• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제50권10호
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• pp.500-503
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• 2001

The mechanical and electrical properties of the hot-pressed and pressureless annealed SiC+39vol.%$TiB_2$electroconductive ceramic composites were investigated as a function of the liquid additives of $Al_2O_3+Y_2O_3$. The result of phase analysis for the SiC+39vol.%$TiB_2$composites by XRD revealed $\alpha$-SiC(6H), $TiB_2$, and $YAG(Al_5Y_3O_{12})4 crystal phase. The relative density of SiC+39vol.%$TiB_2$ composites was increased with increased $Al_2O_3+Y_2O_3$. contents. The fracture toughness showed the highest value of $7.8 MPa.m^{1/2}$ for composites added with 12 wt % $Al_2O_3+Y_2O_3$. additives at room temperature. The electrical resistivity and the resistance temperature coefficient showed the lowest value of $7.3\times10_{-4}\Omega.cm\; and\; 3.8\times10_{-3}/^{\circ}C$ for composite added with 12 wt% $Al_2O_3+Y_2O_3$. additives at room temperature. The electrical resistivity of the SiC+39vol.%$TiB_2$composites was all positive temperature coefficient resistance(PTCR) in the temperature ranges from $25^{\circ}C\; to\; 700^{\circ}C$.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2003년도 추계학술발표회초록집
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• pp.134-135
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• 2003

The dental implant materials required good mechanical properties, such as fatigue strength, combined with a high resistance to corrosion. For increasing fatigue resistance and delaying onset of stress corrosion cracking, shot peening has been used for > 50 years to extend service life of metal components. However, there is no information on the electrochemical behavior of shot peened and hydroxyapatite(HA) coated Ti-6Al-4V alloys. To increase fatigue strength, good corrosion resistance, and biocompatibility, the electrochemical characteristics of Ti/TiN/HA coated and shot peened Ti-6Al-4V alloys by electron beam physical vapor deposition(EB-PVD) have been researched by various electrochemical method in 0.9%NaCl. Ti-6Al-4V alloys were prepared under the condition of hydrogen and vacuum arc furnace. The produced materials were quenched at 1000$^{\circ}C$ under high purity dried Ar atmosphere and were hold at 500$^{\circ}C$ for 2 hrs to achieve the fatigue strength(1140㎫) of materials. Ti-6Al-4V alloys were prepared under the condition of hydrogen and vacuum arc furnace. Shot peening(SP) and sand blasting treatment was carried out for 1, 5, and 10min. On the surface of Ti-6Al-4V alloys using the steel balls of 0.5mm and alumina sand of 40$\mu\textrm{m}$ size. Ti/TiN/HA multilayer coatings were carried out by using electron-beam deposition method(EB-PVD) as shown Fig. 1. Bulk Ti, powder TiN and hydroxyapatite were used as the source of the deposition materials. Electrons were accelerated by high voltage of 4.2kV with 80 - 120mA on the deposition materials at 350$^{\circ}C$ in 2.0 X 10-6 torr vacuum. Ti/TiN/HA multilayer coated surfaces and layers were investigated by SEM and XRD. A saturated calomel electrode as a reference electrode, and high density carbon electrode as a counter electrode, were set according to ASTM GS-87. The potentials were controlled at a scan rate of 100 mV/min. by a potentiostat (EG&G Co.273A) connected to a computer system. Electrochemical tests were used to investigate the electrochemical characteristics of Ti/TiN/HA coated and shot peened materials in 0.9% NaCl solution at 36.5$^{\circ}C$. After each electrochemical measurement, the corrosion surface of each sample was investigated by SEM.

