• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.7
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• pp.3437-3443
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• 2013

The polymer insulators have been extensively used as an alternate material of ceramic insulators. However, when they are used in practical conditions, there are many problems of decreasing performance and shortening lifetime due to the exposures of degradation factors applied from the outdoor situations. Accordingly, the analysis of polymer degradations has been getting influential too late as one of important subjects for improvements of safety and reliability. Heat, water treatments are arbitrary simulated for finding out the initiations and processes of surface degradation on the polymer surface. Especially, this study is focused on the chemical changes properties. From the analysis of hydrophilic and hydrophobic molecular structures, final modeling of surface degradation is accomplished. We checked the contact angle depending on heat and moisturized accelerated degradation and ran an XPS analysis to check the mechanism change of the surface of the PCB polymer composite. The surface that had a tendency to attract moisture showed a decrease in the contact angle and generated a large amount of carboxyl($-COO^*$) radicals. The hydrophobized surface showed an increase in the contact angle and had a stable chemical composition constituted of the breakaway of oxygen radicals and the formation of double bond by carburization.

• Journal of the Microelectronics and Packaging Society
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• v.6 no.1
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• pp.51-58
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• 1999

The effects of glass composition on the wettability and reactivity with $ZrO_2$substrate was evaluated and fabrication variables and glass compositions was investigated. Various glass compositions was investigated. Alkaline earth silicate glass show good wettability and lower viscosity and crystallization of glass could be prevented by $B_2O_3$.The sealant glass begin to wet on $ZrO_2$substrate below $900^{\circ}C$ and porosity occurred in various glass compositions, the crystallization and porosity in the glass could be prevented by the addition of flux into glass composition. But flowability and reactivity of glass with $ZrO_2$substrate was enhanced. Processing variables should be optimized to reduce the porosity by enhancing the sintering of glass powder. Many silicate glasses were investigated for the applications of high temperature sealants. Wetting and bonding of glass was good enough to seal together between $ZrO_2$and other ceramic components of SOFC. But porosity and reaction layer were occurred in the sealant glass. It will be possible to produce glass sealant without porosity and reaction layer at the interface by optimization of processing variable and modify the glass compositions. In present study, wettability of glass-filler composite was investigated. The porosity, shape of filler and interfacial reactions of sealant glass with fillers were examined.

• Composites Research
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• v.30 no.2
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• pp.77-83
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• 2017

Liquid silicon infiltration, which is one of the methods of producing fiber reinforced ceramic composites, has several advantages such as low fabrication cost and good shape formability. In order to confirm LSI process feasibility of SiC fiber, $SiC_f/SiC$ composites were fabricated using three types of SiC fibers (Tyranno SA, LoxM, Tyranno S) which have different crystallinity and oxygen content. Composites that were fabricated with LSI process were well densified by less than 2% of porosity, but showed an obvious difference in 3-point bending strength according to crystallinity and oxygen content. When composites in LSI process was exposed to a high temperature, crystallization and micro structural changes were occurred in amorphous SiOC phase in SiC fiber. Fiber shrinkage also observed during LSI process that caused from reaction in fiber and between fiber and matrix. These were confirmed with changes of process temperature by SEM, XRD and TEM analysis.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.27 no.6
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• pp.491-497
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• 2001

Polymethylmethacrylate(PMMA) is currently commonly used material for the reconstruction of bone defects and fixation of joint prosthetics following congenital and acquired causes. Although PMMA has widespread use, it does not possess the ideal mechanical characteristics with osteoconductivity and osteoinductivity required. In order to overcome these problem, addition of bovine bone drived defatting demineralized bone(BDB) powders to a PMMA bone cement was done for improvement of physical property and bone forming characteristics of composite. In order to investigate the influence of BDB reinforcement on the PMMA, we measured physical property of compressive, tensile, flexural strength, and scanning electron microscopic examinations. The results were obtained as follows: 1. The PMMA forms a solid cellular matrix with open cells about $100{\mu}m$ in variable size and incorporating BDB. BDB aggregates inside the cells form a porous network that is accessible from the outer surface. 2. The physical properties were compressive strength of mean $22.74{\pm}1.69MPa$, tensile strength of mean $22.74{\pm}1.69MPa$, flexural strength of mean $77.53{\pm}6.93MPa$. Scanning electron microscopic examinations were revealed that there was DBD particles form a highly porous agglomerates. BDB can be added PMMA in the form of dried powders, the composites are applicable as bone substitutes. BDB and PMMA mixture is shown to produce a class of composites that due to their microstructure and improved mechanical properties may be suitable for application as bone subsitutes. The mechanical and material properties of the BDB-PMMA bone substitute composites are competitive with those properties of a porous ceramic matrix of other hydroxyapatite and with those of natural bones.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.35-36
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• 2008

