Freeze-dried sulfates with metal composition of Mn3Co2Ni were prepared from a mixed aqueous solution of Mn, Co, Nisulfates, and then were calcined at 900-1000°C for 1 h to obtain uniform fine grained-spinel powders which can be useful for producing desirable electric properties in a thermistor. The freeze-dried and calcined materials were characterized and their sinterability was examined.
It was inferred from TG, DTA and X-ray measurements (Figs.4 and 5) that the freezedried sulfate was in the form of crystalline particles with a composition of Mn₃Co₂Ni(SO₄)₆·15-16H₂ and was completely decomposed to form spinel above 1000°C. The particle size and shape of the as-freeze-dried materials were independent of the concentration of sulfate solutions as shown in Fig.7. The powders obtained by calcining at 1000°C for 1 h formed porous spherical body in shape consisting of primary particles with uniform fine grain size. The average size, for example, is 1-2 gm for the material prepared from a 21.8 wt% sulfate solution. The particle diameter of primary partices increases with an increase in the concentration of the starting sulfate solutions. Furthermore, smaller grained-powders were successfully obtained by improving the calcination conditions using two-step firing one at 900°C and the other at 1000-1200°C (Fig.9). The calcined powders were expected to have a high sinterability from the preliminary sintering examination (Fig.10) at 1000-1400°C for 10 min using the powder calcined at 1000°C in air.791

View full abstract

Hydrothermal conditions for the synthesis of mullite powders from mixed alkoxide containing Al₂O₂:SiO₂=3: 2(mole ratio) were investigated at 300-600°C under 10-100 MPa for 2-168 h. Above 20 MPa, fine crystalline mullite powders were obtained at 600°C within 2 h. To produce homogeneous mullite powders, the hydrothermal treatments below 30 MPa at 600°C were preferable, because hydralsite(2Al₂O₂:SiO₂·H₂) and AS(H)-11 (5 Al₂O₂·2SiO₂ n H₂) were produced prior to mullite above 30 MPa at 600°C. In the produce prepared at 600°C under 20 MPa for 2 h, accicular particles of 100 nm in length and 20 nm in width were observed under the transmission electron microscope(TEM). The particles grew up to more than 1, um in length and 20 nm in width at 600°C under 20 MPa for 168 h. The energy dispersive spectrometry(EDS) proved that the prepared particles had the constant Al₂O₂/SiO₂mole ratio(=3/2). The synthesized particles was revealed to be mullite by IR absoption method.

View full abstract

Homogeneous precipitation method using urea was applied at 65-95°C for the formation of iron(III) compounds particles from aqueous solutions of FeCl₃, Fe(NO₃)₃ and Fe(NH₄)(SO₄)₂. Precipitate formed was a mixture of α-FeO(OH), /β-FeO(OH) and α-Fe₂O₃ from FeCl₃, while single phase precipitate of β-FeO(OH) was obtained at high concentration of urea. Precipitation from Fe(NO₃)3 solutions resulted in a mixture of α-FeO(OH), α-Fe₂O₃ and γ-FeO(OH), whereas that from Fe(NH₄) (SO₄)₂ resulted in Fe(O₂)₂(NH₄)(OH)₆(SO₄)₂ and α-FeO(OH). Precipitate of Fe3(NH₄)(OH)₆(SO₄)₂was obtained as a single phase only when the degree of precipitation was below -70%. Particles ofβ-FeO(OH) produced from FeCl₃was in spindle or rod-like shape. The particle size increased with decrease in urea concentration, with decrease in reaction temperature and with increase in FeCl₃ concentration. The aspect ratio of β-FeO(OH) particles increased as they grew in size.

View full abstract

Silicon nitride powders such as amorphous, α- and β-Si₃N₄ were ground by a vibration ball mill, a pot and balls of which were made of silicon nitride, in methanol medium containing various concentrations of water, and the mechanochemical activation (the amount of ammonia formation, the variation of specific surface area of the ground powders and the relative crystallinity) has been investigated.
Silicon nitride powders were activated by fine grinding and ammonia was produced by the presence of water contained in methanol. The amount of formed ammonia increased with an increase of grinding time and was closely related to the concentration of water contained in methanol. Reaction rate was expressed as r=k[C_H2O ][C_site (t)]₇ (n>1) under some assumption. The activity sequence per unit specific surface area of three types of silicon nitride for this reaction was amorphous> α-> β-Si₃N₄. The specific surface area of ground powders decreased with an increase of hydrated ratio, and the rate of decrease was in the following order: amorphous> α-> β-Si₃N₄. This sequence corresponded to that of amount of formed ammonia. Infrared spectra of treated powders revealed that the surface layer of Si₃N₄ was changed into SiO₂. In the case of grinding in the medium of purified methanol free from water, the specific surface area of ground powders increased with an increase of grinding time, and the rate of increase was as follows: α-> β->amorphous Si₃N₄. The relative crystallinity(It) for α-and β-Si₃N₄ decreased by grinding and an enlargement of lattice distance (d) was observed.

View full abstract

By utilizing W/O microemulsion phase, BaCO₂ fine particles were prepared by bubbling of CO₂ into poly(oxyethyene ether) nonionic surfactant/aqueous Ba(OH)₂ solution/cyclohexane or "isooctane" systems under various conditions. Particles of a different size and shape were formed in the fifferent solubility regions of Ba(OH)₂ in surfactant solutions, i. e., in the colorless solution, rodlike particles having axis ratio of ca.23-39 were formed, whereas monodisperse ellipsoidal particles were formed in the blue translucent of (Figs.2 and 3, Table 2). This difference could be explained in relation with the formation of W/O microemulsion phase. The size of particles formed in the W/O microemulsion phase was controlled by the size of water pool therein. This was also indicated from the change in the size and shape of particles with concentration of Ba(OH)₂ and with temperature (Tables 3 and 4). The formation and growth proceses of the particles in W/O microemulsion phase were also discussed from the electron micrographs of particles formed by bubbling of different amounts of CO₂ (Fig.4).

View full abstract

Homogeneously mixed fine powders of Tio₂-P₂O₅ system in which the melting points of component oxides were much different were prepared by wet chemical synthesis from Ti-alkoxide and phosphoric acid in ethanol solution, and by rapid drying with HPT method proposed by P. Reynen and his co-workers (sample HPT). The powder was also prepared by slow drying in air (sample A). The reaction between the components and the homogeneity of chemical compositions in the powder and its sintering were discussed from the results of TG-DTA, IR absorption spectra, shrinkage curves by a dilatometer, and X-ray diffraction and SEM images after heat treatment at several temperatures from 250 to 1, 000°C. Powder (HPT) particles had irregular shapes because of rapid drying, and were about 0.11 pm in diameter. On the other hand, powder (A) particles were spherical and about 0.1'0.3 pm in diameter. Both powders (HPT and A), of which the molar ratio of Ti₂-P₂O₅was 5/2, were X-ray amorphous below 500°C. They began to shrink at about 600°C, which was near to the glass transition temperature of the glass of the same composition. Between 500 and 700°C, unknown crystalline phase was deposited and it changed to crystalline 5 Ti₂-P₂O₅ between 700 and 800°C. HPT-dried powder began to change to 5 Ti₂-P₂O₅ at ternperature about 40°C lower than sample A. From these results, both powder samples were considered to have good homogeneity of chemical compositions and glass-like structure. HPT-dried powder sintered more easily than the powder (A) which was dried slowly.

