Mg69Zn27Ca4 alloys with diameters of 1.5, 2 and 3 mm were fabricated using copper mold injection casting method. Microstructural analysis reveals that the alloy with a diameter of 1.5 mm is almost completely composed ...Mg69Zn27Ca4 alloys with diameters of 1.5, 2 and 3 mm were fabricated using copper mold injection casting method. Microstructural analysis reveals that the alloy with a diameter of 1.5 mm is almost completely composed of amorphous phase. However, with the cooling rate decline, a little α-Mg and MgZn dendrites can be found in the amorphous matrix. Based on the microstructural and tensile results, the ductile dendrites are conceived to be highly responsible for the enhanced compressive strain from 1.3% to 3.1% by increasing the sample diameter from 1.5 mm to 3 mm. In addition, the Mg69Zn27Ca4 alloy with 1.5 mm diameter has the best corrosion properties. The current Mg-based alloys show much better corrosion resistance than the traditionally commercial wrought magnesium alloy ZK60 in simulated sea-water.展开更多
The microstructural evolution and corrosion behavior of Ni_(62)Nb_(33)Zr_(5)bulk metallic glasses(BMGs)after annealing treatment(AT)at different crystallization temperatures and cryogenic treatment(CT)at−100℃are expe...The microstructural evolution and corrosion behavior of Ni_(62)Nb_(33)Zr_(5)bulk metallic glasses(BMGs)after annealing treatment(AT)at different crystallization temperatures and cryogenic treatment(CT)at−100℃are experimen-tally investigated.Appropriate AT and CT can both improve the thermal stability and comprehensive corrosion resistance of as-cast BMG in 3.5 wt.%NaCl solution.The annealed and cryo-treated BMGs exhibit one more finite diffusion layer loop in the electrical equivalent circuit than the as-cast BMG,indicating the complexity of the corrosion behavior.Superior corrosion resistance is obtained in the cryo-treated BMG because the high degree of amorphization caused by CT reduces the structural inhomogeneity.Lower C_(d)and higher R_(d)values are obtained for the cryo-treated BMG,revealing the formation of a more stable passive film.Among the annealed BMGs,the fully crystallized sample exhibits a higher anti-corrosion performance owing to the existence of Nb-rich oxides in the crystallization products.The passive film is found to be composed mainly of Nb_(2)O_(5)and ZrO_(2),demonstrating that Nb and Zr are conducive to reacting with oxygen to form a passive film.Based on the goal of maintaining a fully amorphous phase,appropriate CT causing structural homogeneity of the BMG is a simple and effective means to improve the comprehensive corrosion resistance.展开更多
Ti47Cu38-xZr7.5Fe2.5Sn2 Si1 Ag2 Tax(x=1-4;at%,the same below)bulk metallic glasses(BMGs)with good bio-corrosion resistance and mechanical properties were fabricated by copper mold casting.Critical diameter of the Ti-b...Ti47Cu38-xZr7.5Fe2.5Sn2 Si1 Ag2 Tax(x=1-4;at%,the same below)bulk metallic glasses(BMGs)with good bio-corrosion resistance and mechanical properties were fabricated by copper mold casting.Critical diameter of the Ti-based BMGs with 1 at%-4 at%Ta was 3 mm.The Ta-incorporated Ti-based BMGs exhibit higher open current potential and parallel passive current density in comparison with those of Ti-6 Al-4 V alloy in 0.9 wt%NaCl and Hank’s solution,implying their good corrosion resistance.The pitting corrosion potential of the Ti-based BMGs gradually increases up to about 1.25 V with Ta addition increasing up to 4 at%in 0.9 wt%NaCl solution.Among the present Ti-based BMGs,the alloy bearing2 at%Ta exhibits the optimal integration of mechanical properties,including the compressive fracture strength exceeding 2000 MPa,relative low Young’s modulus of98 GPa,plastic strain of 3.4%and high hardness of HV599.The Ta-bearing Ti-based bulk metallic glasses with integration of relative high GFA,good mechanical properties and high bio-corrosion resistance are beneficial for biomedical applications.展开更多
The influence of Zr content on corrosion behaviors of the Ni61.5Nb 38.5xZrx(x=1,3,5,7,9 at.%) bulk metallic glasses(BMGs) in 1 M HCl aqueous solution was investigated by potentiodynamic polarization measurements and X...The influence of Zr content on corrosion behaviors of the Ni61.5Nb 38.5xZrx(x=1,3,5,7,9 at.%) bulk metallic glasses(BMGs) in 1 M HCl aqueous solution was investigated by potentiodynamic polarization measurements and X-ray photo-electron spectroscopy(XPS).It was found that these BMG alloys possess superior corrosion resistance,that is,with large passive region of about 1.5 V and low passive current density(as low as 0.05 Am-2 for Ni61.5Nb31.5Zr7).XPS analysis indicates that the high corrosion resistance is attributed to the formation of Nb-and Zr-enriched surface films formed in the aggressive acid solution.The Zr substitution for Nb effectively reduces the Ni content,particularly the metallic state Ni content in the surface films,which depresses the electrical conduction of the surface films and reduces the passive current density,thus leading to the enhancement of the corrosion resistance of these Ni-Nb-Zr BMGs.These alloys may potentially be useful for engineering applications.展开更多
