Porous Glass Tube Research Articles

Pore Structure and Gas Diffusion Features of Ionic Liquid-Derived Carbon Membranes

In the present study, the concept of Ionic Liquid (IL)-mediated formation of carbon was applied to derive composite membranes bearing a nanoporous carbon phase within their separation layer. Thermolytic carbonization of the supported ionic liquid membranes, prepared by infiltration of the IL 1-methyl-3-butylimidazolium tricyanomethanide into the porous network of Vycor® porous glass tubes, was applied to derive the precursor Carbon/Vycor® composites. All precursors underwent a second cycle of IL infiltration/pyrolysis with the target to finetune the pore structural characteristics of the carbonaceous matter nesting inside the separation layer. The pore structural assets and evolution of the gas permeation properties and separation efficiency of the as-derived composite membranes were investigated with reference to the duration of the second infiltration step. The transport mechanisms of the permeating gases were elucidated and correlated to the structural characteristics of the supported carbon phase and the analysis of LN2 adsorption isotherms. Regarding the gas separation efficiency of the fabricated Carbon/Vycor® composite membranes, He/CO2 ideal selectivity values as high as 4.31 at 1 bar and 25 °C and 4.64 at 0.3 bar and 90 °C were achieved. In addition, the CO2/N2 ideal selectivity becomes slightly improved for longer second-impregnation times.

Influence of Dissolved Ions on the Water Purification Performance of TiO2-Impregnated Porous Silica Tubes

TiO2-coated porous silica glass tubes containing macropores were fabricated and evaluated for their water-purification capacity using aqueous solutions of methylene blue. From the results of photocatalytic degradation tests at different initial methylene blue concentrations, the equilibrium adsorption constant (K) was determined to be 4.6 × 10−2 L µmol−1, and the Langmuir-Hinshelwood rate constant (kLH) was calculated as 2.6 µM min−1. To determine the influence of ions on the efficiency of methylene blue degradation, we examined both Milli-Q water (soft water) and Contrex water (hard water) as solvents, and confirmed the reduced purification for the Contrex solution. It was, therefore, considered that the presence of inorganic salts decreased the photocatalytic efficiency. Furthermore, variations in the methylene blue decomposition ability were observed between anion-free and cation-free Contrex. Finally, we concluded that the efficiency of photocatalytic decomposition of TiO2 was influenced by multiple parameters, including the presence of anions and cations, as well as the solution pH.

Photocatalytic activity of transparent porous glass supported TiO 2

A porous glass tube with a composition of 96SiO 2·4B 2O 3 (wt%) supported TiO 2 shows high photooxidation activity due to its transparency and large surface area. The surface area of the porous glass tube supported TiO 2 is 10,000 times larger than that of conventional materials. TiO 2 crystals supported are anatase type. Transparency of the porous glass tube is very important. Herein, sol–gel and chemical vapor deposition (CVD) processes were employed as TiO 2 supporting processes. CVD process is more effective. For instance, an aqueous methylene blue solution with 1 ppm concentration almost thoroughly decomposes at a contact time of 300 s using porous glass tube supported TiO 2 prepared by CVD process under irradiating with 10 W low-pressure mercury lamp, on the other hand, opaque porous alumina tube supported TiO 2 was only 25%. The smaller the pore size of the porous glass tube, the larger the transparency and the permeation resistance through porous glass tube. Hence, porous glass tube with ca. 40 nm pore diameter is suitable from the standpoint of a practical use.

Fabrication and characterization of metallic glasses with a specific microstructure for micro-electro-mechanical system applications

Metallic glass microstructures with high aspect ratios for micro-electro-mechanical system applications have been fabricated by micro-electro-discharge machining and selective electrochemical dissolution methods. Micro-holes and three-dimensional microstructures machined on the La62Al14Ni12Cu12, Zr55Al10Ni5Cu30 and Cu46Zr44Al7Y3 bulk metallic glasses by micro-electro-discharge machining are evaluated by using X-ray diffraction, scanning electron microscopy, and nanoindentation. The experimental results demonstrate that the machined samples kept their amorphous structure without devitrification, and their machining characteristics are related to the thermo-physical properties of the alloys and the electrode diameters. Porous, single-pore and thin-walled Zr-based metallic glass tubes with micro-pore structures can be prepared by selective electrochemical dissolution method. The high aspect ratio microstructures fabricated by the two methods have the potential applications as micro-nozzles, polymer micro-injection molding tools, micro-channels or micro-flow meters in micro-electro-mechanical system devices.

