• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.322-323
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• 2012

This study discussed the formation of phosphate conversion coatings on AZ31 Mg alloy (AZ31) from the zinc phosphating bath with various concentrations of sodium fluoride (NaF). The effects of NaF on the formation, structure, composition and electrochemical behavior of the phosphate coatings were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD) weight balances, open circuit potential (OCP) transients, potentiodynamic polarization curves and immersion test. The coatings were composed of two layers: an outer $Zn_2(PO_4)_3.4H_2O$ (hopeite) crystal layer and an inner amorphous of $MgZn_2(PO_4)_2$. NaF concentration is emphasized to be highly effective in the formation of the hopeite crystal and etching and coating rates. Potentiodynamic polarization and immersion test showed that the coatings formed in the zinc phosphating bath with addition of NaF have much higher corrosion resistance than bare AZ31.

• Journal of Electrochemical Science and Technology
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• v.4 no.1
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• pp.27-33
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• 2013

The consequences of electrode density and thickness for electrochemical performance of lithium-ion cells are investigated using 2032-type coin half cells. While the cathode composition is maintained by 90:5:5 (wt.%) with $LiCoO_2$ active material, Super-P electric conductor and polyvinylidene fluoride polymeric binder, its density and thickness are independently controlled to 20, 35, 50 um and 1.5, 2.0, 2.5, 3.0, 3.5 g $cm^{-3}$, respectively, which are based on commercial lithium-ion battery cathode system. As the cathode thickness is increased in all densities, the rate capability and cycle life of lithium-ion cells become significantly worse. On the other hand, even though the cathode density shows similar behavior, its effect is not as high as the thickness in our experimental range. This trend is also investigated by cross-sectional morphology, porosity and electric conductivity of cathodes with different densities and thicknesses. This work suggests that the electrode density and thickness should be chosen properly and mentioned in detail in any kinds of research works.

• Membrane and Water Treatment
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• v.13 no.4
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• pp.173-181
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• 2022

Polyvinylidene fluoride (PVDF) flat sheet hydrophobic membranes were prepared using 16 wt% PVDF in Dimethyl acetamide (DMAc) by phase inversion technique for desalination application using Membrane Distillation (MD). In this work, the effect of coagulation mediums such as ethanol and water as well their synergistic behavior on the fabricated PVDF membrane morphology was studied using SEM. Moreover, other characteristics required for the membrane distillation applications namely porosity, hydrophobicity and tensile strength were measured using the gravimetric method, sessile drop method and universal testing machine respectively. It was observed that the membrane morphology paradigm shifted from the finger-like structure to the sponge-like structure on increasing the ethanol concentration in coagulant. The porosity of the fabricated membrane was under the required MD range and found to be 57.3% at 16 weight % of PVDF in DMAc solvent under a pure ethanol coagulant bath. Moreover, the top surface contact angle ranges from 85° to 115° on increasing the bath concentration from CBC 0 to CBC 100 at 16 weight % of PVDF in DMAc solvent.

• Bulletin of the Korean Chemical Society
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• v.26 no.1
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• pp.38-42
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• 2005

Bis(2-methylbenzaldehyde)butane-2,3-dihydrazone(TDSB) was used as new N-N Schiff's base which plays the role of an excellent ion carrier in the construction of a La(III) membrane sensor. The best performance was obtained with a membrane containing, 30% poly(vinyl chloride), 60% benzyl acetate, 6% TDSB and 4% sodium tetraphenyl borate. This sensor reveals a very good selectivity towards La(III) ions over a wide variety of cations, including alkali, alkaline earth, transition and heavy metal ions. The proposed electrode exhibits a Nernstian behavior (with slope of 19.8 mV per decade) over a wide concentration range (1.0 ${\times}$ 10$^{-5}$-1.0 ${\times}$ 10$^{-1}$ M). The detection limit of the sensor is 7.0 ${\times}$ 10$^{-6}$ M. It has a very short response time, in the whole concentration range ($\sim$5 s), and can be used for at least twelve weeks in the pH range of 3.0-9.4. The proposed sensor was successfully applied as an indicator electrode for the potentiometric titration of a La(III) solution, with EDTA. It was also successfully applied in the determination of fluoride ions in three mouth wash preparations.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.350-351
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• 2005