The impact of sustainable reduced tillage （RT） on the physical properties of soil is well documented worldwide; however, there is no precise information about the influence of long-term RT or no-till （NT） on the s...The impact of sustainable reduced tillage （RT） on the physical properties of soil is well documented worldwide; however, there is no precise information about the influence of long-term RT or no-till （NT） on the soils at the boundary for grain maize-growing in the semi-humid subarctic climate conditions of the Baltic states, especially on the formation of a hard- ened upper soil layer （10-15 cm in depth） --＂loosening hardpan＂. This study was carried out at the Research Station of Aleksandras Stulginskis University, Lithuania from 2009-2012. The investigations were based on a long-term （since 1988） field experiment. The aim of the investigation was to ascertain the influence of reduced primary tillage on the main soil＇s physical properties. This study examined soils that were deep ploughing （DP）, shallow ploughing （SP）, deep cultivation （DC）, shallow cultivation （SC）, and no-till （NT）. Reducing the tillage intensity to NT had no significant effect on the structural soil＇s composition; however, the stability of the structure of the 〉1 and 〉0.25 mm-size fractions was significantly higher in the non-reversibly tilled （DC, SC） and NT plots. The penetration resistance of the DP soils was less after primary tillage and wintering, and became similar to the NT plots at the end of the maize growth season. After primary tillage and wintering, the soil moisture content in the upper soil layer （0-5 cm depth） of the NT plots was 17-49 and 16-18% higher than that in the DP. Long-term reduction of primary tillage up to NT generally had no significant effect on the moisture content and soil bulk density of the 0-10 and 10-20 cm layers. The results showed that long-term RT stabilized the physical quality of soil. Less soil penetration resistance was established in the DP plots compared to both RT and NT, however, indicators of the formation of a uniform ＂loosening hardpan＂ layer were not found. It is summarized that long-term RT or NT systems stabilize, or may increase, t展开更多
High cost has undoubtedly become the biggest obstacle to the commercialization of proton exchange membrane fuel cells(PEMFCs),in which Pt-based catalysts employed in the cathodic catalyst layer(CCL)account for the maj...High cost has undoubtedly become the biggest obstacle to the commercialization of proton exchange membrane fuel cells(PEMFCs),in which Pt-based catalysts employed in the cathodic catalyst layer(CCL)account for the major portion of the cost.Although nonprecious metal catalysts(NPMCs)show appreciable activity and stability in the oxygen reduction reaction(ORR),the performance of fuel cells based on NPMCs remains unsatisfactory compared to those using Pt-based CCL.Therefore,most studies on NPMC-based fuel cells focus on developing highly active catalysts rather than facilitating oxygen transport.In this work,the oxygen transport behavior in CCLs based on highly active Fe-N-C catalysts is comprehensively explored through the elaborate design of two types of membrane electrode structures,one containing low-Pt-based CCL and NPMCbased dummy catalyst layer(DCL)and the other containing only the NPMC-based CCL.Using Zn-N-C based DCLs of different thickness,the bulk oxygen transport resistance at the unit thickness in NPMC-based CCL was quantified via the limiting current method combined with linear fitting analysis.Then,the local and bulk resistances in NPMC-based CCLs were quantified via the limiting current method and scanning electron microscopy,respectively.Results show that the ratios of local and bulk oxygen transport resistances in NPMCbased CCL are 80%and 20%,respectively,and that an enhancement of local oxygen transport is critical to greatly improve the performance of NPMC-based PEMFCs.Furthermore,the activity of active sites per unit in NPMCbased CCLs was determined to be lower than that in the Pt-based CCL,thus explaining worse cell performance of NPMC-based membrane electrode assemblys(MEAs).It is believed that the development of NPMC-based PEMFCs should proceed not only through the design of catalysts with higher activity but also through the improvement of oxygen transport in the CCL.展开更多
基金National Natural Science Foundation of China(No.51365050)National Corn Modern Industrial Technology System Construction Project of China(CARS-02)+1 种基金Talent Project of Shihezi University(No.RCZX201307)Project of Southern Xinjiang(No.2014BA058)
基金Project(NCET-11-0554)supported by the Program for New Century Excellent Talents in UniversityProject(2011BAE22B04)supportedby the National Key Technology R&D Program of ChinaProject(51271206)supported by the National Natural Science Foundation of China
文摘Mg69Zn27Ca4 alloys with diameters of 1.5, 2 and 3 mm were fabricated using copper mold injection casting method. Microstructural analysis reveals that the alloy with a diameter of 1.5 mm is almost completely composed of amorphous phase. However, with the cooling rate decline, a little α-Mg and MgZn dendrites can be found in the amorphous matrix. Based on the microstructural and tensile results, the ductile dendrites are conceived to be highly responsible for the enhanced compressive strain from 1.3% to 3.1% by increasing the sample diameter from 1.5 mm to 3 mm. In addition, the Mg69Zn27Ca4 alloy with 1.5 mm diameter has the best corrosion properties. The current Mg-based alloys show much better corrosion resistance than the traditionally commercial wrought magnesium alloy ZK60 in simulated sea-water.
