• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.149-152
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• 2001

A great deal of attention has been focused on the application of miniaturized piezoelectric transformers to the low power source for the microsystem. The dielectric and piezoelectric properties of Pb(Mn,W,Sb,Nb)O$_3$-Pb(Zr,Ti)O$_3$ ceramics have been investigated on different calcination(750$^{\circ}C$∼950$^{\circ}C$) and sintering(1100$^{\circ}C$∼1300$^{\circ}C$) temperatures. The perovskitic phase was formed by the solid phase reaction of the oxides. Anisotropic (k$\sub$t/k$\sub$p/) properties of electromechanical coupling coefficient and piezoelectric coefficient have been proven to be depending on processing temperatures. The value of electromechanical coupling factor of K$\sub$p/>0.51 and a mechanical quality factor of Q$\sub$m/>2000 were obtained. The piezoelectric transformer was prepared using this ceramics with the composition of Pb(Mn,W,Sb,Nb)O$_3$-Pb(Zr,Ti)O$_3$ We studied the influence of different processing temperature on the microstructure and piezoelectric properties of complex PZT-based ceramics. and the characteristic of piezoelectric transformer.

• Bulletin of the Korean Chemical Society
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• 제35권1호
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• pp.141-146
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• 2014

A series of bimetallic Cu-Zn/$SiO_2$ catalysts were prepared via thermal decomposition of the as-synthesized $CuZn(OH)_4(H_2SiO_3)_2{\cdot}nH_2O$ hydroxides precursors. This highly dispersed Cu-solid base catalyst is extremely effective for hydrogenation of ethyl acetate to ethanol. The reduction and oxidation features of the precursors prepared by coprecipitation method and catalysts were extensively investigated by TGA, XRD, TPR and $N_2$-adsorption techniques. Catalytic activity by ethyl acetate hydrogenation of reaction temperatures between 120 and $300^{\circ}C$, different catalyst calcination and reduction temperatures, different Cu/Zn loadings have been examined extensively. The relation between the performance for hydrogenation of ethyl acetate and the structure of the Cu-solid base catalysts with Zn loading were discussed. The detected conversion of ethyl acetate reached 81.6% with a 93.8% selectivity of ethanol. This investigation of the Cu-Zn/$SiO_2$ catalyst provides a recently proposed pathway for ethyl acetate hydrogenation reaction to produce ethanol over Cu-solid base catalysts.

• Journal of Ceramic Processing Research
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• 제20권spc1호
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• pp.109-112
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• 2019

γ-dicalcium silicate(γ-C2S) is known as a polymorphism of belite. Due to its high CO2 fixed capacity and the low CO2 emission production process, γ-C2S has attracted more and more attention of researchers. For the further development of application of γ-C2S in building construction industry. In this study, we aim to investigate the method for synthesizing high purity of γ-C2S. The influence of different raw materials and calcination temperatures on the purity of γ-C2S was also evaluated. Several Ca bearing materials were selected as the calcium source, the materials which' s main component is SiO2 were used as the silicon source. Raw materials were mixed and were calcined under different temperatures. The results reveal that the highest purity could be obtained using Ca(OH)2 and SiO2 powder as raw materials. And for the practical application, a relatively economic synthesis method using natural mineral materials- limestone and silica sand as raw materials was developed, by this method, the purity of the synthetic γ-C2S was 77.6%.

• 한국세라믹학회지
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• 제29권4호
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• pp.253-258
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• 1992

ZnO varistors were prepared by the organochemical method which used citric acid and ethylene glycol as gelling agents. The microstructure of the sintered specimens exhibited small grains, uniform grain size distribution, and few intragranular pores. Thermal decomposition of the organic resin formed during the powder preparation process was completed around 450$^{\circ}C$. No significant changes were observed in microstructure and current voltage characteristic with respect to calcination temperatures. A major advantage of the organochemical method used in this experiment is a possible uniform mixing of trace amounts of dopants. Therefore, this powder preparation method seems promising in investigating the effect of Li or In ion, which is added in ppm level to ZnO varistors, on the pulse respose characteristic.

• The Korean Journal of Ceramics
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• 제1권2호
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• pp.81-85
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• 1995

PST-series spcimens with stoichimetric and nonstoichimtric compositins were prepared and the effects of compositionl modification on phase formation and dielectric presponse were investigated. The phases formed on calcination were mainly perovskite and trace amount of phyrochlore(s), with an increase of the latter phase(s) as the composition became more ononstoichiometric. The sintered samples showed thermal hysteresis and diffuseness in phase transition with a small degree of frequency relaxation. Temperatures corresponding to maximum values of dielectric constant and loss were relatively insensitive to the composition change while the maximum values were very sensitive to that.

