Mg-based materials are one of the most promising hydrogen storage candidates due to their high hydrogen storage capacity,environmental benignity,and high Clarke number characteristics.However,the limited thermodynamic...Mg-based materials are one of the most promising hydrogen storage candidates due to their high hydrogen storage capacity,environmental benignity,and high Clarke number characteristics.However,the limited thermodynamics and kinetic properties pose major challenges for their engineering applications.Herein,we review the recent progress in improving their thermodynamics and kinetics,with an emphasis on the models and the influence of various parameters in the calculated models.Subsequently,the impact of alloying,composite,and nanocrystallization on both thermodynamics and dynamics are discussed in detail.In particular,the correlation between various modification strategies and the hydrogen capacity,dehydrogenation enthalpy and temperature,hydriding/dehydriding rates are summarized.In addition,the mechanism of hydrogen storage processes of Mg-based materials is discussed from the aspect of classical kinetic theories and microscope hydrogen transferring behavior.This review concludes with an outlook on the remaining challenge issues and prospects.展开更多
In order to improve the hydriding and dehydriding kinetics of the Mg2Ni-type alloys,Ni in the alloy is substituted by element Co. The nanocrystalline and amorphous Mg2Ni-type Mg2Ni1-xCox (x=0,0.1,0.2,0.3,0.4) alloys w...In order to improve the hydriding and dehydriding kinetics of the Mg2Ni-type alloys,Ni in the alloy is substituted by element Co. The nanocrystalline and amorphous Mg2Ni-type Mg2Ni1-xCox (x=0,0.1,0.2,0.3,0.4) alloys were synthesized by melt-spinning technique. The structures of the as-cast and spun alloys were studied with an X-ray diffractometer (XRD) and a high resolution transmission electronic microscope (HRTEM). An investigation on the thermal stability of the as-spun alloys was carried out with a differential scanning calorimeter (DSC). The hydrogen absorption and desorption kinetics of the alloys were measured with an automatically controlled Sieverts apparatus. The results demonstrate that the substitution of Co for Ni does not alter the major phase of Mg2Ni but results in the formation of secondary phase MgCo2. No amorphous phase is detected in the as-spun Co-free alloy,but a certain amount of amorphous phase is clearly found in the as-spun Co-containing alloys. The substitution of Co for Ni exerts a slight influence on the hydriding kinetics of the as-spun alloy. However,it dramatically enhances the dehydriding kinetics of the as-cast and spun alloys. As Co content (x) increases from 0 to 0.4,the hydrogen desorption capacity increases from 0.19% to 1.39% (mass fraction) in 20 min for the as-cast alloy,and from 0.89% to 2.18% (mass fraction) for the as-spun alloy (30 m/s).展开更多
A partial substitution of Ni by Mn was implemented in order to improve the hydriding and dehydriding kinetics of the Mg2Ni-type alloys. The nanocrystalline and amorphous MgzNi-type Mg2Nil-xMnx （x=0, 0. 1, 0.2, 0.3, ...A partial substitution of Ni by Mn was implemented in order to improve the hydriding and dehydriding kinetics of the Mg2Ni-type alloys. The nanocrystalline and amorphous MgzNi-type Mg2Nil-xMnx （x=0, 0. 1, 0.2, 0.3, 0.4） alloys were synthesized by the melt-spinning technique. The structures of the as-cast and spun alloys were studied by X-ray diffractometry （XRD）, scanning electron microscopy （SEM） and high resolution transmission electron microscopy （HRTEM）. The hydrogen absorption and desorption kinetics of the alloys were measured with an automatically controlled Sieverts apparatus. The results show that the as-spun Mn-free alloy holds a typical nanocrystalline structure, whereas the as-spun alloys containing Mn display a nanocrystalline and amorphous structure, confirming that the substitution of Mn for Ni intensifies the glass forming ability of the Mg2Ni-type alloy. The hydrogen absorption and desorption capacities and kinetics of the alloys increase with increasing the spinning rate, for which the nanocrystalline and amorphous structure produced by the melt spinning is mainly responsible. The substitution of Mn for Ni evidently improves the hydrogen desorption performance. The hydrogen desorption capacities of the as-cast and spun alloys rise with the increase in the percentage of Mn substitution.展开更多
