Thermodynamics of phase equilibrium in nonuniform fields

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Abstract
We obtain conditions of phase equilibrium of a substance in a nonuniform potential field of forces. If the force per mass unit is phase dependent, the field may induce a shift of phase equilibrium. In this case, chemical potentials of the substance do not coincide at the phase boundary with equal temperatures and pressures for each phase. The equality condition at the phase boundary in the presence of the field for the full chemical potentials of the phases, including the additional field component, can be reduced to the equality condition of the chemical 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 reaches its spinodal state. An example of such a transition is the case of a liquid current-carrying conductor in its own magnetic field rapidly turning to a dispersion state (drops in vapor). Similar phenomena can occur at the final stage of electrical explosion of conductors. We also show that for a liquid dielectric in a nonuniform external electric field the thermodynamical equilibrium state is liquid with vapor bubbles, the latter being localized into the domain of the higher value of the field.