The electrochemical behavior of Si-C material synthesized by heating the mixture of silicon and polyvinylidene fluoride (PVDF). Coin cells of the type 2025 were made using the synthesized material and the electrochemical studies were performed. Si-C/Li cells were made by using the developed Si-C material. Charge/discharge test was performed at 0.1C hour rate. Initial charge and discharge capacities at Si-C material derived from 20 wt.% of PVDF was found to be 1,830 and 526 mAh/g respectively. Initial charge/discharge characteristics of the electrode were analyzed. The level of reversible specific capacity was about 216 mAh/g at Si-C material derived from 20 wt.% of PVDF, IIE, intercalation efficiency at initial charge/discharge, was 68 %. Surface irreversible specific capacity was 31 mAh/g, and average specific resistance was 2.6 ohm*g.

• Journal of Electrochemical Science and Technology
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• v.12 no.4
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• pp.424-430
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• 2021

The element iron (Fe) is affordable and abundantly available, and thus, it finds use in a wide range of applications. As regards its application in rechargeable lithium-ion batteries (LIBs), the electrochemical reactions of Fe must be clearly understood during battery charging and discharging with the LIB electrolyte. In this study, we conducted systematic electrochemical analyses under various voltage conditions to determine the voltage at which Fe corrosion begins in general lithium salts and organic solvents used in LIBs. During cyclic voltammetry (CV) experiments, we observed a large corrosion current above 4.0 V (vs. Li/Li⁺). When a constant voltage of 3.7 V (vs. Li/Li⁺), was applied, the current did not increase significantly at the beginning, similar to the CV scenario; on the other hand, at a voltage of 3.8 V (vs. Li/Li⁺), the current increased rapidly. The impact of this difference was visually confirmed via scanning electron microscopy and optical microscopy. Our X-ray photoelectron spectroscopy measurements showed that at 3.7 V, a thick organic solid electrolyte interphase (SEI) was formed atop a thin fluoride SEI, which means that at ≥3.8 V, the SEI cannot prevent Fe corrosion. This result confirms that Fe corrosion begins at 3.7 V, beyond which Fe is easily corrodible.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.5
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• pp.421-424
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• 2007

Thermal behavior of $Li_{1-x}CoO_2$ has been investigated employing DSC (Differential Scanning calorimetry) and TGA (Thermogravimetry Analyzer), and the crystal parameters were calculated from XRD (X-ray diffraction).for the commercial rectangular pouch cell(1000 mAh).The cathode materials coated over aluminium foil current collector is made up of a blend consisting of active material $LiCoO_2$(size $20\;{\mu}m$, 94 wt%), conducting material super p black (SPB, 3 wt%) and binder polyvinylidene fluoride (PVDF, 3 wt%). The anode is a mix consisting of carbon (92 wt%) and PVDF(8 wt%) coated over copper foil. The cells for the experiments were first preconditioned by cycling three times and stabilized at OCV=3.0, 3.5, 4.2, 4.35 and 4.5 V. The stabilized cathode material was used for thermal and crystal parameter investigations.

• Journal of Korean society of Dental Hygiene
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• v.9 no.4
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• pp.670-684
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• 2009

