• Journal of Korean Society on Water Environment
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• v.23 no.3
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• pp.371-376
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• 2007

The features of precipitating reaction of fluorine have been examined under several aquatic conditions by employing calcium ion as a precipitant. Based on MINTEQ program, fluorine was found to exist in the forms of $H_2F_2$ and HF in strong acidic environment and change into $F^-$ with increasing pH. In the experimental condition, the precipitating reaction of fluorine progressed rapidly within a few minutes after the reaction started and reached its equilibrium in 10 minutes. As the addition of precipitant was increased, removal of fluorine by the formation of precipitate was promoted and its was also enhanced by the rise of pH. The precipitating reaction of fluorine was impeded when its initial concentration was low and X-ray analysis showed that the crystalline structure of precipitate was mainly $CaF_2$ with partly NaF. Coexisting phosphate in solution influenced the fluorine removal by impeding the precipitate formation and similar effect was found when metallic ion such as $Zn^{2+}$ was present with fluorine.

• Archives of Plastic Surgery
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• v.35 no.4
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• pp.407-412
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• 2008

Purpose: Hydrofluoric acid(HF) is one of the most dangerous mineral acids with the dissociated fluoride ions. The initial corrosive burn is caused by free hydrogen ion, and the second and more severe burn is caused by penetration of fluoride ions into subcutaneous tissues. Silver is a cation producing dressing, an effective antimicrobial agent, but older silver-containing formulations are rapidly inactivated by wound environment, requiring frequent replenishment. But, $Acticoat^{(R)}$ is a relatively new form of silver dressing which helps avoid the problems of earlier agents. The aim of this study is to evaluate effects of $Acticoat^{(R)}$, silver-containing dressing on the treatment for HF injury wound. Methods: From september 2006 to september 2007, the study was carried out with 10 patients who had HF partial thickness burns. $Acticoat^{(R)}$ dressing and 10% calcium gluconate wet gauze dressings in 10 cases. As a principle, in the emergency treatment, partial or complete removal of the nail and early bullectomy along with copious washing with normal saline was done, depending on the degree of HF invasion of the wound. Wound was dressed with $Acticoat^{(R)}$ and 10% calcium gluconate solution. The effect of dressing was investgated by serial bacterial culture and wound exudates assessment. Results: We therefore reviewed 10 cases of HF-induced chemical burns and treatment principle. The 10 cases who came to the hospital nearly immediately after the injury healed completely without sequelae. Conclusion: As the industrial sector develops, the use of HF is increasing more and more, leading to increased incidences of HF-induced chemical burns. The education of patients regarding this subject should be empathized accordingly. In conclusion, $Acticoat^{(R)}$ dressing is a better choice for HF partial thickness burn injuries because of shorter healing time, less pain and more comfortable dressing.

• Korean Journal of Metals and Materials
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• v.56 no.12
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• pp.915-920
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• 2018

With the development of modern microelectronics technologies, the power density of electronic devices is rapidly increasing, due to the miniaturization or integration of device elements which operate at high frequency, high power conditions. Resulting thermal problems are known to cause power leakage, device failure and deteriorated performance. To relieve heat accumulation at the interface between chips and heat sinks, thermal interface materials (TIMs) must provide efficient heat transport in the through-plane direction. We report on the enhanced thermal conduction of $Al_2O_3-based$ polymer composites, fabricated by the surface wetting and texturing of thermally conductive hexagonal boron nitride(h-BN) nanoplatelets with large anisotropy in morphology and physical properties. The thermally conductive polymer composites were prepared with hybrid fillers of $Al_2O_3$ macro beads and surface modified h-BN nanoplatelets. Hexagonal boron nitride (h-BN) has high thermal conductivity and is one of the most suitable materials for thermally conductive polymer composites, which protect electronic devices by efficient heat dissipation. In this study, we synthesized hexagonal boron nitride nanoparticles by the pyrolysis of cost effective precursors, boric acid and melamine. Through pyrolysis at $900^{\circ}C$ and subsequent annealing at $1500^{\circ}C$, hexagonal boron nitride nanoparticles with diameters of ca. 50nm were synthesized. We demonstrate that the addition of a small amount of calcium fluoride ($CaF_2$) during the preparation of the melamine borate adduct significantly enhanced the crystallinity of the h-BN and assisted the growth of nanoplatelets up to 100nm in diameters. The addition of a small amount of h-BN enhanced the thermal conductivity of the $Al_2O_3-based$ polymer composites, from 1.45W/mK to 2.33 W/mK.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.2
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• pp.197-202
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• 2023