In order to improve the hydrogenation and dehydrogenation performances of the Mg2Ni-type alloys, Mg was partially substituted by La in the alloy, and melt spinning technology was used for the preparation of the Mg20-x...In order to improve the hydrogenation and dehydrogenation performances of the Mg2Ni-type alloys, Mg was partially substituted by La in the alloy, and melt spinning technology was used for the preparation of the Mg20-xLaxNi10 （x=0, 2, 4, 6） hydrogen storage alloys. The structures of the alloys were studied by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and high-resolution transmission electron microscopy （HRTEM）. It was found that no amorphous phase formed in the as-spun La-free alloy, but the as-spun alloys containing La held a major amorphous phase. When La content x≤2, the major phase in the as-cast alloys was Mg2Ni phase, but with further increase of La content, the major phase of the as-cast alloys changed into LaNi5＋LaMg3 phase. Thermal stability of the as-spun alloys was studied by differential scanning calorimetry （DSC）, showing that spinning rate was a negligible factor on the crystallization temperature of the amorphous phase. The hydrogen absorption and desorption kinetics of the as-cast and as-spun alloys were measured using an automatically controlled Sieverts apparatus, confirming that the hydrogen absorption and desorption capacities and kinetics of the as-cast alloys clearly increased with rising La content. For La content x=2, the as-spun alloy displayed optimal hydrogen desorption kinetics at 200 ℃.展开更多
Hydrogen storage composites Nd2Mg17-50 wt.%Ni-x wt.%CeO2（x=0, 0.5, 1.0, 1.5, 2.0） were obtained by induction-ball milling method. The catalytic effect of CeO_2 on hydriding kinetics of Nd_2Mg17-50 wt.%Ni composite w...Hydrogen storage composites Nd2Mg17-50 wt.%Ni-x wt.%CeO2（x=0, 0.5, 1.0, 1.5, 2.0） were obtained by induction-ball milling method. The catalytic effect of CeO_2 on hydriding kinetics of Nd_2Mg17-50 wt.%Ni composite was investigated. X-ray diffraction（XRD） and high resolution transmission electron microscopy（HRTEM）, selected area electron diffraction（SAED） analyses showed that Nd_2Mg17-50 wt.%Ni alloy had a multiphase structure, consisting of NdMg12, NdMg_2Ni, Mg_2Ni and Ni phases and the addition of catalyst CeO_2 prompted the composites to be partly transformed into amorphous strucutre. The CeO_2 improved the maximum hydrogen capacity of Nd_2Mg17-50 wt.%Ni alloy from 3.192 wt.% to 3.376 wt.%（x=1.0）. What＇s more, the increment of diffusion coefficient D led to the faster hydriding kinetics, which was calculated by Avrami-Erofeev equation. The dehydrogenation temperature reduced from 515.54 to 504.72 K was mainly caused by the decrease of activation energy from 93.28 to 69.36 kJ /mol, which was proved by the Kissinger equation.展开更多
MgH_(2),albeit with slow desorption kinetics,has been extensively studied as one of the most ideal solid hydrogen storage materials.Adding such catalyst as Ni can improve the desorption kinetics of MgH_(2),whereas the...MgH_(2),albeit with slow desorption kinetics,has been extensively studied as one of the most ideal solid hydrogen storage materials.Adding such catalyst as Ni can improve the desorption kinetics of MgH_(2),whereas the catalytic role has been attributed to different substances such as Ni,Mg_(2)Ni,Mg_(2)NiH0.3,and Mg_(2)NiH4.In the present study,Ni nanoparticles(Ni-NPs)supported on mesoporous carbon(Ni@C)have been synthesized to improve the hydrogen desorption kinetics of MgH_(2).The utilization of Ni@C largely decreases the dehydrogenation activation energy from 176.9 to 79.3 kJ mol^(−1) and the peak temperature of dehydrogenation from 375.5 to 235℃.The mechanism of Ni catalyst is well examined by advanced aberration-corrected environmental transmission electron microscopy and/or x-ray diffraction.During the first dehydrogenation,detailed microstructural studies reveal that the decomposition of MgH_(2)is initially triggered by the Ni-NPs,which is the rate-limiting step.Subsequently,the generated Mg reacts rapidly with Ni-NPs to form Mg_(2)Ni,which further promotes the dehydrogenation of residual MgH_(2).In the following dehydrogenation cycle,Mg_(2)NiH4 can rapidly decompose into Mg_(2)Ni,which continuously promotes the decomposition of MgH_(2).Our study not only elucidates the mechanism of Ni catalyst but also helps design and assemble catalysts with improved dehydriding kinetics of MgH_(2).展开更多
The nanocrystalline Mg2Ni-type electrode alloys with nominal compositions of Mg20Ni10-xCux (x = 0, 1, 2, 3, 4) were synthesized by melt-spinning technique. The microstructures of the alloys were characterized by XRD, ...The nanocrystalline Mg2Ni-type electrode alloys with nominal compositions of Mg20Ni10-xCux (x = 0, 1, 2, 3, 4) were synthesized by melt-spinning technique. The microstructures of the alloys were characterized by XRD, SEM and HRTEM. The hydrogen absorption and desorption kinet-ics of the alloys were measured using an auto-matically controlled Sieverts apparatus. The re- sults show that all the as-spun alloys hold ty- pical nanocrystalline structure. The substitution of Cu for Ni does not change the major phase Mg2Ni but it leads to the formation of the sec-ondary phase Mg2Cu. The hydrogen absorption capacity of the alloys first increases and then decreases with rising Cu content, but the hy-drogen desorption capacity of the alloys mono- tonously grows with increasing Cu content. The melt spinning significantly improves the hydro- genation and dehydrogenation capacities and kinetics of the alloys.展开更多
