Max Planck Institute For Festkorperfoschung

Stuttgart Mühlhausen, Germany

Max Planck Institute For Festkorperfoschung

Stuttgart Mühlhausen, Germany
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Isfahani T.D.,Iran University of Science and Technology | Isfahani T.D.,Max Planck Institute For Festkorperfoschung | Javadpour J.,Iran University of Science and Technology | Khavandi A.,Iran University of Science and Technology | And 3 more authors.
Powder Technology | Year: 2012

Nanosized alumina powders were synthesized by mechanochemical treatment of stoichiometric mixture of anhydrous AlCl 3 and CaO. X-ray powder diffraction (XRD), differential thermal and thermogravimetric analysis (DSC-TG), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to understand the formation mechanism and the exact phase transformation sequence in this system. Milling of the initial raw materials resulted in the formation of crystalline CaO and partially amorphous AlCl 3, with no sign of chemical reaction between the constituents. Heating the as-milled powder led to the formation of amorphous aluminum hydroxide (Al(OH) 3) and calcium chloride (CaCl 2). Based on the results obtained in this study, AlCl 3 hydrolyses in the heating stage and CaO adsorbs the produced HCl forming CaClOH and CaCl 2 crystalline phases. Heat treatment of the amorphous Al(OH) 3 resulted in the formation of amorphous alumina (Al 2O 3). Amorphous alumina transformed into η-, κ-, and αAl 2O 3 when calcined at higher temperatures. Based on Rietveld refinement, it was concluded that η-Al 2O 3 and κ-Al 2O 3 phases are stable up to an average critical crystallite size of around 13nm and 39nm respectively. © 2012 Elsevier B.V..


Isfahani T.D.,Iran University of Science and Technology | Isfahani T.D.,Max Planck Institute For Festkorperfoschung | Javadpour J.,Iran University of Science and Technology | Khavandi A.,Iran University of Science and Technology | And 2 more authors.
Advances in Applied Ceramics | Year: 2013

Al2O3 nanopowders were synthesised via mechanochemical method using AlCl3 and CaO as raw materials. The effect of thermal treatment on the structural evolutions and morphological characteristics of the nanopowders was investigated using X-ray diffractometry, transmission electron microscopy, scanning electron microscopy, differential thermal analysis and Rietveld refinement. The results showed that the average crystallite size of Al2O3 was <100 nm up to ̃1200°C. The activation energy for Al2O3 nanocrystallite growth during calcinations was calculated to be ̃22 598 and 30 195 J mol-1 for η- and Κ-alumina respectively, while for α-Al2O3, it was 8373 and 34 131 J mol -1 at temperatures up to 1200°C and .1200uC respectively. The mechanism of nanocrystalline growth of Al2O3 polymorphs during annealing is also discussed. © 2013 Institute of Materials, Minerals and Mining.


Dallali Isfahani T.,Iran University of Science and Technology | Dallali Isfahani T.,Max Planck Institute For Festkorperfoschung | Javadpour J.,Iran University of Science and Technology | Khavandi A.,Iran University of Science and Technology | And 3 more authors.
International Journal of Refractory Metals and Hard Materials | Year: 2012

Studies on the synthesis and formation mechanism of zirconia nanopowder prepared by mechanochemical technique have been carried out by means of X-ray powder diffraction (XRPD), differential thermal and thermogravimetric analysis (DSC-TG), Fourier transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM). A dry powder mixture of anhydrous ZrCl 4 and CaO was milled in stoichiometric ratio to produce ZrO 2. The milling resulted in the formation of crystalline CaO and partially amorphous ZrCl 4 while there was no sign of chemical reactions during milling. Heating the as-milled powder resulted in the formation of amorphous zirconium hydroxide (ZrOH) 4) and calcium chloride (CaCl 2(2H 2O)). According to our results, ZrCl 4 hydrolyses during the heating stage while CaO adsorbs the produced HCl forming CaClOH and CaCl 2 subsequently. Heat treatment of Zr(OH) 4 resulted in the production of zirconia (ZrO 2). Based on Rietveld refinement it has been shown that an average critical crystallite size around 46 nm exists above which tetragonal zirconia (t-ZrO 2) transforms to monoclinic zirconia (m-ZrO 2). © 2011 Elsevier Ltd. All rights reserved.

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