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분체공학,유동층,고분자,재료(무기, 유기) : 혼합용매법에 의한 Mullite 전미분체 생성기구에 관한 연구
황운연 ( Hwang Un Yeon ),이정운 ( Lee Jeong Un ),박형상 ( Park Hyeong Sang ),김용렬 ( Kim Yong Lyeol ),구기갑 ( Gu Gi Gab ) 한국화학공학회 2003 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.41 No.4
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.
공정시스템 , 이동현상 , 화학공정안전 : 졸 - 겔법에 의한 다공성 알루미나 미분체 제조에 관한 연구 - 1 . 물과 알콕시드의 비가 알루미나 미분체의 물리적 특성에 미치는 영향
황운연(Un Yeon Hwang),이성원(Sung Won Lee),이정운(Jung Woon Lee),박형상(Hyung Sang Park),구기갑(Kee Kahb Koo),김용렬(Yong Ryul Kim),윤호성(Ho Sung Yoon),유승준(Seung Joon Yoo) 한국화학공학회 2001 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.39 No.2
Porous alumina particles were prepared using a mixed solvent to control the reaction rate of Al-alkoxide and the particle shape. Monodispersed alumina particles with submicron size were obtained in the condition of [H₂O]/[Al-alkoxide] ratio of 2-8 in the mixed solvent. In contrast, precipitation of agglomerates and large powders were obtained in the condition of [H₂O/[Alalkoxide]≥15. As the increase of the [H₂O]/[Al-alkoxide] ratio, the crystal structure of as-prepared particles was continuously varied from amorphous Al(OH)₃ to pseudo-boehmite with chemical composition of AlO(OH). From BET analysis, the pore structure of the particles calcined at 600℃ had been changed from ink-bottle to open cylinder shape with increasing of dte [H₂O]/[Al-alkoxide] ratio. The specific surface area and pore diameter of samples calcined at 600℃ were 521-865 ㎡/g and 6.6-14 ㎚ respectively. The specific surface area of samples calcined at 1,100 ℃ was 35-120 ㎡/g respectively.
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.
황운연(Un Yeon Hwang),이승구(Seung Gu Lee),최진훈(Jin Hoon Choi),이정운(Jung Woon Lee),박형상(Hyung Sang Park),유승준(Seung Joon Yoo),윤호성(Ho Sung Yoon),김용렬(Young Ryul Kim) 한국화학공학회 2000 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.38 No.5
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℃.
황운연(Un Yeon Hwang),이승구(Seung Gu Lee),이정운(Jung Woon Lee),박형상(Hyung Sang Park),유승준(Seung Joon Yoo),윤호성(Ho Sung Yoon),김용렬(Yong Ryul Kim) 한국화학공학회 2000 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.38 No.6
In this study, transparent yttria stabilized zirconia(YSZ)-gel and ZrO₂-gel were prepared by the alkoxide-acetylacetone chelation method of Zirconium-n-propoxide. Transparent ZrO₂-gel.could be prepared through 1 hour reaction and three hours aging in the condition of 0.4 S [Acac]/[Zr-n-p]=R S 0.6. The gelation time was increased with increasing the molar ratio R. The molar ratio R had an important effect upon the inner structures of gel and the crystallization process. YSZ-gel of the four kinds of composition was prepared in the condition of [Acac]/[Zr-n-p] = 0.5. Crystallization behavior of these gels depended upon the concentration of Y₂O₃. All samples dried at 60℃ for 24 hr were amorphous by XRD analysis, and the first crystalline phase obtained beyond 450℃ from the dried samples was the cubic one. The 2.SYSZ and 4.5YSZ samples passed through the cubic phase were transformed into the tetragonal phase was at arround 600℃ and 1,000℃, respectively. For 6.5YSZ and 8.5YSZ, cubic structure was developed continuously without transformation of crystal structure by 1,000 ℃. An exothermic peak around 450 ℃ on DTA analysis associated with the crystallization to cubic phase and the formation of ZrOCO₃(lattice), H₂O, and CO₂. The third exotherm (about 850 ℃) during the calcination was attributed to the liberation of CO₃^(2-) .