View full abstract

Thin films composed of SnO₂ ultrafine particles were prepared by RF-sputtering of a SnO₂sintered target under the atmosphere of Ar, and their characteristics were examined by X-ray diffraction method and transmission electron microscopy. The pressure of Ar during the sputtering was a determining factor for the formation of the ultrafine particles. Thin films of almost spherical SnO2 fine particles with about 10 nm in diameter were obtained at the Ar pressure of 13-40 Pa, while amorphous-like films were obtained at the Ar pressure of 4Pa. The intensity of X-ray diffraction lines shows that these ultrafine particles of SnO₂ are stacked on the film with orientating their C-axes or the axes inclined to the C-axes vertical to the glass substrate.
The density of the sputtered films of SnO₂ultrafine particles was 3.5-4.0 g/cm³, which was almost 50-60% of the theoretical density of SnO₂. This value was much large than that of the films of SnO₂ ultrafine particles prepared by the evaporation method of Sn under Ar and O₂ atmosphere. The former had larger mechanical strength than the latter, and no breakage or peeling off from the substrates was observed in the former films when an adhesive tape stuck on the films was pulled vertically to the films. Thermal stability of the SnO₂ ultrafine particles at high temperature was also examined and only 10% of increase in the particle size was observed after a heat treatment at 450°C for 6 h in air.
The sputtered films of the ultrafine particles are considered to be applicable to gas sensors and catalysts, since they have rather high thermal stability and high mechanical strength.

View full abstract

An experimental scale appratus was constructed for synthesizing needle-like zinc oxide fine particles continously through the gas phase oxidation of zinc vapor, and the morphology of these particles was analyzed statistically.
For the synthesis of needle-like zinc oxide particles, metallic zinc was melted in a highly dense and pure graphite crucible. The vapor generated was led to a nozzle made of alumina (2 mm^φ) by an inert carrier gas, blown out of the nozzle and oxidized to form zinc oxide. The reaction was highly exothermic, and the flame was formed at the nozzle. The top region of the flame was blown by a cold air flow to quench the zinc oxide particles. The zinc oxide particle formed has a tetrapod-like shape, with three to four needles joined together at the center. By assuming the shape of these needles to be cylindrical, their width and length were determined from the electron micrograph. The length, width and volume of the particles are approximately represented by the log-normal distribution, rather than the normal distribution. This tendency was not affected by the conditions of synthesis. No systematic relation was found between the conditions of synthesis and the particle morphology.

View full abstract

Reduction processes of hematite with hydrogen were studied thermogravimetrically using particles of different size, of which the average size were 0.23 and 0.69 prn respectively, over the temperatures between 252.5 and 383°C under the conditions without an external diffusion effect.
An overall, e duction course of fine hematite particles consisted of two steps which were from hematite to magnetite quantitatively and then to iron. Fractional reductions at the first step fitted well the Mampel's equation, so that this process was confirmed to be an interfacial reaction. At the second step, presence of wustite could not be recognized as an intermediate from an X-ray powder diffractometry and the feature of fractional reduction curves. The reduction rates were expressed by the following equation using a numerical method, dx₂/dt₂=k(1-x₂)^mx₂ⁿ, which indicated on an autocatalytic reaction.
In the case of moderately coarse hematite particles, a nucleation process was observed at an initial stage in addition to the interfacial reaction process. At the second step, the autocatalytic reduction process was also observed, followed by a gaseous diffusion process through a product layer at the later stage. A thickness of the product layer, from which the diffusion process initiated, was estimated to be around 1300 A.

View full abstract

A mist of the equimolar mixed solution of lanthanum nitrate and cobalt nitrate was treated successively in three furnaces of different temperatures to prepare the fine particles of CoLaO₃. The temperatures of the furnaces were set for the evaporation of water, the decomposition of the mixed metal salts, and the crystallization of the decomposed compound, respectively. The particles were spherical (0.4-1 μm) and porous, and a particle consists of a network structure of the primary particles (ca.50 nm) with irregular. hollows. An electron diffraction pattern suggests that a particle is consisted of a small number of single crystals.
The concentration of the solution of raw materials and the temperatures of the decomposition and crystallization furnaces were found to be the most effective for determining the properties of the particles. In this method, the lower the concentration of the solution is, the finer oxide particles are produced. The degree of the crystallization increased with increasing temperature of crystallization furnace. The specific surface area of the particles showed a maximum at the temperature of 700°C, and also changed markedly with the temperature of the decomposition furnace. The maximum may be observed as a result of the competition between the thermal decomposition of the nitrates and the sintering of the resultant oxide particles.
The crystalline oxide was formed at a low temperature and in a short time by the mist decomposition method. The reason may be a short diffusion distance in the solid phase reaction as well as the effect of water vapor which is present in the gas phase. The investigation of the effect of water vapor on the rate of the crystallization of CoLaID, revealed that the rate increased with increasing partial pressure of water vapor. The catalytic activities for the oxidation of propane were measured, and the activities of the samples prepared by this method were compared with that of the sample prepared by an ordinary method.

View full abstract

Highly-dispersed iron oxides were prepared at room temperature by photooxidation of a small quantity of [Fe(CO)₅] supported on silica gel (surface ar ea 500 m²/g). X-Ray powder patterns showed the formation of very fine particles of γ-Fe₂O₃ phase, which was ferromagnetic at room temperature (Fig.3). At temperatures below about 100K, the magnetization at 18 kOe increased remarkably (Fig.2). MOssbauer spectra taken at liquid He temperature clearly showed the presence of iron oxide phase characterized by the internal field of-470 kOe (Fig.5). These observations suggested the formation of a new phase of X-ray amorphous iron oxide. The analysis of the superparamagnetic curve observed at liquid He temperature showed that each particle contains less than 100 Fe³⁺ ions. Formation mechanism for the γ-Fe₂O₃ phase was discussed on the assumption that the X-ray amorphous iron oxide is a precursor of the -Fe2O3.

View full abstract

Ultrafine particles (below 0.1 pm) of TiN, AIN + Al and Si were produced by an arc melting of Ti, Al and Si in nitrogen atmosphere at 0.1 MPa pressure.
(1) Ti-N System Reaction product of Ti-N system was a black powder and a golden-yellow block residual. These products were analyzed by means of X-ray diffraction and proved to be 100% TiN having cubic crystal structure. The sizes of the TiN powders were determined by electron microscope as O.01 to 0.1 pm (average 0.045 pm).
(2) Al-N System Reaction product of Al-N system was a gray powder and proved to be a mixture of 32%A1N ultrafine particles and Al ultrafine particles by chemical and X-ray analyses. A1N particles were needle like platelets having hexagonal structure (below 0.1 pm size) and Al particles had spherical figure (below O.1 pm in size).
(3) Si-N Sytem Reaction product in this system was a yellow-brown powder and proved to be 100% Si ultrafine particles (below 0.1 pm in size) by X-ray diffraction and electron microscope.
A plasma gas-molten metal reaction, involving activated nitrogen (atomic form) plays an important role in the formation of ultrafine particles. A driving force of the formation of ultrafine particles can be explained as follows;
In an arc melting of metals such as Ti, Al, Si in nitrogen atmosphere, the molten metal simultaneously contacts with two gas phases, one is the atomic nitrogen and another is the molecular nitrogen. The extent of dissolution of atomic nitrogen is much greater than that of molecular one. A supersaturated nitrogen in molten metal beyond the arc will evolve and carry metal vapor into the non-arc gas phase (N2), a kind of enhanced evaporation of metal.
The metal vapor react with nitrogen in the atmosphere to form ultrafine particles such as nitride (TiN), nitride+metal (AIN+ Al), and metal (Si) depending on the nitrogen affinity of metals.

