• International Journal of Oral Biology
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• v.44 no.3
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• pp.108-114
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• 2019

In the present study, rutile phase titanium dioxide nanoparticles ($R-TiO_2$ NPs) were prepared by hydrolysis of titanium tetrachloride in an aqueous solution followed by calcination at $900^{\circ}C$. The composition of $R-TiO_2$ NPs was determined by the analysis of X-ray diffraction data, and the characteristic features of $R-TiO_2$ NPs such as the surface functional group, particle size, shape, surface topography, and morphological behavior were analyzed by Fourier-transform infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy, transmission electron microscopy, dynamic light scattering, and zeta potential measurements. The average size of the prepared $R-TiO_2$ NPs was 76 nm, the surface area was $19m^2/g$, zeta potential was -20.8 mV, and average hydrodynamic diameter in dimethyl sulfoxide (DMSO)-$H_2O$ solution was 550 nm. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and morphological observations revealed that $R-TiO_2$ NPs were cytocompatible with oral cancer cells, with no inhibition of cell growth and proliferation. This suggests the efficacy of $R-TiO_2$ NPs for the aesthetic white pigmentation of teeth.

• Journal of the Korean Ceramic Society
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• v.55 no.6
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• pp.618-624
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• 2018

We developed a mass production method that simultaneously controls the phase transformation and crystal size of $TiO_2$ coatings on multiwalled carbon nanotubes (MWCNTs). Initially, MWCNTs were successfully coated with amorphous 15-20-nm-thick $TiO_2$ by an in-situ sol-gel method. As the calcination temperature increased in both air and argon atmospheres, the amorphous $TiO_2$ was gradually transformed into the fully anatase phase at approximately $600^{\circ}C$, a mixture of the anatase and rutile phases at approximately $700^{\circ}C$, and the fully rutile phase above approximately $800^{\circ}C$. The crystal size increased with increasing calcination temperature. Moreover, above $600^{\circ}C$, the size of crystals formed in air was approximately twice that of crystals formed in argon. The reason is thought to be that MWCNTs, which continuously supported the stresses associated with the reconstructive phase transformation, disappeared owing to complete oxidation in air at these high temperatures.

• Korean Journal of Materials Research
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• v.12 no.12
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• pp.947-954
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• 2002

HCl concentration and reaction time are the decisive factors in determining the structure of precipitates in the process of synthesis of $TiO_2$ particles from aqueous $TiOCl_2$ solution by precipitation and the volumetric proportion of brookite phase in $TiO_2$ particles can be controlled by these two factors. As reaction rate increases with increase of reaction temperature, the reaction time, at which maximum volumetric proportion of brookite phase in $TiO_2$ particles was obtained, was reduced. The brookite was transformed directly to rutile phase with only increase of reaction time. And precipitation was delayed with increase of HCl concentration because the amount of $H_2$O, which is necessary source of oxygen for conversion of $Ti^{+4}$ to $TiO_2$, was relatively reduced with increase of that. Brookite in the mixture phase powder was finally transformed to rutile phase via anatase through heat-treatment.

• Journal of Powder Materials
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• v.9 no.2
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• pp.110-115
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• 2002

In order to obtain the nano size $10wt%Cu-TiO_2$composite powders by mechanical alloying method for useful composite catalysis, the effects of mechanical alloying time on the formationof $10wt%Cu-TiO_2$ composite powders were analyzed. The phase transformation behaviors were experimented as the heat treating temperature increased. Homogeneous 10wt% Cu-rutile type $TiO_2$composite powders were synthesized in 40 hours by mechanical alloying. After 60 hours mechanical alloying 50 nm size $TiO_2$powders were obtained. Both the phase of mechanically alloyed 10 wt% $Cu-TiO_2$ and pure $TiO_2$ powders were not transformed to anatase after annealing at the temperature range between 350 to 500 $^{\circ}C$. The intermetallic compound of $Cu_2Ti_4$O was formed after 10 hours mechanical alloying, however it could be considered that this intemetallic phase dose not prevent the transformation of rutile $TiO_2$ to the anatase phase after heat treatment at the temperature between 350 and $550^{\circ}C$.

• Korean Journal of Materials Research
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• v.12 no.8
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• pp.641-649
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• 2002

The redox properties of a homogeneously-precipitated $TiO_2$ rutile powder with a BET surface area of ~$200 m^2$/g, consisting of an acicular primary particle, were characterized using photocatalytic reaction in aqueous 4-chlorophenol, Cu-EDTA and Pb-EDTA solutions under ultraviolet irradiation, compared to those of commercial P-25 X$200 m_2$ powder with a spherical primary particle as well as home-made anatase $TiO_2$ powder with ~$200 m^2$/g BET surface area. Here, the anatase powder also includes mainly the primary particles very similar to the acicular shapes of the rutile $TiO_2$ powder. The rutile powder showed the fastest decomposition rate and the largest amount in the photoredor, compared with the anatase or P-25 powder, while the anatase powder unexpectedly showed the slowest rate and the smallest amount in the same experiments regardless of almost the same surface area. From results, the excellent photoredox abilities of this rutile powder appears to be due to specific powder preparation method, like a homogeneous precipitation leading to direct crystallization from the solution, regardless of their crystalline structures even when having the similar particle shape and surface area.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.5
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• pp.181-188
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• 2006

Rutile single crystals grown by skull melting method were cut parallel and perpendicular to growth axis, and both sides of the cut wafers (${\phi}5.5mmx1.0mm$) were then polished to be mirror surfaces. The black wafers were changed into pale yellow color by annealing in air at 1200 and $1300^{\circ}C$ for $3{\sim}15\;and\;10{\sim}50$ hours, respectively. After annealing, structural and optical properties were examined by specific gravity (S.G), SEM-electron backscattered pattern (SEM-EBSP), X-ray diffraction (XRD), FT-IR transmittance spectra, laser Raman spectroscopy (LRS), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). These results are analyzed increase of weight in air, decrease of weight in water and specific gravity, shown secondary phase of needle shape, diffusion of oxygen ion and increase of $Ti^{3+}$. From the above results, we suggest that the skull melting method grown rutile single crystals contain defect centers such as $O_v,\;Ti^{3+},\;O_v-Ti^{3+}$ interstitials and $F^+-H^+$.

