The thermal expansion behavior of sintered Nd–Fe–B magnets is a crucial parameter for production and application.However, this aspect has not been thoroughly investigated. In this study, three different sintered Nd...The thermal expansion behavior of sintered Nd–Fe–B magnets is a crucial parameter for production and application.However, this aspect has not been thoroughly investigated. In this study, three different sintered Nd–Fe–B magnets with varying Co content(Co = 0, 6, 12 wt%) were prepared using the conventional powder metallurgy method, and four magnets oriented under different magnetic fields were prepared to compare. The thermal expansion behavior for the magnets was investigated using a linear thermal dilatometry in the temperature range of 20℃–500℃. It was found that, the coefficient of thermal expansion(CTE) increases with the increase of Co contents, while the anisotropy of thermal expansion decreases.The introduction of Co leads to continuous changes from negative to positive thermal expansion in the vertically oriented direction, which is important for the development of zero thermal expansion magnets. The thermal expansion of nonoriented magnets was found to be isotropic. Additionally, the anisotropy of thermal expansion increases with the increase of orientation degree. These results have important implications for the development of sintered Nd–Fe–B with controllable CTE.展开更多
Systematical researches were accomplished on WC-Co with different Co contents(6%,10%and 12%,mass fraction).Based on the XPS and EDX,from orthogonal pretreatment experiments,it is indicated that the acid concentration,...Systematical researches were accomplished on WC-Co with different Co contents(6%,10%and 12%,mass fraction).Based on the XPS and EDX,from orthogonal pretreatment experiments,it is indicated that the acid concentration,the time of the acid pretreatment and the original Co content have significant influences on the Co-removal depth(D).Moreover,the specimen temperature,original Co content and Co-removal depth dependences of the Co evolution in nucleation,heating(in pure H2 atmosphere)and growth experiments were discussed,and mechanisms of Co evolutions were summarized,providing sufficient theoretical bases for the deposition of high-quality diamond films on WC-Co substrates,especially Co-rich WC-Co substrates.It is proven that the Co-rich substrate often presents rapid Co diffusion.The high substrate temperature can promote the Co diffusion in the pretreated substrate,while acts as a Co-etching process for the untreated substrates.It is finally found that the appropriate Co-removal depth for the WC-12%Co substrate is 8-9μm.展开更多
The Co content dependence of crystal structure and specific magnetization of Fe1-xCox-SiO2granular solid prepared by the sol-gel method have been studied. It is found that the crystal structure, Iattice parameter and ...The Co content dependence of crystal structure and specific magnetization of Fe1-xCox-SiO2granular solid prepared by the sol-gel method have been studied. It is found that the crystal structure, Iattice parameter and specific magnetization of the FeCo alloy particles depend on the Co content.展开更多
Ultrafine WC-Co-VC cemented carbides are used extensively in a variety of industrial environments due to their excellent mechanical properties and outstanding wear resistance.Co content affects the service performance...Ultrafine WC-Co-VC cemented carbides are used extensively in a variety of industrial environments due to their excellent mechanical properties and outstanding wear resistance.Co content affects the service performance of the cemented carbides.In the present study,the influ-ences of Co content on microstructure,physical,and mechanical properties were investigated systematically.Ultrafine WC-Co-VC cemented carbides with Co content varying from 4 wt%and 7 wt%and assistance of VC(0.35 wt%)as inhibitor of WC grain growth were prepared.The physical and mechanical properties were tested and the microstructure characteristics were observed by optical microscope(OM)and scanning electron microscopy(SEM).From the results,it is found that with Co content increasing,both the cobalt magnetism and bending strength increase,while the coercive force,Rockwell hardness,density,and abrasive wear resistance decrease.In addition,the OM and SEM results show that the increase of Co content in WC-Co-VC cemented carbides tends to reduce the quantity and size of micro-pores,and make the fracture mode change from brittle fracture to ductile fracture.展开更多
