Papers by Keyword: Morphology Control

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Authors: Ha Rim An, Hyo Jin Ahn
Abstract: We controlled morphologies of F-doped SnO2 (FTO) thin films via an electrochemical method. To obtain rough and porous surface of the FTO thin films, a potentiostat/galvanostat was used. Field-emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) were employed to demonstrate the morphological changes of FTO surface. The electrical and optical properties of the FTO thin films were analyzed using Hall effect measurement system and UV-vis spectrophotometry. Also, morphology controlled the FTO thin films would be applied to dye-sensitized solar cells.
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Authors: Xing Fa Ma, Ming Jun Gao, Xiao Chun He, Guang Li
Abstract: To examine the effects of morphologies of one-dimentional metal oxides on their surface properties, two typical morphologies of manganese dioxide (one is nanorod, the other is nanofiber) as a model of metal oxide were prepared with hydrothermal approach under similar conditions. The adsorption properties of Pb2+ in aqueous solution were carried out by using surface active group of MnO2 with different morphologies. The results indicated that the sorption capacities for Pb2+ were dramaticly increased via tailoring the morphology of MnO2. The products were characterized with SEM (Scanning Electron Microscopy), XRD (X-ray Diffraction), FTIR (Fourier-Transform Infrared), atomic absorption spectrophotometer, and so on. These results illustrated that it was feasible to improve the removal efficiency of heavy metal ions dramatically in aqueous solution by tailoring the morphology of nanostructured MnO2.
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Authors: Ming Xu Xia, Jian Guo Li, Zhong Yun Fan
Abstract: Semisolid process can be used as grain refining method to replace conventional chemical grain refining approach. Typical semisolid slurry making techniques were introduced in the paper as potential semisolid grain refining methods. The temperature and morphology control for grain refining through semisolid process were enhanced to achieve fine particle size and large particle number rather than spheroidal particle shape or low viscosity of the slurry comparing with conventional rheo-forming process. The grain refinement effect was demonstrated by a 40 mm cylinder casting of AZ31 alloy.
431
Authors: Wojciech L. Suchanek, Richard E. Riman
Abstract: This paper briefly reviews hydrothermal synthesis of ceramic powders and shows how understanding the underlying physico-chemical processes occurring in the aqueous solution can be used for engineering hydrothermal crystallization processes. Our overview covers the current status of hydrothermal technology for inorganic powders with respect to types of materials prepared, ability to control the process, and use in commercial manufacturing. General discussion is supported with specific examples derived from our own research (hydroxyapatite, PZT, 􀄮-Al2O3, ZnO, carbon nanotubes). Hydrothermal crystallization processes afford excellent control of morphology (e.g., spherical, cubic, fibrous, and plate-like) size (from a couple of nanometers to tens of microns), and degree of agglomeration. These characteristics can be controlled in wide ranges using thermodynamic variables, such as reaction temperature, types and concentrations of the reactants, in addition to non-thermodynamic (kinetic) variables, such as stirring speed. Moreover, the chemical composition of the powders can be easily controlled from the perspective of stoichiometry and formation of solid solutions. Finally, hydrothermal technology affords the ability to achieve cost effective scale-up and commercial production.
184
Authors: Yoshitake Masuda, Kazumi Kato
Abstract: TiO2 was crystallized to form particles in aqueous solutions containing ammonium hexafluorotitanate and boric acid. XRD diffraction patterns indicated they were in a single phase of anatase TiO2. TiO2 particles prepared at 90 °C exhibited N2 adsorption-desorption isotherms of type IV. BET specific surface area of the particles was estimated to 13 m2/g. On the other hand, TiO2 particles prepared at 50 °C exhibited N2 adsorption-desorption isotherms of type I. BET specific surface area of the particles was estimated to 168 m2/g. Crystal growth of TiO2 was strongly affected by synthesis temperature. Nano-sized pores or surface structure of TiO2 particles prepared at 50 °C would increase N2 adsorption volume to realize high BET specific surface area. Additionally, aqueous solution process described here had an advantage that TiO2 crystallized at ambient temperature. Anatase TiO2 was prepared without annealing at high temperature which caused aggregation of particles and disappearance of surface nanostructures. The particles with large surface area can be thus utilized for catalyst, cosmetic, photocatalyst, dye-sensitized solar cell or sensors.
