• 한국재료학회지
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• 제33권4호
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• pp.135-141
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• 2023

The volatilization of alkali ions in (K,Na)NbO₃ (KNN) ceramics was inhibited by doping them with alkaline earth metal ions. In addition, the grain growth behavior changed significantly as the sintering duration (t_s) increased. At 1,100 ℃, the volatilization of alkali ions in KNN ceramics was more suppressed when doped with alkaline earth metal ions with smaller ionic size. A Ca²⁺-doped KNN specimen with the least alkali ion volatilization exhibited a microstructure in which grain growth was completely suppressed, even under long-term sintering for t_s = 30 h. The grain growth in Sr²⁺-doped and Ba²⁺-doped KNN specimens was suppressed until t_s = 10 h. However, at t_s = 30 h, a heterogeneous microstructure with abnormal grains and small-sized matrix grains was observed. The size and number of abnormal grains and size distribution of matrix grains were considerably different between the Sr²⁺-doped and Ba²⁺-doped specimens. This microstructural diversity in KNN ceramics could be explained in terms of the crystal growth driving force required for two-dimensional nucleation, which was directly related to the number of vacancies in the material.

• 환경위생공학
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• 제15권1호
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• pp.95-101
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• 2000

This study was investigated to the reaction of alumina sintering with alkaline. The soluble $NaAlO_2$ was made after the commercial ${\alpha}-Al_2O_3$ was calcinated with NaOH. The reaction of alumina was carried out to be based on the effects of calcination temperature, time, and the mixing ratio of ${\alpha}-Al_2O_3/NaOH$. The alumina was calcined over $500^{\circ}C$ with NaOH powder after it was sieved with 170/270 mesh. The calcined alumina with NaOH powder was dissolved into $25^{\circ}C$ distilled water and filtrated, and HCI was added to adapt pH 6.5~7.5. The residue was separated with vacuum pump for filtration after it was adapted to proper pH, and aluminum compound was precipitated with $Al(OH)_3$. The investigation was carried out with the variables; the calcination temperature($500-900^{\circ}C$), the calcination time (30~90 min), and the concentration of HCI when leaching(0.5~3.0N) respectively. In this investigation, the main product of ${\alpha}-Al_2O_3$ and NaOH was $NaAlO_2$ and the maximum conversion ratio was 91.4% under the optimum conditions as followed ; the ratio of NaOH/${\alpha}-Al_2O_3$ was 1.5 and the calcination conditions were $800^{\circ}C$ and 90 min.

• 한국재료학회지
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• 제32권2호
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• pp.85-93
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• 2022

Porous mullite-corundum ceramics were prepared using organic foam impregnation method with alumina and silica as raw materials. The influence of alkaline treatment and surfactant modification on polyurethane foam were studied. Effects of sintering process and material composition on porous mullite-corundum ceramics were investigated. The results show that the hang-pulp quantity of polyurethane foam increases with alkaline treatment. After treatment with 3 wt% SDS solution, the hang-pulp quantity of polyurethane foam further improved. Open porosity of sample decreased with elevation of sintering temperature and holding time, and compressive strength of sample showed a trend opposite to the change of porosity. The open porosity of the sample was enhanced by the increase of m(Al₂O₃/SiO₂); the compressive strength decreased with increase of m(Al₂O₃/SiO₂). However, when m(Al₂O₃/SiO₂) was 2.5, the compressive strength of the sample reached 6.23 MPa, and the open porosity of the sample was 80.7 %.

• 한국재료학회지
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• 제17권2호
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• pp.107-114
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• 2007

Porous Ti compacts were fabricated by spark plasma sintering (SPS) method and their in vitro and in vivo biocompatibilities were investigated. Alkaline phosphatase (ALP) activity representing the activity of osteoblast was increased when osteoblast-like MG-63 cells were cultured on the Ti powder surface. Some genes related to cell growth were over-expressed through microarray analysis. The porous Ti compact with 32.2% of porosity was implanted in the subcutaneous tissue of rats to confirm in vivo cytotoxicity. 12 weeks post-operation, outer surface and inside the porous body was fully filled with fibrous tissue and the formation of new blood vessels were observed. No inflammatory response was confirmed. To investigate the osteoinduction, porous Ti compact was implanted in the femur of NZW rabbits for 4 months. Active in-growth of new bone from the surrounded compact bone was observed around the porous body. From the results, The porous Ti compacts fabricated by spark plasma sintering might be available for the application of the stem part of artificial hip joint.

