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Dielectric/Magnetic Nanowires Synthesized by the Electrospinning Method for Use as High Frequency Electromagnetic Wave Absorber

  • Jwa, Yong-Ho
    • Proceedings of the Materials Research Society of Korea Conference
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    • 2009.11a
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    • pp.14-14
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    • 2009
  • High frequency electromagnetic(EM) waves are increasingly being applied in industries because of saturationat lower frequency bands as a result of huge demand. However, electromagneticinterference (EMI) has become a serious problem, and as a result, highfrequency EM absorbers are now being extensively studied. Also, recentdevelopments in absorber technology have focused on producing absorbers thatare thin, flexible, and strong. Hence, one-dimension ferrous nano-materials area potential research field, because of their interesting electronic andmagnetic properties. Commercially, EM wave absorbing products are made ofcomposites, which blend the insulating polymer with magnetic fillers. Inparticular, the shape of the magnetic fillers, such flaky, acicular, or fibrousmagnetic metal particles, rather than spherical, is essential for synthesizingthin and lightweight EM wave absorbers with higher permeability. High aspectratio materials exhibit a higher permeability value and therefore betterabsorption of the EM wave, because of electromagnetic anisotropy. Nanowires areusually fabricated by drawing, template synthesis, phase separation, selfassembly, and electrospinning with a thermal treatment and reduction process.Producing nanowires by the electrospinning method involves a conventionalsol-gel process that is simple, unique, and cost-effective. In thispresentation, Magnetic nanowire and dielectric materials coated magneticnanowire with a high aspect ratio were successfully synthesized by theelectrospinning process with heat treatment and reduction. In addition toestimating the EM wave absorption ability of the synthesized magnetic anddielectric materials coated magnetic nanowire with a network analyzer, weinvestigated the possibility of using these nanowires as high-frequency EM waveabsorbers. Furthermore, a wide variety of topics will be discussed such as thetransparent conducting nanowire and semiconducting nanowire/tube with theelectrospinning process.

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A Study on Microstructure and Thoughness of Electrogas Weldments (일렉트로가스 용접부의 조직 및 인성에 관한 연구)

  • 이해우;장태원;이윤수;석한길;강성원
    • Journal of Welding and Joining
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    • v.14 no.1
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    • pp.68-74
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    • 1996
  • The microstructure of HAZ and the mechanical properties in weldments such as hardness and toughness were studied for mild steel and AH36 grade TMCP steel, as increasing heat input with electrogas welding process. The results of this study can be summarized as follow: 1) In the HAZ of mild steel, the width of coarse grained zone was larger than that of the nomalized zone, however in the case of TMCP steel, the nomalized zone was wider than the coarse grained zone. 2) The grain size of HAZ become coarse with increasing heat input. And at the same heat input, the grain size of TMCP steel was more coarser than that of mild steel. 3) According to the change of heat input, the deviation of hardness values was not significant, and the maximum values of hardness was not in HAZ but in the weld metal. And the hardness values in root part was higher than in face part. 4) Even though the HAZ grain size of mild steel was larger than that of TMCP steel, the impact values for mild steel was higher than those for TMCP steel, and the impact values in face part was higher than those in root part.

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Effect of Heat Input on the Mechanical Properties of SA508 class 3 Steel Weldments with Submerged Arc Welding (SA508 class 3 서브머지드 아크용접부의 기계적 성질에 미치는 입열량의 영향)

  • Seo Yun-seok;Koh Jin-Hyun;Kim Nam-Hoon;Oh Se-Yong;Choo Kee-Nam
    • Journal of Welding and Joining
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    • v.22 no.5
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    • pp.38-45
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    • 2004
  • The present study is to investigate the effect of heat input on the microstructure, tensile properties and toughness of single-pass submerged arc bead-in-groove welds produced on SA508 class 3 steels. The heat input was varied in the range of 1.6, 3.2 and 5.0 kJ/mm. The toughness of weld metals was evaluated by using subsize Charpy V-notch specimens in the temperature range of -19$0^{\circ}C$ to 2$0^{\circ}C$. The weld microstructure and fractography were observed by optical and scanning electron microscopies, respectively. With increasing heat inputs, tensile strength and hardness of weld metals were decreased while elongation was increased. The poor notch toughness at 1.6 kJ/mm was attributed to the formation of ferrite with aligned second phase and banitic microstructure with high yield strength while that at 5.0 kJ/mm was due to the presence of grain boundary and polygonal ferrites. The microstructure of the intermediate energy input welds consisted of a high proportion of acicular ferrite with limited polygonal ferrites, which provide improved notch toughness.

