• Corrosion Science and Technology
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• v.14 no.5
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• pp.239-246
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• 2015

Stainless steel is generally known to have characteristics of excellent corrosion resistance and durability, but in a marine environment it can suffer from localized corrosion due to the breakdown of passivity film due to chloride ion in seawater. Furthermore, the damage behaviors are sped up under a cavitation environment because of complex damage from electrochemical corrosion and cavitation-erosion. In this study the characteristics of electrochemical corrosion and cavitation erosion behavior were evaluated on 16.7Cr-10Ni-2Mo stainless steel under a cavitation environment in natural seawater. The electrochemical experiments have been conducted at both static conditions and dynamic conditions inducing cavitation with different current density parameters. The surface morphology and damage behaviors were compared after the experiment. After the cavitation test with time variables morphological examinations on damaged specimens were analyzed by using a scanning electron microscope and a 3D microscope. the galvanostatic experiment gave a cleaner surface morphology presented with less damage depth at high current density regions. It is due to the effect of water cavitation peening under the cavitation condition. In the cavitation experiment, with amplitude of $30{\mu}m$ and seawater temperature of $25^{\circ}C$, weight loss and cavitation-erosion damage depth were dramatically increased after 5 hours inducing cavitation.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.152-152
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• 2016

Anodizing is a technology to generate thicker and high-quality films than natural oxide films by treating metals via electrochemical methods. It is a technique to develop metals for various uses, and extensive research on the commercial use has been performed for a long time. Aluminum anodic oxide (AAO) is generate oxide films, whose sizes and characteristics depending on the types of electrolytes, voltages, temperatures and time. Electrochemical manufacturing method of nano structure is an efficient technology in terms of cost reduction, high productivity and complicated shapes, which receives the spotlight in diverse areas. The sulfuric acid was used as an anodizing electrolyte, controlling its temperature to $10^{\circ}C$. The anode was 5083 Al alloy with dimension of $5(t){\times}20{\times}20mm$ while the cathode was the platinum. The distance between the anode and the cathode was maintained at 3 cm. Agitation was introduced by magnetic stirrer at 300 rpm to prevent localized temperature rise that hinders stable growth of oxide layer. In order to observe surface characteristics with applied current density, the electrolyte temperature, concentration was maintained at constant condition for $10^{\circ}C$, 10 vol.%, respectively. To prevent hindrance of stable growth of oxide layer due to local temperature increase during the experiment, stirring was maintained at constant rate. In addition, using galvanostatic method, it was maintained at current density of $10{\sim}30mA/cm^2$ for 40 minutes. The cavitation experiment was carried out with an ultrasonic vibratory apparatus using piezo-electric effect with modified ASTM-G32. The peak-to-peak amplitude was $30{\mu}m$ and the distance between the horn tip and specimen was 1 mm. The specimen after the experiment was cleaned in an ultrasonic, dried in a vacuum oven for more than 24 hours, and weighed with an electric balance. The surface damage morphology was observed with 3D analysis microscope. As a result of the investigation, differences were observed surface hardness and anti-cavitation characteristics depending on the development of oxide film with applied current density.

• Journal of the Korea Institute of Building Construction
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• v.15 no.2
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• pp.169-175
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• 2015

Recently, a stone is preferred as a cladding materials because of its outstanding durability and luxurious character. However, because of running out of natural resources and restriction of production, it is expected that difficulty of stable supply, and thus alternative cladding materials for concrete wall is needed. Therefore, in this research, as an alternative cladding materials, exposed-aggregate concrete is studied using saccharin based retarder. For evaluating factors, changing water-to-cement ratio, dosages of saccharin-based retarder, and timing of water jet washing were tested on the surface properties of exposed-aggregate concrete. As a result, the most favorable surface performance was obtained at 0.75 day after the placing in 25% of water-to-cement ratio, and at one day after the placing in 35 and 55% of water-to-cement ratio, 1.5 day after the placing in 65% of water-to-cement ratio with $24m{\ell}/m^2$ of retarder application.

• Journal of the Korea Institute of Building Construction
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• v.10 no.1
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• pp.147-153
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• 2010

The recycling of demolished concrete as an alternative source of coarse aggregates for the production of new concrete can help to solve the growing waste disposal crisis and the problem of the depletion of natural aggregates. The purpose of this study is to investigate the chloride migration of recycled aggregate concrete containing pozzolanic materials by the chloride migration coefficient. The specimens were made with recycled coarse aggregate at various replacement ratios (10, 30, 50%) and metakaolin, blast furnace slag, and fly ash is replaced for recycled concrete with a mixing ratio of 20%. The major results are as follows. 1) The compressive strength of recycled aggregate concrete containing pozzolanic materials increases as the curing age and chloride diffusivity decreases. 2) When the replacement ratio of recycled coarse aggregate is 30%, the chloride migration coefficient of recycled concrete containing blast furnace slag or metakaolin that shows a value similar to or lower than that of plain concrete at all ages.

• Journal of the Korea Institute of Building Construction
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• v.20 no.5
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• pp.425-432
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• 2020

The appearance of Korean traditional roof tiles is beautiful and excellent in water resistance, fire resistance and durability, but a high sintering temperature of 1,200℃ or higher is required. Therefore, due to the economical and heavy weight problem, the current trend is to use different roof finishing materials than Korean traditional roof tiles. By adding nanoaluminosilicate to clay and kaolin, which are the materials of the clay roof tiles, the sintering temperature is sintered at a low temperature of 1,000℃ or less, and the optimal mixing and material process is designed to satisfy the characteristics required as a Korean traditional roof tile. The results of this study again demonstrate the superiority of Korean traditional tiles with roof finishing materials using nanoaluminate. The properties of Korean traditional roof tiles that satisfy the criteria of KS F 3510 by applying fire resistance of natural minerals and nanoparticle technology to flexural strength of 2800N, Bulk specific gravity of 2.0g/㎤ and absorption rate of less than 10.0%, through which and researched materials development.