• 한국세라믹학회지
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• 제32권5호
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• pp.635-641
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• 1995

The effects of A-site substitution with alkaline-earth ions (Ca, Sr and Ba) on the perovskite-phase formation and dielectric properties for Pb1-xMx(Zn1/3Nb2/3)O3 (0.0 x 0.5)-based relaxors were studied. Considerable improvements in the sinterability and the extent fo perovskite formation were observed with increasing the A-site substitution (x) and sintering temperature. The maximum dielectric permittivity appeared at x=0.1 for Sr and Ba substitutiion, while the relative dielectric permittivity was almost invariant in the case of Ca ion substitution. Curie temperature decreased with increasing relative amount of Sr and Ba ions but was almost invariant in case of Ca ion substitution. With increasing the amount of x, the diffuseness parameter ($\delta$) increased but the maximum dielectric constant decreased, demonstrating an enhanced diffuse phase transition (DPT) in the presence of alkaline-earth cations.

• Journal of the Optical Society of Korea
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• 제19권3호
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• pp.217-221
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• 2015

Developing a metallization that has low cost and high efficiency is essential in solar-cell industries, to replace expensive silver-based metallization. Ni/Cu two-step metallization is one way to reduce the cost of solar cells, because the price of copper is about 100 times less than that of silver. Alkaline electroless plating was used for depositing nickel seed layers on the front electrode area. Prior to the nickel deposition process, 2% HF solution was used to remove native oxide, which disturbs uniform nickel plating. In the subsequent step, a nickel sintering process was carried out in $N_2$ gas atmosphere; however, copper was plated by light-induced plating (LIP). Plated nickel has different properties under different bath conditions because nickel electroless plating is a completely chemical process. In this paper, plating bath conditions such as pH and temperature were varied, and the metal layer's structure was analyzed to investigate the adhesion of Ni/Cu metallization. Average adhesion values in the range of 0.2-0.49 N/mm were achieved for samples with no nickel sintering process.

• 환경위생공학
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• 제15권1호
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• pp.62-68
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• 2000

This study was investigated to the recovery of alumina from the first calcined waste pottery using alkaline sintering. This study was based on calcination result of a commercial ${\alpha}-Al2_O_3$ with NaOH powder. $NaAlO_2$ was formed by calcination of ${\alpha}-Al_2O_3$ with NaOH and conversion of $NaAlO_2$ from ${\alpha}-Al_2O_3$ was 91.4% at calcination condition ; weight ritio of $NaOH/{\alpha}-Al2_O_3$ 1.5, $800^{\circ}C$, and 90min. The first calcined waste porrery from the manufacturing Procedure of H Ltd. was grinded to 170/270mesh by a ball mill and calcined over $500^{\circ}C$ with NaOH powder. The calcined sample was dissolved in $25^{\circ}C$ water and sodiumaluminosilicate solid was formed. After filtration, the contained aluminum was leached out by dissolving sodiumaluminosilicate solid in 1N HCl. We estimated the efficiency of Al extraction from waste pottery by ICP analysis and NaOH was added to the filtrate and then aluminum compound was precipitated with $Al(OH)_3$ and recovered. The investigation was carried out with the variables ; the calcination temperature($500-900^{\circ}C$), the calcination time(30~90min), and the weight ratio of NaOH/waste pottery(0.5~1.5). The treatment efficiency of the waste pottery and the recovery of Al as 97.9%, 91.9% were obtained under the optimum conditions as followed ; the weight ratio of NaOH/waste pottery was 1.5 and the calcination conditions were $900^{\circ}C$ and 60min.

