氢化燃烧合成Mg-Mg2Ni储氢合金组成和性能研究

利用氢化燃烧合成法制备了镁基储氢合金Mg-Mg2Ni,分析了镁镍配比和镁粉粒径对HCS产物组成和储氢性能的影响.研究结果表明,HCS产物主要由Mg2Ni及Mg的氢化物MgH2、Mg2NiH4和Mg2NiH0.3组成,没有Ni相的存在,当Mg:Ni＞2:1时,较粗镁粉原料的使用对燃烧合成产物Mg2Ni的氢化活性影响不大,但会降低反应剩余Mg的氢化活性.随原料中镁镍配比的增加,HCS产物中MgH2的相对含量逐渐增加,HCS产物的氢化动力学性能逐渐降低,吸氢量却先增加后降低,Mg:Ni=7.85:1时具有最大的吸氢量4.87wt.%,同时由较细镁粉得到的HCS产物的氢化速率和吸氢量大于较粗镁粉,但两者之间的差别会随镁镍配比的降低而减小.     

镁的氢化反应对氢化燃烧合成储氢合金Mg2NiH4纯度的影响

本文主要通过改变在镁氢化反应温度的保温时间,研究不同合成压力、合成温度下,中间反应-镁的氢化反应对氢化燃烧合成Mg2NiH4的影响.初步探讨了镁的氢化反应与燃烧合成Mg2Ni反应及其氢化反应的内在联系.研究结果表明:镁的充分氢化在促进Mg-Ni燃烧合成反应的同时有效地提高了Mg2Ni的氢化活性,这一结果为工业化低压合成纯Mg2NiH4提供了可行途径,但在低温下仅延长镁的氢化时间,产物中少量的Ni很难消除.     

氢化燃烧合成Mg_2NiH_4的影响因素研究

研究了气氛压力、燃烧温度和保温时间对合成Mg2NiH4的影响,对产物进行了XRD和SEM分析,结果表明,在镁镍共晶温度附近,于氩气气氛中燃烧合成1h就能生成大量的Mg2Ni,保温2h,反应更为完全。随着氢压的增大,镁镍氢化物有明显的增加,在2.2MPa时,金属镍完全消失。随着合成温度的升高,镁镍氢化物有所增加,但温度太高,不利于Mg2NiH0.3进一步氢化形成Mg2NiH4。适当的保温时间可促进镁镍合成反应的进行。     

氢化燃烧合成法制备Mg-Mg2Ni储氢合金氢化物

以镁-镍共晶组分为研究对象,利用氢化燃烧合成法成功制备了Mg-Mg2Ni镁基储氢合金氢化物,研究表明,产物主要由MgH2,Mg2NiH4及不完全氢化的Mg2N2Ni0.3所组成,同时初始合成氢压、降温时Mg2Ni及Mg氢化保温时间等参数的改变对产物纯度影响不大,且难以消除不完全氢化的Mg2NiH0.3,分析认为合成过程中Mg2Ni表面包裹的Mg是限制Mg2Ni氢化的主要原因.     

掺钛对氢化燃烧合成镁镍储氢合金的影响

借助于XRD、TG-DSC和SEM等技术研究了掺钛对氢化燃烧合成镁镍储氢合金的合成条件及合金性能的影响.结果表明:掺钛使Mg2NiH4的合成温度有一定的提高,600℃时才能大量生成Mg2NiH4;氢压的提高有利于Mg2NiH4的形成,而过高的合成温度和过长的保温时间将不利于Mg2NiH4的形成;钛的掺入使Mg2NiH4的晶胞有一定的增大;掺钛的Mg2NiH4放氢分解温度为259.8℃,比未掺钛的降低了120℃左右;掺钛试样的总放氢量为2.43%;掺钛试样在300℃、0.1MPa下的吸放氢时间为6min,活化可适当提高吸放氢量.     