A new approach of ball-milled Mg_2Ni in tetrahydrofuran (THF) to improve thehydriding kinetics of Mg_2Ni alloy is suggested and studied. It is found that the modified alloydisplayed the improved activity for hydriding...A new approach of ball-milled Mg_2Ni in tetrahydrofuran (THF) to improve thehydriding kinetics of Mg_2Ni alloy is suggested and studied. It is found that the modified alloydisplayed the improved activity for hydriding even at relatively low temperature (e.g., 323-373 K).In the case of the sample milled in THF for 20 h, the hydrogen content (mass fraction) reaches 1.6 %at 323 K, 2.1% at 348 K and 3.4% at 448 K, respectively. The use of THF during grinding led to thechange of the structure, which is reflected by the broadening and weakening of the diffraction peaksin the XRD spectra. The XPS analysis shows that Mg (2s) binding energy peak of Mg_2Ni aftermodification shifted from a lower binding energy to a higher one, indicating the charge transferencebetween Mg and THF and the formation of catalytically active electron donor-acceptor (EDA)complexes on the surface of modified Mg_2Ni alloy.展开更多
Micro-fine sphericalpowders are recommended for selective laser melting(SLM). However, they are mostly expensive due to the complex manufacturing technique and low yield. In this paper, using lowcost treated hydride-d...Micro-fine sphericalpowders are recommended for selective laser melting(SLM). However, they are mostly expensive due to the complex manufacturing technique and low yield. In this paper, using lowcost treated hydride-dehydride(HDH) Ti powders, commercial pure Ti(CP-Ti) was successfully fabricated by SLM. After 4-h milling, the resulting powders become near-spherical with no obvious angularity, and have optimal flowability with the apparent density of 1.64 ± 0.02 g/cm^3, tap density of 2.10 ± 0.04 g/cm^3,angle of repose 40.11?±0.09?, and Carr's index of 77.74 ± 0.15. The microstructure was determined with full acicular martensitic β phase. The CP-Ti can achieve superior mechanical properties with the ultimate tensile strength of 876.1 ± 20.5 MPa and elongation of(14.7 ± 0.5)%, which exhibit distinctly competitive compared to the as-cast CP-Ti or Ti-6 Al-4 V. Excellent mechanical properties together with its low-cost make SLM-fabricated CP-Ti from modified HDH Ti powders show promising applications.展开更多
Low cost hydride-dehydride (HDH) Ti-6Al-4V (Ti-64) alloy powder was employed to investigate the metallurgical quality and mechanical properties of laser formed samples. With appropriate control of the laser forming pr...Low cost hydride-dehydride (HDH) Ti-6Al-4V (Ti-64) alloy powder was employed to investigate the metallurgical quality and mechanical properties of laser formed samples. With appropriate control of the laser forming processing parameters and the loose density of HDH powder, two kinds of defect, i.e. porosity and ill-bonding, can be avoided. Rare earth Nd powder was added to HDH Ti-64 powder to purify laser formed alloy. The results show that with a few additive of Nd, the microstructure of laser formed alloy changes from Widmanstatten morphology to a basket weave microstructure. Accordingly an appropriate addition of Nd is effective to improve both the strength and ductility of laser formed HDH Ti-64 alloy. The values of tensile test meet the wrought specification with the content of Nd ranging from 0.1%-0.2%(mass fraction).展开更多
High hydrogen absorption and desorption rates are two significant index parameters for the applications of hydrogen storage tanks.The analysis of the hydrogen absorption and desorption behavior using the isothermal ki...High hydrogen absorption and desorption rates are two significant index parameters for the applications of hydrogen storage tanks.The analysis of the hydrogen absorption and desorption behavior using the isothermal kinetic models is an efficient way to investigate the kinetic mechanism.Multitudinous kinetic models have been developed to describe the kinetic process.However,these kinetic models were de-duced based on some assumptions and only appropriate for specific kinetic measurement methods and rate-controlling steps(RCSs),which sometimes lead to confusion during application.The kinetic analysis procedures using these kinetic models,as well as the key kinetic parameters,are unclear for many researchers who are unfamiliar with this field.These problems will prevent the kinetic models and their analysis methods from revealing the kinetic mechanism of hydrogen storage alloys.Thus,this review mainly focuses on the summarization of kinetic models based on different kinetic measurement methods and RCSs for the chemisorption,surface penetration,diffusion of hydrogen,nucleation and growth,and chemical reaction processes.The analysis procedures of kinetic experimental data are expounded,as well as the effects of temperature,hydrogen pressure,and particle radius.The applications of the kinetic models for different hydrogen storage alloys are also introduced.展开更多
