• 한국주조공학회지
• /
• 제18권5호
• /
• pp.474-480
• /
• 1998

Microstructural characteristics of semi-solid state processed hypereutectic Al-Si alloys have been investigated. Main concern of the present study is to investigate the effects of P and Sr addition on the size and morphology change of the primary Si particles. Refinement of the primary Si particles was observed with the addition of P and Sr at the early stage of semi-solid state processing, but such a refining effects became negligible resulting in Si particles with a near-spherical morphology with continuous stirring. This implies that the microstructural transformation mechanism became more dependent to stirring effects than to the alloying effects during semi-solid state processing. Brittle fracture and agglomeration were proposed as the mechanisms for microstructural alterations during semi-solid state processing.

• Carbon letters
• /
• 제13권2호
• /
• pp.99-108
• /
• 2012

The sol-gel technique has been studied to fabricate a homogeneous Fe-Mo/MgO catalyst. Ambient effects (air, Ar, and $H_2$) on thermal decomposition of the citrate precursor have been systematically investigated to fabricate an Fe-Mo/MgO catalyst. Severe agglomeration of metal catalyst was observed under thermal decomposition of citrate precursor in air atmosphere. Ar/$H_2$ atmosphere effectively restricted agglomeration of bimetallic catalyst and formation of highly-dispersed Fe-Mo/MgO catalyst with high specific surface-area due to the formation of Fe-Mo nanoclusters within MgO support. High-quality thin-multiwalled carbon nanotubes (t-MWCNTs) with uniform diameters were achieved on a large scale by catalytic decomposition of methane over Fe-Mo/MgO catalyst prepared under Ar-atmosphere. The produced t-MWCNTs had outer diameters in the range of 4-8 nm (average diameter ~6.6 nm) and wall numbers in the range of 4-7 graphenes. The as-synthesized t-MWCNTs showed product yields over 450% relative to the utilized Fe-Mo/MgO catalyst, and indicated a purity of about 85%.

• 한국대기환경학회지
• /
• 제27권6호
• /
• pp.681-691
• /
• 2011

The size distributions of smoke particles from fire are prerequisite for the studies on fire detection and adverse health effects. Above the flame of the fire, coagulation dominates and the smoke particles grow from 1 to 50 nm up to 100 to 3,000 nm, sizes ranging from the free-molecular regime to the continuum regime. The characteristics of the agglomeration of the smoke particles are well known, independently for each of the free-molecular and continuum regimes. However, there are not many systematic studies in the entire regime by the complexity of the mechanisms. The purpose of this work is to find the characteristics of the development of the size distribution of smoke particles by agglomeration in the entire size range covering the free-molecular regime, via transition regime, to the near-continuum and continuum regime for each variation of parameters such as fractal dimension, primary particle size and dimensionless coagulation time. In this work, the dynamic equation for the discrete-size spectrum of the particles was solved using a nodal method based on the modification of a sectional method. In the calculation, the collision frequency function for the entire regime, which is derived by using the concept of collision volume and general enhancement function, was applied. The self-preserving size distribution for the entire regime is compared with the ones for the free-molecular or continuum regimes for each variation of the parameters.

• Earthquakes and Structures
• /
• 제13권6호
• /
• pp.589-598
• /
• 2017

In this paper, dynamic response of the horizontal concrete beam subjected to seismic ground excitation is investigated. The structure is reinforced by $Fe_2O_3$ nanoparticles which have the magnetic properties. The hyperbolic shear deformation beam theory (HSDBT) is used for mathematical modeling of the structure. Based on the Mori-Tanaka model, the effective material properties of concrete beam is calculated considering the agglomeration of $Fe_2O_3$ nanoparticles. Applying energy method and Hamilton's principle, the motion equations are derived. Harmonic differential quadrature method (HDQM) along with Newmark method is utilized for numerical solution of the motion equations. The effects of different parameters such as volume fraction and agglomeration of $Fe_2O_3$ nanoparticles, magnetic field, boundary conditions and geometrical parameters of concrete beam are studied on the dynamic response of the structure. In order to validation of this work, an exact solution is used for comparing the numerical and analytical results. The results indicated that applying magnetic field decreases the of the structure up to 54 percent. In addition, increase too much the magnetic field (Hx>5e8 A/m) does not considerable effect on the reduction of the maximum dynamic displacement.

