Heat flux calorimetry in intermetallic compound-H-2(g) systems: heat measurements and modeling in the low pressures range

A heat conduction calorimeter has been used to determine enthalpies of soli d-gas reactions in systems, such as intermetallic compounds-H-2(g). It is s hown that the significance of the heat measurements must be carefully analy zed by controlling several parameters, which may influence the heat transfe r conditions during the absorption and desorption reactions. For this type of reaction, the measured heat flow is strongly dependent on the heat transfers through the gas phase in the low pressure range (Knudsen regime). It is demonstrated, experimentally and confirmed with simple mode ls, that heat measurements can provide erroneous enthalpies due to our inab ility to account for the unavoidable modifications of the heat losses in th e transition region. Experiments were carried out on the ZrNi-H-2 system. ( C) 2001 Elsevier Science B.V. All rights reserved.