• 한국재료학회지
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• 제4권4호
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• pp.477-482
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• 1994

열처리에 따른 함수 티타니아의 구조변화를 X-선 회절, 투과전자현미경, 적외선 흡수 및 라만 분광분석 등을 통하여 조사하였다. 과산화수소와 사염화티타의 혼합용액으로부터 $30^{\circ}C$, pH 9에서 함수 티타니아를 제조하였다. 침전물은 완전하게는 결정화되지 않은 anatase형의 티타니아였다. $700^{\circ}C$까지 열처리온도가 증가함에 따라 anatase의 결정성은 증가하였으며, 입성자은 높은 온도에서 일어났다. $700^{\circ}C$에서 anatase로부터 rutile형이 생성되었다.

• 대한화학회지
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• 제22권6호
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• pp.423-430
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• 1978

트리옥산을 니트로벤젠 용매중에서 Ti$Cl_4$로서 중합시킬때 개시 반응기구를 연구하였다. 중합반응속도를 측정한결과 미량의 물이나 메탄올을 첨가하면 반응속도가 급격히 감소하였으며 중합을 개시하는 데는 조촉매로서 다른 물질이 필요 없음이 알려졌다. 유전상수 측정결과에 의하면 중합과정중 양성이온이 생기지 않으며 중합제나 개시제 용액의 전기전도도를 측정한 결과 개시 반응은 니트로벤젠 용매중에서 개시제가 동종간 주고 받기반응에 의하여 생긴 Ti$Cl_3^+$ 양이온에 의하여 일어난다는 것이 판명되었다.

• 한국세라믹학회지
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• 제28권11호
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• pp.892-896
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• 1991

The cyrstallization behavior of lead titanate powders prepared by sol-gel and coprecipitation techniques was investigated. The lead titanate precursors were derived from a mixed solution of lead nitrate and titanium tetrachloride at 4$0^{\circ}C$ to 43$^{\circ}C$ and pH of 9.00 to 9.75. The X-ray diffraction patterns of the dried gel and coprecipitated powders showed it to be amorphous. DTA runs of the powders indicated crystallization to occur at 475~48$0^{\circ}C$. However, the amorphous powders were partially crystallized at 400~45$0^{\circ}C$ with sufficient annealing time. The room temperature Raman spectra from heat-treated powders changed continuously from amorphous to crystalline state with increasing heat-treating temperature. By annealing coprecipitated powders, a dramatic change in the Raman spectra due to the structural relaxation as the annealing temperatures increased, was clearly visible. i.e., coprecipitated, gel, and crystalline structure, in turn.

• Bulletin of the Korean Chemical Society
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• 제30권10호
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• pp.2245-2248
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• 2009

This paper demonstrates room temperature chemical vapor deposition (RTCVD) for fabricating titania inverse opals. The colloidal crystals of monodisperse polymer latex spheres were used as a sacrificial template. Titania was deposited into the interstices between the colloidal spheres by altermate exposures to water and titanium tetrachloride (Ti$Cl_4$) vapors. The deposition was achieved under atmospheric pressure and at room temperature. Titania inverse opals were obtained by burning out the colloidal template at high temperatures. The filling fraction of titania was controlled by the number of deposition of Ti$Cl_4$ vapor. The morphology of inverse opals of titania were investigated. The optical reflection spectra revealed a photonic band gap and was used to estimate the refractive index of titania.

• Bulletin of the Korean Chemical Society
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• 제13권2호
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• pp.176-179
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• 1992

New method for preparing cyclopentanediol from bicyclic ketal is described. Bicyclic ketal is cleaved to give 1,5-diketone, which is then reductively coupled intramolecularly to yield 1,2-cyclopentanediol. A solution of bicyclic ketal (1a) in methylene chloride was treated with aluminum chloride(2 eq.)-sodium iodide(l.5 eq.) at ambient temperature for 3 h to give the 1,5-diketone (2a) in 71% yield after basic work-up followed by short path column chromatography. A solution of the 1,5-diketone (2a) in THF was reacted with titanium tetrachloride(6 eq.)-Mg(Hg)(0.3 eq.) at $0^{\circ}C$ for 4 h to give the 1,2-cyclopentanediol (3a) in 75% yield after basic work-up followed by short path column chromatography.

• 폴리머
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• 제32권4호
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• pp.366-371
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• 2008

The controlled/living cationic polymerization of $\alpha$-methylstyrene (${\alpha}MeSt$) and sequential block copolymerization of isobutylene (IB) with ${\alpha}MeSt$ were achieved using 2-chloro-2,4,4-trimethylpentane (TMPCl)/titanium tetrachloride ($TiCl_4$)/titanium isopropoxide ($Ti(OiPr)_4$)/2,6-ditert-butylpyridine (DtBP) initiating system in $CH_3Cl$/hexane(50/50 v/v) solvent mixture at $-80^{\circ}C$. The polymerization rate decreased with increasing $[Ti(OiPr)_4]/[TiCl_4]$ ratio in the homopolymerization of ${\alpha}MeSt$. The effects of $[Ti(OiPr)_4]/[TiCl_4]$ ratios and $PIB^+$ molecular weight on the polymerization rate and blocking efficiency were also investigated. Well-defined poly(isobutylene-b-$\alpha$-methylstyrene)s were demonstrated by $^1H$-NMR and triple detection SEC; refractive index (RI), multiangle laser light scattering (MALLS) and ultraviolet (UV) detectors. Blocking efficiencies for the poly(isobutylene-b-$\alpha$-methylstyrene)s of almost 100% were obtained when ${\alpha}MeSt$ was induced by PIB's of $M_n\;{\geq}\;41000$ at $[Ti(OiPr)_4]/[TiCl_4]=1$. Differential scanning calorimetry (DSC) of the block copolymers showed two glass transition temperatures, thereby demonstrating microphase separation.

