• Polymer(Korea)
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• v.38 no.2
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• pp.150-155
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• 2014

Polycaprolactone (PCL) is a synthetic biodegradable polymer with excellent mechanical properties. $TiO_2$ (titanium dioxide) has a hydrophilic, high density and excellent biocompatibility. In this work, we produced three-dimensional porous scaffolds with PCL and $TiO_2$ nanoparticles using a salt-leaching method. Physical properties of the scaffolds were analyzed by FE-SEM, FTIR, TGA and compressive strength. Interestingly, the addition of $TiO_2$ nanoparticles decreased the water absorption and swelling ratio of the porous scaffolds. However, the compressive strength was increased by $TiO_2$. CCK-8 assay, which is generally used for the analysis of cell growth, shows that $TiO_2$ nanoparticles have no cytotoxicity. Taken together, we suggest that the PLC/$TiO_2$-scaffold can be used for biomedical applications.

• Journal of Korean Neurosurgical Society
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• v.61 no.6
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• pp.737-746
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• 2018

Objective : The purpose of this study was to compare the cosmetic outcome and complications after cranioplasty (CP) due to three different implant materials, and analyze the mean implant survival and cumulative survival rate based on these results. Methods : We reviewed 108 patients retrospectively who underwent CP between January 2014 and November 2016. Autologous bone (AB; 45 patients) and synthetic materials with porous polyethylene (PP; 32 patients) and custom-made 3-dimensional printed titanium mesh (CT; 31 patients) were used as implants. Results : Regardless of implanted materials, more than 89.8% of the CP patients were satisfied with the cosmetic outcome. No statistically significant difference was observed among the three groups. The overall postoperative complication rates of each group were 31.1% in the AB group, 15.6% in the PP group and 3.2% in the CT group. The CT group showed lower complication rates compared with AB and PP groups (${\chi}^2$-test : AB vs. PP, p=0.34; AB vs. CT, p=0.00; PP vs. CT, p=0.03). The AB and PP groups demonstrated a higher post-CP infection rate (11.1% and 6.3%) than the CT group (3.2%). However, no significant difference in the incidence of post-CP infection was observed among the three groups. The PP and CT groups demonstrated a higher mean implant survival time and cumulative survival rate than the AB group at the last follow-up (p<0.05). Conclusion : In comparison with AB and PP, cranioplasty with CT shows benefits in terms of lower post-CP complication, less intraoperative bleeding loss, shorter operation time and in-hospital stay. The PP and CT groups showed higher implant survival time and cumulative survival rate compared with the AB group.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.6
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• pp.44-51
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• 1997

Crinding of stainless steel, aluminium alloy, copper alloy, and titanium alloy are difficult to obtain high quality finish, because they have the mechanical properties such as low hardness, high toughness. The low hardness and the high toughness result in the loading of wheel and the poor surface finish. In order to perform the grinding operations for these sorts of materials easily, the discontinuous grinding wheel wiht multi-porous grooves has been newly developed. The multi-porous grooves inthe discontinuous grinding wheel were formed during grinding wheel manufacturing process. In this paper, discontinuous grinding wheels having intermittent ratio 0.66, 0.81 and number of grooves 18,32 have been manufactured and grinding surface characteristics of these grinding wheels for SUS304 have been analyzed. Discontinuous grinding temperature according to intermittent ratiohas been also estimated by simulation. The discontinuous grinding wheels increase the grinding performance considerably. It is desirable to use the discontinuous grinding wheel in grinding the materials with high efficiency and accuracy.

• Korean Journal of Materials Research
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• v.19 no.6
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• pp.325-329
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• 2009

Titanium dioxide thin films were fabricated as hydrogen sensors and its sensing properties were tested. The titanium was deposited on a $SiO_2$/Si substrate by the DC magnetron sputtering method and was oxidized at an optimized temperature of $850^{\circ}C$ in air. The titanium film originally had smooth surface morphology, but the film agglomerated to nano-size grains when the temperature reached oxidation temperature where it formed titanium oxide with a rutile structure. The oxide thin film formed by grains of tens of nanometers size also showed many short cracks and voids between the grains. The response to 1% hydrogen gas was ${\sim}2{\times}10^6$ at the optimum sensing temperature of $200^{\circ}C$, and ${\sim}10^3$ at room temperature. This extremely high sensitivity of the thin film to hydrogen was due partly to the porous structure of the nano-sized sensing particles. Other sensor properties were also examined.

• Bulletin of the Korean Chemical Society
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• v.34 no.2
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• pp.519-523
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• 2013

When atomic layer deposition (ALD) is performed on a porous material by using an organometallic precursor, minimum exposure time of the precursor for complete coverage becomes much longer since the ALD is limited by Knudsen diffusion in the pores. In the previous report by Min et al. (Ref. 23), shrinking core model (SCM) was proposed to predict the minimum exposure time of diethylzinc for ZnO ALD on a porous cylindrical alumina monolith. According to the SCM, the minimum exposure time of the precursor is influenced by volumetric density of adsorption sites, effective diffusion coefficient, precursor concentration in gas phase and size of the porous monolith. Here we modify the SCM in order to consider undesirable adsorption of byproduct molecules. $TiO_2$ ALD was performed on the cylindrical alumina monolith by using titanium tetrachloride ($TiCl_4$) and water. We observed that the byproduct (i.e., HCl) of $TiO_2$ ALD can chemically adsorb on adsorption sites, unlike the behavior of the byproduct (i.e., ethane) of ZnO ALD. Consequently, the minimum exposure time of $TiCl_4$ (~16 min) was significantly much shorter than that (~71 min) of DEZ. The predicted minimum exposure time by the modified SCM well agrees with the observed time. In addition, the modified SCM gives an effective diffusion coefficient of $TiCl_4$ of ${\sim}1.78{\times}10^{-2}\;cm^2/s$ in the porous alumina monolith.

