• 한국전기전자재료학회논문지
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• 제15권9호
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• pp.788-793
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• 2002

The glass-electroceramics were composed of glass composition(CaO, $SiO_2$, $B_2$ $O_3$) and electroceramic composition(BaO, N $d_2$ $O_3$, B $i_2$ $O_3$ and Ti $O_2$) Their dielectric properties have been investigated as a function of sintering temperature and glass contents. In the ceramics composed of 0.16BaO-0.15(N $d_{0.87}$,B $i_{0.13}$)$_2$ $O_3$-0.69Ti $O_2$with glass ［EG-2782］ 3wt% addition and sintered at 108$0^{\circ}C$ for 2h, we could obtain microwave properties of dielectric constant $\varepsilon$$_{r}$ = 80.1, quality factor Q $\times$f = 810(at 3.5 GHz) and temperature coefficient of resonant frequency $\tau$$_{f}$ = -1.3 ［ppm/$^{\circ}C$］. These experimental results show that dielectric constant and temperature coefficient of resonant frequency could be estimated by empirical equations involving the rule of mixture.e.

• 한국재료학회지
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• 제8권2호
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• pp.173-178
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• 1998

$MgB_4O_7$ 열형광체의 활성체는 란탄계 금속인 Tb, Tm, Dy, La, Ho 및 Nd를 첨가하여 $580^{\circ}C$의 Ar 분위기에서 2시간동안 소결하여 제작하였다. 활성화에너지와 glow 곡선의 주 Peak의 세기는 peak shape법과 초기상승법의 두방법에 의해 결정했으며, 최적활성에너지는 $0.76\pm0.02eV$(Tm 첨가시), $0.94\pm0.03eV$(Tm 첨가시) 및 $0.72\pm0.02eV$(Dy 첨가시)였다. 이들 열형광체들은 저 에너지 X-선에 대해 매우 높은 감도를 나타냈으므로 방사선 센서 소자로 개발하기 위한 기초자료가 될 것으로 생각된다.

• E2M - 전기 전자와 첨단 소재
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• 제8권5호
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• pp.611-618
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• 1995

The (Sr$_{1-x}$ .Ca$_{x}$)TiO$_{3}$+0.6[mol%]Nb$_{2}$O$_{5}$ (0.05.leq.x.leq.0.2) ceramics were fabricated to form semiconducting ceramics by sintering at about 1350[.deg. C] in a reducing atmosphere(N$_{2}$ gas). Metal oxides, CuO, was painted on the both surface of the specimens to diffuse to the grain boundary. They were annealed at 1100 [.deg. C] for 2 hours. The 2nd phase formed by thermal diffusing from the surface lead to a very high apparent dielectric constant. According to increase of the frequency as a functional of temperature, all specimens used in this study showed the dielectric relaxation, and the relaxation frequency was above 106 [Hz], it move to low frequency with increasing resistivity of grain. The specimens showed three kinds of conduction mechanisms in the temperature range 25-125 [.deg. C] as the current increased: the region I below 200 [V/cm] shows the ohmic conduction. The region rt between 200 [V/cm] and 2000 [V/cm] can be explained by the Poole-Frenkel emission theory, and the region III above 2000 [V/cm] is dominated by the tunneling effect.fect.

• 대한전기학회논문지
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• 제44권12호
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• pp.1610-1616
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• 1995

The (Sr$_{1-x}$ .Ca$_{x}$)TiO$_{3}$(0.05.leq.x.leq.0.2) ceramics were fabricated to form semiconducting ceramics by sintering at about 1350[.deg. C] in a reducing atmosphere (N$_{2}$ gas). After being fired in a reducing atmosphere, metal oxides, CuO, was painted on the both surface of the specimens to diffuse to the grain boundary. They were annealed at 1100[.deg. C] for 2 hours. The 2nd phase formed by thermal diffusing from the surface lead to a very high apparent dielectric constant. The results of the capacitance-valtage measurements indicated that the grain boundary was composed of the continuous insulating layers. The capacitance is almost unchanged below about 20[V], but decreased slowly over 20[V]. The conduction mechanism of the specimens observed in the temperature range of 25~125[.deg. C], and is divided into three regions having different mechanism as the current increased: the region I below 200[V/cm] shows the ohmic conduction. The region II between 200[V/cm] and 2000[V/cm] can be explained by the Poole-Frenkel emission theory, and the region III above 2000[V/cm] is dominated by the tunneling effect.ct.

