• The Journal of Korean Academy of Prosthodontics
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• v.47 no.3
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• pp.342-347
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• 2009

Statement of problem: when using resin for class II restoration, micoleakage by instrumentation can be regarded as the primary negative characteristic. A review of the available literature suggests that using flowable resin as liner to decreased microleakage. Purpose: The aim of this study was to determine the influence of the nanofilled flowable resin lining on marginal microleakage after load cycling in class II composite restoration fillings using nanofiller resin. Material and methods: 24 extracted premolars were prepared with class II cavity. F group was restored the nanofilled resin with the nanofilled flowable resin as liner. NF group was restored the nanofilled resin only. After restoration, an experiment was performed on 2 groups using a 300N load at 104, 105 and 106 cycles. Prior to and before each load cycling, it was gauged length on total marginal microleakage, axial marginal microleakage and buccal, gingival, lingual marginal microleakage. Data were analyzed with the Mann-Whitney test & Kruskal-Wallis test. Results: There were statistically significant differences between 2 groups and between individual groups. (P <.05) The result showed less microleakage in teeth restored by the nanofilled resin, which was lined by the nanofilled flowable resin. Conclusion: There was significant reduction in microleakage when the nanofilled flowable resin lining was placed underneath the nanofilled resin in class II composite restoration fillings.

• Korean Journal of Materials Research
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• v.9 no.3
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• pp.315-321
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• 1999

Metal matrix composites have been extensively studied because of their excellent characteristics for structural application. $Al_2O_3$ and SiC have been used as a common reinforcement owing to their good mechanical properties. However the manufacturing cost of these ceramic reinforcement is expensive, so the use of the composites has been restricted to special purposes. In this study, we tested the application possibility as a reinforcement of $Al_2O_3$-TiC powder synthesized by SHS(Self-propagating High-temperature Synthesis) process to Al alloy matrix composite. Also, $Al_2O_3$ short fibers were added with the synthesized powders in order to apply to the Al matrix hybrid composites. Squeeze infiltration casting process was used to make the composite with 25vol% of reinforcement. Microstructure and crystal structure were examined by SEM, OM and XRD, also the mechanical properties were studied by the compressive test and wear test.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.6
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• pp.263-271
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• 2015

Commercial AR(Alkali Resistant)-glass fiber has a good chemical resistant property, but also has a problem of difficulty in fiberizing process because of high viscosity in melted glass compare with E-glass fiber which is the most widely used for reinforced fiber of composite materials. In this study, we fabricated AR-glass fiber with low zirconia contents compare with commercial AR-glass fiber relatively, and measured properties against E-glass fiber. We obtained transparent clear glass with zirconia contents of 0.5~16 wt% by melting at $1600^{\circ}C$ for 2 hours. These AR-glass samples had high visible transmittance of 89~90 %, softening temperature of $703{\sim}887^{\circ}C$. And softening temperatures of them were increased according to the increasing zirconia contents. Compare with E-glass, AR-glass contains 4 wt% zirconia has different value of $-94^{\circ}C$ in softening temperature, $+68^{\circ}C$ at Log3 temperature and $-13^{\circ}C$ at Log5 temperature in viscosity. We could verify good alkali resistant property of the AR-glass fiber with SEM after dipping in alkali solution for 48~72 hours, and also high tensile strength, 1.7 times compare with E-glass fiber at 48 hours and 2.2 times at 72 hours. We conclude that this AR-glass fiber can be widely used as general alkali resistant glass fiber because of easy manufacturing condition and good properties even though it has low zirconia contents.

• The Journal of Korean Academy of Prosthodontics
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• v.54 no.3
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• pp.193-202
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• 2016

Purpose: This study was performed in order to assess the effect of the surface treatment methods and the use of bonding agent on the shear bond strength (SBS) between the aged CAD-CAM (computer aided design-computer aided manufacturing) hybrid materials and added composite resin. Materials and methods: LAVA Ultimate (LU) and VITA ENAMIC (VE) specimens were age treated by submerging in a $37^{\circ}C$ water bath filled with artificial saliva (Xerova solution) for 30 days. The surface was ground with #220 SiC paper then the specimens were divided into 9 groups according to the combination of the surface treatment (no treatment, grinding, air abrasion with aluminum oxide, HF acid) and bonding agents (no bonding, Adper Single Bond 2, Single Bond Universal). Each group had 10 specimens. Specimens were repaired (added) using composite resin (Filtek Z250), then all the specimens were stored for 7 days in room temperature distilled water. SBS was measured and the fractured surfaces were observed with a scanning electron microscope (SEM). One-way ANOVA and Scheffe test were used for statistical analysis (${\alpha}=.05$). Results: Mostly groups with bonding agent treatment showed higher SBS than groups without bonding agent. Among the groups without bonding agent the groups with aluminum oxide treatment showed higher SBS. However there was no significant difference between groups except two subgroups within LU group, which revealed a significant increase of SBS when Single Bond Universal was used on the ground LU specimen. Conclusion: The use of bonding agent when repairing an aged LAVA Ultimate restoration is recommended.

