• 대한치과기공학회지
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• 제39권1호
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• pp.43-52
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• 2017

Purpose: Physical and chemical properties of gold is most suitable to be restored of teeth to its original state. Recently zirconia was used instead of gold because of esthetical and intimacy of human body. Because of high strength and high abrasion resistance of zirconia, all zirconia artificial tooth lead to wear the original tooth of opposite site. To preserve this original tooth, zirconia artificial tooth covered with dental ceramic glass was used. When joining the zirconia core and dental ceramic glass, difference of their thermal expansion coefficient and wetting ability is generated the residual stress at interface lead to crack. In order to solve this problem, intermediate layer what is called zir-liner was imported to decrease the residual stress and increase the bonding strength. Methods: In this study, to identify the optimum conditions for manufacturing process, various methods to rough the surface of zirconia core were adopted, and vary the thickness of interlayer, and analyzed bond strength. Results: Bond strength of sanding specimens group showed higher than that of non-sanding specimens group, and once applied intermediate layer with sanding specimens showed highest bond strength with 28 MPa. SEM photomicrographs of zirconia cores fired at $1500^{\circ}C$ showed parallel straight lines in sanding and pockmarked surface in blasting surfaces as abrasion traces. Observation of the destruction section after shear test by SEM were carried out. Liner applied non-sanding group and non-liner applied sanding group all showed interfacial crack. Sandblasting group with non-liner showed remained dental ceramic glass on the surface of zirconia. Sandblasting group with once applied liner showed partially remained liner and dental ceramic glass on the surface of zirconia. XRD analysis revealed that sandblasting group showed higher monoclinic peaks than other specimens group and this result was due to the high collision energy for stress induced phase transformation. Conclusions: A study on the improvement of bonding strength between zirconia and dental ceramic glass steadily carried out for the future to practical use.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제55권10호
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• pp.461-466
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• 2006

In the present work, we investigated the photodissolution and photodiffusion effect on the interface of Ag/chalcogenide $As_{40}Ge_{10}Se_{15}S_{35}$ thin film by measuring the absorption coefficient, the optical density, the resistance change of Ag layer. It was found that the photodissolutioniphotodiffution ratio depends on the magnitude of photon energy absorbed in the chalcogenide thin film and the depth of photodiffution was proportional to the square root of the exposed time. Also, we have investigated the holographic grating formation with P-polarization states on chalcogenide $As_{40}Ge_{10}Se_{15}S_{35}$ thin film and $As_{40}Ge_{10}Se_{15}S_{35}/Ag$ double layer structure thin film. Holographic gratings have been formed using He-Ne laser (632.8 nm) which have a smaller energy than the optical energy gap, $E_g\;_{opt}$ of the film, i. e., an exposure of sub-bandgap light $(h{\upsilon} under P-polarization. As the results, we found that the diffraction efficiency on $As_{40}Ge_{10}Se_{15}S_{35}/Ag$ double layer structure thin film was more higher than that on single $As_{40}Ge_{10}Se_{15}S_{35}$ thin film. Also, we obtained that the maximum diffraction efficiency was 0.27 %, 1,000 sec on $As_{40}Ge_{10}Se_{15}S_{35}\;(1{\mu}m)/Ag$ (10 nm) double layer structure thin film by (P: P) polarized recording beam. It will offer lots of information for the photodoping mechanism and the analyses of chalcogenide thin films.

• 한국환경보건학회지
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• 제36권3호
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• pp.236-246
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• 2010

In preparative anti-corrosive coating experiments, polyaniline was obtained by reacting an oxidizing agent with the monomer aniline. Further, the primer coating was prepared using a variety of widely-used materials such as urethane resin. For the top coating, epoxy resin and acrylic urethane resin were used. Characteristics of the coatings were assessed according to KS and ASTM specifications, and the structure of the polyaniline was characterized using FT-IR and TGA. For analysis of anti-corrosive properties in salt-spray experiments, measurements of the oxidation state of iron and surface atomic analysis were conducted using XPS and SEM-EDX. Unlike general anti-corrosive coatings which exhibit anti-corrosive effects only as a primer coating, the anti-corrosive coatings using polyaniline as the anti-corrosive pigment showed a marked synergistic effect with the top coatings. In other words, the top coatings not only produce a fine view effect, but also increase, through interaction with the primer coatings, the resistance to diffusion of corrosive factors from the external environment. It was also found that, unlike the heavy metal oxide-forming layer of the passive barrier alone, the polyaniline anti-corrosive pigment oxidized iron at the interface with the iron substrate to form a passive barrier in the oxidic layer, and itself formed a potential barrier layer with anti-corrosive factors from the external environment. Although the passive layer was damaged, the damaged area did not become completely oxidized iron; on the contrary, it showed a tendency to reduction. This can be interpreted such that a passive layer is formed again on the damaged area, and that at the same time there is a tendency to self-healing.