• Journal of the Korean Ceramic Society
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• v.35 no.4
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• pp.325-332
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• 1998

Crystalline TiO2 ultrafine powders were prepared simply by heating and stirring aqueous TiOCl2 solution with {{{{ {Ti }^{4+ } }} concentration of 0.5 M from room temperature to 10$0^{\circ}C$ under 1 atmoshpere. The crystallinity and the particle shape of TiO2 ultrafine powders obtained by simple precipitation method were analyzed us-ing XRD(X-ray diffractometer). SEM(scanning electron microscopy) and TEM(transmission electron mi-croscopy) TiO2 crystalline precipitate with rutile phases is fully formed at the temperatures of up to $65^{\circ}C$ and then TiO2 crystalline precipitate with anatase phase starts to be formed above temperatures $65^{\circ}C$ showing its full formation at 10$0^{\circ}C$ These behaviors of TiO2 crystalline precipitate directly from an aqueous TiOCl2 solution would be caused due to the existence of {{{{ OMICRON ^2+ }} ions from distilled water which oxydize TiOCl2 to TiO2 not hydrolyzing it to Ti(OH)4 Here thermodynamically stable TiO2 rutile phase generally formed at higher temperature is practically precipitated at lower temperatures in this study This may be due to the precipitation by very slow reaction enough to make TiO2 particles allocated into stable rutile structure.

• Journal of the Mineralogical Society of Korea
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• v.30 no.3
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• pp.127-136
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• 2017

High pressure has been applied to check the pressure effect on the powdered $TiO_2$-complex, which was synthesized for ultra-violet rays cutoff and antimicrobial applications. $TiO_2$-complex consists of anatase, rutile and silver chloride. Grain size was determined to be ~34 nm. Both anatase and rutile begin structural phase transitions to $ZrO_2$ (baddeleyite)-type crystal structures at 14~16 GPa, then sustain their phases up to 22.7 GPa. Under decompression to 0.0001 GPa (ambient pressure), rutile transforms to another phase with ${\alpha}-PbO_2$ structure, while anatase retains its high pressure structure upon complete decompression. Silver chloride peaks disappear at the low pressures.

• Transactions on Electrical and Electronic Materials
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• v.2 no.2
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• pp.37-41
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• 2001

Photo catalytic characteristics of nano-sized TiO$_2$ powder with rutile phase produced using homogeneous precipitation process at low temperatures (HPPLT) were compared with those of commercial P-25 powder by Degussa Co. The TiO$_2$ powder by HPPLT showed very higher photoactivity in the removal rate, showing lower pH values in the solution, than the P-25 powder when eliminating metal ions such as Pb and Cu from aqueous metal-EDTA solutions. This can be inferred the more rapid photo-oxidation or -reduction of metal ions from the aqueous solution, together with relatively higher efficiencies in the use of electron-hole pair formed on the surface of TiO$_2$ particle, under UV light irradiation. Also, in the view of the TiO$_2$ particle morphology, compared to the well-dispersed spherical P-25 particle, the agglomerated TiO$_2$ particle by HPPL T consists of acicular typed primary particle with the thickness ranged of 3∼7 nm, which would be more effective to the photocatalytic reactions without electron-hole recombination on the surface of the TiO$_2$ particle under the UV light irradiation. It is, therefore, thought that the higher photo activity of the rutile TiO$_2$ powder by HPPLT in the aqueous solutions resulted from having its higher specific surface area as well as acicular shape primary particle with very thin thickness.

• Korean Journal of Materials Research
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• v.22 no.5
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• pp.249-252
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• 2012

Fe doped $TiO_2$ nanoparticles were prepared under high temperature and pressure conditions by mixture of metal nitrate solution and $TiO_2$ sol. Fe doped $TiO_2$ particles were reacted in the temperature range of 170 to $200^{\circ}C$ for 6 h. The microstructure and phase of the synthesized Fe doped $TiO_2$ nanoparticles were studied by SEM (FE-SEM), TEM, and XRD. Thermal properties of the synthesized Fe doped $TiO_2$ nanoparticles were studied by TG-DTA analysis. TEM and X-ray diffraction pattern shows that the synthesized Fe doped $TiO_2$ nanoparticles were crystalline. The average size and distribution of the synthesized Fe doped $TiO_2$ nanoparticles were about 10 nm and narrow, respectively. The average size of the synthesized Fe doped $TiO_2$ nanoparticles increased as the reaction temperature increased. The overall reduction in weight of Fe doped $TiO_2$ nanoparticles was about 16% up to ${\sim}700^{\circ}C$; water of crystallization was dehydrated at $271^{\circ}C$. The transition of Fe doped $TiO_2$ nanoparticle phase from anatase to rutile occurred at almost $561^{\circ}C$. The amount of rutile phase of the synthesized Fe doped $TiO_2$ nanoparticles increased with decreasing Fe concentration. The effects of synthesis parameters, such as the concentration of the starting solution and the reaction temperature, are discussed.