• Applied Chemistry for Engineering
• /
• v.10 no.3
• /
• pp.362-366
• /
• 1999

Membranes for biosensor were prepared from poly(vinyl chloride) (PVC)l derivatives using the solution casting method, and their gas permeabilities were studied. The polymer membranes dried slowly in air showed higher permeability coefficients than those dried in vacuum. The permeabilily coefficients of carboxylated poly(vinyl chloride) (CPVC) membranes for $O_2$ and $CO_2$ decreased as the pressure of the feed gas increased. The addition of dioctylphthalate (DOP) enhanced the permeation rates for $O_2$ and $CO_2$. For example, the permeability coefficients of CPVC membranes containing 30 wt. % DOP for $O_2$ and $CO_2$ at 100 psig were 2.03 and 0.96 Barrer, respectively, which were about 4~5 times higher than those of the membranes without DOP. Poly(vinyl chloride-co-vinyl acetate-co-vinyl alcohol) (Syn-PVCAcAl) obtained by hydrolysis of poly(vinyl chloride-co-vinyl acetate (PVCA) showed a higher permeability coefficient for $CO_2$ in the presence of DOP than that for commercial PVCAcAl, but did not show any significant difference in permeability for $O_2$.

• Applied Chemistry for Engineering
• /
• v.21 no.5
• /
• pp.495-499
• /
• 2010

To develop chemical and biosensors, this paper studies sensing characteristics of bulk carbon nanotube (CNT) electrodes by means of their electrical impedance properties due to their large surface area and excellence chemical absorptivity. The sensors were fabricated in the form of film and nano web style by using composite process for mass production. The bulk composite electrodes were fabricated with singlewall and multi-wall carbon nanotubes based on host polymers such as Nafion and PAN, using a solution-casting and an electrospinning technique. The resistance and the capacitance of electrodes were measured with LCR meter under the various amounts of buffer solution to study the electrical impedance change properties of them. On the experimental of sensor electrode, impedance characteristics of the composite electrode are affected by its host polymer and nanofiller and its sensing response showed saturated result after applying some amounts of buffer solution for test chemical. Especially, the capacitance values showed drastic changes while the resistance values only changed within few percent range. It is deduced that the ions in the solution penetrated and diffused into the electrodes surface changed the electrical properties of the electrodes much like a doping effect.

• Journal of the Korean Vacuum Society
• /
• v.17 no.5
• /
• pp.466-472
• /
• 2008

Purple Gold is the alloy consisting of 78wt%Au-22wt%Al, and is expressed as a chemical formula, $AuAl_2$. Lately it is being used for the material of accessories or the decorative ornaments, being one of the colored golds having the peculiar purple color, like White Gold and Pink Gold. Purple Gold has the weak point in shaping through casting process due to the bad malleability and castability, being the intermetalic compound of Au and Al. Therefore, it is possible to produce the final product only by the cutting and the grinding process or to use it as a decorative coat with the thin film evaporation. This study implemented two kinds of thin film experiments. One is the case that heat treatment was made after Au and Al deposition evaporated separately with a weight ratio 78:22 on the 200nm$SiO_2$/Si substrate. The other is the case that the surface deposition was made through the vacuum evaporation, keeping the glass substrate temperature remain room temperature, using the bulk $AuAl_2$ as a source. The final film property was measured, focusing on the Purple Gold's color and thickness through the bare eye inspection, the microstructure analysis, the surface resistance analysis, the color difference analysis, and XRD analysis. Purple Gold was not formed, as the excessive surface agglomeration occurred, in case of being produced and treated thermally with 12.5nmAu/40nmAl/200nm$SiO_2$/Si structure. Our results suggest that of Purple Gold films, showing the same purple color as the bulk's, were successfully deposited with the direct thermal evaporation from the $AuAl_2$ bulk source.

• Membrane Journal
• /
• v.27 no.2
• /
• pp.199-204
• /
• 2017

In this study, a study was carried out for the separation of metal ions in lignin extract discharged from the pulp process. alumina powders were mixed with DMAc (N, N-dimethylacetamide) solvent and PESf (Polyethersulfone) polymer, PVP (polyvinylpyrrolidone) dispersant was added and slip casting method was used to prepare the membrane. The membrane was measured for pore size through a CFP (Capillary Flow Porometer) device and the surface and cross-section of the membrane were observed through a FE-SEM (Field Emission Scanning Electron Microscope). The flux was calculated by measuring the filtered weight per hour using a separation experiment device. Pore size measurements were performed under increasing pressure from 0 psi to 30 psi. The pore size of the membrane was $0.4{\mu}m$ and the flux decreased from the initial flux value of $6.36kg{\cdot}m^{-2}{\cdot}h^{-1}$ to $1.98kg{\cdot}m^{-2}{\cdot}h^{-1}$ due to the fouling of the membrane. After the permeation experiment, membrane contaminants were removed by simple washing. Separation experiments showed that Na contained in the initial lignin extract was reduced by 69%, Fe was removed by 87%, K by 95%, Ca by 93% and Mg by 96%.

