Halder, R and Bandyopadhyay , S (2019) Tailorable nano MgO.xAl2O3 spinel compositions along line of homogeneity via gel combustion route: Influence on phase evolution. Materials Chemistry and Physics, 235. Art No-UNSP 121736. ISSN 0254-0584

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Abstract

Very fine sized (∼5–15 nm) magnesium aluminate spinel (MgO.xAl2O3) powder of different degree of solid solubility (x = 1, 1.25, 1.50, 1.75, and 2) have been attempted for synthesis following a gel combustion method to meet its high demand in the fields of refractory, photo catalysis, sensor and strategic applications, etc. Nitrates of magnesium and aluminum were used as oxidants for exothermic reactions fuelled by urea added with formaldehyde solution acting as reductant. Thermal decomposition reactions of polymer gels resulting in phases containing varied cationic ratio (Mg2+:Al3+) were investigated through DTA-TGA studies. Phase identification of synthesized powders derived from varying mole ratio of metal nitrates was performed by X-ray diffractometry (XRD) through Rietveld refinement using HighScore Plus software and was reconfirmed by Fourier Transform Infrared Spectroscopy (FTIR). Particle morphology was examined under Field Emission Scanning Electron Microscope (FESEM) & Transmission Electron Microscope (TEM). XRD pattern revealed the as-synthesized stoichiometric magnesium aluminate spinel (MgAl2O4) powder to be in amorphous state. In contrast, increasing trends in the extent of crystallinity in the as-synthesized form was obvious for alumina richer compositions. Dependence of development of crystallinity was explained in the light of thermal stability of polymer containing varied valent cations. Unlike crystallinity, a reverse trend is observed in case of cell parameter of the as-synthesized different non-stoichiometric spinel varieties where lattice parameter decreased with increasing alumina concentrations following Vegard's law. Variation in cell dimension against alumina concentration is caused by the insertion of smaller substituting Al3+ ions (0.054 nm) for Mg2+ ions (0.072 nm) in the unit cell. TEM observation reveals that the synthesized powder is aggregate of fine nano crystals. Crystallites were larger with increasing alumina concentration. An initial sintering behavior of the powder synthesized at 1400 °C has also been reported. Initial sintering trials were attempted under spark plasma sintering process.

Item Type:	Article
Subjects:	Refractories
Divisions:	UNSPECIFIED
Depositing User:	Bidhan Chaudhuri
Date Deposited:	21 Nov 2019 05:48
Last Modified:	21 Nov 2019 05:48
URI:	http://cgcri.csircentral.net/id/eprint/4685

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