103
Authors: Chuan Hui Gao, Li Ding, Yu Min Wu, Chuan Xing Wang, Jun Xu
Abstract: A low-cost raw material, bittern obtained from the production process of sea salt, was used to prepare magnesium oxysulfate hydrate (MgSO4·5Mg (OH)2·2H2O, abbreviated as 152MOS) whiskers via hydrothermal synthesis with ammonia and magnesium sulfate as the other starting raw materials. The bittern was firstly filtered and then used directly without de-coloring. X-ray powder diffraction (XRD), transmission electron microscope (TEM), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDX) and scanning electron microscope (SEM) were employed to investigate the composition and morphology of the products. It was found that the 152MOS whiskers synthesized from bittern at 190°C for 3 hours exhibited fanlike morphology. The formation of the fanlike whiskers was inhibited and most of the whiskers presented as single fibers when ethanol was used as crystal control agent in the hydrothermal process. From the two-dimensional steps observed at tips of the whiskers, a possible growth mechanism was speculated that it was the extension of dislocations that made the growth of the whiskers.
986
Authors: Yu Ming Tian, Ming Xia Xu, Xiang Zhi Liu, Lei Ge, Ping Zhang
Abstract: A two-step anodization process was used to fabricate wide-range highly ordered porous anodic alumina membrane (PAA) in the electrolyte of oxalic acid through different anodic voltages. The effect of anodic voltage, pretreatments and pore-expanding time on the microstruture of PAA membrane was also studied in the process of two-step anodization. In a certain range, with the increase of anodic voltage, the pore diameter almost increases linearly while the pore density almost decreases linearly. The PAA template with anneal and electropolishing process has better regularity. In a certain time range, the pore diameter increases obviously with the pore-expanding time. It was demonstrated by XRD that the crystal constitution of the PAA without heat treatment was polycrystalline structure which contained Baehmite phase (Al2O3.H2O), Gibbsite phase (Al2O3.3H2O) and θ-Al2O3 phase. After heat treatment at 500°C for 0.5h, only the θ-Al2O3 phase was retained.
2232
Authors: Hui Ling Du, Yan Jun Zhou, Jin Gang Qi, Jian Zhong Wang, Ai Min Liu
Abstract: It is very important for spheroidic metal cobalt powders production to control the morphology of cobalt oxalate powders precursor. The spheroidic cobalt oxalate powders were prepared by conventional precipitation when a pulsed electromagnetic field (PEMF) was introduced. Scanning electron microscopy (SEM) images and X-ray powder diffraction (XRD) were used to characterize morphologies and phase structures of the cobalt oxalate powders. The research results show that a pulsed electromagnetic field (PEMF) play a key role in the process of preparation of spheroidic cobalt oxalate powders. In addition, a possible morphology control mechanism was preliminarily discussed based on the effects of PEMF on the process of growth of cobalt oxalate particles.
554
Authors: Xin Tong Xu, Jian Pang Zhai, Irene Ling Li, Shuang Chen Ruan
Abstract: SAPO-11 and SAPO-47 crystals have been synthesized using diethylamine (DEA) as the structure-directing agent (SDA) and their morphology have been controlled successfully by varying aging duration. The single crystals were obtained in a short aging duration while film and island-like crystals were obtained in a long aging duration. The effect of SiO2/Al2O3 ration and content of HF on SAPO-47 crystals have been investigated. High molar ration of SiO2/Al2O3 and high content of HF is tend to synthesize larger crystals of SAPO-47. All the samples were characterized by XRD and SEM.
1737
Authors: Masaya Kotaki, T. Kuriyama, I. Narisawa, Mototsugu Sakai, L. Bouwhuis
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