• Journal of the Korean institute of surface engineering
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• v.41 no.6
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• pp.292-300
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• 2008

Dental implant system is composed of abutment, abutment screw and implant fixture connected with screw. The problems of loosening/tightening and stability of abutment screw depend on surface characteristics, like a surface roughness, coating materials and friction resistance and so on. For this reason, surface treatment of abutment screw has been remained research problem in prosthodontics. The purpose of this study was to investigate the stability of TiN and WC coated dental abutment screw, abutment screw was used, respectively, for experiment. For improving the surface characteristics, TiN and WC film coating was carried out on the abutment screw using EB-PVD and sputtering, respectively. In order to observe the coating surface of abutment screw, surfaces of specimens were characterized, using field emission scanning electron microscope(FE-SEM) and energy dispersive x-ray spectroscopy(EDS). The stability of TiN and WC coated abutment screw was evaluated by potentiodynamic, and cyclic potentiodynamic polarization method in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. The corrosion potential of TiN coated specimen was higher than those of WC coated and non-coated abutment screw. Whereas, corrosion current density of TiN coated screws was lower than those of WC coated and non-coated abutment screw. The stability of screw decreased as following order; TiN coating, WC coating and non-coated screw. The pitting potentials of TiN and WC coated specimens were higher than that of non-coated abutment screw, but repassivation potential of WC coated specimen was lower than those of TiN coated and non-coated abutment screws due to breakdown of coated film. The degree of local ion dissolution on the surface increased in the order of TiN coated, non-coated and WC coated screws.

• Korean Journal of Materials Research
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• v.13 no.1
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• pp.36-42
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• 2003

The oxidation behaviors of Y-Cr bilayer deposited on ferritic steel by magnetron-sputtering for application of the Fe-Cr alloys as interconnectors of planar-type solid oxide fuel cells (SOFCs) were studied. After oxidation at $800^{\circ}C$ for 40 hours, the major phase of $Y_2$$O_3$and the minor phase of $YCrO_3$, $Mn_{1.5}$ $Cr_{1.5}$ $O_4$and Cr$_2$SiO$_4$were formed in the Y/Cr bilayered samples, while the major phase of Cr$_2$O$_3$and the minor phase of $Y_2$$O_3$were formed as the major phase in the Cr/Y bilayered samples. The Log(ASR/T) that expresses electric resistance of the Y/Cr coated specimen with nonconducting $_Y2$$O_3$oxide showed high value of -2.80 Ω$\textrm{cm}^2$$K^{-1}$ / and that of the Cr/Y coated specimen with conducting $Cr_2$$O_3$oxide appeared to be -4.11 Ω$\textrm{cm}^2$$^{K}$ . The electric resistance of the Y/Cr coated specimen was largely increased due to the formation of high resistance oxide scales. However, the Cr/Y coated specimen did not show any increase in the electric resistance and had the long-term stability of oxidation because there was no formation of the secondary phases with low conductivity.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.7
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• pp.1213-1217
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• 2008

Poling is an important process in fabricating PZT ceramic devices such as filters and resonators and activates piezoelectricity to sintered PZT ceramics. Tolerance of the operating frequency of these devices is tightly required in applications. And a factor to attribute the tolerance is the temperature dependence of the resonance frequency of PZT ceramics. In this paper the relationship of poling strength and temperature dependence of resonance frequency of PZT specimens was studied. The $Pb(Zr_{0.53}Ti_{0.47})O_3$ ceramics were fabricated and the poling strengths were chosen to be 0.5, 1.5, 2.5 and 3.5 [kV/mm]. The dielectric constant of the specimen poled in poling strength 0.5 [kV/mm] was less than that of unpoled specimen and the specimen poled in higher electric field had the higher dielectric constant. (002) peak in X-ray diffraction patterns of the specimens increased as poling strength increased. And the change of resonance frequency of the specimens according to the variation of temperature was measured. Resonance frequency of all specimens increased as the temperature increased. The specimen poled in higher electric field had the smaller positive temperature coefficient of resonance frequency. The effect that temperature coefficient of resonance frequency becomes smaller is obtained when Zr mole in PZT composition equation increase. Controlling the poling strength is believed to be a method to adjust the temperature stability of resonance frequency of the PZT ceramic devices.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.543-546
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• 2000

