Papers by Author: Han Mei Ao

Abstract: Mullite nanocomposite was synthesized using kaolin with different Si/Al molar ratios in the range of 1.1- 4.31. The synthesized samples were analyzed and characterized using XRD and SEM techniques and effects of Si/Al molar ratio on mullite nanocrystal morphology have been investigated. SEM results showed that the mullite nanocomposite synthesized from kaolin with different Si/Al molar ratios had different morphologies and distribution patterns of particle size. It was found that the mullite nanocrystals with relatively homogenous grain-size distribution, low aspect ratio, and little agglomeration were produced from the precursors made from kaolin with a Si/Al ratio of 1.1-2.33 at calcination temperature of 1100-1250 oC.

Abstract: Mullite precursor was prepared from kaoline when calcined at 1250 °C，when the concentration of sodium hydroxide of 3 mol/l; crystallization temperature of 80 °C; holding time of 3 h and precursor concentration of 0.15 g/ml, the morphology of the prepared mullite nanocomposite appears spherical-like, and it has good crystallization property and low agglomeration, and the average size of the particles is about 60.9 nm. Both the thermodymics and kinetics of mullite precursor have been studied. The results are as follows: the reaction started when the calcine temperature T﹥495°C; mullite precursor formed when the reaction system temperature 1000 °C; the activation energy of precursor Ea=928.3 KJ/mol; the reaction order n=1.33. We have reported our successful experiments to use kaolin to synthesize mullite nanocomposite with satisfying, spherical morphology, relatively homogenous grain average size of 60.9 nm, and little aggregation[1-2]. This paper presents an investigation of the thermodynamics and kinetics of the precursor preparation process.

Abstract: In this research, raw kaolin is processed by oxidation-reduction fining method and then baked to produce mullite precursor, which can prepared multi-phase mullite nanocrystals at low temperature hydrothermal conditions under normal pressure. According to the analysis of the controlling factors of NaOH mole ratio in the hydrothermal system, reaction temperature, holding time and the precursor concentration, etc., we studied the effect of above-mentioned factors on the grain size of product. The results show that when NaOH concentration 3mol/L, hydrothermal reaction temperature 80°C, holding time 3 h, precursor concentration 0.15g/ml, the morphology of the prepared nanocomposite with grains size of 60 ~ 90nm appears spherical-like, also the uniform dispersion can be acquired.

Abstract: In order to reach the standard of the RoHS that the content of Cr6+ lower than 200ppm in ferrite, this reserch focused on the factors that influence on the content of Cr6+ during the preparation of Strontium Ferrite. The results show that the content of Cr6+ in Strontium Ferrit can be controlled among 91~117 ppm, and the optimum condition is as follows: the quality ratio of raw materials/graphite=10:1.25, the rate of the N2 flow 0.1~0.15 L/min, sintered temperature 950~1020°C, residence time 25~35min at the corresponding temperature point, granularity of the mixed system lower than 0.1~0.3mm.

Abstract: A new method of synthesizing mullite nanocomposite from raw natural kaolin is presented in the paper. Raw kaolin is processed by oxidation-reduction fining method and then baked to produce fine kaolin powder. The fine kaolin powder is further synthesized into mullite nanocomposite by open-system hydrothermal crystallization method under normal pressure. With proper controls of NaOH mole ratio in the hydrothermal solution, crystallization time, and constant temperature, the average grain size of synthesized nanocomposite changed from 80nm to 100nm. The morphology of the nanocomposite could gradually change from platy to short prismatic, lamellar, and needle-like with increasing nucleation rate.