In order to optimize the dehydriding process for producing nanocrystalline Mg alloy powders by hydriding-dehydriding treatment,nano-structured as-hydrided Mg-3%Al-1%Zn(AZ31 Mg)(mass fraction)alloy powders were thermal...In order to optimize the dehydriding process for producing nanocrystalline Mg alloy powders by hydriding-dehydriding treatment,nano-structured as-hydrided Mg-3%Al-1%Zn(AZ31 Mg)(mass fraction)alloy powders were thermally dehydrided at various temperatures from 275 to 375℃.The kinetics of hydrogen desorption was examined by hydrogen discharge measurement during dehydriding.The microstructure of the as-hydrided and the subsequently fully dehydrided alloy powders was investigated by X-ray diffraction analysis(XRD)and transmission electron microscopy(TEM),respectively.Both the desorption kinetics and the grain size of the alloy after complete dehydriding were found to be strongly dependent on the processing temperature.The higher the temperature,the faster the desorption,and the more significant the grain growth.When the desorption temperature was raised from 300 to 375℃,the time to achieve complete dehydriding was shortened from 190 to 20 min,and the average grain size increased correspondingly from 20 to 58 nm.展开更多
Mg-Li alloy is a lightweight hydrogen storage material with high hydrogen capacity,but its poor kinetics limited its practical applications.In this work,MCM-22 molecular sieve was added to Mg-Li alloy by friction stir...Mg-Li alloy is a lightweight hydrogen storage material with high hydrogen capacity,but its poor kinetics limited its practical applications.In this work,MCM-22 molecular sieve was added to Mg-Li alloy by friction stir processing(FSP)as the catalyst to enhance the kinetic properties of Mg-Li alloy(denoted as Mg-Li-MCM-22).The resulting Mg-Li-MCM-22 possesses the reversible hydrogen storage capacity of ca.6 wt.%and can release 5.62 wt.%hydrogen within 50 min at 623 K,showing improved kinetics.The Chou model and Johnson-Mehl-Avrami-Kolmogorov(JMAK)model calculations reveal that the lattice defects generated by FSP improve the kinetics of hydrogen adsorption/desorption.The pinning effect of MCM-22 particles produces more grain boundaries and dislocations,thus,increasing the diffusion rate of hydrogen atoms and providing more nucleation sites,therefore,reducing the dehydrogenation activation energy.This work provides a new strategy for the preparation of hydrogen storage materials.展开更多
In this study, we present a model whereby the centre of the atomization channel is shown to be the optimal location for the spectrometric data acquisition in a quartz cell atomizer. The study aims to explore the hydri...In this study, we present a model whereby the centre of the atomization channel is shown to be the optimal location for the spectrometric data acquisition in a quartz cell atomizer. The study aims to explore the hydride generation technique which is normally coupled with efficient thermal source to apply determination of heavy metals in water samples via spectrometric analysis. The arsenic hydride generation process and the atomization of the generated hydride in a quartz cell atomizer were studied analytically as model case studies. The hydride generation (HG) process was analyzed by adopting two hypotheses, the nascent hydrogen and formation of intermediate hydroboron species, where the results based on the second hypothesis are found to be more realistic for design purposes. Moreover, the release of the generated hydride from the liquid phase and their transport to the gas phase is simulated in a helical tubular section, in which the actual tubular section length required for separation is deduced. The analytical results have been verified experimentally by measuring the signal intensity for the free arsenic atoms against several reaction tube lengths, in which increasing the tubular section length from 12 cm to 100 cm results in signal amelioration by no more than 6.6%. Furthermore, the atomization of the hydride and the distribution of the generated free atoms are deduced in two configurations of tubular quartz atomizers. The results obtained from both studied cases illustrate that a high concentration of the free analyte atoms is generated in the first part of the atomization channel, saturates to a maximum in a position at the atomizer centre, and dissipates at the inside wall of the tubular atomizer before reaching the atomizer outlet edge, which is found to be in total agreement with the current understanding of atomization mechanism in tubular atomizer and emphasizes the fact that the centre of the quartz cell atomizer is the best location for the spectrometric data acquisition.展开更多
