Study On Preparation Of Spherical Nanometer MgO Reunion Powders

One of typical alkaline earth metal oxides, Mg O was widely applied in refractory materials, medical, food and other fields. For comparison, nanometer Mg O possesses better performance due to surface effect, volume effect, etc. It can be applied to nano ceramics, catalyst and other new fields, but agglomeration and uncontrollable morphology of nanometer Mg O restricted its applications. Meanwhile, the spherical Mg O reunion powders with large specific surface area and uniform particle size distribution were widely applied in batteries, catalyst, bactericides, nanostructured ceramic coatings due to the advantage of high reactivity, strong chemical stability and powerful combining ability with matrix. In this paper, the spherical nanometer Mg O reunion powders were prepared via emulsion assisted with homogeneous precipitation to solve the problem of limited application, and the main contents can be stated as follows.Using urea as precipitant, magnesium nitrate as salt solution, the nanometer Mg O powders were prepared with homogeneous precipitation under the environment of high-temperature airtight. The effects of concentration of Mg(NO3)2 solution, urea/Mg(NO3)2 molar ratio, reaction time, reaction temperature on the average particle size and particle size distribution of the nanometer Mg O powders were studied. The characterization of precursor powders and nanometer Mg O powders was tested by TG-DTA, BET, XRD,LPSA and SEM. The results show that the as-prepared powders possessed particles was about 30 nm and uniform particle size distribution. Finally, the preparation mechanism of nanometer Mg O via homogeneous precipitation method was proposed, which indicates that the hydrolysis reaction of urea plays a key role during the whole process, the selection of appropriate reaction time and temperature will determine the performance of the nanometer Mg O powders.In order to achieve the aim of controllable morphology reunion particles, the relation of emulsion viscosity between water content and emulsifier, as well as the relation of emulsion conductivity between water content were studied. In addition, the effects of emulsification ways and mixed emulsifier’s HLB values on the stability of emulsion were investigated. The results show that the emulsion with 5.5 HLB values prepared by the digital homogeneous emulsifying machine has excellent stability. Moreover, a ternary system phase diagram of W/O emulsion was proposed according to experiments, and the existent domain of stable emulsion consists of milky white zone and transparent zone. The results obtained from morphological observation of emulsion indicate that the as-prepared micron-scale emulsion with well sphericity and uniform dispersion can be used as soft template for the preparation of spherical reunion powders.The nanometer Mg O reunion powders with well sphericity and narrow size distribution were synthesised via emulsion assisted with homogeneous precipitation method, and the impact of experimental factors on the properties of powders was also investigated. The experimental results indicate that the fast factors were the influence of M value(emulsifier volume fraction), N value(water volume fraction), the emulsifying stirring speed and calcination heating rate on the morphology and particle size distribution, the concentration of Mg(NO3)2 solution, reaction time, urea/Mg(NO3)2 molar ratio and reaction temperature is the second.The BET values of powders were selected as the observation index of orthogonal test, the L9(34)orthogonal table was projected for the sake of high specific surface area while maintaining spherical shape. Then the reunion powders were prepared using optimal technological conditions obtained from orthogonal experiment, and the resulting powder was characterized by BET, XRD and SEM. The experimental results show that the reunion powders possessed well sphericity and outstanding dispersity, the particle size distribution : 2μm~50μm and the average particle size was about 30μm and 54.65m2/g BET value. Finally, the preparation mechanism of nanometer Mg O reunion powders via emulsion assisted with homogeneous precipitation was discussed. The result shows that the properties of reunion powders were determined by the stable emulsion, the emulsifying strirring speed and the calcination heating rate.