Thin porous glass tubes

Thin porous glass tubes were prepared by extruding a polymer solution containing suspended glass powder to a tubular precursor at room temperature, which was then heat treated at elevated temperatures to remove the polymer and sinter the particles to a porous or dense structure with sufficient mechanical strength. In extruding these thin tubular precursors, polyethersulfone (PESF) and N-methyl-2-pyrrolidone (NMP) were used as the polymer binder and the solvent, respectively. Porous glass tubes can be obtained directly by sintering the tubular precursor at relatively lower temperatures. Heated at higher temperatures (i.e. 900 °C), the glass tubes became gas tight. Subsequently, the sodium borosilicate glass tubes were leached in hot water to remove the soluble phase formed by phase separation during cooling. The characterizing technique involved XRD, SEM and gas permeation measurements. SEM examination indicated that during leaching, the glass developed pores of about 0.1 μm size consistent with gas permeation measurements.

Light-response of N2 Permeation Using Gold Colloid-coated Porous Glass Modified by Azo Derivative Including Thiol

Abstract Photo responsive gas separation membrane modified by organic azo derivative including thiol group on the gold colloid-coated porous glass tube was shown that the nitrogen gas permeance was increased by the stimulation of UV light and stopped the permeation by stopping the irradiation.

Formation of Silicalite‐1 in Channels of Novel SiO2–ZrO2 Porous Glass Tubes Used as Both a Silica Source and a Substrate

Silicalite‐1 has been prepared using a novel SiO2–ZrO2 porous glass tube as both a silica source and a substrate. The SiO2–ZrO2 glass tube was found to possess sufficient physical strength to enable practical use as a separation and catalytic membrane after silicate‐1 deposition within its channel. This is in contrast to porous SiO2 glass which cannot be used to synthesize a silicalite‐1 deposited membrane with enough physical strength to perform gas permeance measurements.

Separation of Tritium Compounds Using Porous VYCOR Glass Tube Wall

ABSTRACTTritium compounds need to be separated to each chemical form for reasonable and continuous monitoring of tritium compounds. In this study, the continuous monitoring of HT in the air containing HT and HTO was investigated using the separation cell made of porous Vycor glass tube. The apparatus for a continuous and selective monitoring of tritium compounds in the air containing HT and HTO was constructed of radioactive gas monitor, ion chamber and the separation cell. An air containing tritium compounds (HT, HTO, etc.) was provided by Research Reactor Institute of Kyoto University. In the air containing of HT and HTO, HT is found to permeate selectively through the pores of the porous Vycor glass tube wall.

Electrochemical reduction of nitrous oxide by the protons transported through polyelectrolyte-coated porous glass

An electrochemical method for the reduction of nitrous oxide has been developed, in which N 2O is completely reduced to N 2 on a metal cathode by protons generated on the anode and transported through a polyelectrolyte-coated porous glass. The cathode was a metal wire wound around a porous glass tube, and the metals used were zinc, lead, iron, and copper. The anode was made from grains of glassy carbon packed in the tube. The reduction was affected by kinetic factors, including the adsorption rate of N 2O onto the cathode, the transport rate of protons through the polyelectrolyte-coated porous glass and the hydrogen overpotential of the cathode metal. Of the metals used, it was found that the most efficient for the N 2O reduction was zinc.

Methanol vapor separation through the silica membrane prepared by the CVD method with the aid of evacuation

Two types of the silica membrane were prepared by the CVD with the aid of evacuation. Porous glass tubes with outer diameter of 5 mm, inner diameter of 4 mm were used as supports. Mean pore diameters of the supports were 4 nm (CVD-1) and 2 nm (CVD-2), respectively. Tetraethoxysilane (TEOS, Si(OC 2 H 5 ) 4 ) and oxygen were used as reactants. The inside of the membrane modules were evacuated with a vacuum pump to deposit silica near the pores preferentially. Due to evaluate methanol vapor separation, mixed gas separation of the membranes were measured using H 2 -10%CH 3 OH and CO-10%CH 3 OH gas mixtures at 373 and 473 K. At 473 K, the separation factors of H 2 /CH 3 OH were about 6 for CVD-1 and about 20 for CVD-2. These value were higher than that of the porous glass membrane with mean pore diameter of 4 nm (H 2 /CH 3 OH=1.2). The separation factor for CVD-2 was about 5 times as large as the theoretical Knudsen value (H 2 /CH 3 OH=4).

