• Journal of the Korean Ceramic Society
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• v.23 no.3
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• pp.87-93
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• 1986

Yttria-bismuth-stabilized zirconia was investigated with respect to the amount of $Bi_2O_3$ addition in the ran-ge of 0.5~5mol% to the base composition of $(ZrO_2)_{0.92}(Y_2O_3)_{0.08}.Bismuth was introduced into the ma-terial with $Bi_2O_3-SiO_2$ glasses in order to reduce the evaporation of components. The sinterbility evaporation of components phase formation and microstructure were evaluated depending on the amount of $Bi_2O_3-SiO_2$ glass addition. Two probe A. C conductivity measurement was subjected to all the specimens and the result was discussed on the possible substitution of $Bi^{3+}$ for $Zr^{4+}$ and interistial $Si^{4+}$ in the fluorite structure of zirconia crystal there-upon the possible change in the capability of oxygen transference within the material. It was found that the addition of $Bi_2O_3$ could improve the sinterbility of material very much while not so much.oxygen sensing material suitable for relative low temperature firing.

• Journal of the Korean Ceramic Society
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• v.44 no.4 s.299
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• pp.198-201
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• 2007

Multi-walled carbon nanotube (M-CNT)/Nafion nanocomposites were prepared by solution casting to elucidate the effect of M-CNT addition, from 0 to 7 wt%, on the viscoelastic behavior of the composites. The M-CNT bundles induced by the Nafion polymer were determined to be uniformly distributed for the 1 wt% M-CNT/Nafion nanocomposites. The 1 wt% M-CNT/Nafion composite exhibited the highest blocking stress of 2.3 kPa due to its high elastic modulus of 0.485 GPa. From a dynamic mechanical analysis, the 1 wt% M-CNT had the highest storage and loss moduli compared with the other samples in all frequency and temperature ranges. From the storage modulus data, the M-CNT loaded composites had similar $T_g$ values near $120^{\circ}C$. The glass transition temperatures of the M-CNT loaded composites were $120^{\circ}C$ (1 wt%), $117^{\circ}C$ (3 wt%), $117^{\circ}C$ (5 wt%), and $135^{\circ}C$ (7 wt%), suggesting that the effect of the M-CNTs on the Nafion film begins at 1 wt%. Thus, it has been concluded that the 1 wt% M-CNT disported composite is attractive for actuator applications.

• Journal of the Korean Ceramic Society
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• v.45 no.3
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• pp.179-184
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• 2008

(40-x)BaO${\cdot}xFe_2O_3{\cdot}60P_2O_5$ glasses with $5{\leq}x{\leq}35mol%$ were investigated by ESR spectroscopy. Two resonances observed near g=2.0 and g=4.3. The line at g=4.3 disappeared with the increase of the $Fe_2O_3$ content. The resonance at $g{\approx}2.0$ displayed characteristic signal consisting of superposed extremely broad and narrow components. The broader one indicates the presence of the association of two or more $Fe^{3+}$ ions, antiferromagnetically and the narrow one is related to the microclusters involving iron ions. Temperature dependence of the ESR integrated intensity revealed short-range antiferromagnetic character for $x{\geq}15mol%$.

• Journal of the Korean Ceramic Society
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• v.48 no.6
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• pp.516-519
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• 2011

Indium tin oxide (ITO) coatings were made using an ITO slurry and an ITO sol. This was achieved by dispersing nanosized ITO powder in a mixed solvent without any dispersant and developing an adhesive ITO sol from indium acetate and tin tetrachloride in a mixture of DMF and n-butanol. Coating was carried out in one step by spin coating an ITO slurry, which was then followed by an ITO sol over it. Here, the sol penetrates into the nano ITO particle layers to make them adhere to each other as well as to a glass substrate. This is then followed by sintering at 500$^{\circ}C$ for 1 h to produce a uniform film consisting of ITO particles of about 50 nm and 10 nm. ITO films were obtained with sheet resistances from 450 to 1500 ohm/${\Box}$ by varying spin speed and concentration. Transmittance is higher than 90% at 550 nm.

• Journal of Technologic Dentistry
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• v.29 no.2
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• pp.119-128
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• 2007

Although there are many different ways that restorations can be made, it can be said that the biocompatibility of abutment and crown is very important in this experiment. When placed in the actual oral cavity, the differences were obvious. Compared to In-ceram Aluminium, the structure that is obtained after firing reveals a particularly homogeneous distribution of the crystal and glass phase. The In-ceram aluminium system had many problems, such as having weak tensile strength, and having low bonding strength due to the shrinking that occurs after firing. Because of the opaque finish of the metal frame, the two may look similar from the outside, but it is evident that there are differences between using a metal frame and In-ceram. VITA VM9 has been designed as a special ceramic featuring a fine structure or stabilized Zro2 substructures, and so the VITA VM9 excels in its light refraction and reflection behavior, which is similar to natural teeth. It also has outstanding chemical balance, which presents advantages such as considerably reduced accumulation of plaque on the ceramic surface.? This ultimately results in easier care and cleaning for the patient.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.362-367
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• 2008

