• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.169-172
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• 2006

In the present work, silicon nitride was fabricated with $Y_3Al_5O_{12}$ as sintering additive and its mechanical properties were investigated. Silicon nitride with 3, 5, 7wt% of $Y_3Al_5O_{12}$ was prepared and sintered by a Hot Pressing (HP) technique at 1750, $1800^{\circ}C$ for 2 hours. The Process was fulfilled under different process pressures of 30, 45MPa respectively. Mechanical properties (density, strength, hardness, fracture toughness) were investigated as a function of $Y_3Al_5O_{12}$ contents in $Si_3N_4$. $Si_3N_4-Y_3Al_5O_{12}$ ceramics showed similar mechanical properties compared with $Si_3N_4-Y_2O_3-Al_2O_3$ ceramics. But its high temperature strength was higher than $Si_3N_4-Y_2O_3-Al_2O_3$ceramics considerably.

• Journal of Electrochemical Science and Technology
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• v.3 no.1
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• pp.29-34
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• 2012

The structural changes of $Li_{1-x}Ni_{0.5}Co_{0.2}Mn_{0.3}O_2$ cathode material for lithium ion battery during the first charge was investigated in comparison with $Li_{1-x}Ni_{0.8}Co_{0.15}Al_{0.05}O_2$ using a synchrotron based in situ X-ray diffraction technique. The structural changes of these two cathode materials show similar trend during first charge: an expansion along the c-axis of the unit cell with contractions along the a- and b-axis during the early stage of charge and a major contraction along the c-axis with slight expansions along the a- and b-axis near the end of charge at high voltage limit. In $Li_{1-x}Ni_{0.5}Co_{0.2}Mn_{0.3}O_2$ cathode, however, the initial unit cell volume of H2 phase is bigger than that of H1 phase since the c-axis undergo large expansion while a- and b- axis shrink slightly. The change in the unit cell volume for $Li_{1-x}Ni_{0.5}Co_{0.2}Mn_{0.3}O_2$ during charge is smaller than that of $Li_{1-x}Ni_{0.8}Co_{0.15}Al_{0.05}O_2$. This smaller change in unit cell volume may give the $Li_{1-x}Ni_{0.5}Co_{0.2}Mn_{0.3}O_2$ cathode material a better structural reversibility for a long cycling life.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.348-350
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• 1997

Because of internal voids ininsulators give rise to partial discharge(PD), which cause local breakdown and even entire insulation breakdown. Treeing due to PD is one of the main causes of breakdown of the insulating materials and reduction of the insulation life. Therefore the necessity for establishing a method to diagnose the aging of insulation materials and to predict the breakdown of insulation has become important. From this viewpoint, our studies diagnose insulation degradation using the method of computer sensing system, which has the advantages of PD and acoustic emission(AE) sensing system. To use advantages of these two methods can be used effectively to search for treeing location and PD in some materials. In analysis method of degradation. We analyzed the PD pulse and AE pulses by regression analysis, compared to these obtained the correlation coefficient and determination coefficient by T-distribution and saw that PD and AE pulses show a similar pattern on the whole. Finally using statically operator such as the center of gravity(G), the gradient of the discharge distribution(C), we have analyzed for the prediction of life which we can be obtained the time, occurred of many pulse of small discharge amplitude.

• The Journal of Advanced Prosthodontics
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• v.12 no.5
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• pp.251-258
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• 2020

PURPOSE. The bond strengths between resin denture teeth with various compositions and denture base resins including conventional and CAD/CAM purposed materials were evaluated to find influence of each material. MATERIALS AND METHODS. Cylindrical rods (6.0 mm diameter × 8.0 mm length) prepared from pre-polymerized CAD/CAM denture base resin blocks (PMMA Block-pink; Huge Dental Material, Vipi Block-Pink; Vipi Industria) were bonded to the basal surface of resin teeth from three different companies (VITA MFT^®; VITA Zahnfabrik, Endura Posterio^®; SHOFU Dental, Duracross Physio^®; Nissin Dental Products Inc.) using resin cement (Super-Bond C&B; SUN MEDICAL). As a control group, rods from a conventional heat-polymerizing denture base resin (Vertex™ Rapid Simplified; Vertex-Dental B.V. Co.) were attached to the resin teeth using the conventional flasking and curing method. Furthermore, the effect of air abrasion was studied with the highly cross-linked resin teeth (VITA MFT^®) groups. The shear bond strengths were measured, and then the fractured surfaces were examined to analyze the mode of failure. RESULTS. The shear bond strengths of the conventional heat-polymerizing PMMA denture resin group and the CAD/CAM denture base resin groups were similar. Air abrasion to VITA MFT^® did not improve shear bond strengths. Interfacial failure was the dominant cause of failure for all specimens. CONCLUSION. Shear bond strengths of CAD/CAM denture base materials and resin denture teeth using resin cement are comparable to those of conventional methods.