• 한국재료학회지
• /
• 제31권11호
• /
• pp.626-634
• /
• 2021

Cu matrix composites reinforced with chopped carbon fiber (CF), which is cost effective and can be well dispersed, are fabricated using electroless plating and hot pressing, and the effects of content and alignment of CF on the thermal properties of CF/Cu composites are studied. Thermal conductivity of CF/Cu composite increases with CF content in the in-plane direction, but it decreases above 10% CF; this is due to reduction of thermal diffusivity related with phonon scattering by agglomeration of CF. The coefficient of thermal expansion decreases in the in-plane direction and increases in the through-plane direction as the CF content increases. This is because the coefficient of thermal expansion of the long axis of CF is smaller than that of the Cu matrix, and the coefficient of thermal expansion of its short axis is larger than that of the Cu matrix. The thermal conductivity is greatly influenced by the agglomeration of CF in the CF/Cu composite, whereas the coefficient of thermal expansion is more influenced by the alignment of CF than the aggregation of CF.

• Steel and Composite Structures
• /
• 제45권4호
• /
• pp.555-562
• /
• 2022

Improving the mechanical properties of concrete in the construction industry in order to increase resistance to dynamic and static loads is one of the essential topics for researchers. In this work, vibration analysis of elastic nanocomposite beams reinforced by nanoparticles based on mathematical model is presented. For modelling of the strucuture, sinusoidal shear deformation beam theory (SSDBT) is utilized. Mori-anak model model is utilized for obtaining the effective properties of the strucuture including agglomeration influences. Utilizing the energy method and Hamilton's principal, the motion equations are calculated. The frequency of the elastic nanocomposite beam is obtanied by analytical method. The aim of this work is investigating the effects of nanoparticles volume percent and agglomeration, length and thickness of the beam on the frequency of the structure. The results show that the with enhancing the nanoparticles volume percent, the frequency is increased. In addition, the water absorption of the concrete is presented in this article.

• Korean Chemical Engineering Research
• /
• 제53권3호
• /
• pp.333-338
• /
• 2015

본 연구에서는 재생가스조성에 따른 건식 흡수제의 재생률, $CO_2$ 흡수능 그리고 응집 특성에 관한 연구를 실시하였다. 실험은 내경 0.05 m, 높이 0.8 m이며 석영으로 제작된 회분식 기포 유동층 반응기에서 수행되었으며 흡수제는 연속공정의 흡수반응기 후단에서 채취한 입자를 사용하였다. 반응성에 관한 연구는 재생반응 유동화 기체의 조성을 $CO_2$, $H_2O$, $N_2$의 농도를 다양하게 변화시키며 수행하였다. 실험결과 재생온도가 증가함에 따라 흡수반응 동안의 흡수능이 증가하는 경향을 나타내었으며 재생기체에 포함된 수분의 함량이 증가함에 따라 흡수능이 다소 감소하는 경향을 나타내었다. 재생반응기체로 $N_2$ 100%를 사용한 경우 흡수반응 동안의 흡수능이 가장 높게 나타났으며, ($H_2O+N_2$)를 사용한 경우, $CO_2$ 100%를 사용한 경우, ($H_2O+CO_2$)를 사용한 경우 순으로 흡수능이 감소하는 경향을 나타내었다. 또한, 응집특성에 관한 연구는 흡수제의 입자크기 변화와 흡수반응기체에 포함된 수분의 농도가 응집에 미치는 영향을 살펴보았다. 실험결과 수분함량이 높고 입자크기가 작을수록 응집입자가 많이 생성되는 것으로 나타났다.