In the present work, we address electric fatigue behavior in bending piezoelectric actuators using an acoustic emission technique. Electric cyclic fatigue tests have been performed up to ten million cycles on the fabricated specimens. To confirm the fatigue damage onset and its pathway, the source location and distributions of the AE behavior in terms of count rate are analyzed over the fatigue range. It is concluded that electric cyclic loading leads to fatigue damages such as transgranular damages and intergranular cracking in the surface of the PZT ceramic layer, and intergranular cracking even develops into the PZT inner layer, thereby degrading the displacement performance. The electric-induced fatigue behavior seems to show not a continuous process but a step-by-step process because of the brittleness of PZT ceramic. Nevertheless, this fatigue damage and cracking do not cause the final failure of the bending piezoelectric actuator loaded up to 107 cycles. Investigations of the AE behavior and the linear AE source location reveal that the onset time of the fatigue damage varies considerably depending on the existence of a glass-epoxy protecting layer.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.10
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• pp.856-865
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• 2008

Damage mechanisms in bending piezoelectric actuators under electric fatigue loading are addressed in this work with the aid of an acoustic emission (AE) technique. Electric cyclic fatigue tests have been performed up to $10^7$ cycles on the fabricated bending piezoelectric actuators. An applied electric loading range is from -6 kV/cm to +6 kV/cm, which is below the coercive field strength of the PZT ceramic. To confirm the fatigue damage onset and its pathway, the source location and distributions of the AE behavior in terms of count rate and amplitude are analyzed over the fatigue range. It is concluded that electric cyclic loading leads to fatigue damages such as transgranular damages and intergranular cracking in the surface of the PZT ceramic layer, and intergranular cracking even develops into the PZ inner layer, thereby degrading the displacement performance. However, this fatigue damage and cracking do not cause the final failure of the bending piezoelectric actuator loaded up to $10^7$ cycles. Investigations of the AE behavior and the linear AE source location reveal that the onset time of the fatigue damage varies considerably depending on the existence of a glass-epoxy protecting layer.

• Journal of the Korean Ceramic Society
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• v.26 no.4
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• pp.479-486
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• 1989

According to the phase diagram, 6Bi2O3.GeO2 composition melts congruently at 93$0^{\circ}C$ and forms a stable ${\gamma}$-6Bi2O3.GeO2 crystal phase below the melting point. But when the melt of this composition was cooled at a rate 1-15$0^{\circ}C$/min without tapping by a glass rod or impurity addition, a metastable $\delta$-6Bi2O3.GeO2 crystal phase was formed. It is due to that as the nucleation energy barrier of $\delta$-6Bi2O3.GeO2 crystals, which have more open and defective structure, is lower than that of ${\gamma}$-6Bi2O3.GeO2 crystals. When impurities or ${\gamma}$-6Bi2O3.GeO2 crystals existed in the melt, stable ${\gamma}$-6Bi2O3.GeO2 crystal phase was formed at various cooling rate. It is because of that the impurities or the ${\gamma}$-6Bi2O3.GeO2 crystals role as a seed crystal and as a result the nucleation energy barrier of ${\gamma}$-6Bi2O3.GeO2 crystals is lowered.

• Journal of the Korean Ceramic Society
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• v.32 no.7
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• pp.783-792
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• 1995

Sol-Gel derived ferroelectric PZT thin films were fabricated on ITO/Glass and Si/SiO2 substrates. In order to investigate the effect of catalysts on the densification and crystallization of PZT thin films, a nitric acid or ammonium hydroxide was added to the PZT stock solution at the state of partial hydrolysis reaction. The measured pH for a stable PZT sol was 5.2~9.3. In case of an acid-catalyzed PZT sol, a highly condensed particulate PZT sol was formed by accelerating the hydrolysis reaction. But weakly branched polymeric PZT sol was formed with a base-catalyzed condition. The difference in densification behavior was not found in the pH range of added catalyst, but the refractive index of PZT thin film was increased rapidly as the annealing temperature increased. The PZT thin film annealed at 54$0^{\circ}C$ for 10 min was fully densified and its refractive index was above 2.4. When the annealing temperature increased, the transition from the pyrochlore phase to perovskite appeared at 54$0^{\circ}C$. The base-catalyzed PZT thin film suppressed to form the pyrochlore phase and proceeded effectively to convert the perovskite phase. This was due to the formation of polymeric molecular structure by controlling the hydrolysis and condensation reaction through the additiion of the ammonium hydroxide.

• Journal of the Korean Ceramic Society
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• v.32 no.7
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• pp.799-808
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• 1995

Transparent conductive films of aluminium doped zinc oxide (AZO) have been prepared by using the DC magnetron sputtering with the ZnO : Al (Al2O3 2 wt%) oxide target oriented to c-axis. Electrical and optical properties depended upon the O2/Ar gas ratio. The optical transmittance and sheet resistance of the AZO coated glass was 60~65% and 75Ω/$\square$, respectively at the O2/Ar gas ratio of 0. With the increase of the oxygen partial pressure to 2.0$\times$10-2, they were increased to the values of 81% and 1kΩ/$\square$, respectively. The films with the resistivities of 1.2~1.4$\times$10-3 Ω.cm, mobilities of 11~13 $\textrm{cm}^2$/V.sec and carrier concentrations of 3.5$\times$1020~4.0$\times$1020/㎤ were produced at the optimum O2/Ar gas ratio, which was 0.5$\times$10-2~1.0$\times$10-2. According to XRD analysis, the films have only one peak corresponding to the (002) plane, which indicates that there is a strong preferred orientation of the films. The grain size of ZnO films were calculated to 200~320 $\AA$, which was increased with the O2/Ar gas ratio and Ar gas flowrate.