• Journal of Surface Science and Engineering
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• v.37 no.6
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• pp.307-312
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• 2004

Extensive efforts have been made in an attempt to utilize photocatalytic properties of $TiO_2$ in visible range. $TiO_2$ and TiO-N thin films were made by the DC reactive magnetron sputtering method at $300^{\circ}C$. Various gases (Ar, $O_2$ and $N_2$) were used and Ti target was impressed by 0.6 kW-5.8 kW power range. The hysteresis phenomenon of the $TiO_2$ thin film as a function of the discharge voltage characteristic was observed to be higher as applied power increases. That of TiO-N thin film was occurred at the 5.8 kW power. The cross section and surface roughness of thin films were observed by FE-SEM and AFM. Average surface roughness of TiO-N thin film was observed as $15.9\AA$ and that of $TiO_2$ as $13.2\AA$. The crystal phases of both $TiO_2$ and TiO-N thin films were found to be anatase structure. The atomic $\beta$-N (396 eV peak in N 1s XPS) was shown in the rutile crystal of TiO-N and was considered acting as the origin of wavelength shift to the visible light.

• Resources Recycling
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• v.25 no.5
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• pp.64-74
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• 2016

Titanium and iron are closely related in nature, although titanium is the ninth most abundant element in the Earth's crust. Iron in titanium ores must be removed for use as feedstocks in the manufacture of titanium dioxide pigments and pure $TiCl_4$ for metal titanium. In this study, various beneficiation processes of ilmenite for production of $TiO_2$ have been reviewed and compared. Most of these processes involve a combination of pyrometallurgy and hydrometallurgy. These beneficiation processes of ilmenite generate considerable quantities of wastes primarily in the form of iron salt, iron oxide and acidic effluents. Therefore, it is important that recovery of acid value from waste and conversion of iron bearing waste to useful materials for development of new beneficiation processes of ilmenite.

• Journal of the Mineralogical Society of Korea
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• v.20 no.4
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• pp.289-302
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• 2007

Separation process of heavy minerals was performed with sand from Dunjang beach of Jaeundo, Shinangun, Chonnam, and the feasibility study separating heavy minerals was carried out, and their properties were studied. Samples were selected in three parts, which were upper part, middle part and lower part, with depth. Samples of heavy mineral groups separated with the spiral separator were chosen as starting materials, and they were separated with 3 times of table separation. Heavy minerals presenting in this area were ilmenite, zircon, rutile, anatase, monazite, and xenotime. In the results of 3 times of table separation, minor content of quartz, orthoclase, albite and muscovite were existed as gangue minerals. Accordingly, we concluded that additional specific gravity separation was needed. In the results of separation of heavy minerals by hand picking, it was confirmed that heavy minerals had various genesis because of their various roundness and color.

• Korean Journal of Materials Research
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• v.22 no.7
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• pp.358-361
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• 2012

Co and Ni as catalysts in $SnO_2$ sensors to improve the sensitivity for $CH_4$ gas and $CH_3CH_2CH_3$ gas were coated by a solution reduction method. $SnO_2$ thick films were prepared by a screen-printing method onto $Al_2O_3$ substrates with an electrode. The sensing characteristics were investigated by measuring the electrical resistance of each sensor in a chamber. The structural properties of $SnO_2$ with a rutile structure investigated by XRD showed a (110) dominant $SnO_2$ peak. The particle size of the $SnO_2$:Ni powders with Ni at 6 wt% was about 0.1 ${\mu}m$. The $SnO_2$ particles were found to contain many pores according to a SEM analysis. The sensitivity of $SnO_2$-based sensors was measured for 5 ppm of $CH_4$ gas and $CH_3CH_2CH_3$ gas at room temperature by comparing the resistance in air to that in the target gases. The results showed that the best sensitivity of $SnO_2$:Ni and $SnO_2$:Co sensors for $CH_4$ gas and $CH_3CH_2CH_3$ gas at room temperature was observed in $SnO_2$:Ni sensors coated with 6 wt% Ni. The $SnO_2$:Ni gas sensors showed good selectivity to $CH_4$ gas. The response time and recovery time of the $SnO_2$:Ni gas sensors for the $CH_4$ and $CH_3CH_2CH_3$ gases were 20 seconds and 9 seconds, respectively.

• 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.

• Korean Journal of Materials Research
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• v.20 no.3
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• pp.167-173
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• 2010

In this study, we used activated carbon (AC) and titanium oxysulfate as a titanium precursor to prepare carbon/titania composites. We then mixed it with bentonite in different ratios to make a carbon/titania/bentonite monolith for use in architecture bricks by using Phenolic rosin (PR) as a bonding agent. The physicochemical properties of the prepared composites were analyzed by BET surface area, scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), self-cleaning effect and bactericidal tests. The BET surface areas increased as the ratio of carbon/titania composites increased. The SEM microscopy showed that the $TiO_2$ and bentonite were coated on the surface of the AC. The XRD patterns showed a mixture structure of anatase and rutile of $TiO_2$ with a clear $SiO_2$ structure. The EDX spectra of the carbon/titania/bentonite monolith confirmed the presence of various elements, namely C, O, Ti and Si, as well as other, impure elements. Moreover, to determine the self-cleaning effect of the carbon/titania/bentonite monolith, we used methylene blue (MB, $C_{16}H_{18}N_3S{\cdot}Cl{\cdot}3H_2O$) in an aqueous solution under the irradiation of visible light. Accordingly, all of the samples had excellent degradation of the MB solution. Furthermore, it was observed that the composites with sunlight irradiation had a greater effect on E. coli than any other experimental conditions.