基金supported by the Chongqing Special Key Project of Technology Innovation and Application Development,China(cstc2019jscx-dxwt B0029)the National Natural Science Foundation of China(51871143)+5 种基金the Science and Technology Committee of Shanghai(19010500400)the Shanghai Rising-Star Program(21QA1403200)Chongqing Research Program of Basic Research and Frontier Technology(No.cstc2019jcyj-msxm X0306)the Start-up Funds of Chongqing University(02110011044171)the Senior Talent Start-up Funds of Jiangsu University(4111310024)the Independent Research Project of State Key Laboratory of Mechanical Transmissions(SKLMT-ZZKT-2021M11)
文摘Mg-based materials are one of the most promising hydrogen storage candidates due to their high hydrogen storage capacity,environmental benignity,and high Clarke number characteristics.However,the limited thermodynamics and kinetic properties pose major challenges for their engineering applications.Herein,we review the recent progress in improving their thermodynamics and kinetics,with an emphasis on the models and the influence of various parameters in the calculated models.Subsequently,the impact of alloying,composite,and nanocrystallization on both thermodynamics and dynamics are discussed in detail.In particular,the correlation between various modification strategies and the hydrogen capacity,dehydrogenation enthalpy and temperature,hydriding/dehydriding rates are summarized.In addition,the mechanism of hydrogen storage processes of Mg-based materials is discussed from the aspect of classical kinetic theories and microscope hydrogen transferring behavior.This review concludes with an outlook on the remaining challenge issues and prospects.
基金Project(2006AA05Z132) supported by the National High-tech Research and Development Program of ChinaProjects(50871050, 50961009) supported by the National Natural Science Foundation of China+1 种基金Project(2010ZD05) supported by the Natural Science Foundation of Inner Mongolia, ChinaProject(NJzy08071) supported by the High Education Science Research Program of Inner Mongolia, China
文摘In order to improve the hydriding and dehydriding kinetics of the Mg2Ni-type alloys,Ni in the alloy is substituted by element Co. The nanocrystalline and amorphous Mg2Ni-type Mg2Ni1-xCox (x=0,0.1,0.2,0.3,0.4) alloys were synthesized by melt-spinning technique. The structures of the as-cast and spun alloys were studied with an X-ray diffractometer (XRD) and a high resolution transmission electronic microscope (HRTEM). An investigation on the thermal stability of the as-spun alloys was carried out with a differential scanning calorimeter (DSC). The hydrogen absorption and desorption kinetics of the alloys were measured with an automatically controlled Sieverts apparatus. The results demonstrate that the substitution of Co for Ni does not alter the major phase of Mg2Ni but results in the formation of secondary phase MgCo2. No amorphous phase is detected in the as-spun Co-free alloy,but a certain amount of amorphous phase is clearly found in the as-spun Co-containing alloys. The substitution of Co for Ni exerts a slight influence on the hydriding kinetics of the as-spun alloy. However,it dramatically enhances the dehydriding kinetics of the as-cast and spun alloys. As Co content (x) increases from 0 to 0.4,the hydrogen desorption capacity increases from 0.19% to 1.39% (mass fraction) in 20 min for the as-cast alloy,and from 0.89% to 2.18% (mass fraction) for the as-spun alloy (30 m/s).
基金Projects(50871050,50961001) supported by the National Natural Science Foundation of ChinaProject(2010ZD05) supported by the Natural Science Foundation of Inner Mongolia,ChinaProject(NJzy08071) supported by the High Education Science Research Program of Inner Mongolia,China
文摘A partial substitution of Ni by Mn was implemented in order to improve the hydriding and dehydriding kinetics of the Mg2Ni-type alloys. The nanocrystalline and amorphous MgzNi-type Mg2Nil-xMnx （x=0, 0. 1, 0.2, 0.3, 0.4） alloys were synthesized by the melt-spinning technique. The structures of the as-cast and spun alloys were studied by X-ray diffractometry （XRD）, scanning electron microscopy （SEM） and high resolution transmission electron microscopy （HRTEM）. The hydrogen absorption and desorption kinetics of the alloys were measured with an automatically controlled Sieverts apparatus. The results show that the as-spun Mn-free alloy holds a typical nanocrystalline structure, whereas the as-spun alloys containing Mn display a nanocrystalline and amorphous structure, confirming that the substitution of Mn for Ni intensifies the glass forming ability of the Mg2Ni-type alloy. The hydrogen absorption and desorption capacities and kinetics of the alloys increase with increasing the spinning rate, for which the nanocrystalline and amorphous structure produced by the melt spinning is mainly responsible. The substitution of Mn for Ni evidently improves the hydrogen desorption performance. The hydrogen desorption capacities of the as-cast and spun alloys rise with the increase in the percentage of Mn substitution.
