The Phase Diagram Of La-Ni-Sn Ternary System And The Electrochemical Property Of LaNi_5-XSn_X Alloys

The 673K isothermal section of La-Ni-Sn ternary system, the crystal structure of the new found ternary compound and the electrochemical property of LaNi5-xSnx electrode alloys have been investigated. There are three parts in this thesis.1. The 673K isothermal section of La-Ni-Sn ternary systemThe phase relationships in the La-Ni-Sn ternary system at 673K have been investigated by means of x-ray powder diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Most of this ternary system was studied at 673K. At this temperature, a new ternary compound whose atom ratio is close to La:Ni:Sn=1:1 :3 has been found. The existences of 15 binary compounds La7Ni3, LaNi, La2Ni3 La7Nii6, LaNi3, La2Ni7, LaNi5, Ni3Sn, Ni3Sn2, Ni3Sn4, La5Sn3, La5Sn4, LaSn, La3Sn5, LaSn3 and 7 other ternary compounds LaNi5Sn, LaNi4Sn2, LaNi2Sn2, La3Ni2Sn6, La3Ni2Sn7, La3Ni8Sni6, LaNiSn have beenconfirmed too. There are 31 three-phase regions in the 673K isothermal section. Due to the lower melting point of Sn (about 504K), a small part of ternary system that lies in the Sn-rich part was studied at 483K. There is a three-phase area in the 483K isothermal section in our phase diagram: LaSn3+Ni3Sn4+Sn. Under our experiment condition, it is proved that there exists La7Nii6 at 673 K in La-Ni system, not LaNi2. The compound La3Ni doesn't exist in this work. In the La-Sn system, the La2Sn3 and La11Sn10 were not found either.2. The crystal structure of the new ternary compound LaNiSn3The crystal structure of the new ternary compound has been partly studied. According to the research result of Rigaku D/max-RC automatic X-ray diffractometer and EPMA, this new compound is LaNiSn3, with a monoclinic structure, a space group of C2(5), a=1.3702nm, b=0.8953nm, c=0.4480nm, =119.419 (8) .3. The electrochemical property of LaNi5-xSnx electrode alloysApart from the phase diagram of La-Ni-Sn system, the electrochemical property of LaNi5-xSnx has also been investigated. The open recycling batteries were made with LaNi5.xSnx cathode and Ni(OH)2 anode in the mixture electrolyte of 6mol/L KOH and 0.2mol/L LiOH. By analyzing theexperiment results from the automatic charger-discharger-DC-5 battery testing instrument, we found that the little substitution of Sn for Ni in LaNi5 could improve the stability of LaNi5 hydrogen storage electrode and the charge-discharge property in large electrical current of electrodes.