• Journal of the Korean Ceramic Society
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• v.35 no.8
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• pp.791-794
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• 1998

• Journal of the Korean Ceramic Society
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• v.24 no.3
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• pp.263-269
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• 1987

It is investigated that the determination of the correlation between the change of microstructure and electrical properties. Yttria is added to the compositiojn of rhombohedral region in Pb(Mg1/3Nb2./3)O3-PbTiO3-PbZrO3 ternary system. Average grian size, lattice parameters and distribution of yttrium are characterized by XRD, SEM and EDS. Electrical properties are determined by measurement of Curie temperature, piezoelectric properties and hysteresis loops. The results are as follows; 1. Both lattice parameters, a and ${\alpha}$, are changed by addition of yttria to the composition of rhomboheadral region in Pb(Mg1/3Nb2./3)O3-PbTiO3-PbZrO3 ternary system and Curie temperature is proportional to the values at (90-${\alpha}$).

• Corrosion Science and Technology
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• v.8 no.4
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• pp.139-142
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• 2009

Recently, quaternary titanium alloys of the system Ti-Nb-Ta-Zr received considerable research interest as potential implant materials because of their excellent mechanical properties and biocompatibility. However, only few reported works were available on the corrosion behavior of such alloys. Hence, in the present work, electrochemical corrosion of Ti-35Nb-5Ta-7Zr alloy, which has been fabricated by arc melting and heat treatment, was studied in 0.9 wt% NaCl at $37\pm1^{\circ}C$, along with biomedical grade Ti-6Al-4V and CP-Ti. The phase and microstructure of the alloys were investigated employing XRD and SEM. The results of electrochemical studies indicated that the corrosion resistance of the quaternary alloy was inferior to that of Ti-6Al-4V and CP Ti.

• Journal of the Korean Ceramic Society
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• v.25 no.6
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• pp.694-698
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• 1988

Pb(Zr, Ti)O3-Pb(Co, Nb)O3 systems were investigated by x-ray diffraction method. System contains rhombohedral, tetragonal, and pseudocubic structures at room temperature. Crystal symmetry was changed from 4-fold symmetry to 3-fold symmetry by substituting Pb(Co1/3, Nb2/3)O3 ; PCN, to Pb(Zr0.52, Ti0.48)O3 ; PZT. As the substituted PCN concentration was increased, an increase in a-axis direction and a decrease in c-axis in the perovskite structure were occurred simultaneously, so that the crystal symmetry was changed into such way. In the higher sinteringtemperatures, the unit cell distortions occurred rather in the lower substitution range of PCN. The ferroelectric properties were maximized at the region that tetragonal and rhombohedral or pseudocubic structures were coexist.

• Corrosion Science and Technology
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• v.2 no.2
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• pp.68-74
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• 2003

The effects of Niobium on the structure and properties(especially electric properties) of passive film of Zirconium alloys in pH 8.5 buffer solution are examined by the photo-electrochemical analysis. For Zr-xNb alloys (x = 0, 0.45, 1.5, 2.5 wt%), photocurrent began to increase at the incident energy of 3.5 ~ 3.7 eV and exhibited the $1^{st}$ peak at 4.3 eV and the $2^{nd}$ peak at 5.7 eV. From $(i_{ph}hv)^{1/2}$ vs. hv plot, indirect band gap energies $E_g{^1}$= 3.01~3.47 eV, $E_g{^2}$= 4.44~4.91 eV were obtained. With increasing Nb content, the relative photocurrent intensity of $1^{st}$ peak significantly increased. Compared with photocurrent spectrum of thermal oxide of Zr-2.5Nb, It was revealed that $1^{st}$ peak in photocurrent spectrum for the passive film formed on Zr-Nb alloy was generated by two types of electron transitions; the one caused by hydrous $ZrO_2$ and the other created by Nb. Two electron transition sources were overlapped over the same range of incident photon energy. In the photocurrent spectrum for passive film formed on Zr-2.5Nb alloy in which Nb is dissolved into matrix by quenching, the relative photocurrent intensity of $1^{st}$ peak increased, which implies that dissolved Nb act as another electron transition source.

