-complexes to α-, β-, γ-, and δ-FeOOH and Fe3O4 in aqueous solutions were investigated by processing measurements with infrared, far infrared, and Mossbauer spectra and X-ray diffraction of oxidation products. The effect of oxidation rate and addition of Cu2+ or PO43- ion on the oxidation of Fe (II) hydroxo-complexes were also studied. It has been found that in the present experimental condition the process of oxidation depends on the pH-value of solution as follows: in basic solution (pH 12.5∼13.5) Fe(OH)2→α-FeOOH, in the slightly acidic solution (pH 6∼6.5) β-Fe2(OH)3Cl→Green rust I→γ-FeOOH, and in neutral or slightly basic solution (pH 7∼8) Fe(OH)2→Fe3O4 and β-Fe2(OH)3Cl→Green rust I→Fe3O4. The infrared spectra of Fe(OH)2 and Green rust I, an oxidation intermediate, have been obtained. The rapid oxidation of Fe(II) hydroxo-complexes in solutions with the addition of H2O2 results in the formation of δ-FeOOH. The oxyhydroxide has also been obtained by removing water from the Fe (II)-complexes, and leaving them in air to be oxidized. The broad absorption band at 450cm-1 has been shifted for 480cm-1 with the increase in size of δ-FeOOH crystallite formed by the oxidation of Fe(OH)2 with H2O2. In the presence of Cu2+ or PO43- ion, freshly precipitated Fe(II) hydroxo-complexes are oxidized into amorphous δ-FeOOH with air in solutions. This transformation is considered to have been caused by the catalytic effect of Cu2+ or PO43- ion in the oxidation of Fe(II)-complexes.
Since metakaolin obtained by dehydration of kaolin minerals at a temperature ranging from 500°C to 800°C shows high electric resistivity, and has stabilizing effect on vinyl chloride resin, it is used as fillers of vinyl chloride for making insulated electric wire. In view of the fact that metakaolin of good quality has not yet been available in Japan, and so for most of its supply its importation from abroad has been relied upon, fundamental research attempts have been made to find a method of producing metakaolin of fine quality from Japanese kaolin minerals, the products of Zeeklite Chem. Mining Co. As a result of experiments on dehydration of Japanese kaolin minerals using thermogravimetric analysis, differential thermal analysis and X-ray methods, it has been made evident that the reaction is of first order. Some of the Japanese kaolin minerals dehydrated at a temperature of 800°C, surpass the imported metakaolin in whiteness. The particle size of the dehydrated product is somewhat coarser than that of the raw materials. Several properties of the metakaolin-vinyl chloride compounds were measured by JIS K 6723 method, elucidating that Japanese metakaolin from the products of Zeeklite Chem. Mining Co. can be used as fillers of vinyl chloride for insulated electric wires.
For the measurement of particle size distribution the microscopic method has unequaled advantage over all other methods in that it can simultaneously determine both the particle size and the particle shape. Availing ourselves of such advantage of the microscopic method (in this experiment Shimadzu's Particle Size Frequency Analyzer for Microscope, Type SF-10 was used) we have been enabled to obtain the particle size distribution respecting both the length diameter and the mean diameter of the particles, and to obtain at the same time also the particle size distribution respecting Stokes' diameter by using the specific gravity balances, (in this experiment Shimadzu's Recording Sedimeter Type RS-11 was used). These experiments have afforded data to discuss how particle size disptribution is subject to the effect given by the particle shape. Among the sample powder used in these experiments will be mentioned α-alumina, glass ball and oxide iron.
The effects of packing structure of powder on the angle of repose were studied. The results are as follows: the angle of repose increases when the powder is packed more densely, the angle of repose is small when the particles are spherical, becomes larger with an increase in irregularity of the particles' shape, and attains its largest with the needle like particles. This effect appears to be due to the entanglement of particles. When the sample is composed of spherical particles of uniform size, the angle of repose is especially small. In order to examine this phenomena, model experiments with steel balls were used. The results show that a little irregularity or hole in the packing structure gives a great effect on the angle of repose. Moreover, it was found that the friction force between the particles and their substratum on which the particles were heaped had great influence upon the occurrence of the irregularity in structure. The friction force between the powder bed and the material of substratum and the angle of repose of powder were measured. The results show generally an increase in the angle of repose with increasing friction force up to a certain value, after which there is a small increase of the angle of repose with increased friction force. An experimental equation was obtained showing the relation of these values.
