Vaterite is generally known as an unstable form of calcium carbonate, but pure vaterite was obtained from the reaction of concentrated aqueous solutions of the CaCl2-Na2CO3 system. Ordinarily in the mechanism of precipitation reaction an important part is played by the degree of concentration of the reactants, whose influence is especially noticeable on the number of the stages. From diluted aqueous solutions of reactants in the CaCl2-Na2CO3 system, it is known that there is only one step of reaction as follows; CaCl2+Na2CO3→CaCO3(Calcite)+2NaCl In concentrated reactant a transparent gelatinic membrane appears at the phase boundary of CaCl2 solution (>2N) and Na2CO3 solution (>2N) in the initial stage, which becomes translucent in 15 minutes or more, and the following process of reaction has been observed; CaCl2+Na2CO3→Oriented substance in the initial period at the interface. (a transparent gelatinic membrance) →CaCO3·mNa2CO3·nH2O →CaCO3·Na2CO3·n'H2O →CaCO3 (Vaterite) or CaCO3 (Calcite) at room temperature. Studies were made of the X-ray diffraction, the infrared absorption spectra, the high-resoltion nuclear magnetic resonance and the electron spin resonance, during the transparent stage and the following stages at the room temperature or 77°K. The result shows that the gelatinic substance is in an amorphous state showing a broad peak at about 15° (θ) by the x-ray diffraction and that CO32-ions are not distributed at random but orient themselves in a definite way, making an angle of 45°-90° with the interface as revealed by the polarized infrared absorption. The experiment also indicates that the gelatinic substance is viscous in spite of its high water content, and that its watering redient has been restricted by stronger hydrogen-bonds than the original solution. It is interesting to notice the presence of from three to five broad lines of proton magnetic resonance absorption (60Mc) extending from the water level to high magnetic fields. The E.S.R. signal of gelatinic substance appears at the point of 2.004 (G-Value) at 77°K. It is possible that this points to the presence of H2O-. This fact suggests that H2O gets strongly polarized in the ionic fields and makes a spur of radical in the gelatinic substance. The gelatinic substance gradually precipitates by separation of H2O and produces the double salts at room temperature as follows: CaCO3·Na2CO2·nH2O (n≅13), CaCO3·Na2CO3·5H2O (Gaylussite), CaCO3·Na2CO3·2H2O and CaCO3·Na2CO3·H2O (Pirssonite). The major product of the double salts is gaylussite and it is subject to decomposition into vaterite under cectain conditions. The production of pure vaterite is possible under the following condition. Original solution; 6N CaCl2-2N Na2CO3, Reaction temperature; 20-30°C, Mixing ratio (mol ratio); CaCl2:Na2CO3=1:3, Reaction time; 30-50min, The stirrer must be worked slowly (200r/min). When the precipitation is complete the precipitate must be filtered rapidly and washed in the mixture of H2O (70%) -Methanol (30%) and then with ether.
This paper is concerned with the precipitation of copper powder from aqueous cupric sulphate solution by hydrogen pressure reduction. Experiments have been done in 3l stainless autoclave, equipped with the sampling device and the magnetic induction agitation system. The results obtained are as follows: (1) It is easy to precipitate metallic copper from acidic copper sulphate solution, but the addition of certain organic compounds to the reduction charge is indispensable to prevent the plating and plastering of copper on the wall of the autoclave. A kind of acryl compounds have been used in this research. The addition of this dispersion agent effects the reduction rate and the physical characteristics of the precipitated powder. (2) Although the reaction proceeds without catalyst, the addition of fine copper powder as seed increases the rate a little. (3) The addition of ammonium sulphate to the reduction charge effects a marked buffering action to depress the increase of the acidity from the reaction. The reduction rate increases with the amount of ammonium sulphate added and the initial reduction rate is in proportion to it, (4) The initial reduction rate is proportional to the hydrogen partial pressure and the initial copper concentration. (5) The following reducing conditions appear to be optimum: Cu 50g/l, dispersion agent 0.1g/l. (NH4)2SO4/Cu=1 (molar ratio), 150°C, PH2 20-30kg/cmcm2. (6) From the results as stated above, the initial reduction rate can be represented by an equation of the form: (Received June 4, 1965)
They tried the jet grinding of brittle materials by a new apparatus, which is similar to the air ejector in its construction. Fig. 2 shows the main part of this mill. The pulverizing mechanism was assumed from the view point of pressure distribution and size distribution of the grinding producis. The experimental results show that D-2 type diffuser is most efficiencial for pulverizing as shown in Fig. 10. The pressure distribution in D-2 type diffuser is shown in Fig. 4 and the slze distribution in Fig. 7 in the form of Rosin-Rammler diagram. The relative position of the air nozzle to the entrance of feed of material is also effective for pulverizing as shown in Fig. 12. It is concluded that the pulverization is performed by the following two methods. (1) The pulverization by the collision of feed materials in front of the air nozzle. (2) The pulverization by the collision and mixing at the diffuser.