In order to improve the cyclic stability of La-Mg-Ni system （Ce2Ni7-type） alloy electrode, small amount of Co was added in La0.75Mg0.25Ni3.5 alloy. The effect of Co on electrochemical performance and microstructure ...In order to improve the cyclic stability of La-Mg-Ni system （Ce2Ni7-type） alloy electrode, small amount of Co was added in La0.75Mg0.25Ni3.5 alloy. The effect of Co on electrochemical performance and microstructure of the alloys were investigated in detail. XRD results showed that the alloys had multiphase structure composed of （La, Mg）2Ni7, LaNi5 and small amount of LaNi2 phases. The discharge capacity of the alloys first increased and then decreased with increasing Co content. At a discharge current density of 900 mA/g, the HRD of the alloy electrodes increased from 81.3% （x=0） to 89.2 % （x=0.2）, and then reduced to 87.8 % （x=0.6）. After 60 charge/discharge cycles, the capacity retention rate of the alloys enhanced from 52.67% to 61.32%, and the capacity decay rate of the alloys decreased from 2.60 to 2.05 mAh/g per cycle with increasing Co content. The obtained results by XPS and XRD showed that the fundamental reasons for the capacity decay of the La-Mg-Ni system （Ce2Ni7-type） alloy electrodes were corrosion and oxidation as well as passivation of Mg and Lain alkaline solution.展开更多
In this paper, Ni/Zr–Yb–O catalysts with different sodium contents are prepared by a co-precipitation method, using aqueous Na2CO3 solution as a precipitant, and the effect of sodium on the catalyst structure and ca...In this paper, Ni/Zr–Yb–O catalysts with different sodium contents are prepared by a co-precipitation method, using aqueous Na2CO3 solution as a precipitant, and the effect of sodium on the catalyst structure and catalytic performance for syngas methanation is extensively investigated using five Ni/Zr–Yb–O catalysts, containing 0, 0.5, 1.5,4.5 and 13.5 wt% Na^+, those are denoted as Cat-1, Cat-2, Cat-3, Cat-4 and Cat-5 respectively. It is found that the interaction between Ni and support determines the catalytic performance of Ni/Zr–Yb–O and the residual sodium content negatively affects the interaction between Ni and support. Cat-1 exhibits an excellent catalytic performance.During a long run time of 380 h, no deactivation is observed and both CO conversion and CH4 selectivity maintain a level above 90%. However, Cat-3 and Cat-5 suffer rapid deactivation under the same reaction condition. The characterization results indicate the strong interaction between Ni and support enables Cat-1 to possess well dispersed Ni species, resistance to sintering and carbon deposition and thus the excellent catalytic performance. However, the presence of sodium ions over Ni/Zr–Yb–O degrades the interaction between Ni and support and the catalytic performance, especially for the stability. The relative weak interaction between Ni and support results in severe sintering of both ZrO2 and Ni under the reaction condition, carbon deposition and the poor catalytic performance.展开更多
基金the National Key Research and Development Program of China (Grant No. 2021YFB3502900)the National Natural Science Foundation of China (Grant No. 51871063)+1 种基金the Key Technology Research and Development Program of Shandong Province, China (Grant No. 2019JZZY020210)the Major Projects in Inner Mongolia Autonomous Region, China。
文摘The thermal expansion behavior of sintered Nd–Fe–B magnets is a crucial parameter for production and application.However, this aspect has not been thoroughly investigated. In this study, three different sintered Nd–Fe–B magnets with varying Co content(Co = 0, 6, 12 wt%) were prepared using the conventional powder metallurgy method, and four magnets oriented under different magnetic fields were prepared to compare. The thermal expansion behavior for the magnets was investigated using a linear thermal dilatometry in the temperature range of 20℃–500℃. It was found that, the coefficient of thermal expansion(CTE) increases with the increase of Co contents, while the anisotropy of thermal expansion decreases.The introduction of Co leads to continuous changes from negative to positive thermal expansion in the vertically oriented direction, which is important for the development of zero thermal expansion magnets. The thermal expansion of nonoriented magnets was found to be isotropic. Additionally, the anisotropy of thermal expansion increases with the increase of orientation degree. These results have important implications for the development of sintered Nd–Fe–B with controllable CTE.
基金Projects(51275302,51005154)supported by the National Natural Science Foundation of ChinaProject(2015M580327)supported by the China Postdoctoral Science FoundationProject(2016T90370)supported by the China Postdoctoral Science Foundation Special Funded Project
文摘Systematical researches were accomplished on WC-Co with different Co contents(6%,10%and 12%,mass fraction).Based on the XPS and EDX,from orthogonal pretreatment experiments,it is indicated that the acid concentration,the time of the acid pretreatment and the original Co content have significant influences on the Co-removal depth(D).Moreover,the specimen temperature,original Co content and Co-removal depth dependences of the Co evolution in nucleation,heating(in pure H2 atmosphere)and growth experiments were discussed,and mechanisms of Co evolutions were summarized,providing sufficient theoretical bases for the deposition of high-quality diamond films on WC-Co substrates,especially Co-rich WC-Co substrates.It is proven that the Co-rich substrate often presents rapid Co diffusion.The high substrate temperature can promote the Co diffusion in the pretreated substrate,while acts as a Co-etching process for the untreated substrates.It is finally found that the appropriate Co-removal depth for the WC-12%Co substrate is 8-9μm.