• Membrane Journal
• /
• v.28 no.3
• /
• pp.187-195
• /
• 2018

In this work, the morphology of polyvinylidene-co-hexafluoropropylene (PVDF-co-HFP) membranes were systemically investigated using phase inversion technique, to target membrane contactor applications. As the presence of macrovoids degrade the mechanical integrity of the membranes and jeopardize the long-term stability of membrane contactor processes (e.g. wetting), a wide range of dope compositions and casting conditions was studied to eliminate the undesired macrovoids. The type of solvent had significant effect on the membrane morphology, and the observed morphology were correlated to the physical properties of the solvent and solvent-polymer interactions. In addition, to fabricate macrovoid-free structure, the effects of different coagulation temperatures, inclusion of additives, and addition of nonsolvents were investigated. Due to the slow crystallization rate of P(VDF-co-HFP) polymer, it was found that obtaining porous membrane without macrovoids is difficult using only nonsolvent-induced phase separation method (NIPS). However, combined other phase inversion methods such as evaporation-induced phase separation (EIPS) and vapor-induced phase separation (VIPS), the desired membrane morphology can be obtained without any macrovoids.

• Korean Journal of Materials Research
• /
• v.10 no.6
• /
• pp.415-421
• /
• 2000

The effect of silica binder content on the mechanical properties of zircon shell mold was investigated. Content of binder silica sol to refractory powder in weight[$R_W$] was adjusted from 0.18 to 0.43. Sintering of the shell mold was carried out in the temperature range of $871^{\circ}C$ to $1400^{\circ}C$. Green strength of the shell mold at room temperature increased with increasing $R_W$ and sintering temperature up to $1300^{\circ}C$. However, the mold with $R_W$ of 0.43 that sintered at $1400^{\circ}C$ for 3 hours showed relatively low strength and large level of porosity. The mechanical behavior of the shells is supposed to attributed to the difference in thermal expansion coefficient between refractory powder and binder silica. The optimum value of $R_W$ for zircon-based shell molds was found to be 0.33.

• Korean Journal of Environmental Agriculture
• /
• v.22 no.2
• /
• pp.124-129
• /
• 2003

The objectives of this study are to manufacture an efficient $TiO_2$, photocatalyst and to delineate optimum operational parameters for TCE (trichloroethylene) degradation in a photocatalytic oxidative reactor. The $TiO_2$ photocatalyst irradiated by 365 nm UV light is expected to increase degradation of TCE in solution by a series of photocatalytic oxidations in the reactor. A new membrane $TiO_2$ photocatalyst wns eventually developed by coating a mixture of Davan-C(0.24 wt%) and PVA(0.16 wt%) on the surface of slips using the slip-casting method. Results show that increase in the number of coating of $TiO_2$ sol on surface of photocatalysts and in the surface thickness improved the endurance and photocatalysts, but these physical modifications caused significant decrease in the overall degradation efficiency of TCE. Pre-aeration or recirculation of the influents to the reactors containing TCE increased degradation efficiency of TCE. The optimum operational conditions far the surface area of photocatalysts and UV light intensity appeared to be $1.47\;mL/cm^2$ and $225\;W/cm^2{\times}100$, respectively, in the reactor. Based on the overall experimental results, the photocatalytic oxidation of TCE with the new membrane $TiO_2$ photocatalyst is found to be very effective under the operational conditions delineated in this study.

