Zeroth-Order Nucleation Transition under Nanoscale Phase Separation

Materials with nanoscale phase separation are considered. A system representing a heterophase mixture of ferromagnetic and paramagnetic phases is studied. After averaging over phase configurations, a renormalized Hamiltonian is derived describing the coexisting phases. The system is characterized by direct and exchange interactions and an external magnetic field. The properties of the system are studied numerically. The stability conditions define the stable state of the system. At a temperature of zero, the system is in a pure ferromagnetic state. However, at finite temperature, for some interaction parameters, the system can exhibit a zeroth-order nucleation transition between the pure ferromagnetic phase and the mixed state with coexisting ferromagnetic and paramagnetic phases. At the nucleation transition, the finite concentration of the paramagnetic phase appears via a jump.

An Upper Limit to O2 Evolution as Test for Radical and Nonradical Mechanisms for the Fenton Reaction

The origin of an upper limit to the amount of O2 evolved in the rapid reaction between Fe2+ and H2O2 was investigated at a high concentration of H2O2. Using a nonradical model, including the formation of a primary Fe2+–biperoxy complex with a diminished rate of formation of the active intermediate FeO2+, agreement has been reached for the first time with the experimental data obtained by Barb et al. A limited formation of O2 requires that a finite concentration of H2O2 should be present in the reaction mixture when [Fe2+] falls to zero. It has been shown that in Barb et al.’s model the condition for such a state ([Fe2+] = 0, [H2O2] > 0) does not exist. Free radical based models fail as mechanisms for the Fenton reaction.

Kinetic dielectric decrement revisited: phenomenology of finite ion concentrations

A phenomenological theory describes how water is dynamically depolarized by the motion of ions in finite concentration solutions.