Various compositions of Fe-Co double oxalates were prepared by adding mixed solution of Fe and Co chlorides to oxalic acid solution. The structure and interplanar distance of the resulting precipitates were determined by X-ray powder diffraction. The linear change of the interplanar distances with composition is convincing that the coprecipitated Fe-Co double oxalates are solid solutions. The thermal analysis of the hydrogen reduction process of Fe-Co double oxalates was carried out using differential thermal analysis and thermogravimetric analysis, and these data revealed that the oxalates were reduced to metallic state at relatively low temperature. The results of X-ray powder diffraction and electron microscopic observation show that the fine particles thus obtained are alloy particles with crystal structure and lattice spacings identical with those of corresponding bulk specimens at reduced temperature. The particles are in the typical skeleton form consisting of much smaller unit particles. The size of skeleton form particle is deter- mined by the size of the oxalate particle. On the other hand the size of the unit particles can be changed by reduced temperature and time. It is possible to obtain the skeleton particles with the unit particle siz less than 300 angstroms.
The effect of calcination and ball-milling on the properties of Ni·Zn-and Mn·Zn-ferrite powders was studied and the results are discussed on the basis of theoretical considerations on tap density. It is shown that the ball-milling has two different effects on the powder properties depending on whether the temperature of calcination is above or below the recrystallization temperature. It is found that striking correlations exist among these properties, and that the tap density is one of the most useful and convenient parameters not only for the evaluation of powder history but also for the prediction of sintering performance.
Bader1) proposed an empirical equation (1) based on the measurements of air permeability of snow. A large portion of this report is concerned with the meaning of the parameters a and ε0 in Bader's formula. Our purpose has been to measure the permeability of various packings and to determine whether the parameters obtained from the permeability measurements could be used to define the type of the packings. It has been found that Eq. (1) has general application to homogeneous and heterogeneous beds of powders of various materials, sizes and shapes. The parameter a for the same powders is constant not influenced by the structure of beds, and the relationship between a and the mean volume-surface diameter d is expressed by the Eq. (3). The parameter ε0 of homogeneous beds is found to increase with decrease in the particle size below a critical diameter concerned with the materials and the shapes, and for the particle sizes greater than the critical diameter it is constant. The differences in the value of the constants for the different powders appear to depend chiefly on the particle shape. For mixtures of powders of two or three different sizes ε0 is smaller than that for onecomponent systems. For the beds with aggregates in it ε0 is smaller than that for the homogeneous beds, and for the beds in which two layers of different porosities are piled up ε0 is greater than that for the homogeneous beds.
Some experimental observations are presented here worked on models concerning the relationship betwen the packing characteristics and the shrinking behavior of the packed bodies, constructed of contractile powder and non-contractile powder, and subjected to special treatment such as drying or sintering. Steel balls each of 1.43cm in diameter were used as models for non-contractile powder, and sugar balls each of 1.39cm in diameter as models for contractile powder. The mixed bodies having the 1-x volume parts of steel balls and the x volume parts of sugar balls, where x is varied as 10, 20…90 respectively, were kept in the measuring container illustrated in Fig. 1 and Fig. 3. Three types of regular packing arrangements, cubic, orthorhombic, and double-nested, were chosen in these tests as shown in Fig. 3 and Fig. 5. When the experiment was started, the water was regulated at constant temperature, and was poured into the container vessel to dissolve the contractile model powder (Sugar balls). The regular arrangement in the packed bed was affected and the heights of the bed were brought to contract. These contracting actions varied according to the dissolving action of the water to the sugar balls, that is in proportion to the dissolubility of the sugar balls and the temperature of the dissolving water. The resulting contraction is remarkable. The mathematical statement in these behaviors can be expressed as (6) where εx' is contracting strain of the packed bodies, ε'mx the theoretical strain calculated from the additivity of two components, Va' the ratio of packed volume to real volume of the powders, and V'ma the same ratio of additional value. Based on the above equation (6) the following argument is possible. The cubic arrangelnent could be destroyed easily, but the double-nested arrangement is stable on account of the bridge forming properties, and the orthorhombic arrangement lies midway, that is the latter could be more liable to distruction than the double-nested structure, and more stable than the cubic structure. These numerical statement are shown in Fig. 10-12.
