• Clean Technology
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• v.20 no.1
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• pp.51-56
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• 2014

In this study, PSf-$Al(OH)_3$ beads were prepared by immobilizating aluminum hydroxide $Al(OH)_3$ with polysulfone (PSf). The removal experiments of the fluoride ions by PSf-$Al(OH)_3$ beads were conducted batchwise and the parameters such as pH, initial fluoride concentration, and coexisting ions were investigated. The maximum removal capacity obtained from Langmuir isotherm was 52.4 mg/g and the optimum pH region of fluoride ions was in the range of 4 to 10. The removal process of fluoride ions by PSf-$Al(OH)_3$ beads was found to be controlled by both external mass transfer at the earlier stage followed by internal diffusion at the later stage. The presence of coexisting anions such as $HCO_3{^-}$, $SO{_4}^{2-}$, $NO_3{^-}$, and $Cl^-$ had a negative effect on removal of fluoride ions by PSf-$Al(OH)_3$ beads.

• Applied Chemistry for Engineering
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• v.7 no.3
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• pp.473-480
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• 1996

Synthesis of n-perfluorooctanesulfonyl fluoride(n-PFOSF), which is valuable precursor perfluoro-chemicals, was studied by electrochemical fluorination(ECF). Of prime concern was to investigate the cyclic voltamograms of Ni electrode in anhydrous hydrogen fluoride(AHF) with and without the reactants and to measure fluorine evolution potential. In a batch cell, chronoampherometric electrolysis and various chemical analysis such as GC, GC/MS and IR were used to understand the amphere change of electrode and the reaction paths. Fluorine equilibrium potential was found to be about 2.8V(vs. $Cu/CuF_2$) from the cyclic voltammograms and decay curves of anode potential in AHF. In batch processes, the ECF proceeded in two distinguished steps. The first step proceeded electrochemically and the second one chemically. Under 7V(vs. $Cu/CuF_2$), amount of crude products was proportional to the applied anode potential. Above 7V(vs. $Cu/CuF_2$), it had a hundred percentage with weight ratio of reactants and productivity of PFOSF was almost constant.

• Journal of dental hygiene science
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• v.15 no.1
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• pp.46-53
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• 2015

The purpose of this study is to identify the awareness of oral health workforce and the attitude concerning the health insurance benefit on topical fluoride application. The subjects are 173 dentists and 288 dental hygienists. The data were collected using a self-administered questionnaire and analyzed using SPSS 12.0 statistical program. The findings of the study were as follows: Agree's (including strongly agree) ratios regarding to the health insurance benefit of topical fluoride application was 92.5% for dentists and 90.8% for dental hygienists. Appropriate age of health insurance benefit about the topical fluoride application was elementary, middle and high school students (8~19 years). This response ratio was high 45.7% for dentists and 43.2% for dental hygienists. Appropriate copayment (mean value) of health insurance about topical fluoride application coverage showed that NaF, $SnF_2$ solution and acidulated phosphate fluoride gel were 25,782 Korean Won (KRW) for dentist and 14,282 KRW for dental hygienist. Fluoride varnish copayment was 31,705 KRW for dentist and 17,979 KRW for dental hygienist. Fluoride iontophoresis copayment was 40,156 KRW for dentist, and 21,210 KRW for dental hygienist. The frequency of health insurance benefits about topical fluoride application was high in 'unlimited (37.5%)' for the dentists and 'two times (31.3%)' for dental hygienists. In conclusion, topical fluoride application should be included as one of the health insurance benefit items for oral health.

• Applied Chemistry for Engineering
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• v.32 no.6
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• pp.632-639
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• 2021

In this research, fluorine doping was performed to enhance the photocatalytic activities of WO₃ which were measured using methylene blue dye. WO_3-xF_x photocatalyts were prepared by a vaper phase fluorination during a sintering for preparing WO₃ photocatalysts from a WCl₆ precursor. The bandgap energy of WO₃ photocatalysts decreased from 2.95 eV to 2.54 eV, and the oxygen vacancies site increased by about 55% after fluorine doping. In addition, the initial degradation efficiency of methylene blue showed that the fluorine doped sample showed a 6-fold increase in photocatalytic activities from 10% to 60% compared to that of the untreated sample. It is believed that fluorine is doped to reduce the band gap of photocatalysts, enabling the catalytic activity with low energy, and that oxygen vacancies-generated surface defects increase the visible light absorption region of WO₃ photocatalysts, thereby increasing photocatalytic activity. In this study, it was confirmed that fluorine-doped WO_3-xF_x photocatalysts with an excellent photocatalytic activity can be manufactured easily using a one-step vaper phase fluorination that does not require a post-treatment process.

