Powder Technology and Application II

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Authors: Yong Tian Wang
Abstract: In this paper we describe the synthesis of nanocrystalline boron nitride (BN) with a hollow morphology by the reaction of NH4BF4 and NaNH2 at 500 oC for 24h. Characterized by XRD, FTIR, XPS, TEM, and EDXA spectra, the composition and morphology of the products were confirmed. The possible formation mechanism was also discussed.
Authors: Yu Liang An, Qing Yi Hou, Xia Yuan, Gang Zhang
Abstract: A novel and practical route for preparing carbon coating metal nanomaterials using polyvinyl alcohol as the starting materials was presented. Carbon coating iron nanoparticles can be effectively synthesized by carbonizing polyvinyl alcohol using Fe as catalyst in hydrogen flow. The carbohydrate was carbonized in a controllable way that leads to a large amount of carbon coating iron nanoparticles. Transmission electron microscopy (HRTEM), energy dispersive X-ray (EDX) and thermogravimetric analysis (TG) were employed to characterizing nanomaterials. The growth mechanism of carbon coating iron nanoparticles is briefly discussed in term of composition and structure of precursor.
Authors: Han Ping Zhang, Xiao Li Wang, Xu Ming Wang, Sheng Jian, Qun Zhao
Abstract: The run-of-mine of complex lead-zinc ores in Yunnan contains 3.26% lead and 2.54% zinc. When traditional selective flotation flowsheet was adopted, 3.77% yield and 61.92% grade of lead concentrate as well as 5.65% yield and 38.67% grade of zinc concentrate were achieved. Simultaneously, 72.39% lead recovery and 3.83% zinc grade in lead concentrate as well as 80.64% zinc recovery and 6.39% lead grade in zinc concentrate were obtained. Lead concentrate and zinc concentrate obtained from selective flotation contain each other severely, resulting in low recovery of lead and zinc and severe loss of metal, which influences subsequent smelting flowsheet. In addition, due to requirement of large amount of depressant and activator while separating lead and zinc in the process of mineral processing, the cost is very high and the compositions of tail water which can not be recycled by the plant are very complicated. For the combined flowsheet of beneficiation and metallurgy, bulk flotation flowsheet was adopted. Therefore, 11.22% yield of combined lead and zinc concentrate with 25.55% lead grade, 18.33% zinc grade and 86.36% lead recovery were obtained. Gravity separation technology was utilized to separate combined concentrate of lead and zinc. After selecting out part of high quality lead concentrate, the remaining combined concentrate of lead and zinc was treated by acid leaching under high pressure. The final leaching efficiency of zinc was able to reach 97%. The new combined flowsheet has lots of advantages such as shorter flowsheet of beneficiation, simpler reagents, more direct reuse of backwater and higher recovery of metals.
Authors: Xiang Zhong Ren, Li Zhang, Ying Kai Jiang, Pei Xin Zhang, Jian Hong Liu, Qian Ling Zhang
Abstract: AgCl@polypyrrole(PPy) nanocomposites were synthesized through in situ chemical oxidation polymerization by using poly(vinylpyrrolidane) (PVP) as dispersant, and some Au colloid were prepared by using KBH4 as reductant and sodium citrate as stabilizer, then the Au nanoparticles-AgCl@PPy hybrid material was formed by physical chemical reaction. Fourier transform infrared spectrometer (FTIR) and electron dispersive spectrometer (EDS) data suggested that the hybrid material were composed of Au, AgCl and PPy. An amperometric glucose biosensor was fabricated by adsorbing glucose oxidase (GOx) to an Au nanoparticles-AgCl@PPy hybrid material modified platinum electrode. The biosensor exhibited a super highly sensitive response to H2O2.
Authors: Yong Tian Wang
Abstract: Thermal reduction process has been employed for the synthesis of carbon nanotubes (CNTs), during which ether was used as carbon source and metallic sodium play a role of reducing agent. The obtained CNTs have a diameter range of 50 nm and length range of 200-1000 nm. The as-prepared product was characterized by X-ray powder di.raction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED).
