• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.2
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• pp.634-643
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• 2020

In this study, the rheological and tribological properties of urea grease were studied according to the type and amount of polytetrafluoroethylene (PTFE) powders added to the urea grease, which is the most widely used among solid lubricants, to develop an optimal lubrication system. Urea grease was synthesized using 4,4'-methylenebis(phenyl isocyanate)(MDI), oleylamine, and cyclohexylamine, and PTFE powders prepared by dispersion or suspension polymerization process were then added. The basic rheological and tribological properties of the prepared greases were compared. The worked penetration numbers of urea grease decreased with increasing amount of PTFE powders, but both PTFE powders caused no significant changes in heat resistance and copper corrosion resistance. The shear viscosity increased with increasing PTFE powder content, and the dispersion-type PTFE powder was more effective in increasing the viscosity. In the value of the loss coefficient = 1, the shear stress was higher for the grease containing PTFE powders than the non-PTFE added grease, and the dispersion-type PTFE-added grease showed higher viscosity than the suspension-type PTFE-added grease. Finally, urea grease was found to have a low-performance improvement in terms of wear reduction effects by adding PTFE powders, but the load-bearing performance was up to 2.5 times higher for the dispersion-type PTFE and five times higher for the suspension-type PTFE.

• Conservation Science in Museum
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• v.17
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• pp.101-116
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• 2016

Ceramic cultural artifacts restored with gypsum-based materials are prone to decay over time due to gypsum's natural absorption and release of atmospheric moisture, often leading to distortion and peeling of painted layers. This study proposes a new restoration material which utilizes extra hard stone, significantly superior in strength to regular gypsum. In order to enhance its physical properties and make it suitable for restoration of ceramics, extra hard stone is mixed with metakaolin. This mixture far surpasses regular gypsum in compressive strength(119MPa vs. 26MPa) while also maintaining a much lower wear rate(0.88% vs. 2.53%). Furthermore, the water absorption rate(2.9%) of the mixed material is over five times lower than that of regular gypsum(17.2%). When examined using a SEM(Scanning Electron Microscope), this mixture also proved superior to extra hard stone in terms of hardened density. The addition of metakaolin increases the mixture's strength and water resistance over that of extra hard stone and also improves its surface density, making it ideal for the restoration of ceramics. It has already been used to repair ceramic objects in the Museum's collection: Clay basin(sinan 18892), Buncheong ware bottle with incised peony design(jubsu 2034), Buncheong ware bowl with chrysanthemum(jubsu 1730). Results thus far have shown the mixture to be easy to inject and layer as well as harden into an even surface, which allows for smooth application of paint for color matching.

• Information Systems Review
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• v.16 no.3
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• pp.135-160
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• 2014

Most Social Network Service (SNS) provide online chat, video and file sharing, blogging and others. Because of this advantage, people depend on SNS to communicate with others. However, recently SNS encourage people to reveal too much information broadly so SNS users are concerned about privacy invasion and data spill. They also feel fatigue in process of touching people they don't know while using SNSs. That is the reason why they attempt to switch from opened SNS to Closed SNS. Therefore, the purpose of this study is to empirically investigate and analyze the effect of the factors on the SNS users' switching behavior when using SNS. To accomplish this purpose, this research adopted "Push-Pull-Mooring (PPM)" framework. The PPM is proposed by population geologist, who used it to explain the incentives of demographic migration. Following PPM model, this research empirically examines the three categories of antecedents for SNS switching intention toward closed SNS: push (i.e., weak connection, privacy concern, relative complexity), pull (i.e., enjoyment, belongingness, peer influence), mooring (i.e., SNS fatigue, user resistance) factors. The survey was conducted for 285 users on SNS communities in Korea. The results of this study are as follows; First, wear connection and privacy concern are significantly related to SNS switching intention. Second, enjoyment and belongingness are significantly related to SNS switching intention. Finally, the results show that SNS fatigue has a moderating effect on the links between push factors and SNS switching Intention. Also, user resistance has a moderating effect on the links between pull factors and SNS switching Intention. These findings contribute to the SNS literature both theoretically and practically.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.4
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• pp.409-417
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• 2014

