  First order phase transitions (PTs) with more than one globally conserved
charge, so-called non-congruent PTs, have characteristic differences compared
to congruent PTs (e.g., dimensionality of phase diagrams, location and
properties of critical points and endpoints). In the present article we
investigate the non-congruence of the nuclear liquid-gas PT at sub-saturation
densities and the deconfinement PT at high densities and/or temperatures in
Coulomb-less models, relevant for heavy-ion collisions and neutron stars. For
the first PT, we use the FSUgold relativistic mean-field model and for the
second one the relativistic chiral SU(3) model. The chiral SU(3) model is one
of the few models for the deconfinement PT, which contains quarks and hadrons
in arbitrary proportions (i.e. a "solution") and gives a continuous transition
from pure hadronic to pure quark matter above a critical point. The study shows
the universality of the applied concept of non-congruence for the two PTs with
an upper critical point, and illustrates the different typical scales involved.
In addition, we find a principle difference between the liquid-gas and the
deconfinement PTs: in contrast to the ordinary Van-der-Waals-like PT, the phase
coexistence line of the deconfinement PT has a negative slope in the
pressure-temperature plane. As another qualitative difference we find that the
non-congruent features of the deconfinement PT become vanishingly small around
the critical point.
