• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.471-474
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• 2005

This study investigates the nano/microstructure, the aging response, and the mechanical/tribological properties of the eutectic regions in rheoformed A356 alloy-T5 parts using nano/micro-indentation and mechanical scratching, combined with optical microscopy and atomic force microscope (AFM). Most eutectic Si crystals in the A356 alloy showed a modified morphology as fine-fibers. The loading curve for the eutectic region was more irregular than that of the primary Al region due to the presence of various particles of varying strength. The aging responses of the eutectic regions in the rheoformed A356 alloys aged at $150^{\circ}C$ for different times (0, 2, 4, 8, 10, 16, 24, 36, and 72 h) were investigated. Both Victors hardness $(H_v)$ and indentation $(H_{IT})$ test results showed a similar trend of aging curves, and the peak was obtained at the same aging time of 10 h. A remarkable size-dependence of the tests was found.

• Korean Journal of Materials Research
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• v.31 no.7
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• pp.386-391
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• 2021

The formation of CaCO₃ in microalgal culture is investigated and applied for effective separation of microalgae. The presence of several cationic ions in the culture medium mediates the formation of 3 types of mineral precipitates depending on the concentration of mineral precursors, Ca²⁺ and CO₃^2-, amorphous nano-flakes, rhombohedral calcites, and spherical vaterites. While amorphous phased precipitates are formed for all concentrations of mineral precursor, only calcites are formed for 30 mM solutions of mineral precursor, and mixtures of calcites and vaterites are formed for 50 and 100 mM solutions of mineral precursor. The harvesting efficiency is also dependent on the concentration of the mineral precursor: from 90 % for 10 mM to 99 % for 100 mM after 60 mins' of gravitational sedimentation. The formation of nano-flakes on the surface of microalgal cells induces the flocculation of microalgae by breaking the stable dispersion. The negatively charged surface of the microalgal cell is compatible not only with nano-flake attachment but also with the growth of calcitic crystals in which microalgal cells are embedded.

• Advances in nano research
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• v.10 no.3
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• pp.211-219
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• 2021

The evaluation of the corrosion resistance of titanium with a TiO2 nanotubes top layer was carried out (TiO2 NT). These nanostructures were evolved into anatase nanoparticles without heat treatment in an aqueous medium, which is a novel phenomenon. This work analyzes the layer between the nanotube bottom and the substrate, which is thin and still susceptible to corrosion. The bottom of TiO2 nanotubes having Fluor resulting from the synthesis process changed between amorphous to crystalline anatase with a crystallite size of about 4 nm, which influenced the corrosion rates. Four kinds of samples were evaluated. A) NT by Ti anodizing; B) NTSB for Ti plates, either modifying its surface or anodizing the modified surface; C) NT-480 for anodized Ti and heat-treated (480℃) for reaching the anatase phase; D) NTSB-480 for Ti plates, first, modifying its surface using sandblast, after that, anodizing the modified surface, and finally, heat-treated to 480℃ to compare with samples having induced crystallization and passivation. Four electrochemical techniques were used to evaluate the corrosion rates. The surfaces having TiO2 nanotubes with a sandblast pre-treatment had the highest resistance to corrosion.

• Journal of the Korean Magnetics Society
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• v.14 no.4
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• pp.149-161
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• 2004

The fusion of nano technology and information technology is essential to sustain the present growth rate and to induce new industry in this ever-growing information age. Considering Korean industry whose competitiveness lies heavily on information related technologies, this field will be inevitable for future. Nano materials can be described as novel materials whose size of elemental structure has been engineered at the nanometer scale. Materials in the nanometer size range exhibit fundamentally new behavior, as their size falls below the critical length scale associated with any given property. " Bottom-up' techniques involve manipulating individual atoms and molecules. Bottom-up process usually implies controlled or directed self assembly of atoms and molecules into nano structures. It resembles more closely the processes of biology and chemistry, where atoms and molecules come together to create structures such as crystals or living cells. Nano scale sensors are included in the electronics area since the diverse sensing mechanisms are often housed on a semiconductor substrate and usually give rise to an electronic signal. The application of nano technology to the chemical sensors should allow improvements in functionality such as gas sensing. In this presentation, we will discuss about the nano scale information materials and devices fabricated by using the organic/inorganic nano templates.

• Transactions on Electrical and Electronic Materials
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• v.11 no.3
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• pp.134-137
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• 2010

We have proposed a transflective liquid crystal display (LCD) driven by the fringe field using a liquid crystal (LC) with a negative dielectric anisotropy. The device used different twist angles of the liquid crystals (LC) in the transmissive (T) and the reflective (R) regions when voltage is applied. With the optimization of the pixel electrode width and the distance between them, the LC directors in the R- and T-regions can be rotated by about $22.5^{\circ}$ and $45^{\circ}$ on an average, respectively. As a result, a high image quality transflective LCD with a single gap, a single gamma, and a wide viewing angle characteristics in both the R- and T- regions can be realized.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.5
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• pp.85-90
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• 2017

Mica-glass ceramics has features such as micro-sized crystals, high strength, chemical resistance, semitransparent optical properties, etc. Due to its superior material properties, mica glass ceramics have increasing applications in dental and medical components, insulation boards, chemical devices, etc. In many applications, especially for dental and medical components, ultra-precise polishing is required. However, it is known to be a very difficult-to-grind material because of its high hardness and brittle properties. Thus, in this study, a newly developed ultra-precise polishing method is applied to obtain nano-level surface roughness of the mica glass ceramics using magnetorheological (MR) fluids and nano abrasives. Nano-sized ceria particles were used for the polishing of the mica glass ceramics. A series of experiments were performed under various polishing conditions, and the results were analyzed. A very fine surface roughness of Ra=6.127 nm could be obtained.

