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Title: The effect of solution chemistry on the preparation of MgAl{sub 2}O{sub 4} by hydrothermal-assisted sol-gel processing

Abstract

Preparation of magnesium aluminate spinel powder by hydrothermal-assisted sol-gel processing from MgAl{sub 2}(OCH{sub 2}CH{sub 2}OR){sub 8}, R=CH{sub 3} (1), CH{sub 2}CH{sub 2}OCH{sub 3} (2), MgAl{sub 2}[OCH(CH{sub 3}){sub 2}]{sub 8} (3) and MgAl{sub 2}(O- {sup s}Bu){sub 8} (4) in toluene and parent alcohol has been investigated. Coordination status of aluminum atom in precursors was determined by {sup 27}Al NMR and correlation between coordination number of aluminum and development of spinel phase in hydrothermal-assisted sol-gel processing has been studied. The gels obtained from hydrothermal-assisted hydrolysis of magnesium-aluminum alkoxides that contain six-coordinated aluminum atoms in solution (1 and 2) after calcination at 700 deg. C resulted in the formation of pure spinel phase, whereas in similar hydrolysis and calcination processes of precursors that contain four-coordinated aluminum (3 and 4) spinel phase forms along with some Al{sub 2}O{sub 3} and MgO. Selected powders obtained from hydrothermal-assisted sol-gel processing were characterized by thermal analysis (TGA/DSC), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Results indicate that the coordination status of aluminum in the precursor is very crucial for the formation of pure phase spinel. The morphology of prepared spinels was studied by SEM and the results showed that the solvent in hydrothermal-assisted sol-gel processingmore » has a marked effect on the morphology of the resulting MgAl{sub 2}O{sub 4}. In hydrothermal-assisted sol-gel processing of aluminum-magnesium alkoxides in hydrophobic solvent, spherical particles are formed, while in the parent alcohol, non-spherical powders are formed.« less

Authors:
 [1];  [2];  [2]
  1. Department of Chemistry, Shahid Beheshti University, Tehran 1983963113 (Iran, Islamic Republic of). E-mail: m-pouramini@cc.sbu.ac.ir
  2. Department of Chemistry, Shahid Beheshti University, Tehran 1983963113 (Iran, Islamic Republic of)
Publication Date:
OSTI Identifier:
21000610
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Research Bulletin; Journal Volume: 42; Journal Issue: 3; Other Information: DOI: 10.1016/j.materresbull.2006.06.011; PII: S0025-5408(06)00253-4; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALKOXIDES; ALUMINATES; ALUMINIUM; ALUMINIUM OXIDES; CALCINATION; CALORIMETRY; CERAMICS; COORDINATION NUMBER; DIMETHYL SULFIDE; GELS; HYDROLYSIS; MAGNESIUM OXIDES; MORPHOLOGY; NUCLEAR MAGNETIC RESONANCE; SCANNING ELECTRON MICROSCOPY; SOL-GEL PROCESS; SPINELS; THERMAL GRAVIMETRIC ANALYSIS; TOLUENE; X-RAY DIFFRACTION