• Korean Journal of Materials Research
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• v.5 no.7
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• pp.858-868
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• 1995

Texture development and martensitic phase transformation, on rolling, are compared in two Hadfield's steels, one having low carbon content(0.65wt% C), the other high carbon content(1.35wt%). In spite of small difference in stacking fault energy(about 2 mJm$^{-2}$ ) between two Hadfield's steels, the differences in texture development are observed. In low carbon steel, the textures developed are similar to those of low stacking fault energy metals in low strain range. However, the abnormal textures such as {111} , {110} <001> are strongly developed at high strain, which are due to the disturbance of u martensite in the development of textures formed at the packets of shear bands or at the grain boundaries. In contrast to low carbon Hadfield's steel( LCHS), the texture development of high carbon Hadfield's steel(HCHS) is simitar to those of low stacking fault energy metals in the whole strain range. This may be due to the fact that the amount of deformation induced martensite was small, as observed by A.C. magnetic susceptibility and iron particle tests.

• Korean Institute of Interior Design Journal
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• v.22 no.5
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• pp.114-125
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• 2013

Kengo Kuma used to be very known well as a critic before being an architect. He usually mentioned quite unique type of comments for subjects whenever his criticism, also even his works results have been able to be targets of criticism materials by his method. His works are the achievements of challenges based on his continuous dynamic criticism. Hence, to have well understanding of his architectural thinking and works result, his complexes criticism structure must be needed to understand. And also, this study is using 'KJ Method' type to analyze his architectural thinking which is complicated making by a type of non-linear. Kengo Kuma's structures of architectural thinking and critiques perspective of modern architecture have been created by 'KJ Method'. Critiques types of keywords and consequences words collected from among the local dedicated professional architecture books to get this research result. First of all, Kengo Kuma desired even modern architecture problems to be melt as a specific architecture result such as modern type of power structure. To have result, Kengo Kuma had experienced sensible activity through materials which have specific characteristic. Also place of materiality created to get relationship between environments and architecture. Secondly, he wanted to recover troubled traditional Japanese architectural perspective which blocked relationship by dichotomy as a right way. In conclusion, this research reaches Kengo Kuma's type of architecture which strongly emphasizes harmony among related components such as human being, materials, substances based on accepted natural environments and lives' principle. Also, much more specific methods have been derived by related works results analyzing which have similar characteristic as Kengo Kuma's one.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.159-159
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• 2017

Ti-6Al-4V alloy have been used for dental implant because of its excellent biocompatibility, corrosion resistance, and mechanical properties. However, the integration of such implant in bone was not in good condition to achieve improved osseointergraiton. For solving this problem, calcium phosphate (CaP) has been applied as coating materials on Ti alloy implants for hard tissue applications because its chemical similarity to the inorganic component of human bone, capability of conducting bone formation and strong affinity to the surrounding bone tissue. Various metallic elements are known to play an important role in the bone formation and also affect bone mineral characteristics. Especially, Zn is essential for the growth of the human and Zn coating has a major impact on the improvement of corrosion resistance. Plasma electrolytic oxidation (PEO) is a promising technology to produce porous and firmly adherent inorganic Zn containing TiO2(Zn-TiO2)coatings on Ti surface, and the a mount of Zn introduced in to the coatings can be optimized by altering the electrolyte composition. In this study, effect of Zn content on the corrosion behavior of Ti-6Al-4V alloy after plasma electrolytic oxidation were studied by SEM, EDS, XRD, AC impedance, and potentiodynamic polarization test. The potentiodynamic polarization and AC impedance tests for corrosion behaviors were carried out in 0.9% NaCl solution at similar body temperature using a potentiostat with a scan rate of 1.67 mV/s and potential range from -1500 mV to +2000 mV. Also, AC impedance was performed at frequencies ranging from 10 MHz to 100 kHz for corrosion resistance.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.153-153
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• 2017