• Journal of Construction Engineering and Project Management
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• v.8 no.3
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• pp.1-23
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• 2018

Since the protection the of human being from natural disaster and atmospheric factors have become an essential requirement, some attempts have been taken place to provide shelter and create a safe environment to a more comfortable life with welfare. For this purpose, using existing resources in nature and exploiting them in a different manner have been taken into account. Initially, the performed exploitations for construction had the least damage to the environment, but over time and as a result of population growth, aggressive exploitation of nature has led to destroying effects on the environment and resulted in consequences such as pollution and environmental destruction. Thus, the construction industry has been identified as the top pollutant factors of the environment. Among various construction factors, the building materials used in this industry are considered as the most important effective factors on the environment, as they have direct influences on the environment from the beginning of construction of the final steps. This research focuses on the review of the most of the existing green materials definitions and various approaches towards using eco-efficient construction materials. It presents and discusses possible ways of reducing the destructive effects on the environment by selecting and using green materials, review current literature and highlight the necessity of applying such materials in future constructions in all communities. This paper provides a base for this purpose that sustainable development communities and environment is realized by elimination of environmental pollution and approaching the criteria of green building by using sustainable materials.

• Clean Technology
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• v.14 no.3
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• pp.193-203
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• 2008

A surfactant is used to assist the effect of cleaning, dispersibility and adhesion during leather manufacturing process. Existing surfactant for that process includes many hydrophilic groups that may cause problem such as stain, bad water resistance and poor durability, etc. It is potential problem to make high-performance property for future leather market. In this study, we have synthesized the fluorinated surfactant of which property decreases surface tension, increases dispersion, cleaning effect and the better chrome absorption by the high bond energy of C-F to complement weakness that the present alkyl derivative surfactants have. Using fluorinated surfactant, we can confirm that dispersion is increased, chrome absorption ratio is augmented with high osmosis and coherence, chrome content in the tanning waste water is reduced, BOD and COD contents are diminished and physical characteristics are improved.

• Journal of the Korea Concrete Institute
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• v.13 no.2
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• pp.123-129
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• 2001

Pozzolan is to improve the strength and the durability of concrete as a result of the pozzolanic reaction, Broadly speaking, pozzolanic materials can be artificial materials, such as slica fume and fly ash, and natural material, such as rice husk ash, clay, volcanic ash, clayish pozzolan. Hwangtoh is a mineral which belongs to a group of matakaolin, especially halloysite, and the main elements is SiO$_2$, Al$_2$O$_3$, Fe$_2$O$_3$. The purpose of this study is to examine the application of Hwangtoh for the concrete admixtures, the composition of this study is shown as follows. Chapter I is analysis for properties of concrete as the kinds of admixture, and Chapter H is analysis for properties of concrete as the replacement ratio of activated Hwangtoh. As a result of this study, Hwangtoh is found to have high practical use as pozzolanic material, and the pertinent range of replacement ratios of Hwangtoh on cement are 10∼20 %.

• Journal of the Korean Society of Clothing and Textiles
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• v.33 no.5
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• pp.752-763
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• 2009

The purpose of this study was to develop an effective marketing strategy for socks made of paper mulberry fiber, a new natural fiber, by understanding consumers' concerns and perception about the product and its quality in several dimensions. The first survey determined their perception of the products' image before using it. The second survey gauged consumer satisfaction with product quality after a two-week home-use test. Factor analysis using Cronbach's a and ANOVA analysis were performed for statistical analysis. In conclusion, consumer image perceptions of socks of mulberry fiber were classified into four categories -'practicality', 'wellbeing', 'high-quality' and 'traditionality'. The survey revealed differences between men's and women's perception of the 'practicality' and 'high-quality' factors. The women recognized a mulberry fiber sock as being more practical but of lower quality than did the men. And the quality satisfaction of the product was classified into four factor 'durability', 'suitability, 'wearability' and 'care-easiness'. In the case of 'suitability', men were more satisfied with the product than the women and in 'suitability' and 'wearability', a group of over 40' year-old consumers was more satisfied. The analysis of a relationship between image perception and satisfaction showed that a consumer group that perceived this product to have more 'practicality', 'high-quality' and 'well-being' was also more satisfied with the product. However, the 'traditionality' factor was unrelated to consumer satisfaction.

• Journal of the Korean institute of surface engineering
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• v.49 no.2
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• pp.159-165
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• 2016

The hydrogen has been recognized as a clean, nonpolluting and unlimited energy source that can solve fossil fuel depletion and environmental pollution problems at the same time. Water electrolysis has been the most attractive technology in a way to produce hydrogen because it does not emit any pollutants compared to other method such as natural gas steam reforming and coal gasification etc. In order to improve efficiency and durability of the water electrolysis, comprehensive studies for highly active and stable electrocatalysts have been performed. The platinum group metal (PGM; Pt, Ru, Pd, Rh, etc.) electrocatalysts indicated a higher activity and stability compared with other transition metals in harsh condition such as acid solution. It is necessary to develop inexpensive non-noble metal catalysts such as transition metal oxides because the PGM catalysts is expensive materials with insufficient it's reserves. The optimization of operating parameter and the components is also important factor to develop an efficient water electrolysis cell. In this study, we optimized the operating parameter and components such as the type of AEM and density of gas diffusion layer (GDL) and the temperature/concentration of the electrolyte solution for the anion exchange membrane water electrolysis cell (AEMWEC) with the transition metal oxide alloy anode and cathode electrocatalysts. The maximum current density was $345.8mA/cm^2$ with parameter and component optimization.