Synthesis, Characterization And Property Of Spinel Metal Oxides

Spinel metal oxides CoAl₂O₄, CoxZn1-xAl₂O₄, MnFe₂O₄and NiAl₂O₄nanocrystals weresuccessfully synthesized by solution combustion. The effect of fuel type, amount of fuel,fuel/oxidant ratio and fuel/metal nitrates ratio on the phase composition and morphology of theas-synthesized products were systematically studied by X-ray diffraction （XRD）, scanningelectron microscope （SEM）, BET, UV-Vis DRS. The result showed that fuel type, fuel dose,fuel/oxidant ratio and fuel/metal nitrates ratio played an important role in synthesis products.1. Nano-crystalline CoO and NiO was synthesized by solution combustion method usingmetal nitrates as oxidant and ethylene glycol as fuel at300℃. The results showed that fuel typeand fuel-to-oxidant ratio played an important role in metal oxides synthesis. CoO and NiOnanocrystals could be directly synthesized through solution combustion synthesis by controllingthe ethylene glycol-to-oxidant ratio in air atmosphere without further calcination and reducingprocess.2. Blue spinel CoAl₂O₄was synthesized by solution combustion method using Co（NO3）2and Al（NO3）3as oxidant and ethanolamine as fuel at300℃. The results showed that fuel type,fuel-to-oxidant ratio and fuel/metal nitrates ratio play a predominant role in CoAl₂O₄synthesis.Pure spinel CoAl₂O₄powders with a crystallite size of27nm could be directly synthesizedthrough solution combustion synthesis by controlling synthesis parameter in air atmosphere at300℃without further calcination process. Among all tested fuels, ethanolamine is the suitablefuels for CoAl₂O₄synthesis. The effect of fuel dose on the phase composition and morphology ofthe as-synthesized products was the result of both F/NO₃^-and F/M. CoAl₂O₄with the bestcrystalline form and bright-colored was prepared in stoichiometric ratio（F/NO₃^-is0.38）,correspond F/M is1.03. When NH4NO3was used as NO₃^-regulator, CoAl₂O₄with the bestcrystalline form was prepared in F/NO₃of0.33and in F/M of1.03.3. Zn ion doped CoxZn1-xAl₂O₄blue cobalt pigment was synthesized by NH4NO3-assistedsolution combustion method using Zn（NO₃）₂, Co（NO₃）₂and Al（NO3）3as oxidant andethanolamine as fuel at300℃. Compared with tradition solid state reaction, NH4NO3-assistedsolution combustion method have advantage of low reaction temperature, short reaction time andone-step synthesis without further calcination process. The CoxZn1-xAl₂O₄system allows for a reduction of the production costs and also for minimizing the environmental damage, as theamount of Co is reduced.4. Spinel MnFe2O4power was synthesized by solution combustion method using Mn（NO₃）₂and Fe（NO₃）₃as oxidant and glycine as fuel at300℃without further calcination process. Theadsorption property was studied by UV-vis spectra.（1）. Fuel type and amount of fuel played an important role on the phase composition andmorphology of the as-synthesized products. Among all tested fuels, glycine and alanine are thesuitable fuels for MnFe2O4synthesis. For glycine, the optimal fuel-to-oxidant ratio isstoichiometric ratios or fuel rich ratio（+32%）, which result in a suitable flame temperature forMnFe2O4formation, and for alanine is fuel lean ratio（-33%）. Both too little fuel and too muchfuel would lead to poor of the MnFe₂O₄phase.（2）. Compared with traditional non salt-assisted solution combustion, a novel and facilsalt-assisted solution combustion was developed. The salt introdution inhibits the formation ofhard agglomerates during the combustion synthesis, results in drastic increase in specific surfaceareas of the resultants and also has apparent effect on the particle morphology.（3）. The as-synthesis MnFe2O4have a good adsorption capacity for Congo red at neutral pH.The adsorption capacity was measured as43.52mg Congo red per gram of MnFe₂O₄. This goodadsorption performance is mainly attributed to the electrostatic attraction between the surface ofthe particles and the Congo red species in solution and the high surface area available as a resultof the small particle size.5. Spinel NiAl₂O₄was synthesized by solution combustion method using Ni（NO3）2andAl（NO₃）₃as oxidant and ethanolamine as fuel at300℃. The results showed that fuel type,amount of fuel and fuel-to-oxidant ratio play a predominant role in NiAl₂O₄synthesis. Amongall tested fuels, ethanolamine is the suitable fuels for NiAl₂O₄synthesis. The effect of amount offuel on the phase composition and morphology of the as-synthesized products was the result ofboth F/NO₃^-and F/M. NiAl₂O₄with the best crystalline form was prepared in stoichiometricratio（F/NO₃^-is0.38）, correspond F/M is1.03. When NH4NO3was used as NO₃^-regulator andF/M is1.03, NiAl₂O₄with the best crystalline form was prepared in F/NO₃^-of0.26.