Vaporization thermodynamics and heat capacities of Ti5Ge3 and Ti6Ge5

Thermodynamic stabilities of titanium germanides Ti5Ge3 and Ti6Ge5 have bee n studied by means of high-temperature Knudsen effusion mass spectrometry ( KEMS) and differential scanning calorimetry (DSC). Thermodynamic activities of Ti and Ge have been measured over the two-phase mixtures of Ti5Ge3 + Ti 6Ge5 in a temperature range of ca. 1680-1880 K by direct comparison with so lid Ti and liquid Ge metals. The standard free energies of formation of Ti5 Ge3 and Ti6Ge5 at high temperature were determined from the activity data. Heat capacities of Ti5Ge3 and Ti6Ge5 were measured by DSC in the temperatur e region 300-700 K. Standard enthalpies of formation of Ti5Ge3 and Ti6Ge5 a t 298 K were calculated by the third-law method with the use of estimated a bsolute entropy and high-temperature heat capacity data. The results obtain ed are: 1/8Ti(5)Ge(3), -69.8+/-5 kJ; 1/11Ti(6)Ge(5), -70.1+/-5 kJ. The resu lts obtained in this work are compared with previous estimates and measurem ents. (C) 2000 Published by Elsevier Science S.A. All rights reserved.