Microwave-assisted combustion synthesis of nanocrystalline MgAl2O4 spinel powder

Effect of Urea Excess on the Properties of the MgAl2O4 Obtained by Microwave-Assisted Combustion

“…According these authors, to synthesize magnesium aluminate spinel by combustion route with urea (total valencies +6), employing Al(NO 3 ) 3 O (g), where (c) is crystalline and (g) is gas, would require n = 6.66 mol. Therefore, the masses of urea used were 1.0, 1.5, 2.0 and 2.5 times the stoichiometric quantity (~400 g), calculated from n value determined as described by Ganesh et al 30 , divided by a factor that led to obtaining 1-2 g of magnesium aluminate. After the complete dissolution of the reactants, under continuous heating for 20 min and constant stirring, the concentrated solution was submitted to microwave radiation in a conventional house microwave that was adapted for synthesis, and adjusted to a power of 675 W for 10 min.…”

“…The determination of the nitrates masses as well as of the fuel, the urea, were made on the basis of the chemical knowledge of the propellants and explosives, as it was described by Ganesh et al 30 . According these authors, to synthesize magnesium aluminate spinel by combustion route with urea (total valencies +6), employing Al(NO 3 ) 3 O (g), where (c) is crystalline and (g) is gas, would require n = 6.66 mol.…”

“…This minimizes the formation of thermal gradients 33 . Due to the advantages presented by microwave-assisted combustion 34,35 30 compared the routes of conventional combustion and microwave-assisted combustion. They concluded that the microwave preparation was more advantageous, since the powders had crystals in the range of 20-50 nm, while by conventional oven combustion the powders obtained were presented as agglomerates of fine crystals, in the range of 100-250 nm.…”

“…However, many of those are complex, expensive, have several steps, require long time for synthesis, require high temperatures and produce nonhomogeneous and generally low surface area solids 28 . In the case of solution combustion method, it has been extensively used recently, due to its several advantages, such as simplicity, low cost, short synthesis time and less amount of external energy required, also it produce powders of oxides more homogeneous, more crystalline and of higher purity [29][30][31] . This technique basically consists of using aluminum and magnesium nitrates as oxidants and an organic compound (urea, glycine, sorbitol, citric acid, among others) as fuel.…”

STRUCTURAL AND PHOTOLUMINESCENCE CHARACTERIZATION OF MgAl2O4:Eu PHOSPHOR SYNTHESIZED BY COMBUSTION METHOD.

“…1 The average crystallite size was estimated from the full width at half maximum (FWHM) of the diffraction peaks by using the Scherrer formula [8] The estimated average crystalline size is about 36 and 30 nm. It has been reported that the particle size of MgAl 2 O 4 spinel synthesized by various methods have been in the range of 43-55 nm [9]. Eu materials prepared at 500 0 C were recorded under emission monitored at 440 nm.…”