View full abstract

The ultrafine particles (UFP) of nickel, cobalt, iron and iron-cobalt were prepared by hydrogen reduction of chlorides of those metals. Chloride powder which dropped into nickel crucible placed inside of the container (boiler) vapourizes, and the chloride vapour carried by argon gas is introduced into a reactor, where it flows upwards and reacts with hydrogen, giving metallic fine particles. UFP come out from the reactor like black smoke or soot and are easily collected by filteration. They form "necklace" which is generally observed for magnetic particles.
Higher reaction temperature favours the production of smaller particles in diameter within the range from 750 to 950°C. The increase in total gas flow rate results in smaller particles in average diameter. Shorter reaction length gives smaller particles in the case of 17 l/min of total flow rate of gas but in the case of 25 //min nearly the same diameter. These results suggest that the concentration of chloride, vapour plays an important role in this process. Hydrogen flow rate does not affect the particle diameter at the rate higher than 2.5 l/min. UFP obtained at various reaction conditions have log-normal distributions of particle size with very narrow range of geometric standard deviations, 1.39-1.63, while their median diameters extend from 30 to 110 nm. UFP by inert-gas-evaporation process also have the same feature, suggesting that the particle growth by both methods have similar mechanisms.
These metal particles are stable in open air except for iron particles, and contain several percents of chlorine which can be reduced to 0.1% by washing with water. When iron chloride and cobalt chloride are charged to different boilers, the obtained particles contain iron and cobalt uniformly and are considered to be alloy particles.
The mechanism of the formation of UFP are supposed to be as follows. The supersaturation ratio for these reactions is as high as to allow the instantaneous irreversible formation of free metal atom (or at least very small clusters) at the moment of contact with the reacting gases. This homogeneous nucleation is succeeded by a rapid coagulation of atoms (clusters)in Knudsen flow regime. The kinetic equations of the coagulation were solved numerically. After 10-5s, the size distribution function of the particles, obtained from the model calculation, becomes self-preserving, similar to the distributions obtained from experiments. This model is supported by experimental findings of size dependency on the concentration of chloride vapour and on the retention time in the reactor.

View full abstract

Water-based magnetic fluid is obtained by adsorbing anionic surfactant as a secondary adsorption layer on the hydrophobic surface of magnetite colloid prepared by monomolecular adsorption of oleate. Magnetic fluid prepared by sodium dodecylbenzenesulfonate possesses the following qualities: the viscosity is low, pH range to disperse magnetite colloid stably is wide, and the coagulation and redispersion of magnetite colloid can be controlled by pH. The method of concentrating magnetite particle in diluted water based magnetic fluid was investigated. The results were as follows:
( 1) The addition of inorganic electrolyte as a flocculant led to rapid coagulation of magnetite particle. The critical coagulation concentrations of electrolytes closely corresponded to Schultz-Hardy's law. Concentrated magnetic fluid was obtained by filtering the coagulated magnetite particle, followed by the addition of alkaline solution and surfactant to the cake.
( 2 ) The use of sodium salt as a flocculant and of HC1, H2SO4, and NaOH for adjusting pH was appropriate for concentrating magnetic fluid because the viscosity of concentrated magnetic fluid did not increase.
( 3 ) This concentration method of dilute water-based magnetic fluid was applied to concentrate a fluid that had been produced by water washing of products in sink and float separation system in which magnetic fluid had been used, and the loss of magnetic fluid was less than 1 liter per ton of separated prod

View full abstract

The electrical properties of colloidal graphite films composed of fine graphite particles with different sizes and size distributions have been examined in detail to elucidate the effect of the particle size or the size distribution of graphite particles on the textures of the coated films. Sheet resistivity or specific resistivity was measured by a DC four terminal method for various films heat-treated in the temperature range from 110°C to 400°C. From an empirical equation representing the thickness dependence of sheet resistivity in films, the uniformity of the films could be estimated. A rapid decrease in the sheet resistivity of the films heat-treated in range 200-300°C was directly associated with decreasing barrier resist ance on contact areas of graphite particles and polymer colloids. The specific resistivity of films after heating at 400°C was found to be correlated with the packing density of graphite particles in the films. Additionally, the packing density of graphite particles was strongly dependent on colloidal graphite samples examined. The remarkable difference in film tex ture between the examined samples was confirmed by microstructural observation with SEM. Flow properties of sample suspensions showed that the diffrence in film texture was probably caused by different orientation property of suspended graphite particles, which might depend on the size distribution of the suspended particles, under a given shear stress. These results suggest that particle size distribution is an important quality govering the texture uniformity and the packing of graphite particles in colloidal graphite films.

View full abstract

Microstructure and chemical composition of porous films on aluminum, anodized in an aqueous solution of sulfuric acid, followed by chemical dissolving and/or electrolytic coloring, were studied by TEM and IR spectrophotometer. TEM micrographs of vertical sections ultramicrotomed from the film which was dissolved chemically in sulfuric acid revealed to be colloid-like or network-like structure and that of traverse to be the layered structures of five and/or three layers. In the core of the colloidal layer, there was relatively high crys talline alumina layer, the thickness of which was about 4 nm. Arrangement of the ultrafine particles which composed the colloidal layer was not at random, but in alignment. S ize distribution of the ultrafine particles followed Gaussian curve and average diameter was nm. Barrier layer of the electrolytically colored film which was pretreated by sulfuric acid solution for 15 minutes appeared to be multi-layered colloidal structure. IR spectra indicated that SO₂^- ion and absorbed water were present among the colloidal layers, and as the duration of dissolution became longer, the amount of the ion decreased and that of the absorbed water increased.

View full abstract

Electrification (η) generated on titania particle surfaces by contact between the surfaces and a reference iron powder was measured using a recently developed blow-off apparatus. This contact electrification in the gas phase was compared with the zeta (ξ) potential in deionized water. Samples used were about 40 commercially available titania pigments, 0.15-0.3μm i n diameter whose surfaces were coated with alumina and silica colloids. The following results were observed.
( 1 ) The electrification tendency in n is the same as that inξ; (-) SiO₂-TiO₂(water pH 6.8)-Fe₂O₃-Al2₂O₃ (+).
(2 ) Linear shifts are found both in 77 and in c' toward positive direction with an increase in alumina content on the titania surface, while they shift to the negative direction with an increase in silica content.
( 3 ) In alumina-silica coated samples, the silica has larger effect on n than the alumina.
Results ( 1) and ( 2 ) suggest a common origin for the electrification in gas phase and in water. A reasonable model for the origin is proposed in relation to the acid-base properties of metal oxides, and is explained by a more general concept of the electronegativity in metal ions, which determines the acid-base properties. Result ( 3 ) is discussed in connection with microstructure of the particle surfaces.