Ferroeleclric 0.05PZN-xPZT(90/10)-(0.95-x)PZT(10/90) (x=0.65, 0.85) specimens were fabricated by the mixed-oxide method and cold-pressing method using sol-gel derived PZT(90/10) and PZT(10/90) powders. All specimens show a uniform ferroelectric grain without the presence of the pyrocholre phase. Average grain size increased with an increase in sintering temperature, the value for the x=0.65 specimen sintered at 125$0^{\circ}C$ was 14.4$\mu$m. The dielectric constant and dielectric loss of the x=0.65 specimen sintered at 125$0^{\circ}C$ were 1247, 2.06%, respectively. All specimens showed fairly good temperature and frequency stability of dielectric constant with the range from -2$0^{\circ}C$ to 6$0^{\circ}C$ and 100Hz to 10MHz. The coercive field and the remanent polarization of x = 0.65 specimen sintered at 125$0^{\circ}C$ were 8.5 kV/cm and 13 $\mu$C/cm$^2$, respectively. The pyroelectric coefficient of the x=0.65 specimen sintered at 125$0^{\circ}C$ was 5.64$\times$10$^{-8}$ C/cm$^2$K, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.05a
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• pp.17-21
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• 1995

Tw types of Pb(Mn$\sub$1/3/Nb$\sub$2/3/)O$_3$+PZT Ceramics had been fabricated by hot-pressing method. One had cause grain and the other had fine grain doe to Cr$_2$O$_3$ addition. These specimen were poled by applying the DC electric field in various steps. The effects of thermal aging on their piezoelectric characteristics and temperature stability of the frequency were investigated.

• Journal of the Korean Ceramic Society
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• v.27 no.6
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• pp.721-728
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• 1990

Hydroxyapatite powders were synthesized with Ca/P=1.67 and pH=11 by precipitaton method, after characterization of these specimen, behavior in Ringer's solution and biocompatibility of hydroxyapatite, such as cytotoxity test and implantation test, were investigated. The hydroxyapatite ceramics had structural stability in Ringer's solution, and hydroxyapatite ceramics did not prevent cell growing and exhibit any cytotoxic effects. In implantation of hydroxyapatite ceramics into muscle under abdome of guinea pig, hydroxyapatite ceramics did not show any symptom of rejection for cellular texture.

• Journal of the Korean Ceramic Society
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• v.26 no.5
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• pp.698-704
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• 1989

Basic investigation for the flexural strength and water stability of hardened cement pastes using ordinary portland cement with water-soluble polyer (hydroxypropyl methyl cellulose ; HPMC) was carried out with 0.2 of water cement ratio. For molding of the specimen, the paste was mixed by twin roll mill. According to increase in the content of HPMC, the setting time of cement paste was delayed and the flexural strength was increased. The maximum flexural strength of hardened cement paste with 5.0wt% of HPMC was about 330 kg/$\textrm{cm}^2$. The expansion of the hardened cement paste immersed in water was increased with the content of water soluble polymer(HPMC). Consequently, the strength and the water stability of the hardened cement pastes were remarkably reduced by the expansion of them.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1991.10a
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• pp.20-23
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• 1991

In this study, 0.05Pb(Mn$\_$1/3/Nb$\_$2/3/)O$_3$+ 0.95Pb(Zr/Ti)O$_3$+x[wt%]Cr$_2$O$_3$piezoelectric ceramics were fabricated by Hot-press method, and its structural, dielectrical, piezoelectrical properties, temperature stability and aging characteristics were investigated. Among the MPB and tetragonal compositions, the specimens with 0.2, 0.3 and 0.4 [wt%] Cr$_2$O$_3$ additive amount had the poisson ratio more than 1/3. At tetragonal phase, the aging was small, and the temperature stability was improved by Cr addition. The specimen most suitable to the HF device substrate was the one with the composition of 47/53 (Zr/Ti) an 0.4 [wt%] Cr$_2$O$_3$addition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.5
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• pp.1679-1688
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• 1996

Laser flash technique was applied to measure thermal properties of FGM made by a CVD method. System stability and reproducibility of this measuring system were proved and calibrated with glassy carbon used as reference material. Specimens was prepared by cutting FGM diagonally. Measurements were performed for a wide range of temperatures up to 1500K. Relative heat capacity of the FGM specimen was scattered with in $\pm$13% at room temperature and at high temperature above 1200K, and $\pm$3% at medium temperature range. On the other hand, thermal diffusivity data showed excellent reproducibility and stability through the whole temperature range. In conclusion, the multi-target radiometer can be applied to measure the thermal properties of non homogeneous materials like FGM.

• Corrosion Science and Technology
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• v.4 no.5
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• pp.207-210
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• 2005

Coating performance of various coating systems including chlorinated rubber and epoxy/urethane used most for steel structures of highway in Korea, was evaluated by exposing test specimen to complex deterioration factors such as ultraviolet ray, moisture, freeze-thaw cycle and salt. Deteriorated specimens were evaluated by chalking and rust grades according to ASTM, and measurement of color differences and adhesion. In overall coating performances such as corrosion resistance, photochemical stability, and adhesion, ceramic/ urethane, moisture-curable urethane/ urethane, etc. were superior. As for other coating materials tested in this study, superior materials against certain deterioration factors may be inferior against other factors. Accordingly, in order to select suitable maintenance coating materials for the use, it is thought that investigation of suitability through experiment should precede selection of materials, especially for unusual coatings or paints.