镁基储氢合金氢化物Mg2NiH4的制备及性能研究

以不经压制的Mg、Ni混合粉末为原料,利用氢化燃烧合成法在合成温度850 K和1.8 MPa初始合成氢压下制备了镁基储氢合金氢化物Mg2NiH4,并利用XRD及PCT仪分析了其物相组成和储氢性能.研究表明,产物由单一物相Mg2NiH4组成,无未反应的Ni和不完全氢化的Mg2NiH0.3;相对于传统熔炼法制备的Mg2Ni,氢化燃烧合成产物具有更高的氢化活性,在没有任何活化处理的前提下,第一次吸氢就能以很快的速度达到饱和吸氢量,同时在任何吸氢温度下均具有较好的吸氢动力学性能,且随温度的降低,最大吸氢量降低幅度较小,平台压和吸放氢温度的关系为:lgP(0.1 MPa)=-3 187.6/ T 6.362 4(吸氢),lgP(0.1 MPa)=-3 468.4/T 6.694 3(放氢).     

氢化燃烧合成Mg2NiH4产物高活性特征及分析

氢化燃烧合成法(HCS法)是镁基储氢合金制备的新方法,具有省能、省时、产物高活性等显著优点,近年来引起了国内外广泛关注.本文通过XRD、SEM和PCT等手段研究了氢化燃烧合成Mg2NiH4产物高活性的特征,并从物相组成、颗粒特性和氢化反应等方面揭示了HCS产物高活性的机理.结果表明,氢化燃烧合成Mg2NiH4产物在没有任何活化处理的前提下,第一次吸氢就能达到饱和吸氢量,且在不同温度下均具有比传统熔炼法产物Mg2Ni高的氢化活性;纯的物相组成、多孔的颗粒特性、大量微裂纹的存在和小的晶粒尺寸是其高活性的内在原因.本研究对控制HCS产物的微结构并进一步改善其储氢性能具有重要意义.     

氢化燃烧合成法制备镁基储氢合金Mg2NiH4

采用自行设计制作的反应设备，研究了氢化燃烧合成法制备Mg2NiH4的工艺参数。主要探讨了合成反应动力学因素：压力、合成温度、氢化保温时间对产物纯度的影响。实验结果表明，在初始压力为1．5MPa下，合成条件分别为：合成温度808K，合成保温时间120min，氢化保温时间60min及合成温度850K，合成保温时间60min，氢化保温时间90min时均可制备出纯的Mg2NiH4。     

Mg95Ni5-30wt%La0.7Mg0.3Ni2.8Co0.5复合物的吸放氢性能研究

先采用氢化燃烧合成法制备Mg95Ni5,然后将氢化燃烧合成产物与30%(质量分数)La0.7Mg0.3Ni2.8Co0.5合金进行机械球磨复合,球磨时间分别为5、10、15和20h;将Mg95Ni5的氢化燃烧合成产物直接球磨10h用于对比研究.采用X射线衍射仪、扫描电镜、能谱仪及气体反应控制器研究了材料的相组成、微观形貌、颗粒化学成分以及吸放氢性能.研究表明,球磨10h的Mg95Ni5/La0.7Mg0.3Ni2.8Co0.5复合物具有最佳的吸放氢性能,在373K,50s内基本达到饱和吸氢量3.78%(质量分数);在523K,1800s内放氢量为3.83%(质量分数);其起始放氢温度为425K,与Mg95Ni5相比降低了35K,吸放氢性能的改善与复合物的组织结构密切相关.此外,La0.7Mg0.36Ni2.8Co0.5的加入改善了复合物的放氢动力学性能.     

掺铜对氢化燃烧合成Mg2NiH4的影响

采用XRD、TG DSC、SEM研究了掺铜对氢化燃烧合成镁镍储氢合金性能的影响,研究表明掺铜使Mg2NiH4的合成时间延长;随掺铜量的增加,形成的Mg2NiH4量减少;掺铜使Mg2NiH4的分解温度降低约140℃。并探讨了温度降低的原因。     