View full abstract

Homogeneity in a powder mixture comprising two components has been investigated from the viewpoint of static electrification, which is generated spontaneously on a particle surface by contact between the surface and other component particles. A recently developed blow-off apparatus is used for measuring the electrification. One component of the mixture is chosen from commercially available titania pigments whose particle size is 0.2-0.3 pm. These pigments show electric charges ranging from large negative to large positive values, depending both on the kind and the quantity of surface coating materials, when they are brought into contact with a reference iron powder. The other component is carbon black powders, 0.02gm in diameter size, with negative charging properties. These powders are mixed together with ethanol in a paint conditioner and dried. The -homogeneity is related to optical reflection density of the mixture; large reflection density means better homogeneity, when two mixtures containing the same carbon black content are compared.
Better homogeneity is found below 20% carbon black content in the mixtures, as the blowoff charge on the titania shifts toward a large positive value. The charge of the mixture lies at a more negative side (carbon black side) than the value calculated from the values for each component by assuming a simple additive law. These results lead to the conclusion that carbon black particles cover a titania particle surface more effectively with increase in electrostatic attractive force induced by the charging between these two component particles. This is supported by SEM observation.
Sample powders electrification in ethanol was also measured by a zeta potential meter. The charging tendency is almost the same as that in air (blow-off charging). Since this suggests that the electrification on sub-micron particles originates from acid-base properties on their surfaces, mixture homogeneity behaviors are foreseen to be similar, even when the surrounding media is changed from ethanol to other liquids or gases.

View full abstract

The magnesium ultrafine particles in organic solvents were produced by means of gas evaporation technigue combined with the matrix isolation method and with gas flow-solution trap method developed by our laboratory. The yield of ultrafine particles was examined as a function of carrier gas flow rate. In order to elucidate the surface effect on the magnetic properties of ultrafine particles, two colloidal systems, particles in tetrahydrofuran (THF)and particles in hexane, were examined by conduction electron spin resonance (CESR) and by static magnetic susceptibility using Faraday method in the temperature range from 2K to 150 K. In the Mg/THF system, there were two peaks in a CESR spectrum. The power saturation techique showed that these components had different longitudinal relaxation times and came from different origins. The component with the 1 G full line width had a long longitudinal relaxation time and showed a typical power saturation curve which is characteristic of localized spins. On the other hand, the component with the 6 G full line width had short longitu dinal relaxation time and slightly increased even at the power level of 100 mW. This behavior shows that the latter component can be correlated with the conduction electron in the metal particles, since the CESR of bulk metal scarecely saturate even at 200 mW. The magnetic susceptibility of this sample showed there were two components, the one exhibited Curie like behavior showing the increment of the magnetic susceptibility at low temperature and the other exhibited a quite unusual behavior showing the decrement of the magnetic susceptibility at low temperature. The latter behavior is characteristic of the quantum effect which is expected of very small metal particles at low temperature. The component which showed Curie law was connected with the 1 G component in the CESR spectrum. From a Curie constant, 2.1 × 10^-5 emu·K/g and an average particle diameter, 60Å the concentration of this component was calculated to be 6 spins per one particle.
The carefully prepared ultrafine particles of magnesium in a high purity hexane gave a strong peak of CESR spectrum whose full, line width was 6 G, in agreement with the case of Mg/THF system. The magnetic susceptibility of this sample showed a typical behavior expected of the quantum effect, that is, the paramagnetism at a higher temperature region rapidly decreases with decreasing temperature. The depression of the 1 G component for this sample supports the conclusion that the 1 G component arises from surface impurities in the ultrafine particles. The possibility of controlling the surface state in this system was briefly discussed.

View full abstract

A study has been made on the oxidation characteristics of ultrafine iron particles (average diameter: 100 nm) freshly prepared by using an arc melting of iron in 50% H₂-50% Ar atmosphere "hydrogen plasma-metal" reactions. All procedures of handling and measurement of particles obtained were carried out in a glove box which was connected directly to the apparatus for production of the particles.
The oxidation kinetics at room temperature of the fresh ultrafine iron particles were studied with an electric balance to measure the weight change of particles at various oxygen partial pressures under 0.1 MPa total pressure.
At low oxygen partial pressures in the range of 4.9 to 642 Pa, it was found that oxidation process followed a parabolic rate law except the initial transient period (5-50 min). The thickness of oxide film on the ultrafine particle of iron was calculated to be approximately 2 nm by assuming the oxide film to be γ-Fe₂O₃ when the particle was passivated.

View full abstract

In order to develop new magnetic recording media, fine particles of iron nitride were prepared by different two methods. In the first method, iron metal particles were nitrized with ammonia gas and in the second case, iron chloride was used as a starting material. First, acicular iron powder (0.3, μ) was nitrized with NH3-H2 gas mixture at 400°C, and γ′-Fe₄N was obtained when the concentration of the NH3 was kept in the range between 65to 80%. The coercive force of thus obtained γ′-Fe₄N was about 700 Oe and the saturation magnetization was about 120 emu/g. Some test magnetic tapes which were prepared by using present γ′-Fe₄N showed good characteristics for the high density recording. For the second method, the vapor phase reaction in FeC12-NH3 system was studied. Three different temperatures, 780, 880 and 980°C were chosen for the reaction. The main products obtained at 780 and 880°C were Fe₃N and α-Fe, while at 980°C they were γ′-Fe₄N and γ-and α-iron. The shape of these products were granular or sheet like. The magnetic measurements were also carried out for these materials. The highest coercive force of the obtained materials was about 200 Oe which is not sufficient value for the magnetic recording media.

View full abstract

A powder reaction generally starts with phase-boundary reactions followed by a transport through a bulk of a newly formed phase. The importance of the phase-boundary reaction, which takes place in the initial reaction stage, increases with a decrease in powder size for measuring the reactivity of powders. However, the discussions now have been concerned with the diffusion transport in the bulk phases. This is mainly due to the difficulties encountered in the isothermal kinetic measurements of the initial reaction stage at high temperatures.
In this paper, emanation thermal analysis (ETA) was applied to the initial reactivity measurements of Fe₂O₈ (150-200 mesh), Fe₂O₈ preheated at 1300°C for 1 h (150-325 mesh), and Fe203-ZnO mixture (1: 1 in mol) in N2-flow atmosphere over the temperature range from 25 to 1250°C. ETA is a dynamic technique used for the detection or quantitative measurement of radioactive inert gas (radon) released from activated powders during a controlled temperature program. The apparatus used for ETA is commercially available Netzsch device (ETA 4O3STA 409 type) for simultaneous ETA-DTA-TG measurements. The samples were labeled by the impregnation method using 223Th solution (3 μCi/ml) and 226Ra solution (4 μCi/ml).
The ETA curves obtained indicated a new information concerning changes of the surface layer less than about 100 nm under the working condition at high temperature. The stages in gas release during a linear temperature increase were grouped according to the temperatures of self-diffusion of the matrix atoms or normal volume diffusion of radon (40 to 50%of the melting temperature, Tm, in the absolute temperature scale). The characteristic changes in the ETA curves were observed in the following two parts: ( 1 ), at temperature lower than Tm, a diffusion part due to the diffusion in intergranular space and open pores of the dispersed solid, and ( 2 ) at temperature higher than Tm, a diffusion part due to the diffusion of radon in the solid matrix of the dispersed solid. The latter part may be closely correlated to the initial reactivity in the solid-solid systems.

