Papers by Keyword: Precursor

Abstract: A mathematical model for the growth of gallium nitride in a vertical impinging metalorganic chemical vapor deposition (MOCVD) reactor is developed. The dependence of the GaN film and the uniformity of the deposited layers on the inlet flow is investigated. Based on the simulation results, the uniformity of the precursor distribution is better, with the increasment of the inlet flow, so the quality of GaN film is superior.

Abstract: In this paper, TiO₂/diatomite and Ce-TiO₂/diatomite were prepared by sol-gel method in order to improve the spectrum responding range and its photocatalytic effect. The obtained samples were characterized by means of X-ray Diffractometer (XRD), Scanning Electron Microscope (SEM), Infrared Absorption Spectroscopy (FT-IR) and so on, and the photocatalytic activity was evaluated by methylene blue degradation. The heat stability of TiO₂/diatomite was improved by Ce-doped; TiO₂ was successfully loaded on diatomite through physical and chemical action. The de-coloring ratio of methylene blue of the two composite materials were similar under UV light, Ce-TiO₂/diatomite was higher under visible light, it reached to 80%, and it kept 65% after the five times repeated using of Ce-TiO₂/diatomite.

Abstract: A fast method of microwave pyrolysis was provided to prepare α-Al₂O₃ powders. Aluminum hydroxide and Aluminum ammonium sulfate doclecahydrate were used as raw materials to obtain α-aluminum oxide powder by microwave pyrolysis, respectively. Thermo-Gravimetric/Differential Thermal Analyzer (TG/DTA) and X-ray Diffraction (XRD) analysis were employed to investigate pyrolysis process and the transformation of metastables Al₂O₃ in the process of heating different precursors. Meanwhile, Flied Emission Scanning Electron Microscopy (FESEM) was applied to observe microstructure and grain growth, and the phase composition was characterized by XRD. The results indicated that the high purity α-Al₂O₃ was obtained which met the demands of market, and the sample obtained from aluminum hydroxide performed high purity, small particle size and, while the sample from ammonium aluminum sulfate showed lower purity and larger grain size.

Abstract: This paper presents a short review of research work on the development of synthesizing the colossal magnetoresistance materials through sol-gel method. Although there are a lot number of methods available, sol-gel method has been widely used and some excellent work has been reported. Two different manganite systems, which are LSMO and PSMO, that have been prepared through sol-gel method was choose for the discussion purpose. It was found that both systems were successfully prepared via the sol-gel method. Both systems showing better magnetoresistance properties compare to sample prepared through solid state reaction. X-ray diffraction technique was used to study the structural characteristic. Atomic force microscope and field emission scanning electron microscope were used in order to investigate surface morphology. Resistivity as a function of temperature was measured by a standard four-probe method.

Abstract: Triethynylborazine-polyhydromethylsiloxane copolymers (TEB-PHMSs) were prepared through hydrosilylation reaction between -C≡CH attached to boron and ≡Si-H. The structures of TEB-PHMSs were characterized by Fourier transform Infrared (FT-IR) and Nuclear Magnetic Resonance (NMR) spectroscopy. Their cure behavior were examined by Differential Scanning Calorimeter (DSC) and FT-IR, and then thermostability and ceramization of cured TEB-PHMS were investigated by Thermogravimetric analysis (TGA), pyrolysis-GC-MS, X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The results indicated that TEB-PHMSs could be cured and converted into an outstanding thermostable SiBCN ceramics.

Abstract: A low cost and simple fabrication of Cu-In-Se polycrystalline thin film for copper indium diselenide solar cell was prepared in a two-step process. The first step, a Cu In precursor film was prepared from copper acetate monohydrate and indium acetate mixed solution. The solution was coated on molybdenum-coated soda lime glass using the spin coating technique at room temperature following annealing in air at 500^°C for 20 minutes. The effect between spin parameters and film thickness of as-deposited Cu-In film were investigated. The second step, selenium was added in the precursor film by selenization process at 450^°C in Se atmosphere for 30 minutes in a low vacuum tube furnace with background pressure of 10^-2 mbar. The crystallographic properties of Cu-In-Se thin films were identified by X-ray diffractometer (XRD), the surface and cross-sectional morphology of films were observed by scanning electron microscopy (SEM). The chemical compositions of films were characterized by energy dispersive spectroscopy (EDS). It was found that the thickness of Cu-In films deposited on molybdenum-coated soda lime glass were approximately 1 μm. The EDS analysis showed the composition ratio in atomic % of Cu/In as approximately as 0.77. The XRD results reveal that the as-deposited Cu-In films consist of a mixture of copper oxide (CuO) and indium oxide (In₂O₃) phase at the annealing temperature of 500^°C. Furthermore, CuO and In₂O₃ phase were converted to (112) oriented chalcopyrite copper indium diselenide after selenization process.