• The korean journal of orthodontics
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• v.38 no.4
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• pp.275-282
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• 2008

Objective: The purpose of this study was to investigate the effect of using laser for ceramic bracket bonding of porcelain surfaces and to compare it with conventional treatment of porcelain surfaces. Methods: Ninety feldspathic porcelain specimens were divided into 9 groups of 10, with each group having different surface treatments performed. Surface treatment groups were orthophosphoric acid, orthophosphoric acid with silane, hydrofluoric acid, hydrofluoric acid with silane, sandblasted, sandblasted with silane, laser etched, laser etched with silane, and glazed surface served as a control group. In the laser etched groups, the specimens were irradiated with 2-watt superpulse carbon dioxide ($CO_2$) laser for 20 seconds. Ceramic brackets were bonded with light-cure composite resin and all specimens were stored in water at $37^{\circ}C$ for 24 hours. Shear bond strength was determined in megapascals (MPa) by shear test at 1 mm/minute crosshead speed and the failure pattern was assessed. For statistical analysis, one-way ANOVA and tukey test were used. Results: Statistical analysis showed significant differences between the groups. The HFA + S group showed the highest mean shear bond strength ($13.92{\pm}1.94\;MPa$). This was followed by SB + S ($10.16\;{\pm}\;1.27\;MPa$), HFA ($10.09\;{\pm}\;1.07\;MPa$), L + S ($8.25\;{\pm}\;1.24\;MPa$), L ($7.86\;{\pm}\;0.96\;MPa$), OFA + S ($7.22\;{\pm}\;1.09\;MPa$), SB ($3.41\;{\pm}\;0.37\;MPa$), OFA ($2.81\;{\pm}\;0.37\;MPa$), G ($2.46\;{\pm}\;1.36\;MPa$), Bond failure patterns of HFA and silane groups, except L + S, were cohesive modes in porcelain while adhesive failure was observed in the control group and the rest of the groups. Conclusions : A 2-watt superpulse $CO_2$ laser etching of porcelain surfaces can provide a satisfactory result for porcelain surface treatment for ceramic bracket bonding. Laser irradiation may be an alternative conditioning method for the treatment of porcelain surfaces.

• Journal of the Korean Ceramic Society
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• v.41 no.12 s.271
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• pp.929-932
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• 2004

It is known that small amount of MgO in excess is often added to develop pure perovskite single phase of PMN-based composite, however, extra MgO precipitates in grains and inhibits densification of PMN. In this study PMN-PT-BT (PBT) powder was prepared by a conventional mixed oxide method using $(MgCO_3)_4{\cdot}Mg(OH)_2{\cdot}5H_{2}O$ instead of MgO. The precursor was heated at $500^{\circ}C/1h$ and its surface was modified with MgO sol. This effect was investigated in the aspects of sintering and dielectric properties. Small amount of added MgO sol ($0.5{\sim}1.0wt\%$) enhanced sintering substantially below $1000^{\circ}C$. The PBT with $0.5wt\%$ MgO sol sintered at $900^{\circ}C/2h$ had density of $7.62\;g/cm^3$, room temperature dielectric constant of 14800, loss of dielectric constant of $1.1\%$, which were comparable to those of the PBT sintered at $1000^{\circ}C/2h$. It was noticeable that the extra MgO precipitated mostly on triple points and grain boundaries and resulted in inhibition of grain growth.

• Journal of the Korean Ceramic Society
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• v.41 no.6
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• pp.456-463
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• 2004

To enhance the performance of anode-supported SOFC, single cell fabrication procedure was changed for better and resulting power generating characteristics of single cell were investigated. Liquid condensation process was employed for the granulation of NiO/YSZ powder mixture and the produced powder granules were compacted into anode green substrate by uni-axial pressing. YSZ electrolyte was printed on green substrate via screen-printing method and co-fired at 1400$^{\circ}C$ for 3 h. LSM/YSZ composite cathode of which the composition and heat treatment condition was adjusted to minimize the polarization#resistance with AC-impedance spectroscopy, was screen printed. The final single cell size from this multi-step procedure was 5${\times}$5 $\textrm{cm}^2$ and 10${\times}$10 $\textrm{cm}^2$. The maximum power densities of 5${\times}$5 and 10${\times}$10 single cells were about 0.45 W/$\textrm{cm}^2$ and 0.22 W/$\textrm{cm}^2$ at 800$^{\circ}C$, which are two times superior than those from single cells fabricated by the conventional process in previous our work.

