SEMIBATCH PRECIPITATION ACCOMPANYING GAS-LIQUID REACTION

To obtain large particles of insoluble product by precipitation accompanying a gas-liquid reaction, a sparged stirred vessel was operated continuously for the gaseous and liquid reactants but batchwise for the product particles. Except at the beginning of run, most particles formed floes. With increasing concentration of product particles, the average size of floes increased for CaC0₃ but remained unchanged or decreased slightly for SrCO₃ and BaC0₃The effect of agitation on the floc size was significant for CaC03 but scarcely observed for SrC0₃ and BaC0₃ The mass per unit volume of sedimented floes of the three species increased with increasing concentration of product particles, and under the same conditions, they decreased in the following order: CaC0₃ SrC0₃ BaC0₃     

Structures and dehydrogenation activities of vanadium oxide overlayers on supports

A method has been devised to prepare reduced Co clusters in zeolite Y. Sodium acetate is impregnated after exchanging Co²⁺ ions into the zeolite. During calcination the acetate is partially or completely oxidized to sodium oxide. This not only stabilizes Co²⁺ ions in supercages, impeding their migration to smaller cages, but it also neutralizes the protons that are formed during the reduction of the Co²⁺ ions with H₂. As a result, the temperature of effective reduction is lowered by up to 350 °C, depending on the calcination program. In unmodified zeolites, Co reduction requires a temperature above 750 °C, which inevitably induces partial destruction of the zeolite lattice; this novel method permits complete reduction of Co without damaging the zeolite lattice. It is predicted that this novel method should be applicable to other zeolite encaged metals of low reducibility such as Ni.     

Feasibility Study of Hydrogen Generator with Molten Slag Granulation

A huge amount of hot molten oxides, such as steelmaking slag and molten municipal waste, is discharged at present without heat recovery, in spite of its very high potential. For example, hot molten slag as a by‐product in the Japanese steelmaking industry, over 1723 K in temperature, reaches as much as 30 million tonnes annually. To recover heat of the viscous slag chemically, the strongly endothermic reaction CH₄+H₂O →3H₂+CO was selected and then the property of dry granulation of the molten slag by Rotary Cup Atomizer (RCA) for expanding surface area of the slag was experimentally studied. The purpose of this paper was, therefore, to study slag granulation under various conditions for promoting heat exchange between slag and gas, in which the influence of the rotating speed and the shape of the cup on the slag drop size was mainly examined. The collected slag drops were correlated with operating conditions such as rotating speed, cup shape, etc. Most significantly, the molten slag was successfully granulated under the dry conditions without water impingement. The rotating speed of the cup influenced the diameter and shape of the slag drops very strongly. The higher rotating speed made the slag drops smaller, more spherical and uniform. Drops with 5 to 6 mm of average dimension were obtained at a rotating speed of 15 rps (900 rpm), and drops with about 1 mm at 50 rps (3000 rpm). In the former case, the shape of the obtained drops changed from spherical to ribbon‐like. These results will be useful to establish new heat recovery processes with hydrogen generation from molten slag with many benefits. Energy analysis and cost evaluation were also conducted, to study the benefit of the proposed process.     

Preparation of Tubular Silicalite Membranes by Hydrothermal Synthesis with Electrophoretic Deposition as a Seeding Technique

Preparation of tubular silicalite membranes by hydrothermal synthesis with electrophoretic deposition (EPD) as a seeding technique was investigated. Two micrometers of small silicalite seeds were produced by an open-system hydrothermal synthesis at 100°C. These seeds were dispersed in 1-propanol and seeded on porous tubular stainless-steel supports by EPD; it had a high productivity and uniformity. The seeded support was then hydrothermally treated, and a tubular silicalite membrane was obtained. The pervaporation performance of this membrane showed a separation factor α of 70 with a total flux of 0.35 kg·(m²·h)⁻¹ for a 5 vol% EtOH aqueous solution at 30°C.     

Development of radially movable multichannel Reynolds stress probe system for a cylindrical laboratory plasma

A new radially movable multichannel azimuthal probe system has been developed for measuring azimuthal and radial profiles of electrostatic Reynolds stress (RS) per mass density of microscale fluctuations for a cylindrical laboratory plasma. The system is composed of 16 probe units arranged azimuthally. Each probe unit has six electrodes to simultaneously measure azimuthal and radial electric fields for obtaining RS. The advantage of the system is that each probe unit is radially movable to measure azimuthal RS profiles at arbitrary radial locations as well as two-dimensional structures of fluctuations. The first result from temporal observation of fluctuation azimuthal profile presents that a low-frequency fluctuation (1-2 kHz) synchronizes oscillating Reynolds stress. In addition, radial scanning of the probe system simultaneously demonstrates two-dimensional patterns of mode structure and nonlinear forces with frequency f = 1.5 kHz and azimuthal mode number m = 1.     