Abstract: A new method that nanoSrTiO₃ electronic ceramics powder was prepared from nitrilotriacetic acid complexes by thermal decomposition was proposed. The reaction of Ti⁴⁺ and ta^3-(H₃ta=C₆H₆O₆N) and H₂O₂ is occurred to form [Ti₂O(O₂)₂(ta)₂]^4- complex ions, which react with Sr²⁺ to produce Sr₂[Ti₂O(O₂)₂(ta)₂] precursor, and then is washed, dried and annealed at 900°Cfor 3h to prepare nanoSrTiO₃ powder. The results of SEM analysis show that SrTiO₃ powders were spheric shape with narrow size distribution and the mean particle sizes about 80 nm. XRD investigation show that the powders of SrTiO₃ had the crystalline of the pseudo-cubic structure. The Sr/Ti mole ratio (1.000±0.005) and the purity of 99.8% were confirmed by chemical analysis. Compared with conventional thermal decomposition method of oxalate, the proposed new method, by which the high-quality SrTiO₃ powder is prepared, shows simple technology.

Abstract: In order to explore the optimal method to prepare high performance activated carbon precursors from medium temperature coal tar pitch, orthogonal tests are adopted to study the effects of oxygen-blowing time in the pretreatment process as well as carbonization temperature and carbonization time in activation and carbonization processes on the adsorption capacities of activated carbon. Moreover, the effects of additives (coke powder and anionic surfactant) on the adsorption capacities of activated carbon are examined. The results show that the factors affecting the adsorption capacities of pitch-based activated carbon, in order of importance, are carbonization temperature, oxygen-blowing time, carbonization time and additives. The optimal conditions for preparation of activated carbon precursor from medium temperature pitch are: 4h for oxygen-blowing time, 400°C for carbonization temperature, 60 minutes for carbonization time and no additives. The iodine absorption capacity of the prepared activated carbon precursor which is activated for 100 min at 800°C is 1739mg/g.

Abstract: This paper presents the work done for the preparation of precursor for producing Ti-Al-V-Y alloy via FFC Cambridge process. The aim of the work is also to investigate the uniformity of the phases formed during the pre-processing of the precursor.The importance of the alloy for mechanical and medical applications is well known. Titanium oxide (TiO₂), vanadium oxide (V₂O₅), aluminium oxide (Al₂O₃) and yttrium oxide (Y₂O₃) were selected as raw materials for precursor. The expected composition for the new alloy is Ti-6Al-4V-0.5Y. Water was used as a binder for the precursor. The materials were pre-mixed by ball milling for 24 hours and pressed using 13 mm die. The pressed mixtures were then sintered in the furnace at 900°C for 24 hours. The sintered samples were analysed using the optical microscope, electron micrograph with EDX and XRD. The result of the optical micrograph showed that the raw materials were uniformly mixed and well distributed with the presence of porosities. Electron micrograph further verified the morphology of the materials and the elements distribution in the precursor. The overlapping of yttrium and vanadium, Y(VO₄) was observed and verified by XRD. The derived formulated precursor was then ready for further work of reduction to Ti-Al-V-Y alloy using FFC Cambridge process.

Abstract: As disinfection by-products, the taste and odor (T&O) compounds were produced by chlorination at the end of water treatment. The existence of T&O compounds causes the pipe water with unpleasant odor and reducing water quality. Based on the latest research achievements at home and abroad, the characteristics and formation mechanisms of typical T&O compounds produced by chlorination are introduced. The new analytical method of electronic nose is also expounded. In addition, the common control technologies, such as pre-oxidation, activated carbon adsorption and bio-membrane, are reviewed. Since the precursors of T&O compounds shows small molecular, stable structure and low concentration, some coupling technologies including ozone-GAC, permanganate-PAC, and bio-membrane and GAC treatments, are employed effectively.Key words: chlorination; odor and taste compounds; disinfection by-products; precursor; electronic nose