Desorption behaviour and microstructure change of nanostructured hydrided AZ31 Mg alloy powders

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.     

镁-镍/石墨烯复合物的储氢性能

分别通过物理法和化学法制备石墨烯载镍催化剂(Ni/Graphene),并采用球磨预处理或超声分散的方式与镁粉混匀,结合氢化燃烧合成和机械球磨复合技术制备镁-镍/石墨烯(Mg-Ni/Graphene)复合物储氢材料。采用X射线衍射仪、扫描电镜及气体反应控制器研究了材料的相组成、微观形貌和吸放氢性能。比较发现,添加化学法制备的Ni/Graphene并采用球磨预处理的Mg-Ni/Graphene复合物具有最佳的吸放氢性能,复合物的起始放氢温度降低,放氢速率加快。其在373 K温度下,100 s内就基本能达到饱和吸氢量6.21%(质量分数);553 K,1800 s内完全放氢,且放氢量达到6.05%。球磨预处理使得Ni/Graphene更均匀的与Mg接触,利于发挥Ni的催化作用和石墨烯优异的导电导热性。化学法制备的Ni/Graphene原位还原出纳米晶Ni,有利于形成纳米级Mg2NiH4晶粒,促进复合物储氢性能的改善。     

纳米晶氢化态镁及镁合金粉末的脱氢动力学研究

实验研究了纳米晶氢化态镁及AZ31镁合金粉末的脱氢过程,获得了不同温度下的脱氢动力学数据。通过运用Johnson-Mehl-Avrami(JMA)方程对实验数据进行拟合处理,对两种材料的固态热分解脱氢反应动力学进行了理论分析,确定了反应级数,获得了动力学方程表达式,求出了相应的动力学参数及反应活化能。在此基础上,阐明了纳米晶氢化态镁及AZ31镁合金脱氢动力学差异的原因。     

Enhanced Hydriding and Dehydriding Kinetics of as-Spun Nanocrystalline Mg2Ni-Type Alloy Substituting Ni with Cu

为了改善Mg2Ni型合金的吸放氢动力学性能,用Cu部分替代合金中的Ni。用快淬工艺制备了纳米晶Mg2Ni1-xCux(x=0,0.1,0.2,0.3,0.4)贮氢合金,用XRD、SEM、HRTEM分析了铸态及快淬态合金的微观结构;用自动控制的Sieverts设备测试了合金的吸放氢动力学性能。结果表明,快淬态合金具有纳米晶结构,Cu替代Ni不改变合金的主相Mg2Ni,但导致形成第二相Mg2Cu。随Cu含量的增加,合金的吸氢量先增加而后减小,但合金的放氢量随Cu含量的增加而单调增加。快淬显著提高合金的吸放氢量并改善合金的吸放氢动力学。     

Mg_2Ni系贮氢合金制备方法的研究进展

本文综述了熔炼法、机械合金化法、烧结法、扩散法、氢化燃烧合成法、表面处理法等制备Mg2Ni合金的基本原理和主要工艺。介绍了扩散法和球磨法等制备技术的联用,总结并讨论了这些合金制备技术制取的合金的充放氢性能和电化学性能及其对合金性能的影响。较先进的机械合金化法制备Mg2Ni系贮氢合金复合材料是比较理想的途径。     

多壁碳纳米管载镍对镁基合金储氢性能影响

采用化学法制备多壁碳纳米管载镍催化剂(Ni/MWNTs),并将其加入到镁粉中,结合氢化燃烧合成(HydridingCombustionSynthesis,HCS)和机械球磨(MechanicalMilling,MM),即HCS+MM复合技术制备Mg85-Nix/MWNTs15-x(x代表质量百分数,x=3,6,9,12)合金。通过X射线衍射仪、透射电子显微镜、扫描电镜以及气体反应控制器研究了材料的晶体结构、微观形貌和吸放氢性能。结果表明:Mg85-Ni9/MWNTs6合金具有最佳综合吸放氢性能,其在373K,吸氢量达到5.68%(质量分数,下同),且在100s内就基本达到饱和吸氢量;在523K,1800s内的放氢量达到4.31%。Ni/MWNTs催化剂的添加,不但起到催化的作用,而且MWNTs具有优异的纳米限制作用,使得催化剂的粒径限制在纳米级,有利于限制产物中Mg2NiH4颗粒的长大。另外Ni与MWNTs存在协同催化作用,当它们达到一定比例时,对合金的吸放氢促进作用达到最优化,明显改善了合金的吸放氢性能。     