基金supported by 863 Program (2006AA05Z132)the National Natural Science Foundations of China (50871050 and 50701011)+1 种基金Natural Science Foundation of Inner Mongolia, China (200711020703)High Education Science Research Project of Inner Mongolia, China (NJzy08071)
文摘In order to improve the hydrogenation and dehydrogenation performances of the Mg2Ni-type alloys, Mg was partially substituted by La in the alloy, and melt spinning technology was used for the preparation of the Mg20-xLaxNi10 （x=0, 2, 4, 6） hydrogen storage alloys. The structures of the alloys were studied by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and high-resolution transmission electron microscopy （HRTEM）. It was found that no amorphous phase formed in the as-spun La-free alloy, but the as-spun alloys containing La held a major amorphous phase. When La content x≤2, the major phase in the as-cast alloys was Mg2Ni phase, but with further increase of La content, the major phase of the as-cast alloys changed into LaNi5＋LaMg3 phase. Thermal stability of the as-spun alloys was studied by differential scanning calorimetry （DSC）, showing that spinning rate was a negligible factor on the crystallization temperature of the amorphous phase. The hydrogen absorption and desorption kinetics of the as-cast and as-spun alloys were measured using an automatically controlled Sieverts apparatus, confirming that the hydrogen absorption and desorption capacities and kinetics of the as-cast alloys clearly increased with rising La content. For La content x=2, the as-spun alloy displayed optimal hydrogen desorption kinetics at 200 ℃.
基金Project supported by National Natural Science Foundation of China(51161015,51371094)the Natural Science Foundation of Inner Mongolia,China(2013MS0722,2014MS0529)Talent Incubation Funding of School of Materials and Metallurgy(2014CY012)
文摘Hydrogen storage composites Nd2Mg17-50 wt.%Ni-x wt.%CeO2（x=0, 0.5, 1.0, 1.5, 2.0） were obtained by induction-ball milling method. The catalytic effect of CeO_2 on hydriding kinetics of Nd_2Mg17-50 wt.%Ni composite was investigated. X-ray diffraction（XRD） and high resolution transmission electron microscopy（HRTEM）, selected area electron diffraction（SAED） analyses showed that Nd_2Mg17-50 wt.%Ni alloy had a multiphase structure, consisting of NdMg12, NdMg_2Ni, Mg_2Ni and Ni phases and the addition of catalyst CeO_2 prompted the composites to be partly transformed into amorphous strucutre. The CeO_2 improved the maximum hydrogen capacity of Nd_2Mg17-50 wt.%Ni alloy from 3.192 wt.% to 3.376 wt.%（x=1.0）. What＇s more, the increment of diffusion coefficient D led to the faster hydriding kinetics, which was calculated by Avrami-Erofeev equation. The dehydrogenation temperature reduced from 515.54 to 504.72 K was mainly caused by the decrease of activation energy from 93.28 to 69.36 kJ /mol, which was proved by the Kissinger equation.
基金supported by the National Natural Science Foundation of China(Nos.22279111,51971195,and 11935004)the Natural Science Foundation of Hebei Province(No.B2020203037)Subsidy for Hebei Key Laboratory of Applied Chemistry after Operation Performance(No.22567616H).
文摘MgH_(2),albeit with slow desorption kinetics,has been extensively studied as one of the most ideal solid hydrogen storage materials.Adding such catalyst as Ni can improve the desorption kinetics of MgH_(2),whereas the catalytic role has been attributed to different substances such as Ni,Mg_(2)Ni,Mg_(2)NiH0.3,and Mg_(2)NiH4.In the present study,Ni nanoparticles(Ni-NPs)supported on mesoporous carbon(Ni@C)have been synthesized to improve the hydrogen desorption kinetics of MgH_(2).The utilization of Ni@C largely decreases the dehydrogenation activation energy from 176.9 to 79.3 kJ mol^(−1) and the peak temperature of dehydrogenation from 375.5 to 235℃.The mechanism of Ni catalyst is well examined by advanced aberration-corrected environmental transmission electron microscopy and/or x-ray diffraction.During the first dehydrogenation,detailed microstructural studies reveal that the decomposition of MgH_(2)is initially triggered by the Ni-NPs,which is the rate-limiting step.Subsequently,the generated Mg reacts rapidly with Ni-NPs to form Mg_(2)Ni,which further promotes the dehydrogenation of residual MgH_(2).In the following dehydrogenation cycle,Mg_(2)NiH4 can rapidly decompose into Mg_(2)Ni,which continuously promotes the decomposition of MgH_(2).Our study not only elucidates the mechanism of Ni catalyst but also helps design and assemble catalysts with improved dehydriding kinetics of MgH_(2).