• 한국재료학회지
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• 제10권11호
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• pp.760-769
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• 2000

Nb, Ti 및 V를 0.15%씩 각각 첨가한 3종의 HSLA 주강을 오스테나이징 온도 및 템퍼링 시간을 변화시킨후 기계적 특성등을 관찰한 결과 다음과 같은 결론을 얻었다. 오스테나이징 온도를 $1150^{\circ}C$로 하여 2시간 가열시킨 경우 첨가원소의 종류에 관계없이 경도가 가장 증가하였으며 $1100^{\circ}C$이하의 온도에서는 서서히 경도가 감소하는 경향을 나타내었다. 오스테나이징 온도를 $1150^{\circ}C$로 하여 2시간 가열시킨 경우 Nb, Ti, V 첨가원소중에서 경도가 가장 높게 나타난 것은 Ti 첨가 HSLA 주강이며 오스테나이트 온도변화에 따라 경도차가 나는 주된 이유는 베나이트 조직의 상대적인 양과 고용강화에 주로 기인하였다. $1150^{\circ}C$에서 오스테나이징한 Ti 첨가 HSLA 주강의 경우를 제외하고는 대부분의 경우에 있어 C-Mn 주강을 대체 하기위한 최소 충격값이 2kg-m/$\textrm{cm}^2$이상의 충격치를 나타내었다. $1150^{\circ}C$에서 2시간 오스테나이징한 경우 첨가원소의 종류에 관계없이 10분정도 템퍼링에서 경도가 증가하여 V 첨가 HSLA 주강을 제외하고는 그이후는 템퍼링 시간이 증가함에 따라 일정하게 유지되는 경향을 나타내었다.

• 한국세라믹학회지
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• 제22권1호
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• pp.19-24
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• 1985

The synthetic method was studied on the $SrTiO_3$ powder of pure and homogeneous ultra fine particle of $SrTiO_3$. Pure and ultra fine particle was synthesized from $Sr(OH)_2$.$8H_2O$ and Ti(OH) at 3$0^{\circ}C$~9$0^{\circ}C$ in the $N_2$ gas atmosphere.

• 한국세라믹학회지
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• 제46권3호
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• pp.330-335
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• 2009

We investigated the effects of the re-oxidation temperature and time on the positive temperature coefficient (PTC) of resistivity characteristics of Sm-doped $BaTiO_3$ sintered at $1200{\sim}1260^{\circ}C$ for 2 h in a reducing atmosphere (3% $H_2/N_2$), followed by re-oxidization processes in air, in which re-oxidization temperature and time were $600{\sim}1000^{\circ}C$ and $1{\sim}10$h, respectively. The result reveals that Smdoped (Ba,Ca)$TiO_3$ ceramics fired in a reducing atmosphere exhibit low PTC characteristics, whereas the sample re-oxidized at $800^{\circ}C$ for 1 h in air exhibit pronounced PTC characteristics. The room-temperature resistivity and jumping characteristics of resistivity (${\rho}_{max}/{\rho}25^{\circ}C$) decrease with Sm contents. The PTC characteristics with reoxidization time at $800^{\circ}C$ have improved about $2{\sim}3$ orders of magnitude whereas differed according to the sintering temperature. The 0.7 at% Sm-doped (Ba,Ca)$TiO_3$ samples reveal the best PTC characteristics in the present range of formula and processes.

• 열처리공학회지
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• 제20권1호
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• pp.17-21
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• 2007

In this study, brazing characteristics of the dissimilar Ti and Cu metals using a Zr-base amorphous filler ($Zr_{41.2}Ti_{13.8}Cu_{12.5}Ni_{10.0}Be_{22.5}$ in at.%) have been investigated for various bonding temperatures. In the sample brazed at $790^{\circ}C$ for 10 min., the Ti-rich phases in the joint were observed, while the Cu-rich phases were obtained in the sample brazed at $825^{\circ}C$ for 10 min.. Such a different microstructure and composition in the joints could be explained by the degree of the dissolution reaction. At $790^{\circ}C$, the reaction between the Zr-rich liquid phase and the Ti base metal was actively occurred to form Ti-rich liquid phase in the joint. As the temperature increased to $825^{\circ}C$, however, the reaction between the Ti-rich liquid phase and the Cu base metal was promoted to form the Cu-rich liquid phase in the joint finally. Such a different interface reaction is attributed to the reactivity or solubility between the Zr as a main element in the filler and the Ti and Cu as a base metal element.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제48권6호
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• pp.429-435
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• 1999