The application of the coating supports the mechanical characteristics of the implant, and various materials and coatings are currently being used in the implant in a way to accelerate adhesion. Especially, plasma electrolytic oxidation (PEO) coating has been proposed continually with good surface treatment of titanium alloys. Also, the PEO process can incorporate Ca and P ions on the titanium surface through variables varied factor. PEO process for bioactive surface has carried out in electrolytes containing Ca and P ions. Natural bone is composed of mineral elements such as Mg, Si, Zn, Sr, and Mn, etc. Especially, Mg and Si of these elements play role in bone formation and growth after clinical implantation of bio-implants. In this study, corrosion charateristics of PEO-treated Ti-6Al-4V alloy in solution containing Si and Mg ions has been investigated using several experimental techniques. The PEO-treated surfaces were identified by X-ray diffraction, using a diffractometer (XRD, Philips X' pert PRO, Netherlands) with Cu $K{\alpha}$ radiation. The morphology was observed by field-emission scanning electron microscopy (FE-SEM, Hitachi 4800, Japan) and energy-dispersive X-ray spectroscopy (EDX, Oxford ISIS 310, England). The potentiodynamic polarization and AC impedance tests for electrochemical degradations were carried out in 0.9% NaCl solution at similar body temperature using a potentiostat with a scan rate of 1.67mV/s and potential range from -1500mV to + 2000mV.

• Explosives and Blasting
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• v.35 no.4
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• pp.19-26
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• 2017

The most widely used method for determining the blast effects of explosives is the Trauzl lead block test. This test is used to measure the explosive power (strength) of a substance by determining volume increase, which is produced by the detonation of a test explosive charged in the cavity of a lead block with defined quantity and size. In this paper, Trazul lead block test and AUTODYN numerical analysis were conducted to evaluate the coupling medium effect of blast hole. The effects of coupling materials can be expressed as the expansion of the cavity in a standard lead block through explosion of the explosives. The tests were conducted with emulsion explosives. The coupling mediums used as the filling material around a explosive charge were air, sand, water and gelatine. Results of test and numerical analysis showed that expansion of lead block were much more affected by water&gel than by sand and air. The water and gel showed similar results. As expected, the transmitted pressure and dynamic strain was higher in water and gelatine coupled blast hole than in air and sand.

• Journal of the Korean Society of Earth Science Education
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• v.1 no.1
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• pp.72-84
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• 2008

This study is focused on the main concepts of gravity and geomagnetics which are introduced in the earth science textbooks of high school in 7th curriculum. This study examines the validity and accuracy of the Earth Science textbooks and shows some effective teaching plans by using the latest materials. This study also illustrates the main concepts of gravity and geomagnetics through presenting some effective and practical teaching-learning methods. The results of the study were as follows: First of all, a number of main concepts of six textbooks of high school were selected; the field of gravity, the direction and dimension of gravity, the measurement of gravity, the main reason of gravity anomaly and geoid, earth terrestrial magnetic field, secular variation of goemagnetics. Secondly, most Earth Science textbooks of high school explains the main concepts of the gravity and geomagnetics in similar ways. Those textbooks, however, don't put an emphasis on the essential contents which has been regarded as important thing in terms of the current educational course of study. The high school textbooks also use the material which is too old-fashioned and has some problems of accuracy and validity. Especially, many main concepts of the textbooks and scientific data(such as the direction of gravity, the measurement of gravity, the main reason of gravity anomaly, the use of geoid, secular variation) are different with those of South Korea, In addition, some materials(graphs and diagrams) are very old ones and they don't have authentic information.Finally, Among the various main concepts, some important ideas (the direction of the gravity and the method of measuring gravity, the measurement and use of gravity anomaly, the definition of geoid and secular variation of geomagnetics) should be corrected by showing the latest and authentic materials.