The effect of niobium on the formation of NbC phase and solidification structure in high carbon equivalent grey cast iron was investigated.The experimental results indicated that an increase in the niobium content is ...The effect of niobium on the formation of NbC phase and solidification structure in high carbon equivalent grey cast iron was investigated.The experimental results indicated that an increase in the niobium content is favorable to refining the graphite and eutectic cell;and the pearlite lamellar spacing is reduced.Based on the thermodynamic calculation the formation of NbC is prior to the eutectic reaction.The reduction in the pearlite lamellar spacing is mainly attributed to the decrease of eutectic temperature with the addition of niobium.Additionally,properties including hardness and wear resistance were improved after the addition of niobium.展开更多
Niobium-promoted Fe/CNTs catalysts were prepared using a wet impregnation method.Samples were characterized by nitrogen adsorption,H2-TPR,TPD,XRD and TEM.The Fischer-Tropsch Synthesis(FTS) was carried out in a fixed-b...Niobium-promoted Fe/CNTs catalysts were prepared using a wet impregnation method.Samples were characterized by nitrogen adsorption,H2-TPR,TPD,XRD and TEM.The Fischer-Tropsch Synthesis(FTS) was carried out in a fixed-bed microreactor at 220 ℃,1 atm and H2/CO=2 for 5 h.Addition of niobium into Fe/CNTs increased the dispersion,decreased the average size of iron oxide nanoparticles and the catalyst reducibility.Niobium-promoted Fe catalyst resulted in appreciable increase in the selectivity of C5+ hydrocarbons and suppressed methane formation.These effects were more pronounced for the 0.04%Nb/Fe/CNTs catalyst,compared to those observed from other niobium compositions.The 0.04%Nb/Fe/CNTs catalyst enhanced the C5+ hydrocarbons selectivity by a factor of 67.5% and reduced the methane selectivity by a factor of 59.2%.展开更多
The purpose of this study was to determine the impact of niobium addition as an inoculation element on the microstructure and electrochemical properties of EN-FGL250 gray cast iron. Niobium additions are in a powder f...The purpose of this study was to determine the impact of niobium addition as an inoculation element on the microstructure and electrochemical properties of EN-FGL250 gray cast iron. Niobium additions are in a powder form and have a 0.5 mm particle size at dfferent proportions of 1 wt.% and 3 wt.%. The addition was done during casting of the metal in the mold at the last cooling step of the melt cast iron. These additions have a significant impact on the phenomenon of solidifi cation as the metal powder deposited in the sand molds creates new centers of germination and absorbs a lot of heat. The cooling rate directly affects the microstructure and electrochemical behavior. This is confirmed by SEM observations and electrochemical tests. Furthermore, the addition of niobium transforms the microstructure of gray cast iron from cellular structure into totally dendritic structure. As a consequence, the niobium addition affected the shape and size of graphite, thus considerably reducing the corrosion current density by increasing the polarization resistance Rp.展开更多
这是一篇工艺矿物学领域的论文。锂、铍、铌、钽等稀有金属作为国家战略性新兴资源,主要应用于国防、航空、航天等工业领域,近年来备受地质学家的关注。湖北某地铌钽铁矿为含铌粗面质火山岩及火山碎屑岩矿床,本文对该矿石进行了系统的...这是一篇工艺矿物学领域的论文。锂、铍、铌、钽等稀有金属作为国家战略性新兴资源,主要应用于国防、航空、航天等工业领域,近年来备受地质学家的关注。湖北某地铌钽铁矿为含铌粗面质火山岩及火山碎屑岩矿床,本文对该矿石进行了系统的工艺矿物学研究,查明矿石中主要含铌的矿物有铌铁矿,铌铁金红石、赤褐铁矿和钛铁矿、黄铁矿等,铌铁矿为该矿石选别铌精矿的主要回收矿物。大部分铌矿物嵌布粒度均小于0.04 mm,铌铁矿粒度微细,多为0.5~8μm,但在-0.037 mm 90%时单体解离度可达71.11%,可考虑用磁选方法分离铌铁矿和脉石矿物;矿石中脉石矿物以绢云母、斜长石为主,磨细后泥化严重,应注意泥级物质团聚对选矿实验的影响。展开更多
基金supported by CITIC-CBMM R&D project (No.036)Graduate Innovation Fund of Shanghai University (No.SHUCX 102233)
文摘The effect of niobium on the formation of NbC phase and solidification structure in high carbon equivalent grey cast iron was investigated.The experimental results indicated that an increase in the niobium content is favorable to refining the graphite and eutectic cell;and the pearlite lamellar spacing is reduced.Based on the thermodynamic calculation the formation of NbC is prior to the eutectic reaction.The reduction in the pearlite lamellar spacing is mainly attributed to the decrease of eutectic temperature with the addition of niobium.Additionally,properties including hardness and wear resistance were improved after the addition of niobium.
