• Resources Recycling
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• v.31 no.4
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• pp.34-39
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• 2022

In this study, effects of ultrasonic energy on the cementation reaction and copper recovery rate were investigated for different types of iron samples, such as plate, chip, and powder, for recovering copper from waste etchant, which contained ~3.5% copper. The cementation reaction using the ultrasonic energy was more effective than the simple stirring reaction, with the former exhibiting a high copper recovery rate than the latter for the same time interval. When cementation was performed for 25 min with ultrasonic treatment, rather than simple stirring, the copper recovery rate of the plate, chip, and powder improved from 7.0% to 12.0%, 14.0% to 46.1%, and 41.9% to 77.2%, respectively. Therefore, the use of ultrasonic energy could detach the copper recovered by the cementation reaction from the surface of the iron samples, thereby increasing the copper recovery rate. Owing to the use of ultrasonic energy, the copper recovery rate increased by 2-6 times, and the recovered copper exhibited a decreased particle size compared to that obtained via simple stirring.

• Journal of Internet of Things and Convergence
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• v.9 no.3
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• pp.93-98
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• 2023

In this paper, an artificial neural network based on simulated annealing was constructed. The mapping relationship between the parameters of micro-scaled flow channels electrochemical machining and the channel shape was established by training the samples. The depth and width of micro-scaled flow channels electrochemical machining on stainless steel surface were predicted, and the flow channels experiment was carried out with pulse power supply in NaNO3 solution to verify the established network model. The results show that the depth and width of the channel predicted by the simulated annealing artificial neural network with "4-7-2" structure are very close to the experimental values, and the error is less than 5.3%. The predicted and experimental data show that the etching degree in the process of channels electrochemical machining is closely related to voltage and current density. When the voltage is less than 5V, a "small island" is formed in the channel; When the voltage is greater than 40V, the lateral etching of the channel is relatively large, and the "dam" between the channels disappears. When the voltage is 25V, the machining morphology of the channel is the best.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.34 no.1
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• pp.1-7
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• 2024

β-Ga₂O₃ is a material with a wide band gap of ~4.8 eV and a high breakdown-voltage of 8 MV/cm, and is attracting much attention in the field of power device applications. In addition, compared to representative WBG semiconductor materials such as SiC, GaN and Diamond, it has the advantage of enabling single crystal growth with high growth rate and low manufacturing cost [1-4]. In this study, we succeeded in growing a 10 mm thick β-Ga₂O₃ single crystal doped with 0.3 mol% SnO₂ through the EFG (Edge-defined Film-fed Growth) method using multi-slit structure. The growth direction and growth plane were set to [010]/(010), respectively, and the growth speed was about 12 mm/h. The grown β-Ga₂O₃ single crystal was cut into various crystal planes (010, 001, 100, ${\bar{2}}01$) and surface processed. The processed samples were compared for characteristics according to crystal plane through analysis such as XRD, UV/VIS/NIR/Spec., Mercury Probe, AFM and Etching. This research is expected to contribute to the development of power semiconductor technology in high-voltage and high-temperature applications, and selecting a substrate with better characteristics will play an important role in improving device performance and reliability.

• Journal of the korean academy of Pediatric Dentistry
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• v.27 no.1
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• pp.45-53
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• 2000

Enamel microabrasion is a means by which superficial enamel discoloration is removed using hydrochloric acid and fine pumice. As enamel microabrasion alone may not be sufficient in cases of deeper discoloration, composite resin restoration is recommended in areas where there is remaining discoloration. The purpose of this study was to investigate the effects of different methods and number of applications of enamel microabrasion on the shear bond strength of composite resin to enamel. Untreated control was designated as group 1. 5-second applications of a mixture of 18% HCl and fine pumice were performed 5 and 10 times on groups 2 and 3, respectively. A commercially available mixture of 10% HCl and abrasives(PREMA) was applied using a 10 : 1 gear reduction handpiece 5 and 10 times on groups 4 and 5, respectively, with each application lasting 20 seconds. After etching with 37% phosphoric acid, composite resin was bonded. Thermocycling was performed and shear bond strength was measured. The following results were obtained : 1. Group 2 showed the highest bond strength$(24.36{\pm}3.34)$, while group 3 showed the lowest$(19.35{\pm}3.43)$, Shear bond strength decreased in the following order: 2>4>5>1>3. 2. Group 2 showed bond strength significantly higher compared to groups 1 and 3(p<0.05). 3. There were no significant differences between groups 2 and 3, which had been microabraded using HCl and pumice, and groups 4 and 5, to which PREMA had been applied, when bond strengths were compared(p>0.05). 4. When modes of fracture were examined, adhesive failure was observed in groups 3 and 4, while cohesive failure was observed in groups 1, 2, 3 and 4. Only mixed failures were found group 5. 5. When viewed using a SEM, groups 2 and 3, which had been microabraded using HCl and pumice, showed surface appearances similar to that of enamel etched with phosphoric acid. Groups 4 and 5, treated with PREMA, exhibited a smooth surface similar to that of group 1. All oops showed similar, typical surface characteristics following phosphoric acid etching.

