Study On Synthesis Of Nano-sized MgAl₂O₄ Powders By High-molecular Networks Micro-zone Precipitation

Nano-sized magnesium aluminate spinel powders (MgAl₂O₄) were synthesized by high-molecular networks micro-zone precipitation. As starting materials, aluminum nitrate, magnesium nitrate and urea, which are low cost and easily available, were dissolved in deioned water, and mixed solution was added in, which was composed of acrylamide, as organic monomer, and N,N'-Methylene-bis-acrylamide, as cross linker. Further magnetic stirring is performed to obtain uniform solution. After a small quantity of ammonium persulfate, (NH₄)₂S₂O₈, used as initiator, was added to the uniform solution and mixed homogeneously by stirring, the mixed solution was heated at 60～65℃in water bath, and then acrylamide and the cross linker polymerized to form gel with the structure of three-dimensional space network, and the substances in the solution were distributed uniformly in the micro-zones formed by polymerization. And then, the gel was treated in saturated vapor, about 110～120℃. At the same time, CO(NH₂)₂ was hydrolyzed and its hydrolyzates reacted with metal ions, Al³⁺ and Mg²⁺, and precipitation was generated in the micro-zones formed by high-molecular networks. After being dried at 95℃, the precursor was calcined at 700～1100℃for 2 hours to obtain MgAl₂O₄ powders.Technological parameters have certain effects on the particle size and patterns of MgAl₂O₄ powders when they are changed. The effects were discussed in this paper, including concentrations of starting materials and monomer, the weight ratio of monomer and cross linker and the temperature of calcination. The results show that the higher the concentrations of starting materials are, the longer the starting time of gel is and the bigger the particle size is; The particle size diminishes with the increase of the concentrations of monomer; MgAl₂O₄ powders began to be generated at 600～700℃, and with the increase of calcined temperature, the grains grow better.The precursor and powders were detected by modern technologies such as TGA/DTA, XRD, TEM and FT-IR to characterize their phase compositions, microstructure and grain sizes. The results show that MgAl₂O₄ powders obtained are of spinel phase, sphericity, single component, good crystallization, small size and narrow particle distribution.High-molecular networks micro-zone precipitation method is very simple, inexpensive and convenient. It breaks through the limitation of traditional technologies which prepares MgAl₂O₄ at high temperature. After the precursor is calcined at lower temperature, Nano-sized MgAl₂O₄ powders, which are stable at high temperature, can be obtained. So it is suitable for synthesizing nano-sized materials of complex oxides.