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졸-겔법에 의한 구형 mullite 전미분체의 제조 및 mullite 화 공정기구의 해석 1. 졸 - 겔 공정변수가 mullite 전미분체의 제조와 mullite 화에 미치는 영향
황운연(Un Yeon Hwang),이승구(Seung Gu Lee),구기갑(Kee Kahb Koo),박형상(Hyung Sang Park),유승준(Seung Joon Yoo),윤호성(Ho Sung Yoon) 한국화학공학회 1999 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.37 No.3
In this study, spherical fine pre-mullite particles were prepared by partial hydrolysis method to control the reaction rate difference of two alkoxides and by mixed solvent method to control the particle shape. The optimum conditions for preparing spherical pre-mullite particles were; ([TEOS]= 0.0333 ㏖/ℓ, [ASB] =0.1 ㏖/ℓ, [H₂O] =0.5 ㏖/ℓ, [acetonitrile]= 40 vo1%, [HPC] 0.l g/ℓ). A1₂O₃ : SiO₂ molar ratio of pre-mullite particles determined by XRF analysis was about 3:2. Mullitization reactions were studied by DTA, XRD, and FT-IR analysis. Pre-mullite particles were determined amorphous by XRD analysis, and all pre-mullite powders showed an exothermic peak around 990 ℃ on DTA analysis associated with crystallization to spinel phase. The samples passing through the spinel phase were transformed into the T-mullite at around 1,100 ℃ and the transformation to O-mullite took place about 1,250 ℃. [H₂O]/[Si-alkoxide] molar ratio added in the partial hydrolysis reaction had an important effect upon the mullitization of pre-mullite powder, the pre-mullite particles of the highest degree of SiO-Al bonding were obtained when [H₂O]/[Si-alkoxide] was I and the particles crystallized to O-mullite at low temperature (1224.43 ℃) than other particles.
곽동희,유승준,Se-Il Lee,김광길,황경준,이재욱,Un-Yeon Hwang,박형상,Jong-Ok Kim 한국화학공학회 2008 Korean Journal of Chemical Engineering Vol.25 No.5
Nanosized TiO2 sol synthesized by sol-gel method was successfully coated on the porous red clay tile (PRC tile) with micrometer sized pores. PRC tile was first coated with a low-firing glaze (glaze-coated PRC tile) and then TiO2 sol was coated on the glaze layer. A low-fired glaze was prepared at various blending ratios with frit and feldspar, and a blending ratio glazed at 700 oC was selected as an optimum condition. Then TiO2 sol synthesized from TTIP was dip-coated on the glazed layer (TiO2/glaze-coated PRC tile), and it was calcined again at 500 oC. Here, these optimum calcination temperatures were selected to derive a strong bonding by a partial sintering between TiO2 sol particles and glaze layer. Photocatalytic activity on the TiO2/glaze-coated PRC tile was evaluated by the extent of photocatalytic degradation of methylene blue and acetaldehyde. Methylene blue with the high concentration of 150 mg/l on the surface of TiO2/glaze-coated PRC tile was almost photodegraded within 5 hours under the condition of average UV intensity of 0.275 mW/cm2, while no photodegradation reaction of methylene blue occurred on the glaze-coated PRC tile without TiO2. Another photocatalytic activity was also evaluated by measuring the extent of photocatalytic degradation of gaseous acetaldehyde. The photodegradation efficiency in TiO2/glaze-coated PRC tile showed about 77% photocatalytic degradation of acetaldehyde from 45,480 mg/l to 10,536 mg/l after the UV irradiation of 14 hours, but only about 16% in the case of the glaze-coated PRC tile.
