The reaction kinetics of alloys based on magnesium are known to be greatly improved by the partial substitution of Mg with rare earths and transition metals,particularly Ni.The enhanced superficial hydrogen dissociati...The reaction kinetics of alloys based on magnesium are known to be greatly improved by the partial substitution of Mg with rare earths and transition metals,particularly Ni.The enhanced superficial hydrogen dissociation rate,the weakened Mg-H bond and the lower activation energy following element replacement are thought to be related to the better performance.The experimental alloys Ce5Mg_(95-x)Ni_(x)(x=5,10,15)were smelted by the vacuum induction melting.The phase transformation and structural evolution of experimental alloys before and after reaction with hydrogen were char-acterized by X-ray diffraction,scanning electron microscopy and transmission electron microscopy.The cast specimens contain CeMg_(12),Mg and Mg_(2)Ni phases,and the increase in Ni content results in an obvious growth of Mg_(2)Ni phase.The isothermal and non-isothermal hydrogenation and dehydrogenation kinetics of the experimental specimens were investi-gated using the Sievert apparatus,differential scanning calorimetry and thermal gravimetric analyzer.The activation energy may be calculated using the Arrhenius and Kissinger equations.The experimental alloys have been shown to have good activation properties,with a reversible hydriding and dehydriding capacities of around 5.0 wt.%in the first cycle.The initial dehydrogenation temperature of MgH_(2) decreases from 557.5 to 537.7 K with changing Ni content from 5 to 15 at.%.The dehydrogenation activation energy also reduces from 77.09 to 62.96 kJ/mol,which explains the improved hydrogen storage performance caused by Ni substitution.It can be shown that the impact of Ni on the decomposition enthalpy of MgH_(2) is quite modest,with the absolute enthalpy(ΔHr)only decreasing from 78.48 to 76.15 kJ/mol.展开更多
Mg85Zn5Ni10 ternary alloy was synthesized through vacuum induction melting for the first time.Phase compositions and microstructures of Mg85Zn5Ni10 alloy powders were analyzed by X-ray diffraction (XRD)and scanning el...Mg85Zn5Ni10 ternary alloy was synthesized through vacuum induction melting for the first time.Phase compositions and microstructures of Mg85Zn5Ni10 alloy powders were analyzed by X-ray diffraction (XRD)and scanning electron micro- scopy (SEM).By utilizing a Sieverts apparatus,the hydrogenation and dehydrogenation properties of Mg85Zn5Ni10 powders were measured systematically.XRD and SEM results indicated that the Mg85Zn5Ni10 alloy powders contained the major phase Mg,the eutectic Mg-Mg2Ni and Mg-MgZn2 mixtures.The possible reaction pathway can be inferred as follows:Mg +Mg2Ni +MgZn2 +H2←→MgH2+Mg2NiH4 +MgZn2,indicating that MgZn2 did not react with H2. After activation,the Mg85Zn5Ni10 alloy powders could absorb 5.4 wt.% hydrogen reversibly and held an excellent hydrogenation kinetics at a relatively low temperature.At 360 ℃,the alloy powders desorbed 5.351 wt.% hydrogen in 264 s.However,it only had fast dehydrogenation kinetics above 300 ℃.The existence of MgZn2 contributed to improving the kinetic properties.During the hydriding and dehydriding,the formed cracks and defects promoted the kinetics and thermodynamic properties.The activation energy for dehydrogenation was 75.514 kJ/mol.The enthalpy change values of hydrogenation and dehydrogenation were calculated to be -73.064 kJ/mol and 76.674 kJ/mol,respectively,indicating that melting with Ni and Zn could improve the thermodynamic property of Mg slightly.展开更多
In this paper,the as-cast Mg85Cu5Ni10 alloy and Mg85Cu5Ni10-x wt%CeO2(x=0,4,8)alloys were prepared successfully by vacuum induction smelting and ball milling.The microstructure,hydrogen absorption/desorption kinetics ...In this paper,the as-cast Mg85Cu5Ni10 alloy and Mg85Cu5Ni10-x wt%CeO2(x=0,4,8)alloys were prepared successfully by vacuum induction smelting and ball milling.The microstructure,hydrogen absorption/desorption kinetics and thermodynamics performances of the alloys were studied in detail.The results show that the Mg85Cu5Ni10 alloys with CeO2 additive have faster hydrogenation/dehydrogenation kinetics and better thermodynamic properties.The dehydrogenation activation energy is reduced to 81.211 kJ/mol from 119.142 by adding 8 wt%CeO2.CeO2 contributes to producing structural defects,nanocrystallines,grain boundaries,partial amorphous,lattice dislocations and cracks which are favorable to provide more hydrogen diffusion channels during hydriding/dehydriding process.Meanwhile,CeO2 additive weakens the bond energy of Mg-H.These micro structural changes caused by CeO2 additive improve the hydrogen storage performance of Mg85Cu5Ni10 markedly.展开更多
基金supported by the National Natural Science Foundation of China(Nos.51871125,51761032,51901105 and 52001005)Major Science and Technology Innovation Projects in Shandong Province(2019JZZY010320)+1 种基金Natural Science Foundation of Inner Mongolia,China(2019BS05005)Inner Mongolia University of Science and Technology Innovation Fund(2019QDL-B11).