文摘The nanocrystalline Mg2Ni-type electrode alloys with nominal compositions of Mg20Ni10-xCux (x = 0, 1, 2, 3, 4) were synthesized by melt-spinning technique. The microstructures of the alloys were characterized by XRD, SEM and HRTEM. The hydrogen absorption and desorption kinet-ics of the alloys were measured using an auto-matically controlled Sieverts apparatus. The re- sults show that all the as-spun alloys hold ty- pical nanocrystalline structure. The substitution of Cu for Ni does not change the major phase Mg2Ni but it leads to the formation of the sec-ondary phase Mg2Cu. The hydrogen absorption capacity of the alloys first increases and then decreases with rising Cu content, but the hy-drogen desorption capacity of the alloys mono- tonously grows with increasing Cu content. The melt spinning significantly improves the hydro- genation and dehydrogenation capacities and kinetics of the alloys.
基金This work is supported by the State Key Project for Fundamental Research (TG2000026406) and the National Natural Science Foundation of China (No. 50071053).
文摘A new approach of ball-milled Mg_2Ni in tetrahydrofuran (THF) to improve thehydriding kinetics of Mg_2Ni alloy is suggested and studied. It is found that the modified alloydisplayed the improved activity for hydriding even at relatively low temperature (e.g., 323-373 K).In the case of the sample milled in THF for 20 h, the hydrogen content (mass fraction) reaches 1.6 %at 323 K, 2.1% at 348 K and 3.4% at 448 K, respectively. The use of THF during grinding led to thechange of the structure, which is reflected by the broadening and weakening of the diffraction peaksin the XRD spectra. The XPS analysis shows that Mg (2s) binding energy peak of Mg_2Ni aftermodification shifted from a lower binding energy to a higher one, indicating the charge transferencebetween Mg and THF and the formation of catalytically active electron donor-acceptor (EDA)complexes on the surface of modified Mg_2Ni alloy.
基金supported by Fundamental Reseearch Funds for the Central Universities (No. FRF-GF-17-B39)
文摘Micro-fine sphericalpowders are recommended for selective laser melting(SLM). However, they are mostly expensive due to the complex manufacturing technique and low yield. In this paper, using lowcost treated hydride-dehydride(HDH) Ti powders, commercial pure Ti(CP-Ti) was successfully fabricated by SLM. After 4-h milling, the resulting powders become near-spherical with no obvious angularity, and have optimal flowability with the apparent density of 1.64 ± 0.02 g/cm^3, tap density of 2.10 ± 0.04 g/cm^3,angle of repose 40.11?±0.09?, and Carr's index of 77.74 ± 0.15. The microstructure was determined with full acicular martensitic β phase. The CP-Ti can achieve superior mechanical properties with the ultimate tensile strength of 876.1 ± 20.5 MPa and elongation of(14.7 ± 0.5)%, which exhibit distinctly competitive compared to the as-cast CP-Ti or Ti-6 Al-4 V. Excellent mechanical properties together with its low-cost make SLM-fabricated CP-Ti from modified HDH Ti powders show promising applications.
基金Projects (S0331010) supported by the National Natural Science Foundation of Chinaproject (05XE0131) supported by the Talent Cultivating Program of Northwestern Polytechnical University
文摘Low cost hydride-dehydride (HDH) Ti-6Al-4V (Ti-64) alloy powder was employed to investigate the metallurgical quality and mechanical properties of laser formed samples. With appropriate control of the laser forming processing parameters and the loose density of HDH powder, two kinds of defect, i.e. porosity and ill-bonding, can be avoided. Rare earth Nd powder was added to HDH Ti-64 powder to purify laser formed alloy. The results show that with a few additive of Nd, the microstructure of laser formed alloy changes from Widmanstatten morphology to a basket weave microstructure. Accordingly an appropriate addition of Nd is effective to improve both the strength and ductility of laser formed HDH Ti-64 alloy. The values of tensile test meet the wrought specification with the content of Nd ranging from 0.1%-0.2%(mass fraction).
基金This work was financially supported by the Chongqing Special Key Project of Technology Innovation and Applica-tion Development,China(No.cstc2019jscx-dxwtB0029)the National Natural Science Foundation of China(Nos.51871143 and U2102212)+1 种基金the Science and Technology Committee of Shanghai,China(No.19010500400)the Shanghai Rising-Star Program(No.21QA1403200).
