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1344-28-1Relevant articles and documents
Synthesis of thermally stable χ-alumina by thermal decomposition of aluminum isopropoxide in toluene
Mekasuwandumrong, Okorn,Kominami, Hiroshi,Praserthdam, Piyasan,Inoue, Masashi
, p. 1543 - 1549 (2004)
Thermal decomposition of aluminum isopropoxide in toluene at 315°C resulted in χ-alumina that had high thermal stability, whereas the reaction at lower temperatures resulted in formation of an amorphous product. The χ-alumina thus obtained directly transf
Direct evidence of temperature variation within ceramic powder compact during pulse electric current sintering
Zhang, Dongming,Zhang, Lianmeng,Guo, Jingkun,Tuan, Wei-Hsing
, p. 680 - 683 (2006)
Pulse electric current sintering (PECS) is a powerful technique for the preparation of nanoceramics. However, the temperature distribution within the ceramic powder compact during PECS is not uniform. In the present study, aluminum hydroxide powder is used as an in situ temperature indicator to determine the temperature uniformity. The phase evolution within the powder compact is taken to estimate its temperature distribution. The temperature is highest near the top surface of the compact; it then reduces with increasing distance away from the top surface of the compact. The temperature variation can be significantly reduced by inserting a carbon paper in between graphite punches and graphite mold and also by reducing the heating rate.
Effect of milling on the formation of nanocrystalline x-Al 2O3 from gibbsite
Chaitree, Wasu,Jiemsirilers, Sirithan,Mekasuwandumrong, Okorn,Praserthdam, Piyasan,Charinpanitkul, Tawatchai,Panpranotw, Joongjai
, p. 3377 - 3383 (2010)
Gibbsite (FG) with mean particle diameter (d50 = 3μm) was milled in an attrition mill for 12 and 24 h using alumina balls as grinding media and calcined at different temperatures in the range of 350°-600°C. The properties of the alumina obtained were determined by X-ray diffraction, N2 physisorption, thermogravimetric/ differential thermal analyses, and transmission electron microscopy.Without milling, the alumina obtained normally contained the mixed phases between γ- and x-phase alumina. On the other hand, high purity of nanocrystalline vphase alumina (100 wt%) can be produced by calcination of the 24-h milled FG at 600°C. The isothermal kinetics measurements revealed that the rate constant (κ) for phase transformation increased as the particle size of gibbsite decreased and the calculated activation energy for transformation from FG to alumina decreased from 20.6 to 14.7 and 6.8 kJ/mol after milling for 12 and 24 h, respectively. The physical properties of nanocrystalline x-alumina obtained by the calcination of milled FG were comparable to those produced by the solvothermal method. The present results offer a simple way to prepare a large amount of pure x-phase alumina for particular industrial applications.
Experimental and ab initio infrared study of χ-, κ- and α-aluminas formed from gibbsite
Favaro,Boumaza,Roy,Ledion,Sattonnay,Brubach,Huntz,Tetot
, p. 901 - 908 (2010)
χ-, κ- and α-alumina phases formed by dehydration of micro-grained gibbsite between 773 and 1573 K are studied using infrared spectroscopy (IR). The structural transitions evidenced by X-ray diffraction (XRD) were interpreted by comparing IR measurements with ab initio simulations (except for the χ form whose complexity does not allow a reliable simulation). For each phase, IR spectrum presents specific bands corresponding to transverse optical (TO) modes of Al-O stretching and bending under 900 cm-1. The very complex χ phase, obtained at 773 K, provides a distinctive XRD pattern in contrast with the IR absorbance appearing as a broad structure extending between 200 and 900 cm-1 resembling the equivalent spectra for γ-alumina phase. κ-alumina is forming at 1173 K and its rich IR spectrum is in good qualitative agreement with ab initio simulations. This complexity reflects the large number of atoms in the κ-alumina unit cell and the wide range of internuclear distances as well as the various coordinances of both Al and O atoms. Ab initio simulations suggest that this form of transition alumina demonstrates a strong departure from the simple pattern observed for other transition alumina. At 1573 K, the stable α-Αl2?3 develops. Its IR spectra extends in a narrower energy range as compared to transition alumina and presents characteristics features similar to model α-Αl2?3{dot operator} Ab initio calculations show again a very good general agreement with the observed IR spectra for this phase. In addition, for both κ- and α-Αl2?3, extra modes, measured at high energy (above 790 cm-1 for κ and above 650 cm-1 for α), can originate from either remnant χ-alumina or from surface modes.
