• Title/Summary/Keyword: Pseudo-boehmite

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Preparation of Porous Boehmite Gel from Waste AlCl3 Solution (AlCl3 폐액으로부터 다공성 Boehmite Gel의 제조)

  • Park, Byung-Ki;Lee, Hak-Soo;Kim, Young-Ho;Lee, Jung-Min
    • Journal of the Korean Ceramic Society
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    • v.41 no.11
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    • pp.864-871
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    • 2004
  • Porous pseudo-boehmite gel was prepared through the aging process of amorphous aluminum hydroxides gel precipitated by the hydrolysis reaction of dilute NaOH solution and AlCl$_3$ solution. In this study, the synthesis method was studied on porous pseudo-boehmite gel having maximum pore volume, as being investigated the changes of crystal structure, infrared rays absorption spectrum, BET surface area and pore structure when the hydrolysis reaction is controlled in the range of pH 7.6~11.6 and the aging process is hold up for 2~24 h at 60~10$0^{\circ}C$. We could find that the gel precipitates deposited in in range of pH 7.6~9.6 were developed into porous pseudo-boehmite which surface area was 250~357 $m^2$/g, pore volume was 0.4~0.7 cc/g and average pore size was 58~l14$\AA$. However, the gel precipitates deposited in range of pH 10.6~11.6 were developed into bayerite which pore volume was very little.

Hydrolysis of Aluminum Nitride Powder (AlN 분말의 가수분해 특성)

  • 최상욱;정홍식;황진명
    • Journal of the Korean Ceramic Society
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    • v.31 no.1
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    • pp.79-87
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    • 1994
  • Aluminum nitride was hydrolyzed in contact with water, evolving the reaction heat of 172 cal/g within 12 hours to form alumina trihydrates. At 4$0^{\circ}C$ >, amorphous alumina hydrate was easily produced by the spontaneous breaks of AlN particle at the beginning of the hydrolysis process, while bayerite was formed by the dissolution-recrystallization processes of amorphous alumina hydrate at the temperature between 4$0^{\circ}C$ and 6$0^{\circ}C$, and pseudo-boehmite was generated on the surface of AlN particle by the condensation process of the corresponding phase at 6$0^{\circ}C$ <. The longer the hydrolysis timje or the higher the value of pH in solution, the more the bayerite phase was produced. However, pseudo-boehmite was easily generated under the following favorable conditions; when the hydrolysis reaction occured rapidly at the beginning and when the absorption of OH radical on the surface of AlN particle was disturbed by ethyl alcohol in a solution. However, aluminum nitride was hardly hydrolyzed in a solution of pH 2.0.

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Characteristics of $\gamma$-Alumina Prepared from Rehydrated Amorphous Alumina (수화한 무정형 알루미나로부터 제조된 $\gamma$-Alumina의 특성)

  • Kim, Yun-Seop;Go, Hyeong-Sin;Seo, Jeong-Gwon;Lee, Jeong-Min;Ha, Baek-Hyeon
    • Korean Journal of Materials Research
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    • v.11 no.11
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    • pp.978-985
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    • 2001
  • The amorphous alumina was obtained by flash calcination of Bayer gibbsite[$Al(OH)_3$aluminum trihydroxide]. Rehydration and pore characteristics of $r-A1_2O_3$ prepared from rehydrated amorphous alumina were investigated. Crystal phases of pseudo-boehmite and bayerite were changed when amorphous alumina was hydrated at various conditions such as time, the ratio of water/alumina and pH. Specific surface areas and pore volumes of $r- A1_{2O}_3$ were influenced by the reaction time, water/alumina and PH of rehydration. The total pore volume of $r-A1_{2O}_3$increases with increasing the reaction time and ratio of water/alumina. Especially, the pure pseudo-boehmite of single phase could be prepared, when amorphous alumina was hydrated in the range of pH 6.5-8.0 in water/alumina= 10 at $90^{\circ}C$ for 7hr. The $r-Al_{2O}_3$, obtained by calcination of the prepared pseudo-boehmite at $500^{\circ}C$ for 2hrs, is characterized by the specific surface area of $265m^2$/g, total pore volume of $0.75cm^3$/g.

