• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.2
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• pp.140-145
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• 2015

This study focused on the development of a fundamental technology for coating of concrete surface using slime produced from bacteria. To assign self-purification ability and improve durability performance of concrete, Rhodobater capsulatus that generates slime were selected and absorption technology for the selected bacteria was then examined. From the production of slime and growth activity of the bacteria, the optimum medium for Rhodobater capsulatus can be recommended as maltose. Furthermore, image analysis showed that high porous resin powder is more effective for absorption of the Rhodobater capsulatus than the other materials tested.

• Resources Recycling
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• v.17 no.5
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• pp.60-65
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• 2008

A study on the removal of silver(Ag) in copper electrolyte was carried out to produce high purity copper by using various method such as ion exchange resin, activated carbon adsorption, copper cementation with powder and wire, CuS precipitation. Parameters, such as reaction time, reaction temperature, addition amount etc. were investigated to determine the effective condition of silver removal. CuS precipitation and ion exchange using Lewatit TP214 was found to be effective. Especially, silver content in copper electrolyte was reduced from 10 ppm to less than 0.1 ppm by ion exchange with Lewatit TP214.

• Journal of Dental Rehabilitation and Applied Science
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• v.37 no.1
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• pp.1-15
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• 2021

Additive manufacturing (AM) for dental materials can produce more complex forms than conventional manufacturing methods. Compared to milling processing, AM consumes less equipment and materials, making sustainability an advantage. AM can be categorized into 7 types. Polymers made by vat polymerization are the most suitable material for AM due to superior mechanical properties and internal fit compared to conventional self-polymerizing methods. However, polymers are mainly used as provisional restoration due to their relatively low mechanical strength. Metal AM uses powder bed fusion methods and has higher fracture toughness and density than castings, but has higher residual stress, which requires research on post-processing methods to remove them. AM for ceramic use vat polymerization of materials mixed with ceramic powder and resin polymer. The ceramic materials for AM needs complex post-processing such as debinding of polymer and sintering. The low mechanical strength and volumetric accuracy of the products made by AM must be improved to be commercialized. AM requires more research to find the most suitable fabrication process conditions, as the mechanical properties and surface of any material will vary depending on the processing condition.

• Applied Chemistry for Engineering
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• v.17 no.3
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• pp.267-273
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• 2006

We have prepared PP/Ba-ferrite composite fabrics by a melt-blown spinning method and investigated the relationship between the properties of PP/Ba-ferrite composite fabrics and melt-blown processing factors. A PP composite containing Ba-ferrite as a magnetic particulate filler was prepared in the form of pellet from PP resin and Ba-ferrite powder by melt compounding using a single extruder. Screw turning force (rpm), DCD (die-to-collector distance), and Ba-ferrite content were changed. We measured diameters of fiber, mechanical, thermal, and magnetic properties for the composited PP fabrics. The elongation was increased and a fiber diameter and tensile strength were decreased as the spinning distance increased or screw turning force decreased. The crystallinity was increased with increasing spinning distance according to XRD. It was assumed that the orientation of crystalline domain in the neat PP without ferrite was increased by drawing in mechanical direction, however, the orientation in the PP composite was decreased according to XRD analysis. We measured a magnetic property of PP nonwoven fabric containing Ba-ferrite powder. A coercive force, maximum magnetization, and residual magnetization are reduced with the spinning distance. According to the result of TGA measurement, the heat resistance was increased with the Ba-ferrite powder content and with decreasing the spinning distance.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.2
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• pp.253-258
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• 2016

The $MnO_x-WO_3-TiO_2$ nanoscale powders were synthesized by sol-gel method in order to prevent the biological fouling on the ships and offshore structures. Powder characteristics and antifouling performance were investigated with respect to the crystalline, microstructure and surface property for application in self-polishing copolymer resins. The high antifouling activity of $TiO_2$-system biocide was attributed to its redox potential and soluble metal ions originating from tungsten oxides according to the improvements in the powder characteristics. Based on their physio-chemical characterizations, the specific surface areas of powders were about $90m^2/g$ and the grain size was in the region 100 ~ 150 nm. Powder characteristics and surface properties were improved by the addition of $WO_3$. Antifouling performance were analyzed according to their surface properties and static immersion tests to determine the effects of the $TiO_2$-system compounds. The surface of 2 wt. % added sample was clean for 5 month. This may be attributed to the ability of $MnO_x-WO_3-TiO_2$ powders to act as a promoter in antifouling agents.

