Study On The Preparation Of Nanometer Magnesia By Sol-gel Auto Combustion

Sol-gel auto combustion technique is a novel method which perfectly combines the sol-gel process and lower temperature combustion process. Nitrates were used as raw materials and carboxylic acids like citric acid, succinic, malic were used as fuel. Dried gel precursors exhibit auto-catalytic combustion behavior. When the dried gel was ignited at any point, the combustion rapidly propagated until all the gel was completely burnt. Lower reaction temperature and shorten time are then possible to form a desirable phase with narrow grain size. The target products were enwrapped with the organic compounds which are not decomposed completely, and then were obtained with homogeneity and higher specific area after further heat treatment, often exhibit good lamella structure. This technique offer many advantages, such as cheap precursors, a lower reaction temperature, simple and economic preparation procedure, better control of materials morphology.Nanometer MgO were synthesized by sol-gel auto combustion technique using magnesium nitrate as raw material and citric acid as chelating agent. This technique was compared with traditional sol-gel technique. IR spectra of dried gels were examined to investigate the structure of the precursors. By studying on the different TG curves of magnesium citrate gel which was prepared by different methods, we found that combustion process occurred and the nitrate ions acted as oxidant in combustion process, and appropriate way of heat treatment were selected according to TG curves. MgO were measured respectively by transmission electron microscopy (TEM) and atomic force microscopy (AFM). TEM photographs of synthesis powders by sol-gel auto-combustion showed the crystallites with small grain size and homogeneous morphologies. TEM were also used to investigate the influencing factor of particle size of MgO. Average particle size of the powder was 8.7 run which was calculated by the XRD from the Scherrer formula. The BET curves showed that the specific surface of the sample is 26.34m~2/g. Precursors prepared by different conditions were characterized by FT-IR and XRD. We have analyzed the morphologies of powders from different precursors and conjectured the reasons. The curves of demarcation of different precursors were protracted by experimental data.