Since the oil price has been significantly jumped for recent some years, the diesel engine of the merchant ship has been mainly used the heavy oil of low quality. Thus, it has been often exposed to severely corrosive environment more and more because temperature of the exhaust gas in a combustion chamber is getting higher and higher with increasing of using the heavy oil of low quality. As a result, wear and corrosion of most parts surrounded with combustion chamber is more serious compared to the other parts of the engine. Therefore, an optimum weldment for these parts is very important to prolong their lifetime in a economical point of view. In this study, four types of filler metals such as Inconel 625, 718, 1.25Cr-0.5Mo and 0.5Mo were welded with SMAW and GTAW methods in the forged steel which would be generally used with piston crown material. And the corrosion properties of weld metal, heat affected zone and base metal were investigated using electrochemical methods such as measurement of corrosion potential, anodic polarization curves, cyclic voltammogram and impedance etc. in 35% H2SO4 solution. The weld metal and base metal exhibited the best and worst corrosion resistance in all cases of filler metals. In particular, the weld metal welded with filler metals of Inconel 718 revealed the best corrosion resistance among the filler metals, and Inconel 625 followed the Inconel 718. Hardness relatively indicated higher value in the weld metal compared to the base metal. Furthermore, Inconel 625 and 718 indicated higher values of hardness compared to 1.25cr-0.5Mo and 0,5Mo filler metals in the weld metal.

• Clean Technology
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• v.24 no.1
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• pp.9-14
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• 2018

In this study, Material life cycle evaluation was performed to analyze the environmental impact characteristics of TiN-Zr membrane manufacturing process. The software of MLCA was Gabi. Through this, environmental impact assessment was performed for each process. Transition metal nitrides have been researched extensively because of their properties. Among these, TiN has the most attention. TiN is a ceramic materials which possess the good combination of physical and chemical properties, such as high melting point, high hardness, and relatively low specific gravity, high wear resistance and high corrosion resistance. With these properties, TiN plays an important role in functional materials for application in separation hydrogen from fossil fuel. Precursor TiN was synthesized by sol-gel method and zirconium was coated by ball mill method. The metallurgical, physical and thermodynamic characteristics of the membranes were analyzed by using Scanning Electron Microscope (SEM), Energy Dispersive X-ray (EDS), X-ray Diffraction (XRD), Thermo Gravimetry/Differential Thermal Analysis (TG/DTA), Brunauer, Emmett, Teller (BET) and Gas Chromatograph System (GP). As a result of characterization and normalization, environmental impacts were 94% in MAETP (Marine Aquatic Ecotoxicity), 2% FAETP (Freshwater Aquatic Ecotoxicity), 2% HTP (Human Toxicity Potential). TiN fabrication process appears to have a direct or indirect impact on the human body. It is believed that the greatest impact that HTP can have on human is the carcinogenic properties. This shows that electricity use has a great influence on ecosystem impact. TiN-Zr was analyzed in Eco-Indicator '99 (EI99) and CML 2001 methodology.

• Applied Chemistry for Engineering
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• v.34 no.4
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• pp.434-443
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• 2023

We have investigated the performance improvement of grease by synthesizing calcium sulfonate grease as an alternative to lithium grease, which is widely used globally. Since the composition ratio of the grease, when manufactured, is usually 50% base oil and 50% thickener, using grease as a lubricant in a cryogenic environment is not encouraged due to its inferior low-temperature performance. In this study, we have synthesized three types of calcium sulfonate grease with paraffin oil and PAO-based base oil and thickener. Furthermore, lithium grease was synthesized via saponification with PAO-based base oil, lithium hydroxide, 12-hydroxystearic acid, and sebacic acid. We have measured low-temperature characteristics using a rheometer and low-temperature torque meter, and tribology characteristics were obtained using a four-ball lubricant tester and schwingung reibung verschleiß (SRV). As a result, the flow point of the calcium sulfonate grease synthesized with a PAO-based base oil and thickener was found to be -40℃, overcoming the existing calcium sulfonate grease's low-temperature limitation. Moreover, the synthesized calcium sulfonate grease showed low-temperature performance similar to that of lithium grease synthesized with PAO base oil, but superior anti-wear, extreme pressure, coefficient of friction, heat resistance, adhesion, and corrosion resistance. It is thus expected to commercially replace the existing lithium grease.

• Journal of Ecology and Environment
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• v.48 no.1
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• pp.17-23
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• 2024

