• 자원리싸이클링
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• 제26권6호
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• pp.91-96
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• 2017

알칼리 용융법과 수 침출을 이용하여 탄화텅스텐(WC)으로부터 텅스텐(W) 회수에 관한 연구를 실시하였다. 알칼리 용융 처리는 알칼리염의 종류, 용융온도 및 용융시간을 변화시키면서 실시하였으며, 수 침출은 $25^{\circ}C$, 2시간 및 슬러리 농도 10 g/L로 고정하여 실시하였다. 알칼리염으로 질산나트륨($NaNO_3$)만 단독으로 사용한 경우, W의 수 침출율은 63.3%이었지만, 용융 첨가제인 수산화나트륨(NaOH) 혼합량이 증가할수록 침출율은 증가하였으며, 몰비 $WC:NaNO_3:NaOH=1:2:2$로 혼합한 용융물에서는 97.8%까지 증가하였다. NaOH는 용융 반응의 반응열 증가로 인한 반응 촉진제 역할을 한 것으로 판단된다.

• 자원리싸이클링
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• 제14권6호
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• pp.3-9
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• 2005

본 연구에서는 CRT용 폐세륨연마재 건조분말로부터 수산화세륨을 선택적으로 분리회수 하고자 하였다. 폐세륨연마재에는 산화희토류가 약 $64.5\%$ 함유되어 있으며, 이중 산화세륨은 $36.5\%$로서 전체 희토류 중 $56.3\%$를 차지한다. 산화세륨은 희토류원소들 중에서 가장 안정된 형태로 이에 대한 분해가 용이하지 않다. 그러므로 황산화반응을 이용하여 산화희토류 및 산화세륨을 분해하고 수침출을 통하여 희토류의 분리 $\cdot$회수율을 향상시키고자 하였다 침출용액의 희토류는 황산나트륨을 이용한 복염[$\Re{\cdot}Na(SO_{4})_{2}$] 형태로 회수한 후, 수산화나트륨 수용액에 투입하여 수산화희토류 슬러리를 제조하였다. 공기 접촉에 의하여 3가 수산화세륨을 4가 수산화세륨으로 산화시킨 후 산도조절에 의하여 기타 수산화희토류로부터 수산화세륨을 분리하였다.

• Advances in concrete construction
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• 제13권1호
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• pp.25-34
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• 2022

The production of geopolymer is considered as a cleaner process due to much lower CO₂ emission than that from the production of Portland cement. This paper presents a study of the potential use of recycled steel fibre (RSF) coming from the recycling process of the old tires in geopolymer mortars. Ground expanded perlite (EP) is used as a source of alumino-silicate and sodium hydroxide (NaOH=5, 10, 15, and 20M) is used as alkaline medium for geopolymer synthesis. RSFs were added to the mortar mixtures in four different volume fractions (0, 0.5, 1.0, and 1.5% of the total volume of mortar). The unit weight, ultrasound pulse velocity, flexural and compressive strength of expanded perlite based geopolymer mortar (EPGM) mixtures were determined. The microstructures of selected EPGMs were examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses. The optimum molarity of sodium hydroxide solution was found to be 15M for geopolymer synthesis by EP. The test results revealed that RSFs can be successfully used for fibre-reinforced geopolymer production.

• 한국작물학회지
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• 제29권1호
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• pp.98-101
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• 1984

인삼종자의 내과지는 배생장을 현저히 억제시켰다. 이 억제작용은 내과지에 의한 수분흡수 때문이 아니라 기계적인 것으로 추측되어졌다. 수산화나트리움 2.5％ 용액에 인참종자를 10분 내지 30분 침적시키므로써 배생장을 촉진시킬 수 있었으나 황산처리는 인삼종자의 배생장에 영향을 주지 못했다.

• 한국수소및신에너지학회논문집
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• 제33권4호
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• pp.343-352
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• 2022

Co/Al₂O₃ nanopowder was used as a catalyst to investigate the effect of catalyst support, reduction temperature, sodium borohydride (NaBH₄) concentration, sodium hydroxide (NaOH) concentration, and reaction temperature on the characteristics of NaBH₄ hydrolysis. The Co/Al₂O₃ nanopowder showed a high catalytic activity among various catalysts. Catalyst reduction at 250℃ exhibited a relatively good activity. The activity decreased with an increase in the NaBH₄ concentration. Conversely, the activity increased and then decreased with an increase in the NaOH concentration. Additionally, the activity increased with an increase in the reaction temperature. The value of apparent activation energy was 40.81 kJ/mol, which was lower than the other Co-based catalysts. Thus, Co/Al₂O₃ nanopowder catalyst can be widely used for NaBH₄ hydrolysis owing to its superior catalytic activity.

