Ultrafine alumina power was obtained by calcining the precursor at 1 200 ℃ for 2 h, which was prepared by homogeneous precipitation method using aluminium salts and urea as raw materials. The effects of anions on the...Ultrafine alumina power was obtained by calcining the precursor at 1 200 ℃ for 2 h, which was prepared by homogeneous precipitation method using aluminium salts and urea as raw materials. The effects of anions on the morphology, particle size, surface area and configuration of the precursors were studied. The results show that the reactions of urea with aluminium nitrate and aluminium chloride result in agglomerates gels with bad filtering performance, the morphology is fibrillar. Aluminium sulphate-urea reactions result in the direct formation of amorphous powders with good filtering performance, of which morphology are regular spherical particles with larger granularity and smaller surface area. The reaction of mutual compound of aluminium sulphate and aluminium nitrate with molar ratio of 40:60 with urea can produce precursor with good filtering performance, spherical morphology, and uniform granularity distribution in the particle size range of 2-3 μm.展开更多
The precursor of ultrafine In 2O 3 powder was prepared by the hydrolysis, peptization and gelation of InCl 3·4H 2O used as raw material. After calcination, ultrafine In 2O 3 powder was obtained. The particl...The precursor of ultrafine In 2O 3 powder was prepared by the hydrolysis, peptization and gelation of InCl 3·4H 2O used as raw material. After calcination, ultrafine In 2O 3 powder was obtained. The particles were characterized by the methods of thermo gravimetric and differential thermal analysis (TG DTA), X ray diffractometry (XRD) and transmission electron microscopy (TEM), respectively.展开更多
The ultrafine powders of YBa2Cu3O7-x with the size of 100nm were synthesized by Sol-Gel process using cit-rate as complex and ammonium hydroxide to adjust pH of solu-tion. The process of Sol formation and Gel polymeri...The ultrafine powders of YBa2Cu3O7-x with the size of 100nm were synthesized by Sol-Gel process using cit-rate as complex and ammonium hydroxide to adjust pH of solu-tion. The process of Sol formation and Gel polymerization of YBa2Cu3O7-x in the Sol-Gel synthetic reaction has bee studied. The particle size ,pruity, sintering activity and superconducting properties of YBa2Cu3O7-x prepared by Sol-Gel method are better than by solid state reaction.展开更多
The effects of rare earth doping on the formation process of α-FeOOH crystallite and the properties of γ-Fe2O3 magnetic powder were investigated. The growth of needle α FeOOH crystallite was completed by the basic ...The effects of rare earth doping on the formation process of α-FeOOH crystallite and the properties of γ-Fe2O3 magnetic powder were investigated. The growth of needle α FeOOH crystallite was completed by the basic process. The experimental results show that the rare earth doping can increase the aspect axial ratio of needle α-FeOOH grains. its anti-sintering capability during the heat-treatment and the thermostability of γ-Fe2O3 magnetic properties. The magnetic properties of γ-Fe2O3 doping with rare earth are as follows: the coercivity Hc=36.3 kA/m (445 Oe), the ratio saturation magnetization σs=90.4μWbm/kg (72 emu/g), the ratio remanent magnetization σr=54 μWbm/kg (43 emu/g), and the temperature coefficient of remanent magnetization of γ-Fe2O3 doping with 0.1 mol% Dy can reach -5 ×10-4℃-1.展开更多
Two-step steam reforming of methane (SRM) is a novel chemical looping process towards the production of pure hydrogen and syngas (synthesis gas), consisting of a syngas production step and a water-splitting step. Rene...Two-step steam reforming of methane (SRM) is a novel chemical looping process towards the production of pure hydrogen and syngas (synthesis gas), consisting of a syngas production step and a water-splitting step. Renewable energy can be used to drive this process for hydrogen production, especially solar energy. CeO2-Fe2O3 complex oxide oxygen carrier was prepared by the impregnation method and characterized by means of X-ray diffractometer (XRD), Raman spectroscopy (Raman) and hydrogen programmed reduction (H2-TPR). CH4 temperature programmed and isothermal reactions were adopted to test syngas production reactivity, and water splitting reaction was employed to investigate water-splitting activity. Moreover, two-step SRM performance was evaluated by a successive redox cycle. The results showed that CO-uncontaminated H2 and highly selective syngas (with H2/CO ratio close to 2) could be respectively obtained from two steps, and CeFeO3 formation was found in the first redox cycle and proved to be enhanced by the redox treatment. After 10 successive cycles, obvious CeFeO3 phase was detected, which may be responsible for favorable successive redox cycle performances.展开更多
