• Title/Summary/Keyword: Ultrafine TiO$_2$ Powder

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Synthesis of Ultrafine TiC-5%Co Powder by Using Co Nitrate and TiO(OH)2 Slurry and Evaluation of Sintered Materials Prepared by Mixing WC-Co (Co 질산염과 TiO(OH)2 슬러리를 이용한 초미립 TiC-5%Co 제조 및 WC-Co 분말과의 혼합에 따른 소결체 특성)

  • Hong, Seong-Hyeon;Kim, Byoung-Kee
    • Journal of Powder Materials
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    • v.15 no.2
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    • pp.107-113
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    • 2008
  • Ultrafine TiC-5%Co powders were synthesized by spray drying of aqueous solution of TiO$(OH)_2$ slurry and cobalt nitrate, followed by calcination and carbothermal reaction. The oxide powders with carbon powder was reduced and carburized at $900^{\circ}C{\sim}1250^{\circ}C$ under hydrogen atmosphere. During reduction, CO gas was mainly evolved by reducing reaction of oxides. Ultrafine TiC-5%Co powders were easily formed by carbothermal reaction at $1250^{\circ}C$ due to using ultrafine powders as raw materials. The ultrafine WC-TiC-Co alloy prepared by sintering of mixed powder of ultrafine WC-13%Co powder and ultrafine TiC-5%Co powder has higher sintered density and mechanical properties than WC-TiC-Co alloy prepared by commercial WC, TiC and Co powders.

Synthesis and Characterization of $TiO_2$ Ultrafine Powder by Chemical Vapor Deposition (화학 증착법에 의한 $TiO_2$ 초미분의 제조 및 입자 특성에 관한 연구)

  • 염선민;이성호;김광호
    • Journal of the Korean Ceramic Society
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    • v.32 no.1
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    • pp.37-44
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    • 1995
  • TiO2 fine powders were synthesized using oxygenolysis and hydrolysis reaction of TiCl4 vapor in gas phase. The TiO2 powder synthesized showed morphological differences depending on reaction system as follows: TiCl4-O2 reaction system produced the monosized particles having polyhedral shape with well-defined crystal planes and the particles did not agglomerate into secondary particles. TiCl4-H2O reaction system, whereas, produced the spherical secondary particles which consisted of fine primary particles. Other powder characteristics such as particle size, impurity content and rutile content are also reported in this study.

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Synthesis of the Ultrafine $BaTiO_3$ power by hydrothermal Process

  • Bae, Dong-Sik;Han, Kyong-Sop;Park, Sang-Heul
    • Proceedings of the Korea Association of Crystal Growth Conference
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    • 1997.10a
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    • pp.87-89
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    • 1997
  • The BaTiO$_3$ fine powder was prepared by hydrthermal method using titanium tetrahydoxide (Ti(OH)$_4$) and barium dihydroxide (Ba(OH)$_2$.8$H_2O$) as raw materials. The fine powder was obtained at temperatures as low as 160 to 185$^{\circ}C$. The properties of the BaTiO$_3$ powder were studied as a function of various parameters (reaction temperature, reaction time, Ba/Ti=ratio, etc). The average particle size of the BaTiO$_3$ increased with increasing reaction temperature. After hydrothermal treatment at 17$0^{\circ}C$ for 8 h, the average particle size of the BaTiO$_3$ powder was about 30 nm and the particle size distribution was narrow.

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Preparation of Ba2Ti9O20 by Coprecipitation Method (공침법에 의한 Ba2Ti9O20의 합성)

  • 이경희;이병하;오권오
    • Journal of the Korean Ceramic Society
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    • v.25 no.6
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    • pp.671-676
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    • 1988
  • Preparation of high purity ultrafine Ba2Ti9O20 powder was investigated by coprecipitation method. Formation of Ba2Ti9O20 powder from precipitate of coprecipitation takes place at 120$0^{\circ}C$, which is 20$0^{\circ}C$ lower than that from mechanical mixtures of BaCO3 and TiO2. This is apparently due to the nature of the compounds formed by the reaction of mixtures of aqueous solutions of BaCl2 and TiCl4 with an ammoniacal solution of ammonium carbonate and ammouium hydroxide. In this method, the Ba2Ti9O20 powders show low callcining and sintering temperature and it has good sintering and dielectric constant at room temperature.

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Photo Catalytic Ability of Acicular Shaped TiO$_{2}$ Rutile Powder in Aqueous Metal-EDTA Solutions

  • Kim, Sun-Jae;chang-Joo choi;Park, Soon-Dong;Hwang, Jong-Sun;Han, Byung-Sung
    • 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.