PTC thermistor are characterized by an increase in the electrical resistance with temperature. The PTC materials of middle Curie point were produced or that of high Curie point (above $200^{\circ}C$), it was determined that compositional modifications of $Pb^{2+}$ for $Ba^{2+}$ produce change sin the Curie point to higher temperature. PTC ceramic materials with the Curie point above $120^{\circ}C$ were prepared by adding $PbTiO_3$, PbO or $Pb_3O_4$ into $BaTiO_3$. Thereby, adding $Pb^{2+}$ into $BaTiO_3$-based PTC material to improve Tc was studied broadly, however, weal know that PbO was poisonous and prone to volatilize, then to pollute the circumstance and hurt to people, so we should dope other innocuous additives instead of lead to increase Tc of composite PTC material. In order to prepare lead-free $BaTiO_3$-based PTC with middle Curie point, the incorporation on $Bi_{1/2}K_{1/2}TiO_3$ into $BaTiO_3$-based ceramics was investigated on samples containing 0, 1, 2, 3, 4, and 50mol% of $Bi_{1/2}K_{1/2}TiO_3$. $Bi_{1/2}K_{1/2}TiO_3$ was compounded as standby material by conventional solid-state reaction technique. The starting materials were $Bi_2O_3$, $K_2CO_3$, $BaCO_3$ and $TiO_2$ powder, and using solid-state reaction method, too. The microstructures of samples were investigated by SEM, DSC, XRD and dielectric properties. Phase composition and lattice parameters were investigated by X-ray diffraction.

• Korean Journal of Materials Research
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• v.4 no.2
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• pp.143-151
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• 1994

On PT/Ti/Si substrates, PZT thln fllms are deposited at $300^{\circ}C$ by rf magnetron sputtering uslng a $(PbZr_{52}, Ti_{48})O_{3}$ composltc cerarnlc target. To abtaln, the stable phase, perovskltc structure, furnace annealmg techmque had been cmplo:~d In PbO amb~ent for the $550^{\circ}C$-$750^{\circ}C$ temperature ranges. On Pt(250$\AA$)/Ti(500$\AA$)/Si, Pt(1000)$\AA$/Ti(500$\AA$)/Si substrates, effects of Ti layer and Pt thickness are studled. Though thickness of the Pt layer 1s 1000$\AA$). oxygen diffusion is not prevented and accelerated by Ti layer actlng for oxygen sink sites durmg furnace annealing. The upper TI layer 1s transformed Into TIOX by oxyen dlffuslon and lower Ti layer Into silicide with in-diffused Pt. The formation of TiOx layer seems to affect the orlentatton of the PZT layer. Furnace annealed f~lm shows ferroelectr~c and electrical properties wth a remanent polarlzation of 3.3$\mu A /\textrm{cm}^2$, , coerclve fleld of 0.15MV/cm, a=571 (10kHz), leakage current 32.65$\mu A /\textrm{cm}^2$, , breakdown voltage of 0.4OMV/cm.

• Journal of the Korean Magnetics Society
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• v.15 no.2
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• pp.67-75
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• 2005

For th aim of lightweight microwave absorbers, conductive and magnetic microspheres are fabricated by plating of Co films on hollow ceramic microspheres of low density. Metal plating was carried out in a two-step electroless plating process (pre-treatment of activation and plating). Uniform coating of the film with about $2{\~}3{\cal}um$ thickness was identified by SEM. High-frequency magnetic and microwave absorbing properties were determined in the rubber composites containing the Co-coated microspheres. Due to conductive and ferromagnetic behavior of the Co thin films, high dielectric constant and magnetic loss can be obtained in the microwave frequencies. Due to those electromagnetic properties, high absorption rate (25 dB) and thin matching thickness ($2.0{\~}2.5{\cal}mm$) are predicted in the composite layers containing the metal-coated microspheres of low density (about 0.84 g/cc) for the electromagnetic radiation in microwave frequencies.

