열처리 분위기가 Eu 이온이 첨가된 Li-Al-O계 형광체 특성에 미치는 영향

김정석,천채일,채기웅,Kim, Jeong Seog,Cheon, Chae Il,Chae, Ki-Woong 한국세라믹학회 2014 한국세라믹학회지 Vol.51 No.1

New green phosphor is synthesized by reducing $LiAlO_2:xEu^{3+}$ phosphors in a low pressure $H_2$ atmosphere. The $LiAlO_2:xEu^{3+}$ prepared by a solid state reaction method is reported as red phosphor. The effect of the reduction treatment on the $LiAlO_2:xEu^{3+}$ on the crystalline phase change and photoluminescence (PL) property are characterized. The reduced phosphor had a broad green light spectrum centered at 524 nm. The PL intensity of the reduced phosphor increased to a maximum at the reduction temperature of $1100^{\circ}C$. The PL intensity decreased with a further increase in the reduction temperature. The crystalline phase constituting the reduced phosphor varied with the temperature. A new crystalline phase $Li_2Al_4O_7$ was observed at $1100^{\circ}C$. The origin of the green-light emission is discussed in relation to the crystalline phase change.

밀스케일과 적점토를 원료로한 축열재에서 원료성분과 소성조선에 따른 특성 변화

김정석,김홍,Kim, Jeong-Seog,Kim, Hong 한국자원리싸이클링학회 1999 資源 리싸이클링 Vol.8 No.1

적점토와 밀스케일, 물유리를 원료로한 축열용 난방재를 개발하기 위해 제반 기초적 실험을 수행하였다. 원료배합 및 소성 조건에 따른 축열재 시료의 소성특성, 열용량, 항절력, 미세조직 등을 분석하였다. 소성체의 수축은 적점토의 비율이 높을수록 증가하였다. $300^{\circ}C$까지는 건조수축이, $300~700^{\circ}C$ 영역에서는 산화철의 상변화에 의한 완만한 팽창, $1200^{\circ}C$ 이상에서는 급격한 팽창을 나타내었다. 항절력은 밀스케일 : 적점토 비가 1:1에서 3:1로 변함에 따라 5.6MPa에서 2.35MPa로 감소하였다. 열용량은 밀스케일 : 적점토의 비율이 1:1~3:1인 경우, $1.25~1.35J/g^{\circ}C$의 값을 나타내었다. 시험편과 공기와의 접촉을 제한함으로써, 시료 내 밀스케일 성분이 소성과정에서 용융하여 시편 표면으로 용출되는 현상을 억제시킬 수 있었고, 이에 따라 균일한 표면의 시료를 제작할 수 있다. 밀스케일의 첨가는 소성체를 다공질화시켜, 축열재의 축열 후 냉각속도를 낮추는데 기여할 것으로 판단된다. Firing characteristics, transverse rupture strength, and heat capacity were studied of the heat-reservoir refractory materials made of red-firing clay, mill scale, and water glass. The firing shrinkage increased with increase of the clay proportion in samples. The volume of fired bodies showed shrinkage by drying up to $300^{\circ}C$, steady expansion in the 300-$700^{\circ}C$ range due to phase transition of iron oxides. and drastic expansion above $1200^{\circ}C$. Flexural strength decreased from 5.6 Mpa to 2.35 Mpa with the decrease of the ratio of clay to mill scale from 1:1 to 1:3 Heat capacities changed from 1.1 Joul/g$^{\circ}$C to 1.35 Joul/g$^{\circ}$C with the ratio of millscale to clay ratio from 1:1 to 1:3. Mill scale in the specimen appears to exist as liquid phase during firing. Firing the specimens in air leads to the eruption of the molten mill scale to the sample surfaces. Contrarily, firing samples in a refractory sagger with a cover suppressed the eruption of the molten mill scale to the surfaces. The addition of mill scale gave rise to porous sintered bodies which would delay cooling rates of heat-reservoir brick.

