Abstract: A differential calorimeter which operates in the range of 600-1500 K was con- structed on the basis of DTA principle. This apparatus has some modifications up- on Hoster's calorimeter. Its reliability was proved by measuring some systems whose enthalpies of formation or phase transformation have been given out in the published literatures.
The calorimeter was used to determine the enthalpies of formation of 9 alloys (with x_Fe=0.53) of Fe-Cr-V system, which no one up to now has measured except Malinsky and Claisse who did only one of these alloys. We also used it to determine the enthalpies of the sigma-alpha phase transformation of these alloys. The data obtained in present work were compared with that of Malinsky and Claisse for the ternary system, Dench and Spencer for the binary systems, and good coincidence was found between them. The experimental results thow that on the pseudobinary system of x_Fe=0.53, the enthalpies of formation of bcc Fe-Cr-V alloys change its sign from positive on the Fe-Cr side to negative on the Fe-V side.