• Journal of the Korean Ceramic Society
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• v.42 no.8 s.279
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• pp.561-566
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• 2005

For the homogeneous dispersion of $ZrO_2$ particles in $Al_2O_3/ZrO_2$ceramics, Zr-precusors were mixed with oxide $Al_2O_3$powders by chemical routes such as partial precipitation or partial polymerization of Zr-nitrate solutions. In case of the mechanical mixing of ultrafine $Al_2O_3$ and $ZrO_2$ oxide powders, relatively homogeneous dispersion was difficult to achieve so that the particle size and distributions of $ZrO_2$ were relatively inhomogeneous after sintering at high temperature. But when the Zr-Y-hydroxide were co-precipitated to ultrafine $Al_2O_3$ oxide powders followed by calcinations, homogeneous dispersion of nano-sized $ZrO_2$ particles in $Al_2O_3/ZrO_2$ composite ceramics were obtained. But because of the coalescence of dispersed $ZrO_2$ particles, dispersed $ZrO_2$ was grown up to more than 0.2${mu}m$ (200 nm) when sintered at the temperature of higher than $1500^{\circ}C$ But when the sintering temperature was kept to lower than $1400^{\circ}C$ by using nano-sized $\alpha-alumina$, the particle size of dispersed $ZrO_2$ could be sustained below 0.1 ${\mu}m$. But the coalescence of dispersed $ZrO_2$ between $Al_2O_3$ particles could not be avoided so that the mechanical properties were not enhanced contrary to the expectations. So Zr-polyester precursors were precipitated and coated to the surface of ultrafine $\alpha-alumina$ powders by the polymerization of Ethylene Glycol with Citric Acid and Zirconium Nitrate. By this dispersion much more uniform dispersion of $ZrO_2$ was achieved at $1450\~1600^{\circ}C$ of sintering temperature ranges. And due to especially discrete dispersion of $ZrO_2$ between $Al_2O_3$ particles, their mechanical strength was more enhanced than mechanical mixing or hydroxide precipitation methods.

• Journal of the Korean Ceramic Society
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• v.36 no.2
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• pp.193-202
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• 1999

Al powder, AlN powder, SiC whisker and sintering aids were wet-mixed, and then the specimens prepared with mixed powder were reacted by nitridation at 600∼1400$^{\circ}C$ for 5 hrs. It was cleat that the higher nitridation and the more SiC whisker content were, the better bending strength was. The specimen of Al50/AlN50 reacted at 1400$^{\circ}C$ for 5hrs had the nitridation percent of 97%, the shrinkage under 2%, and the relative density of 78%. And the maximum bending strength of reaction-bonded specimen was 250 MPa. The specimens completely nitrided were post-sintered at 1700, 1800 and 1900$^{\circ}C$ for 2hrs. The post-sintered body had the shrinkage under 6% and the relative density of 86%. Because of the formation of solid solution between AlN and SiC whisker over 1800$^{\circ}C$, the promotion of mechanical properties according to SiC whisker addition was not observed. The post-sintered body had the maximum bending strength of 195 MPa.

• Journal of the Korean Ceramic Society
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• v.40 no.8
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• pp.777-783
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• 2003

The mechanical properties of B$_4$C/Al composites normally depend on the species and quantity of reaction products between B$_4$C and Al and then the control of reaction products is necessary to make desirable composites for lightweight advanced or armor materials. TiB$_2$ is chemically inert with aluminum and has a lower contact angle (85$^{\circ}$ at 100$0^{\circ}C$) to liquid aluminum than B$_4$C. Thus, TiB$_2$ coating on B$_4$C may lower infiltration temperature of aluminum when the B$_4$C/Al composites is fabricated by infiltration process. In this study, the effects of TiB$_2$ on the microstructure and mechanical properties of the B$_4$C/Al composites have been investigated. TiB$_2$ coated B$_4$C powder was prepared using the sol-gel technique. It was found that the B$_4$C surface is homogeneously covered with TiB$_2$ having a particles size of 20-50 nm. While the B$_4$C/Al composites prepared by infiltration after TiB$_2$ coating had 17 wt% of unreacted Al, on the other hand, the B$_4$C/Al composites without coating included 14 wt% of Al. As a result, the composites infiltrated after the coating showed higher fracture toughness and lower hardness. This strongly suggests that TiB$_2$ not only lowers the infiltration temperature, but also inhibits the reaction between B$_4$C and Al.