• 구강회복응용과학지
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• 제30권1호
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• pp.16-22
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• 2014

목적: 본 연구의 목적은 동일한 모형에서 제작된 지르코니아 single 코핑과 3-unit 구조물의 변연 및 내면 적합도를 평가하는 것이다. 연구 재료 및 방법: 상악 우측 제2소구치가 상실되고 상악 제1소구치와 제2대구치가 지대치로 형성된 에폭시 모형(epoxy model)을 제작한 후 레이저 스캐너를 이용하여 스캔 하였다. CAD 소프트웨어를 이용하여 지르코니아 구조물을 디자인하고 CAM을 사용하여 지르코니아 single 코핑과 3-unit 구조물을 제작 하였다. 지르코니아 single 코핑은 상악 제1소구치, 제2대구치에서 각각 10개씩 제작 되었고 지르코니아 3-unit 구조물도 10개가 제작 되었다. 적합도 측정을 위하여 제작된 실리콘 복제(silicone replica)를 4등분하고 각 면의 측정 위치(P1, P2, P3, P4, P5)에서 디지털 현미경을 사용하여 적합도를 측정하였다. 각 위치에서 측정된 불일치 값들은 변연 불일치(MG, P1), 축 불일치(AG, P2와 P3의 평균), 교합 불일치(OG, P4와 P5의 평균)의 세 범주로 분류하였다. 결과: Single 코핑에서 변연 불일치의 범위는 18.47 - 40.54 ${\mu}m$, 축 불일치의 범위는 39.73 - 73.61 ${\mu}m$, 교합 불일치의 범위는 116.90 - 134.69 ${\mu}m$이었다. 3-unit 구조물에서 변연 불일치의 범위는 45.95 - 87.44 ${\mu}m$이고, 축 불일치의 범위는 23.78 - 57.00 ${\mu}m$이고, 교합 불일치는 99.89 - 131.06 ${\mu}m$이었다. 결론: 본 연구의 결과에 따르면 single 코핑에 비해 3-unit 구조물의 변연 불일치가 증가하였지만 임상학적 수용 범위(- 120 ${\mu}m$) 내에 있었으며 3-unit 구조물의 불일치 증가를 방지하기 위해서 더욱 균질한 지르코니아 블록 사용과 소결공정들을 조절해야 할 것이다.

• 한국전기전자재료학회논문지
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• 제30권6호
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• pp.356-360
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• 2017

We investigated the phase evolution, microstructure, and microwave dielectric properties of Na- and Zr-doped $Ba(Mg_{0.5}W_{0.5})O_3$ [i.e., ($Ba_{1-2x}Na_{2x})(Mg_{0.5-x}Zr_xW_{0.5})O_3$] ceramics. $BaWO_4$ as a secondary phase was observed in all compositions, and it increased as the dopant concentration increased. All specimens revealed a dense microstructure. For the composition of x=0.01, polyhedral grains were observed. As the dopant concentration increased, the densification and the grain growth were promoted by a liquid phase. The quality factor($Q{\times}f_0$) decreased remarkably, whereas the dielectric constant (${\varepsilon}_r$) tended to decrease as the dopant concentration increased. The dielectric constant, quality factor, and temperature coefficient of the resonant frequency of the composition of x=0.01 sintered at $1,700^{\circ}C$ for 1 h were 18.6, 216,275 GHz, and $-22.0ppm/^{\circ}C$, respectively.

• 자원리싸이클링
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• 제12권6호
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• pp.19-25
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• 2003

제철소 냉연 공정의 염산 폐액에서 ruthner process 공법으로 제조된 산화철을 사용하여 2차 배소 온도변화에 따른 산화철의 분체 특성을 조사하였고, 산화철과 스트론튬을 건식 혼합 및 가소후 Sr-ferrite 자석을 제조하여 자기적 물리적 특성을 조사하였다. Ruthner proces의 산화철을 2차 배소를 실시한 경우, Cl- 함량이 적고 분체 특성이 안정적인 배소온도는 $800^{\circ}C$ 부근으로, 평균 입자(APS)는 1.5 $mu extrm{m}$, apparent bulk density(ABD)는 1.4 g/$m\ell$ 이며, Cl- 함유량은 0.05% 이하를 나타내었다. Ruthner process에서 제조된 산화철을 vibrating disk mill에서 1차 분쇄를 실시한 경우, Sr-ferrite magnet의 보자력(HcJ)은 229 kA/m에서 251 kA/m로 향상하였다. Sr-ferrite magnet의 소결 온도 변화에 따른 잔류자속밀도와 보자력의 희귀식은 Br≒-0.258HcJ＋494의 함수 관계를 나타내고 있으며, 성형 중 가한 자장 방향과 수직방향에 따른 수축비는 산화철의 2차 배소 온도 $800^{\circ}C$까지는 1.6으로 안정적인 판상형으로 결정 성장을 나타내고 있으나, 그 이상의 온도로 2차 배소한 산화철을 사용한 경우에는 소결에서 결정이 더 커진 것으로 판단된다.