Calcium fluoride (CaF₂) single crystal is applied to numerous industrial applications, especially for optical uses. To have excellent optical transmission properties, however, CaF₂ crystals should be carefully fabricated through liquid-phase crystal growth techniques. In this study, as one of the early stage research activities to grow CaF₂ crystals with a good transmittance at the ultraviolet wavelength range, computational thermodynamic models were provided to deepen the understanding of the crystal growing processes of CaF₂ under various conditions. To remove point defects and oxygen impurities in the grown CaF₂ crystals, the system was thermodynamically evaluated to get optimal process conditions. From the reviews of previous experimental studies, computational thermodynamic approaches were found to be an effective and powerful tool to understand the meaning of the crystal growth processes and to obtain optimal process conditions.

• Restorative Dentistry and Endodontics
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• v.49 no.1
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• pp.6.1-6.16
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• 2024

Objectives: This study aimed to investigate the elemental analysis and microhardness of a bioactive material (Activa) and marginal tooth structure after storage in different media. Materials and Methods: Fifteen teeth received cervical restorations with occlusal enamel and gingival dentin margins using the tested material bonded with a universal adhesive, 5 of them on the 4 axial surfaces and the other 10 on only the 2 proximal surfaces. The first 5 teeth were sectioned into 4 restorations each, then stored in 4 different media; deionized water, Dulbecco's phosphate buffered saline (DPBS), Tris buffer, and saliva. The storage period for deionized water was 24 hours while it was 3 months for the other media. Each part was analyzed by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analysis for different substrates/distances and the wt% of calcium, phosphorus, silica, and fluoride were calculated. The other 10 teeth were sectioned across the restoration, stored in either Tris buffer or saliva for 24 hours or 3 months, and were evaluated for microhardness of different substrates/areas. Data were analyzed using analysis of variance and Tukey's post hoc test. Results: Enamel and dentin interfaces in the DPBS group exhibited a significant increase in calcium and phosphorus wt%. Both silica and fluoride significantly increased in tooth structure up to a distance of 75 ㎛ in the 3-month-media groups than the immediate group. Storage media did not affect the microhardness values. Conclusions: SEM-EDS analysis suggests an ion movement between Activa and tooth structure through a universal adhesive while stored in DPBS.

• Applied Chemistry for Engineering
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• v.17 no.5
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• pp.483-489
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• 2006

The behavior of rare earth compounds such as $La_{2}O_{3}$, $CeO_{2}$, and $Ca(OH)_{2}$ on the removal of fluoride and heavy metals in the steel wastewater has been investigated. The removal mechanism of fluoride by rare earth elements has been known to be the formation of insoluble compounds between $F^{-}$ and cations such as $La^{3+}$ and $Ce^{4+}$ produced by the dissociation of rare earth compounds (To reduce the running cost of the fluoride wastewater treatment facility, their fluoride removal efficiencies were compared with those of inexpensive rare earth minerals such as natural lanthanide and cerium compound used as a glass polishing agent). All of the rare earth oxides used in this study showed a higher removal efficiency of fluoride than $Ca(OH)_{2}$ in the wastewater. In the case of artificial HF solution, the removal efficiency of fluoride showed in the order: $CeO_{2}$-mineral < $CeO_{2}$ < $Ca(OH)_{2}$ < $La_{2}O_{3}$-mineral < $La_{2}O_{3}$. However, the removal efficiency of fluoride in the wastewater increased in the following order: $Ca(OH)_{2}$ < $CeO_{2}$ mineral < $CeO_{2}$ < $La_{2}O_{3}$ mineral < $La_{2}O_{3}$. All agents showed high efficiencies for the removal of Mn and total Cr in the rare earth compounds. In the case of $Ca(OH)_{2}$, fluoride removal decreased with increasing pH while. However, the rare earth compounds showed a higher fluoride removal in higher pH condition, the optimum pH condition seemed to be around 7 considering both water quality and fluoride removal. Under the pH 7 condition, the $Ca(OH)_{2}$ was superior to rare earth compounds in Mn removal and the lanthanide was superior to others in total Cr removal.