文摘The Co content dependence of crystal structure and specific magnetization of Fe1-xCox-SiO2granular solid prepared by the sol-gel method have been studied. It is found that the crystal structure, Iattice parameter and specific magnetization of the FeCo alloy particles depend on the Co content.
基金financially supported by the National Natural Science Foundation of China (No.51074189)
文摘Ultrafine WC-Co-VC cemented carbides are used extensively in a variety of industrial environments due to their excellent mechanical properties and outstanding wear resistance.Co content affects the service performance of the cemented carbides.In the present study,the influ-ences of Co content on microstructure,physical,and mechanical properties were investigated systematically.Ultrafine WC-Co-VC cemented carbides with Co content varying from 4 wt%and 7 wt%and assistance of VC(0.35 wt%)as inhibitor of WC grain growth were prepared.The physical and mechanical properties were tested and the microstructure characteristics were observed by optical microscope(OM)and scanning electron microscopy(SEM).From the results,it is found that with Co content increasing,both the cobalt magnetism and bending strength increase,while the coercive force,Rockwell hardness,density,and abrasive wear resistance decrease.In addition,the OM and SEM results show that the increase of Co content in WC-Co-VC cemented carbides tends to reduce the quantity and size of micro-pores,and make the fracture mode change from brittle fracture to ductile fracture.
基金the National Natural Science Foundation of China (50701011)Natural Science Foundation of Inner Mongolia, China (200711020703)Science and Technology Planned Project of Inner Mongolia, China (20050205)
文摘In order to improve the cyclic stability of La-Mg-Ni system （Ce2Ni7-type） alloy electrode, small amount of Co was added in La0.75Mg0.25Ni3.5 alloy. The effect of Co on electrochemical performance and microstructure of the alloys were investigated in detail. XRD results showed that the alloys had multiphase structure composed of （La, Mg）2Ni7, LaNi5 and small amount of LaNi2 phases. The discharge capacity of the alloys first increased and then decreased with increasing Co content. At a discharge current density of 900 mA/g, the HRD of the alloy electrodes increased from 81.3% （x=0） to 89.2 % （x=0.2）, and then reduced to 87.8 % （x=0.6）. After 60 charge/discharge cycles, the capacity retention rate of the alloys enhanced from 52.67% to 61.32%, and the capacity decay rate of the alloys decreased from 2.60 to 2.05 mAh/g per cycle with increasing Co content. The obtained results by XPS and XRD showed that the fundamental reasons for the capacity decay of the La-Mg-Ni system （Ce2Ni7-type） alloy electrodes were corrosion and oxidation as well as passivation of Mg and Lain alkaline solution.
基金Supported by the National Natural Science Foundation of China(21673187,21336009,21576228)National Key Technology Support Program of China(2014BAC10B01).
文摘In this paper, Ni/Zr–Yb–O catalysts with different sodium contents are prepared by a co-precipitation method, using aqueous Na2CO3 solution as a precipitant, and the effect of sodium on the catalyst structure and catalytic performance for syngas methanation is extensively investigated using five Ni/Zr–Yb–O catalysts, containing 0, 0.5, 1.5,4.5 and 13.5 wt% Na^+, those are denoted as Cat-1, Cat-2, Cat-3, Cat-4 and Cat-5 respectively. It is found that the interaction between Ni and support determines the catalytic performance of Ni/Zr–Yb–O and the residual sodium content negatively affects the interaction between Ni and support. Cat-1 exhibits an excellent catalytic performance.During a long run time of 380 h, no deactivation is observed and both CO conversion and CH4 selectivity maintain a level above 90%. However, Cat-3 and Cat-5 suffer rapid deactivation under the same reaction condition. The characterization results indicate the strong interaction between Ni and support enables Cat-1 to possess well dispersed Ni species, resistance to sintering and carbon deposition and thus the excellent catalytic performance. However, the presence of sodium ions over Ni/Zr–Yb–O degrades the interaction between Ni and support and the catalytic performance, especially for the stability. The relative weak interaction between Ni and support results in severe sintering of both ZrO2 and Ni under the reaction condition, carbon deposition and the poor catalytic performance.