• The korean journal of orthodontics
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• v.26 no.4
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• pp.389-399
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• 1996

Remineralization of acid-etched enamel across the time has been one of the curiosities in the context of the orthodontic biomechanics(Arends J. et al., IRL Press, 1, 1985), nevertheless, is so far controversial. It was the aim of this study to observe the remineralization patterns of acid-etched enamel across the time and whether the existence of fluoride might carry out any modifications. The intact buccal surfaces of the first bicuspids which was extracted for orthodontic treatment were ground smooth, and etched with a 38w/w% phosphoric acid for 60 seconds, The surface was observed by the scanning electron microscope and surface microhardness was measured after immersion in the fluoride or non-fluoride containing remineralizing solution for 0 hour, 12 hours, 1 day, 3 days, 7 days, 14 days, 28 days, and 42 days. The following results and conclusions were drawn; 1. Surface microhardness increased in both fluoride containing and non-fluoride containing solution group with time lapse. 2. In fluoride containing solution group, the surface microhardness sharply increased at the 12 hours group, on the other hand, surface microhardness increased at 3 days in non-fluoride containing solution group. 3. The difference in microhardness value between two groups manifested gradual decrease. 4. Scanning electron microphotographs disclosed that the fluoride containing solution group generated spiculate sub-stances in the 12 hours group, which was increased in number and size with time lapse. 7 days later, spherical composure was began to be produced, The spiculate substances so much increased in number that the etched enamel surface looked like flat in 42 days. 5. In non fluoride-containing solution group, there was no surface change at 42 days, perceivable in scanning electron microphotographs which could be defined as remineralization though the surface was a little rougher than the incipient etched surface. These results demonstrate that the action of the fluoride is exceedingly pertinent in the remineralization of acid-etched enamel and the remineralization process goes uninterruptedly with time lapse.

• Korean Journal of Dental Materials
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• v.45 no.4
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• pp.257-274
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• 2018

The purpose of this study was to evaluate the effect of acid-treatment conditions on the surface properties of the RBM (Resorbable Blast Media) treated titanium. Disk typed cp-titanium specimens were prepared and RBM treatments was performed with calcium phosphate ceramic powder. Acid solution was mixed using HCl, $H_2SO_4$ and deionized water with 4 different volume fraction. The RBM treated titanium was acid treated with different acid solutions at 3 different temperatures and for 3 different periods. After acid-treatments, samples were cleaned with 1 % Solujet solution for 30 min and deionized water for 30 min using ultrasonic cleanser, then dried in the electrical oven ($37^{\circ}C$). Weight of samples before and after acid-treatment were measured using electric balance. Surface roughness was estimated using a confocal laser scanning microscopy, crystal phase in the surface of sample was analyzed using X-ray diffractometer. Surface morphology and components were evaluated using Scanning Electron Microscope (SEM) with Energy Dispersive X-ray spectroscopy (EDX) and X-ray Photoemission Spectroscopy (XPS). Values of the weight changes and surface roughness were statistically analyzed using Tukey-multiple comparison test (p=0.05). Weight change after acid treatments were significantly increased with increasing the concentration of $H_2SO_4$ and temperature of acid-solution. Acid-treatment conditions (concentration of $H_2SO_4$, temperature and time) did not produce consistent effects on the surface roughness, it showed the scattered results. From XRD analysis, formation of titanium hydrides in the titanium surface were observed in all specimens treated with acid-solutions. From XPS analysis, thin titanium oxide layer in the acid-treated specimens could be evaluated. Acid solution with $90^{\circ}C$ showed the strong effect on the titanium surface, it should be treated with caution to avoid the over-etching process.

• Applied Chemistry for Engineering
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• v.25 no.5
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• pp.447-454
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• 2014

Organic solar cells (OSCs) have intensively studied in recent years due to their advantages such as cost effectiveness and possibility of applications in flexible devices. In spite of the high power conversion efficiency (PCE) of 10 %, the OSCs still have a draw back of their low environmental stability due to the oxidization of aluminum cathode and etching of transparent conducting oxide as electrode. To solve these problems, the inverted structured OSCs (I-OSCs) having greatest potential for achieving an improvement of device performances are suggested. Therefore, there are a lot of studies to develope of interface layer based on organic/inorganic materials for the electron transport layer (ETL) and passivation layer, significant advancements in I-OSCs have driven the development of interface functional materials including electron transport layer. Recent efforts to employing 2D/3D zinc oxide (ZnO) based ETL into I-OSCs have produced OSCs with a power conversion efficiency level that matches the efficiency of ~9 %. In this review, the technical issues and recent progress of ZnO based ETL in I-OSCs to enhancement of device efficiency and stability in terms of materials, process and characterization have summarized.

