• Korean Chemical Engineering Research
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• 제52권5호
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• pp.678-687
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• 2014

The catalytic performance of silicon carbide supported nickel catalysts modified with or without second metal (Co, Cu and Zn) for the methanation of CO has been investigated in a fixed-bed reactor using a feed consisting of 25% CO and 75% $H_2$ without any diluent gas. It has been found that the introduction of Co species can clearly improve the catalytic activity of Ni/SiC catalyst, whereas the addition of Cu or Zn can result in a significant decrease in the catalytic activity. The characterizations by means of XRD, TEM, XPS, CO-TPD and $H_2$-TPR indicate that the addition of Co could decrease the particle size of active metal, increase active sites on the surface of methanation catalyst, improve the chemisorption of CO and enhance the reducibility of methanation catalysts. Additionally, the special interaction between Co species and Ni species is likely favorable for the dissociation of adsorbed CO on the surface of catalyst, and this may also contribute to the high activity of 5Co-Ni/SiC catalyst for CO methanation reaction. For 5Cu-Ni/SiC catalyst and 5Zn-Ni/SiC catalyst, Cu and Zn species could cover partial nickel particles and decrease the chemisorption amount of CO. These could be responsible for the low methanation activity. In addition, a 150h stability test under 2 MPa and $300^{\circ}C$ showed that 5Co-Ni/SiC catalyst was very stable for CO methanation reaction.

• 한국세라믹학회지
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• 제35권8호
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• pp.864-870
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• 1998

The effect of {{{{ {{Nb }_{2 }O }_{5 } }} and CoO addition on the temperature dependence of the {{{{ {BaTiO }_{3 } }}-based ceramic capa-citor has been studied. X7R with moderate temperature dependence has been developed by means of pre-cisely controlled {{{{ {{Nb }_{2 }O }_{5 } }}/CoO ratio. Dielectric constant(K) and dissipation factor(DF) were 3500 and 1.5% respectively. As the content of {{{{ {{Nb }_{2 }O }_{5 } }} was increased the curie temperature(Tc) was shifted to lower tem-perature and the dielectric constant at Tc was decreased. The proper addition of CoO with {{{{ {{Nb }_{2 }O }_{5 } }} improved the temperature dependence of dielectric properties of the {{{{ {BaTiO }_{3 } }}-based ceramic capacitor.

• 한국건설순환자원학회논문집
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• 제11권2호
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• pp.112-119
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• 2023

본 연구에서는 고로슬래그 미분말-제올라이트로 구성된 지오폴리머 페이스트의 알칼리계 활성화제(Ca(OH)₂, CSA)의 종류 및 첨가량에 따른 압축강도 및 화학적 조성의 변화와 CO₂ 포집량을 비교평가 하였다. 지오폴리머 페이스트에 첨가되는 알칼리계 활성화제의 첨가량이 증가할수록 굳기 전 페이스트의 유동성은 감소하였으며, 압축강도가 증가하였다. 활성화제 종류에 따른 평가 결과, CSA보다 Ca(OH)₂를 첨가하는 것이 압축강도 향상 효과가 큰 것으로 확인되었다. CO₂ 양생에 따른 화학적특성의 변화를 비교평가 한 결과, 모든 실험 수준에서 알칼리계 활성화제의 첨가량이 증가할수록 탄산화 전 C-S-H, C-A-S-H gel의 생성량이 증가하였으며, 탄산화 이후 CaCO₃ 생성량이 증가하였다. 알칼리계 활성화제 첨가로 인하여 고로슬래그 미분말과 제올라이트의 반응성이 증가하였으며, 첨가량이 증가할수록 반응성도 증가하는 경향이 나타났다. 열중량 분석결과, 알칼리계 활성화제의 첨가량이 증가할수록 CO₂ 양생에 따른 CaCO₃ 분해구간 에서의 질량감소율이 증가하였으며, 10 % 첨가 시 Ca(OH)₂의 경우 10.3 wt%, CSA의 첨가 시 8.77 w%의 CO₂ uptake가 발생하였으며, 활성화제를 첨가하지 않은 경우보다 각 4.21배, 3.88배 증가한 것으로 확인되었다.