CaWO₄-Li₂WO₄-Eu₂O₃계 형광체의 PL 특성과 결정구조

김정석,최진호,정봉만,강현주,Kim, Jeong-Seog,Choi, Jin-Ho,Jeong, Bong-Man,Kang, Hyun-Ju 한국세라믹학회 2006 한국세라믹학회지 Vol.43 No.1

Photoluminescence (PL) and crystal structures of the $(l-x)CaWO_4-xLi_2WO_4$ binary system added with $Eu_2O_3$ activator have been characterized. The $CaWO_4\;and\;Li_2WO_4$ have the scheelite and phenakite structures respectively. The $CaWO_4-Li_2WO_4-Eu_2O_3$ phosphors show the red luminescence of 613 nm peak wavelength. The wavelength range of excitation spectral band is $380\~470$ nm with the peak wavelength of 397 nm. The $0.88(0.5CaWO_4-0.5Li_2WO_4)-0.12Eu_2O_3$ showed the most superior luminescence characteristics. The effect of co-doping elements such as $Al_2O_3$ and rare-earth oxides on PL has been characterized. The co-doping elements deteriorated the luminescence intensity except the $Al_2O_3$ and $Gd_2O_3$. The PL characteristics of $CaWO_4-Li_2WO_4-Eu_2O_3$ phosphors have been compared to those of the alkali europium double molybdates (tungstates) of scheelite-related structure such as $LiEu(MoO_4)_2$ and $CsEu(MoO_4)_2$. The crystal structures of $(l-y)[(l-x)CaWO_4-xLi_2WO_4]-yEu_2O_3$ phosphors have been characterized using XRD data and rietveld refinement.

수용액 합성법의 2단계 성장온도 변화를 통한 ZnO 결정의 선택적 용해 현상

김정석,채기웅,Kim, Jeong-Seog,Chae, Ki-Woong 한국세라믹학회 2011 한국세라믹학회지 Vol.48 No.4

ZnO hexagonal rods grown in aqueous solution can be changed into a tubular shape by two-step aging in the course of the growing process. In the first step, hexagonal ZnO rods is grown by aging at $90^{\circ}C$ under a highly supersaturated aqueous solution giving rise to a fast precipitation rate. Meanwhile, during the second step aging at $60^{\circ}C$ in the same aqueous solution, the hexagonal polar face (001) having higher surface energy than (010) side planes dissolves to minimize surface energy. Hence the flat (001) face changes to a craterlike face and the hexagonal rod length of ZnO decreases at an initial-stage of this step aging. The formation of the (101) wedge-type faces is ascribed to the resultant of competitive reactions between the dissolution of polar face minimizing the surface energy which is a dominant reaction at the initial stage and the precipitation reaction dissipating supersaturation. At a later stage of the second-step the reaction rates of these two processes in the aqueous solution become similar and the overall reaction is terminated.

Ferroelectric and ferromagnetic properties of BiFeO₃ - PrFeO₃ - PbTiO₃ solid solutions

김정석(Jeong Seog Kim),천재일(Chae Il Cheon),최용남(Yong Nam Choi),장평우(Pyung Woo Jang) 한국자기학회 2002 한국자기학회 학술연구발표회 논문개요집 Vol.12 No.2

