• Journal of Electrochemical Science and Technology
• /
• v.6 no.2
• /
• pp.65-74
• /
• 2015

This work examines the characterization and corrosion behaviour of laser alloyed UNSG10150 steel with three different premixed composition Zn-Sn binary powders using a 4.4 kW continuous wave (CW) Rofin Sinar Nd:YAG laser processing system. The steel alloyed samples were cut to corrosion coupons, immersed in sulphuric acid (0.5 M H₂SO₄) solution at 30℃ using electrochemical technique and investigated for its corrosion behaviour. The morphologies and microstructures of the developed coated and uncoated samples were characterized by Optic Nikon Optical microscope (OPM) and scanning electron microscope (SEM/EDS). Moreover, X-ray diffractometer (XRD) was used to identify the phases present. An enhancement of 2.7-times the hardness of the steel substrate was achieved in sample A₁ which may be attributed to the fine microstructure, dislocations and the high degree of saturation of solid solution brought by the high scanning speed. At scanning speed of 0.8 m/min, sample A₁ exhibited the highest polarization resistance R_p (1081678 Ωcm² ), lowest corrosion current density i_corr (4.81×10⁻⁸A/cm² ), and lowest corrosion rate Cr (0.0005 mm/year) in 0.5 M H₂SO₄. The polarization resistance R_p (1081678 Ωcm² ) is 67,813-times the polarization of the UNSG10150 substrate and 99.9972% reduction in the corrosion rate.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.21 no.1
• /
• pp.34-40
• /
• 2011

The bulk density, water absorption and microstructure of the artificial aggregates were controlled as a function of sintering temperature (1100 and $1200^{\circ}C$) and time (10~60 min) in the fabrication process of the artificial aggregates by the direct sintering process using dredged soil, the inorganic wastes. Also, the physical properties of the artificial aggregates fabricated according to the different sintering methods such as the direct sintering method used in this study and the increasing temperature sintering method used in the previous report, were compared and analysed. The bulk density of aggregates sintered at $1200^{\circ}C$ by the direct sintering method showed below 1.0, and the thickness of a shell and the pore size of the black core were increased with sintering temperature. Also, in the same sintering temperature, the area of black core was decreased, the thickness of shell was increased and the water absorption was decreased with sintering time. The black core of artificial aggregates of bulk density below 1.0 had the similar microstructure, regardless of sintering methods. In contrast, the shell of aggregates fabricated by the increasing temperature sintering method showed more dense microstructure than that by direct sintering method, hence the water absorption of aggregate sintered using direct sintering was relatively high. Thus, the direct sintering method is suitable for fabrication of artificial aggregates in ceramic carriers or absorbents applications.

• Journal of the Korean Magnetics Society
• /
• v.11 no.5
• /
• pp.184-188
• /
• 2001

Using a DC-sputter and changing the substrate temperature to room temperature and 200$\^{C}$, we manufactured each Co-22%Cr alloy thin-films, which has a uniform micro-structure at room temperature, and a fine self-organized nato structure (SONS) at the inside of the grain at the elevated temperature. We also investigated the microstructure and domain structure using a transmission electron microscope (TEM) and a magnetic force microscope (MFM). We managed to corrode selectively Co-enriched phase, then investigate the microstructure using a TEM. We found that it has a uniform composition when it is manufactured at room temperature, but, we found that it has a unique microstructure, which has a plate-like fine Co-enriched phase, with the formation of SONS at the inside of the grain at the elevated temperature. In MFM characterization, we found maze-type domains at the period of 5000 when the substrate temperature maintains at room temperature. We define that the maze-type domain has a disadvantage at the high density recording because it generates noises easily as the exchange coupling energy between the grains is big. On the other hand, there is only a fine domain structure at the period of 500 when the substrate temperature maintains at 200 $\^{C}$. We define that the fine domain structure has an advantage at the high density magnetic recording because it has thermal stability due to small exchange coupling energy.

• Transactions on Electrical and Electronic Materials
• /
• v.15 no.5
• /
• pp.235-240
• /
• 2014

Nanocomposites made of linear low density polyethylene (LLDPE) and organo-modified montmorillonite (O-MMT) were processed by melt compounding from a commercially available premixed LLDPE/nanoclay masterbatch, at different nanoclay loadings, by co-rotating twin-screw extruder. The morphological and dielectric properties of LLDPE/O-MMT nanocomposites were investigated to understand the structure-dielectric properties relationship in the nanocomposites. The microstructures of the materials were characterized by wide angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Initial findings by FTIR spectroscopy characterization indicated the absence of any chemical interaction between LLDPE and nanoclay during the extrusion process, while DSC showed that a 1% wt loading of nanoclay particles increased the degree of crystallinity of the nanocomposites samples. On the other hand, XRD, SEM, TEM and AFM indicated that nanoclay layers were intercalated or exfoliated in the LLDPE matrix. A correlation between the structure and dielectric properties of LLDPE/O-MMT nanocomposites was found and discussed.