文摘The reaction kinetics of alloys based on magnesium are known to be greatly improved by the partial substitution of Mg with rare earths and transition metals,particularly Ni.The enhanced superficial hydrogen dissociation rate,the weakened Mg-H bond and the lower activation energy following element replacement are thought to be related to the better performance.The experimental alloys Ce5Mg_(95-x)Ni_(x)(x=5,10,15)were smelted by the vacuum induction melting.The phase transformation and structural evolution of experimental alloys before and after reaction with hydrogen were char-acterized by X-ray diffraction,scanning electron microscopy and transmission electron microscopy.The cast specimens contain CeMg_(12),Mg and Mg_(2)Ni phases,and the increase in Ni content results in an obvious growth of Mg_(2)Ni phase.The isothermal and non-isothermal hydrogenation and dehydrogenation kinetics of the experimental specimens were investi-gated using the Sievert apparatus,differential scanning calorimetry and thermal gravimetric analyzer.The activation energy may be calculated using the Arrhenius and Kissinger equations.The experimental alloys have been shown to have good activation properties,with a reversible hydriding and dehydriding capacities of around 5.0 wt.%in the first cycle.The initial dehydrogenation temperature of MgH_(2) decreases from 557.5 to 537.7 K with changing Ni content from 5 to 15 at.%.The dehydrogenation activation energy also reduces from 77.09 to 62.96 kJ/mol,which explains the improved hydrogen storage performance caused by Ni substitution.It can be shown that the impact of Ni on the decomposition enthalpy of MgH_(2) is quite modest,with the absolute enthalpy(ΔHr)only decreasing from 78.48 to 76.15 kJ/mol.
基金Project(51071181)supported by the National Natural Science Foundation of ChinaProject(2013FJ4043)supported by the Natural Science Foundation of Hunan Province,China
基金National Natural Science Foundations of China (51761032,51471054 and 51871125).
文摘Mg85Zn5Ni10 ternary alloy was synthesized through vacuum induction melting for the first time.Phase compositions and microstructures of Mg85Zn5Ni10 alloy powders were analyzed by X-ray diffraction (XRD)and scanning electron micro- scopy (SEM).By utilizing a Sieverts apparatus,the hydrogenation and dehydrogenation properties of Mg85Zn5Ni10 powders were measured systematically.XRD and SEM results indicated that the Mg85Zn5Ni10 alloy powders contained the major phase Mg,the eutectic Mg-Mg2Ni and Mg-MgZn2 mixtures.The possible reaction pathway can be inferred as follows:Mg +Mg2Ni +MgZn2 +H2←→MgH2+Mg2NiH4 +MgZn2,indicating that MgZn2 did not react with H2. After activation,the Mg85Zn5Ni10 alloy powders could absorb 5.4 wt.% hydrogen reversibly and held an excellent hydrogenation kinetics at a relatively low temperature.At 360 ℃,the alloy powders desorbed 5.351 wt.% hydrogen in 264 s.However,it only had fast dehydrogenation kinetics above 300 ℃.The existence of MgZn2 contributed to improving the kinetic properties.During the hydriding and dehydriding,the formed cracks and defects promoted the kinetics and thermodynamic properties.The activation energy for dehydrogenation was 75.514 kJ/mol.The enthalpy change values of hydrogenation and dehydrogenation were calculated to be -73.064 kJ/mol and 76.674 kJ/mol,respectively,indicating that melting with Ni and Zn could improve the thermodynamic property of Mg slightly.
基金Project supported by the National Natural Science Foundation of China(51761032,51901105,51871125)。
文摘In this paper,the as-cast Mg85Cu5Ni10 alloy and Mg85Cu5Ni10-x wt%CeO2(x=0,4,8)alloys were prepared successfully by vacuum induction smelting and ball milling.The microstructure,hydrogen absorption/desorption kinetics and thermodynamics performances of the alloys were studied in detail.The results show that the Mg85Cu5Ni10 alloys with CeO2 additive have faster hydrogenation/dehydrogenation kinetics and better thermodynamic properties.The dehydrogenation activation energy is reduced to 81.211 kJ/mol from 119.142 by adding 8 wt%CeO2.CeO2 contributes to producing structural defects,nanocrystallines,grain boundaries,partial amorphous,lattice dislocations and cracks which are favorable to provide more hydrogen diffusion channels during hydriding/dehydriding process.Meanwhile,CeO2 additive weakens the bond energy of Mg-H.These micro structural changes caused by CeO2 additive improve the hydrogen storage performance of Mg85Cu5Ni10 markedly.
