Reaction Rates of Amorphous Iron Hydroxide with Nickel and Cobalt Ions in High Temperature Water

Abstract

Reactions of Ni and Co ions with amorphous iron (ill) hydroxide, which was synthesized by electrolysis of iron electrode, have been studied in high temperature water using an in situ method of a modified magnetic balance and using a reaction model. Formation of NiFe,O. and CoFe 2 0 4 from the amorphous iron (ill) hydroxide were explained by the reaction model incorporating two phenomena, i.e. dehydration of the iron(ill) hydroxide and diffusions of Ni and Co ions into it. The dehydration rate followed Avrami's equation. Apparent activation energy of the dehydration was 4.39 x 10 4 J/mol for the amorphous iron (ill) hydroxide used in the experiments. The diffusions of Ni and Co ions into the particle were evaluated from the diffusion equation for spherical coordinates. The diffusion coefficient of Ni ion into the amorphous iron(ill) hydroxide was much higher than that of Co ion, while its apparent activation energy was about 5.5 x 10 4 J/mol, a value close to that of Co ion. However, the diffusion rate of Co ion into a-Fe,O, was faster than that of Ni ion. Calculated values from the reaction model showed good agreement with experimental values.

Water chemistry technology – one of the key technologies for safe and reliable nuclear power plant operation

“…Cobalt behaviors on the fuel surfaces were confirmed by experiments related to effects of surface roughness on crud deposition rates, boiling-induced deposition of ionic species on fuel surfaces, and chemical reaction of ionic species and crud on the fuel surfaces [12,32,33]. The effects of nickel ion on 60 Co deposition on stainless steel piping were confirmed by surface characterization of exposed specimens [34].…”

Deposition of Colloidal Magnetite on Stainless Steel in Simulated Steam Generator Conditions—Experiments and Modeling

“…Since such interactions occur at very small distances compared to the t of the diffusion layer, the surface boundary layer approximation (SFBLA) [14] is In turn, consolidation of the particles is assumed to be the result of crystallizat magnetite-type oxide, which has the ability to bind individual magnetite part gether, preventing their detachment from the surface. Several authors [15][16][17][18] sug the crystallization of magnetite is governed by the mechanism of Johnson-Mehlgorov-Avrami (JMKA) for simultaneous nucleation and growth [19]. It is assum the rate-determining stage of the process is dehydration of Fe(OH)2, which is t soluble form of Fe in slightly alkaline high-temperature, high-pressure electroly as the secondary coolant of nuclear plants: This model deals with the specific case in which an energy barrier occurs due to the presence of electrostatic repulsion between colloidal particles and the surface of the tube material.…”

“…In turn, consolidation of the particles is assumed to be the result of crystallization of a magnetite-type oxide, which has the ability to bind individual magnetite particles together, preventing their detachment from the surface. Several authors [15][16][17][18] suggest that the crystallization of magnetite is governed by the mechanism of Johnson-Mehl-Kolmogorov-Avrami (JMKA) for simultaneous nucleation and growth [19]. It is assumed that the rate-determining stage of the process is dehydration of Fe(OH) 2 , which is the main soluble form of Fe in slightly alkaline high-temperature, high-pressure electrolytes, such as the secondary coolant of nuclear plants:…”