• The Journal of the Korea Contents Association
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• v.13 no.4
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• pp.312-319
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• 2013

The purpose of this study was to evaluate the efficacy of gargle and toothpaste containing low concentration with sodium fluoride on the remineralization through the surface microhardness and mineral content in enamel. After 4 weeks-application, the enamel surface was measured using microhardness tester and the calcium (Ca) and phosphorous (P) concentration of mineral content by electron probe microanalyzer (EPMA) analysis. By combining fluoridated gargle with toothpaste, a remineralized enamel resulted in significantly significant differences among the four groups (p<0.05). The Ca change treated with 0.23% fluoridated toothpaste and 0.02% fluoridated gargle with 0.23% toothpaste demonstrated the highest among the other groups. In conclusion. the fluoridated gargle with toothpaste by low concentration showed a significantly greatest synergistic effect on remineralization of the enamel than the other groups.

• Journal of the korean academy of Pediatric Dentistry
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• v.33 no.2
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• pp.201-206
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• 2006

A recent laboratory study has demonstrated improved caries lesion resistance with enamel that was exposed to $CO_2$ laser irradiation for very short time period. When topical fluoride treatment was performed before or after laser irradiation, reductions in dental caries. The purpose of this scanning electron microscopic(SEM) study and atomic force microscope study was to characterize surface alterations in tooth enamel after in vitro laser irradiation alone and combined topical fluoride treatment either before or after laser irradiation. The treatment effects of laser irradiation led to the formation of an irregular, mild porosities and fine fissures, also created granular materials. But when laser irradiation was followed by APF, the enamel surface had homogenous architecture. The result led to the caries resistance effects by these granular structures have been considered to represent redeposited mineral phases due to the mobilization of calcium, phosphate, and fluoride from lased enamel.

• Journal of the korean academy of Pediatric Dentistry
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• v.43 no.4
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• pp.391-400
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• 2016

The purpose of this study was to evaluate the difference of remineralization effects of various anti-cariogenic toothpastes on artificial carious lesions in primary and permanent teeth using quantitative light-induced fluorescence-digital (QLF-D) system. Sound human primary (n = 48) and permanent teeth (n = 48) were randomly divided into following groups : control group (Group 1), fluoride toothpaste (Group 2), functionalized tricalcium phosphate (fTCP) + fluoride toothpaste (Group 3), and casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) toothpaste (Group 4). Specimens were prepared by exposure in a demineralizing solution and then treated using the different toothpastes twice daily during 14 days. All specimens were analyzed with the QLF-D system. QLF data analysis indicated three different toothpastes showed significant remineralizing effects compared to Group 1 in both primary and permanent teeth. Also, the remineralizing effects in Group 3 and 4 were significantly higher than in Group 2. This study suggested that the toothpastes containing fTCP + fluoride and CPP-ACP have the significant anti-cariogenic effects on enamel demineralization in both primary and permanent teeth, and QLF-D is an useful device to assess the incipient carious lesion and remineralization effects of the anti-cariogenic materials quantitatively. Therefore, clinicians can consider the QLF-D system for the evaluation of demineralization and remineralization in primary and permanent teeth.

• The Journal of the Acoustical Society of Korea
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• v.42 no.5
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• pp.412-421
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• 2023

Ultrasound brain stimulation is spot-lighted by its capability of inducing brain cell activation in a localized deep brain region and ultimately treating impaired brain function while the efficiency and directivity of neural modulation are highly dependent on types of stimulus waveforms. Therefore, to optimize the types of stimulation parameters, we propose a cell-cultivable ultrasonic transducer having a series stack of a spin-coated polymer piezoelectric element (Poly-vinylidene fluoride-trifluorethylene, PVDF-TrFE) and a parylene insulating layer enhancing output acoustic pressure on a glass-coverslip which is commonly used in culturing cells. Due to the uniformity and high accuracy of stimulus waveform, tens of neuronal cell responses located on the transducer surface can be recorded simultaneously with fluorescence microscopy. By averaging the cell response traces from tens of cells, small changes to the low intensity ultrasound stimulations can be identified. In addition, the reduction of stimulus distortions made by standing wave generated from reflections between the transducers and other strong reflectors can be achieved by placing acoustic absorbers. Through the proposed ultrasound transducer, we could successfully observe the calcium responses induced by low-intensity ultrasound stimulation of 6 MHz, 0.2 MPa in astrocytes cultured on the transducer surface.