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Fabrication of Mono-Dispersed Ultrafine BaTiO$_3$ Powder Using Microwave (마이크로파를 이용한 초미세 균일 분산 BaTiO$_3$ 분말 제조)

  • 김현상;최광진;이상균;김영대;심상준;우경자;김경림;조영상
    • Journal of the Korean Ceramic Society
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    • v.36 no.4
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    • pp.343-353
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    • 1999
  • Microwave(2.45 GHz) was used as energy source in hydrothermal reaction to fabricate ultrafine BaTiO3 powder. Using microwave of 700 W, crytal BaTiO3 began to fom after 5 min in microwave-autoclave sys-tem. The crystallinity was not noticeably increased with increasing longer reaction time than 10 min. On the other hand in microwave-reflux system crytal BaTiO3 began to form after 15min and the crystallinity was not noticeably increased with increasing longer reaction time than 1hr,. In either case particle size dis-tribution was considerably uniform due to the effect of homogeneous heating by microwave. In addition mi-crowave heating gave an extremely small degree of particle agglomeration compared to electric heating. Av-erage sizes of as-synthesized powders were 30-60nm. Ba/Ti ratio in sol played an important role in det-ermining the particle size. It seems that excess barium forms different phases such as Ba(OH)2 which makes thin layer on the surface of BaTiO3 powder. This thin layer would inhibit the agglomeration of Ba-TiO3 powders and keep the small grain size. In microwave-autoclave system tetragonal-BaTiO3 was formed directly by the reaction of only 15 min. In the case of microwave-reflux system tetragonal-BaTiO3 was formed by driyng over 25$0^{\circ}C$.

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Study on Photocatalytic Reaction Using Acicular TiO2 Rutile Powder (침상구조의 루틸상 TiO2 초미분체를 이용한 광촉매 반응에 대한 연구)

  • Hwang, Doo-Sun;Ku, Suk-Kyeong;Kim, Kwang-Su;Min, Hyung-Seob;Lee, Eun-Gu;Kim, Sun-Jae
    • 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.

Synthesis and kinetic of ultrafine titanium carbide particles by Mg-thermal reduction of liquid metal chlorides (마그네슘의 금속염 환원에 의한 초미립 탄화티탄 분말 합성거동)

  • 이동원;백진호;김병기
    • Journal of Powder Materials
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    • v.11 no.4
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    • pp.322-327
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    • 2004
  • Ultrafine titanium carbide particles were synthesized by the reaction of liquid-magnesium and vaporized TiCl$_{4}$+C$_{x}$Cl$_{4}$(x = 1 and 2) solution. Fine titanium carbide particles with about 50 nm were successfully produced by combining Ti and C atoms released by chloride reduction of magnesium, and vacuum was then used to remove the residual phases of MgCl$_{2}$ and excess Mg. Small amounts of impurities such as O, Fe, Mg and Cl were detected in the product, but such problem can be solved by more precise process control. The lattice parameter of the product was 0.43267 nm, near the standard value. With respect to the reaction kinetics, the activation energy for the reactions of TiCl$_{4}$+C$_{2}$Cl$_{4}$and Mg was found to 69 kJ/mole, which was about half value against the use of TiCl$_{4}$+CCl$_{4}$, and such higher reactivity of the former contributed to increase the stoichiometry until the level of TiC$_{0.96}$ and decrease the free carbon content below 0.3 wt.%.

Formation Mechanism of Ultrafine $TiO_2$ Powders from Aqueous $TiOCl_2$ Solution by Homogeneous Precipitation Process at Low Temperature (저온 균일침전법으로 $TiOCl_2$ 수용액에서 얻은 $TiO_2$ 초미분체의 형성기구)

  • 김선재;이희균;박순동;전치중;이창규;김흥회;이은구
    • Journal of the Korean Ceramic Society
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    • v.37 no.5
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    • pp.473-478
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    • 2000
  • The TiO2 powder with the values of the large specific surface area more than 150$m^2$/g has been prepared with the homogeneous precipitation process below 5$0^{\circ}C$ and its formation mechanism was investigated using the SEM, TEM and Raman Spectroscopy. With the spontaneous hydrolysis of aqueous TiOCl2 solutions, all the precipitates were fully and homogeneously crystallized with the rutile TiO2 phase simply by heating, which as transformed to the anatase TiO2 phase as increasing the addition of SO42- ions to the aqueous TiOCl2 solution. The precipitates were formed with spherical secondary particles which consisted of acicular, spherical and mixed primary particles corresponding to the rutile, anatase and mixed phases, respectively. It can be thought that the formation and phase determination of crystalline TiO2 powders even at ambient temperature would be related with the existence of the capillary force. This force might be varied depending on the shape change of the primary particles.

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