The pore structure of hot-pressed polystyrene and polyvinyl chloride powder compacts prepared at 40-100°Cand 1-8t/cm2 was studied by means of mercury porosimeter. Most polystyrene compacts have two peaks in the open pore size distribution curve, one at 0.01μ and the other at 1-5μ inradius. It has been found that the first peak corresponds to the pore on the surface of starting powder particle and the second to interparticle voids. The latter has been found to shift to smaller radius with increasing compacting pressure and/or temperature. The effects of compacting conditions on open and total pore volumes were studied. And it has been shown that the compacting pressure at which the open pore volume remains unchanged with further increase of pressure decreases as compacting temperature is raised. The increase in the open pore volume was observed on heating the polyvinyl chloride powder compacts prepared at room temperature. This might be explained by irreversible displacement of particles due to the expansion or stretching of particles and other factors. Different features both in the pore structure and its dependence on compacting conditons were observed between the poly-styrene and polyvinyl chloride powder compacts. This would be ascribed to the differences in their softening characteristics and powder parameters. On the basis of the experimental results and discussion, the mechanism of pore volume variation has been presented, and it is suggested that the deformation caused by softening and compression of powder particles is one of the most important factors to be considered in plastic powder compact.
As an approach to reviewing the packing properties of fine powders, the relationships between particle characteristics such as particle size, shape, surface roughness and adsorbed matter, and static properties of powders have been studied. In this experiment, the white alundum, zinc powder, calcium carbonate and mica powder were used as samples. The angle of repose, porosity and packing property were measured as static property of powders. The results obtained are summarized as follows: As particle size decreases, the angle of repose and porosity increases. But the value becomes constant under the critical size of the particles at hard coagulated powder. And it has little relation with the particles shape, surface roughness and surface adsorbed layer at the fine powders. The packing property has been studied by the tapping compressed method. The relationship between the apparent density of powder bed and the tapping frequency can be correlated to Kuno's equation. The packing coefficient k1 at the first stage of packing corresponds to the constant b of Kawakita's equation, that is related to the coagulation force of powder. The k1 decreases with the particle size, and take minimum value at about 3μ, and then it increases again. These results suggest that the unit particles will build up the coagulated secondary particle, and the static properties of fine powders are influenced by the characteristics of the coagulated particles.
About 4 samples of effluent fume dusts from the LD pure oxygen refining process from 3 different localities in Japan were studied in the light of pneumoconiosis mineralogy an electron by mean of microscope and by micron photo-tub methods and X-ray powder methods and through differential thermal and chemical analysis. The following results have been obtained. (1) The particles of siderosis minerals in the effluent fume dusts and the sludges from the LD pure oxygen refining process are below 1 micron in size of iron oxide particulate matters. (2) The siderosis heavy minerals are below 0.1 micron in size, the siderosis light minerals are 1 micron to 0.1 micron in size of iron oxide particulate matters. (3) The pneumoconiosis mineralogical composition in the effluent fume dusts are maghemite (γ-Fe2O3) and Kokaneite(β-Fe2O3). (4) The pneumoconiosis mineraIogical composition in <0.1 micron in size of LD-sludges are magnetite(Fe3O4), hematite(α-Fe2O3), Kokaneite(β-Fe2O3), maghemite(γ-Fe2O3). (5) The pneumoconiosis mineralogical composition in 1 micron-0.1 micron in size of LD-sludges are goethite-hydrogoethite (α-Fe2O3·H2O·-α-Fe2O3·H2O·aq), akaganeite-hydroakaganeite (β-Fe2O3· H2O-β-Fe2O3·H2O·aq), lepidocrocite-hydrolepidocrocite (γ-Fe2O3·H2O-γ-Fe2O3·H2O·aq), hydro-magnetite (Fe3O4·aq), hydrohematite (α-Fe2O3·aq), hydrokokaneite (β-Fe2O3·aq), hydrgmaghemite (γ-Fe2O3·aq), green rust (1)-hydrogreen rust (1) (Fe3O4·2H2O (?)-Fe3O4·2H2O·aq (?)) 25), green rust (11)-hydrogreen rust (11) (Fe3O4·4/3 H2O (??)-Fe3O4·4/3 H2O aq (??))25), amorphous ferric oxide hydrate (Fe2O3·nH2O).