• Korean Journal of Materials Research
• /
• v.14 no.8
• /
• pp.565-572
• /
• 2004

The microstructures of variously heat treated hypoeutectoid($0.45\%$ carbon) and eutectoid($0.85\%$ carbon) steel were characterized by magnetic coercivity measurement. The effect of spheroidization of cementites on the coercivity was investigated for $0.45\%$ carbon steel. In case of $0.85\%$ carbon steel, microstructural parameters such as prior austenite grain size, phase and pearlite interlamellar spacing were measured along with coercivity to investigate the relationships between them. Prior austenite grain size had little effect on the measured coercivity. Coercivity was observed to be high in order of martensite, pearlite and ferrite phases. The linear decrease of coercivity with increasing pearlite interlamellar spacing was found. The effect of each microstructural factor on the coercivity and the potential of coercivity as a nondestructive evaluation parameter for assessing microstructures of steel products are discussed.

• Journal of the Korean Ceramic Society
• /
• v.51 no.5
• /
• pp.406-412
• /
• 2014

In this study, flat-tubular-type alumina filters were manufactured using alumina powder of two sizes ($2.4{\mu}m$ ALM-44 and $0.4{\mu}m$ AP 400) by an extrusion process. The manufactured alumina filter was sintered at $1200-1600^{\circ}C$ for 1 h. As particle size increased, the largest pore size, average pore size and porosity increased; but density and linear shrinkage decreased. The alumina filter fabricated using ALM-44 powder sintered at $1500^{\circ}C$ was confirmed as the best water treatment filter after investigation of the bending strength, water permeability and impurity-removal efficiency of the experimental filters. This flat-tubular-type alumina filter is expected to be useful not only for direct water treatment, but also for use as a support filter during coating processes, to control pore size.

• Journal of the Korean Ceramic Society
• /
• v.51 no.5
• /
• pp.481-486
• /
• 2014

Environmental barrier coatings (EBCs) are used to protect SiC-based ceramics or composites from oxidation and corrosion due to reaction with oxygen and water vapour at high temperatures above $1000^{\circ}C$. Mullite ceramics have been studied for environmental barrier coatings for Si-based ceramics. More recently, rare earth silicate ceramics have been identified as more water vapour-resistant materials than mullite for environmental barrier coatings. In this study, we fabricate mullite and yttrium silicate ceramics by an atmospheric plasma spray coating method using spherical granules fabricated by spray drying. As a result, EBCs with thicknesses in the range of $200-300{\mu}m$ are successfully fabricated without any macroscopic cracks or interfacial delamination. Phase and microstructure analysis are conducted, and the basic mechanical properties, such as hardness and indentation load-displacement curves are evaluated.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.22 no.5
• /
• pp.806-811
• /
• 2013

In this study, to prevent the nonhomogeneity of fiber orientation during the molding of GFRP composites, GFRP prepreg was fabricated using roving fiber and polypropylene resin. Analyses on the degree of impregnation, tensile strength, and microstructure were conducted on the fabricated prepregs. A lower pulling speed, higher resin temperature, and longer die length showed a greater degree of impregnation of the prepreg. The scanning electron microscope (SEM) micrograph showed, a homogeneous fiber orientation. As a result, fundamental techniques for improved productivity were suggested for the manufacturing field.

• Advances in nano research
• /
• v.1 no.4
• /
• pp.183-192
• /
• 2013

One-dimensional multiferroic nanostructured composites have drawn increasing interest as they show tremendous potential for multifunctional devices and applications. Herein, we report the synthesis, structural and dielectric characterization of barium titanate ($BaTiO_3$)-bismuth ferrite ($BiFeO_3$) composite fibers that were obtained using a novel sol-gel based electrospinning technique. The microstructure of the fibers was investigated using scanning electron microscopy and transmission electron microscopy. The fibers had an average diameter of 120 nm and were composed of nanoparticles. X-ray diffraction (XRD) study of the composite fibers demonstrated that the fibers are composed of perovskite cubic $BaTiO_3$-$BiFeO_3$ crystallites. The magnetic hysteresis loops of the resultant fibers demonstrated that the fibers were ferromagnetic with magnetic coercivity of 1500 Oe and saturation magnetization of 1.55 emu/g at room temperature (300 K). Additionally, the dielectric response of the composite fibers was characterized as a function of frequency. Their dielectric permittivity was found to be 140 and their dielectric loss was low in the frequency range from 1000 Hz to $10^7$ Hz.

• 한국신재생에너지학회:학술대회논문집
• /
• 2010.06a
• /
• pp.94.2-94.2
• /
• 2010

Indium tin oxide (ITO) Thin films were grown on Non-alkarai glass Substrates by PVD method and Subsequently Subjected to ($100^{\circ}C-350^{\circ}C$) Thermal Annealing (TA) In Nitr Oxygen ambinent. Most of all, The effect of TA treatment on the structural properties were studied by using X-Ray diffraction and atomic force microscopy, while optical properties were studied by UV-Transmittance measurements. After TA treatment, the XRD spectra have shown an effective relaxation of the residual compressive stress, As a result, XRD peaks increase of the intensity and narrowing of full width at half-maximun (FWHM). In addtion The microstructure, The surface morphology, the optical transmittance changed and improved, and we investigated The effects of temperature, Time and atmosphere during the TA on the structural and electrical properties of the ITO/glass on TA at $300^{\circ}C$. As a results, the films are highly transparent (80%～89%) in visible region. AFM analysis shows that the films are very smooth with root mean square surface roughness 0.58nm -2.75nm thickness film. It is observed that resistivity of the films drcreases T0 $1.05{\times}10^{-4}{\Omega}cmt$ $6.06{\times}10^{-4}{\Omega}cm$, while mobility increases from $152cm^2/vs$ to $275cm^2/vs$.