• 한국분말재료학회지
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• 제26권4호
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• pp.282-289
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• 2019

Ti has received considerable attention for aerospace, vehicle, and semiconductor industry applications because of its acid-resistant nature, low density, and high mechanical strength. A common precursor used for preparing Ti materials is $TiCl_4$. To prepare high-purity $TiCl_4$, a process based on the removal of $VOCl_3$ has been widely applied. However, $VOCl_3$ removal by distillation and condensation is difficult because of the similar physical properties of $TiCl_4$ and $VOCl_3$. To circumvent this problem, in this study, we have developed a process for $VOCl_3$ removal using Cu powder and mineral oil as purifying agents. The effects of reaction time and temperature, and ratio of purifying agents on the $VOCl_3$ removal efficiency are investigated by chemical and structural measurements. Clear $TiCl_4$ is obtained after the removal of $VOCl_3$. Notably, complete removal of $VOCl_3$ is achieved with 2.0 wt% of mineral oil. Moreover, the refined $TiCl_4$ is used as a precursor for the synthesis of Ti powder. Ti powder is fabricated by a thermal reduction process at $1,100^{\circ}C$ using an $H_2-Ar$ gas mixture. The average size of the Ti powder particles is in the range of $1-3{\mu}m$.

• 한국결정학회지
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• 제3권1호
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• pp.1-8
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• 1992

졸겔 및 공침법으로 제조된 티탄산 납 분말의 형태를 하소온도와 하소시간의 함수로 조사하였다. 질산 납과 사염화 티탄의 혼합용액을 사용하여 40-43℃ 및 9.0-9.7 pH에서 PbTiO3 전구체를 제조하였으며, 350-1000℃에서 1-10시간동안 공기중에서 이들을 히소시켰다. 하소온도와 시간의 증가에 따라 입자의 크기가 증가하고 응집이 심화되었다. 졸겔법으로 제조된 분말을 700℃에서 히소시킬 때, 초기에 형성된 침상형 혹은 각주 형의 입자들은 하소가 진행됨에 따라 다면체형으로 변한뒤, 모서리가 둥근 다면체형 입자로 성장하였다. 공침법으로 제조된 분말은 결정화 과정중에 형태가 변화되지 않았다.

• 한국산학기술학회논문지
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• 제6권6호
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• pp.457-460
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• 2005

금속 알콕사이드의 가수분해법인 졸-겔 공정을 이용하여 일차로 $TiO_2$와 $ZrO_2$ 나노 입자를 합성하고 난 후 $TiO_2$ 나노입자와 PbO를 혼합하여 $PbTiO_3$의 나노 입자를 얻었다. 2차 공정으로 나노입자 크기의 $ZrO_2$와 혼합하여 최종적으로 $PbZrTiO_3(PZT)$ 분말을 합성하였다. 소결된 압전체의 결정상을 분석하기 위하여 X-선 회절분석을 시행하였으며, 소결전 합성분말의 모양과 크기를 투과전자현미경을 이용하여 관찰하였으며 $900^{\circ}C$의 저온에서 소결한 $PbZrTiO_3$시편의 미세조직을 관찰하기 위하여 주사전자현미경을 이용하였다. 합성된 입자들의 크기는 각각 $TiO_2$는 약 20 ${\~}$ 30nm, $ZrO_2$는 15${\~}$30nm이였으며, $900^{\circ}C$ 저온에서 소결한 PZT 시편의 SEM 관찰결과 평균 입경은 $2{\~}4{\mu}m$의 페로 브스카이트 결정으로 치밀한 조직을 나타내었으며, 우수한 압전 특성도 나타내었다.

• Journal of Mechanical Science and Technology
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• 제17권9호
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• pp.1388-1396
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• 2003

The hydrodynamic instability of the three-dimensional boundary layer on a rotating disk introduces a periodic modulation of the mean flow in the form of stationary cross flow vortices. The instability labeled Type II by Faller occurs first at lower Reynolds number than that of well known Type I instability. Detailed numerical values of the amplification rates, neutral curves and other characteristics of the two instabilities have been calculated over a wide range of parameters. Presented are the neutral stability results concerning the two instability modes by solving the appropriate linear stability equations reformulated not only by considering whole convective terms but also by correcting some errors in the previous stability equations. The present stability results agree with the previously known ones within reasonable limit. Consequently, the flow is found to be always stable for a disturbance whose dimensionless wave number is greater than 0.75. Some spatial amplification contours have been computed for the stationary disturbance wave, whose azimuth angle $\varepsilon$= 11.29$^{\circ}$ to 15$^{\circ}$ and for the moving disturbance wave, whose azimuth angle $\varepsilon$ = 12.5$^{\circ}$ to 15$^{\circ}$. Also, some temporal amplification contours have been computed for the stationary disturbance wave, whose azimuth angle $\varepsilon$= 11.29$^{\circ}$ to 15$^{\circ}$ and for the moving disturbance wave, whose azimuth angle $\varepsilon$= 12$^{\circ}$ to 15$^{\circ}$. The flow instability was observed by using a white titanium tetrachloride gas over rotating disk system. When the numerical results are compared to the present experimental data, the numerical results agree quantitatively, indicating the existence of the selective frequency mechanism.