• Corrosion Science and Technology
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• v.9 no.4
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• pp.171-174
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• 2010

MAO (micro-arc oxidation) is an eco-friendly convenient and effective technology to deposit high-quality oxide coatings on the surfaces of Ti, Al, Mg and their alloys. The roles of the electrolyte concentration and relative cathode electrode area sizes in the grown oxide film during titanium MAO were investigated. The higher the concentration of the electrolyte, the lower the $R_{total}A$ value. The oxide film produced by the lower concentration of the electrolyte is thinner and less uniform than the film by the higher concentration, which is thick and porous. The cathode area size must be bigger than the anode area size in order to minimize the voltage drop across the cathode. The ratio of the cathode area size to the anode area size must be bigger than 8. Otherwise, the cathode will be another source for voltage drop, which is detrimental to and slows down the oxide growth.

• Proceedings of the Membrane Society of Korea Conference
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• 2004.05a
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• pp.39-42
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• 2004

Ceramic membranes have attracted a great attention because they have excellent resistance to most organic solvents and can be used over a wide temperature range. Especially, titania (titanium oxide, TiO$_2$) shows excellent chemical resistance and can be used both acidic and alkali solutions, and therefore, titania is one of the most promising materials for the preparation of porous membranes; titania membranes having pore sizes in the range of nanofiltration (NF) to ultrafiltration (UF) membrane have been prepared by the sol-gel process (Tsuru 2001).(omitted)

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.189.1-189.1
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• 2013

Titanium dioxide (TiO2) is a wide bandgap semiconductor possessing photochemical stability and thus widely used for photocatalysis. However, enhancing photocatalytic efficiency is still a challenging issue. In general, the efficiency is affected by physio-chemical properties such as crystalline phase, crystallinity, exposed crystal facets, crystallite size, porosity, and surface/bulk defects. Here we propose an alternative approach to enhance the efficiency by studying interfaces between thin TiO2 layers to be stacked; that is, the interfacial phenomena influencing on the formation of porous structures, controlling crystallite sizes and crystallinity. To do so, multi-layered TiO2 thin films were fabricated by using a sol-gel method. Specifically, a single TiO2 thin layer with a thickness range of 20~40 nm was deposited on a silicon wafer and annealed at $600^{\circ}C$. The processing step was repeated up to 6 times. The resulting structures were characterized by conventional electron microscopes, and followed by carrying out photocatalytic performances. The multi-layered TiO2 thin films with enhancing photocatalytic efficiency can be readily applied for bio- and gas sensing devices.

• Journal of the Korean Ceramic Society
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• v.53 no.2
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• pp.227-233
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• 2016

In order to make a highly ordered three-dimensional porous structure of titania ceramics, porogen beads of PS [Polystyrene] and PMMA [poly(methylmetacrylate)] were prepared by emulsion polymerization using styrene monomer and methyl methacrylate monomer, respectively. The uniform beads of PS or PMMA latex were closely packed by centrifugation as a porogen template for the infiltration of titanium butoxide solution. The mixed compound of PS or PMMA with titanium butoxide was dried and the dry compacts were calcined at $450^{\circ}C-750^{\circ}C$ according to the firing schedule to prepare micro- and meso- structures of polycrystalline titania with monodispersed porosity. Inorganic frameworks composed of $TiO_2$ were formed and showed a three Dimensionally Ordered Microstructure [3DOM] of $TiO_2$ ceramics. The pulverized particles of the $TiO_2$ ceramic skeleton were characterized using XRD analysis. A monodispersed crystalline micro-structure with micro/meso porosity was observed by FE-SEM with EDX analysis. The 3DOM $TiO_2$ skeleton showed opalescent color tuning according to the direction of light.

• Journal of the Korean institute of surface engineering
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• v.35 no.6
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• pp.383-390
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• 2002

To investigate behaviors of Ti and O elements and microstructures of anodic titanium oxide films, the films were prepared by anodizing pure titanium in $H_2$S $O_4$, $H_3$P $O_4$, and $H_2O$$_2$ mixed solution at 180V. The microstructures and chemical states of the elements were analyzed using SEM, X-ray mapping, AFM, XRD, XPS (depth profile). The films formed on a titanium substrate showed porous layers which were composed of pore and wall, And with increasing anodizing time a hexagonal shape of cell structures were dominant and solace roughness increased. From the XRD result the structure of the Ti $O_2$ layer was anatase type of crystal on the whole. In the XPS spectra it was found that Ti and O were chemically binded in forms of Ti $O_2$, TiOH, $Ti_2$ $O_3$ at Ti 2p, and Ti $O_2$, $Ti_2$ $O_3$, $P_2$ $O_{5}$, S $O_4^{2-}$ at O ls respectively. Concentration of Ti $O_2$ decreased as the depth increased from the surface of the oxide film towards the substrate, but to the contrary concentrations of TiOH and $Ti_2$ $O_3$ increased.d.