• Journal of the korean academy of Pediatric Dentistry
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• v.24 no.1
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• pp.148-172
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• 1997

Sixty human premolar teeth were used for this in vitro study. After each tooth was sectioned mesiodistally, one half was used for the experimental group and the other half for the control. Three groups were made for each fluoride applying method and twenthy teeth were assigned to each group. Ten teeth were used for evaluating total fluoride amount and the other ten were used for firmly-bound fluoride. Fluorshield was used for fluoride-releasing sealant and 1.23% APF, 0.05% NaF were used for topical application fluorides. Each tooth was cleaned with a tooth brush using nonfluoride containing pumice before the experiment. In the sealant group, fluoroshield was applied to the enamel surface without etching procedure and stored in $37^{\circ}C$ saline for 30 days. After 30 days, sealant was removed with explorer without scratching the enamel surface and washed with distilled water and dried. In the APF group, each tooth was immersed in 1.23% APF for 30 min then washed and dried in the same manner. In the NaF group, each tooth was immersed in 0.05% NaF for 24 hours then washed and dried as described above. After each fluoride regimen was applied, ten teeth were randomly selected from each group and immersed in 1M KOH solution for 24 hours to remove loosely-bound fluoride possibly deposited by the three different fluorides applied. In each group, total fluoride amount deposited and the amount of enamel removed by acid biopsy were calculated. After loosely-bound fluoride was removed, firmly-bound fluoride deposited and the amount of enamel removed by acid biopsy were also calculated. Total fluoride amount deposition was significantly increased in the APF and NaF groups, but not in the sealant group. Amount of enamel removed by acid-biopsy was also significantly diminished in the APF and NaF groups, but not in the sealant groups. After loosely-bound fluoride was removed from each groups, no statistical difference was found in the amount of firmly-bound fluoride in any groups. Also no effect of firmly-bound fluoride on enamel dissolution was shown in any groups after loosely-bound fluoride was removed from each group. In conclusion, topical application method of APF or NaF is more effective than fluoride-releasing sealant application to make $CaF_2$ coating on enamel surface and $CaF_2$ coating is the main source for anticariogenic effect of fluoride. However, longterm anticariogenic effect of fluoride-releasing sealant should be further evaluated.

• Korean Chemical Engineering Research
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• v.44 no.5
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• pp.513-519
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• 2006

We developed two kinds of the microchip for application to electrophoresis based on both glass and quartz employing the MEMS fabrications. The poly-Si layer deposited onto the bonding interface apart from channel regions can play a role as the optical slit cutting off the stray light in order to concentrate the UV ray, from which it is possible to improve the signal-to-noise (S/N) ratio of the detection on a chip. In the glass chip, the deposited poly-Si layer had an important function of the etch mask and provided the bonding surface properly enabling the anodic bonding. The glass wafer including more impurities than quartz one results in the higher surface roughness of the channel wall, which affects subsequently on the microflow behavior of the sample solutions. In order to solve this problem, we prepared here the mixed etchant consisting HF and $NH_4F$ solutions, by which the surface roughness was reduced. Both the shape and the dimension of each channel were observed, and the electroosmotic flow velocities were measured as 0.5 mm/s for quartz and 0.36 mm/s for glass channel by implementing the microchip electrophoresis. Applying the optical slit with poly-Si layer provides that the S/N ratio of the peak is increased as ca. 2 times for quartz chip and ca. 3 times for glass chip. The maximum UV absorbance is also enhanced with ca. 1.6 and 1.7 times, respectively.

• Journal of the korean academy of Pediatric Dentistry
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• v.35 no.3
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• pp.509-515
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• 2008

It is widely believed that the increase in the prevalence of dental erosion is due to soft drinks. The purpose of this study was to assess the influence of soft drinks and etchant on the erosion of tooth enamel and the effect of tooth brushing on the abrasion of eroded enamel, and the effect of milk, saliva and Tooth $Mousse^{(R)}$ on the remineralization. The changes in tooth enamel surface were observed by scanning electron microscophy. The results were as follows; 1. The pH of Coca-Cola and Chilsung-Cider were higher than the pH of FineEtch 37 and $Tyrian^{TM}SPE$. 2. The SEM photos revealed that the pattern of the surface eroded by Coca-Cola and Chilsung-Cider were more obvious than that eroded by etchants. 3. The results of remineralization by saliva, milk, Tooth $Mousse^{(R)}$ were not different from each other. 4. The remineralization by saliva decreased tooth brushing abrasion.