基金the National Natu-ral Science Foundation of China(No.51971102)Open Research Fund of Songshan Lake Materials Laboratory(No.2021SLABFK08)Sci-ence and Technology Program of University of Jinan(No.XKY2117).
文摘The microstructural evolution and corrosion behavior of Ni_(62)Nb_(33)Zr_(5)bulk metallic glasses(BMGs)after annealing treatment(AT)at different crystallization temperatures and cryogenic treatment(CT)at−100℃are experimen-tally investigated.Appropriate AT and CT can both improve the thermal stability and comprehensive corrosion resistance of as-cast BMG in 3.5 wt.%NaCl solution.The annealed and cryo-treated BMGs exhibit one more finite diffusion layer loop in the electrical equivalent circuit than the as-cast BMG,indicating the complexity of the corrosion behavior.Superior corrosion resistance is obtained in the cryo-treated BMG because the high degree of amorphization caused by CT reduces the structural inhomogeneity.Lower C_(d)and higher R_(d)values are obtained for the cryo-treated BMG,revealing the formation of a more stable passive film.Among the annealed BMGs,the fully crystallized sample exhibits a higher anti-corrosion performance owing to the existence of Nb-rich oxides in the crystallization products.The passive film is found to be composed mainly of Nb_(2)O_(5)and ZrO_(2),demonstrating that Nb and Zr are conducive to reacting with oxygen to form a passive film.Based on the goal of maintaining a fully amorphous phase,appropriate CT causing structural homogeneity of the BMG is a simple and effective means to improve the comprehensive corrosion resistance.
基金financially supported by the National Natural Science Foundation of China(Nos.51671008 and 51701008)the Aeronautical Science Foundation of China(No.2013ZE51060)China Postdoctoral Science Foundation(No.2017M620575)。
文摘Ti47Cu38-xZr7.5Fe2.5Sn2 Si1 Ag2 Tax(x=1-4;at%,the same below)bulk metallic glasses(BMGs)with good bio-corrosion resistance and mechanical properties were fabricated by copper mold casting.Critical diameter of the Ti-based BMGs with 1 at%-4 at%Ta was 3 mm.The Ta-incorporated Ti-based BMGs exhibit higher open current potential and parallel passive current density in comparison with those of Ti-6 Al-4 V alloy in 0.9 wt%NaCl and Hank’s solution,implying their good corrosion resistance.The pitting corrosion potential of the Ti-based BMGs gradually increases up to about 1.25 V with Ta addition increasing up to 4 at%in 0.9 wt%NaCl solution.Among the present Ti-based BMGs,the alloy bearing2 at%Ta exhibits the optimal integration of mechanical properties,including the compressive fracture strength exceeding 2000 MPa,relative low Young’s modulus of98 GPa,plastic strain of 3.4%and high hardness of HV599.The Ta-bearing Ti-based bulk metallic glasses with integration of relative high GFA,good mechanical properties and high bio-corrosion resistance are beneficial for biomedical applications.
