Papers by Author: Nan Chun Chen

Paper TitlePage

Authors: Wei Wang, Nan Chun Chen, Quan Hong Li, Xin Tang
Abstract: According to the conditions of preparation of mullite composites by open-system hydrothermal crystallization method, surface energies of mullite crystal were calculated by the first principle plane pseudo-potential. Growth habit plane of mullite composites was also discussed and analyzed. The calculation results demonstrate that surface energies of (001), (010), (100), (210) and (120) of mullite crystal are 0.337KeV•nm-2, 0.029KeV•nm-2, 0.027KeV•nm-2, 0.032KeV•nm-2, 0.037KeV•nm-2, respectively. That is to say, the surface energies of mullite crystal follow the order of (001) >> (210) > (120) > (100) > (010). It is also found that E(001) is much larger than others. According to Curie-Wulff principle, growth rate of crystal face is directly proportional to its surface energy, which shows that growth rate of mullite crystal in (001) direction is the fastest and mullite crystal is favorable for one-dimensional growth to columnar.
Authors: Nan Chun Chen, Dong Chen
Abstract: Natural and raw high-silica kaolins are firstly processed into fine kaolin powders with oxidation-reduction bleaching method before mixed with Al2O3 powders and then baked to produce mullite composite oxides at temperature between 1050-1150°C. The mullite composite oxides are further made into composite mullite nanocrystals by using open-system hydrothermal crystallization method under normal pressure. Analysis of the final products show that the mullite nanocrystals are texturally homogenous at an average size around 80-100 nm and have high thermal stability.
Authors: Nan Chun Chen, Han Mei Ao, Quan Hong Li, Quan Tang
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.
Authors: Nan Chun Chen, Dong Chen
Abstract: The synthesis and characterization of mullite composite nanocrystaline from high-silica kaolin sampled from Tianyang County of Guangxi Zhuang Autonomous Region is presented in this paper. Rough kaolin is firstly grounded and processed to remove impurities, iron and carbon before burned to produce composite oxides with mullite as major components. The composite oxides are further synthesized into composite mullite nanocrystaline by using hydrothermal crystallization process under low temperature and normal pressure. Tests on the composite nanocrystalline by TEM, TG-TDA, and X-ray diffraction methods show that the nanocrystalline range in size from 40 to 100 nm and are well textured. They also show significantly enhanced thermal stability at temperature as high as 1000oC.
Authors: Nan Chun Chen, Quan Tang, Xiao Hu Zhang, Wei Wang, Meng Ying Li
Abstract: Type-A zeolites molecular sieve is prepared after crystallization of the type-A zeolites molecular sieve precursor, which is prepared from Stellerite, at temperature of 90 ~ 100°C for 6 hours. It has a complete structure, with crystallinity of 98%, volume average particle size of 3.72µm and particle size distribution which is less than 10µm over 90%. Multi-member rings structure in the type-A zeolites molecular sieve cover each other, forming the cage (β-cage, α-cage, octahedral cage) structure. Nuclei and nanometer particles are formed after the further congregation reaction, and then gather and grow, result in the formation of nanometer crystal particles and transformation to micrometer particles.
Authors: Feng Zhan, Nan Chun Chen
Abstract: Talc was modified by aluminate coupling agent (ACA) before filling it into high density polypropylene (HDPP) to prepare talc/HDPP composites. Scanning electron microscopy (SEM), wear testing machine, electronic universal testing machine, and impact testing machine were used to analyze the surface modification and the effects of modified talc on friction and mechanical properties of modified talc/HDPP composites. The results indicate that after modified the lamellar structure of talc particles are open and the dispersion of particles are improved, and the edges and corners of surface become softer. Friction properties indicate that when the talc content is 8 wt%, both µ and K are at a lower value, which show that have better wear resistance. The frictional surface is relatively smooth and no furrow trace has found. Mechanical properties show that with talc content increasing, tensile strength and flexural strength of composites increase.
Authors: Xiao Hu Zhang, Nan Chun Chen
Abstract: Natural Stellerite has a big reserve volume, but has some shortcomings which are irregular ducts and Connotation impurities and so on. So, it is necessary to use Stellerite to prepare zeolite X for enhancing purity and property. It tests Products by XRD, FT-IR and Stereo Microscope. The study shows that optimum parameter is n(SiO2)/n(Al2O3)=3, n(Na2O)/n(SiO2) =1.1-1.2 and n(H2O)/ n(Na2O)=30-40. The gel ages at room temperature for 12 h, and then keeps at 95 °C for 7h. The pure zeolite X could be prepared.
Authors: Nan Chun Chen, Han Mei Ao, Dong Chen
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.
Authors: Nan Chun Chen, Han Mei Ao, Zhi Liang Zhan
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.
Authors: Nan Chun Chen, Han Mei Ao, Wei Wang, Quan Hong Li, Ai Ping Deng
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.
Showing 1 to 10 of 10 Paper Titles