Thermodynamic and degradation studies of LaNi4.8Sn0.2-H using isotherms and calorimetry

• Published in: Journal of alloys and compounds 1995-12, Vol.231 (1-2), p.473-478
• Main Authors: Luo, S., Luo, W., Clewley, J.D., Flanagan, Ted B., Bowman, R.C.
• Format: Article
• Language: English
• Subjects: Calorimetry; Degradation of LaNi4.8Sn0.2-H; Intermetallic hydrogen system; Thermodynamics
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/0925-8388(95)01870-0

Isotherms measured in this research indicate that the LaNi4.8Sn0.2-H system has a miscibility gap with a critical temperature of about 525 K. Hysteresis, which is smaller for this alloy-H system than for the parent compound-H system, LaNi5H, disappears at about 500 K; this is consistent with the estimated miscibility gap phase diagram. van 't Hoff plots over an extended temperature range have been constructed for samples from different preparations. The results for all of the samples are similar: |ΔHf,dplat| = 16.4 ± 0.1kJ (mol1/2H2)−1 and|ΔSf,dplat| = 52.5 ± 0.5J K−1 (mol1/2H2)−1 where the superscripts f and d refer to results from plots of the formation and decomposition plateau pressure respectively. In the temperature range from about 500 K to 550 K the LaNi4.8Sn0.2Hn was kept at high hydrogen contents in order to determine whether degradation occurs. It was not discernible following storage for 24 h at a hydrogen content of n = 4.5 (124 bar) at 523 K. Another sample was kept for 13 d at 550 K at n = 0.9 (125 bar) and it also did not appear to have degraded judging from its subsequent isotherms.