Hydriding mechanism of Mg2Ni in the presence of oxygen impurity in hydrogen

For the case where oxygen is present as an impurity in hydrogen, a hydriding mechanism is proposed along with hydriding cycling of the Mg₂Ni alloy. The large chemical affinity of magnesium for oxygen leads to the selective oxidation of magnesium and to the segregation of the more noble nickel component. The consequence is a progressive decrease in hydrogen storage capacity of Mg₂Ni along with hydriding cycling. The segregated nickel provides active sites for chemisorption of oxygen and hydrogen. The chemisorbed oxygen accelerates the surface segregation of nickel or can form water vapour with hydrogen, or (least favourably) directly oxidizes nickel. The chemisorbed hydrogen can form water vapour with oxygen, can hydride Mg₂Ni or can reduce the nickel oxide eventually formed. All these reactions are exothermic, causing an increase in temperature during the hydriding process.     

A hydriding kinetic model of the Mg2Ni-H2 system

The hydriding kinetics of an Mg₂Ni alloy are investigated under hydrogen pressures from 2.5 to 8 bar (0.25 to 0.8 MPa) at various temperatures (543 ?T ? 583 K). The hydriding reaction of Mg₂Ni progresses by a nucleation and growth mechanism. The rate-controlling step is analysed to be the forced flow of hydrogen molecules through pores, interparticle channels or cracks of the sample, involving heat-transfer control.     

Effect of surface oxidation on the hydriding and dehydriding of Mg<Subscript>2</Subscript>Ni alloy produced by hydriding combustion synthesis

Hydriding combustion synthesis (HCS) has been regarded as an innovative process for the preparation of high active magnesium-based hydrogen storage alloys. For the purpose of understanding the interrelation of the unique hydrogen storage properties and the surface characteristics of the HCS product, the samples of Mg₂Ni alloy/hydride with and without exposure to air were prepared from the HCS product of Mg₂NiH₄. The hydriding and dehydriding properties were compared and the surface compositions were analyzed by means of X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES). It was shown that the air exposure considerably decreases the hydriding activity of Mg₂Ni. Absorbing of 3.0 wt.% of hydrogen under the conditions of 603 K and 3.0 MPa after the air exposure takes 1500 s, which is six times longer than for the unexposed alloy. The hydrogen desorption of the hydride are also impeded by the air-exposure, which results in the increase of dehydriding temperature from 450 K to 540 K. XPS and AES analyses indicated that Mg segregates and exists in the form of hydroxide on the surface of the air-exposed sample, which is responsible for the degradation of the hydriding and dehydriding properties. It was confirmed that the fresh surfaces generated during the dehydriding process of the as-synthesized hydride product contributes to the high activity of the HCS product in the first cycle of the hydriding determination.     

Using MgO to improve the (de)hydriding properties of magnesium

Of all the materials presently being investigated to safely store high volumes of hydrogen for mobile applications; magnesium remains the most attractive. Magnesium is a light, low cost metal with high capacity for hydrogen storage but its (de)hydriding kinetics have to be improved for practical applications. Recently, hydrogen kinetics in magnesium have been significantly improved by mechanically milling magnesium hydride with catalyst transition metals or metal oxides. Here, we report that similar improvements can be achieved without using a catalyst. Our results demonstrate that magnesium hydride milled with magnesium oxide exhibits dehydriding and hydriding kinetics as fast as those obtained with catalyst transition metals or metal oxides.     

Verification of the rate-controlling steps in the hydriding reaction of Mg2Ni

The rate-controlling steps in the hydriding reaction of Mg₂Ni are verified by comparing the incubation periods in the hydriding reaction of the Mg₂Ni alloy and a mechanically-alloyed mixture of 2Mg and Ni, by using gas mixtures of hydrogen and argon, and by varying the sample weight in the hydriding reaction.     

不同制样方式对氢化燃烧合成Mg2NiH4的影响

采用XRD、SEM、TG DSC研究了不同的制样方式对氢化燃烧合成Mg2NiH4的影响,结果表明:相同条件下,镁粉、镍粉直接氢化燃烧合成比镁粉、镍粉压片和镀镍镁片更容易合成Mg2NiH4。生成的Mg2NiH4更纯,放氢温度也相对集中。