Morphology of Lead Titanate Prepared by Wet Chemical Methods (습식화학법으로 제조된 티탄산 납의 형상)

  • 최병철;이문호
    • Korean Journal of Crystallography
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    • v.3 no.1
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    • pp.1-8
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    • 1992
  • The morphology of lead titanate powders prepared by sol-gel and coprecipitation techniques was investigated as a function of firing temperature and soaking time. PbTiO3 precursor powders were derived from a mixed solution of lead nitrate and titanium tetrachloride at 40℃ to 43℃ and pH of 9.0 to 9.7, and fired at temperatures 350-1000℃ for 1-10h in air. An increase of particle size and agglomeration with increasing calcination temperature and duration could be observed. By annealing sol-gel derived powder at 700℃, the tially-formed acicular(and/or prismatic) primary particles transformed to polyhedral shape with soaking time, and further soaking caused coarsening the polyhedral particles with rounded edges. However, the morphology of the coprecipitated powders was not varied during crystallization.

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Evaluation of Weldability on Identical and Dissimilar Welding Parts of Austenite Stainless Steel by GTAW (오스테나이트 스테인리스강에 대한 가스텅스텐 아크용접 시동종 및 이종 용접부의 용접성 평가)

  • Han, Min-Su;Park, Jae-Cheul;Kim, Seong-Jong
    • Journal of Advanced Marine Engineering and Technology
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    • v.35 no.1
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    • pp.68-74
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    • 2011
  • This papers investigated the mechanical characteristics and the weldability of identical as well as dissimilar welding by GTAW for STS 304 and STS 316L. It is applied to double wall gas pipe of duel fuel engine for LNG carrier. Consequently, the weldability of dissimilar and identical welded zone of STS 304 decreased compared to base metal significantly. The result of microstructure observation for welded zone, a degree of acicular ferrite in welding zone for STS 304 presented more than STS 316L. The hardness of welding zone for STS 304 presented higher value than that for STS 316L by this effect.

The effect of Heat input, Shielding Gas(Ar80% + $CO_2$20%), PWHT on the mechanical properties of HSB600 steel Weldments (HSB600강 용접에서 입열량, 보호가스, 용접후 열처리가 미세조직과 기계적 특성에 미치는 영향)

  • Ju, Dong-Hwi;Lim, Young-Min;Kim, Nam-Hoon;Koh, Jin-Hyun
    • Proceedings of the KAIS Fall Conference
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    • 2011.12b
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    • pp.394-397
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    • 2011
  • The effects of heat input(1.4~3.2kJ/mm), shielding gas(Ar80%+$CO_2$20%) and postweld heat treatment(PWHT, $600^{\circ}C$, 40hr.) on the TMCP HSB600 steel weldments made by GMAW process were investigated. The tensile strength and CVN impact energy of as-welded specimens decreased with increasing heat input. The fine-grained acicular ferrite was mainly formed in the low heat input while polygonal and side plate ferrites were dominated in the high inputs. High performance steel for bridges requires higher performance in tensile and yield strength, toughness, weldability, etc. Thus, the purpose of the experiment is to study HSB 600 in GMAW.

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The Fabrication of High Strength 7XXX Aluminum Alloy Powders by Centrifugal Disc Atomization (원심분무법에 의한 고강도 7XXX 알루미늄 합금 분말의 제조)

  • Lee, Tae-Hang;Im, Seong-Moo;Cho, Sung-Suk
    • Journal of Korea Foundry Society
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    • v.10 no.6
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    • pp.528-537
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    • 1990
  • 7XXX aluminum alloy powders produced by the self-manufactured rotating disc atomizer were investigated to determine the influence of the atomization parameters on the particle size distributions in air atmosphere. The particle size distributions are almost always bimodal with the dominant mode on the large particle size. Average powder size of 7XXX aluminum alloy is $74/{\mu}m~125/{\mu}m$ when melt is poured with the rate of 9g /sec at 730$^{\circ}C$ on a rotating disc of 30㎜ diameter at 6300rad/sec. The mass of finer particle increased when disc diameter, angular velocity, pouring temperature increased and pouring rate decreased. The powder shapes of bimodal change from acicular to tear-drop and from tear-drop to ligament with increasing powder size. Powder shape was determined by the atomization mechanism and oxidation in liquid state. Microstructure of powders appeared to be cell and cellular dendrite. The SDAS of Al-7.9wt%Zn-2.4wt%Mg-1.5wt%Cu-0.9wt%Ni Powders is $0.8{\mu}m~1.0{\mu}m$ for the powders of $size+44{\mu}m~53{\mu}m$ and $1.6{\mu}m∼1.8{\mu}m$ for the powders of $size+105{\mu}m~125{\mu}m$, repectively.