• Bulletin of the Korean Chemical Society
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• 제25권10호
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• pp.1521-1524
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• 2004

The effect of $H_2$ gas on the carbon nanotubes (CNTs) synthesis with CO-$H_2$ gas mixture was investigated using mass measurements and scanning electron microscopy (SEM). The maximum weight and yield of the synthesized carbon were obtained when the mixture ratio of $H_2$: CO was 3 : 7 and 9 : 1, respectively. In case of 100% carbon monoxide (CO) without hydrogen ($H_2$) addition, the weight of carbon increased, but CNTs were not observed. The CNTs began to be made when the contents of $H_2$ reaches at least 10%, their structures became more distinct with an increase of $H_2$ addition, and then the shapes of CNTs were more thin and straight. When the contents of $H_2$ was 80% ($H_2$ : CO = 8 : 2), the shapes and growth of CNTs showed an optimal condition. On the other hand, when the contents of $H_2$ was higher than the critical value, the shapes of CNTs became worse due to transition into inactive surface of catalyst. It was considered that the inactive surface of catalyst resulted from decrease of carbon (C) and $H_2$ concentration by facilitation of methane ($CH_4$) gasification reaction (C + 2$H_2$ ${\rightarrow}$ $CH_4$) between C and $H_2$ gases. It was also found that H2 addition had an influence considerably on the shape and structure of CNTs.

• 한국재료학회지
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• 제13권9호
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• pp.572-580
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• 2003

Synthesizing behavior and microstructural evolution of $CaZrO_3$and $m-ZrO_2$in a thermal reaction process of $ZrSiO_4$-$xCaCO_3$mixtures, where x is 7 and 19, were investigated to determine the addition amount of CaO in CaO:$ZrO_2$:$SiO_2$ternary composition. CaZrO$_3$-Ca$_2$SiO$_4$precursor prepared by the mixture of $ZrSiO_4$and CaCO$_3$in aqueous suspending media was controlled to the acidic (pH=4.0) condition with HCI solution to enhance the thermal reaction. The addition amount of dispersant into the $ZrSiO_4$-$xCaCO_3$slip increased with increasing mole ratio of $CaCO_3$, which was associated with the viscosity of slip. Decarbonation reaction was activated with an increase of the addition amount of $CaCO_3$, showing different final temperatures in $ZrSiO_4$-$7CaCO_3$and $ZrSiO_4$-$19CaCO_3$mixtures as about 980 and 116$0^{\circ}C$, respectively, for finishing decarbonation reaction. The grain morphology was changed to spherical shape for all samples with an increase of sintering temperature. The grain size and phase composition of the synthesized composites depended on the mixture ratio of Zrsi04 and CacO3 powders, indicating that the main crystals were m-ZrO2 ($\leq$3 $\mu\textrm{m}$) and $CaZrO_3$ ($\leq$ 7 $\mu\textrm{m}$) in $ZrSiO_4$$>-7CaCO_3$and $ZrSiO_4$-$19CaCO_3$mixtures, respectively.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 추계학술대회 논문집 Vol.17
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• pp.421-424
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• 2004

In this study, in order to develop low temperature sintering ceramics for ultrasonic vibrator, PNW-PMN-PZT system ceramics were manufactured with the amount of $CaCO_3$ addition and their piezoelectric, dielectric and microstructural characteristics were investigated. $CaCO_3$ addition to PNW-PMN-PZT basic composition was proved to be capable of sintering the ceramics at temperature below $1000^{\circ}C$ due to the effect of $Li_2CO_3-CaCO_3$ liquid phase. However, with increasing the amount of $CaCO_3$ addition, the second phase was appeared. As the results, electromechanical coupling coefficient (kp) and dielectric constant $(\epsilon_r)$ decreased. Taking into consideration electromechanical coupling coefficient (kp) of 0.49, mechanical quality factor (Qm) of 1396, dielectric constant $(\epsilon_r)$ of 1300 and density of $7.78[g/cm^2]$, it was concluded that the 0.25wt% $CaCO_3$ addition composition ceramics sintered at $920^{\circ}C$ was suitable for ultrasonic vibrator application.

