Vol.3, No 2, 2005 pp. 115 - 128
UDC 536.7
STUDYING THERMODYNAMICS OF METASTABLE
STATES
Yuri Kornyushin
Maître Jean Brunschvig Research Unit,Chalet Shalva, Randogne, CH-3975
Abstract. Simple classical thermodynamic approach to the general
description of metastable states is presented. It makes possible to
calculate
the explicit dependence of the Gibbs free energy on temperature, to
calculate
the heat capacity, the thermodynamic barrier, dividing metastable and
more
stable states, and the thermal expansion coefficient. Thermodynamic
stability
under mechanical loading is considered. The influence of the heating
(cooling)
rate on the measured dynamic heat capacity is investigated. A phase
shift
of the temperature oscillations of an ac heated sample is shown to be
determined
by the relaxation time of the relaxation of the metastable
nonequilibrium
state back to the metastable equilibrium one. This dependence allows
one
to calculate the relaxation time. A general description of the
metastable
phase equilibrium is proposed. Metastable states in AB3 alloys are
considered.
Reasons for the change from the diffusional mechanism of the
supercritical
nucleus growth to the martensitic one as the heating rate increases are
discussed. The Ostwald stage rule is derived.
PROUČAVANJE TERMODINAMIKE
METASTABILNIH
STANJA
Prezentovan je jednostavan klasičan termodinamički pristup u opisu
metastabilnih
stanja. On omogućava izračunavanje eksplicitne zavisnosti Gibsove
slobodne
energije od temperature, toplotni kapacitet, termodinamička barijera
koja
razdavaja metastabilna stanja od onih stabilnijih, kao i toplotni
koeficijent
širenja. Razmatrana je termodinamička stabilnost pod mehaničkim
opterećenjem,
kao i uticaj brzine zagrevanja (hlađenja) na dinamički toplotni
kapacitet.
Pokazano je da je fazni pomeraj temperaturnih oscilacija određen
vremenom
relaksacije metastabilnog neravnotežnog stanja u metastabilno stabilno.
Razmatrana su metastabilna stanja u AB3 legurama. Izvedeno je
Ostvaldovo
pravilo.