• The Journal of Korean Academy of Prosthodontics
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• v.49 no.2
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• pp.128-137
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• 2011

Purpose: Resonance frequency analysis, Periotest, and removal torque (RT) test were known as the methods to assess implant stability. The results of these methods are affected by the bone condition, implant diameter and shape. The purpose of this study is to access the meaning and the correlationship of the resonance frequency analysis, Periotest and RT test in osseointegration simulated acrylic resin when the engaged bone thickness and peri-implant bone defect are changed. Materials and methods: To simulate osseointegration, the fixture was fixed to an aluminum mold with a screw. Acrylic resin powder and liquid were poured into the mold for polymerization. The engaged resin thickness with implant was controlled. Simulated cortical bone thicknesses were 1, 3, 5 and 10 mm. Additional 1, 3 and 5 mm peri-implant bone defects were simulated. Three types of implants were used; 4 mm diameter implants of straight shape, 4 mm diameter implants of tapered shape and 5 mm diameter implants of tapered shape. Five fixtures per each type were tested in respective bone condition. Resonance frequency analysis and Periotest were evaluated in all bone conditions. Peak removal torque was measured at simulated cortical bone thicknesses of 1 and 3 mm. The statistical analysis was performed with the Kruskal-Wallis test, Mann-Whitney U test, and Spearman test using a 95% level of confidence. Results: With increasing engaged bone depth, the Implant Stability Quotient (ISQ) values increased and the Periotest values (PTVs) decreased (P<.001, P<.001). With increasing peri-implant bone defect, ISQ values decreased and PTVs increased (P<.001). When the diameter of implant increased, ISQ values increased and Periotest values (PTV) decreased (P<.001). There was a strong correlation between ISQ values and PTVs (r = -0.99, P<.001). Furthermore, the peak removal torque values had weak correlations with both ISQ values and PTVs (r = 0.52, P<.001 ; r = -0.52, P<.001). Conclusion: This study confirmed favorable implant stability with increasing engaged bone depth and implant diameter and decreasing peri-implant bone defect. ISQ values and PTVs showed strong correlation with each other and not with the peak removal torque values.

• The korean journal of orthodontics
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• v.23 no.1 s.40
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• pp.75-88
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• 1993

Recent reports indicate that shorter etching times than 60 seconds can be adopted without affecting the bond strength and clinical disadvantages. The purpose of this in vitro study was to compare the shear bone strength and to measure depth of etch at different etching time length. One hundred and eight extracted bovine lower central incisors were embedded each in a tooth cup with cold-cure acrylic resin. The facial surfaces of the teeth were ground wet with 600-, 800-, 1000-, and 1200-grit Sic papers, and finally polished with a water slurry of extrafine silicon carbide powder, washed with tap water, and dried with hot air. Nine groups of nine prepared teeth were etched with a commercial($38\%$ phosphoric acid solution) for 0, 5, 10, 15, 20, 30, 60, 90, and 120 seconds, respectively, rinsed with tap water, and dried with hot air. One conditioned teeth from every group was selected randomly for the scanning electron microscopic examination, and the remaining eight teeth of the groups were used for measuring the push shear bond strength after bonding brackets and immensing them in the $36.5^{\circ}C$ water for 24 hours. Another nine groups of three teeth were used for measuring the depth of etch and surface roughness with a surface profilometer. after pieces of adhesive tape of 3mm inner diameter positioned on the ground enamel surfaces, and etched with the above mentioned. The data obtained form the above expeiments were analysed statistically with one way ANOVA and Dunkan's multiple range test with the $95\%$ confidence level. The results and conclusion of the study were as follows; 1. The results of shear bond strength for the given experimental etching times were not statistically different, but showed the tendency of decreasing shear bone strength after over 60 seconds etching times. 2. On the scanning election microscopic examination, it was observed that the morphological patterns of etched enamel surface for 5 to 20 seconds were similar and consitent, and those for 30 to 120 seconds showed increasing over-etched patterns depending on the length of etching times. 3. The depth of etch was increased almost proportionally by the length of etching times, but it was not associated with the shear bond strength. 4. The surface roughness increased depending on the length of etching times, but it was not associated with the shear bond strength. 5. This experiment indicated that proper etching time with $38\%$ phosphoric acid solution is in the range of 5 to 30 seconds.

