退火热处理对Nd0.75Mg0.25(Ni0.8Co0.2)3.5储氢合金结构和性能的影响

Effects of Annealing Treatment on Microstructure and Properties of Nd0.75Mg0.25(Ni0.8Co0.2)3.5 Hydrogen Storage Alloys

摘要:

采用中频感应熔炼制备Nd0.75Mg0.25(Ni0.8Co0.2)3.5储氢合金，在0.03 MPa氩气氛围进行退火，退火温度分别为850，900和950 ℃，保温时间均为7 h。分别对合金的电化学性能、气态储氢性能和合金的微观结构进行研究。结果表明，合金在退火热处理前后的相组成没有发生明显变化，主相均为Ce2Ni7型(Nd,Mg)2(Ni,Co)7相和CaCu5型NdNi5相。合金中晶粒尺寸随着退火温度的升高而增大，相界面则减少，退火消除晶格应力、增加成分均匀性、增加储氢容量；同时有部分Mg在热处理过程中损失导致储氢容量的下降。900 ℃热处理使得Nd0.75Mg0.25(Ni0.8Co0.2)3.5合金表现出较好的储氢性能，最大电化学放电容量为359 mAh/g，合金电极在100次循环后容量保持率为90.3%，气态储氢容量达到1.65%（质量分数，下同）。

Abstract:

Nd0.75Mg0.25(Ni0.8Co0.2)3.5 hydrogen storage alloys were prepared by mid-frequency induction melting, and were annealed at 850, 900 and 950 oC for 7 h in 0.03 MPa argon atmosphere. The electrochemical properties, hydrogen storage properties and microstructure of the alloys were investigated. The results show that annealing has little influence on the variation of phase composition in the alloys, and the main phases are Ce2Ni7 type (Nd,Mg)2(Ni,Co)7 phase and CaCu5 type NdNi5 phase. Average grain size and element homogenization of the alloys increase with increasing the annealing temperature, the area of phase interface and the grain stress decrease, and hydrogen storage capacity increases. Simultaneously, the loss of Mg element in the alloys decreases the hydrogen storage capacity owing to higher annealing temperature. So Nd0.75Mg0.25-(Ni0.8Co0.2)3.5 alloy annealed at 900 oC exhibit better hydrogen storage properties; the max discharge capacity of alloy electrode is about 359 mAh/g, the capacity retention rates is about 90.3% after 100 cycles, and the hydrogen absorption capacity is about 1.65 wt%.