• 자원리싸이클링
• /
• 제28권5호
• /
• pp.74-79
• /
• 2019

구리이온농도를 117.15 mg/L로 조절한 모의 광산배수용액 제조하고, 세멘테이션제로서 철분을 투입하여 세멘테이션 공정 중 구리이온제거효율에 대한 철분당량, 철분크기, 교반속도의 영향을 조사하였다. 교반속도가 200 rpm의 경우, 온도 $20^{\circ}C$에서 2 당량의 철분을 투입하면 90분에 51 %의 구리가 제거되었으나 16 당량의 철분을 투입하면 60분에 99 % 이상의 구리가 제거되었다. $48{\mu}m$ 이하와 $150{\mu}m$ 크기의 철분을 2당량 투입하여 구리제거율을 관찰한 결과 200 rpm에서는 큰 차이를 나타내지 않았으나 교반속도를 400 rpm으로 증가시킨 경우 두 입도 모두에서 구리제거효율을 크게 증가하였으며, 이는 200 rpm에서 철분의 입자가 응집되어 비표면적이 감소된 것이 원인으로 SEM분석을 통해 확인하였다. 교반속도 600 rpm, 반응온도 $20^{\circ}C$, $48{\mu}m$ 이하 철분 2 당량의 조건에서 60 분에 99 % 이상의 구리가 제거된 것을 확인하였다.

• 국제지역연구
• /
• 제20권3호
• /
• pp.45-80
• /
• 2016

본 논문은 동남아시아의 2000년대 이후의 도시화의 현황에 대해 도시면적비율, 도시화율, 도시인구밀도 등의 세 가지 지표를 중심으로 살펴보았다. 또한 Williamson의 가설을 활용하여 도시화가 경제성장에 미치는 영향에 대한 실증분석을 실시하였다. 그리고 추정계수를 활용하여 도시화가 경제성장에 긍정적인 영향을 미치기 시작하는 임계점을 산출하고 동남아시아 각 국가들의 현황과 비교 분석하였다. 동남아시아의 도시화율의 증가세에 비해 도시인구밀도가 더욱 빨리 증가하고 있다는 것을 보여주고 있고 이는 인구과밀화 현상이 빨리 진행되고 있음을 의미한다. 실증분석결과를 보면 본 연구에서 상정한 두 가지 추정방정식 모두에서 Williamson의 가설과 반대되는 결과를 얻었다. 이는 경제발전단계 및 소득수준이 낮은 국가인 경우 도시화가 경제성장에 긍정적 영향을 미치지만, 소득수준이 일정수준(임계점)을 넘어서게 되면 도시화가 오히려 경제성장에 부정적인 영향을 미칠 수 있다는 본 연구의 가설이 지지되지 못함을 의미한다. 동남아시아의 도시화는 지역화경제 및 도시화경제로 대표되는 집적의 경제가 일정정도 실현되고 있고 또한 지식이전 및 아이디어의 활발한 교환, 생산성의 향상 등을 통해 경제성장에 긍정적인 영향을 미치고 있음을 의미한다. 따라서 동남아시아의 도시화의 의미를 고찰함에 있어 경제성장에 긍정적 영향을 미치는 집적의 경제, 지식이전 등의 효과를 극대화하기 위한 정책적 배려와 노력이 필요다고 할 수 있다.

• 한국분말재료학회지
• /
• 제16권2호
• /
• pp.131-137
• /
• 2009

This paper deals with the effects of the surfactant and preplate process (sensitization and activation) on electroless copper plating on carbon nano-fiber (CNF). Ultrasonic irradiation was applied both during dispersion of CNF and during electroless plating containing preplate process. The dispersion of CNF and flatness of the plated copper film were discussed based on the changes in surfactant concentration and preplate process time. It was clearly shown that high concentration of surfactant and long time of preplate process could promote the agglomeration of CNF and uneven copper plating on CNF.