Authors: Yi Min Zhu, Yue Xin Han, Guo Liang Liu
Abstract: A precipitation-pyrolysis process was used for the synthesis of cubic nano-MgO powder. The main effect factors on the size and shape of nano-MgO powder such as mechanical stirring rate, organic reagent, and calcinations of the process were investigated. XRD and TEM were used to study on composition, morphology and size of nano-MgO powder. The results indicate that at the condition of mechanical stirring rate 510 rmp, glycol as organic crystal controller, calcination time 3 h, cubic nano-MgO powder was prepared with average size of 35 nm. FTIR results show that cubic nano-MgO powder has abnormal infrared absorption behaviors compared with that of micron scale.
Authors: Jian Guang Xu, Shi Bo Guo, Jian Hui Yan, Da Gong Zhang
Abstract: Si3N4 particle reinforced MoSi2 composite powder has been successfully synthesized combustion synthesis method. XRD and SEM results showed that the combustion product was mainly composed by MoSi2 and Si3N4. The as-prepared Si3N4/MoSi2 composite powder has been pressureless sintered at 1600°C for 1h. The microstructure and mechanical properties of the composite were investigated. Relative densities of the monolithic material and composite were 92.2% and 89.6%, respectively. The composite has higher Vicker’s hardness and flexural strength than monolithic MoSi2. Especially the room-temperature fracture toughness of the composite is from 4.21MPa•m1/2 for MoSi2 to 7.25MPa•m1/2 for composite, increased by 72.2%, respectively. The morphology of fractured surface of composite revealed the mechanism of improving mechanical properties of MoSi2 matrix. The results of this work showed that in situ Si3N4/MoSi2 composite powder prepared by combustion synthesis could be successfully pressureless sintered and significant improvement of mechanical properties could be achieved.
Authors: Li Xia Li, Yue Xin Han, Li Mei Bai
Abstract: CaCO3 whiskers were synthesized with soluble phosphates by one-step carbonization method, controlling mechanisms were investigated via XRD and FTIR, and it has been indicated that the most stable calcium phosphates in thermodynamics, hydroxyapatite was formed through the reaction of soluble phosphates and Ca(OH)2 in advance before CO2 was introduced, and then [CO32-(OH)] entered the crystal lattices of hydroxyapatite to replace partially [PO43-] to yield B-carbonate hydroxyapatite in the early stage of blowing CO2, which induced aragonite to heterogeneously nucleate as nucleation center and grew into calcium carbonate whiskers by the continuous stack of Ca2+ and CO32-, while other HA selectly adsorbed onto the flanks of CaCO3 to control crystal morphology.
Authors: Pei Xin Zhang, Mu Chong Lin, Qiu Hua Yuan, Zhen Zhen Fan, Xiang Zhong Ren, Dong Yun Zhang
Abstract: With the acetates of nickel, manganese and cobalt as raw materials and lithium hydroxide as precipitation agent, the precursor Ni1 / 3 Co1 / 3 Mn1 / 3 (OH) 2 was first prepared by chemical coprecipitation method, which was then mixed and ballmilled with certain stoichiometric ratios of LiOH∙H2O, and ultimately obtained LiCo1/3Mn1/3Ni1/3O2 after calcination process. Single-factor experiment method, in conjunction with XRD, SEM, and charge-discharge test, was utilized to study the influence of various factors, including the dispersion way of precursor, pH value of reaction solution, and the content of ballmilling lithium on the electrochemical properties of LiCo1/3Mn1/3Ni1/3O2. The results indicated that: (1) the material dispersed by ultrasonic treatment revealed excellent cycling performance, its ratio of capacity fading decreased at least 34.1% compared to those without ultrasonic process; (2) the optimum conditions of fabricating LiCo1/3Mn1/3Ni1/3O2 may be summarized as the treatment of ultrasonic dispersion, suitable pH value (12~13) and stoichiometric ratio (1.0) of ballmilling lithium.

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