Hebei Messi Biology Co., Ltd. stated that there are many methods for preparing nano magnesium oxide. Magnesium nitrate hexahydrate is used as a precursor, and nano magnesium oxide powder is synthesized by citric acid sol-gel method. Characterization and comparison with magnesium oxide powder prepared by precipitation method show that the sol-gel method has the advantages of high purity, good uniformity, low temperature, easy reaction control, etc., and can be made into various forms such as bulk fiber film powder according to needs.
Nano magnesium oxide material is a new type of high-functional fine inorganic material. It is mainly used as an accelerator and activator for chloroprene rubber, butyl rubber, nitrile rubber and fluororubber. It is a filler for adhesives, plastics, paints, and paper. It can also be used to manufacture ceramics, enamel, refractory materials and magnesium oxide cement. It is used as an antacid and laxative in medicine. Active nano magnesium oxide materials have strong adsorption and high surface chemical activity. They can be used as efficient dissociative adsorbents to adsorb toxic chemicals such as chlorinated hydrocarbons, organic phosphides and acidic gases for environmental protection. Nano magnesium oxide film has good high temperature resistance and can be applied to the inner wall of high temperature furnaces and can also be used in the aerospace field. It also has good wear resistance and certain moisture-proof and anti-corrosion effects.
Taking magnesium nitrate hexahydrate as a precursor, nano magnesium oxide powders with different particle sizes (10-100nm) and crystallinity were synthesized by citric acid sol-gel method. The mechanism of action of citric acid, the effect of different process conditions (water, anhydrous ethanol, and the amount of citric acid added) on the stability of sol-gel, and the effect of calcination temperature on the particle size and crystallinity of powder crystals were studied. The results show that when citric acid is not introduced, the stability of the gel is poor. The particle size of the magnesium oxide product is large and the agglomeration is serious. After the introduction of citric acid, a stable gel system can be formed when water: magnesium nitrate hexahydrate: citric acid: ethanol = 100:9:9:2.1 (molar ratio). When the formed gel is heated, a redox reaction occurs, in which NO-3 provides an oxidizing atmosphere and COO-3 serves as a fuel. NO-3 and COO-3 in the gel structure undergo an “in-situ” oxidation-reduction reaction at a certain temperature, thereby causing self-propagating combustion. Until all the dry gel is burned out, a loose powder is formed.
The nano magnesium oxide obtained by the sol-gel method has a narrow particle size distribution, good dispersibility, high purity, easy reaction control, few side reactions, simple process operation, and low calcination temperature, which can greatly reduce the cost of raw materials. The particle size obtained by the sol-gel method tends to be consistent. The sol-gel method can control the microstructure of the material at the early stage of material preparation. The sol-gel method has broad application prospects in nano oxides.
When the precursor mixture is stirred at 80°C, a large number of bubbles will be generated, and a foamy anhydrous gel will be formed as the standing time increases. The foaming phenomenon is more obvious when calcined at 500°C. Based on a large number of experiments, we found that the foaming temperature is related to the viscosity of the precursor mixture sol. Generally speaking, foaming can occur when the concentrations of nitrate and citric acid are relatively low. Through multiple experiments, we know that foaming is directly related to the concentration of citric acid, but not to the concentration of nitrate. The annual of the colloid is mainly determined by citric acid. The higher the concentration of citric acid, the greater the viscosity, and the higher the foaming temperature. Foaming is a basic characteristic of sol. The phenomenon is the expansion of the sol volume, and a porous foam-like anhydrous dry gel is obtained. The colloid will foam during the heating process.
Citric acid, as a typical complexing agent, forms a complex with metal ions and then undergoes a sol-gel process, but the metal ions are evenly distributed in the gel. Citric acid is a hydroxycarboxylate with a low molecular weight. Some carboxyl groups can replace the abundant hydroxyl groups on the surface of the oxide, combine with metal ions to form a monomolecular adsorption layer, so that the surface of the particles is negatively charged and repel each other, which plays a dispersing role. The foaming process can effectively control the agglomeration of powders by preventing the formation of chemical bonds, preventing network collapse and reducing the self-propagating temperature.
The sol-gel method can obtain nano-magnesium oxide powder with uniform grain size, good dispersion and high crystallinity, and at the same time lays the foundation for the future development of nano-magnesium oxide film materials. The intervention of citric acid makes the reaction system more stable and plays a good dispersing role. The precipitation method is used to prepare nano-magnesium oxide, with low raw material prices, simple processes, and low equipment requirements; it also has low energy consumption and is suitable for industrial production. The obtained nano-magnesium oxide is evenly dispersed.