분체공학 , 유동층 , 재료 ( 무기 , 유기 , 고분자 ) : 혼합용매법에 의한 구형 TiO2-SiO2 미분체의 제조 및 이소프로판올 분해 특성에 관한 연구
황운연(Un Yeon Hwang),서진석(Jin Seok Seo),이정운(Jung Woon Lee),최진훈(Jin Hoon Choi),박형상(Hyung Sang Park),김용렬(Yong Ryul Kim),유승준(Seung Joon Yoo),윤호성(Ho Sung Yoon) 한국화학공학회 2001 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.39 No.1
The physical properties which affect on the activity of photocatalysts are active site number and surface area, etc. Recently, to control these properties, `Sol-Gel` methods are used to synthesize photocatalysts. In this study, we synthesized spherical TiO₂-SiO₂ photocatalysts by mixed solvent method, and analyzed the changes in morphology of the catalysts with synthesis conditions by SEM and the changes in physical properties of the particles and the variation of the crystal structure with Ti concentration and calcination temperature by TGA, BET, FT-IR and XRD. Then we investigated the effects of the physical properties and [Ti]/[Si] ratio on phobocatalytic degradation of iso-propanol. The particle size was demeaned with increasing HPC concentration and decreasing Ti concentration. The surface area of the catalysts was decreased by increasing Ti concentration and calcination temperature. As Ti concentration was increased, Ti-O-Si bond number was increased, and by calcination, the number was increased until 400 ℃, then decreased with increasing calcination temperature. The extent of photodegradation of isopropanol was higher as photocatalysts have more Ti, but the turnover frequency of the Ti was higher as the catalysts have less Ti. Because (Ti^(3+)-O^-) number and the surface area of the photocatalysts are decreased by increasing calcination temperature, the photodegradation of organic material is decreased.
황운연(Un Yeon Hwang),이정운(Jung Woon Lee),최진훈(Jin Hoon Choi),박형상(Hyung Sang Park),유승준(Seung Joon Yoo),윤호성(Ho Sung Yoon),김용렬(Young Ryul Kim) 한국화학공학회 2000 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.38 No.5
This study is to clarify the existing outstanding problems concerning (i) the nature of the exothermic reaction, (ii) the structure and composition of the spinet phase, and (iii) the mechanism of mullite formation. The structure of pre-mullite particles could be interpreted to be one where SiO₄tetrahedron and AlO_6 octahedron are bonded at random by sharing oxygen atom. The composition of the spinet phase was most likely 2Al₂O₃·SiO₂, and it is regarded that 4 Si^(4+) and 4 Al^(3+) occupy the available 8 tetrahedral sites and 12 Al^(3+) occupy the available 16 octahedral sites leaving 4 octahedral sites being left vacancy. On this basis, the composition of the unit cell of spinel is 口₄Al_(12)^(vi)[Al₄Si₄]^(iv)O_(32), where □ represents a vacancy in the octaheral coordination state. The sample passed through the spinet phase was transformed into the T-Mullite at around 1,100℃ and transformation of T-Mullite to O-Mullite could take place about 1,250℃. In the mullititation process as mentioned above, change of coordination number of Al^(3+) ion and diffusion of SiO₂into the crystal cccured continuously with increasing calcination temperature until the 3 : 2 mullite is formed.