• Journal of Adhesion and Interface
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• v.17 no.1
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• pp.7-14
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• 2016

Epoxy composites with concentrations of 5-70 wt% of silica particles were prepared in order to improve mechanical property and poor thermal stability. The mechanical and thermal properties were investigated and compared to the corresponding properties of neat epoxy composite. Furthermore, the effects of silane compound treatment on silica particles were observed by the experimental results of the tensile strength, glass transition temperature, and thermal stability of epoxy composite. Tensile strength of epoxy composites was measured by universal testing machine (UTM) and after that, the structure and morphology analysis of epoxy nanocomposites were analyzed by field emission scanning electron microscope (FE-SEM) and energy dispersive spectroscopy (EDS). The increased solid content of CA0030 particle improved the tensile strength of epoxy/ modified composites to give 30-50 MPa. The thermal expansion coefficients (CTE) of neat epoxy resin and epoxy/silica composites measured with a thermomechanical analyzer (TMA) showed that the incorporation of silica particles was helpful to reduce the CTE of neat epoxy resin.

• Journal of the Korean Society for Marine Environment & Energy
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• v.12 no.1
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• pp.23-28
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• 2009

There is several ways of recycling methods for waste FRP boats. The main one is mechanical recycling that is one of the simple and technically proven methods. It recently has been reported that FRP can be recycled by separating into laminated glass fiber layers instead of crushing into powder. Even though the mechanical recycling is a good way for the eligibility of laminated glass fiber reinforced material, the system should have another option which can collect resin of FRP. Because the resin is still very useful renewable energy source, that cannot be discarded, But FRP is made up of laminated glass fiber(roving cloth layer) which is fire retardant substances and very hard to break into each layer. Due to the high cost of fossil energy the waste plastics should be regenerated to the source of renewable energy. Laminated glass fiber which is recyclable in a very limited way, is currently a serious barrier to waste FRP boat regenerating. This study is to propose a new extracting method which is efficient and environment friendly FRP waste regenerating system. The recycled glass fiber which is obtained by the separation of the roving layer from FRP waste has been found to be useful for concrete(FRC) products or concrete(FRC) structures as fiber reinforced material. And it can be successively applied to renewable energy applications using the waste resins of FRP residue without laminated glass fiber.

• Journal of Conservation Science
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• v.37 no.2
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• pp.135-143
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• 2021

Conservation treatment that involved filling the lifting parts of wooden cultural heritage is carried out by obtaining wood or wood powder of the same species and mixing it with synthetic resin or natural glue to charge the blank area. Various concentrations and mixing ratios of adhesives and additives are used, depending on the type and condition of the target. Accordingly, in this study, we determined the conditions of the filler suitable for conservation treatment of wooden sculptures with lifted or separated bark in the National Museum of Modern and Contemporary Art. The optimal filler conditions for each adhesive were selected based on drying speed, shrinkage and expansion rates, and physical deformation degree. Then, to verify their actual applicability, these fillers were applied to wood and exposed to high-humidity environment and their cross-sections were observed. The fillers showed stable application in the following order: animal glue, PVAc adhesive, acrylic adhesive. In conclusion, a 1:2 mixture of animal glue and wood powder is a suitable filler for conservation treatment of wooden sculpture with lifted bark. The results of this study suggest appropriate ways to stabilize the bark that was lifted or separated from a wooden sculpture, thus enabling the future conservation treatment of the artworks under similar conditions.