基金Ministry of Science,Technology and Innovation(E-Science Fund,03-02-02-SF0036)Ministry of Higher Education Malaysia(FRGS/2/2010/SG/UTP/02/3)Universiti Teknologi PETRONAS(31/09.10)
文摘Niobium-promoted Fe/CNTs catalysts were prepared using a wet impregnation method.Samples were characterized by nitrogen adsorption,H2-TPR,TPD,XRD and TEM.The Fischer-Tropsch Synthesis(FTS) was carried out in a fixed-bed microreactor at 220 ℃,1 atm and H2/CO=2 for 5 h.Addition of niobium into Fe/CNTs increased the dispersion,decreased the average size of iron oxide nanoparticles and the catalyst reducibility.Niobium-promoted Fe catalyst resulted in appreciable increase in the selectivity of C5+ hydrocarbons and suppressed methane formation.These effects were more pronounced for the 0.04%Nb/Fe/CNTs catalyst,compared to those observed from other niobium compositions.The 0.04%Nb/Fe/CNTs catalyst enhanced the C5+ hydrocarbons selectivity by a factor of 67.5% and reduced the methane selectivity by a factor of 59.2%.
文摘The purpose of this study was to determine the impact of niobium addition as an inoculation element on the microstructure and electrochemical properties of EN-FGL250 gray cast iron. Niobium additions are in a powder form and have a 0.5 mm particle size at dfferent proportions of 1 wt.% and 3 wt.%. The addition was done during casting of the metal in the mold at the last cooling step of the melt cast iron. These additions have a significant impact on the phenomenon of solidifi cation as the metal powder deposited in the sand molds creates new centers of germination and absorbs a lot of heat. The cooling rate directly affects the microstructure and electrochemical behavior. This is confirmed by SEM observations and electrochemical tests. Furthermore, the addition of niobium transforms the microstructure of gray cast iron from cellular structure into totally dendritic structure. As a consequence, the niobium addition affected the shape and size of graphite, thus considerably reducing the corrosion current density by increasing the polarization resistance Rp.
文摘这是一篇工艺矿物学领域的论文。锂、铍、铌、钽等稀有金属作为国家战略性新兴资源,主要应用于国防、航空、航天等工业领域,近年来备受地质学家的关注。湖北某地铌钽铁矿为含铌粗面质火山岩及火山碎屑岩矿床,本文对该矿石进行了系统的工艺矿物学研究,查明矿石中主要含铌的矿物有铌铁矿,铌铁金红石、赤褐铁矿和钛铁矿、黄铁矿等,铌铁矿为该矿石选别铌精矿的主要回收矿物。大部分铌矿物嵌布粒度均小于0.04 mm,铌铁矿粒度微细,多为0.5~8μm,但在-0.037 mm 90%时单体解离度可达71.11%,可考虑用磁选方法分离铌铁矿和脉石矿物;矿石中脉石矿物以绢云母、斜长石为主,磨细后泥化严重,应注意泥级物质团聚对选矿实验的影响。