Studies on the thermal reactions of aluminium oxides and hydroxides
Novak, C.,Pokol, G.,Tomor, K.,Koemives, J.,Gal, S.
, p. 765 - 770 (1988)
The gibbsite →χ-alumina decomposition (in air) and the χ-alumina →boehmite transformation (under hydrothermal conditions) were investigated isothermally. Reaction products were characterized by TG and X-ray diffraction. The rate of the gibbsite →χ-alumina
PREPARATION OF ALUMINAS THE EFFECT OF HEAT TREATMENT ON THE PROPERTIES OF ALUMINA.
Al-Mashta,Al-Derzi,Al-Saadi,Al-Daghistani
, p. 269 - 277 (1988)
Aluminum hydroxide was prepared by precipitation from aluminum nitrate solution with ammonia solution. Thermal decomposition of the solid hydroxide was studied by means of TG, DTG and DTA. The sample was thermally treated in the temperature interval betwe
Preparation and microstructural and textural characterization of single-phase aluminum oxides
Kul'ko,Ivanova,Litvak,Kryukova,Tsybulya
, p. 714 - 721 (2004)
Conditions for the preparation of single-phase η-, -, and χ-aluminas were determined. The structures of η- and χ-aluminas were characterized. With the use of high-resolution electron microscopy, it was found that η-Al2O3 particles exhibited the most developed {111} face and consisted of coherently joined domains with a pronounced platelet shape. Planar defects in the (111) plane occurred in the η-Al2O3 particles. Microstructural differences between single-phase η-Al2O3 and γ-Al2O 3 with a defect spinel structure were revealed. It was found that the η-Al2O3, χ-Al2O3, and -Al2O3 oxides are characterized by uniformly porous structures with average pore diameters of 47, 55, and 110 A, respectively.
Synthesis of thermally stable micro spherical χ-alumina by thermal decomposition of aluminum isopropoxide in mineral oil
Mekasuwandumrong, Okorn,Silveston, Peter L.,Praserthdam, Piyasan,Inoue, Masashi,Pavarajarn, Varong,Tanakulrungsank, Waraporn
, p. 930 - 934 (2003)
Thermal decomposition of aluminum isopropoxide (AIP) in mineral oil at 250-300 °C over a 2 h duration results in χ-alumina powders having high thermal stability. The mechanism of the process involves the formation of amorphous complex before further decomposition takes place. Phase transformation of the obtained products was also investigated. It was found that χ-alumina synthesized by this method transformed directly to α-alumina at temperature higher than 1000 °C.
Formation of the morphology of continuous-precipitation aluminum hydroxides in the course of industrial synthesis
Lamberov,Aptikasheva,Egorova,Levin,Gil'manov
, p. 171 - 177 (2005)
X-ray phase and differential thermal analyses were used to study in detail how the morphology of aluminum hydroxides changes in separate stages of the technological process. The assumption that two pseudoboehmite modifications differing in crystallite dim
Mesostructured forms of the transition phases η- and χ-Al 2O3
Zhang, Zhaorong,Pinnavaia, Thomas J.
, p. 7501 - 7504 (2008)
A surfactant-templated route to mesostructured forms of the transition alumina phases η-Al2O3 and χ-Al2O 3 is described. The surface areas and pore-size distributions of these novel forms of alumina are substantially improved with respect to those of conventional forms of these phases. Wormholelike pores are visible in the TEM image shown of mesostructured η-Al2O3. (Figure Presented).