• Korean Journal of Materials Research
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• v.18 no.10
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• pp.515-520
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• 2008

We fabricated 10 nm-$TiO_2$ thin films for DSSC (dye sensitized solar cell) electrode application using ALD (atomic layer deposition) method at the low temperatures of $150^{\circ}\;and\;250^{\circ}$. We characterized the crosssectional microstructure, phase, chemical binding energy, and absorption of the $TiO_2$ using TEM, HRXRD, XPS, and UV-VIS-NIR, respectively. TEM analysis showed a 10 nm-thick flat and uniform $TiO_2$ thin film regardless of the deposition temperatures. Through XPS analysis, it was found that the stoichiometric $TiO_2$ phase was formed and confirmed by measuring main characteristic peaks of Ti $2p^1$, Ti $2p^3$, and O 1s indicating the binding energy status. Through UV-VIS-NIR analysis, ALD-$TiO_2$ thin films were found to have a band gap of 3.4 eV resulting in the absorption edges at 360 nm, while the conventional $TiO_2$ films had a band gap of 3.0 eV (rutile)${\sim}$3.2 eV (anatase) with the absorption edges at 380 nm and 410 nm. Our results implied that the newly proposed nano-thick $TiO_2$ film using an ALD process at $150^{\circ}$ had almost the same properties as thsose of film at $250^{\circ}$. Therefore, we confirmed that the ALD-processed $TiO_2$ thin film with nano-thickness formed at low temperatures might be suitable for the electrode process of flexible devices.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.87-87
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• 2010

Adsorption and subsequent catalytic reactions of ethanol and acetaldehyde on chemically modified rutile TiO2(001) surfaces are probed by x-ray photoemission spectroscopy (XPS) using synchrotron radiation. TiO2 is a well-known photocatalyst for various catalytic reactions including oxidation of organic molecules. In this respect, the surface atomic structure has been found to play a vital role in determining the catalytic reactivity and selectivity of TiO2. In this study, we employ an atomically well-ordered reduced TiO2(001) surface which is prepared in a UHV chamber by repeated Ar+-sputtering and annealing (900 K) cycles. We systematically modify the surface by treating the surface with H2O or O2 at room temperature (RT). The catalytic reactivity of the surface-modified TiO2(001) is evaluated by dosing ethanol/acetaldehyde onto the surface at RT and by subsequent annealing to higher temperatures (400~600 K). XPS spectra of C 1s core level are intensively used to probe any change in the oxidation state of carbon atoms. We find that the reactivity as well as the saturation coverage are significantly affected by the RT-treatment of the TiO2 surface with H2O or O2. For both reactant molecules (ethanol/acetaldehyde), oxidation reactions are found to be enhanced on the O2-treated surface compared with the reduced or H2O-treated surfaces. Possibly reaction pathways are discussed based on the observed XPS spectra.

• Korean Journal of Metals and Materials
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• v.50 no.1
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• pp.52-58
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• 2012

Hydrogen-delayed fracture (HDF) was analyzed from the deposited weld metals of 600-MPa and 800-MPa flux-cored arc (FCA) welding wires, and then from the diffusible hydrogen behavior of the weld zone. Two types of deposited weld metal, that is, rutile weld metal and alkali weld metal, were used for each strength level. Constant loading test (CLT) and thermal desorption spectrometry (TDS) analysis were conducted on the hydrogen pre-charged specimens electrochemically for 72 h. The effects of microstructures such as acicular ferrite, grain-boundary ferrite, and low-temperature-transformation phase on the time-to-failure and amount of diffusible hydrogen were analyzed. The fracture time for hydrogen-purged specimens in the constant loading tests decreased as the grain size of acicular ferrite decreased. The major trapping site for diffusible hydrogen was the grain boundary, as determined by calculating the activation energies for hydrogen detrapping. As the strength was increased and alkali weld metal was used, the resistance to HDF decreased.

• Korean Journal of Metals and Materials
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• v.50 no.3
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• pp.201-205
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• 2012

The effects of various manganese precursors for the low-temperature selective catalytic reduction (SCR) of $NO_x$ were investigated in terms of structural, morphological, and physico-chemical analyses. $MnO_x/TiO_2$ catalysts were prepared from three different precursors, manganese nitrate, manganese acetate(II), and manganese acetate(III), by the sol-gel method. The manganese acetate(III)-$MnO_x/TiO_2$ catalyst tended to suppress the phase transition from the anatase structure to the rutile or the brookite after calcination at $500^{\circ}C$ for 2 h. It also had a high specific surface area, which was caused by a smaller particle size and more uniform distribution than the others. The change of catalytic acid sites was confirmed by Raman and FT-IR spectroscopy and the manganese acetate(III)-$MnO_x/TiO_2$ had the strongest Lewis acid sites among them. The highest de-NOx efficiency and structural stability were achieved by using the manganese cetate(III) as a precursor, because of its high specific surface area, a large amount of anatase $TiO_2$, and the strong catalytic acidity.