• Title/Summary/Keyword: bayerite

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Synthesis and Characterizations of Aluminum Hydroxide Using NaOH Additional Amounts and Polyalmuniumchloride (Polyaluminumchloride와 NaOH 첨가량에 따른 수산화알루미늄 합성에 관한 연구)

  • Hwang, Dae Ju;Cho, Kye Hong;Choi, Moon Kwan;Ahn, Ji Whan;Han, Choon;Lee, Jong Dae
    • Korean Chemical Engineering Research
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    • v.48 no.2
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    • pp.205-211
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    • 2010
  • The water-sewage cohesion agent(polyaluminumchloride(PAC)) and NaOH were used to synthesize $Al(OH)_3$. For various additions of NaOH, characteristics of the synthesized $Al(OH)_3$ was analysed by XRD, SEM and PSA. According to XRD analysis, small amount of NaOH(NaOH:PAC=15g:100g) resulted in amorphous form of $Al(OH)_3$. By increasing NaOH(NaOH:PAC=20g:100g), the mixture of gibbsite(37%), bayerite(35%) and boehmite(28%) were produced. By adding more NaOH(NaOH:PAC=25g:100g), binary mixtures of gibbsite(67%) and bayerite(33%) were formed. Finally, high addition of NaOH(NaOH:PAC=30g:100g) gave the high concentration of gibbsite(gibbsite:bayerite=83:17). Also, SEM analysis indicated that the product featured the plate form with 20 and 30g of NaOH addition. Furthermore it was found that the particle size of the product decreased with the addition of NaOH.

The Effect of pH and temperature on the Morphology of Aluminum Hydroxides formed by Hydrolysis Reaction (알루미늄의 수화 반응시 pH와 온도에 따른 형상 변화)

  • 오영화;이근회;박중학;이창규;김흥회;김도향
    • Journal of Powder Materials
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    • v.11 no.2
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    • pp.118-123
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    • 2004
  • A formation of aluminum hydroxide by hydrolysis reaction in the water has been studied by using nano aluminum powder fabricated by pulsed wire evaporation(PWE) method. The hydroxide type and morphology depending on temperature and pH were examined by structural analysis. The Boehmite($Al_2O_3$.$H_2O$ or AIO(OH)) was predominantly formed in high temperature region over 4$0^{\circ}C$, while the Bayerite($Al_2O_3$.$H_2O$ or $Al(OH)_3$) below $30^{\circ}C$ of hydrolysis temperature. The Boehmite formation was preferred to the Bayerite in acidic solution in the same hydrolysis temperature. The slowly formed Bayerite phase showed facet crystalline structure, while the fast formed Boehmite was fine fiber with a large aspect ratio of several nm in diameter and several hundred nm in length, and with much larger specific surface area(SSA) than that of Bayerite. The highest SSA was about $420m^2$/g.

Study of Hydrolysis of Al Powder and Compaction of Nano Alumina by Spark Plasma Sintering(SPS) (Al 분말의 수화 반응과 스파크 플라즈마 열처리법으로 제조된 알루미나 성형체 연구)

  • Uhm Y. R.;Lee M. K.;Rhee C. K.
    • Journal of Powder Materials
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    • v.12 no.6 s.53
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    • pp.422-427
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    • 2005
  • The $Al_2O_3$ with various phases were prepared by simple ex-situ hydrolysis and spark plasma sintering (SPS) process of Al powder. The nano bayerite $(\beta-Al(OH)_3)$ phase was derived by hydrolysis of commercial powder of Al with micrometer size, whereas the bohemite (AlO(OH)) phase was obtained by hydrolysis of nano Al powder synthesized by pulsed wire evaporation (PWE) method. Compaction as well as dehydration of both nano bayerite and bohemite was carried out simultaneously by SPS method, which is used to fabricate dense powder compacts with a rapid heating rate of $100^{\circ}C$ per min. under the pressure of 50MPa. After compaction treatment in the temperature ranges from $100^{\circ}C\;to\; 1100^{\circ}C$, the bayerite and bohemite phases change into various alumina phases depending on the compaction temperatures. The bayerite shows phase transition of $Al(OH)_3{\to}{\eta}-Al_2O_3{\to}{\theta}-Al_2O_3{\to}\alpha-Al_2O_3$ sequences. On the other hand, the bohemite experiences the phase transition from AlO(OH) to ${\gamma}-Al_2O_3\;at\;350^{\circ}C.$ It shows AlO(OH) ${\gamma}-Al_2O_3{\to}{\delta}-Al_2O_3{\to}{\alpha}-Al_2O_3$ sequences. The ${\gamma}-Al_2O_3$ compacted at $550^{\circ}C$ shows a high surface area $(138m^2/g)$.

