TY - JOUR
TI - Influence of the degree of irreversibility of thermal and mechanical treatment regime on the final qualities of a reacting-system
AU - Grigorova Veneta G
AU - Roussev Dimitar G
JN - Thermal Science
PY - 2006
VL - 10
IS - 1
SP - 65
EP - 80
PT - Article
AB - The final qualities of interest (such as grain size, chemical purity, degree of stability, transition order) of new compounds, synthesized in solid state transformation processes (chemical reactions, phase transitions) can be controlled through the evaluation of the entropy generation in the system. Thermally activated chemical reaction (LiCoPO4 synthesis) and mechanically activated phase transition (PdSe2 transformation) are discussed as examples. The LiCoPO4 qualities of interest are grain size (less that 0.5 μm) and chemical purity (up to 98%). The pyrite structured PdSe2 qualities of interest are: transition-order and degree of stability. The requirements are first-order transition and as higher as possible degree of stability. The grain size of LiCoPO4 and degree of stability of PdSe2 have been de scribed by the calculation of the entropy generation in the treatment process; the chemical purity of LiCoPO4 – by the reaction co-ordinate and the transition order of PdSe2 – by the behavior of the thermodynamic potential – first partial derivative in the transition point. To compute the thermodynamic functions under request, the behavior of the treated system has been investigated by measuring the driving force of its conversion process. In the case of thermal treatment (LiCoPO4) the absorbed heat flux has been measured whereas for the case of mechanical treatment (PdSe2) the applied pres sure and its corresponding material’s specific volume have been measured. Experiments and calculations have been carried out for LiCoPO4 to establish empirical equations, giving the relation ship between the heating regime parameters and final product grain size. For PdSe2, the relation ships between the compression regime parameters and thermodynamic potential and the degree of stability have been received by numerical calculations.