Bi 가 치환된 BaO.$Nd_{2}O_{3}$.$4TiO_{2}$ 세라믹스의 마이트로파 유전특성

천재일,김정석,Cheon, Jae-Il,Kim, Jeong-SeoG 한국재료학회 1998 한국재료학회지 Vol.8 No.7

BaO.$Nd_{2}O_{3}$.$4TiO_{2}$세라믹스에서 Bi 치환위치 및 Bi 치환 량에 따른 상, 미세구조, 마이크로파 유전특성 등을 조사하였다. BaO.$Nd_{2}O_{3}$.$4TiO_{2}$ 세라믹스의 Nd 치환되어 $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$고용체 (0$\leq$x$\leq$0.2)를 형성하였다. $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$에서 Bi 치환 량이 x=0에서 x=0.2까지 증가됨에 따라 입자크기가 계속 증가하였으며, 유전상수는 84에서 108까지 계속 증가하였고, 공진 주파수의 온도계수는 $44 ppm^{\circ}C$에서 $-30ppm^{\circ}C$로 계속 감소하였다. $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$조성에서 Bi 치환 량이 x=0.04에서 0.08사이일 때 가장 양호한 마이크로파 유전특성이 얻어졌으며 이 때의 유전상수 (${\varepsilon}_r$)는 89~92, Q, f는 5855-6091 GHz, 그리고 공진 주파수의 온도계수 (${\tau}_f$)는 -7.7-7.5 ppm/$^{\circ}C$이었다. The effect of Bi-substitution in $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$ ceramic was studied on the formation of crystal phases, microstructure, and microwave dielectric properties. $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$, solid solution (0$\leq$x$\leq$0.2) were formed by Bi-substitution into the Nd site of $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$ ceramics. Average grain size increased with Bi-substitution. Dielectric constant(${\varepsilon}_r$) increased from 84 to U8, and the temperature coefficient of resonant frequency(${\tau}_f$) decreased from 44 ppm/$^{\circ}C$ to -30 ppm/$^{\circ}C$ when Bi contents increased up to x=0.2 in $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$ solid solutions. $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$ solid solutions with x=0.04~0.08 showed the most superior microwave dielectric properties, those are ${\varepsilon}_r$= 89-92, Q . f = 5855~6091 GHz, and (${\tau}_f$)= -7.5-7.5 ppm/$^{\circ}C$.

수용액 합성법에 의한 ZnO 이중 나노구조물의 합성

채기웅,김정석,Chae, Ki-Woong,Kim, Jeong-Seog,Cao, Guozhong 한국세라믹학회 2009 한국세라믹학회지 Vol.46 No.6

Double-layered ZnO nanostructures have been synthesized by aqueous solution method on (001) plane of ZnO nanorod. A stepwise changing of aqueous solution concentration gave rise to a new nano-structured layer consisting of either multiple of nanorods or nanowires with much smaller radii than that of the ZnO nanorod on which the new layer was grown. As the first step the ZnO nanorods have been grown to have the (001) preferential orientation in the aqueous solution consisting of 0.1M zinc nitrate and 0.1 M HMT. This preferentially aligned ZnO nanorods have been regrown in either a less diluted solution of 0.01M zinc nitrate and 0.01 M HMT or a more diluted solution of 0.005M zinc nitrate and 0.01 M HMT. A new nano-layer consisting of numerous aligned nanorods or nanowires has been produced on the (001) planes of ZnO nanorods. The growth mechanism for this double layered ZnO nanostructure is ascribed to the (001) polar surface energy instability and inhibition of (001) plane growth due to the step-wise change of aqueous solution concentration; ZnO nuclei formed on the (001) plane grow preferentially in (010) plane instead of (001) plane to reduce the total surface energy. Surface area of ZnO nanostructure can be increased in orders of magnitudes by forming a new layer consisting of smaller nanorods/nanowires on (001) plane of ZnO nanorods.

수열 합성 공정 조건이 티탄산 납의 상 형성에 미치는 영향

김경아,김정석,천채일,Kim, Kyoung-A,Kim, Jeong-Seog,Cheon, Chae-Il 한국세라믹학회 2011 한국세라믹학회지 Vol.48 No.1

Lead titanate ($PbTiO_3$) powder was prepared from lead nitrate ($Pb(NO_3)_2$) and titania ($TiO_2$) by hydrothermal route. Phase formation process was investigated by observing the phases formed in various experimental conditions like different KOH concentration, reaction temperature and time. $PbTiO_3$ powder was fabricated when the KOH concentration was 0.8M or higher. An intermediate compound, $PbTi_{0.8}O_{2.6}$, was formed at first by a reaction between PbO and $TiO_2$ and changed into $PbTiO_3$ powder with a perovskite crystal structure. A $PbTiO_3$ phase was formed in a shorter time when a KOH concentration was increased from 0.8M to 8M because a driving force for a $PbTiO_3$ formation was increased due to an increase in a degree of supersaturation. And $TiO_2$ (rutile) and $3PbO{\cdot}H_2O$ were observed at room temperature in a 0.8M KOH solution and $TiO_2$(rutile) and PbO (litharge) in a 8M KOH. A $PbTiO_3$phase was also formed in a shorter time at a higher reaction temperature as a reaction temperature influenced the rates for a dissolution and a precipitation.

