• 한국재료학회지
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• 제31권7호
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• pp.397-402
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• 2021

In this study, binderless-WC, WC-6 wt%Co, WC-6wt% 1 and 2.5 B₄C materials are fabricated by spark plasma sintering process (SPS process). Each fabricated WC material is almost completely dense, with a relative density up to 99.5 % after the simultaneous application of pressure of 60 MPa. The WC added Co and Co-B₄C materials resulted in crystalline growth. The WC with HCP crystal structure has respective interfacial energy (basal facet direction: 1.07 ~ 1.34 J·m^-2, prismatic direction: 1.43 ~ 3.02 J·m^-2) that depends on the grain growth direction. It is confirmed that the continuous grain growth, biased by the basal facet, which has relatively low energy, is promoted at the WC/Co interface. As abnormal grain growth takes place, the grain size increases more than twice from 0.37 to 0.8 um. It is found through analysis that the hardness property also greatly decreases from about 2661.4 to 1721.4 kg/mm², along with the grain growth.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2016년도 임시총회 및 하계학술연구발표회
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• pp.137-137
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• 2016

• 한국재료학회지
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• 제22권12호
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• pp.664-668
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• 2012

ZnO nanorods were successfully fabricated on Zn foil by chemical bath deposition (CBD) method. The ZnO precursor concentration and immersion time affected the surface morphologies, structure, and electrical properties of the ZnO nanorods. As the precursor concentration increased, the diameter of the ZnO nanorods increased from ca. 50 nm to ca. 150 nm. The thicknesses of the ZnO nanorods were from ca. $1.98{\mu}m$ to ca. $2.08{\mu}m$. ZnO crystalline phases of (100), (002), and (101) planes of hexagonal wurtzite structure were confirmed by XRD measurement. The fabricated ZnO nanorods showed a photoluminescene property at 380 nm. Especially, the ZnO nanorods deposited for 6 h in solution with a concentration of 0.005M showed a stronger (101) peak than they did (100) or (002) peaks. In addition, these ZnO nanorods showed a good electrical property, with the lowest resistance among the four samples, because the nanorods were densely in contact and relatively without pores. Therefore, a ZnO nanorod substrate is useful as a highly sensitive biochip substrate to detect biomolecules using an electrochemical method.

• 한국재료학회지
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• 제21권1호
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• pp.50-55
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• 2011

Energy resistance welding (ERW) is a pipe-producing process that has high productivity and low manufacturing cost. However, the high heat input of ERW degrades the mechanical property of the pipe. This study investigates the effect of heat input and alloying elements on microstructure and mechanical properties of ERW pipes. As the heat input increased, the ferrite amount increased. The ferrite amount in the weld centerline was larger than t at in the weld boundary. Medium carbon steels (S45C and K55) having 0.3~0.4wt.% carbon yielded a significant difference of ferrite amount in the weld centerline and weld boundary. High alloyed steels (DP780 and K55) having 1.5~1.6wt.% Mn showed a ferrite rich zone in the weld centerline. These phenomena are probably due to decarburization and demanganisation in the weld centerline. As the ferrite fraction increased, the hardness decreased a little for the S45C steels. In addition, DP780 steels and K55 steels showed that the hardness drops when those steels have a ferrite rich zone. But we demonstrated the good tensile property of the DP780 steels and K55 steels in which Mn is included.

• Corrosion Science and Technology
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• 제2권1호
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• pp.7-11
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• 2003

Photoelectrochemical response and electrochemical impedance behavior was investigated for passive film formed on sputter-deposited Cr alloy in $0.1kmol{\cdot}m^{-3}$. Photoelectrochemical action spectrum could be separated into two components, which were considered to be derived from $Cr_2O_3$ ($E_g\sim3.6eV$) and $ Cr(OH)_3 $ ($E_g\sim2.5eV$). The band gap energy, $E_g$, of each component was almost constant for various applied potentials. polarization periods and alloying additives. The photoelectrochemical response showed negative photo current for most potentials in the passive region. Therefore, the photo current apparently exhibited p-typesemiconductor behavior. On the other hand, Mort-Schottky plot of the capacitance showed positive slope, which means that passive film formed on Cr alloy has n-type semiconductor property. These apparently conflicting results are rationally explained assuming that the passive film on Cr alloy formed in the acid solution has n-type semiconductor property with a fairly deep donor level in the band gap and forms an accumulation layer in the most of potential region in the passive state.

• 한국응용과학기술학회지
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• 제26권3호
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• pp.288-296
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• 2009

In this study, the silica-based hybrid material with high barrier property was prepared by incorporating ethylene-vinyl alcohol (EVOH) copolymer, which has been utilized as packaging materials due to its superior gas permeation resistance, during sol-gel process. In preparation of this EVOH/$SiO_2$ hybrid coating materials, the (3-glycidoxy-propyl)-trimethoxysilane (GPTMS) as a silane coupling agent was employed to promote interfacial adhesion between organic and inorganic phases. As confirmed from FT-IR analysis, the physical interaction between two phases was improved due to the increased hydrogen bonding, resulting in homogeneous microstructure with dispersion of nano-sized silica particles. However, depending on the range of content of added silane coupling agent (GPTMS), micro-phase separated microstructure in the hybrid could be observed due to insufficient interfacial attraction or possibility of polymerization reaction of epoxide ring in GPTMS. The oxygen barrier property of the mono-layer coated BOPP (biaxially oriented polypropylene) film was examined for the hybrids containing various GPTMS contents. Consequently, it is revealed that GPTMS should be used in an optimum level of content to produce the high barrier EVOH/$SiO_2$ hybrid material with an improved optical transparency and homogeneous phase morphology.