A series of nanosized CeO2-Fe2O3 mixed-oxide nanocomposites with different Ce4+/Fe3+molar ratios were successfully prepared by a co-precipitation technique.The surface area increased with Fe2O3 content increasing up t...A series of nanosized CeO2-Fe2O3 mixed-oxide nanocomposites with different Ce4+/Fe3+molar ratios were successfully prepared by a co-precipitation technique.The surface area increased with Fe2O3 content increasing up to 60 wt%in the composite.However,with further increase in Fe2O3 content,the surface area began to decrease.The reduction processes of the CeO2-Fe2O3 nanocomposites were studied in a hydrogen atmosphere at 300-600℃.The reduction rates increased by increasing both the temperature and Fe2O3 content in the nanocomposites.The microstructure of the reduced composites at 500℃illustrated the presence of a considerable number of macro-and micro-pores.The activation energy values were calculated which were in the range of 3.56-5.37 kJ mol-1 at the initial stages(up to 35%reduction)and 5.21-10.2 kJ·mol-1 at the final stages(up to 80%reduction)of reduction.The rate-controlling mechanisms in both the initial and final reduction stages were determined,and the initial reaction stage was controlled by combined gaseous diffusion and interfacial chemical reaction mechanisms for all the composites except for pure CeO2,which was controlled by a chemical reaction mechanism.The final reaction stage was controlled by a gaseous diffusion mechanism for some composites,while for the others it was controlled by combined gaseous diffusion and interfacial chemical reaction mechanisms.The hydrogen sorption properties of the nanocomposites were studied by pressure composition isotherms using a volumetric method.Hydrogen storage in the nanocomposites increased by increasing the temperature because of the formation of oxygen vacancies which enhance atomic H adsorption and function as strong adsorption sites forming more metal hydride covalent bonds.展开更多
基金Project(5JJ3010) supported by the Natural Science Foundation of Hunan Province, China
文摘Ultrafine alumina power was obtained by calcining the precursor at 1 200 ℃ for 2 h, which was prepared by homogeneous precipitation method using aluminium salts and urea as raw materials. The effects of anions on the morphology, particle size, surface area and configuration of the precursors were studied. The results show that the reactions of urea with aluminium nitrate and aluminium chloride result in agglomerates gels with bad filtering performance, the morphology is fibrillar. Aluminium sulphate-urea reactions result in the direct formation of amorphous powders with good filtering performance, of which morphology are regular spherical particles with larger granularity and smaller surface area. The reaction of mutual compound of aluminium sulphate and aluminium nitrate with molar ratio of 40:60 with urea can produce precursor with good filtering performance, spherical morphology, and uniform granularity distribution in the particle size range of 2-3 μm.
文摘The precursor of ultrafine In 2O 3 powder was prepared by the hydrolysis, peptization and gelation of InCl 3·4H 2O used as raw material. After calcination, ultrafine In 2O 3 powder was obtained. The particles were characterized by the methods of thermo gravimetric and differential thermal analysis (TG DTA), X ray diffractometry (XRD) and transmission electron microscopy (TEM), respectively.
文摘The ultrafine powders of YBa2Cu3O7-x with the size of 100nm were synthesized by Sol-Gel process using cit-rate as complex and ammonium hydroxide to adjust pH of solu-tion. The process of Sol formation and Gel polymerization of YBa2Cu3O7-x in the Sol-Gel synthetic reaction has bee studied. The particle size ,pruity, sintering activity and superconducting properties of YBa2Cu3O7-x prepared by Sol-Gel method are better than by solid state reaction.