• 한국전기전자재료학회논문지
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• 제22권1호
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• pp.22-28
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• 2009

We investigated the sintering and electric properties of ZnO-1.0 at% $TeO_2$ (ZT1) and 1.0 at% Mn-doped ZT1(ZT1M1) system. $TeO_2$ itself melts at $732^{\circ}C$ in air but forms the $ZnTeO_3$ or $Zn_2Te_3O_8$ phase with ZnO as increasing temperature and therefore retards the densification of ZnO to $1000^{\circ}C$. In ZT1M1 system, also, the densification of ZnO was retarded up to $1000^{\circ}C$ and then reached > 90% of theoretical density above $1100^{\circ}C$. It was found that a good varistor characteristics(nonlinear coefficient $a{\sim}60$) were developed in ZT1M1 system sintered at $1100^{\circ}C$ due to Mn which known as improving the nonlinearity of ZnO varistors. The results of C-V characteristics such as barrier height (${\Phi}_b$), donor density ($N_D$), depletion layer (W), and interface state density ($N_t$) in ZT1M1 ceramics were $1.8{\times}10^{17}cm^{-3}$, 1.6 V, 93 nm, and $1.7{\times}10^{12}cm^{-2}$, respectively. Also we measured the resistance and capacitance of grain boundaries with temperature using impedance and electric modulus spectroscopy. It will be discussed about the stability and homogeneity of grain boundaries using distribution parameter ($\alpha$) simulated with the Z(T)"-logf plots.

• 대한화장품학회지
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• 제11권1호
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• pp.21-31
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• 1985

폴리옥시에틸렌 도데실 에테르 유도체로 안정화된 헥산 - 물의 유화계에서 소량의 장쇄알칸 및 장쇄알칸올이 유화안정도에 미치는 효과를 비교 검토하였다. 장쇄알칸의 계면장력 및 원심분리에 의한 유화 안정도에 거의 영향을 주지 않았으나 장쇄알칸올은 계면장력을 현저히 저하시켰으며, 원심분리시 coalescence에 의한 유화파괴 방지에 효과적이었다. 그러나 시간 경과에 따른 유화안정도는 장쇄알칸이 장쇄알칸올 보다 더욱 효과적이었고 또 탄화수소쇄 길이가 길어질수록 더욱 효과적이었다. 이러한 것을 유화제를 변경시켰을 경우에도 마찬가지였다. 이것은 장쇄알칸을 첨가함으로써 분산상의 소수결합력을 증대시켜 물에 대한 용해도가 감소되어 분자확산에 의한 유화파괴가 어려워지기 때문이다. 즉 이러한 유화계에서 유화파괴는 coalescence보다는 분자확산에 의해 지배됨을 알 수 있다.

• 대한치과보철학회지
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• 제41권6호
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• pp.762-771
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• 2003

Statement of problem. In dentistry, the minimally prepared inlay resin-bonded fixed partial denture (FPD) made of new ceromer / fiber-reinforced composite (FRC) was recently introduced. However, the appropriate dimensions for the long-term success and subsequent failure strength are still unknown. Purpose. The aim of this study was to investigate the most fracture-resistible thickness combination of the ceromer / FRC using a universal testing machine and an AE analyzer. Material and Methods. A metal jig considering the dimensions of premolars and molars was milled and 56-epoxy resin dies, which had a similar elastic modulus to that of dentin, were duplicated. According to manufacturer's instructions, the FRC beams with various thicknesses (2 to 4 mm) were constructed and veneered with the 1 or 2 mm-thick ceromers. The fabricated FPDs were luted with resin cement on the resin dies and stored at room temperature for 72 hours. AE (acoustic emission) sensors were attached to both ends, the specimens were subjected to a compressive load until fracture at a crosshead speed of 0.5 mm/min. The AE and failure loads were recorded and analyzed statistically. Results. The results showed that the failure strength of the ceromer/FRC inlay FPDs was affected by the total thickness of the connectors rather than the ceromer to FRC ratio or the depth of the pulpal wall. Fracture was initiated from the interface and propagated into the ceromer layer regardless of the change in the ceromer / FRC ratio. Conclusion. Within the limitations of this study, the failure loads showed significant differences only in the case of different connector thicknesses, and no significant differences were found between the same connector thickness groups. The application of AE analysis method in a fiber-reinforced inlay FPD can be used to evaluate the fracture behavior and to analyze the precise fracture point.