Development of a light-responsive permeation membrane modified by an azo derivative on a porous glass substrate

A photo-responsive gas separation membrane modified by an organic azo derivative in a porous glass tube shows decreased gas permeance upon stimulation with an Xe- lamp, which returns the starting level upon stopping the irradiation.

Permeation of methanol vapor through silica membranes prepared by the CVD method with the aid of evacuation

Silica membranes were prepared by depositing silica on porous glass tubes with the aid of evacuation using tetraethoxysilane as a reactant in the temperature range 673–773 K. The basic permeation properties of methanol vapor in gas phase were investigated. This membrane appears to hinder permeation of methanol vapor. This behavior is quite different from the original porous glass and other reported membranes. The separation factors of He/CH 3OH were 7.1 at 373 K and 16.9 at 473 K. These values are much higher than the Knudsen value (He/CH 3OH=2.8). The permeances of He and N 2 through this membrane were also measured for varying temperatures in order to investigate the permeation mechanism. Gas permeation through the membrane was predominantly governed by an activated diffusion mechanism.

Application of organic-inorganic polymer hybrids as selective gas permeation membranes

The gas permeability of polymer hybrid membranes has been investigated. The membranes were prepared by dip-coating a methanol solution of poly(N-vinylpyrrolidone) (PVP) and methyltrimethoxysilane (MTMOS) on porous glass tubes. The permeance was measured by using N 2 , CO 2 and He separately at a pressure of 1 kg cm –2 . It was found that the permeance of these gases all increased with temperature in the PVP hybrid membranes. In particular, the permeance of He increased at a much greater rate with temperature, resulting in high selectivity against N 2 . For instance, the permeance of He is 150 times greater than that of N 2 at 100 °C. The results indicate the dense structure of PVP hybrid membranes as confirmed by SEM observations. The hybrid membranes also exhibited high selectivity of CO 2 against N 2 . This could be attributed to the high polarity of amide groups in PVP chains which would facilitate the sorption of CO 2 . These polymer hybrid membranes were also found to have high thermal stability compared to organic polymer membranes.

Effects of pore size on separation mechanisms of microfiltration of oily water, using porous glass tubular membrane

The effects of the average pore size in porous glass tube membranes on the performance of the cross-flow microfiltration were investigated using oil-in-water emulsion. The flux decline with filtration time was divided into two stages. The filtration mechanism in the first stage can be explained by three types of blocking filtration models such as the complete type for pore size 0.27 μm membrane, the intermediate type for pore size 0.75 μm membrane and the standard type for pore size 1.47 μm. The second stage can be also explained by the cake filtration model. The oil rejection is found to decrease with time initially, but is soon stabilized at a constant level. This was explained by the comparison among the average pore size, the pore size distribution of used membrane and the droplet distribution of the feed emulsion. The surfactant transmission of the cake filtration stage was 49% for 0.27 μm membrane, 80% for 0.75 μm membrane and 99% for 1.47 μm membrane.

A Study on Development of an Electrolysis System with Vertically Circulating Mercury Capillary Bundle Electrode and Its Characteristics

An electrolysis system with a vertically circulating mercury capillary bundle electrode was developed with a very large electrode area in a minimum space by force feeding mercury and an aqueous solution containing metal ion into a fiber bundle packed densely within a small porous glass tube. In order to test the characteristics and stability of the electrolysis system, the reduction voltammograms of uranyl and ferric ions were measured with changes in the mercury and aqueous flow rates. The aqueous flow rate had a large effect on the electroreaction of the metal ion occurring on the interface between the mercury and the aqueous solution and had to be regulated at an appropriate value for the good development of limiting current shape. The limiting current is linearly proportional to the aqueous flow rate. With a mercury flow rate high enough to keep a capillary continuum of mercury in the fiber bundle, the mercury flow rate had almost no effect on the electroreaction. This developed system was confirmed to be effective and stable enough to control rapidly and continuously the oxidation state of metal ions fed into the system under an appropriate aqueous flow rate, having the property of a high overpotential against the hydrogen evolution reaction.