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Preparation of High Purity Alumina by Alkoxide Process (Aluminum Isopropoxide의 가수분해법에 의한 고순도 $\alpha$-Al2O3의 제조)

  • 백행남;이명기;곽중협;서태수
    • Journal of the Korean Ceramic Society
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    • v.26 no.3
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    • pp.445-451
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    • 1989
  • Hydrolysis of aluminum isopropoxide with excess water in the presence of excess isopropyl alcohol resulted in the formation of boehmite in independence of temperature of hydrolysis and aging. Stoichiometric and substoichiometric amount of water hydrolyzed aluminum isopropoxide to pseudo-boehmite and amorphous one, respectively. $\alpha$-Al2O3 with 0.3${\mu}{\textrm}{m}$ in median size was produced by calcination of boehmite, bseudo-boehmite and amorphous boehmite at 125$0^{\circ}C$, 120$0^{\circ}C$, and 115$0^{\circ}C$ for one hour, respectively. Singnificant reduction in particle size was found during transition from $\theta$-Al2O3 to $\alpha$-Al2O3. $\alpha$-Al2O3 produced in this study was relatively uniform spherical and its purity was found to be over 99.9%.

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Pore Characteristics of Porous Alumina Ceramics Fabricated from Boehmite Hydrosol and Alumina Particles (Boehmite 수화졸의 알루미나로 제조한 다공성 알루미나 세라믹스의 기공특성)

  • 오경영
    • Journal of the Korean Ceramic Society
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    • v.33 no.5
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    • pp.547-555
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    • 1996
  • Porous alumina ceramics were fabricated by pseudo-boehmite phydosol-gel process within/without commercial $\alpha$-alumina particles average 1 and 40 micron respectively. The pore characteristics of fired specimens were studied by the measurement of bulk density total porosity thyermal analysis pore volume pore distribution BET area XRD and SEM. with increasing of firing temperature pore volume and BET surface area were decreased and the average pore size was increased to approximately 146$\AA$ upto 80$0^{\circ}C$ by de-watering of [OH] and formation of $\alpha$-alumina. The fired relative density of the alumina-dispersed specimen with average 1 micron particle was increased with the amounts of dispersed particle by bimodal packing theory which is compared to the ones of specimen including of average 40 micron particle. It was confirmed that the percola-tion threshold in porous ceramics with coarser particle (40 micron) has formed between the transformed-alumina from hydrogel and dispersed-alumina of above 50 vol% particle and the total porosity was increased at the threshold point above.

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Effect of MgO on Microstructural Evolution of Alumina Prepared from Hydrosol-Gel Process of Boehmite in Plaster Mold (석고몰드속에서 Boehmite의 Hydrosol-Gel로부터 제조된 알루미나의 미세구조에 미치는 M\ulcorner의 영향)

  • 오경영;정창주
    • Journal of the Korean Ceramic Society
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    • v.30 no.12
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    • pp.1029-1038
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    • 1993
  • The microstructures of aluminas, included of dissolved CaO as $\alpha$-alumina seeded pseudo-boehmite hydrosol was gelled in plaster mold and doped of MgO as dipping of calcines(120$0^{\circ}C$-2h) into Mg-nitrate solution, were compared to the one of which additives are excluded during the gellation. It was formed the boundary layer of 300~350${\mu}{\textrm}{m}$ distance from surface to the inside, containing of approximately 500ppm CaO by dissolved Ca from plaster mold. As the MgO addition to the boundary layer with dissolved CaO, the microstructure of the layer was uniformed and inhibited the grian growth, compared to one of that additives be excluded specimen and of MgO doped-inside region. This result was considered as abnormal grain growth and effect of flat boundary formation be appeared by effects of dissolved CaO, were decreased by MgO co-doping.

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Synthesis of High Purity Al2O3 from Low Grade Bauxite Ore(II) (저품위 Bauxite로부터 고순도 Al2O3의 합성(II))

  • Kwon, Kung-Taek;Song, Yon-Ho;Lee, Chul-Tae
    • Applied Chemistry for Engineering
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    • v.5 no.4
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    • pp.597-608
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    • 1994
  • A new process for the production of high purity ${\alpha}-Al_2O_3$ from ammonium aluminium sulfate solution abtained through the sulfation of low grade bauxite ore with $(NH_4)_2SO_4$, and leaching of the sulfated product was investigated. This process is consisted of solvent extraction for Fe component removal from ammonium aluminum sulfate solution and homogeneous precipitation of Al containing precipitate from the refined ammonium aluminium sulfate solution by using urea as precipitator. The optimum conditions of solvent extraction with Alamine 336 as extractant were shaking time of 4min, organic phase ratio to aqueous phase of 0.25. The types of precipitation products from this precipitation were amorphous alumina gel, pseudo-boehmite and crystalline boehmite in the lower temperature of $100^{\circ}C$, in the range from $125^{\circ}C$ to $150^{\circ}C$, and above $150^{\circ}C$, respectively. And also amorphous alumina gel hydrate in $1000^{\circ}C$ and crystalline boehmite in $1250^{\circ}C$ were tranfered to ${\alpha}-Al_2O_3$, respectively. This alumina was identified as ${\alpha}-Al_2O_3$ of purity 99.7%.

