Study Of LPC Hydrogen Storage Alloy With Technique Of Quenching And Annealing

The effects of alloy elements, rapid solidification, heat treatment on micro-structure and electrochemical properties of hydrogen storage alloy are comprehensively reviewed. Normal-Co, low-Co, free-Co alloys were prepared from Sichuan LPC mischmetal .The alloys were rapidly solidified, and then a portion of the rapidly quenched alloy was annealed. The electrochemical properties of rapid quenched and then annealed alloy were investigated. Mechanism of effects of rapid quenching and annealing on hydrogen storage alloy was discussed.1. Rapidly quenched alloy has a columnar structure. Much dislocation lie in crystal particle and grain boundaries. Rapidly quenched alloy has preferred orientation and fine grain. Crystal lattice distortion increased, and re-crystallizating temperature hoisted. The pressure plateau for the rapidly solidified alloys which were cooled with rate between 10 to 20m/s became flatter and lower than that for the arc-melted alloys. Rapid quench deteriorate activation property, decreased discharge capacity and hydrogen diffusing coefficient. But cycle stability was improved. The discharge voltage plateau droped and became flat at lower cooling rate. Sensitivity on temperature of rapidly solidified alloy increased.2. During heat treatment, cell volume increased, defects decreased, strain released and distribution of alloy composition was homogeneous. The P-C-T plateau for annealed alloys became flatter and lower than that for rapidly solidified alloys. The absolute value of variation of enthalpy and entropy increased. Annealing process improved activation property and discharge capacity. It's more obviously for heat treatment improving cycle stability on normal-Co and low-Co alloy than on free-Co alloy. Normal-Co alloy gave a discharge capacity of 282.1 mAh/g at 1C rate.and the capacity losing rate after 300 cycles was 0.039%. Low-Co alloy gave a discharge capacity of 246.0mAh/g at 1C rate, and the capacity losing rate after 300 cycles was 0.049%. Annealing process increased hydrogen-diffusing coefficient and ameliorated high-rate discharge capability, raised and flatted discharge voltage plateau. Sensitivity on temperature of annealed alloy decreased.3. The research achieved anticipative purpose. A series of alloys, which had long life and good high rate discharge ability, were developed. It was concluded that defects eliminating and composition homogenizing were primary reasons for improvement of cycle stability.