Background: Honey bees play a crucial role in pollination and ecological balance. Apis mellifera L. colonies, especially those located in specific geographic regions, such as the palm garden in Eastern Thailand, are susceptible to potential threats from microbial contaminants. Understanding and detecting microbial organisms in these beehives is essential for the preservation of bee health, honey production, and the broader ecosystem. However, the problem of microbial infection and antibiotic-resistant bacteria is more severe and continuously increasing, resulting in a health, economic, and social crisis. The purpose of this study is to determine the prevalence of microorganisms in A. mellifera beehives in palm gardens in Rayong province, Eastern Thailand. Results: Ten swabs in transport media were swabbed and obtained from different parts of each beehive (1 swab per beehive), for a total of 10 hives. Traditional microbial culture-based methods, biochemical tests, and antimicrobial susceptibility (disc-diffusion) tests were used to detect microbial organisms and antibiotic resistance in bacteria. The swab tests from nine beehives resulted in the detection of Gram-positive bacteria (63.64%), Gram-negative bacteria (27.27%), and fungi/yeast (9.09%). These microorganisms are classified as a group of coagulase-negative Staphylococcus spp. and made up 40.91% of the bacteria discovered. Other bacteria found were Coryneform bacteria (13.64%), Pantoea spp. (13.64%), Bacillus spp. (9.09%), yeast (9.09%), glucose non-fermentative Gram-negative bacilli (9.09%), and Pseudomonas spp. (4.55%). However, due to the traditional culture-based and 0biochemical tests usually used to identify the microbial organisms in clinical specimens and the limitation of identifying some environmental microbial species, the results of the antimicrobial susceptibility test cannot reveal if the organism is resistant or susceptible to the drug. Nevertheless, drug-sensitive inhibition zones were formed with each antibiotic agent. Conclusions: Overall, the study supports prevention, healthcare, and public health systems. The contamination of microorganisms in the beehives may affect the quality of honey and other bee products or even the health of the beekeeper. To avoid this kind of contamination, it is therefore necessary to wear personal protective equipment while harvesting honey and other bee products.

• Progress in Medical Physics
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• v.20 no.2
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• pp.80-87
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• 2009

Phase transformation, superelastic characteristics and variation of surface residual stress were studied for Nitinol shape memory alloy through application of UNSM technology, and life extension methods of stent were also studied by using elastic resilience and corrosion resistance. Nitinol wire of ${\phi}1.778$ mm showed similar surface roughness before and after UNSM treatment, but drawing traces and micro defects were all removed by UNSM treatment. It also changed the surface residual stress from tensile to compressive values, and XRD result showed less intensive austenite peak and clear martensite and additional R-phase peaks after UNSM treatment. Fatigue resistance could be greatly improved through removal of surface defects and rearrangement of surface residual stress from tensile to compressive state, and development of surface modification system to improve not only bio-compatability but also resistance to corrosion and wear will make it possible to develop vascular stent which can be used for circulating system diseases which run first cause of death of recent Koreans.

• Journal of the korean academy of Pediatric Dentistry
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• v.36 no.3
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• pp.440-447
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• 2009

This study was performed to compare the wear resistance of sealant and flowable resins for analyzing the effect of flowable resin as a sealant in preventive resin restorations. Specimens were made and Vicker's hardness number and surface roughness were measured. SEM observations of the polished and abraded surfaces were established. Kruskal-Wallis rank test and Mann-Whitney U test at the significant level of ${\alpha}$=0.05 were used. The following results were obtained: 1. The microhardness was decreased among groups in following order: Z350 (3M ESPE, U.S.A), Estelite (Tokuyama Dental, Japan) and Ultraseal (Ultradent, U.S.A). There were significant differences in all groups (p<0.0001). 2. The surface roughness was decreased among groups in following order: Ultraseal XT plus, Palfique Estelite LV and Filtek Z350 flowable. However, there is no statistically significant differences in roughness among Estellite, Z350 and Ultraseal at the significance level of ${\alpha}$=0.05, with p=0.116 3. SEM observation of the unworn and worn surfaces revealed the qualitative differences in the wear appearance among groups. The results in this study indicate that flowable resin is better than sealant in aspect of physical properties.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.5915-5922
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• 2013

In this study, with the aim of improving the performance of shale to allow for its use as coarse aggregate for concrete, we coated shale aggregates with water repellents and polymers and evaluated their physical properties such as density, water absorption rate, wear rate, and stability depending on the coating method. In addition, the effects of the performance improvement were evaluated by assessing the properties of fresh concrete produced by varying the shale substitution ratio, as well as the compressive strength, flexural strength, and freeze-thaw resistance according to curing ages. The test results revealed that the absolute dry densities of all coated aggregates satisfied the standard density for coarse aggregates for concrete(>$2.50g/cm^3$),and the absorption rate of the shale aggregate coated with water repellent decreased by about 50% compared with that of uncoated shale. The wear rate of the polymer-coated shale decreased by up to 13.0% compared with that of uncoated shale. All coated aggregates satisfied the stability standard for coarse aggregates for concrete(${\leq}12$). The water repellent-induced performance improvement decreased the shale aggregates' slump by about 20~30mm compared with that of the uncoated shale aggregates, and the air content of the repellent-coated shale aggregate increased by up to 0.9% compared with that of the uncoated shale aggregate. The compressive strength of the polymer-coated shale aggregates at a curing age of 28 days was RS(F) 95.7% and BS(F) 90.0%, and the flexural strength was RS(F) 98.0 % and BS(F) 92.0% of the corresponding values of concretes produced using plain aggregates. Furthermore, the concrete using polymer-coated shale aggregates showed a dynamic modulus of elasticity of RS(F) 91% and BS(F) 88% after 300 freeze-thaw cycles, thus demonstrating improved freeze-thaw durability.