基金supported by the National Natural Science Foundation of China(Grant Nos.50825402 and 50731005)the National Basic Research Program of China(Grant No.2011CB606301)
文摘The influence of Zr content on corrosion behaviors of the Ni61.5Nb 38.5xZrx(x=1,3,5,7,9 at.%) bulk metallic glasses(BMGs) in 1 M HCl aqueous solution was investigated by potentiodynamic polarization measurements and X-ray photo-electron spectroscopy(XPS).It was found that these BMG alloys possess superior corrosion resistance,that is,with large passive region of about 1.5 V and low passive current density(as low as 0.05 Am-2 for Ni61.5Nb31.5Zr7).XPS analysis indicates that the high corrosion resistance is attributed to the formation of Nb-and Zr-enriched surface films formed in the aggressive acid solution.The Zr substitution for Nb effectively reduces the Ni content,particularly the metallic state Ni content in the surface films,which depresses the electrical conduction of the surface films and reduces the passive current density,thus leading to the enhancement of the corrosion resistance of these Ni-Nb-Zr BMGs.These alloys may potentially be useful for engineering applications.
基金partly funded by a grant from the Research Council of Lithuania (MIP-116/2012)
文摘The impact of sustainable reduced tillage （RT） on the physical properties of soil is well documented worldwide; however, there is no precise information about the influence of long-term RT or no-till （NT） on the soils at the boundary for grain maize-growing in the semi-humid subarctic climate conditions of the Baltic states, especially on the formation of a hard- ened upper soil layer （10-15 cm in depth） --＂loosening hardpan＂. This study was carried out at the Research Station of Aleksandras Stulginskis University, Lithuania from 2009-2012. The investigations were based on a long-term （since 1988） field experiment. The aim of the investigation was to ascertain the influence of reduced primary tillage on the main soil＇s physical properties. This study examined soils that were deep ploughing （DP）, shallow ploughing （SP）, deep cultivation （DC）, shallow cultivation （SC）, and no-till （NT）. Reducing the tillage intensity to NT had no significant effect on the structural soil＇s composition; however, the stability of the structure of the 〉1 and 〉0.25 mm-size fractions was significantly higher in the non-reversibly tilled （DC, SC） and NT plots. The penetration resistance of the DP soils was less after primary tillage and wintering, and became similar to the NT plots at the end of the maize growth season. After primary tillage and wintering, the soil moisture content in the upper soil layer （0-5 cm depth） of the NT plots was 17-49 and 16-18% higher than that in the DP. Long-term reduction of primary tillage up to NT generally had no significant effect on the moisture content and soil bulk density of the 0-10 and 10-20 cm layers. The results showed that long-term RT stabilized the physical quality of soil. Less soil penetration resistance was established in the DP plots compared to both RT and NT, however, indicators of the formation of a uniform ＂loosening hardpan＂ layer were not found. It is summarized that long-term RT or NT systems stabilize, or may increase, t
基金the National Key R&D Program of China(Grant No.2021YFB4001303)the National Natural Science Foundation of China(Grant No.21975157)。
文摘High cost has undoubtedly become the biggest obstacle to the commercialization of proton exchange membrane fuel cells(PEMFCs),in which Pt-based catalysts employed in the cathodic catalyst layer(CCL)account for the major portion of the cost.Although nonprecious metal catalysts(NPMCs)show appreciable activity and stability in the oxygen reduction reaction(ORR),the performance of fuel cells based on NPMCs remains unsatisfactory compared to those using Pt-based CCL.Therefore,most studies on NPMC-based fuel cells focus on developing highly active catalysts rather than facilitating oxygen transport.In this work,the oxygen transport behavior in CCLs based on highly active Fe-N-C catalysts is comprehensively explored through the elaborate design of two types of membrane electrode structures,one containing low-Pt-based CCL and NPMCbased dummy catalyst layer(DCL)and the other containing only the NPMC-based CCL.Using Zn-N-C based DCLs of different thickness,the bulk oxygen transport resistance at the unit thickness in NPMC-based CCL was quantified via the limiting current method combined with linear fitting analysis.Then,the local and bulk resistances in NPMC-based CCLs were quantified via the limiting current method and scanning electron microscopy,respectively.Results show that the ratios of local and bulk oxygen transport resistances in NPMCbased CCL are 80%and 20%,respectively,and that an enhancement of local oxygen transport is critical to greatly improve the performance of NPMC-based PEMFCs.Furthermore,the activity of active sites per unit in NPMCbased CCLs was determined to be lower than that in the Pt-based CCL,thus explaining worse cell performance of NPMC-based membrane electrode assemblys(MEAs).It is believed that the development of NPMC-based PEMFCs should proceed not only through the design of catalysts with higher activity but also through the improvement of oxygen transport in the CCL.
