THERMODYNAMICS OF PHASE-EQUILIBRIUM IN NONUNIFORM FIELDS

We obtain conditions of phase equilibrium of a substance in a nonunifo rm potential field of forces. If the force per mass unit is phase depe ndent, the field may induce a shift of phase equilibrium. In this case , chemical potentials of the substance do not coincide at the phase bo undary with equal temperatures and pressures for each phase. The equal ity condition at the phase boundary in the presence of the field for t he full chemical potentials of the phases, including the additional fi eld component, can be reduced to the equality condition of the chemica l potentials under different pressures for each phase. Thus the field- induced phase equilibrium becomes impossible for a given geometry, and the system has to change its phase abruptly when one of the phases re aches its spinodal state. An example of such a transition is the case of a liquid current-carrying conductor in its own magnetic field rapid ly turning to a dispersion state (drops in vapor). Similar phenomena c an occur at the final stage of electrical explosion of conductors. We also show that for a liquid dielectric in a nonuniform external electr ic field the thermodynamical equilibrium state is liquid with vapor bu bbles, the latter being localized into the domain of the higher value of the field.