• 한국세라믹학회지
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• 제29권2호
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• pp.101-106
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• 1992

Sintering behavior, distribution of dopant oxides and electrical properties in the ZnO-Bi2O3-CoO-Sb2O3 and ZnO-Bi2O3-CoO-Sb2O3-Cr2O3 systems were studied. The linear shrinkage of ZnO varistors from 850 to 950$^{\circ}C$ was related to the decomposition reaction (py\longrightarrowsp+Bi2O3) of the pyrochlore phase. In the distribution of the dopant oxides (CoO, Sb2O3, Cr2O3), Co distribute uniformly throughout the sample, the distribution of Sb coincided with small particles (spinel phase, Zn7Sb2O12), and Cr distributed very consistently with Sb. The increase in breakdown voltage, due to the addition of Cr2O3, was not only attributed to the decrease in the ZnO grain size but also to the solution of Cr2O3 in the spinel phase. The leakage current (80% V60 ${\mu}\textrm{A}$) was increased by the addition of Cr2O3.

• 상하수도학회지
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• 제25권3호
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• pp.307-312
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• 2011

The potential of algal-bacterial culture was investigated for advanced treatment of animal wastewater. Fed-batch experiments were carried out to examine treatability of nitrogen and phosphorus in different microbial consortium: Chlorella vulgaris, activated sludge, three microalgae strains (Scenedesmus, Microcystis, Chlorella) and Bacillus consortium, and three microalgae strains and sludge consortium. Single culture of C. vugaris showed the better efficiency for nitrogen removal but was not good at organic matter and phosphorus removal compared with activated sludge. Three microalgae and Bacillus consortium was best culture among the culture and consortium for pollutants removal tested in this experiment. Effect of $CO_2$ addition was studied by using three microalgae and Bacillus consortium. $CO_2$ addition enhanced T-P removal efficiency up to 60%. However, removal efficiencies of T-N and ammonia nitrogen reduced on the contrary.

• 한국자기학회지
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• 제12권5호
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• pp.195-200
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• 2002

각종 산화물을 첨가하여 Co$_2$Z type Ba-ferrite의 저온소결에 관하여 연구하였다. Co$_2$Z type Ba-ferrite 상은 2회 하소과정을 통하여 얻을 수 있었으며, 생성된 상의 XRD peaks는 일부 minor peaks 제외하고는 standard peaks와 거의 일치하였다 제조된 분말은 저온소결을 위하여 ZnO-B$_2$O$_3$ glass리 단독 첨가 및 CuO 또는 Bi$_2$O$_3$와 복합 첨가하였으며, 또한 ZnO-Bi$_2$O$_3$ glass를 단독 첨가하였다. 소결은 900~100$0^{\circ}C$에서 수행하였다. ZnO-B$_2$O$_3$ glass의 단독 첨가 시, 첨가량이 7.5 wt%일 때 가장 높은 수축거동을 나타내었다. ZnO-Bi$_2$O$_3$ glass와 CuO 또는 Bi$_2$O$_3$를 복합 첨가하였을 때, glass를 단독 첨가하였을 경우보다 수축률이 급격히 증가되었다. 또한 ZnO-Bi$_2$O$_3$ glass를 단독 첨가한 시편의 수축률과 초기 투자율은 ZnO-B$_2$O$_3$ glass를 단독 첨가한 시편보다 높은 값을 나타내었다.

• 전기화학회지
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• 제9권2호
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• pp.77-83
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• 2006

Anodic overpotential has been investigated with gas composition changes in a $100cm^2$ class molten carbonate fuel cell. The overpotential was measured with steady state polarization, reactant gas addition (RA), inert gas step addition (ISA), and electrochemical impedance spectroscopy (EIS) methods at different anodic inlet gas compositions, i.e., $H_2:CO_2:H_2O=0.69:0.17:0.14\;atm\;and\;H_2:CO_2:H_2O=0.33:0.33:0.33\;atm$, at a fixed $H_2$ flow rate. The results demonstrate that the anodic overpotential decreases with increasing $CO_2\;and\;H_2O$ flow rates, indicating the anode reaction is a gas-phase mass-transfer control process of the reactant species, $H_2,\;CO_2,\;and\;H_2O$. It was also found that the mass-transfer resistance due to the $H_2$ species slightly increases at higher $CO_2\;and\;H_2O$ flow rates. EIS showed reduction of the lower frequency semi-circle with increasing $H_2O\;and\;CO_2$ flow rate without affecting the high frequency semi-circle.