Porous polydimethylsiloxane membranes treated with aminopropyltrimethoxysilane

Polydimethylsiloxane (PDMS) membranes were made by catalytic hydrosilylation of a siloxane compound having a vinyl group and an SiH group in the presence of 1,4-dioxane. By washing it with water many pores were formed in the membrane. Then, the pore size of the membrane was controlled by treatment of aminopropyltrimethoxysilane (APTMS) solution. When increasing the APTMS concentration, the pore size of the membrane was reduced by the formation of APTMS oligomer on the surface of the membrane. The characteristics of the membrane was examined by IR, ATR-IR, and SEM techniques. Also, the permeation properties of dextrans and polystyrene latexes through the treated membrane were examined by the ultrafiltration method. © 1994 John Wiley & Sons, Inc.     

Dry galloping characteristics and its mechanism of inclined/yawed cables

Mechanism of dry galloping of inclined cable of cable-stayed bridges is described in relation to Karman vortex mitigation. Furthermore, the role of Scruton number Sc on reduced critical velocity Vrcr of the dry galloping is investigated for practical use basing on wind tunnel tests and field observations of dry galloping or pseudo-galloping, which is classified as cable vibration with rain-state but response amplitude is abnormally large. It is verified that as far as the divergent-type of dry galloping, the design criterion subject to Sc-Vrcr proposed by FHWA (Federal Highway Administration of U.S.) seems to be reasonable for practical use, on the other hand, for the unsteady dry galloping, the Saito criterion for Sc-Vrcr diagram seems to be reasonable.     

Nonisothermal crystallization of poly(ethylene terephthalate) and its blends in the injection-molding process

We investigated the nonisothermal crystallization during the cooling process of injection molding of poly(ethylene terephthalate) (PET), PET/talc, and PET/Surlyn blends. We applied the isothermal crystallization parameters obtained by the Hoffman–Lauritzen theory to the kinetics of nonisothermal crystallization and then calculated the relative crystallinity χ/χ_c as a function of the mold temperature. χ/χ_c were nicely interpreted by calculation without effect of the pressure history on crystallization in PET and PET/talc (1 wt %) blends. In contrast, in the PET/Surlyn (3 wt %) blend, crystallization occurred at a lower mold temperature than predicted by our calculation. The transmission electron micrograph near the surface of the injection-molded PET/Surlyn blend showed deformation and stretching of dispersed Surlyn particles, suggesting that orientation of the PET matrix proceeds with the flow in processing. The orientation of the PET matrix resulted in acceleration of the crystallization in the injection molding. © 1995 John Wiley & Sons, Inc.     

Unique and facile solvothermal synthesis of mesoporous WO3 using a solid precursor and a surfactant template as a photoanode for visible-light-driven water oxidation

Mesoporous tungsten trioxide (WO₃) was prepared from tungstic acid (H₂WO₄) as a tungsten precursor with dodecylamine (DDA) as a template to guide porosity of the nanostructure by a solvothermal technique. The WO₃ sample (denoted as WO₃-DDA) prepared with DDA was moulded on an electrode to yield efficient performance for visible-light-driven photoelectrochemical (PEC) water oxidation. Powder X-ray diffraction (XRD) data of the WO₃-DDA sample calcined at 400°C indicate a crystalline framework of the mesoporous structure with disordered arrangement of pores. N₂ physisorption studies show a Brunauer-Emmett-Teller (BET) surface area up to 57 m² g^-1 together with type IV isotherms and uniform distribution of a nanoscale pore size in the mesopore region. Scanning electron microscopy (SEM) images exhibit well-connected tiny spherical WO₃ particles with a diameter of ca. 5 to 20 nm composing the mesoporous network. The WO₃-DDA electrode generated photoanodic current density of 1.1 mA cm^-2 at 1.0 V versus Ag/AgCl under visible light irradiation, which is about three times higher than that of the untemplated WO₃. O₂ (1.49 μmol; Faraday efficiency, 65.2%) was evolved during the 1-h photoelectrolysis for the WO₃-DDA electrode under the conditions employed. The mesoporous electrode turned out to work more efficiently for visible-light-driven water oxidation relative to the untemplated WO₃ electrode.