혼합용매법에 의한 Mullite 전미분체 생성기구에 관한 연구
황운연,이정운,박형상,김용렬,구기갑 한국화학공학회 2003 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.41 No.4
Si-와 Al-알콕시드의 반응속도 차이를 조절하기 위한 부분 가수분해법과 입자 형태를 제조하기 위한 혼합용매법을 이용하여 구형의 미세한 mullite 전미분체를 제조하였다. Mie 이론을 적용시켜 반응시간에 따른 반응용액의 탁도 및 입자 수밀도의 변화를 측정하여 혼합용매법에 의한 입자 생성기구에 대하여 고찰하였다. 알콕시드와 옥탄올 용액에 아세토니트릴을 첨가하면 알콕시드의 용해도가 낮아지고 따라서 알콕시드의 일부가 액적을 형성하며, 액적은 안정화제 (HPC)에 의하여 구형을 유지하게 된다. 그리고 가수분해 및 축합중합 반응에 의하여 액적의 입자 크기는 감소하며, 동시에 혼합용액에 용해되어 있던 알콕시의 가수 분해 및 축합중합 반응에 의하여 미세 입자가 생성된다. 액적형태로 생성된 큰 입자와 미세 입자의 응집에 의하여 최종 입자가 생성되었다. In this study, spherical fine pre-mullite particles were prepared by partial hydrolysis method to control the reaction rate difference of two alkoxides, and by mixed solvent method to control the particle shape. Based on the adaptation of Mie theory, the formation mechanism of pre-mullite particle in alkoxide-octanol-acetonitile system has been investigated by measuring of the turbidity of solution, the number density and the size of the particles during the reaction. As the acetonitrile was added in the alkoxide-octanol solution, the solubility of the alkoxide decreased. A part of alkoxide was segregated from solution in the form of droplets. whereas the rest of the alkoxide existed as dissolved state in octanol. The droplets are stabilized with stabilizer (HPC). In the next step. hydrolysis and condensation reactions of the alkoxide droplets decrease the size of droplets and, at the same time, fine particles are formed from the alkoxide dissolved in octanol. Subsequently, the final particles are produced by aggregation between the large particles through the droplet form and the fine particles.
박형상,윤호성,황운연,유승준,이승구,이정운,최진훈,김용렬 한국화학공학회 2000 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.38 No.5
본 연구에서는 부분가수분해 및 혼합용매법을 이용하여 세 가지 조성의 mullite 전미분체를 제조하였다. FT-IR 분석 결과 mullite 전미분체는 Si^(iv)-O-Al^(vi) 결합을 형성하고 있음을 알 수 있었다. DTA 결과에 의하면 mullite 전미분체의 알루미나 양이 증가할수록 더 낮은 온도에서 1차 발열반응이 일어났고, mullite 전미분체를 1차 발열 반응이 일어나는 온도까지 하소한 후 HF 용액으로 처리된 시료를 1600℃까지 100℃간격으로 하소한 시료에 대한 XRD 분석결과에 의하면 Aksay가 제시한 70.5≤Al₂O₃wt%≤74의 조성범위에서 mullite 단일상이 생성되었다. 그리고 990℃부근에서의 1차 발열반응에 의하여 Si-O-Al 결합을 갖고 있는 Al-Si 스피넬상의 생성과 비정질 SiO₂의 유리현상이 일어났다. 그리고 mullite 전미분체와 침출공정을 거친 시료에 대한 DTA, XRD 및 FT·IR 분석결과를 종합해 보면 스피넬상의 생성과 함께 유리된 비정질 SiO₂가 mullite화 공정에 많은 영향을 미치고 있음을 알 수 있었다. In this study, spherical pre-mullite powders of three composition were prepared by partial hydrolysis on the TEOS and mixed solvent method. From the FC-IR analysis of pre-mullite powders, the structure could be interpreted that SiO₂ tetrahedron and AlO_6 octahedron are bonded randomly by sharing oxygen atom. By the DTA analysis, the amount increase of Al₂O₃composition in the pre-mullite caused the shift of first exotherm to low temperature. As a result of XRD analysis on the pre-mullite and leached sample calcined from 1,200 ℃ to 1,600 ℃, only mullite phase was created in the range from 70.5 wt% to 74.0 wt% alumina, which was identical with the Aksay's range. The first exotherm at about 990 ℃ during the calcination of pre-mullite has been attributed to the formation of Al-O-Si spinet due to the liberation of amorphous silica. By means of the leaching experiment on the silica which coexisted with the spinet phase and the mullitization of leached sample, the amorphous silica liberated at about 990℃ was very essential for the mullitization. Insufficient or lack of amorphous silica can cause the formation of a-alumina with the O-Mullite by the calcination at about 1,400℃.