• Bulletin of the Korean Chemical Society
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• 제23권9호
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• pp.1304-1323
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• 2002

Superconducting BiSrCaCu(Ni)O ceramicss have been prepared by the gel method using an aqueous solution containing a tartaric acid. The aqueous solution of metal salts was concentrated without precipitation. The precursor so prepared was homogeneou s and calcined at $825^{\circ}C$ for 24 h to produce superconducting phase. The thermal decomposition of gels, the formation of superconducting phase, and their ceramic microstructure were studied using IR, TGA, XRD, resistance measurements, and SEM. This method is highly reproducible and leads to powders with excellent homogeneity and small particle size for easy sinterability. The nickel dopant substituting for Cu gives rise to the gradual decrease of the Tc. Phase pure 2212 ceramics were obtained at 825 $^{\circ}C$ for 24 h. SEM pictures showed that liquid phase was formed when the samples were sintered temperatures higher than 825 $^{\circ}C$.

• 한국세라믹학회지
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• 제39권4호
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• pp.336-340
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• 2002

Pure and nano-sized $TiO_2$ and $CaTiO_3$ powders were fabricated by a polymeric steric entrapment route and planetary milling process. An ethylene glycol was used as a polymeric carrier for the preparation of organic-inorganic precursors. Titanium isopropoxide and calcium nitrate were dissolved in liquid-type ethylene glycol without any precipitation. At the optimum amount of the polymer, the metal cations were dispersed in solution and a homogeneous polymeric network was formed. The dried precursor ceramic gels were turned to porous powders through calcination process. The porous powders were crystallized at low temperatures and the crystalline powders were planetary milled to nano size.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2003년도 춘계학술발표논문집
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• pp.91-94
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• 2003

하소온도에 따른 (Zn/sub 0.8.Mg/sub 0.2/)TiO₃ 마이크로파 유전체 세라믹스의 소결거동과 마이크로파 유전특성의 변화를 연구하였다. 저온소결을 위하여 0.45 wt.％Bi₂O₃와 0.55wt.％V₂O/sub 5/를 첨가하였으며, 1000℃이하의 온도에서 소결하여 치밀한 소결체를 얻을 수 있었다. 800℃～1000℃의 범위의 여러 온도에서 하소를 하고 소결 전ㆍ후의 존재상과 미세구조의 분석을 통하여, 하소한 분말에 존재하는 미반응상 및 이차상이 최소화 될 때 높은 Q×f/sub o/값을 갖는 것을 알 수 있었다. 1000℃에서 하소한 후 900℃에서 소결했을 때, 주상이 Hexagonal이고 미세구조가 균일하였으며, 이때 Q×f/sub o/ = 42,000㎓, ε/sub r/ = 22를 나타냈다.

• Bulletin of the Korean Chemical Society
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• 제19권8호
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• pp.856-862
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• 1998

Vanadium oxide catalyst supported on ZrO2-WO3 was prepared by adding the Zr(OH)4 powder into a mixed aqueous solution of ammonium metavanadate and ammonium metatungstate followed by drying and calcining at high temperatures. The characterization of prepared catalysts was performed using solid-state 51V NMR and FTIR. In the case of calcination temperature at 773 K, for the samples containing low loading V2O5 below 18 wt % vanadium oxide was in a highly dispersed state, while for samples containing high loading V2O5 equal to or above 18 wt % vanadium oxide was well crystallized due to the V2O5 loading exceeding the formation of monolayer on the surface of ZrO2-WO3. The ZrV2O7 compound was formed through the reaction Of V2O5 and ZrO2 at 873 K and the compound decomposed into V2O5 and ZrO2 at 1073 K, which were confirmed by FTIR and 51V NMR.

• 한국결정성장학회지
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• 제14권6호
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• pp.267-271
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• 2004

우레아 가수분해법을 이용하여 리튬이차전지용 $LiCoO_2$ 양극 분말을 합성하였다. Li/Co 몰비가 다르고 가수분해에 의해 얻어진 전구체는 다양한 온도에서 열처리되었다. 저온상 $LiCoO_2(LT-LiCoO_2)$와 고온상 $LiCoO_2(HT-LiCoO_2)$는 $500^{\circ}C$에서 2시간 열처리 후 합성되었고, 저온상에서 고온상으로 상전이는 $700^{\circ}C$ 이상에서 완전히 일어났다. 열처리 온도가 증가함에 따라 $LiCoO_2$의 층상구조가 잘 발달하였다. 충방전 실험결과 Li/Co의 몰비가 1.2이고 $800^{\circ}C$에서 열처리한 $LiCoO_2$의 초기용량이 152 mAh/g으로 높았으며, 40회 충.방전 후에는 9.2%의 용량감소를 나타내는 상대적으로 안정한 충방전 특성을 나타내었다.