• Journal of the Korean Ceramic Society
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• v.37 no.11
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• pp.1105-1113
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• 2000

Bioglass 조성 중 45S5 (46.1SiO$_2$.24.4$Na_2$O.26.9CaO.2.6P$_2$O$_{5}$ : 몰비)를 기본 조성으로 하여 46P4 (46.2SiO$_2$.49.5CaO.4.3P$_2$O$_{5}$ : 몰비), 46SF (46.1SiO$_2$24.4$Na_2$O.16.1CaO.2.6P$_2$O$_{5}$.10.8CaF : 몰비) 그리고 55SF (55.1SiO$_2$.9.2$Na_2$O.27.8CaO.3.4P$_2$O$_{5}$.4.5CaF : 몰비)를 제조하여 tris-완충용액 및 유사 생체용액(simulated body fluid)에서 반응시킨 후 생체활성유리의 표면에 생성되는 아파타이트 결정형에 관하여 연구하였다. 45S5 유리를 tris-완충용액에 반응시켰을 경우 6시간 반응시부터 수산화 아파타이트가 생성되었으나 유사 생체용액에 반응시켰을 경우에는 24시간까지도 수산화 아파타이트 결정이 생성되지 못하고 비정질 상태의 칼슘 인산염만 형성되었다. tris-완충용액에 각 조성의 유리를 200시간 반응시킨 경우 불소를 함유하지 않은 유리에서는 잎사귀 모양의 수산화 아파타이트가, 불소를 함유한 유리에서는 구상의 플루오르 아파타이트가 형성되었다. 그러나 유사 생체용액에 각 조성의 유리를 200시간 반응시켰을 경우 불소를 함유하지 않은 유리에서는 누에고치형의 수산화 아파타이트가 형성되었고 불소를 함유한 유리에서는 무정형의 칼슘 인산염이 생성되었다.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.1543-1543
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• 2015

반도체식 가스센서의 한계를 극복하기 위하여 열불소화 방법과 활성화 방법을 이용하여 NO 가스 감지용 가스센서를 제조하였으며, 각각의 특성을 평가하였다. 열불소화 처리된 탄소나노튜브는 열처리 온도에 따라 반도체적 성질이 p-type에서 n-type으로 변화한 후 다시 p-type으로 변화하였으며, 활성화 처리된 탄소나노튜브는 비표면적이 증가할수록 NO 감지에 따른 저항변화가 증가하였다. 저항변화율은 $200^{\circ}C$에서 불소화 처리된 탄소나노튜브가 가장 크게 나탔으나 응답시간을 고려할 경우 $600^{\circ}C$에서 불소화 및 6M의 KOH를 이용한 경우 가장 우수한 특성을 보였다.

• Proceedings of the Korean Society of Dyers and Finishers Conference
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• 2004.11a
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• pp.82-88
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• 2004

• The Journal of the Korean dental association
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• v.23 no.11 s.198
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• pp.987-991
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• 1985

• 대한예방의학회:학술대회논문집
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• 2000.10a
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• pp.288-289
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• 2000

• Journal of Korean Society of Environmental Engineers
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• v.32 no.7
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• pp.730-737
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• 2010

It is very important to remove fluoride ion before treating semiconductor wastewater containing high concentration of ammonia, phosphates, and fluoride ions by struvite formation. Calcium ion was generally added for the removal of fluoride ion. However, calcium ions remained after removal of fluoride ion can deteriorate the performance of struvite crystalization. It should be removed completely before struvite formation. In this study, the effect of fluoride and calcium ion concentration on the struvite crystalization was investigated. Removal efficiencies of ortho-phosphate with struvite formation were more abruptly decreased than those of ammonium nitrogen, as increase of fluoride ion concentration in synthetic wastewater. The structures of struvite formed in synthetic wastewater containing calcium ion of up to 500 mg/L were identical. Purity of struvite was deteriorated as increase of calcium ion over 500 mg/L. Removal efficiencies of ammonium nitrogen were more decreased than those of phosphate ions as increase of cacium ion in synthetic wastewater.