• Journal of the Korean Electrochemical Society
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• v.7 no.2
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• pp.94-99
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• 2004

Anode-supported flat tubular solid oxide fuel cell (SOFC) was investigated to increase the cell power density. The anode-supported flat tube was fabricated by extrusion process. The porosity and pore size of Ni/YSZ ($8mol\%$ yttria-stabilized zirconia) cermet anode were $50.6\%\;and\;0.23{\mu}m$, respectively. The Ni particles in the anode were distributed uniformly and connected well to each other particles in the cermet anode. YSZ electrolyte layer and multilayered cathode composed of $LSM(La_{0.85}Sr_{0.15})_{0.9}MnO_3)/YSZ$ composite, LSM, and $LSCF(La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.7}O_3)$ were coated onto the anode substrate by slurry dip coating, subsequently. The anode-supported flat tubular cell showed a performance of $300mW/cm^2 (0.6V,\; 500 mA/cm^2)\;at\;500^{\circ}C$. The electrochemical characteristics of the flat tubular cell were examined by ac impedance method and the humidified fuel enhanced the cell performance. Areal specific resistance of the LSM-coated SUS430 by slurry dipping process as metallic interconnect was $148m{\Omega}cm^2\;at\;750^{\circ}C$ and then decreased to $148m{\Omega}cm^2$ after 450hr. On the other hand, the LSM-coated Fecralloy by slurry dipping process showed a high area specific resistance.

• Journal of Dental Rehabilitation and Applied Science
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• v.18 no.4
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• pp.289-299
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• 2002

The bond strength is one of the most important factor in establishing long-term success of esthetic restorative dentistry. So, various restorative materials have been introduced to improve the esthetic and physical properties. Ormocer (organically modified ceramic) was developed as a result of such efforts. This study was performed to compare the shear bond strength of ormocer based adhesive with that of existing dentin adhesive. In this study $Admira^{(R)}$ and $Admira^{(R)}$ bond of the ormocer system are grouped together for ADM, Single $Bond^{(R)}$ which is an one-bottle adhesive and Z-250TM which is hybrid composite resin of BIS-GMA system for SIN, and $Definite^{(R)}$ of ormocer and Etch & $Prime^{(R)}$ 3.0 which is a self etching priming/ bonding agent for ETC. The results of this study were as follows. : (1) In the comparison of shear bond strength according to different adhesive system, shear bond strength was increased in the order of ETC group, SIN group, ADM group. There was no significant difference between ADM group and SIN group. However, there was a significant level of difference between ADM and ETC groups as well as SIN and ETC groups( p<0.05). (2) Examination by a scanning electron microscope showed a well established hybrid layer and resin tag in both ADM group and SIN group, while ETC group showed a minimal formation of the hybrid layer when compared with ADM and SIN groups. From the above results, it may be reasonable to start the clinical application of ormocer system, and it is recommended that ormocer system should be used along with an ormocer based adhesive because ormocer system showed the lower shear bond strength when it used with other existing self etching priming/bonding agent. The self etching priming/bonding agent showed relatively low shear bond strength, and it is considered that the further study should be needed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.57-58
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• 2008

PTC thermistor are characterized by an increase in the electrical resistance with temperature. The PTC materials of middle Curie point were produced or that of high Curie point (above $200^{\circ}C$), it was determined that compositional modifications of $Pb^{2+}$ for $Ba^{2+}$ produce change sin the Curie point to higher temperature. PTC ceramic materials with the Curie point above $120^{\circ}C$ were prepared by adding $PbTiO_3$, PbO or $Pb_3O_4$ into $BaTiO_3$. Thereby, adding $Pb^{2+}$ into $BaTiO_3$-based PTC material to improve Tc was studied broadly, however, weal know that PbO was poisonous and prone to volatilize, then to pollute the circumstance and hurt to people, so we should dope other innocuous additives instead of lead to increase Tc of composite PTC material. In order to prepare lead-free $BaTiO_3$-based PTC with middle Curie point, the incorporation on $Bi_{1/2}Na_{1/2}TiO_3$ into $BaTiO_3$-based ceramics was investigated on samples containing 0, 1, 2, 3, 4, and 50mol% of $Bi_{1/2}Na_{1/2}TiO_3$. $Bi_{1/2}Na_{1/2}TiO_3$ was compounded as standby material by conventional solid-state reaction technique. The starting materials were $Bi_{1/2}Na_{1/2}TiO_3$, $BaCO_3$, $TiO_2$ and $Y_2O_3$ powder, and using solid-state reaction method, too. The microstructures of samples were investigated by SEM, DSC, XRD and dielectric properties. Phase composition and lattice parameters were investigated by X-ray diffraction.