• Carbon letters
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• 제24권
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• pp.62-72
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• 2017

The aim of this work was to evaluate the dielectric properties of impregnated and activated palm kernel shells (PKSs) samples using two activating agents, potassium carbonate ($K_2CO_3$) and sodium hydroxide (NaOH), at three impregnation ratios. The materials were characterized by moisture content, carbon content, ash content, thermal profile and functional groups. The dielectric properties were examined using an open-ended coaxial probe method at various microwave frequencies (1-6 GHz) and temperatures (25, 35, and $45^{\circ}C$). The results show that the dielectric properties varied with frequency, temperature, moisture content, carbon content and mass ratio of the ionic solids. PKSK1.75 (PKS impregnated with $K_2CO_3$ at a mass ratio of 1.75) and PKSN1.5 (PKS impregnated with NaOH at a mass ratio of 1.5) exhibited a high loss tangent ($tan{\delta}$) indicating the effectiveness of these materials to be heated by microwaves. $K_2CO_3$ and NaOH can act as a microwave absorber to enhance the efficiency of microwave heating for low loss PKSs. Materials with a high moisture content exhibit a high loss tangent but low penetration depth. The interplay of multiple operating frequencies is suggested to promote better microwave heating by considering the changes in the materials characteristics.

• 한국결정성장학회지
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• 제22권3호
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• pp.152-157
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• 2012

본 연구는 알칼리 활성화제로 NaOH와 물유리를 사용하고 리젝트애쉬와 고로슬래그를 혼합하여 지오폴리머를 제조하였다. 리젝트애쉬와 고로슬래그의 치환율과 물유리와 NaOH의 농도에 따른 압축강도를 측정하였다. 압축강도 측정결과로는 알칼리 활성화제로 NaOH 1 wt%, 물유리 3 wt%와 전량 고로슬래그를 사용한 경우 재령 28일차 강도가 38.91 MPa의 성능을 나타내었다. 압축강도 증진의 중요한 요인은 알칼리 활성화제의 비율과 리젝트애쉬와 고로슬래그의 치환율에 의한 것이었다.

• Advances in concrete construction
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• 제8권3호
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• pp.217-223
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• 2019

This paper presents the mechanical and microstructural properties of the geopolymer paste which was developed by utilizing the industrial by-products, rice husk ash (RHA) and ultra-fine slag. Ultra-fine slag particles with average particle size in the range of 4 to 5 microns. RHA is partially replaced with ultra-fine slag at different levels of 0 to 50%. Sodium silicate to sodium hydroxide ratio of 1.0 and alkaline liquid to binder (AL/B) ratio of 0.60 is taken. Setting time, compressive, flexural strengths were studied up to the age of 90 days with different concentrations of NaOH. The microstructure of the hybrid geopolymer paste was studied by performing the SEM, EDS, and XRD on the broken samples. RHA based geopolymer paste blended with ultrafine slag resulted in high compressive and flexural strengths and increased setting times of the paste. Strength increased with the increase in NaOH concentration at all ages. The ultra-small particles of the slag acted as a micro-filler into the paste and enhanced the properties by improving the CASH, NASH, and CSH. The maximum compressive strength of 70MPa was achieved at 30% slag content with 16M NaOH. The results of XRD, SEM, and EDS at 30% replacement of RHA with ultra-fine slag densified the paste microstructure.

• 한국섬유공학회:학술대회논문집
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• 한국섬유공학회 2003년도 The Korea-Japan Joint Symposium
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• pp.83-84
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• 2003

The microstructure and tensile properties of ramie treated with NaOH and crosslinked with 1, 2, 3, 4-butanetetracarboxylic acid were characterised. X-ray diffraction and FTIR were used to study the crystalline structure o f the resultant ramie yarns. Results showed that the maximum change in the structure of the modified ramie took place at 16% NaOH, which would completely transform Cellulose I to Cellulose II. Also, the crystallinity index and fibre orientation decreased to the minimum value while the absorption properties were enhanced. The average degree of polymerization of the treated ramie yams slightly decreased after NaOH treatment.

• 한국재료학회지
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• 제21권6호
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• pp.327-333
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• 2011

Nanostructured cobalt materials have recently attracted considerable attention due to their potential applications in high-density data storage, magnetic separation and heterogeneous catalysts. The size as well as the morphology at the nano scale strongly influences the physical and chemical properties of cobalt nano materials. In this study, cobalt nano particles synthesized by a a polyol process, which is a liquid-phase reduction method, were investigated. Cobalt hydroxide ($Co(OH)_2$), as an intermediate reaction product, was synthesized by the reaction between cobalt sulphate heptahydrate ($CoSO_4{\cdot}7H_2O$) used as a precursor and sodium hydroxide (NaOH) dissolved in DI water. As-synthesized $Co(OH)_2$ was washed and filtered several times with DI water, because intermediate reaction products had not only $Co(OH)_2$ but also sodium sulphate ($Na_2SO_4$), as an impurity. Then the cobalt powder was synthesized by diethylene glycol (DEG), as a reduction agent, with various temperatures and times. Polyvinylpyrrolidone (PVP), as a capping agent, was also added to control agglomeration and dispersion of the cobalt nano particles. The optimized synthesis condition was achieved at $220^{\circ}C$ for 4 hours with 0.6 of the PVP/$Co(OH)_2$ molar ratio. Consequently, it was confirmed that the synthesized nano sized cobalt particles had a face centered cubic (fcc) structure and with a size range of 100-200 nm.