View full abstract

A new method has been developed to determine the crystal habit, i. e., proportion of the area of (100) face to the total surface area of fine silver halide grains in photographic emulsions, Poo, on the basis of the difference in absorption spectrum between a dye on (100) face and that on (111) face of the grains. For this purpose a cyanine dye, 3, 3'bis(4-sulfobuty1)-9-methylthiacarbocyanine (dye 1), was used, since it exhibited the most notable dependence of absorption spectrum upon crystal habit of the grains among the dyes tested. Namely, dye 1 showed a double band with the absorption maxima at 600 and 525 nm on the (100) face and J band with the absorption maximum at 630 nm on the (111)face. The reflection spectra of thick liquid emulsion layer containing various amounts of dye 1 were treated by the Kubelka-Munk equation to give saturated amounts of the dye adsorbed to (100) and (111) faces of the grains, from which the value P₁₀₀ of was determined for each emulsion with an error of 10%.

View full abstract

Aqueous suspensions of ultrafine silver bromide particles could be prepared by mixing dilute silver ion solutions with bromide ion solutions of much higher concentrations in a stopped-flow rapid solution mixing device. The process of the formation of such particles has been studied by use of a multichannel ultraviolet spectrophotometer which uses a one-dimensional solid state image sensor for measuring and recording time-resolved absorption spectra of the reaction mixture. The mixture initially showed a distinct absorption band at 230-240 nm which was assigned to unstable silver-bromide ion pairs or polybromoargentate complex anions as the precursors of the ultrafine particles. The band decayed with the same time-constant as the growth of the absorption band of product particles characterized by two exciton shoulders at ca.270 and 310 nm. The absorption change ceased in several ten milliseconds, and there was no evidence of further crystal growth within several hundred milliseconds. The reaction time-constant increased with increasing bromide-ion concentration or with decreasing silver-ion concentration, suggesting that the reaction observed was the nucleation of crystalline silver bromide from the precursors. The order of the reaction was 3---4, which was assumed to be the minimum number of silver-bromide ion pairs that constituted a ultrafine silver bromide particle or a "crystal nucleus". This reaction order was considerably, smaller than that of silver chloride, showing the higher stability of small particles of silver bromide.

View full abstract

The internal structure of the latex particles of the carboxylated poly(ethyl acrylate) formed by two-stage feed polymerization was investigated in order to obtain indirect imformation about the core-shell morphology formation by the above polymerization of two types of monomers or monomer mixtures of the same or closely similar hydrophilicity. The latex was prepared by polymerization of ethyl acrylate (EA) containing ¹⁴4C-labeled EA-methacrylic acid (MAA) (91.3: 8.7 mixture in weight) in the presence of EA-MAA copolymer seeds (same composition as in monomer mixture) or in an inversed procedure, and then dissolved progressively from the particle surfaces by increasing pH. The dissolved polymer was separated by ultracentrifigation from the undissolved particles and analyzed by a liquid scintillation counte and the acid titration method. The analytical results showed that ¹⁴C-labeled EA was distributed homogeneously from the surfaces of the particles to the centers, whereas the concentration of MAA was highest at the surfaces and decreased towards inside. This tendency was confirmed for the two samples ment

View full abstract

Monodisperse microbeads of polyacrylonitrile(PAN) with a diameter of about 0.5 gm were prepared by the polymerization of acrylonitrile without agitation in ethyl propionate. The microbeads of crosslinked copolymer of acrylonitrile with N, N'-methylenebis(acrylamide) (4: 1in molar ratio) were almost completely hydrolyzed into polyacrylamide microbeads, when treated with boron trifluoride acetate. PAN microbeads without crosslinkage dissolved in water under similar treatment. On the other hand, the hydrolyzed skin was formed on PAN microbeads and the core of the microbeads was left unchanged, when treated with potassium hydroxide in t-butyl alcohol. By the conductometric titration of the hydrolyzed microbeads, the ionic groups were found to be produced by side reactions; 0.54 meq/g of cation-exchangeable group in the boron trifluoride acetate treated microbeads and 0.29 meq/g of cation-exchangeable and 0.36 meq/g of anion-exchangeable groups in the potassium hydroxide treated microbeads. Amino group(0.053 meq/g) was produced in PAN microbeads, when treated with lithium aluminium hydride; this amount of the amino group was approximately equal to the calculated amount corresponding to the monolayered hydrogenation of the microbeads surfaces. Proteins were remarkably less adsorbed to potassium hydroxide treated-microbeads than to the other microbeads. Proteins can be immobilized onto both the hydrolyzed microbeads and the hydrogenated microbeads by use of glutaraldehyde as a binder. Serum albumin-binding and r-globulin-binding microbeads were agglutinated with the corresonding antisera. The agglutination could be observed with naked eyes on a glass slide, but the optical density change of the suspension reflected the degree of agglutination more sensitively and quantitatively.

View full abstract

Preparation investigated. free systems"of the latices containing Either acrylamide(AA) or with styrene monomer as amide groups with high anionic surface charge was methacrylamide(MAA) was copolymerized in "soap a seed component, using potassium peroxodisulfate and sodium thiosulfate mixture as an initiator. The diameter of the paticles was adjusted from 0.2μm to 0.6μm by varying the adding time of amide from O.5 h to 3 h. The particles containing AA were spherical and well monodispersed, whereas those containing MAA were deformed ones. Carboxyl groups were introduced into their latices by hydrolysis of the amide groups with various amounts of alkali agents. The highest surface charge (e. g. Q1=230 peq/g-L, for L-3) amounted to over ten times greater than that of unhydrolysed ones (e. g. Q1 =19.0, ueq/g-L, for L-u). Using these highly charged anionic latices as model suspensions, the effects of cationic polymer on their flocculation and adsorption behavior have been studied. The destabilization was accomplished with irreversible adsorption due to the electrostatic attraction between the negative charge of the particles and the cationic segments of the added polymer. The saturated amounts of adsorption ((Qa )1 ) in cationic polymer-latex system depended on the amounts of the surface char ge (Q1) of respective latex particles. Further, each maximum destabilization of the latices (optimum polymer concentration, Qo.c ) was produced near the end point for charge neutralization of the particle with a cationic polymer. With increasing the adsorption of cationic polymer, zeta-potentials of the particles reduced gradually, passing through zero and then reversing in their signs (about +30 mV in all cases). From these results, it was found that the destabilization in those systems was due to the charge neutralization and the reversed surface charge of the particles. Furthermore, it was also found that the flocculation and the destabilized region depended on the conformations of adsorbed polymer chains.

