DISORDER PARAMETER, ASYMMETRY AND QUASIBINODAL OF WATER AT NEGATIVE PRESSURES

摘要

The virtual terms "binodal" and "spinodal" are equivalent to the experimental terms "coexistence curve" (CXC) and "metastability limit" (ML), respectively, within an inherent accuracy of any semi-empirical EOS at the des-cription of a real fluid behavior. Any predicted location of mechanical spinodal at positive pressures P_(sp)(T)≥0 merits verification because the Maxwell rule is a model (EOS)-dependent method based on the non-measurable values of chemical potential for both phases. It is not a reliable tool of CXC- and ML-prediction especially at low temperatures between the triple and normal boiling ones [T_l, T_b] where the actual vapor pressures P_s(T) > 0 are quite small while the spinodal pressures P_(sp)'(T)< 0 are huge and negative for a superheated liq-uid. In this paper the alternative substance (non-model)-dependent method of binodal/spinodal formalism consistent with the actual CXC-data: ρ_l, ρ_g, P_s(T) is proposed. The crucial distinction from the conventional results is the novel vir- tual curve of the negative vapor pressures: P_s~- (T) < 0 symmetrical to the actual pressures of saturation: P_s(T )+ P_s~-(T)≈0 . For water this curve crosses the liquid spinodal branch P_(sp)'(T ) at the point: P_(sp)'≈-13, 16 MPa;T_(sp)~0≈605K which is the top of a novel quasibinodal. The respective branches of it (taken at the negative pressures of "saturation": P_s~- < 0 are formed by the liquid-like:ρ~+(T) and gas-like: ρ~-(T) densities of a "coexistence" at the (P_s~-, T) -conditions.The predicted gas-like branch ρ~-(T) is localized completely within the spinodal but the liquid-like-branch ρ (T) has the "near-critical" metastable and even the low-temperature stable parts where ρ (T)≈ρ_l(T).