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Microstructure Characteristics and Identification of Low-Carbon Steels Fabricated by Controlled Rolling and Accelerated Cooling Processes (제어 압연과 가속 냉각에 의해 저탄소강에서 형성되는 미세조직의 특징과 구분)

  • Lee, Sang-In;Hong, Tae-Woon;Hwang, Byoungchul
    • Korean Journal of Materials Research
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    • v.27 no.11
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    • pp.636-642
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    • 2017
  • In the present study the microstructure of low-carbon steels fabricated by controlled rolling and accelerated cooling processes was characterized and identified based on various microstructure analysis methods including optical and scanning electron microscopy, and electron backscatter diffraction(EBSD). Although low-carbon steels are usually composed of ${\alpha}-ferrite$ and cementite($Fe_3C$) phases, they can have complex microstructures consisting of ferrites with different size, morphology, and dislocation density, and secondary phases dependent on rolling and accelerated cooling conditions. The microstructure of low-carbon steels investigated in this study was basically classified into polygonal ferrite, acicular ferrite, granular bainite, and bainitic ferrite based on the inverse pole figure, image quality, grain boundary, kernel average misorientation(KAM), and grain orientation spread(GOS) maps, obtained from EBSD analysis. From these results, it can be said that the EBSD analysis provides a valuable tool to identify and quantify the complex microstructure of low-carbon steels fabricated by controlled rolling and accelerated cooling processes.

CONTROL OF NITROGEN CONTENT FOR THE IMPROVEMENT OF HAZ

  • Bang, Kook-soo;Kim, Byong-chul;Kim, Woo-yeul
    • Proceedings of the KWS Conference
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    • 2002.10a
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    • pp.229-234
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    • 2002
  • The variation of HAZ toughness with nitrogen content and weld cooling rate was investigated and interpreted in terms of both microstructure and the amount of free nitrogen. The presence of free nitrogen in HAZ was investigated by internal friction measurement and its amount was measured by hydrogen hot extraction analysis. Both nitrogen content and weld cooling rate influenced HAZ microstructure and high toughness was obtained at a mixed microstructure of acicular ferrite, feffite sideplate and polygonal ferrite. If nitrogen content is too low or cooling rate is too fast, bainitic microstructure is obtained and toughness is low. On the other hand, if nitrogen content is too high or cooling rate is too slow, coarse polygonal ferritic microstructure is obtained and toughness is deteriorated again. ill addition to the microstructural change, high nitrogen content also resulted in a large amount of free nitrogen. Therefore, nitrogen content should be kept as low as possible even if the mixed micostructure is obtained. In this experimental condition, the maximum toughness was obtained at 0.006% nitrogen content when weld cooling time ($\Delta$t$_{8}$5/)) is 60s.TEX>5/)) is 60s.

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Comparison of Mechanical Properties and Microstructural Charateristies of Tandem GMAW Weld Metal in 490MPa Grade Steel (490MPa급 고장력강 탄뎀 가스메탈아크 용접부에 대한 기계적 성질과 미세조직 비교)

  • Yi, Hui-Jun;Kang, Sung-Soo;Yu, Gum-Bin;Bae, Won-Hak;Moon, Hyun-Soo
    • Journal of Welding and Joining
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    • v.27 no.2
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    • pp.76-81
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    • 2009
  • Tandem GMAW is one of the high performance welding process and used in many industries to increase the productivity. An evaluation is presented of the mechanical properties and microstructural characteristics of the Tandem GMAW and conventional Single GMAW welds in 30mm thickness 490MPa grade steel by comparison method. Welding sequence and bead with and hight was kept, avoiding the effect of the bead shape and welding sequence. Tension, bending, hardness and Charpy impact test results of Tandem GMAW met the requirement of specification and showed similar distribution with conventional Single GMAW. Volume fraction of ferrite phase in weld metal showed little difference between Tandem GMAW and Single GMAW