Papers by Keyword: Mullite Nanocomposite

Abstract: Mullite nanocomposites powders have been successfully synthesized from pretreated coal gangue via hydrothermal crystallization process. The mullite nanocomposites powders are investigated and charactered by laser particle size analysis, X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) analysis, selected area electron diffraction (SAED) analysis and energy-dispersive X-ray (EDX) analysis. Moreover, the reaction mechanism of this process is speculated according to MAS-NMR results. It is indicated that mullite nanocomposites powders can be prepared at 80-90 °C for 3 h with NaOH concentration of 2-4 mol/L and L/S ratio (liquid/solid ratio in mass) of 10 mL/g by using calcined coal gangue as precursor. The agglomerate powder size of D50 is about 3.83-4.71 mm. Furthermore, some imperfective puncheon-shaped crystals exist among a large number of whole puncheon-shaped crystals which are about 30-70 nm in length and about 10-20 nm in diameter. MAS-NMR analysis indicates that the nano-size mullite grow around the central atom-Al, Si of [AlSi]O4 tetrahedral and the growth unit Al[OH]4- exist in this process definitely.

Abstract: Mullite nanocomposites powders have been successfully synthesized from high-aluminium coal fly ash via hydrothermal crystallization process. The mullite nanocomposites powders are investigated and charactered by laser particle size analysis, BET surface area analysis, X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) analysis, selected area electron diffraction (SAED) analysis and energy-dispersive X-ray (EDX) analysis. Moreover, the reaction mechanism is speculated according to MAS-NMR results. The experimental results show that mullite nanocomposites powders can be prepared at 80-90 °C for 3 h with NaOH concentration of 2-4 mol/L and L/S ratio (liquid/solid ratio in mass) of 10 mL/g. The powder size of D₅₀ is about 1.88-3.27 mm. Mullite nanocomposites are mainly rod-like, acicular and fibroid in shape with an range of 30-80 nm in length and an range of 4.5-30 nm in diameter. MAS-NMR analysis indicates that the nano-size mullite grow around the central atom-Al, Si of [AlSi]O₄ tetrahedral and the growth unit Al[OH]₄^- is existed in this process definitely.

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: 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.