The angles of repose of spherical glass powder and α-alumina were measured in various aqueous solutions in order to examine the effect of interparticle force on the angle of repose. NaCl, Na-pirophosphate, Na-polyphosphate and Na-polyacrylate were used for this purpose. The angles of repose were very small within a certain range of concentration of dispersing agents, for example, 10-4∼10-3mol/L of Na-pirophosphate. The measurements of apparent particle size and sedimentation volume confirmed that the powder particles were dispersed in these solutions. In the solution of NaCl, the angle of repose increased slightly with increase of concentration. Abnormally high values were obtained with Na-polyacrylate. In the state of dispersion, for example, in 10-3mol/L Na-pirophosphate, the angle of repose decreased with the decrease of particle size and seemed to be constant in the range smaller than a certain particle size, increasing with the decrease of particle size in the solution of flocculating agent. In these two states, however, the angles of repose became nearly similar as the particle size increased. According to the Verwey-Overbeek theory, the interparticle potentials were obtained by the measurements of ζ-potential. From these results it was explained that the angles of repose were very small and almost constant in the range where the repulsive force were larger than the weight of a particle and that they took another constant value where the weight of a particle were larger than the attractive force.
(1) Hereunder is given a report of experiment made to investigate the effects of having added small amount of glidants, silicic acid and magnesium stearate, on the repose angle and the bulk volume of potassium bicarbonate with different moisture contents. The phenomenon that the repose angle and the bulk volume increased with an increase in moisture contents became less observable by the addition of the glidants. (2) The electrostatic behavior of potassium bicarbonate and sodium bicarbonate was examined by placing them in the electric field. These bicarbonates were found to be positively charged, which disappeared by the addition of the glidants. (3) The adhesive characteristics of each of magnesium stearate and silicic acid in the mixed powder system with sodium bicarbonate were examined by means of an optical microscope as well as a scanning electron microscope. Silicic acid was found dispersed uniformly but intermittently over the surface of the bicarbonate salt, whereas magnesium stearate formed a replica-like film.
Segregation of particles is observed frequently in the treatment of powders. It is necessary sometimes that such segregation will be prevented. A report is made, in the present work, of the kinetic study that was carried out of the segregation process of the binary particle system. First the term“the segregation speed”was proposed to express a quantitative concept as to the possibility of segregation. The relation of the segregation speed and the impulsive force which suffers the packing layer, was studied. The segregation speed was experimentally determined by a pair tapping experiments as shown in Fig. 1(c) and (d). By the speed light picture, the fall-down velocity of the container could be determined, then the impulse can be calculated from eq. (7). The segregation speed may be proportional to the difference between the impulsive force and the surface frictional force among the particles. The relation between the impulse and the segregation speed is shown in Fig. 4. The critical value of the particle diameter ratio r/R was about 0.57 which was determined by the extrapolation of different impulse data as shown in Fig. 5.
When the powder stored in a cylindrical vessel is being tapped, the powder particles flow in a manner somewhat similar to that of convection of boiling water. The particles located around the central axis of the cylinder tend to bounce up more briskly than those located closer to the vessel wall, because of the friction between the particles and the wall. About the cylinder axis, the vacancies made by the relative movement of the powder by the tapping are immediately filled up by the centripetal flow of the powder particles. Consequently, the ascending flow of particles occur around the axis and the descending flow occur on the contrary near the vessel wall. Moreover the rotation of particles is observed which is due to the velocity gradient of the descending powder flow. The segregation of powder particles is presented as occurring in the vessel, and as the result, it is shown that only relatively larger particles are found in the top layer, and only small particles are found in the bottom payer, and it is mixture of large and small particles that is found in between. Percolation was once believed to be the sole mechanical factor for particle segregation. The authors propose in this paper a closer approach to precise explanation that the real segregation mechanism is in the combination of percolation in the top layer and of ascending and descending flow of particles. The authors point out also an additional factor as pertinent to the segregation, in particular, that larger particles are slower than smaller particles in their descending speed.
When vibration is given to binary mixture of coarse and fine granules, the coarser granules are gradually collected in the upper layer and so the finer granules are in the lower layer. To find the amount of such segregation, the coefficient of the segregation was defined, and the experimental formula was proposed to relate this coefficient to the vibration time. In our experiments, spherical glass beads were used for samples, and the vessel used for the experiments was a plastic cylinder. Ten plastic rings, each with inside diameter of 3cm and height of 1.7cm, were piled together to form a cylinder. Coarse granules were first poured into this cylinder, and then fine granules were poured over the coarse. After that, vibration was given the cylinder vertically. The higher the weight ratio of the coarse granules to that of the fine rose, the more easily their segregation took place. Depending on the difference of granular size and the vibrating condition, the state of segregation varied considerably.