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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Synthesis of Aluminum Hydroxide Nanofiber by Electrolysis of Aluminum Plates (전기분해법에 의한 수산화알루미늄 나노화이버 제조)

  • Woo S.H.;Lee M.K.;Rhee C.K.
    • Journal of Powder Materials
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    • v.13 no.2 s.55
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    • pp.108-111
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    • 2006
  • Aluminum hydroxides were synthesized by a simple electrolytic reaction of aluminum plates. The aluminum hydroxide, boehmite (AlO(OH)), was predominantly formed in the application of electrical potential at and above 30V, while the mixture of bayerite ($Al(OH)_3$) and boehmite (AlO(OH)) phases were formed below 20V. The boehmite has a clear fibrous structure controlled on nanometer scale. On the contrary, the bayerite consists of the typical hourglass or semi-hourglass shaped coarse crystals as a result of aggregation of various crystals stacked together. The specific surface area of the boehmite nanofiber was markedly high, approaching at about $302\;m^2/g$.

Synthesis of Aluminum Monohydroxide Nanofiber by Electrolysis of Aluminum Plates

  • Woo, S.H.;Lee, M.K.;Rhee, C.K.
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09a
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    • pp.428-429
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    • 2006
  • Aluminum hydroxides were synthesized by a simple electrolytic reaction of aluminum plates. The aluminum monohydroxide, boehmite(AlO(OH)), was predominantly formed by the application of an electrical potential above 30V, while the mixture of the bayerite$(Al(OH)_3)$ and boehmite(AlO(OH)) phases were formed below 20V. The boehmite has a clear fibrous structure which is controlled on a nanometer scale. On the contrary, the bayerite consists of the typical hourglass or semi-hourglass shaped coarse crystals as a result of an aggregation of the various crystals stacked together. The specific surface area of the boehmite nanofiber was remarkably high, reaching about $300m^2/g$.

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Formation of an Aluminum Hydroxide Fiber by a Hydrolysis of Aluminum Nano Powder (알루미늄 나노 분말의 수화반응에 의한 수산화알루미늄 형성)

  • Lee Geunhee;Oh Young Hwa;Rhee Chang Kyu;Kim Whung Whoe
    • Korean Journal of Materials Research
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    • v.15 no.3
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    • pp.172-176
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    • 2005
  • Formation of aluminum hydroxide by a hydrolytic reaction of nano aluminum powder synthesized by a pulsed wire evaporation (PWE) method has been studied. The type and morphology of the hydroxides were investigated with various initial temperatures and pHs. The nano fibrous boehmite (AlOOH) was formed predominantly over $40^{\circ}C$ of the hydrolytic temperature in acid solution, while the bayerite $(Al(OH)_3)$ was formed predominantly below $30^{\circ}C$ in alkali solution with a faceted crystalline structure. As a result the boehmite showed a much larger specific surface area (SSA) than that of bayerite. The highest SSA of the boehmite was about $409\;m^2/g$.

Process Study on Alumina-zirconia Nanocomposite via Ammonolysis Route

  • Naoya Enomoto;Tang, Jun-Mu;Masato Uehara;Hideaki Maeda;Junichi Hojo;Nakagawa, Zenbe-e
    • Proceedings of the Korea Association of Crystal Growth Conference
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    • 2000.06a
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    • pp.143-150
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    • 2000
  • Wet-chemical process using ammonia to precipitate aluminum ion dissolved in a zirconia sol solution is examined. Formation of crystalline bayerite is unfavorable for fine dispersion of zirconia nanoparticles in alumina matrix after heat treatment. To avoid the bayerite formation, it was preferred to make a precipitation with a diluted ammonia or with an ammonia gas flow at high temperature. By optimizing the precipitation process and the calcination temperature, we successfully prepared the uniform microstructure in which tetragonal zirconia particles of ∼30nm is finely dispersed within the alumina grains.

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Characteristics on ceramic membrane of alumina synthesized by precipitation method(I) (침전법으로 합성된 알루미나 분말을 이용한 세라믹 분리막 제조에 관한 연구(I))

  • 박신서;서규식;김철홍;신민철;이희수;엄우식;이재훈
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.9 no.1
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    • pp.113-118
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    • 1999
  • Aluminum hydrates were synthesized using $AlCl_3$.$6H_2O$as starting material by precipitation method. The phases of obtained powder were amorphous, boehmite, bayerite, nordstrandite depending on the pH of solutions. Aluminum hydrates transformed to $\alpha-Al_2O_3$via $\gamma$- $Al_2O_3$,$\delta$- $Al_2O_3$,and $\theta$-$Al_2O_3$,and particle sizes were grown by increment of heating temperature. The TEX>$\gamma$- $Al_2O_3$ powder was coated on intermediate layer of ceramic membrane by the dip-coating method, and unsupported membrane was also prepared for comparison. The supported layer showed porous structure with small grains, but the unsupported layer revealed interconnected larger grains. Grain growth is dominant in the unsupported layer than in the supported one.

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