• Restorative Dentistry and Endodontics
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• v.24 no.2
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• pp.330-336
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• 1999

In biological systems, the mineral that forms hard tissue is of an apatitic nature, and hydroxyapatite($Ca_5OH(PO_4)_3$: HA) is generally considered as the prototype for such a mineral. Thus, the precipitation of HA, having biological implications, has been the subject of several investigations. Crystal growth studies using HA seeds in supersaturated solutions have enhanced our understanding of the process and mechanism involved in seeded crystal growth. From these studies, it has become apparent that the precipitation rate of HA onto the seed crystals depends on the various conditions, especially on the additives. The relation between the supersaturated solution containing fluoride and the process of HA crystal growth enhances the understanding of mechanism of HA crystal growth. Until recently, the studies have been on the crystal growth of enamel minerals and synthetic HA seeds in the supersaturated solution containing 1~2 ppm fluoride. The purpose of the present investigation is to study the effect that fluoride of high concentration has on the crystal growth kinetics of HA. In order to produce the composition found in the secretory enamel fluid, experimental solutions of 1mM Ca, 3mM P, and 100mM Tris as background electrolyte were used. Then this experimental solutions were added to 0, 2, 4, 6, 8, 10 ppm fluoride. The effect of fluoride at high concentrations on the precipitation was examined in a bench-top crystal growth model adopting a miniaturized reaction column. Chemical analysis was employed for characterization of working solutions before and after the experimentation. Remarkable findings were : 1) the amount of crystal growth was gradually accelerated as the fluoride concentration increased until 6 ppm, but decreased in 8 and 10 ppm fluoride; 2) the amount of fluoride ion consumed in crystal formation was constant despite the increase in fluoride concentration.

• Clean Technology
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• v.27 no.2
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• pp.152-159
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• 2021

Volatile organic compounds (VOCs) occur in indoor and outdoor industrial and urban areas and cause environmental problems. Malodorous VOCs, along with aesthetic discomfort, can have a serious effect on the human body. Compared with the existing method of reducing malodorous VOCs, a wet scrubbing method using an electrolytic oxidant has the advantage of reducing pollutants and regenerating oxidants. This study investigated the optimal conditions for producing OCl^-, a chlorine-oxidant. Experiments were conducted by changing the type of anode and cathode electrode, the type of electrolyte, the concentration of electrolytes, and the current density. With Ti/IrO₂ as the anode electrode and Ti as the cathode electrode, OClproduction was highest and most stable. Although OCl^- production was similar with the use of KCl or NaCl, NaCl is preferable because it is cheap and easy to obtain. The effect of NaCl concentration and current density was examined, and the OCl^- production rate and concentration were highest at 0.75 M NaCl and 0.03 A cm^-2. However, considering the cost of electric power, OCl^- production under the conditions of 1.00 M NaCl and 0.01 A cm^-2 was most effective among the conditions examined. It is desirable to produce OCl^- by adjusting the current density in accordance with the concentration and characteristics of pollutants.

• Korean Journal of Materials Research
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• v.3 no.6
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• pp.632-637
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• 1993

The optical properties and electrochromism of amorphous $WO_3$ thin films were studied. $WO_3$ thin films with thickness of 3000$\AA$~6000$\AA$ were deposited by vacuum evaporat.ion. All these films were transparent and found to be amorphous in structure by X-ray diffraction analysis and the visible wave length refractive indices were found to be between 1.9 and 2.1 and the optical energey gap to be 3.25 eV. Electrochromic devices were made consisting of IT0 transparent electrode, $WO_3$ thin films, $LiCIO_4$- propylene carbonate and Pt counter electrode. In terms of their operation, the amorphous $WO_3$ films were colored blue by a double injection of electrons from the transparent electrode and lithium ions from the $LiCIO_4$-propylene carbonate organic electrolyte and made colorless by electrochemical oxidation reaction. The electrochromic properties of $WO_3$ thin films including coloration and bleaching, optical density and response time were all found to be strongly dependent on the film deposition condition, electrolyte concentration, sheet resistance of the transparent electrode and applied voltage.