공정시스템 , 이동현상 , 화학공정안전 : 졸 - 겔법에 의한 다공성 알루미나 미분체 제조에 관한 연구 - 2 . 물과 알콕시드의 비가 알루미나 미분체의 결정화 공정에 미치는 영향
황운연(Un Yeon Hwang),이성원(Sung Won Lee),이정운(Jung Woon Lee),박형상(Hyung Sang Park),구기갑(Kee Kahb Koo),유승준(Seung Joon Yoo),윤호성(Ho Sung Yoon),김용렬(Yong Ryul Kim) 한국화학공학회 2001 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.39 No.2
Spherical porous alumina particles were prepared by mixed solvent to control the reaction rate of Al-alkoxide and the particle shape with hydroxy-propyl cellulose(HPC). HPC was used as a dispersant to prevent aggregation during the formation of particles. The effect of [H₂O]/[ASB] ratio on the crystallization reactions of as-prepared particles was studied by XRD, FT-IR, and TG-DTA analysis. The mole ratio of water and Al-alkoxide added in the condensation reaction had an important effect on the crystal structure of as-prepared particles and the calcined particles. As the [H₂O]/[ASB] ratio increase, the crystal structure of as-prepared particles was continuously varied from amorphous Al(OH)₃ to pseudo-boehmite with chemical composition of AIO(OH). The samples which have higher crystallinite after drying process were transformed into the δ- and θ-Al₂O₃ at lower calcination temperature, but these sample were transformed into α-Al₂O₃ at higher calcination temperature. This result was thought to be the transformation of the coordination number of Al^(3+) ion in the crystal structure. The particles prepared by [H₂O]/[ASB]=2 condition crystallized to α-Al₂O₃at 600℃ and converted to η-Al₂O₃at 1,100℃ without intermediate phases.
졸 - 겔 법에 의한 단분산 구형 실리카입자 형성에 대한 합성조건 및 전해질의 영향
윤호성,황운연,박형상 ( Ho Sung Yoon,Un Yeon Hwang,Hyung Sang Park ) 한국화학공학회 1996 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.34 No.5
The effects of reaction parameters such as [NH₃], r(H₂O/Si molar ratio) and temperature on hydrolysis, condensation and final silica particles, and the effects of electrolyte addition on the change of final silica particle sizes in the sol-gel process were investigated. In our experimental conditions, the increment of [NH₃] and r accelerates the hydrolysis and condensation and increases the particle size. But particle size decreases when r=20 as compared to when r=10. The activation energies of hydrolysis and condensation are 5.78 and 3.34 ㎉/㏖, respectively, and the increase of the temperature decreases the particle size. The addition of salt to solutions does not affect the reaction rates, but increases the final silica particle sizes. The increase of the electrolyte concentration and the number of counter ions in electric double layer increase the final silica particle sizes due to the mobility of the counter ions in LiCl, NaCl and KCl. These results are quite compatible with DLVO theory in which the increase of κ(Debye-Huckel constant) decreases primary particle size and increases final particle size. Correlating primary particle sizes to final particle sizes obtained by the aggregation growth mechanism shows that the final particles grow through the aggregation of primary particles.
졸 - 겔법에 의한 단분산 구형 실리카입자의 성장에 관한 연구
윤호성,황운연,박형상 ( Ho Sung Yoon,Un Yeon Hwang,Hyung Sang Park ) 한국화학공학회 1996 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.34 No.5
From the formation of the monodispersed silica particle which is a valuable for the industry by Sol-Gel process, the effects of the parameters participated in the process, the growth mechanism and the characteristics of silica particles for each reaction conditions are investigated. In this study, the precursor is TEOS(tetraethoxysilane) and the parameters are [NH₃], r(H₂O/Si molar ratio), temperature. To investigate about the formation of final silica particles, the suspension which performs the polymerization is reacted with molybdic acid, and the evolutions of TEOS and silica particle size are investigated in the reaction time due to the characteristics of molybdic acid with the suspension. The kinetics were performed about the effects of these parameters. Hydrolysis is the rate limiting step and each reaction is performed by S_N-2 reaction and steric effect exists due to the change of alkoxy group. From the results, a constant number of silica particle is formed at early reaction stage. Silica particles grow through the aggregation of smaller particles and nucleation is rate-limiting step for the growth of particles. In the conditions of this study, spherical silica particles are formed, [NH₃] and [H₂O] concentration increase the particle size hut particle size decrease with [H₂₂O] concentration which is a certain above region. Average particle sizes are 187.44-48 3.33 ㎚ and standard deviations in the average particle size are 1.7-2.9% with each experimental condition. From the BET results, specific surface area is 5.5-23.4 ㎡/g and these values decrease with increase size. The average pore size is 50-70 Å.