  We construct new models of outer heat blanketing envelopes of neutron stars
composed of binary ion mixtures (H - He, He - C, C - Fe) in and out of
diffusive equilibrium. To this aim, we generalize our previous work on
diffusion of ions in isothermal gaseous or Coulomb liquid plasmas to handle
non-isothermal systems. We calculate the relations between the effective
surface temperature Ts and the temperature Tb at the bottom of heat blanketing
envelopes (at a density rhob= 1e8 -- 1e10 g/cc) for diffusively equilibrated
and non-equilibrated distributions of ion species at different masses DeltaM of
lighter ions in the envelope. Our principal result is that the Ts - Tb
relations are fairly insensitive to detailed distribution of ion fractions over
the envelope (diffusively equilibrated or not) and depend almost solely on
DeltaM. The obtained relations are approximated by analytic expressions which
are convenient for modeling the evolution of neutron stars.