• Korean Journal of Materials Research
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• v.3 no.6
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• pp.614-623
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• 1993

Electrical characteristics of LiF-$Li_{2}O-B_{2}O_{3}-P_{2}O_5$ glasses with fixed $Li_2O$ content have been investigated by using AC impedance spectroscopy. Part of the total lithium ions present in these glasses contributes to conduction, and the changes in electrical conductivity with composition was inconsistent with the weak electrolyte model. The power law could not be used to determine the hopping ion concentration in these glasses. Both mobile carrier density and mobility have been modified as Li were added in the form of LiF. The formation of $(B-O-P)^-,di^-$, and metaborate group gave additional available sites for Li+ diffusion causing the enhancement of conductivity. The observed maximum conductivity was $2.43 \times 10^{-4}$S/cm at $150^{\circ}C$ at the composition containing 8mol% LiF. The decomposion potential amounted to 5.94V. The Li/glass electrolyte/$TiS_2$ solid-state cell showed open circuit voltage of 3.14V and energy density of 22 Wh/Kg at $150^{\circ}C$.

• Journal of the Mineralogical Society of Korea
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• v.28 no.2
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• pp.95-108
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• 2015

Nano-sized iron colloids are formed as acid mine drainage is exposed to surface environments and is introduced into surrounding water bodies. These iron nanomaterials invoke aesthetic contamination as well as adverse effects on aqueous ecosystems. In order to control them, the characteristics of their behaviour should be understood first, but the cumulative research outputs up to now are much less than the expected. Using zero-valent iron (ZVI) and magnetite, this study aims to investigate the behaviour of iron nanomaterials according to the change in the composition and pH of background electrolyte and the concentration of natural organic matter (NOM). The size and surface zeta potential of iron nanomaterials were measured using dynamic light scattering. Characteristic behaviour, such as aggregation and dispersion was compared each other based on the DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory. Whereas iron nanomaterials showed a strong tendency of aggregation at the pH near point of zero charge (PZC) due to electrostatic attraction between particles, their dispersions became dominant at the pH which was higher or lower than PZC. In addition, the behaviour of iron nanomaterials was likely to be more significantly influenced by cations than anions in the electrolyte solutions. Particularly, it was observed that divalent cation influenced more effectively than monovalent cation in electrostatic attraction and repulsion between particles. It was also confirmed that the NOM enhanced the dispersion nanomaterials with increasing the negative charge of nanomaterials by coating on their surface. Under identical conditions, ZVI aggregated more easily than magnetite, and which would be attributed to the lower stability and larger reactivity of ZVI.

• Journal of Energy Engineering
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• v.20 no.3
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• pp.171-177
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• 2011

PVA/GLA/$Al_2O_3{\cdot}3SiO_2$ composite membranes were prepared through the reaction polyvinyl alcohol (PVA) with glutaraldehyde (GLA) as a cross-linking agent and subsequently adding aluminum silicate ($Al_2O_3{\cdot}3SiO_2$) as an inorganic material. The water uptake decreased as the GDL contents increased due to cross-linking process of PVA with GDL, and the ion conductivity increased as the $Al_2O_3{\cdot}3SiO_2$ contents increased in PVA/GLA/$Al_2O_3{\cdot}3SiO_2$ composite membranes. The cross-linking structure of the polymers was confirmed using IR and the tendency of water uptake. The thermal analysis of the copolymers was carried out by TGA. TGA results showed that PVA/GLA composite membrane were more heat-resistant than PVA due to the cross-linking of PVA, and the heat stability of the composite membranes improved much more as the concentration of $Al_2O_3{\cdot}3SiO_2$ increased. Membranes prepared in this study seem to be have thermal stability and increase a tendency of the cation conductivity up to $60^{\circ}C$, but to be exhibit lower performance tendency at over $90^{\circ}C$. Therefore, it is necessary to do more aggressive effort to explore the possibility of application as an ion-conductive composite electrolyte.

