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

In this paper, magnesium aluminate spinels were prepared by microwave-assisted combustion, using urea as fuel. In order to evaluate the effect of the urea excess used in the synthesis, its mass was added in a range of 1.0 to 2.5 times the stoichiometric amount required. The materials produced were characterized by TGA, FTIR, XRF, XRD, BET, SEM and TEM. The results demonstrated that magnesium aluminate spinel was formed in all solids, but the crystallinity degree and the specific surface area increased according to the amount of urea that was used in the synthesis. The use of excess fuel in the preparation was therefore advantageous, since it eliminated the need of the calcination step, at high temperatures, in order to stabilize the spinel phase and improve the crystallinity of the solid. The heat generated in the combustion process was sufficient to develop the formation of a nanocrystalline structure and produce high purity materials, with a save of 99.4% in energy.本研究采用微波辅助燃烧法，以尿素为燃料制备铝酸镁尖晶石（magnesium aluminate spinel）。为探究合成过程中尿素过量添加的影响，本研究将尿素添加量控制在理论化学计量需求量的1.0至2.5倍范围内。所制备的材料通过热重分析（Thermogravimetric Analysis, TGA）、傅里叶变换红外光谱（Fourier Transform Infrared Spectroscopy, FTIR）、X射线荧光光谱（X-ray Fluorescence Spectrometry, XRF）、X射线衍射（X-ray Diffraction, XRD）、比表面积测试（Brunauer-Emmett-Teller, BET）、扫描电子显微镜（Scanning Electron Microscopy, SEM）及透射电子显微镜（Transmission Electron Microscopy, TEM）进行表征。结果表明，所有产物均生成了铝酸镁尖晶石晶相，且产物的结晶度与比表面积随尿素添加量的提升而升高。因此，制备过程中过量添加燃料具有显著优势：无需再通过高温煅烧步骤即可稳定尖晶石晶相并提升产物结晶度。燃烧过程中产生的热量足以促成纳米晶结构的形成，可制备得到高纯度产物，同时实现了99.4%的能源节约。