• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.4
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• pp.175-178
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• 2018

Copper is a well know material for use as heat sink or heat exchanger. However, copper has a considerable low tensile strength and temperature limit. A material that has a good thermal conductivity, low cost, but also excellent mechanical properties are desired. In order to identify the mechanism for the material properties of cast Cu-Fe alloys, $Cu_{50}-Fe_{50}$ (wt.%) alloy was produced by using a high-frequency induction furnace, a typical metal casting process. The Cu-Fe alloy consists of Cu, ${\alpha}$-Fe, ${\gamma}$-Fe with dendrite structures. The crystal structure and microstructure of the prepared $Cu_{50}-Fe_{50}$ alloy were systematically examined using XRD, FE-SEM, EDS and XRF for electrical devices.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.94-94
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• 2013

The Cr-Zr-N films have much improved mechanical properties and very smooth surface roughness. However, in spite of their outstanding properties, the Cr-Zr-N coatings revealed their mechanical properties deteriorated severely with increasing Zr content at $500^{\circ}C$ ecause of very rapid oxidation. Recently oxynitride films have been widely studied due to their excellent unique mechanical properties and oxidation resistance. In this work, CrZr-O-N films with various O contents were synthesized by unbalanced magnetron sputtering with Cr-Zr segment targets (Cr:Zr volume ratios is 1：1) and all films were prepared in a nitrogen rich mixture of N2 and O2. Characteristics such as crystalline structure, hardness and chemical composition as a function of the O content were investigated by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), microhardness testing system and energy dispersive spectroscopy (EDS). Results showed that the thin films had dense and compact microstructure as O content in the films increases. The microstructure of the thin films consisted of mainly crystalline Cr (Zr)N phase and Cr2O3 phase. The maximum hardness and elastic modulus of the films was measured to be approximately 33.2 GPa and 280.6 GPa from the films with low content of O elements. Detailed experimental results will be presented.

• Journal of the Earthquake Engineering Society of Korea
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• v.2 no.2
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• pp.45-55
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• 1998

Although a number of methods have been proposed to predict the liquefaction potential, few methods have been developed by using the characteristic of material's microstructure. In this research, fundamental procedure is proposed for the assessment of liquefaction potential in saturated soils based on the Disturbed Sate Concept(DSC) model which can provide a unified constitutive model for the characterization of entire stress-strain behavior under cyclic loading. From this concept, the value of disturbance at threshold state (Critical Disturbance, $D_C$) in the deforming microstructure provides the basis for initial liquefaction. This method is verified with respect to data from Cyclic Truly Triaxial test for saturated Ottawa sand. Also, the relationship between liquefaction and initial confinig stress is defined using definition of $D_C$. It is believed that the new procedure for identifying liquefaction based on the DSC model can capture the behavior of liquefation, and as a result, it is shown to be on improvement over the available empirical procedures.

• Journal of the Korean Ceramic Society
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• v.45 no.10
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• pp.644-650
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• 2008

It has been proposed that the Cao-$SiO_2$ binary system can be good basic composition of bioactive glasses and glass-ceramics. In the present study, various kinds of Cao-$SiO_2$ gels were prepared by sol-gel method in order to control the microstructure which are related to their dissolution rate, induction period of apatite formation in body environment. Characterization of the gels were done by wet chemical analysis, SEM observation, FT-IR spectroscopy and XRD. The gelation time decreased with CaO content. However, the volume of all the dried gel decreased to 50% of the wet gels irrespective of increasement of CaO content. All the Cao-$SiO_2$ gels were amorphous and contained a large amount of silanol groups on their surfaces after heat treatment up to $800^{\circ}C$. The interconnected structure of the gel changed to agglomerated spherical powders when Ca content exceed to 20 mol%. Most of the Cao-$SiO_2$ gel showed amorphous when heat-treated up to $900^{\circ}C$. However, quartz and cristobalite was produced when heat-treated at $1000^{\circ}C$ and resultant microstructure of the gel contained microporous structure.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.3
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• pp.170-174
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• 2015

Composite ceramics of alumina-TZP(3Y) have good mechanical and electrical properties. So, They have been used as high strength refractory materials and thick film substrates, etc. In this study, Composite ceramics of alumina-TZP(3Y) were fabricated by uniaxial pressing and sintering at 1,400, 1,500, and $1,600^{\circ}C$, and their microstructures and mechanical properties were investigated. As the TZP(3Y) content in composite ceramics increases from 20 wt.% to 80 wt.%, the fracture toughness increases monotonically, which seems to be related to the higher relative density and/or toughening mechanism by means of stabilized tetragonal zirconia phase at room temperature. In contrast to the fracture toughness, Vickers hardness of the composite ceramics shows maximum value (1,938 Hv) at a 40 wt.% of TZP(3Y). The result of Vickers hardness is likely to be due to more dense sintered microstructure of composite ceramics than pure alumina and reinforcement of composite ceramics with TZP(3Y), considering that Vickers hardness of pure $Al_2O_3$ is greater than that of TZP(3Y). It is also shown that the $ZrO_2$ particles are $l^{\circ}Cated$ between $Al_2O_3$ grains and suppress grain growth each other.