文摘High hydrogen absorption and desorption rates are two significant index parameters for the applications of hydrogen storage tanks.The analysis of the hydrogen absorption and desorption behavior using the isothermal kinetic models is an efficient way to investigate the kinetic mechanism.Multitudinous kinetic models have been developed to describe the kinetic process.However,these kinetic models were de-duced based on some assumptions and only appropriate for specific kinetic measurement methods and rate-controlling steps(RCSs),which sometimes lead to confusion during application.The kinetic analysis procedures using these kinetic models,as well as the key kinetic parameters,are unclear for many researchers who are unfamiliar with this field.These problems will prevent the kinetic models and their analysis methods from revealing the kinetic mechanism of hydrogen storage alloys.Thus,this review mainly focuses on the summarization of kinetic models based on different kinetic measurement methods and RCSs for the chemisorption,surface penetration,diffusion of hydrogen,nucleation and growth,and chemical reaction processes.The analysis procedures of kinetic experimental data are expounded,as well as the effects of temperature,hydrogen pressure,and particle radius.The applications of the kinetic models for different hydrogen storage alloys are also introduced.
基金Project(50574034)supported by the National Natural Science Foundation of ChinaProject(20060213016)supported by Doctoral Education Fund of Ministry of Education of China
文摘In order to optimize the dehydriding process for producing nanocrystalline Mg alloy powders by hydriding-dehydriding treatment,nano-structured as-hydrided Mg-3%Al-1%Zn(AZ31 Mg)(mass fraction)alloy powders were thermally dehydrided at various temperatures from 275 to 375℃.The kinetics of hydrogen desorption was examined by hydrogen discharge measurement during dehydriding.The microstructure of the as-hydrided and the subsequently fully dehydrided alloy powders was investigated by X-ray diffraction analysis(XRD)and transmission electron microscopy(TEM),respectively.Both the desorption kinetics and the grain size of the alloy after complete dehydriding were found to be strongly dependent on the processing temperature.The higher the temperature,the faster the desorption,and the more significant the grain growth.When the desorption temperature was raised from 300 to 375℃,the time to achieve complete dehydriding was shortened from 190 to 20 min,and the average grain size increased correspondingly from 20 to 58 nm.
基金Fundamental Research Funds for Central Universities(No.2022CDJKYJH028)National Natural Science Foundation of China(No.52271091)Chongqing Special Key Project of Technology Innovation and Application Development,China(No.cstc2019jscx-dxwtBX0016).
文摘Mg-Li alloy is a lightweight hydrogen storage material with high hydrogen capacity,but its poor kinetics limited its practical applications.In this work,MCM-22 molecular sieve was added to Mg-Li alloy by friction stir processing(FSP)as the catalyst to enhance the kinetic properties of Mg-Li alloy(denoted as Mg-Li-MCM-22).The resulting Mg-Li-MCM-22 possesses the reversible hydrogen storage capacity of ca.6 wt.%and can release 5.62 wt.%hydrogen within 50 min at 623 K,showing improved kinetics.The Chou model and Johnson-Mehl-Avrami-Kolmogorov(JMAK)model calculations reveal that the lattice defects generated by FSP improve the kinetics of hydrogen adsorption/desorption.The pinning effect of MCM-22 particles produces more grain boundaries and dislocations,thus,increasing the diffusion rate of hydrogen atoms and providing more nucleation sites,therefore,reducing the dehydrogenation activation energy.This work provides a new strategy for the preparation of hydrogen storage materials.
文摘In this study, we present a model whereby the centre of the atomization channel is shown to be the optimal location for the spectrometric data acquisition in a quartz cell atomizer. The study aims to explore the hydride generation technique which is normally coupled with efficient thermal source to apply determination of heavy metals in water samples via spectrometric analysis. The arsenic hydride generation process and the atomization of the generated hydride in a quartz cell atomizer were studied analytically as model case studies. The hydride generation (HG) process was analyzed by adopting two hypotheses, the nascent hydrogen and formation of intermediate hydroboron species, where the results based on the second hypothesis are found to be more realistic for design purposes. Moreover, the release of the generated hydride from the liquid phase and their transport to the gas phase is simulated in a helical tubular section, in which the actual tubular section length required for separation is deduced. The analytical results have been verified experimentally by measuring the signal intensity for the free arsenic atoms against several reaction tube lengths, in which increasing the tubular section length from 12 cm to 100 cm results in signal amelioration by no more than 6.6%. Furthermore, the atomization of the hydride and the distribution of the generated free atoms are deduced in two configurations of tubular quartz atomizers. The results obtained from both studied cases illustrate that a high concentration of the free analyte atoms is generated in the first part of the atomization channel, saturates to a maximum in a position at the atomizer centre, and dissipates at the inside wall of the tubular atomizer before reaching the atomizer outlet edge, which is found to be in total agreement with the current understanding of atomization mechanism in tubular atomizer and emphasizes the fact that the centre of the quartz cell atomizer is the best location for the spectrometric data acquisition.
