Chihiro Matsuura

Solubility of magnetite in high temperature water and an approach to generalized solubility computations

Magnetite solubility in pure water was measured at 423 K in a fully teflon-covered autoclave system. A fairly good agreement was found to exist between the experimental data and calculation results obtained from the thermodynamical model, based on the assumption of Fe3O4 dissolution and Fe2O3 deposition reactions. A generalized thermodynamical approach to the solubility computations under complex conditions on the basis of minimization of the total system Gibbs free energy was proposed. The forms of the chemical equilibria were obtained for various systems initially defined and successfully justified by the subsequent computations. A [Fe3+]T-[Fe2+]T phase diagram was introduced as a tool for systematic understanding of the magnetite dissolution phenomena in pure water and under oxidizing and reducing conditions.

Hydrolysis of zinc ion and solubility of zinc oxide in high-temperature aqueous systems

Hydrolysis constants of the zinc ion were measured at 25, 50, 75, 185, 200, and 225°C through the direct measurement of pH using pH sensors, especially of the yttria-stabilized zirconia membrane-ty...

Solubility of Nickel and Cobalt Oxides in High-Temperature Water

AbstractThe solubility of NiO and CoO in high-temperature water is measured at temperatures between 373 and 523 K in a special batch autoclave system. Great importance has been given to deriving reliable thermodynamical data for the related ionic species at elevated temperatures. The experimental results for NiO seem to be consistent with the previously proposed free-energy data set for Ni2+. Because of the lack of experimental information on the free energy of formation (ΔG°f) for Co2+, the Criss-Cobble approach is used to calculate the values. The estimates are compared with the experimental results. It is concluded that the application of the Criss-Cobble procedure to Co2+ ions is not correct above 423 K. Based on the experiments, a new set of ΔG°f values for Co2+ is proposed.

Fabrication of a poly-electrolyte membrane based on cross-linked PTFE thin film by EB irradiation grafting

Polymer electrolyte fuel cell (PEFC) membranes based on cross-linked polytetrafluoroethylene (RX-PTFE) very thin film have been fabricated by radiation grafting with reactive styrene monomers using electron beam irradiation under nitrogen atmosphere at room temperature. The characteristic properties of obtained materials have been measured by differential scanning calorimetry, thermogravimetric analysis, FT-IR spectroscopy, etc. The glass transition temperatures and thermal decomposition temperatures of grafted materials strongly depend on the yields of styrene grafting onto base materials. The higher yields of grafting give lower thermal stability. The ion-exchange capacity of sulfonated materials is 3.0 mEquiv/g. The other properties of obtained membranes, such as chemical structure and rates of hydrogen gas transmission, are discussed.

Radiation induced reduction of CO2 in iron containing solution

Abstract Ionizing radiation has been applied to the reduction of carbon dioxide which is considered to cause the greenhouse warming problem. Carbon dioxide was subjected to 60 Co γ-rays in the presence of solution containing either ferrous ions or iron powder. Experimental parameters employed are the radiation dose rate, the total dose and the amount of iron powder or ferrous ion. The gaseous reaction products which contain carbon have been identified as carbon monoxide and hydrocarbons of small molecular weight. The following results are considered very interesting: (1) carbon monoxide has been obtained more predominantly than other gaseous products; (2) in the solution with iron powder, a considerable amount of saturated hydrocarbon has been formed in the order of methane, ethane, propane and n -butane. The results have been interpreted by postulating the formation of a metastable conjugate complex among unsaturated hydrocarbon and iron complexes.

Radiation induced CO2 reduction in an aqueous medium suspended with iron powder

Abstract Radiation induced CO 2 conversion to CO and hydrocarbon has been studied using a solution suspended with iron powder and saturated with CO 2 . Due to the corrosion enhanced by γ-rays, H 2 has become the most dominant product of all. Corresponding to the rapid H 2 formation, a little hydrocarbon containing less than 4 carbon atoms has been produced in the initial period of irradiation, whereas CO yield has gradually increased to a considerable amount over a prolonged irradiation period. The CO yield has also shown a marked increase associated with introducing Ni 2+ or Cu 2+ into the solution. It is understood that 5.6 hydrogen atoms are consumed in the termination reaction of H 2 formation.

Solubility of zinc ferrite in high-temperature oxygenated water

Abstract The solubility of zinc ferrite was measured at 423 K, 473 K, and 523 K in an oxygenated water system, which is rather similar to the chemical condition of boiling water reactors. Thermodynamic analysis was performed by a procedure minimizing standard Gibbs free energy of the system at the final state. From both the analysis and the experimental results it was concluded that the dissolution process of ZnFe2O4 in conditions where no redox reaction occurs is described by combination of ZnFe2O4 dissolution and Fe2O3 precipitation equilibria. By fitting to the experimental results, thermodynamic data of ZnFe2O4 are re-analyzed at 423 K, 473 K, and 523 K.

Changes in pH and redox potential during radiation-induced CO2 reduction in an aqueous solution containing iron powder

Abstract A study of the radiation induced CO 2 reduction in a solution containing iron powder with a specific surface area as large as 29 m 2 /g has revealed that H 2 and hydrocarbons are formed irrespective of whether the solution is irradiated with γ-rays or not and that CO is produced only under γ-ray irradiation. By considering the relation between pH and ORP (oxidation-reduction potential) the results obtained are attributed to the considerable decrease in pH. For an initial period, the rate of H + generation is remarkably enhanced by almost 30 times by a collective effect of γ-rays, CO 2 and iron.

STUDY ON THE BEHAVIOR OF RADIOLYTICALLY PRODUCED HYDROGEN IN A HIGH-LEVEL LIQUID WASTE TANK OF A REPROCESSING PLANT: HYDROGEN CONSUMPTION REACTION CATALYZED BY Pd IONS IN THE SIMULATED SOLUTION

Abstract It is well known that not all of the hydrogen formed in high-level liquid waste comes out in the gas phase because hydrogen is consumed by some unclarified secondary reaction. Using a simulated waste solution, it was found that the H2 consumption reaction is not caused by radiation as was thought but is caused by a catalytic effect of Pd ions, which suggests that the same reaction proceeds in actual solution. Using the catalytic reaction rate constant measured in the simulated solution, the analysis showed that the H2 concentration in the gas phase does not reach its explosion limit of 4% even if the sweeping air stops for a long time.

Radiation-induced potential difference between electrodes with and without gamma rays

Abstract Observation were carried out on the potential difference (PD) appearing between two electrodes immersed in solutions purged with Ar, CO 2 , N 2 O and O 2 , where either one of the electrodes was subject to γ-ray irradiation. In the solutions with all other gases than N 2 O, ionizing radiation incurred negative PDs; the electrode under γ-rays showed a potential less noble than the unirradiated one. In the case of O 2 -purging, it was proved that the absolute value of PD was not as large as other examinations, and that a slightly negative PD value (−40 mV) remained even after a suspension of exposure. The experiments with variable loads between electrodes revealed that in the solution with N 2 O the PD decreased with a much shallower gradient with an increase in current than in the solution with Ar and CO 2 .