Properties of the TiO 2 membranes prepared by CVD of titanium tetraisopropoxide

Thin films of TiO 2 were deposited on the inner surface of porous Vycor glass tubes by atmospheric pressure chemical vapor deposition (APCVD) at temperatures ranging from 200 to 400°C using titanium isopropoxide as a precursor. Dense and hydrogen-permselective membranes were formed only in the temperature range between 230 and 300°C. Gas permeation through the dense membrane was governed by an activated diffusion mechanism and the H 2:N 2 permeation ratio was far beyond the range of Knudsen diffusion. At 200 and 400°C, however, highly porous films were formed and the permselectivity of the membrane was not improved at all, because gas permeation through the porous membrane was in the Knudsen diffusion regime. Selectivity (H 2:N 2 permeation ratio) profile showed a maximum value of 57 at a deposition temperature of 250°C. The oxygen added to the reaction environment appeared to have some effects on the stability and the permselectivity of the membrane formed. The permeation properties of the TiO 2 membranes were not so appreciable and the stability of the membrane was poor when compared with dense SiO 2 membranes. The characterization of the TiO 2 films by SEM and TEM reveals that phase change from amorphous to crystalline state occurs at a temperature about 300°C.

Flow of Air, Nitrogen, and Hydrogen through Porous Glass Tubes

Abstract A simple apparatus for obtaining diffusion data for porous tubes is described. It was used for determining the permeation rates of air, nitrogen, and hydrogen through porous 96% SiO2 glass tubes. To increase flow, these tubes were subjected to multiple etch/wash treatments using aqueous NH4F solutions at room temperature followed by successive hot washes in dilute mineral acid and distilled water. Further increases in permeation rates were achieved by subjecting the base glass used in the preparation of the porous glass to long heat treatments at its phase-separation liquidus prior to leaching and etching. Diffusion data show that the permeability of porous glass is not degraded on heating at temperatures up to 800°C, and that the separation ratios of the experimental glasses are in good agreement with values expected from Graham's law of diffusion. The role of heat treatment of the base glass, etch/wash treatments of the porous glass, and moisture in the gas stream are discussed.

Gas separation properties of a new polymer/inorganic composite membrane

Permeability, diffusivity and solubility of gases in polymer/inorganic composite membranes are reported. Membranes were prepared by covering a porous Vycor glass tube with polysilastyrene solution followed by pyrolysis at 382 and 470°C. The experimental data indicate that the gas separation properties of such a membrane are a combination of the transport characteristics of the polymer and the molecular-sieve material. Selectivity factor for H 2/SF 6 increases to 328 for the membrane pyrolyzed at 470°C whereas for the unpyrolyzed polymer it is merely 10.

A method for the determination of the pore size distribution of molecular sieve materials and its application to the characterization of partially pyrolyzed polysilastyrene/porous glass composite membranes

A technique for the determination of the pore size distribution of molecular sieve materials is described. This method is based on the determination of the microporous volume accessible to molecular probes of different sizes. The method is used to follow the molecular sieve structure which develops during the pyrolysis of polysilastyrene (dimethylsilane-methylphenylsilane copolymer). A molecular sieve membrane is prepared by partially pyrolyzing a polysilastyrene solution-coated porous Vycor glass tube.

Separation of hydrogen through palladium thin film supported on a porous glass tube

Studies have been conducted on the characterization of hydrogen separation by a composite membrane consisting of a thin palladium film supported on the outer surface of a porous glass cylinder. The composite membrane was highly permeable to hydrogen, having an extremely high selectivity for hydrogen separation. The high flux was related to the thinness of the palladium film. The addition of copper or silver to the palladium film improved the membrane, making it suitable to be utilized below 573 K, at the same time maintaining the extremely high selectivity. The rate of hydrogen permeation, however, was reduced by the addition of these elements causing the film to become inhomogeneous.