• Journal of the Korean Ceramic Society
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• v.27 no.7
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• pp.934-942
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• 1990

The quarternary system ceramics 0.5[yPb(Zn1/3Nb2/3)O3-(1-y)Pb(Ni1/3Nb2/3)O3]-0.5[xPbTiO3-(1-x)PbZrO3](PZN-PNN-PT-PZ) was fabricated by the columbite precursor method to obtain a stabilized perovskite structure and by conventional method to evaluate the efficiency of the former methd. Dielectric and piezoelectric properties were investigated and the stability of the perovskite phase was studied as a function of PZN and PT contents and firing temperature. In the samples prepared by the columbite precursor method, the pyrochlore phase, which is detrimental to both the dielectric and piezoelectric properties, was not observed in the absence of PZN, and electric properties were improved even when fabricated at low temperature. By adding PZN, some pyrochlore phase appeared and the morphotropic phase boundary of the samples shifted to more Zr-rich composition. The temperature dependence of piezoelectric constant decreased with the addition of PZN, due to the rising of the Curie point.

• Korean Journal of Materials Research
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• v.12 no.3
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• pp.182-189
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• 2002

The Zr-0.2Sn-0.8Nb-X(X = 0~200ppm Si, 0~0.4wt.% Mo and Mn respectively) ingots for test specimens were manufactured by a vacuum arc re-melting method to find out the effect of Si, Mo, and Mn on the corrosion characteristics of the Zr-0.2Sn-0.8Nb alloy. After being heat-treated and rolled repeatedly out to be flat materials, they were finally heat-treated at 51$0^{\circ}C$ for three hours and used as the specimens for corrosion tests. The corrosion behavior of the specimens was studied in both 40$0^{\circ}C$ steam for 200 days and in aqueous 70 ppm LiOH solution at 36$0^{\circ}C$ for 90 days. From the study it was found that Si from 80 to 200 ppm contributed to increasing the corrosion resistance of Zr-0.2Sn-0.8Nb alloy in both steam and LiOH solution. This study also showed that Mn from 0.1 to 0.4% caused to go up the corrosion resistance, whereas Mo played a apart in improving the corrosion resistance only between 0.05 and 0.2 wt.%.

• Journal of the Korean Ceramic Society
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• v.34 no.9
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• pp.915-920
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• 1997

Tetragonal ZrO2 polycrystal (TZP), consisted of 90.24 mol% ZrO2-5.31 mol% Y2O3-4.45 mol% Nb2O5, were prepared using hot-press and mechanical properties and high-temperature degradation were investigated. The specimen, hot-pressed for 1 h at 140$0^{\circ}C$ in Ar atmosphere, exhibited flexural strength of 1010 MPa and fracture toughness of 7.5 MPam1/2 and experienced no low-temperature degradation below 40$0^{\circ}C$. However, as aged for 100h at temperatures higher than 40$0^{\circ}C$, TZP was suffered by high-temperature degradation due to an extensive cavitation caused by the oxidation of carbon. XPS observation revealed that the carbon incorporated in TZPs during hot-pressing exists as either an ether-type CO or a carbonyl-type C=O. Despite of the high-temperature degradation of t-ZrO2 co-doped with Y2O3 and Nb2O5, its flexural strength and fracture toughness were superior to those of the commercial 3 mol% Y2O3-TZP hot-pressed under the identical condition as determined before and after the aging treatments.

• Korean Journal of Materials Research
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• v.11 no.6
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• pp.483-491
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• 2001

The recovery and recrystallization behavior of cold-rolled Zr-based alloys during isothermal annealing at temperatures from $575^{\circ}C$ to $650^{\circ}C$ was studied by thermoelectric power and Vickers microhardness measurement. The recovery and recrystallization resulted in the increase of TEP doe to the extinction of lattice defect, vacancy, dislocation and stacking fault during isothermal annealing after cold- rolling. The completion of recrystallization could be determined much clearly by TEP behavior than by microhardness change in Zr-based alloys. Especially, the recovery and recrystallization were classified separately by TEP behavior in Zr-0.4Nb-xSn alloys. From the analysis of TEP behavior and microhardness, the addition of Sn caused to form the interaction between stain field and dislocation, which resulted in the delay of recovery in Zr-based alloys. The precipitation due the addition of Nb suppressed the grain growth after recrystallization effectively in Zr-based alloys.

• Proceedings of the Korean Magnestics Society Conference
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• 1991.05a
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• pp.79-80
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• 1991