• Proceedings of the KACD Conference
• /
• 2001.05a
• /
• pp.235-237
• /
• 2001

;Dentistry has benefited from tremendous advances in technology with the introduction of new techniques and materials, and patients are aware that esthetic approaches in dentistry can change one's appearance. Increasingly. tooth-colored restorative materials have been used for restoration of posterior teeth. Tooth-colored restoration for posterior teeth can be divided into three categories: 1) the direct techniques that can be made in a single appointment and are an intraoral procedure utilizing composites: 2) the semidirect techniques that require both an intraoral and an extraoral procedure and are luted chairside utilizing composites: and 3) the indirect techniques that require several appointments and the expertise of a dental technician working with either composites or ceramics. But, resin restoration has inherent drawbacks of microleakage. polymerization shrinkage, thermal cycling problems. and wear in stress-bearing areas. On the other hand, Ceramic restorations have many advantages over resin restorations. Ceramic inlays are reported to have less leakage than resin restoration and to fit better. although marginal fidelity depends on technique and is laboratory dependent. Adhesion of luting resin is more reliable and durable to etched ceramic material than to treated resin composite. In view of color matching, periodontal health. resistance to abrasion, ceramic restoration is superior to resin restorationl. Materials which have been used for the fabrication of ceramic restorations are various. Conventional powder slurry ceramics are also available. Castable ceramics are produced by centrifugal casting of heat-treated glass ceramics. and machinable ceramics are feldspathic porcelains or cast glass ceramics which are milled using a CAD/CAM apparatus to produce inlays (for example, Cered. They may also be copy milled using the Celay apparatus. Pressable ceramics are produced from feldspathic porcelain which is supplied in ingot form and heated and moulded under pressure to produce a restoration. Infiltrated ceramics are another class of material which are available for use as ceramic inlays. An example is $In-Ceram^{\circledR}$(Vident. California, USA) which consists of a porous aluminum oxide or spinell core infiltrated with glass and subsequently veneered with feldspathic porcelain. In the 1980s. the development of compatible refractory materials made fabrication easier. and the development of adhesive resin cements greatly improved clinical success rates. This case report presents esthetic ceramic inlays for posterior teeth.teeth.

• Journal of Korea Foundry Society
• /
• v.22 no.1
• /
• pp.42-48
• /
• 2002

Effects of coating treatment of metallic Cu, Ni-P film on $SiC_p$, for $SiC_p$/iron aluminide composites were studied. Porous hybrid preforms were fabricated by reactive sintering after mixing the coated $SiC_p$, Fe and Al powders. Then the final composites were manufactured by squeeze casting after pouring AC4C Al alloy melts in preforms. The change of reactive temperature, density, microstructure of the preforms and microstructure of the composites were investigated. The exprimental results were summarized as follows. The thickness of Cu and Ni-P metallic layer formed on $SiC_p$ by electroless plating method were about $0.5{\mu}m$ and coated uniformly. There was no remakable change in the ignition temperature with variation of the mixing ratio of Fe and Al powder while in the case of coated $SiC_p$ it was lower about $20^{\circ}C$ than in the non-coated $SiC_p$. The maximum reaction temperature increased with increasing Al contents, but decreased with increasing $SiC_p$ contents. Expansion ratio of preform after reactive sintering increased with amount of Cu coated $SiC_p$. In the case of Fe-70at.%Al, the expansion ratio was about 7% up to 8wt.% of $SiC_p$, addition but further addition of $SiC_p$, increased the ratio significantly. And in the case of Fe-50 and 60at.%Al, it was about 20% up to 16wt.% of $SiC_p$ addition and about 28% in 24wt.% of $SiC_p$, addition. The microstructures of compounds showed that the grains became finer as amount of $SiC_p$, and mixing ratio of iron powder increased and the shape of compounds was changed gradually from irregular to spheroidal.

• Korean Chemical Engineering Research
• /
• v.40 no.6
• /
• pp.729-734
• /
• 2002

In this study, the polyaniline films of emeraldine base(EB) and lucoemeraldine base(LEB) form chemically doping with poly(sodium-4 styrenesulfonate, PSS) were prepared by casting the mixed solution of chloroform and m-cresol on ITO(indium tin oxide) electrode. By analyzing UV-vis spectra of the mixed solutions, the effects of the secondary doping by m-cresol were obtained. And the conductivity of polyaniline film was increased with increasing m-cresol content. The results suggest that the improvement of conductivity obtained by secondary doping results primarily from interaction of polyaniline and m-cresol. As the results of analyzing cyclic voltammograms, it was known that the redox peak currents of polyaniline electrode prepared from LEB were larger and more reversible than those of polyaniline electrodes prepared from EB. The charge transfer resistances($R_{ct}$) of polyaniline electrodes were reduced with increasing m-cresol content, and LEB/PSS electrodes were smaller than EB/PSS electrodes. This result agrees to the analysis of the redox peak current of cyclic voltammograms. The solution resistance and the capacity of electrical double layer almost unchanged in all prepared polyaniline electrodes. It was confirmed that solution resistance was independent of frequency factor in AC impedance spectra. Also the polyaniline film doping with PSS was revealed pseudo n-type characteristics of conducting polymer.