氢化燃烧法合成Mg2Ni的贮氢性能

用氢化燃烧法合成了Mg2 Ni,PCT实验结果说明了合成的镁基贮氢合金具有很高的活性和高贮氢量 ,5 5 3K时达到 3.40 %。对Mg Ni系的PCT结果作了处理 ,得出温度和氢平衡压的关系式 :吸氢时lg(p/ 0 .1MPa)=- 34 6 9/T 6 .6 39;放氢时lg(p/ 0 .1MPa) =- 35 5 8/T 6 .6 12。用XRD方法进行了物相分析 ,表明存在在Mg2 Ni的氢化物     

铟对MgH2脱氢性能的影响

将MgH2和In的混合粉末在行星式球磨机上进行球磨,制备了一种Mg H2-In的复合物。利用XRD分析了复合物的相组成以及吸放氢过程中的相转变;用气相色谱仪和差示扫描量热仪测定了复合物的脱氢性能和相转变温度,并用基于Sievert原理的全自动气体吸附仪测定了复合物的吸放氢热力学和动力学性能。结果表明,脱氢过程中Mg3In和Mg(In)固溶体的形成使Mg H2的脱氢反应焓和激活能显著降低,从而降低了Mg H2的脱氢温度,并显著改善了动力学性能。     

热蒸发法制备Mg和Mg-Ni薄膜及其氢化性能

采用热蒸发法制备了纯Mg膜及Mg78Ni22合金膜，研究了薄膜的结构及其氢化性能．Mg膜具有典型的柱状晶结构，择优取向生长趋势明显；Mg78Ni22薄膜由纳米晶Mg2Ni，Mg及少量非晶组成，Mg2Ni相沿着平行于薄膜表面的(001)方向择优生长．纯Mg膜的吸放氢温度分别为593和653K，其吸氢过程遵循形核长大机制．Mg78Ni22薄膜的压力一组成等温曲线存在低压和高压两个平台区，分别对应Mg和Mg2Ni的氢化反应，薄膜内Mg的吸放氢温度可分别降至473和503K，薄膜的最大吸氢量(质量分数)达到5．7％．Mg的氢化性能改善与薄膜中纳米晶Mg2Ni和非晶相起到的催化作用有关．     

经四氢呋喃改性后Mg的储氢性能SCIEI

本文研究了用四氢呋喃(简称THF)改性过的Mg(简称THF-Mg)的吸放氢性能。电子结构,晶体结构及其氢化物的稳定性与微观形貌。THF-Mg经20次吸放氢循环后,在3.5MPa氢压力及643K温度下,吸氢量为3.5wt-％;在1.3Pa真空,643K温度下,放氢量为3.2Wt-％,THF改变了Mg的电子结构,但不改变晶体结构。在吸氢后的产物中,除MgH_2相外,还有新的氢化物相形成。Mg中形成的氢化物是多晶体,晶内广泛存在着的滑移带和孪晶表明,Mg吸氢相变发生较大的畸变。     

固-气反应球磨制备纳米晶MgH2的研究

采用固.气反应球磨制备纳米晶MgH2粉末,测定纯镁粉在球磨过程中的吸氢动力学曲线.借助X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)等分析手段,研究Mg-H2反应球磨过程中的相结构与粉末形貌演变规律.结果表明,在机械球磨驱动作用下,Mg的吸氢过程可分为"缓慢-快速-饱和"3个阶段,其相组成分别对应"Mg(H)-Mg(H)+MgH2-MgH2".在0.5 MPa氢气压条件下,球磨21 h可使Mg完全氢化,获得粉末粒度1～3μm、晶粒尺寸10 nm左右的纳米晶MgH2粉末,其实际氢含量高达7.03%(质量分数,下同).     

Influence of tin on the electrochemical and gas phase hydrogen sorption in Mg2−xSnxNi (x = 0, 0.1, 0.3)

Mg_2−xSn_xNi (x = 0, 0.1, 0.3) alloys were synthesized by reactive ball milling under protective Ar atmosphere and liquid n-heptane. The microstructure and the morphology of the powders were determined by X-ray diffraction and scanning electron microscopy. The as-milled alloys consist of Mg₂Ni nanocrystals with an average grain size in the range 3–7 nm, depending on the alloy composition. Sn containing phases were not detected even in the Sn-rich alloy. Obviously, Sn is dissolved in the Mg₂Ni intermetallic compound. Gas phase sorption of hydrogen was not observed in the alloys containing Sn (Mg_2−xSn_xNi; x = 0.1, 0.3). It was suggested that Sn impedes the process of hydrogen molecules decomposition. The as-milled alloys absorbed reversibly hydrogen electrochemically. Mg₂Ni alloy showed the highest discharge capacity of 300 mAh/g. The capacity of Mg_1.9Sn_0.1Ni and Mg_1.7Sn_0.3Ni was about 260 mAh/g. It was found that Sn improved the cycle life of the electrode.     