View full abstract

The method of preparing the soluble intramolecularly-crosslinked copolymers by radical copolymerization of vinyl monomer and divinyl compound was developed. The copolymeri zation of methyl methacrylate (MMA) and p-divinylbenzene (p-DVB) was carried out in two-steps. Two monomers werefirst copolymerized in the preseuce of a transfar agent (CBr4) at rather low concentration of monomers compared with the usual conditions of the radical polymerzation inbenzene. Then, MMA and benzene were added into the reaction solutions obtained by the first-step of copolymerization, and the reaction was continued. In certain cases, the reaction solutions continued to be fluid, but in most cases, they became a state of macro-gel:, These macro-gel products were swollen in benzene, and then vigorous stirring and ultrasonic irradiaton were applied_ to this sufficiently swollen macro-gel. After these. treatments, the product was fractionated by a stepwise precipitation, Method to give soluble crosslinked polymer efficiently. For example, under the conditions, that [p-DVB]/[MMA]total ([MMA] total means the concentration of MMA calculated from the total amount of this monomer added at the first-and the second-steps of polymerization) was egual to 5.31-10.6 × 10^-3, the soluble copolymer was obtained with very, high conversion (72-97%). The molecular weight was was 5.31×10^-3 and [CBr₄]/[MMA]total was higher than 4.57× 10^-3, the gelation was not observed during the copolymerization. When [CBr₄]/EMMAjtotai was higher than 9.14 ×10^-3, almost all the products behaved as linear polymers in viscometric measurements.

View full abstract

The effects of emulsifiers on the deposition of polymer particles from an anionic ethyl acrylate-methyl methacrylete copolymer emulsion onto an anodized aluminum plate were studied. In a cationic emulsifier, the deposition was not observed. In a nonionic emulsifier, the amount of deposited polymer decreased with an increase in the amount of emulsifier molecules occupied on the particle surfaces. In an anionic emulsifier, the emulsifier molecules occupied on the particle surfaces gave little effects on the deposition. On the other hand, however, those in serum depressed the deposition. The amount of deposited polymer from the small size of copolymer emulsion, which was prepared by the emulsion polymerization in the presence of an anionic emulsifier, was small. The interpretations of these behaviors were described.

View full abstract

Liposome-type artificial red blood cells stabilized with carboxymethylchitin (mean diameter 0.31 pm) were prepared by a two-step emulsification technique. Sheep hemolysate was dispersed as fine droplets in a lecithin solution in dichloromethane to give a W/O emulsion. The W/O emulsion obtained was then dispersed in an aqueous carboxymethylchitin solution to yield a complex W/O/W emulsion. Removal of the organic solvent from the complex emulsion by evaporation left an aqueous suspension of the artificial red blood cells. It was found that the yield of the cells was strongly dependent on the pH of the carboxymethylchitin solution used but almost independent of its ionic strength.
Contrary to an expectation, the flow of suspensions of the artificial red blood cells was of Newtonian type and their relative viscosities were lower than those of sheep red blood cell suspensions at the same concentrations. The relative viscosity increased with increasing cell concentration according to an equation similar to the Einstein equation, suggesting that the hydrodynamic cell-cell interaction is extremely weak.
The artificial red blood cells were disintegrated to produce hemolysis by the action of surfactants. When a comparison was made among those surfactants which have the same alkyl-chain length, the hemolytic activity was in the order of anionic, cationic and nonionic. On the other hand, the cells were quite stable to plasma proteins except albumin, which caused disintegration of the cells to some extent.

View full abstract

The binding characters of various metal cations on the phosphatidylethanolamine (PE) and phosphatidylserine (PS) vesicles were studied by turbidimetric titration and direct measurements of the amounts of ionic adsorption at wide pH ranges. The binding strength of metal cations to these vesicles increased in the following order; K⁺<Mg²⁺<Ca²⁺<Mn2²⁺<La³⁺<Th⁴⁺. Under consideration of the binding character of these ions, the mechanism of vesicle flocculation resulted with these ions was analyzed by comparing the relation between critical flocculation concentration (CFC). and vesicle concentration (Cp), and by comparing the CFC-values of PE and PS vesicles at a constant Cp. The analyses reveal that there are two different mechanisms for the vesicle flocculation. One is the aggregations caused by charge neutralization of polar groups on the vesicle surface which is introduced by the ions, of high binding constants (Th⁴⁺, La³⁺). The other is the interparticle binding (or the interparticle bridging) caused by the bivalent cations (Ca²⁺, Mg²⁺), which is the same mechanism with the cell fusion.

View full abstract

The techniques to control metal-particle size were investigated by using tetraethyl silicate and rhodium nitrate dissolved in ethylene glycol. The particles in the reduced catalyst were in an even size level, and the mean particle size increased with an increase in the concentration of rhodium in the catalyst, varying from 0.34 to 6.89% in weight. The effects of metal-particle size on the decomposition of 1-propanol were explained in terms of the fraction of the metal atoms being located at the corners and edges in the metal crystallites. During the decomposition of the alcohol, 1-propanol adsorbed on the corner and edge atoms to form propionaldehyde (ads), and then the adsorbed species moved to rhodium atoms on the surface planes of the crystallites to be decomposed to carbon monoxide and ethylene, since propionaldehyde was decomposed to carbon monoxide and ethylene at the surface plane atoms of nickel crystallites in Ni/SiO₂ catalyst. Recent studies on the relationship between metal-particle size and its effects on catalytic behavior were also surveyed and discussed in the present communication.

View full abstract

Most metal sols consisting of extremely fine metal particles (colloidal particles) can be prepared by the reduction of aqueous solutions of corresponding metal salts, and they are stabilized by the addition of protective colloid polymers. Among them, noble metal sols such as platinum, palladium, and rhodium are often used as catalysts for hydrogenation of unsaturated compounds. Such sol-type catalysts are, in most cases, hard to be separated from products. Some attempts have been made to immobilize colloidal noble metal particles on inorganic carriers, aiming at producing supported-type catalysts which can be easily recovered after use. Colloidal nickel boride is known to be easily prepared from an ethanol solution of by reduction with NaBH4 in the presence of poly(N-vinylpyrrolidone) (PVP) and exhibits a high catalytic activity for olefin hydrogenation. It has been found that, from a dilute NiCl₂·6H₂O solution (0.1 mmol·dm^-3), colloidal nickel boride (CNB) was obtained even in the absence of PVP and was successfully immobilized on Mg(OH) 2 or CaCO3. Moreover, when nickel boride-forming reaction was carried out in the presence of such carriers, supported nickel borides, CNB/Mg(OH)2 and CNB/CaCO3, were also prepared via colloidal nickel boride (Table 1). A variety of olefins were hydrogenated at 30°C under 1 atm of hydrogen atmosphere using the supported nickel borides as a catalyst. As shown in Table 2, CNB/Mg(OH), was more effective than CNB/CaCO3 for the hydrogenation of unsaturated hydrocarbon compounds while the latter was found to be more effective for the hydrogenation of carbonyl-conjugated olefinic compounds. Various inorganic substances including alkaline earth metal salts, listed in Table 3, have been found to be applicable to the preparation of supported nickel boride from 0.1mmol·dm^-3-NiCl₂·6H₂O solution. On the other hand, from 1mmol·dm^-3-NiCl₂·6H₂O, some inorganic substances gave no supported nickel boride because nickel boride was deposited not on the carrier substances but in the solution phase. The unsuccessful substances, however, gave supported nickel borides from 0.1mmol·dm^-3-NiCl₂·6H₂O solution, which were more effective for the hydrogenation of methyl acrylate than for that of 1-hexene. It is presumed that the immobilizing of colloidal nickel boride on the carrier through adsorption is commpetitive with the aggregation or growth of the colloid in the solution. Supported catalysts of nickel boride might be obtained when the colloid-adsorption is predominant.

