Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5460008 | Journal of Alloys and Compounds | 2017 | 8 Pages |
Abstract
This work focuses on the determination of the standard molar enthalpies of formation ÎfH°(298) of the lithium silicides Li7Si3 and Li12Si7. For this purpose the hydrogenation/dehydrogenation equilibria in the system Li-Si-H were investigated at three different temperatures (450 °C, 475 °C, 500 °C) using a Sieverts type apparatus. The measurements are based on two different sample types: (i) pure silicide Li7Si3 (Li2.33Si) and (ii) a stoichiometric mixture of lithium hydride and silicon in the ratio of Li:Si = 2.33:1. The calculation of the standard enthalpies of formation by using the slopes of the classical Van't Hoff plot results in uncertainties of at least 10%. Due to this relatively large error, an alternative evaluation method based on the linking of the hydrogen equilibrium pressures peq(H2) from the sorption measurements with recently published precise heat capacity and entropy data of the lithium silicides was applied. The obtained values for the standard enthalpy of formation amount to ÎfH°(298) = (â25.3 ± 0.3) kJ/(mol atom) for Li7Si3 and ÎfH°(298) = (â23.5 ± 0.3) kJ/(mol atom) for Li12Si7 exhibiting strongly reduced uncertainties.
Keywords
Related Topics
Physical Sciences and Engineering
Materials Science
Metals and Alloys
Authors
Daniel Thomas, Nadine Bette, Franziska Taubert, Regina Hüttl, Jürgen Seidel, Florian Mertens,