• Korean Journal of Materials Research
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• v.21 no.12
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• pp.697-702
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• 2011

Two-dimensional (2D) nano patterns including a two-dimensional Bravais lattice were fabricated by laser interference lithography using a two step exposure process. After the first exposure, the substrate itself was rotated by a certain angle, $90^{\circ}$ for a square or rectangular lattice, $75^{\circ}$ for an oblique lattice, and $60^{\circ}$ for a hexagonal lattice, and the $90^{\circ}$ and laser incident angle changed for rectangular and the $45^{\circ}$ and laser incident angle changed for a centered rectangular; we then carried out a second exposure process to form 2D bravais lattices. The band structure of five different 2D nano patterns was simulated by a beam propagation program. The presence of the band-gap effect was shown in an oblique and hexagonal structure. The oblique latticed ZnO nano-photonic crystal array had a pseudo-bandgap at a frequency of 0.337-0.375, 0.575-0.596 and 0.858-0.870. The hexagonal latticed ZnO nano-crystallite array had a pseudo-bandgap at a frequency of 0.335-0.384 and 0.585-0.645. The ZnO nano structure with an oblique and hexagonal structure was grown through the patterned opening window area by a hydrothermal method. The morphology of 2D nano patterns and ZnO nano structures were investigated by atomic force microscopy and scanning electron microscopy. The diameter of the opening window was approximately 250 nm. The height and width of ZnO nano-photonic crystals were 380 nm and 250 nm, respectively.

• Ceramist
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• v.10 no.3
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• pp.67-74
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• 2007

Crystallisation kinetics of the erbium doped soda-tellurite glasses were studied using the differential thermal analysis (DTA) and differential scanning calorimetery (DSC) techniques. The DTA curves in the temperature range of 350 K to 650 K were obtained from isochronal heating rates, chosen in the range of 2 to 20 K/min. DSC isothermal curves were used to calculate the fraction of crystals formed on reheating. The apparent activation energies for devitrification were derived by measuring the shifts in the values of $T_g$ and $T_x$ with heating rates, using the Kissinger method. The derived values of apparent activation energies for isochronal and isothermal methods varied in the range of $190-204\;{\pm}\;5\;kJ\;mol^{-1}$. The X-ray powder diffraction analysis of heat treated and transparent samples showed the presence of nano-scale size sodium-tellurite crystals. These crystallites were found to have a strong influence on the full width of half maxima of the transition in $Er^{3+}:\;^4I_{13/2}{\rightarrow}^4I_{15/2}$, which extended from 70 nm in the vitreous materials to 132 nm in glass-ceramic materials.

• Korean Journal of Materials Research
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• v.10 no.1
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• pp.29-33
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• 2000

The amorphous tungsten nitrides, WNx, film could be fabricated by reactive sputtering process. The nitrogen concentration for the amorphization ranges from 10 at% to 40at%. The amorphous $W_{67}N_{33}$ film was crystallized into low resistivity $\alpha$-tungsten phase with equiaxed grains and excess nitrogen after the rapid thermal annealing for 1min at 1273K, which was similar to the resistivity of the sputtered pure tungsten film. The excess nitrogen was depleted from $\alpha$-tungsten crystals and then segregated at $\alpha$-tungsten/poly-Si interface. The segregated nitrogen has favored the formation of the homogeneous diffusion barrier layer comprised of silicon nitride, $Si_3N_4$, nano-crystals, which undertaken the inhibition of the high resistivity tungsten silicide reaction.

• Journal of the Korean Ceramic Society
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• v.47 no.4
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• pp.333-337
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• 2010

Domain structure and polarization switching in (001)-oriented $Pb(Mg_{1/3}Nb_{2/3})O_3-x%PbTiO_3$ (PMN-x%PT) crystals for x=20 and 35at% have been investigated in-situ by scanning force microscope (SFM) in a piezoresponse mode under a step DC electrical voltage. In the initial annealed condition, polar nano domains (PND) and domain striations oriented along {110} were observed in x=20 and x=35, respectively. For x=20, domain switching occurs by heterogeneous nucleation, where nucleation is not confined in the vicinity of domain boundaries, but rather can occur throughout the crystal volume. However, for x=35, domain switching tends to be preferentially initiated near pre-existing twin boundaries. With increasing the applying voltage, the nuclei density increased and assembled into {110} striations, indicating a stress-accommodated domain growth process. At higher voltage, nucleation occurs heterogeneously throughout the crystal volume.