• 한국재료학회지
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• 제18권3호
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• pp.153-158
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• 2008

Fe-aluminides have the potential to replace many types of stainless steels that are currently used in structural applications. Once commercialized, it is expected that they will be twice as strong as stainless steels with higher corrosion resistance at high temperatures, while their average production cost will be approximately 10% of that of stainless steels. Self-propagating, high-temperature Synthesis (SHS) has been used to produce intermetallic and ceramic compounds from reactions between elemental constituents. The driving force for the SHS is the high thermodynamic stability during the formation of the intermetallic compound. Therefore, the advantages of the SHS method include a higher purity of the products, low energy requirements and the relative simplicity of the process. In this work, a Fe-aluminide intermetallic compound was formed from high-purity elemental Fe and Al foils via a SHS reaction in a hot press. The formation of iron aluminides at the interface between the Fe and Al foil was observed to be controlled by the temperature, pressure and heating rate. Particularly, the heating rate plays the most important role in the formation of the intermetallic compound during the SHS reaction. According to a DSC analysis, a SHS reaction appeared at two different temperatures below and above the metaling point of Al. It was also observed that the SHS reaction temperatures increased as the heating rate increased. A fully dense, well-bonded intermetallic composite sheet with a thickness of $700\;{\mu}m$ was formed by a heat treatment at $665^{\circ}C$ for 15 hours after a SHS reaction of alternatively layered 10 Fe and 9 Al foils. The phases and microstructures of the intermetallic composite sheets were confirmed by EPMA and XRD analyses.

• 한국세라믹학회지
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• 제49권6호
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• pp.659-662
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• 2012

Yttrium (Y) and niobium (Nb) doped spherical $Li_4Ti_5O_{12}$ were synthesized to improve the energy density and electrochemical properties of anode material. The synthesized crystal was $Li_4Ti_5O_{12}$, the particle size was less than $1{\mu}m$ and the morphology was spherical and well dispersed. The Y and Nb optimal doping amounts were 1 mol% and 0.5 mol%, respectively. The initial capacity of the dopant discharge and charge capacity were respectively 149mAh/g and 143 mAh/g and were significantly improved compared to the undoped condition at 129 mAh/g. Also, the capacity retention of 0.2 C/5 C was 74% for each was improved to 94% and 89%. It was consequently found that Y and Nb doping into the $Li_4Ti_5O_{12}$ matrix reduces the polarization and resistance of the solid electrolyte interface (SEI) layer during the electrochemical reaction.

• Journal of Pharmaceutical Investigation
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• 제32권1호
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• pp.21-26
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• 2002

The primary culture of human nasal epithelial cell monolayer was performed on a Transwell. The effect of various factors on the tight junction formation was observed in order to develop an in vitro experimental system for nasal transport studies. Human nasal epithelial cells, collected from human normal inferior turbinates, were plated onto diverse inserts. After 4 days, media of the apical surface was removed for air-liquid interface (ALI) culture. Morphological characteristics was observed by transmission electron microscopy (TEM). A polyester membrane of $0.4\;{\mu}m$ pore size was determined as the most effective insert based on the change in the transepithelial electric resistance (TEER) value as well as the $^{14}C-mannitol$ transport study. The ALI method was effective in developing the tight junction as observed in the further increase in the TEER value and reduction in the permeability coefficient $(P_{app})$ of $^{14}C-mannitol$ transport. Results of the transport study of a model drug, budesonide, showed that the primary culture system developed in this study could be further developed and applied for in vitro nasal transport studies.

• 한국주조공학회지
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• 제25권6호
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• pp.259-264
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• 2005

The copper clad steel wire is used extensively as lead wires of electronic components such as capacitors, diodes and glass sealing lamp because the wire combines the strength and low thermal expansion characteristic of Fe-Ni steel with the conductivity and corrosion resistance of copper. In order to fabricate the copper clad steel wire, several processes including electro-plating, tubecladding extrusion process and dip forming process have been introduced and applied. The electroplating process for the production of copper clad steel wire shows poor productivity and induces environmental load generation such as electroplating solution. The dip forming process is suitable to mass production of copper clad steel such as trolley wire. and need expensive manufacturing facilities. The present paper describes the improvement of the conventional continuous casting process to fabricate copper clad steel wire, which its core metal is low thermal expansion Fe-Ni alloy and its sheath material is copper. In particular, the formation of intermetallic compound at interface between core and sheath was investigated in order to introduce optimum continuous casting process parameter for fabrication of copper clad steel wire with higher electrical conductivity. The mechanical strength of copper clad steel wire was also investigated through wiredrawing process with of 95% in total reduction ratio.