The $SrTiO_3$ thin films were prepared on Ag/TiN-coated and p-type bare Si(100) substrates by r.f. magnetron sputtering deposition technique. The electrical properties of the deposited films were investigated, which controlling deposition parameters such as substrate temperature and film thickness. The electrical properties ofthe $SrTiO_3$ films were measured using the capacitance-voltage(C-V) technique. The thickness dependence of the electrical properties of the $SrTiO_3$ films was analyzed of the connection with the films in series. The substrate affected the crystal structure and texture characteristics of the $SrTiO_3$ films. The resistivity of the film, sandwiched between Al and Ag films was measured, as a function of the temperature.

• 한국세라믹학회지
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• 제37권2호
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• pp.122-127
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• 2000

The thermal expansion, thermal stability, mechanical strength and infrared radiative property of Al2TiO5-clay composites, prepared from synthesized Al2TiO5 and clay, were investigated to develop a material for far infrared radiators. The emittance of composites containing 10~50 wt% clay, heated at 1,20$0^{\circ}C$ for 3 h, increased with increasing clay content and emittance was about 0.3 and 0.92 in the ranges of 3,400~2,500 cm-1 and 2,500~400cm-1, respectively. The bulk density and bending strength of the Al2TiO5-clay composites increased with increasing clay content. 50 wt% Al2TiO5-50 wt% clay composite, heat-treated at 1,20$0^{\circ}C$, had an adequate strength for infrared radiators; 80 MPa. The degree of thermal expansion hysteresis decreased with increasing clay content and the mean thermal expansion coefficient increased with increasing clay content. The thermal expansion coefficient of 50 wt% Al2TiO5-50 wt% clay composite heated at 1,20$0^{\circ}C$ was 5.78$\times$10-6/$^{\circ}C$.

• Bulletin of the Korean Chemical Society
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• 제29권8호
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• pp.1495-1498
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• 2008

$TiO_2$ nanopowders were synthesized by new sol-gel combustion hybrid method using acetylene black as a fuel. The dried gels exhibited autocatalytic combustion behaviour. $TiO_2$ nanopowders with an anatase structure and a narrow size distribution were obtained at 400-600 ${^{\circ}C}$. Their crystal structures were examined by powder Xray diffraction (XRD) and their morphology and crystal size were investigated by scanning electron microscopy (SEM). The crystal size of the nanopowders was found to be in the range of 15-20 nm. $TiO_2$ powders synthesized at 500 ${^{\circ}C}$ and 600 ${^{\circ}C}$ were applied to a dye solar cell. An efficiency of 5.2% for the conversion of solar energy to electricity ($J_{sc}$ = 11.79 mA/$cm^2$, $V_{oc}$ = 0.73 V, and FF = 0.58) was obtained for an AM 1.5 irradiation (100 mW/$cm^2$) using the $TiO_2$ nanopowder synthesized by the sol-gel combustion hybrid method at 500 ${^{\circ}C}$.

• 한국주조공학회지
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• 제22권3호
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• pp.114-120
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• 2002

A new titanium based alloy, Ti-10Ta-10Nb, has designed to examine the improved mechanical properties and biocompatibility. A specimen of titanium alloy was melted in a consumable vacuum arc furnace and homogenized at $1050^{\circ}C$ for 24 h. The effect of hot rolling on microstructure was estimated after rolling at $400^{\circ}C$ and $800^{\circ}C$ respectively. Surface of melted alloy by consumable vacuum arc melting was consisted of rough surface and it was changed to sound surface by coating of $ZrO_2$ slurry on copper mold surface. The hardness of Ti-10Ta-10Nb alloy increased with the amount of${\alpha}+{\beta}$ phase. Ti-10Ta-10Nb alloy showed $Widmanst{\"{a}}ten$ structure by hot rolling at $800^{\circ}C$ and in the rolling ${\beta}-region$ was negligible effects on microstructure refining.