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Effect of Titanium Sulfate Addition on Crystal Growth of the Flaky α-Al2O3 (황산티타늄의 첨가가 판상 α-Al2O3의 결정성장에 미치는 영향)

  • Park, Byung-Ki;Cho, Sun-Mi;Lee, Jung-Min
    • Journal of the Korean Ceramic Society
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    • v.42 no.5 s.276
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    • pp.338-345
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    • 2005
  • To prepare the complex gel of flux and pseudo-boehmite used in precursor of the flaky ${\alpha}-A1_2O_3$ crystal, aqueous solution of the mixture of sodium carbonate and sodium phosphate was added with stirring in aqueous solution of the mixture of sodium sulfate, potassium sulfate and titanium sulfate. The complex gel was dried at $110^{\circ}C$ and was crystallized above $1,050^{\circ}C$, and then the effect of the amount of titanium sulfate on size, morphology, thickness and crystal size distribution of the flaky ${\alpha}-A1_2O_3$ crystal was investigated. Addition of titanium sulfate was prevented the aggregation and generation of twin crystal, and had an effect on the crystal size and the thickness during crystal growth. When the amount of titanium sulfate was more than 6 g, particle size was decreased but was free from crystal twining and aggregation. On the other hand, when the amount of titanium sulfate was lower than 6 g, crystal size was increased but crystal twinning and aggregation were noticed.

The Rehydration Properties of Amorphous Alumina Powder in Low Water/Alumina Ratio (낮은물/알루미나 비에서 비정질 알루미나 분말의 수화특성)

  • 박병기;서정권;이정민;서동수
    • Journal of the Korean Ceramic Society
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    • v.35 no.10
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    • pp.1085-1093
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    • 1998
  • Amorphous alumina powder prepared by the fast calcination of aluminum trihydroxide(Al(OH)3 gibbsite) for 0.5 second at 580$^{\circ}C$ was investigated rehydration propeties. Phase composition crystal size and mor-phology surface area pore volume and pore size distribution of pesudo-boehmite and bayerite crystals changed with temperature time water/alumina ratio and particle size when amorphous alumina rehydrated with water. Phase compositions were examined with XRD and DTA and crystal sized morphologies were investigaed with SEM and TEM. Also rehydration properties of amorphous alumina were in-vestigated by measuring the surface area pore volume and pore size distribution.

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Preparation of Fe2O3 Supported γ-alumina Catalyst by Hydrothermal Method (수열법에 의한 Fe2O3 담지 감마알루미나 촉매제조)

  • 박병기;이정민;서동수
    • Journal of the Korean Ceramic Society
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    • v.40 no.7
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    • pp.683-689
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    • 2003
  • The cylindrical ${\gamma}$-alumina pellets were prepared using amorphous alumina and pore generating agent. Its were immersed in aqueous solution of the mixture of Fe(NO$_3$)$_3$.9$H_2O$ and $CH_3$COOH, Fe(NO$_3$)$_3$.9$H_2O$ and $CH_3$COOH and HNO$_3$, and Fe(NO$_3$)$_3$.9$H_2O$ and HNO$_3$. The pellets thus were hydrothermally treated at 20$0^{\circ}C$ for 3 h in autoclave, and were investigated morphologies and changes of crystal pore characteristics, $N_2$ adsorption and desorption isotherms, active sites and mechanical strength etc. According to the preparation method, acicular platelet pseudo-boehmite crystals of 0.1~0.3 ${\mu}{\textrm}{m}$ size were transformed into acicular pseudo-boehmite cristals of 0.5~2 ${\mu}{\textrm}{m}$ size having the same crystal structure. When ${\gamma}$-alumina pellets were immersed in aqueous solution of the mixture of Fe(NO$_3$)$_3$.9$H_2O$ and $CH_3$COOH and then were hydrothermally treated, pore volume between 100 $\AA$ and 1000 $\AA$ was increased from 0.34 ㏄/g to 0.86 ㏄/g, and the gap of $N_2$ adsorption and desorption hysteresis loop was decreased due to increasement of pore size. New active site that could adsorb the C-H functional group was created on the catalist. Also, mechanical strength of catalyst was increased from 1.06 ㎫ to 1.36 ㎫.