• 한국세라믹학회지
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• 제16권1호
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• pp.31-37
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• 1979

The middle point of composition within the system $MgO-Al_2O_3-SiO_2$ has been studied for applicability as ceramics dielectrics. A Kyul Sung Tale of high purity, magnesia clinker of Sam-wha chemical company, C.P. aluminium oxide, calcium carbonate, red lead, barium carbonate which was made into frit were used the raw materials. A number of steatite ceramics were prepared under carefully controlled condition and the water absorption, linear shrinkage, power factor, dielectric constant and dielectric loss were measured at elevated temperature. When we used magnesia clinker as flux, the quantity of this flux was 0.05mole, sintering temperature was continued for 2 hrs. at 1, 27$0^{\circ}C$. From this conditions, we could get the data whose power factor was 0.142%, water absorption was zero, linear shrinkage was 8.76%, dielectric constant was 5.63, dielectric loss was 0.00799. When we used red lead as flux, the quantity of this flux was 0.033mole and 0.066mole, sintering temperature was continued for 2hrs. at 1, 26$0^{\circ}C$. From this conditions, we could get the data whose water absorption was zero, linear shrinkage was 8.03%, and 8.48%, power factor was 0.136% and 0.062%, dielectric loss was 0.0072 and 0.0037. When we used barium carbonate made into frit as flux, the quantity of this flux was 0.02mole, sintering temperature was continued for 2hrs. at 1, 27$0^{\circ}C$. From this conditions, we could get the data whose water absoption was zero, linear shrinkage was 8.44%, power factor was 0.138%, dielectric constant was 5.69, dielectric loss was 0.0074.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.48-48
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• 2008

현재 압전재료로써 사용되고 있는 PZT계 세라믹스는 우수한 압전 및 유전특성으로 초음파 센서, 압전변압기, 액츄에이터, 필터, 레조네이터와 같은 여러 응용분야에 널리 사용되어지고 있다. 그러나 납을 60%이상 포함하므로 환경오염에 의하여 그 사용에 대한 규제가 강화되고 있어 최근에는 납을 함유하지 않은 무연 환경친화형 압전세라믹스가 주목받고 있다. 현재 무연 조성 세라믹스에는 텅스텐-브론즈 형, 비스머스 레이어형, 페로브스카이트 형 등이 이으며, 그 중 페로보스카이트 혈을 제외하고는 보통 소성법 조제시 낮은 압전특성을 갖는다. 그러므로 압전특성을 증가시키기 위하여 Hot pressing, Hot forging, RTGG(Reactive Template Grain Growth), SPS(Spark Plasma Sintering), 그러나 이는 무연 세라믹스의 대량생산 과정에서 어려운 문제를 가지고 있고, 저가격 관점에서 볼 때 보통소성법이 보다 바람직하다. 그래서 보통소성법으로 NKN세라믹스의 소결성을 향상 시키고 비교적 높은 압전특성을 얻기 위해서 $LiSbO_3$, $LiNbO_3$, $LiTaO_3$, alkaline-earth(Mg, Ca, Sr, Ba) 등을 첨가한 논문들이 보고되고 있으며, 이러한 재료들의 kp는 대략 0.3-0.4를 나타내고 있다. 따라서, 본 연구에서는 소결온도를 낮추고자 $Ag_2O$를 소결조제로 사용하였고 유전 및 압전특성을 높이고자 소결시간 변화시켜 시편을 제작하여 NKN 세라믹스의 유전 및 압전특성을 조사하였다.

• 공업화학
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• 제4권2호
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• pp.373-380
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• 1993

알칼리형 연료전지의 수소극 촉매로 사용되는 Raney 니켈의 제조방법과 조촉매 첨가에 따른 전극특성을 전기화학적 방법을 통하여 고찰하였다. Raney 니켈은 소결온도를 $700^{\circ}C$로 하고 니켈 대 알루미늄의 함량비를 중량비 60:40으로 하여 제조한 것이 전극성능이 우수하였다. 조촉매로 티타늄을 첨가하면 촉매활성과 전극특성이 증가함을 알았으며 특히 2w/o의 티타늄이 첨가된 전극이 2.4A/g의 가장 우수한 질량활성을 갖고 있었고 이때의 촉매의 평균 입자크기는 $5.8{\mu}m$였다. 임피던스법에 의해 전극반응의 거동을 평가하였으며 티타늄이 2w/o 첨가된 전극에서의 저항값과 capacity를 측정한 결과 $0.3{\Omega}cm^2$, $0.42F/cm^2$을 나타내었다.