• 한국재료학회지
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• 제20권5호
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• pp.271-277
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• 2010

In this paper two aspects of the percolation and conductivity of carbon black-filled polyethylene matrix composites will be discussed. Firstly, the percolation behavior, the critical exponent of conductivity of these composites, are discussed based on studying the whole change of resistivity, the relationship between frequency and relative permittivity or ac conductivity. There are two transitions of resistivity for carbon black filling. Below the first transition, resistivity shows an ohmic behavior and its value is almost the same as that of the matrix. Between the first and second transition, the change in resistivity is very sharp, and a non-ohmic electric field dependence of current has been observed. Secondly, the electrical conduction property of the carbon black-filled polyethylene matrix composites below the percolation threshold is discussed with the hopping conduction model. This study investigates the electrical conduction property of the composites below the percolation threshold based on the frequency dependence of conductivity in the range of 20 Hz to 1 MHz. There are two components for the observed ac loss current. One is independent of frequency that becomes prevalent in low frequencies just below the percolation threshold and under a high electrical field. The other is proportional to the frequency of the applied ac voltage in high frequencies and its origin is not clear. These results support the conclusion that the electrical conduction mechanism below the percolation threshold is tunneling.

• 한국주조공학회지
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• 제20권6호
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• pp.386-394
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• 2000

In the present study, the effect of yttrium addition on the microstructure and mechanical property of rapidly solidified AZ91 alloy by melt spinning process is estimated. As yttrium was added, the microstructure of RS ribbons and extrudates became finer than those of AZ91, and RE related phases $(Al_2RE)$ were formed. In the case of the addition of 3wt%Y, the microstructure of extrude showed the finest grain size. At room temperature, the AZ91 + 3wt%Y alloy showed the highest tensile strength, 352 MPA due to precipitation of ${\beta}(Mg_{17}Al_{12})$ phase and $Al_2RE$ phase. At the elevated temperature, the mechanical property of AZ91 + 3wt%Y alloy was higher than those of other Mg alloys. The reasons were that $Al_2Y$ compound was thermally stable and suppressed the grain growth. In contrast with $Al_2Y$ compounds, ${\beta}$ phase was thermally unstable and could not suppress the grain growth at the elevated temperature. Therefore, $Al_2Y$ phase contributed to improve the thermal stability of RS AZ91 alloy.

• 폴리머
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• 제30권2호
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• pp.124-128
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• 2006

Heavy weight of the camouflage materials was always the main problem. To solve it, the low infrared emissivity fibers with the radar absorbing property (LIFR) were prepared. The low infrared emissivity fibers (LIF) were firstly melt-spun by co-extrusion of polypropylene (PP) and PP/various fillers master-batches using general conjugate spinning. The infrared emissivity of LW with AA and ZnO was decreased respectively compared with that of pure polypropylene fibers. The infrared emissivity of LIF with 15 wt% Al and 2 wt% ZnO in the sheath-part can reach 0.58. To improve LIF radar absorbing property, LIFR was prepared by filling the 50 wt% ferrite and bronze in the core-part of LIF. The radar absorbing efficacy of LIFR was good and the infrared emissivity was low. For the characterization, fiber electron intensity instrument and differential scanning calorimetry (DSC) were used for the analysis of mechanical properties, thermal and crystallization behavior of the spun-fibers. Scanning electron microscopy (SEM) was carried out to observe the particle distribution of the bicomponent fibers.

• 한국주조공학회지
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• 제20권1호
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• pp.29-37
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• 2000

The purpose of this study is to investigate the effect of misch metal addition on the microstructure and mechanical property of rapidly solidified AZ91 alloy by melt spinning process. As the contents of misch metal(rare earth element:Ce,La, Nd, Pr)was increased, the microstructure of RS ribbons and extrudates became finer than those of AZ91, and RE related phases($Al_{11}RE_3$, $Al_2RE$) were formed. At room temperature, the rapidly solidified AZ91+1 wt%Mm alloy showed the highest tensile strength, 430 MPa due to precipitation strengthening of${\beta}(Mg_{17}Al_{12})$ phase and Al11RE3 phase. At the elevated temperature, the mechanical property of AZ01+3 wt%Mm alloy was higher than those of other Mg alloys. The reasons were that $Al_{11}La_3$ phase was thermally stable and suppressed the grain growth. In contrast with $Al_{11}La_3$ phase, ${\beta}$ phase was thermally unstable and could not suppress the grain growth at the elevated temperature. Therefore, Al11RE3 phase contributed to improve the thermal stability of RS AZ91 Alloy.