Al₂O₃:xCr₂O₃ 고용상의 발광특성과 적색형광체의 연색성 향상을 위한 첨가제로의 응용

채기웅,천채일,김정석,Chae, Ki-Woong,Cheon, Chae-Il,Kim, Jeong-Seog 한국세라믹학회 2010 한국세라믹학회지 Vol.47 No.2

In this article photoluminescence of the $Al_2O_3:xCr_2O_3$ solid solutions prepared by solid state reaction method are represented. The effect of $Cr_2O_3$-activator concentration and heat treatment time on the PL characteristics have been discussed in conjunction with microstructure of phosphor samples. The $Al_2O_3:xCr_2O_3$ phosphors show the highest PL intensity at x=0.003 mole when the samples are reacted at $1600^{\circ}C$ for 5 h. The PL emission and absorption spectra show the maximum peaks at 698 nm and at 398 nm respectively. The CIE color coordinate is (x=0.646, y=0.316) at 0.003 mole $Cr_2O_3$, which value is very close to the NTSC coordinate of red color. This characteristic feature of $Al_2O_3:xCr_2O_3$ has been applied for an additive to improve the color characteristic of other red phosphor $LiEuW_2O_8$ which has a relatively poor color purity with an emission peak centered at 615 nm and with a CIE coordinate (x=0.530, y=0.280). The $Al_2O_3:0.003Cr_2O_3$ phosphor has been mixed with the $LiEuW_2O_8$ phosphor powder and the PL characteristics and CIE color coordinates are characterized. The $Al_2O_3:xCr_2O_3$ phosphor was found effective for improving the CRI (color rendering index) of $LiEuW_2O_8$ phosphor.

소결 조건이 스크린 인쇄법으로 제조한 PZT계 후막의 물성에 미치는 영향

이봉연,천채일,김정석,김준철,방규석,이형규,Lee, Bong-Yeon,Cheon, Chae-Il,Kim, Jeong-Seog,Kim, Jon-Chul,Bang, Kyu-Seok,Lee, Hyeung-Gyu 한국세라믹학회 2001 한국세라믹학회지 Vol.38 No.10

스크린 인쇄법으로 알루미나 기판 위에 PZT 후막을 제조하였으며, 공기 또는 Pb 분위기의 $750{\sim}1050^{\circ}C$에서 1시간 동안 소결하여 소결 조건이 후막의 물성에 미치는 영향을 조사하였다. 공기 중에서 $950^{\circ}C$ 이상의 온도로 소결한 PZT 후막에는 파이로클로 상이 제 2상으로 존재하고 있었으며, Pb분위기에서 소결한 PZT 후막이 공기 중에서 소결한 후막보다 치밀한 미세구조와 큰 유전상수 그리고 잘 발달된 P-E 이력특성을 보였다. $900^{\circ}C$의 Pb 분위기에서 소결한 PZT 후막은 잘 포화된 전형적인 강유전 P-E 이력곡선 모양을 보였으며, 잔류분극과 항전계가 각각 $29.8{\mu}C/cm^2$, 48.4 kV/cm이었다. PZT thick films were fabricated on alumina substrates by a screen printing method. They were sintered at $750^{\circ}C{\sim}1050^{\circ}C$ for 1 h under air or Pb atmosphere. Pyrochlore was observed as a second phase in PZT thick films sintered in air at temperatures of $950^{\circ}C$ and higher. PZT thick films sintered under Pb atmosphere showed denser microstructure, higher dielectric constant, and better-developed P-E hysteresis curve than the films sintered in air. PZT thick films sintered at $900^{\circ}C$ under Pb atmosphere showed the typical ferroelectric hysteresis with remanent polarization of $29.8{\mu}C/cm^2$ and coercive field of 48.4 kV/cm.