• Polymer(Korea)
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• v.34 no.1
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• pp.45-51
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• 2010

This study focuses on the investigation of the possibility of the crosslinked poly (vinyl alcohol) membranes with both poly (acrylic acid-co-maleic acid) (PAM) and 3-(trihydroxysilyl)-1-propane-sulfonic acid (THS-PSA) for the direct methanol fuel cell application. In order to characterize the prepared membranes, the water content, the thermal gravimetric analysis, the ion exchange capacity, the ion conductivity and the methanol permeability measurements were carried out and then compared with the existing Nafion 115 membrane. The ion exchange capacity of the resulting membranes showed 1.6~1.8 meq./g membrane which was improved than Nafion 115, 0.91 meq./g membrane. In the case of the proton conductivity, the THS-PSA introduced membranes gave more excellent $0.042{\sim}0.056\;S{\cdot}cm^{-1}$ than Nafion 115, $0.024\;S{\cdot}cm^{-1}$. On the other hand, the methanol permeability was increased more than Nafion 115 for all the range of THA-PSA concentration.

• Journal of the Korean Electrochemical Society
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• v.11 no.4
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• pp.284-288
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• 2008

Sn-thin film as high capacitive anode for thin film lithium-ion battery was prepared by organic-electrolyte electroplating using Sn(II) acetate. Electrolytic solution including $Li^+$ and $Sn^{2+}$ had 3 reduction peaks at cyclic voltammogram. Current peak at $2.0{\sim}2.5\;V$ region correspond to the electroplating of Sn on Ni substrate. This potential value is lower than 2.91 V vs. $Li^+/Li^{\circ}$, of the standard reduction potential of $Sn^{2+}$ under aqueous media. It is the result of high overpotential caused by high resistive organic electrolytic solution and low $Sn^{2+}$ concentration. Physical and electrochemical properties were evaluated using by XRD, FE-SEM, cyclic voltammogram and galvanostatic charge-discharge test. Crystallinity of electroplated Sn-anode on a Ni substrate could be increased through heat treatment at $150^{\circ}C$ for 2 h. Cyclic voltammogram shows reversible electrochemical reaction of reduction(alloying) and oxidation(de-alloying) at 0.25 V and 0.75 V, respectively. Thickness of Sn-thin film, which was calculated based on electrochemical capacity, was $7.35{\mu}m$. And reversible capacity of this cell was $400{\mu}Ah/cm^2$.

• Journal of the Korean Electrochemical Society
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• v.5 no.2
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• pp.68-73
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• 2002

Modified polymer electrolyte membranes were fabricated by the applying dc magnetron sputter-deposited Pd thin layers on the surface of the $Nafion^{TM}$ membranes in argon atmosphere. The Pd thin films were characterized by investigating its morphology, methanol permeability, and protonic conductivity. The performance of a direct methanol fuel cell(DMFC) with the modifed polymer electrolyte membrane was also tested by the measurement of its currents and voltages under flowing methanol. The Pd thin film could be a barrier layer to methanol crossover, but the protonic conductivity of the modified polymer membrane was reduced. By using the modified polymer eletrolyte membranes, both the methanol permeability and the protonic conductivity were decreased with increasing the thickness of Pd thin film. However, the performances of DMFC were almost independent on the thickness of Pd thim films. The efffcts of methanol concentration in a feeding fuels on the protonic conductivity and the cell performance were also investigated.

• Membrane Journal
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• v.19 no.2
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• pp.96-103
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• 2009

A series of organic-inorganic composite membranes from poly(vinyl chloride) (PVC) graft copolymer electrolyte and heteropolyacid (HPA) were prepared for proton conducting membranes. First, poly(vinyl chloride)-g-poly(styrene sulfonic acid) (PVC-g-PSSA) was synthesized by atom transfer radical polymerization (ATRP) using direct initiation of the secondary chlorines of PVC. HPA nanoparticles were then incorporated into the PVC-g-PSSA graft copolymer though the hydrogen bonding interactions, as confirmed by FT-IR spectroscopy. The proton conductivity of the composite membranes increased from 0.049 to 0.068 S/cm at room temperature with HPA contents up to 0.3 weight traction of HPA, presumably due to both the intrinsic conductivity of HPA particles and the enhanced acidity of the sulfonic acid of the graft copolymer. The water uptake decreased from 130 to 84% with the increase of HPA contents up to 0.45 of HPA weight traction, resulting from the decrease in number of water absorption sites due to hydrogen bonding interaction between the HPA particles and the polymer matrix. Thermal gravimetric analysis (TGA) demonstrated the enhancement of thermal stabilities of the composite membranes with increasing concentration of HPA.