超细纯镁及镁钛粉体的制备及储氢性能

采用直流电弧等离子体方法制备超细纯Mg及Mg-Ti粉体。运用X射线衍射（XRD）,透射电子显微镜（TEM）,压力成分温度（PCT）方法和TG/DTA技术研究粉体吸放氢前后的相组成、微观结构和吸放氢性能。结果表明,大部分超细Mg和Mg-Ti颗粒呈六角形,颗粒大小在50700nm范围内。根据范特霍夫方程计算由PCT曲线获得的吸氢平台压力,Mg-Ti粉的氢化焓约为67kJ/mol H2,显著高于纯镁粉的氢化焓78.6kJ/mol H2。TG/DTA分析表明,氢化后Mg-Ti粉的放氢起始温度为386°C,低于氢化纯镁粉的放氢温度（423°C）。通过电弧蒸发法直接向Mg中添加Ti而获得的Mg-Ti超细粉体可以显著改善镁的储氢热力学性能。     

Mg含量对氢化燃烧合成MgH_2水解制氢性能的影响

系统研究了Mg的添加量及球磨时间对氢化燃烧合成(Hydriding Combustion Synthesis,HCS)Mg H2在Mg Cl2溶液中水解释氢动力学性能的影响。Mg H2-60%Mg(质量分数,下同)经3 h球磨后在5 min内释氢量为993 m L/g(转化率达80%),经15 min可完全水解,副产物为单一的Mg(OH)2。研究表明:镁的添加在降低制氢成本的同时,一方面可提高释氢动力学性能,另一方面也便于副产物回收再生。     

快淬纳米晶和非晶Mg_(20)Ni_(10-x)Co_x(x=0～4)合金的贮氢性能(英文)EI北大核心CSCD

为了改善Mg2Ni型合金的贮氢性能,采用Co部分替代合金中的Ni以及快淬工艺制备了纳米晶和非晶态Mg20Ni10-xCox(x=0,1,2,3,4)贮氢合金。用XRD、SEM、HRTEM分析了铸态及快淬态合金的微观结构,并测试了合金的气态吸/放氢动力学及电化学贮氢性能。结果表明,在快淬无Co合金中没有形成非晶相,但快淬含Co合金中形成一定量的非晶相。Co替代Ni及快淬处理显著地改善了合金的气态吸放氢性能。同时,Co替代Ni也显著地提高了快淬态合金的放电容量和电化学循环稳定性。     

Improvement of the hydrogen-storage kinetics of Mg by reactive mechanical grinding with 10 wt.% Fe2O3 and 5 wt.% Ni

The addition of Fe₂O₃ to Mg is believed to be able to increase the hydriding rate of Mg, and the addition of Ni is thought to be able to increase the hydriding and dehydriding rates of Mg. A sample Mg-(10wt.%Fe₂O₃, 5 wt.%Ni) was prepared by mechanical grinding under H₂ (reactive mechanical grinding). The as-milled sample absorbed 4.61 wt.% of hydrogen at 593 K under 12 bar H₂ for 60 min. Its activation was accomplished after two hydriding-dehydriding cycles. The activated sample absorbed 4.59 wt.% of hydrogen at 593 K under 12 bar H₂ for 60 min, and desorbed 3.83 wt.% hydrogen at 593 K under 1.0 bar H₂ for 60 min. The activated Mg-(10wt.%Fe₂O₃, 5 wt.%Ni) had a slightly higher hydriding rate at the beginning of the hydriding reaction but a much higher dehydriding rate compared with the activated Mg-10 wt.%Fe₂O₃. prepared via spray conversion. After hydriding-dehydriding cycling, Fe₂O₃ was reduced, Mg₂Ni was formed by the reaction of Mg with Ni, and a small fraction of Mg was oxidized.     

HYDROGEN STORAGE PROPERTIES OF Mg MODIFIED WITH TETRAHYDROFURAN

The hydriding and dehydriding behaviors of tetrahydrofuran modified Mg,its electronic struc-ture,crystal structure,micro-morphology as well as its stability have been investigated.Themodifield Mg absorbs 3.5 wt-％ hydrogen at 643 K in 3.5 MPa H_2,its hydride gives off 3.2wt-％ hydrogen at 643 K in a vaccum of 1.3 Pa after 20 cycles of hydriding and dehydriding.Tetrahydrofuran alters the electronic structure of Mg but keeps its crystal struetureunchanged.In hydriding products,a new hydride phase is found in addition to the knownMgH_2 phase.The hydride formed from Mg is polv-erystalline.The wide-spreading slipbands and twins within crystals indicate that the transformation during absorption ofhydrogen causes serious lattice distortions.     