View full abstract

Hydrogen-deuterium reaction over Pd/C and Pd/SiO2 model catalysts prepared under ultrahigh vacuum (UHV) has been examined to reveal the relation between the particle size of supported Pd and their catalytic properties. The mean particle size, d, was adjusted between 0.8-2.3 nm by controlling the amount of palladium evaporated. It was found that ( 1 ) the specific activities of these catalysts towards the H2-D2 exchange reaction (PH, 2.8 × 10^-2 Torr, 25°C) showed maxima at the particle size of ca.1.3 nm and ( 2 ) the apparent activation energies of the reaction decreased with increasing the mean particle size. These results were interpreted from the relation between the mean particle size and the shift of valence band of Pd atom and surface density of low co-ordinated Pd atom.
The outline of the model catalyst method for investigating the catalytic properties of supported metal catalysts was also described.

View full abstract

Nickel fine particle prepared by metal evaporation in helium gas atmosphere at low pressure has been found to be a highly selective and active catalyst for liquid-phase dehydrogenation of 2-propanol and cyclohexanol.
The nickel fine powder catalyst (average diameter: 19.6 or 27.0 nm), pretreated in hydrogen atmosphere (180°C, 1 atm, 1 h) to eliminate surface oxide layers, was dispersed in an alcohol solution by a supersonic treatment and was heated at the refluxing temperature. The evoiution of gas was pursued volumetrically at the atmospheric pressure (Fig.1). Exclusive formation of hydrogen and the corresponding ketone was ascertained by gas chromatographic analysis. Stationary reaction rates were obtained often after the periods of induction and/or rapid initial deactivation, but the rates were affected little by intermitting the reaction (Figs.2-5). From TEM photographs (Fig.7) the initial deactivation was ascribed to the disappearance of very small particles. The dehydrogenation activities amounted to O.055mol·h^-1·g^-1for 2-propanol and 0.26mol·h^-1·g^-1for cyclohexanol, respectively.
The attained activity of the present nickel fine powder catalyst is the highest among solid and homogeneous catalysts ever reported (Table 1) and is sufficient enough to be adopted to the slurry-type liquid-phase endothermic reactor for utilization of low-quality heat, converting it into high-temperature heat in the acetone/hydrogen chemical heat pump system (Fig.9).

View full abstract

Metallic manganese powder with the particle size of 10 pm (Alfa) was found to be readily applicable to C-C bond formation by the Barbier-type addition reaction of the carbonyl compounds. For example, the manganese powder (7 mol equivalents) was first activated with iodine (1 mol) in tetrahydrofuran (THF) at refluxing temperature. To this mixture was added a THF solution of allyl bromide (6 mol) and an aldehyde (or a ketone) (1 mol), and the resulting mixture was heated to reflux to give good yields of homoallyl alcohols. Activation by iodine or mercury metal gave reproducible yields of the adducts. With a, 9unsaturated aldehydes or ketones, 1, 2-addition took place exclusively. Allyl bromides having 8-hydrogens such as 1-bromo-3-methy1-2-butene and 1-bromo-2-butene gave the corresponding benzaldehyde adduct in poor yields, possibly due to the decomposition of the intermediate allylmanganese species. Manganese-mediated reaction of a-bromo ketones with benzaldehyde resulted in the formation of a-benzoyl ketones. Chromium metal particles (2 eum, Alfa)was also found to be applicable to the carbonyl addition of ally! bromide.

View full abstract

olloidal palladium with an average diameter of 18A was prepared by refluxing a solution of palladium(II) chloride and poly(N-vinyl-2-pyrrolidone) in methanol. The colloidal palladium was effective as a catalyst for hydrogenation of methyl linoleate at 30°C under an atmospheric hydrogen pressure. The hydrogenation was highly selective for the formation of the corresponding monoene. The monoenes formed in this reaction course were isolated, and their double bond distribution was determined by ozonolysis. About 85% of the monoenic products retained a double bond at the same position of the original substrate. The colloidal palladium catalyst was easily recovered and reused for hydrogenation, although the activity and the selectivity slightly decreased in repeated uses. The colloidal palladium was also an active and selective catalyst for partial hydrogenation of soybean oil. The high selectivity for monoene formation of the colloidal palladium is discussed in terms of selective adsorption of the diene on the surface of small palladium particles.

View full abstract

The properties and the usefulness of the catalyst produced by ultrafine metal powders were investigated. The ultrafine metal powders produced by the evaporation technique in a low pressure argon gas have been applied on the production of the catalysts for the exhaust gases. The resulting catalysts have a high activity and a long, lifetime.
The catalysts efficiently decrease the most harmful components of nitrogen oxides, carbon monoxide and hydrocarbons and their purification ability is equal to that of the best platinum catalysts.
This is due to the fact that ultrafine metal powders have singularities. These properties of the catalysts produced are confirmed to be as good as those of the conventional precious metal catalysts.

View full abstract

SiO₂- or γ-Al₂O₃-attached [Co₃O₄]catalyst(c) in Scheme 1 was obtained by the controlled oxidation of C₃₀-Co₄(C0)₁₂/SiO₂( a ) or D_2d- or D_4d-CO₄(CO)₁₂/Al₂O₈( d ), derived from Co₂(CO)₈attached on SiO₂ or r-Al₂O₃, respectively. The [Co₃O₄], , catalysts showed remarkably higher activities for CO oxidation at 273 K(Fig.1 and Fig.2) and ethylene hydrogenation at 293 K (Fig.6) than the conventional impregnated or ion-exchanged cobalt catalysts by more than two orders of magnitude. The surface species of the catalysts were characterized by EXAFS (extended x-ray absorption fine structure), UV/VIS diffuse reflectance, IR and Raman spectra, x-ray diffraction, and electron microscopy. The results suggest that the high activity of the attached catalyst( c) can be attributed to small(<1.5 nm) thin raft-like [Co₃O₄], , cluster (n=3(Al₂O₃) or 5(SiO₂)) which have coordinatively unsaturated Co³⁺(CUS)O^2-(CUS) pairs (CUS: coordination unsaturation site) (7%(SiO₂) or 12%(Al₂O₃) of total Co ions).