• The Korean Journal of Food And Nutrition
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• v.31 no.5
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• pp.760-765
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• 2018

In order to observe physical properties of rice depending on reheating, the study cooked rice developed for high quality cooked rice and analyzed physical properties of rice depending on reheating following 24 hr refrigeration. As a result of palatability of cooked rice, Samgkwang had the lowest hardness, while Daebo and Haiami had the highest one. With respect to adhesiveness, toughness and stickiness, Sindongjin exhibited lowest properties. After cooking each rice by cultivars, the study observed their color, texture properties, and microstructure immediately after cooking, after 24 hr of refrigeration and further on. Lightness of cooked rice tended to drop because of refrigeration and reheating. Analysis of texture properties after cooking revealed that Haiami marked the highest points in all categories. When stored for 24 hr after cooking, hardness, viscosity and chewiness increased in cooked rice followed by a decrease after reheating. Observation of the microstructure of cooked rice using a scanning electron microscope revealed that Haiami had its particles in the center as closely condensed. It was apparent that all the cultivars formed stoma in an obvious manner because of refrigeration and reheating. The results of the present study show that physical properties of cooked rice varied according to reheating after cooking and storage depending on the inherent characteristics of rice cultivars.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.2
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• pp.80-84
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• 2015

Mn-Co-Ni oxide system has been used as the NTC thermistors for normal temperature applications. Mn-Co-Ni oxide-based thermistors were sintered at different temperatures for a constant processing time from 900 to $1300^{\circ}C$ for 3 h. The crystal structure, bulk density, microstructure and chemical composition were characterized by XRD, FE-SEM and WD-XRF. The plot of the resistance versus measuring temperature was characterized for the sintered sample at the $1250^{\circ}C$. Moreover, the relationship between log resistivity and reciprocal of absolute temperature of the NTC thermistor was investigated.

• International Journal of Concrete Structures and Materials
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• v.8 no.3
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• pp.213-228
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• 2014

Alkali-activated binder (AAB) is recently being considered as a sustainable alternative to portland cement (PC) due to its low carbon dioxide emission and diversion of industrial wastes and by-products such as fly ash and slag from landfills. In order to comprehend the behavior of AAB, detailed knowledge on relations between microstructure and mechanical properties are important. To address the issue, a new approach to characterize hardened pastes of AAB containing fly ash as well as those containing fly ash and slag was adopted using scanning electron microscopy (SEM) and energy dispersive X-ray spectra microanalyses. The volume stoichiometries of the alkali activation reactions were used to estimate the quantities of the sodium aluminosilicate (N-A-S-H) and calcium silicate hydrate (CSH) produced by these reactions. The 3D plots of Si/Al, Na/Al and Ca/Si atom ratios given by the microanalyses were compared with the estimated quantities of CSH(S) to successfully determine the unique chemical compositions of the N-A-S-H and CSH(S) for ten different AAB at three different curing temperatures using a constrained nonlinear least squares optimization formulation by general algebraic modeling system. The results show that the theoretical and experimental quantities of N-A-S-H and CSH(S) were in close agreement with each other. The $R^2$ values were 0.99 for both alkali-activated fly ash and alkali-activated slag binders.

• Korean Journal of Materials Research
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• v.28 no.2
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• pp.89-94
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• 2018

The properties of 18 K red gold solder alloys were investigated by changing the content of In up to 10.0 wt% in order to replace the hazardous Cd element. Cupellation and energy dispersive X-ray spectroscopy (EDS) were used to check the composition of each alloy, and FE-SEM and UV-VIS-NIR-Colormeter were employed for microstructure and color characterization. The melting temperature, hardness, and wetting angle of the samples were determined by TGA-DTA, the Vickers hardness tester, and the Wetting angle tester. The cupellation result confirmed that all the samples had 18K above 75.0wt%-Au. EDS results showed that Cu and In elements were alloyed with the intended composition without segregation. The microstructure results showed that the amount of In increased, and the grain size became smaller. The color analysis revealed that the proposed solders up to 10.0 wt% In showed a color similar to the reference 18 K substrate like the 10.0 wt% Cd solder with a color difference of less than 7.50. TGA-DTA results confirmed that when more than 5.0 wt% of In was added, the melting temperature decreased enough for the soldering process. The Vickers hardness result revealed that more than 5.0 wt% In solder alloys had greater hardness than 10.0 wt% Cd solder, which suggested that it was more favorable in making a wire type solder. Moreover, all the In solders showed a lower wetting angle than the 10.0 wt% Cd solder. Our results suggested that the In alloyed 18 K red gold solders might replace the conventional 10.0 wt% Cd solder with appropriate properties for red gold jewelry soldering.

• Journal of Welding and Joining
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• v.26 no.4
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• pp.50-54
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• 2008

In this research, anode for SOFC has been manufactured from two different kinds of feedstock materials through thermal spraying process and the properties of the coatings were characterized and compared. One kind of feedstock was manufactured from spray drying method which includes nano-components of NiO, YSZ (300 nm) and graphite. And the other is manufactured by blending the micron size NiO coated graphite, YSZ and graphite powders as feedstock materials. Microstructure, mechanical properties and electrical conductivity of the coatings as-sprayed, after oxidation and after hydrogen reduction containing nano composite which is prepared from spray-dried powders were evaluated and compared with the same properties of the coatings prepared from blended powder feedstock. The coatings prepared from the spray dried powders has better properties as they provide larger triple phase boundaries for hydrogen oxidation reaction and is expected to have lower polarization loss for SOFC anode applications than that of the coatings prepared from blended feedstock. A maximum electrical conductivity of 651 S/cm at $800^{\circ}C$ was achieved for the coatings from spray dried powders which much more than that of the average value.