• 한국분말재료학회지
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• 제29권6호
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• pp.468-476
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• 2022

Yttria-stabilized zirconia (YSZ) has a low thermal conductivity, high thermal expansion coefficient, and excellent mechanical properties; thus, it is used as a thermal barrier coating material for gas turbines. However, during long-time exposure of YSZ to temperatures of 1200℃ or higher, a phase transformation accompanied by a volume change occurs, causing the YSZ coating layer to peel off. To solve this problem, YSZ has been doped with trivalent and tetravalent oxides to obtain coating materials with low thermal conductivity and suppressed phase transformation of zirconia. In this study, YSZ is doped with trivalent oxides, Nd₂O₃, Yb₂O₃, Al₂O₃, and tetravalent oxide, TiO₂, and the thermal conductivity of the obtained materials is analyzed according to the composition; furthermore, the relative density change, microstructure change, and m-phase formation behavior are analyzed during long-time heat treatment at high temperatures.

• 한국방사선학회논문지
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• 제4권4호
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• pp.5-10
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• 2010

$Ca_2SiO_4$를 모체로 한 열형광체에도 활성제로 La를 0.1 wt.%, 0.3 wt.%, 0.5 wt.%, 1.0 wt.%의 농도로 첨가하여 $1000^{\circ}C$의 질소 분위기의 전기로에서 90분 동안 소결한 후 입자의 크기를 $100{\mu}m$로 일정하게 선별한 후 측정에 사용하였다. 저에너지 X-선을 조사한 후 측정한 경우 0.1 wt.%에서 상대적으로 열형광 강도가 크게 나타났다. peak shape 법으로 구한 활성화 에너지는 0.434 ~ 0.516 eV이며, 주파수 인자는 0.5 ~ 0.56으로 2차 발광이었다. 자외선을 조사한 후 측정한 경우 0.3 wt.%에서 상대적인 열형광 강도가 크게 나타났고, 활성화 에너지는 0.415 ~ 0.477 eV이며, 주파수 인자는 0.5 ~ 0.53 으로 2차 발광이었다. 저에너지 방사선에 대한 방사선량과 열형광 강도는 선형적임을 나타내어 열형광선량계로서 좋은 특성을 나타내고 있다. 본 연구에서 제작한 $CaB_4O_7$, $Ca_2SiO_4 열형광체는 저에너지 영역의 방사선에 대하여 우수한 열형광 특성을 가짐을 알 수 있었고, 향후 선량계의 제작에 좋은 물질이 될 것으로 생각한다.

• 대한치과보철학회지
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• 제22권1호
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• pp.33-50
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• 1984

The purpose of this study was to investigate whether the ashed tooth powder is utilized as an alternative material of the implant to recovery the bony defect. For this purpose its biocompatibility was evaluated comparing to the synthetic calcium phosphate compounds, such as Syntograft and Calcitite, as well as the vacuum firing porcelain (Ceramco Inc.) which is anticipated to use as a matrix to aid sintering. Bony defects to exposure the bone marrow, $3{\times}5$ mm in size, were created in the right and left tibias of fifteen rabbits, and then the ashed tooth powder at $950^{\circ}C$, the porcelain powder, Syhtograft and Calcitite were inserted in the defects of twelve rabbits of the experimental group and the blood clot only was filled in the defects of three rabbits of the control group. The experimental and control rabbits were sacrificed at 1st, 2nd 3rd week after implantation and the histologic examination was performed. The ashed tooth powder in order to make the needed form of the implant was molded using the cylindrical mold 1 cm high, 1 cm in diameter under the pressure of $1000kg/cm^2$ and the ashed tooth powder was sintered at $1100^{\circ}C$ for 1 hour and the mixture of the porcelain powder and the ashed tooth powder at the weight ratio of 7:3, 6:4, 5:5, 4:6 were molded in the same manner and were sintered at $925^{\circ}C$. From this sintered material, square shaped implants were prepared in the dimension of $2{\times}4{\times}6mm$. The prepared implants were surgically placed in the subperiosteum of lateral surfaces of the right and left mandibular bodies. The dogs were sacrificed at 4 weeks, and then the specimens were examined using the light and scanning electron microscopes. The results of this study were obtained as follows: 1. Any inflammatory response was not noted after implanting of the ashed tooth powder, Syntograft, Calcitite and the porcelain powder during the whole experimental period after implantation. 2. Induction of the new bone formation was significantly shown in the ashed tooth powder, Syntograft and Calcitite. 3. The more the porcelain powder was contained in the implants, the more the porosity was and the bigger the pore size was under the scanning electron microscope. And there was ingrowing of the fibrous connective and the osteoid tissue. 4. The osteoid tissues were found to be directly fused to the implant of the ashed tooth powder, and the mixture implant of the porcelain powder and the ashed tooth powder at the weight ratio of 4:6 under the light and scanning electron microscopes.