View full abstract

It was found that Ni ultrafine particles (Ni-UFP) prepared by gas evaporation method show some unusual catalytic properties superior to conventional Raney Ni catalysts. Ni-UFP used in this study has an almost spherical shape of an average diameter of 30 nm as shown in Fig.2 and the specific area of 27.3 m²/g.
Ni-UFP was activated as a catalyst by reducing the oxidized surface. It was found sufficient for this purpose to fluidize the commercial Ni-UFP and heat it at 160 to 180°C under hydrogen atmosphere for several tens seconds. Two types of Raney Ni catalysts were prepared for references. One was so called W-4 Ni, and the other was Ni prepared by modified W-4method by using 93°C instead of 50°C for soaking (high temperature-soaked Raney Ni).
Hydrogenation of O.2 ml of 1, 3-cyclooctadiene was carried out over about 0.05 to O.2 g of catalysts at 30°C under an atmospheric pressure of hydrogen. The amount of hydrogen absorbed with reaction time over Ni-UFP and Raney Ni catalysts are shown in Fig.3 and 4, respectively. The initial rapid hydrogen absorption was found to be due to the hydrogenation of 1, 3-cyclooctadiene to cyclooctene (1 st. stage of hydrogenation). The later slow absorption of hydrogen was due to the hydrogenation of cyclooctene to cyclooctane (2 nd. stage of hydrogenation). Fig.5, 6, and 7 show the change of the composition of the reaction mixtures. Rates of 1 st. and 2 nd. stage of hydrogenation were estimated from the initial and later slopes of the hydrogen absorption curves, respectively. These values are listed in table 2. Selectivity for cyclooctene was defined as the ratio of 1 st. stage of hydrogenation rate to 2 nd. one. High temperature-soaked Raney Ni was more active than W-4 Raney Ni. However, the selectivity was not so much dependent on the preparative methods of Raney Ni catalysts. Ni-UFP showed the activity of 2 to 7 times higher and selectivity of 5 to 10times higher than Raney Ni catalysts.

View full abstract

The interesting results were obtained by the mass spectroscopic experiments for LiF vapour. The observed main ions are Li_nF_n-1⁺ produced by the ionic dissociation of (LiF)_n→ Li_nF_n-1⁺+e. In view of the accumulation of the experimental information, the ab initio calculations are performed on Li_nF_m and Li_nF_m⁺+ ions (m≤n≤4) by using the energy gradient method with the 3-21 G* base.
The geometries, ionization energies and spin densities of these compounds are discussed relating with LiF ionic bond nature. For the LinF(m<n) series, their geometries are "flexible" and the ionization energy values are localized within small and narrow energy region.
The calculated appearance potentials of various ions show that the Li_nF_n-1⁺ ions has the smallest values among their family compounds and the experimental results can be explained. For LiF, (LiF)₂ and their cations, we calculate the modes and frequencies of normal vibrations and (S+D)CI potentials. The dissociation mechanisms of LiF⁺ and (LiF)²⁺ ion are also discussed. The potential curve of LiF+ has the shallow minimum with the normal vibration frequency at 286 cm^-1, and the vertical ionization region is near the continuum state: LiF+ Li+ + F. The minimized state of (LiF)²⁺ ion is the transition state: (LiF)₂⁺→ Li₂F⁺+F. The values of Franck-Condon factor of LiF→ LiF⁺, which is evaluated by the Morse function approximation, are presented.

View full abstract

Transparent ultrafine iron(III) oxide pigment having particle diameter of 80Å was prepared by the colloid chemical method as follows: Iron(III) hydroxide precipitate was made by the addition of sodium carbonate solution to iron(III) sulfate solution and the precipitate was peptized by iron(II) chloride solution. The positively charged hydrosol was coagulated by the addition of anionic surfactant such as sodium dodecylbenzenesulfonate, sodium hexanoate, sodium octanoate and sodium dodecanoate. The coagulated colloid particles were transfered into organic solvent by shaking. Then, the organic solvent was removed by the distillation under the reduced pressure and the transparent ultrafine iron(III) oxide pigment obtained was thermally treated at a temperature below decomposition temperature of surfactant. The pigment prepared by the proposed method had the excellent absorbance for ultraviolet rays and the transparency to visible rays. It dispersed well in many organic solvents.

View full abstract

Preparation of monodispersed hematite particles was carried out by forced hydrolysis of aqueous mixed solutions of iron(II) chloride, glycine, and hydrochloric acid. The compositions of mixed solutions were ranged from 0.20 to 1.00 mol·dm^-3 of glycine and from 0.19 to O.71 mol·dm^-3 of hydrochloric acid at the fixed concentration of 2.0× 10^-3 mol·dm^-3 iron(III)chloride solution. The mixed solutions freshly prepared were aged at 100°C for four days in a thermostated air oven. Under the limited set of conditions, the monodispersed double sphere or dumbbell hematite particles were obtained without formation of iron (II) oxide hydroxide. For example, the large double sphere he'matite particles (-4, μm) were formed in the solution of 0.60 moldm-3 glycine and O.47 moldm-3 hydrochloric acid, which grew up with increasing hydrochloric acid concentration. Calculations using known formation constants showed that species of iron (III) chloro and glycinato complexes were dominant (ca.94% of the total iron(II) ions) in the solution at 25°C under the best conditions. Such a situation was considered to prevent formation of iron(III) oxide hydroxide and to keep appropriate concentrations of iron(III) hydroxo complexes for making suitable nucleation and growth of the monodispersed hematite particles.

View full abstract

Formation of monodispersed gallium hydrous oxide particles was studied by hydrolysis of aqueous gallium salt solutions at elevated temperatures. It was confirmed that a heating rate of solution was a very important factor for obtaining the monodispersed particles. For the gallium sulfate system at the fixed [SO₄2-]t[Ga3+]t ratio of 1.9, the monodispersed spherical particles of gallium hydrous oxide were obtained under the limited set of conditions. For example, the spherical particles of 0.4, um were prepared at the compositions of 1.1 ×10-3and 1.2×10-3 mol· dm-3 of total gallium ion and acid (2[H2SO4]±[HNO3]) concentrations respectively. These particles were identified to be amorphous-like gallium oxide hydroxide by X-ray powder diffractometry. The [SO42-]t/[Ga3+]t ratios also affected the shape of particles, which ranged from 2.0 to 0.60 for making the monodispersed spherical particles. In the absence of sulfate ions, only rod-like gallium oxide hydroxide particles were formed. It was concluded that the presence of sulfate ions in the aging solutions was essential to obtain the monodispersed spherical gallium hydrous oxide particles as well as in the case of aluminium and chromium systems. The role of sulfate ions and the effect of heating rate on making the monodispersed particles were discussed.

View full abstract

A Raney type copper catalyst was prepared from a layer of Cu-Al alloy produced along the boundary of a copper plate and aluminum plates by hot-rolling. The fine particle catalyst of.0.03-0.09 pm diameter with the specific surface area of 317 BET m²/m² attained the rate of 10.0 mol/h·m² for 2-propanol dehydrogenation at 300°C, whereas a cleaned copper plate catalyst gave only 0.5 mol/h·m². The catalyst structure and activity were changed by sintering and oxidation-reduction pretreatments (Table 1), which was compared with the thermogravity change for the representative catalysts (Fig.4).

View full abstract

MgO powders were prepared by the vapor phase reaction of Mg vapor and O₂. Each MgO particle was a single crystal and had rectangular parallelepiped or cubic shapes. The lattice parameter was constant (4.211-4.214 A) independently of reaction conditions. The size of MgO particle was ranged from 0.005 to 0.4 pm and was related to the ratio [O₂]/[Mg] and the reaction temperature. The particle size decreased with increasing the ratio of [O₂]/[Mg]and with increasing reaction temperatures.

View full abstract