Objectives : This research analyzed the general characteristics that closely affect the children's dental health and the mothers' dental health knowledge and dental health behavior to identify the correlation of the latter with the status of children's dental health in order to provide the basic data for the development of dental health business that would target children. Methods : Research subjects were selected arbitrarily from three nursery schools located in Busan metropolitan city, targeting 186 children between the ages of four to six and their mothers. The children were subjected to dental Inspection, and the status of their dental caries was studied whereas the mothers were subjected to the surveys on the general characteristics, dental health knowledge and dental health behavior. Results : 1. Level of mothers' dental health knowledge is higher when the mothers' educational level is higher(p=0.02) and when the household's monthly income is higher(p=0.009). 2. When the level of mothers' dental health knowledge is higher, children tended to brush their toothbrushing using proper method(p=0.025). Moreover, when the level of mothers' dental health knowledge is higher, they tended to take their children to dental clinic mostly for preventive measures than for treating cavity(p=0.023). 3. When the level of mothers' dental health knowledge is higher, children's dmft index was significantly low(p=0.02). When the mothers use fluoride-containing toothpaste, children's children' dmft index was even lower(p=0.02). 4. As the children tended to brush their teeth more often, dmft index was lower(p=0.003). When the reason that the children visited dental clinic was more to prevent, than to treat cavity, dmft index was even lower(p=0.000) Conclusions : When the above mentioned results are summarized, it is possible to know that the mothers' dental health knowledge and dental health behavior significantly affect children's dental health. Accordingly, it is necessary to develop maternal and child dental health program that factors in both the mothers and children in order to prevent children's dental caries and to increase their dental health, and continued care is required to discover and treat dental caries early on.

• Journal of the Korea Convergence Society
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• v.6 no.6
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• pp.131-137
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• 2015

To study the effects of oral health education on children, weekly education sessions and surveys were held for 214 preschoolers, 6-7 years of age, in 2 K-area kindergartens for 4 weeks in July 2015. Statistics on oral health behaviors such as children with regular dental checkups(p<0.05), children who underwent fluoride application(p<0.05), children without dental caries diagnosis(p<0.001), children with mothers who underwent oral health education(p<0.05) showed significant difference. Oral health knowledge scores(6 being perfect) increased from pre-education scores of 4.96 to post-education score of 5.54. oral health behavior scores(11 being perfect) also increased from pre-education scores of 7.18 to post-education score of 7.75(p<0.001). Therefore, it is the author's opinion that the development of oral health education programs with relatively short cycles, alongside systematic, practical, and repeated education would be beneficial.

• Journal of the Korean Society of School Health
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• v.14 no.1
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• pp.73-81
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• 2001

The purpose of this study was to collect basic data for the development of effective oral health education program in elementary school. The subjects in this study Were 604 fourth-year, fifth-year and sixth-year students of an elementary school in Seoul, Oral health awareness and behaviors were surveyed and analyzed. The findings of this study were as follows: 1. The most common time for toothbrushing was after dinner(62.0%) and before bedtime(62.3%). By school year, the largest number who brushed their teeth after dinner were fourth and fifth graders while the greatest number who did so after breakfast were sixth graders. Seventy-four percent of respondents brushed the teeth twice or more a day. By school year, the fifth-year students brushed their teeth the least while girls outperformed the boys in daily toothbrushing frequency(p<0.05). Regarding the intake of cariogenic food, 62.1% took that kind of food once or more a day. By school year, the fifth graders took the most (p<0.05), and girls took more cariogenic food than the boys(p<0.05). 2. Ninety percent of the respondents had visited a dental clinic. By grade, the sixth-year students had visited a dental clinic more frequently and girls more frequently than boys. Eighty percent of the respondents visited a dental clinic to receive treatment but just 12.3% visited a dental clinic to prevent oral diseases. Concerning the fear of dental treatment, only 14.4% expressed fear. School year made no difference, yet the percentage of girls who experienced fear was higher than that of boys(p<0.05). Regarding preventive treatment, 39.7% experienced pit and fissure sealing and 24.2% experienced the application of fluorides. All the students hadn't much experience in preventive treatment regardless of school year -- gender didn't make a difference. 3. Fourty-six percent of respondents had a preference for the fluoride mouth rinsing program; 38.4% wanted that program to continue. As to the reason for preference, 38.2% preferred it because of the prevention of dental caries, 43.0%, the largest percentage, didn't favor it because they found it too much trouble to do(some of the respondents gave two different answers). 4. Despite an increase in the frequency of toothbrushing at the right time, they still took cariogenic food frequently. Their visit to a dental clinics also aimed at treatment more than at prevention, and they had very narrow experience of preventive treatment Furthermore, the fluoride mouth rinsing program failed to draw their interest Therefore, it is recommended that a successful oral health education program should be developed.