Si3N4 powders were synthesized by a carbothermal reduction method using a SiO2 + C combustion synthesis precur- sor derived from a mixed solution consisting of silicic acid (Si source), polyacrylamide (additive),...Si3N4 powders were synthesized by a carbothermal reduction method using a SiO2 + C combustion synthesis precur- sor derived from a mixed solution consisting of silicic acid (Si source), polyacrylamide (additive), nitric acid (oxidizer), urea (fuel), and glucose (C source). Scanning electron microscopy (SEM) micrographs showed that the obtained precursor exhibited a uniform mixture of SiO2 + C composed of porous blocky particles up to -20 μm. The precursor was subsequently calcined under nitrogen at 1200-1550℃ for 2 h. X-ray diffraction (XRD) analysis revealed that the initial reduction reaction started at about 1300℃, and the complete transition of SiQ into Si3N4 was found at 1550℃. The Si3N4 powders, synthesized at 1550℃, exhibit a mixture phase of α- and -Si3N4 and consist of mainly agglomerates of fine particles of 100-300 nm, needle-like crystals and whiskers with a diameter of about 100 nm and a length up to several micrometers, and a minor amount of irregular-shaped growths.展开更多
Nb-based powder was fabricated via mechanical grinding. The influence of stearic acid on the grinding process was studied. The slructural evolution and morphological evolution of the milled powder were characterized b...Nb-based powder was fabricated via mechanical grinding. The influence of stearic acid on the grinding process was studied. The slructural evolution and morphological evolution of the milled powder were characterized by X-ray diffraction (XRD), scanning electron mi- croscopy (SEM), and energy dispersive spectroscopy (EDS) analysis. It is indicated that an appropriate amount of stearic acid accelerates the particle refinement process and favors the production of superfine Nb-based particles with good dispersivity and high activity. However, an inappropriate amount of stearic acid has an adverse effect on the refinement process.展开更多
Transition metal carbides(TMC)modified by mesoporous carbon nanosheets(MCNSs)with high activity,fast elec-tron/ion transfer and long durability are considered as promising electrocatalysts for hydrogen evolution react...Transition metal carbides(TMC)modified by mesoporous carbon nanosheets(MCNSs)with high activity,fast elec-tron/ion transfer and long durability are considered as promising electrocatalysts for hydrogen evolution reaction(HER).展开更多
基金supported by the National Natural Science Foundation of China (Nos. 50802006 and 51172017)the Natural Science Foundation of Beijing (No. 2102028)+2 种基金the Fundamental Research Funds for the Central Universities (No. FRF-TP-11-004A)the Fok Ying Tung Education Foundation Fund for Young College Teachers (No. 122016)the Public Foundation of Beijing Key Lab for Advanced Powder Metallurgy and Particulate Materials (USTB)
文摘Si3N4 powders were synthesized by a carbothermal reduction method using a SiO2 + C combustion synthesis precur- sor derived from a mixed solution consisting of silicic acid (Si source), polyacrylamide (additive), nitric acid (oxidizer), urea (fuel), and glucose (C source). Scanning electron microscopy (SEM) micrographs showed that the obtained precursor exhibited a uniform mixture of SiO2 + C composed of porous blocky particles up to -20 μm. The precursor was subsequently calcined under nitrogen at 1200-1550℃ for 2 h. X-ray diffraction (XRD) analysis revealed that the initial reduction reaction started at about 1300℃, and the complete transition of SiQ into Si3N4 was found at 1550℃. The Si3N4 powders, synthesized at 1550℃, exhibit a mixture phase of α- and -Si3N4 and consist of mainly agglomerates of fine particles of 100-300 nm, needle-like crystals and whiskers with a diameter of about 100 nm and a length up to several micrometers, and a minor amount of irregular-shaped growths.
基金the National Basic Research Program of China(No.2011CB606306)the National High Technology Research and Development Program of China(No.2009AA033201)+3 种基金the National Natural Science Foundation of China(No.50974017)the Fundamental Research Funds for the Central Universities(No.FRF-TP-11-004A)the Program for New Century Excellent Talentsin Universities of China(No.NCET-10-0226)Fok Ying Tung Education Foundation for Young College Teachers(No.122016)
文摘Nb-based powder was fabricated via mechanical grinding. The influence of stearic acid on the grinding process was studied. The slructural evolution and morphological evolution of the milled powder were characterized by X-ray diffraction (XRD), scanning electron mi- croscopy (SEM), and energy dispersive spectroscopy (EDS) analysis. It is indicated that an appropriate amount of stearic acid accelerates the particle refinement process and favors the production of superfine Nb-based particles with good dispersivity and high activity. However, an inappropriate amount of stearic acid has an adverse effect on the refinement process.
基金financially supported by the National Natural Science Foundation of China (Nos. 52131307, 52130407, 52071013, 52104359, 51774035 and 52174344)the National Key Research and Development Program of China (No. 2021YFB3701900)+5 种基金the Natural Science Foundation Program of Beijing (Nos. 2202031, 2174079 and 2162027)the Science and Technology Program of Hebei (No. 20311001D)the Fundamental Research Funds for the Central Universities (Nos. FRF-TP-19-003C2, FRF-IDRY-19-025, FRF-IDRY-20-022, FRF-TP-20-032A2 and FRFTP-20-100A1Z)the Scientific and Technological Innovation Foundation of Foshan (No. BK21BE007)the Postdoctoral Research Foundation of Shunde Graduate School of University of Science and Technology Beijing (No. 2020BH014)the Natural Science Foundation Program of Hunan (No. 2021JJ30250)
文摘Transition metal carbides(TMC)modified by mesoporous carbon nanosheets(MCNSs)with high activity,fast elec-tron/ion transfer and long durability are considered as promising electrocatalysts for hydrogen evolution reaction(HER).