Citation Formats

Amini, M.M., Mirzaee, M., and Sepanj, N. The effect of solution chemistry on the preparation of MgAl{sub 2}O{sub 4} by hydrothermal-assisted sol-gel processing. United States: N. p., 2007. Web. doi:10.1016/j.materresbull.2006.06.011.
Amini, M.M., Mirzaee, M., & Sepanj, N. The effect of solution chemistry on the preparation of MgAl{sub 2}O{sub 4} by hydrothermal-assisted sol-gel processing. United States. doi:10.1016/j.materresbull.2006.06.011.
Amini, M.M., Mirzaee, M., and Sepanj, N. Thu . "The effect of solution chemistry on the preparation of MgAl{sub 2}O{sub 4} by hydrothermal-assisted sol-gel processing". United States. doi:10.1016/j.materresbull.2006.06.011.
@article{osti_21000610,
title = {The effect of solution chemistry on the preparation of MgAl{sub 2}O{sub 4} by hydrothermal-assisted sol-gel processing},
author = {Amini, M.M. and Mirzaee, M. and Sepanj, N.},
abstractNote = {Preparation of magnesium aluminate spinel powder by hydrothermal-assisted sol-gel processing from MgAl{sub 2}(OCH{sub 2}CH{sub 2}OR){sub 8}, R=CH{sub 3} (1), CH{sub 2}CH{sub 2}OCH{sub 3} (2), MgAl{sub 2}[OCH(CH{sub 3}){sub 2}]{sub 8} (3) and MgAl{sub 2}(O- {sup s}Bu){sub 8} (4) in toluene and parent alcohol has been investigated. Coordination status of aluminum atom in precursors was determined by {sup 27}Al NMR and correlation between coordination number of aluminum and development of spinel phase in hydrothermal-assisted sol-gel processing has been studied. The gels obtained from hydrothermal-assisted hydrolysis of magnesium-aluminum alkoxides that contain six-coordinated aluminum atoms in solution (1 and 2) after calcination at 700 deg. C resulted in the formation of pure spinel phase, whereas in similar hydrolysis and calcination processes of precursors that contain four-coordinated aluminum (3 and 4) spinel phase forms along with some Al{sub 2}O{sub 3} and MgO. Selected powders obtained from hydrothermal-assisted sol-gel processing were characterized by thermal analysis (TGA/DSC), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Results indicate that the coordination status of aluminum in the precursor is very crucial for the formation of pure phase spinel. The morphology of prepared spinels was studied by SEM and the results showed that the solvent in hydrothermal-assisted sol-gel processing has a marked effect on the morphology of the resulting MgAl{sub 2}O{sub 4}. In hydrothermal-assisted sol-gel processing of aluminum-magnesium alkoxides in hydrophobic solvent, spherical particles are formed, while in the parent alcohol, non-spherical powders are formed.},
doi = {10.1016/j.materresbull.2006.06.011},
journal = {Materials Research Bulletin},
number = 3,
volume = 42,
place = {United States},
year = {Thu Mar 22 00:00:00 EDT 2007},
month = {Thu Mar 22 00:00:00 EDT 2007}
}
  • Ultrafine MgAl{sub 2}O{sub 4} was synthesized by citrate sol-gel process. A model was presented to evaluate the concentration of species in a citric solution for preparing MgAl{sub 2}O{sub 4} ultrafine powder. The evaluated concentration of species can provide valuable information and help in selecting the optimal condition for preparation of MgAl{sub 2}O{sub 4} powder by citrate sol-gel process. The influence of molar ratio of cations, citric acid and pH on the formation of MgAl{sub 2}O{sub 4} was studied. The spinel precursor gel and the ultrafine MgAl{sub 2}O{sub 4} spinel were characterized by X-ray diffraction (XRD), differential thermal analysis, thermogravimetric (TG-DTA)more » and scanning electron microscope (SEM). The results show that the MgAl{sub 2}O{sub 4} spinel phase begins to form at 600 deg. C, and most of MgAl{sub 2}O{sub 4} crystals are spherical with a crystal size about 30-50 nm.« less
  • Nanoporous MgAl{sub 2}O{sub 4} particulates with high porosities were successfully prepared from sol-gel reactions, solvent exchange with castor oil and subsequent combustion and calcination at 700 °C. The products were crystalline and semitransparent. Changes in the metal precursor concentrations allowed control of pore volumes from 0.7 to 1.1 cm{sup 3}/g and average pore sizes from 14 to 19 nm. The specific surface areas are about 200 m{sup 2}/g regardless of the precursor concentrations. After heating at 1000 °C for 10 hours, the products kept about 70% of their original pore volume and about 60% of the original surface area. Heatingmore » at 1100 °C caused a drastic reduction of pore volume and surface area to 40 and 36%, respectively, as the average particle size increased to 23 nm.« less
  • Spinel precursors have been obtained by sol-gel processing using either magnesium nitrate and chemically modified aluminum alkoxide or a double alkoxide as raw materials. The xerogels have been characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), infrared (IR) spectroscopy, and transmission electron microscopy (TEM). It is proposed that the size of the particles is related to the functionality of the aluminum alkoxide. The use of the double alkoxide allowed pure spinel nanosized materials to be obtained.
  • Nano-sized particles of spinel LiMn{sub 2}O{sub 4} and LiCr{sub x}Mn{sub 2-x}O{sub 4} (x = Cr; 0.00-0.40) have been synthesized using phthalic acid as chelating agent for the first time by sol-gel method. When compared to solid-state synthesis method, the sol-gel route reduces heating time of synthesize and to obtain particles of uniform surface morphology. The synthesized samples were characterized through thermo-gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images of the parent compounds show nanospherical grains of LiMn{sub 2}O{sub 4} when compared to chromium-doped ones. XRD patterns of LiMn{sub 2}O{sub 4} ascertainmore » amorphous nature and for high calcined LiCr{sub x}Mn{sub 2-x}O{sub 4} single phase highly crystalline patterns were obtained. TEM images of the parent and chromium-doped spinel particles depict individual grain morphology with well-separated grain boundaries. LiCr{sub 0.10}Mn{sub 1.90}O{sub 4} excels in discharge and cycling behaviour and offer higher columbic efficiency, when compared to un-doped LiMn{sub 2}O{sub 4}. Cyclic voltammograms of LiMn{sub 2}O{sub 4} and LiCr{sub x}Mn{sub 2-x}O{sub 4} exhibit oxidation and reduction peaks corresponding to Mn{sup 3+}/Mn{sup 4+} and Cr{sup 3+}/Cr{sup 4+}.« less
  • The ultrafine high-{Tc}YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} superconductor powders were prepared by the sol-gel method using poly(vinyl alcohol) (PVA) as a protecting agent of metal ions. The conditions of the sol-formation from the aqueous solution of metal nitrates containing PVA were determined, and the thermal decomposition process of the gel precursor was examined to determine the crystallization temperature. It was found that a nearly pure phase of polycrystalline YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} could be obtained by calcining the gel precursor above 900 C for 2 h in air. Polycrystalline YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} powders prepared at 920 C consisted of verymore » uniformly-sized ultrafine particulates with an average particle size of about 25 nm and showed a good superconducting property with {Tc} around 94 K.« less