Improvement in hydrogen sorption properties of Mg by reactive mechanical grinding with Cr2O3, Al2O3 and CeO2

We tried to improve the hydrogen sorption properties of Mg by mechanical grinding under H₂ (reactive mechanical grinding) with oxides Cr₂O₃, Al₂O₃ and CeO₂. The hydriding rates of Mg are reportedly controlled by the diffusion of hydrogen through a growing Mg hydride layer. The added oxides can help pulverization of Mg during mechanical grinding. A part of Mg is transformed into MgH₂ during reactive mechanical grinding. The Mg+10wt.%Cr₂O₃ powder has the largest transformed fraction 0.215, followed in order by Mg+10wt.%CeO₂ and Mg+10wt.%Al₂O₃. The Mg+10wt.%Cr₂O₃ powder has the largest hydriding rates at the first and fifth hydriding cycle, followed in order by Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. Mg+10wt.%Cr₂O₃ absorbs 5.87wt.% H at 573 K, 11 bar H₂ during 60 min at the first cycle. The Mg+10wt.%Cr₂O₃ powder has the largest dehydriding rates at the first and fifth dehydriding cycle, followed by Mg+10wt.%CeO₂ and Mg+10wt.%Al₂O₃. It desorbs 4.44 wt.% H at 573 K, 0.5 bar H₂ during 60 min at the first cycle. All the samples absorb and desorb less hydrogen at the fifth cycle than at the first cycle. It is considered that this results from the agglomeration of the particles during hydriding–dehydriding cycling. The average particle sizes of the as-milled and cycled powders increase in the order of Mg+10wt.%Cr₂O₃, Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. The quantities of hydrogen absorbed or desorbed for 1 h for the first and fifth cycles decrease in the order of Mg+10wt.%Cr₂O₃, Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. The quantities of absorbed or desorbed hydrogen increase as the average particle sizes decrease. As the particle size decreases, the diffusion distance shortens. This leads to the larger hydriding and dehydriding rates. The Cr₂O₃ in the Mg+10wt.%Cr₂O₃ powder is reduced after hydriding–dehydriding cycling. The much larger chemical affinity of Mg than Cr for oxygen leads to a reduction of Cr₂O₃ after cycling.     

Hydrogen generation via hydrolysis of nanocrystalline MgH2 and MgH2-based composites

Nanocrystalline MgH2 and MgH2-based composites with 25% （mass fraction） of Al, Ca, or CaH2 as an individual additive respectively were prepared by ball milling. The crystallite size and morphology of the as-milled powders were characterized and their hydrolysis behaviours were investigated in comparison with commercial polycrystalline MgH2. The results show that the crystallite size of both MgH2 and MgH2-based composites is reduced to less than 13 nm after milling for 15 h. Due to its enhanced specific surface area and unique nanocrystalline structure, the as-milled MgH2 shows much better hydrolysis kinetics than the commercial polycrystalline MgH2, with the hydrolysed fraction upon hydrolysing for 70 min enhances from 7.5% to about 25%. As compared with the as-milled MgH2, the MgH2-based composites with either Call2 or Ca as an additive present further greatly improved hydrolysis kinetics, with the hydrolysed fraction for 80 min achieving about 76% and 62% respectively. However, the addition of Al doesn＇t show any positive effect on the improvement of the hydrolysis kinetics of Mg H2.     

Ce2Mg17及其氢化物添加剂对LiBH4的放氢作用机理研究

为改善LiBH4体系的可逆吸放氢性能,将Ce2Mg17合金(简称为CM)及其氢化物(CeH2.51和MgH2,简称为CMH)分别与LiBH4球磨4 h制得LiBH4-0.02CM和LiBH4-0.02CMH复合储氢体系,采用MS、TPD、XRD和FT-IR等测试手段研究了不同状态Ce-Mg添加剂对复合储氢体系可逆吸放氢性能的影响及其作用机制。结果表明:Ce2Mg17合金本身对改善LiBH4吸放氢性能没有明显作用;而Ce2Mg17氢化物(即MgH2和CeH2.51)可降低复合体系中LiBH4的放氢温度和提高LiBH4的放氢速率,并可明显改善体系的可逆吸放氢性能。进一步分析表明,MgH2和CeH2.51对LiBH4的协同改性作用是有效降低LiBH4热力学稳定性、提高LiBH4-Ce-Mg复合体系可逆吸放氢性能的主要原因。