The measurements of absorption spectra of various powdered materials were carried out by means of a microspectrophotometer. The conditions under which the microspectrophotometer was being operated were discussed. A comparison was made between two transmission curves, one of which was obtained by means of a microspectrophotometer and other one was calculated from the diffuse reflection curve obtained by an elliptic mirror method, and the priority of the former method was clarified. The transmission curves obtained by the microspectrophotometer were essentially identical with the diffuse reflection curves. However, the difference between both the curves was remarkable in the region where the absorption was strong, and the structures were observed on the curve obtained by the microspectrophotometer. With respects to the measurements of the optical band gap for powdered (Zn, Cd) S, the band gap was smaller than what had been expected from the molar composition though the lattice constants (Measured by X-ray analysis) were linear functions of the composition. The relation between the band gap and the composition was found to be linear, with a break at the equimolar composition. Possible reasons for this phenomena were discussed.
Phase transformation of yellow orthorhombic PbO to red tetragonal form was confirmed by grinding at room temperature. The long time grinding in atmosphere converted the PbO powder into white lead, the basic lead carbonate, Pb3(CO3)2(OH)2 finally. The first reaction product in the nitrogen stream was not white lead, but lead oxy-carbonate, PbO. PbCO3. Thus the effect of moisture was prevented well in this condition, though the carbonate formation was not avoided. The line profiles of the X-ray powder diffration patterns of the ground product are fairly sharp. The average size of the crystallites determined by the line breadths is about 200Å in diameter, and this value agrees well with that of the electron microphotograph. The density of the white lead thus obtained is rather high compared with the ordinary one. The sharp line profiles must be due to the crystallization by constant grinding. Consequently it may be assumed that a quasiequilibrium state is established between the decomposition and the formation of white lead crystallites. Pb3(CO3)2(OH)2_??_Decomposition by grindingH2O+CO2X-ray amorphous PbO When the Pb3O4 is converted into a mixture of white lead and α-PbO2 by grinding in atmosphere the product turns dark brown. The photoconductivity measurement of the ground samples was carried out at their early stage of grinding in their visible and near infra-red region. Two new peaks appeared at 680mμ and 950mμ. The peak at 680mμ was largely affected by moisture and in some cases this peak was very high and overlapped the second lower 950mμ peak. The 680mμ peak will be attributed to the absorption of water molecules on the active site of the PbO surface, and the 950mμ peak to some lattice imperfection originated by grinding on the surface region of the PbO grains, respectively. The synthetic reaction of basic lead carbonate by grinding red PbO is explained on the basis of “active states” that appeared in the PbO grains by grinding.
In view of the fact that, as evidenced by the result of the antacid activity test, the artificial magnesium aluminum silicate prepared by hydrothermal treating has failed to equal its co-precipitated substance in neutralizing velocity and in activation energy of reaction with 0.1N-HCl, it is the aim of the present paper to investigate the changes in physicochemical properties of artificial magnesium aluminum silicate prepared by hydrothermal treating. Scarecely have hitherto studies been made of the kind of factors of changes in hydrothermal treating, such as the durability of antacids, bonding state and surface chemistry. As the result of differential radial distribution analysis shows there is but small variation from the specimens used in the hydrothermal treating to the co-precipitated specimens, and this variation is not considered to have much to do with durability. The authors have paid attention to the physicochemical properties of surface as main factors, and conducted measurements of the differential thermal analysis, of the surface area and of the amount of oil absorption in order to examine main factors of indicating durability at hydrothermal treating samples. It is concluded that the durability is influenced by the weak bonding state, and the surface properties mainly by such as the surface area, the hydrophilic property and the hydration structure.
The mechanism of the Rebinder effects in nonmetallic solids is proposed from the point of view of the formation of barrier against the dislocation movement caused by strong chemisorption. The infrared and electronic absorption spectra of N, N-dimethylformamide, hereunder to be symbolized DMFA, adsorbed on the surface of MgO, indicate that its larger portion is adsorbed by the hydrogen bond formation with surface OH group, and that the rest of DMFA is found strongly adsorbed on Lewis on surface OH group acid center, forming a charge transfar surface complex. The spectra show also that, in the case of dimethylsulfoxide, hereunder to be symbolized DMSO, some is found adsorbed by the hydrogen bond and that the rest is adsorbed on Lewis acid center. There was less mobility of near-surface edge dislocation in theca se of the MgO immersed in DMSO than in the case of the MgO immersed in DMFA. The difference in mobility may be attributed to the difference in interaction of adsorbate with the Lewis acid center. The electric and elastic interactions between near-surface edge dislocation and the“adsorption-induced surface defect”are discussed semiquantitatively.