文摘The effects of rare earth doping on the formation process of α-FeOOH crystallite and the properties of γ-Fe2O3 magnetic powder were investigated. The growth of needle α FeOOH crystallite was completed by the basic process. The experimental results show that the rare earth doping can increase the aspect axial ratio of needle α-FeOOH grains. its anti-sintering capability during the heat-treatment and the thermostability of γ-Fe2O3 magnetic properties. The magnetic properties of γ-Fe2O3 doping with rare earth are as follows: the coercivity Hc=36.3 kA/m (445 Oe), the ratio saturation magnetization σs=90.4μWbm/kg (72 emu/g), the ratio remanent magnetization σr=54 μWbm/kg (43 emu/g), and the temperature coefficient of remanent magnetization of γ-Fe2O3 doping with 0.1 mol% Dy can reach -5 ×10-4℃-1.
基金Project support by the National Natural Science Foundation of China (50574046, 50774038)the Natural Science Foundation of Yunnan Prov-ince (2008E030M)+1 种基金the Research Fund for the Doctoral Program of Higher Education of China (20095314120005)2010 Innovation Fund of Kunming University of Science and Technology
文摘Two-step steam reforming of methane (SRM) is a novel chemical looping process towards the production of pure hydrogen and syngas (synthesis gas), consisting of a syngas production step and a water-splitting step. Renewable energy can be used to drive this process for hydrogen production, especially solar energy. CeO2-Fe2O3 complex oxide oxygen carrier was prepared by the impregnation method and characterized by means of X-ray diffractometer (XRD), Raman spectroscopy (Raman) and hydrogen programmed reduction (H2-TPR). CH4 temperature programmed and isothermal reactions were adopted to test syngas production reactivity, and water splitting reaction was employed to investigate water-splitting activity. Moreover, two-step SRM performance was evaluated by a successive redox cycle. The results showed that CO-uncontaminated H2 and highly selective syngas (with H2/CO ratio close to 2) could be respectively obtained from two steps, and CeFeO3 formation was found in the first redox cycle and proved to be enhanced by the redox treatment. After 10 successive cycles, obvious CeFeO3 phase was detected, which may be responsible for favorable successive redox cycle performances.
文摘A series of nanosized CeO2-Fe2O3 mixed-oxide nanocomposites with different Ce4+/Fe3+molar ratios were successfully prepared by a co-precipitation technique.The surface area increased with Fe2O3 content increasing up to 60 wt%in the composite.However,with further increase in Fe2O3 content,the surface area began to decrease.The reduction processes of the CeO2-Fe2O3 nanocomposites were studied in a hydrogen atmosphere at 300-600℃.The reduction rates increased by increasing both the temperature and Fe2O3 content in the nanocomposites.The microstructure of the reduced composites at 500℃illustrated the presence of a considerable number of macro-and micro-pores.The activation energy values were calculated which were in the range of 3.56-5.37 kJ mol-1 at the initial stages(up to 35%reduction)and 5.21-10.2 kJ·mol-1 at the final stages(up to 80%reduction)of reduction.The rate-controlling mechanisms in both the initial and final reduction stages were determined,and the initial reaction stage was controlled by combined gaseous diffusion and interfacial chemical reaction mechanisms for all the composites except for pure CeO2,which was controlled by a chemical reaction mechanism.The final reaction stage was controlled by a gaseous diffusion mechanism for some composites,while for the others it was controlled by combined gaseous diffusion and interfacial chemical reaction mechanisms.The hydrogen sorption properties of the nanocomposites were studied by pressure composition isotherms using a volumetric method.Hydrogen storage in the nanocomposites increased by increasing the temperature because of the formation of oxygen vacancies which enhance atomic H adsorption and function as strong adsorption sites forming more metal hydride covalent bonds.
