Mg22Y2Ni10Cu2储氢合金活化和吸氢性能

Activation and Hydrogen Absorption Properties of Mg22Y2Ni10Cu2 Hydrogen Storage Alloy

在0.04 MPa氦气保护下,采用中频感应熔炼炉冶炼了,以少量Y和Cu分别替代部分Mg和Ni的Mg2Ni型储氢合金,并对合金的结构形貌、相组成、气态吸氢活化与性能进行了系统的研究。研究结果表明:铸态Mg22Y2Ni10Cu2合金具有典型的片层状共晶组织特征,其组成相为Mg2Ni,YMgNi4和少量的Mg相;合金在3 MPa,300℃下5次吸放氢完全活化,Mg和Mg2Ni相能够可逆吸放氢,但在首次活化过程中,Mg2Ni相只有部分转变为Mg2NiH4,而Mg相则能够完全转变为MgH2;同时发现YMgNi4相虽多次吸放氢循环后,都未发现有非晶化现象发生,表明该相与REMgNi4(RE=La,Nd)等其他拉弗斯相相比,具有更高的结构稳定性;合金的吸氢动力学曲线用Avrami-Erofofeev法拟合后表明合金吸氢是一维形核和长大过程;测试了合金的平衡压力-浓度等温(PCT)曲线,计算合金的热力学参数为Mg相的氢化焓变(ΔH)和熵变(ΔS)分别为-78.1 kJ·mol-1,-133.9J·K-1·mol-1,而Mg2Ni相的氢化ΔH和ΔS则分别为-51.8 kJ·mol-1,-103.0J·K-1·mol-1,合金的热力学性能明显改善,表明添加Y和Cu对Mg2Ni型合金的吸氢性能具有一定的催化作用。

Under the protection of 0.04 MPa helium gas,Mg2Ni hydrogen storage alloys were melted in medium frequency induction smelting furnace with a small amount of Y and Cu as substitutes of Mg and Ni,respectively.The structure,morphology,phase composition,hydrogen absorption activation and properties of the alloy were systematically studied.The results showed that as-cast Mg22 Y2 Ni10Cu2 alloy had typical lamellar eutectic structure,and its constituent phases were Mg2Ni,YMgNi4 and a few Mg phases.Mg and Mg2 Ni phases could absorb and desorb hydrogen reversibly after 5 times of hydrogen absorption and desorption at 3 MPa and 300℃,but only part of Mg2 Ni phase could be converted to Mg2 NiH4 during the first activation,while Mg phase could be completely converted to MgH2.It was also found that YMgNi4 phase had no amorphous phenomenon after many hydrogen absorption and desorption cycles,which indicated that YMgNi4 phase had higher structural stability than other Laves phases such as REMgNi4(RE=La,Nd).The kinetic curve of hydrogen absorption of the alloy was fitted by Avrami-Erofeev method,which indicated that hydrogen absorption of the alloy was a one-dimensional nucleation and growth process,and the hydrogenation formation energy(ΔH) and formation entropy(ΔS) of the Mg phase were-78.1 kJ·mol-1 and-133.9 J·K-1·mol-1,respectively,and those for Mg2 Ni phase were-51.8 kJ·mol-1,-103.0 J·K-1·mol-1,respectively.Thermodynamic properties of Mg2 Ni alloy were improved obviously,which indicated that the addition of Y and Cu had a catalytic effect on hydrogen absorption of Mg2 Ni alloy.