Ikuji Takagi

Solubility measurement of zirconium(IV) hydrous oxide

The solubility of zirconium(IV) hydrous oxide was measured in the hydrogen ion concentration (pHc) range from 1 to 13 at 25 °C. The experiment was carried out with I=0.1, 0.5 and 1.0 mol/dm3 (M) of NaClO4 solution. The concentration of Zr was measured by ICP-MS after separating the aqueous phase from the solid phase by ultrafiltration methods. Some differences between the obtained values and literature data were observed due to the size distribution of chemical species. In the lower pHc region, the size distribution of filtrate species was investigated by different pore-size filtration in the range of 3 k to 100 kDa NMWL (nominal molecular weight limit) membranes. The solubility values of mononuclear species were obtained by the Flory model, and by using the specific ion interaction theory (SIT) for ionic strength corrections and the known literature value of the hydrolysis constant β1°, the tentative value of the solubility product (Ksp°) was determined to be −56.94±0.32.

Solubility of Zirconium(IV) Hydrous Oxides

The solubility of zirconium(IV) hydroxide and oxide was measured in the acidic, neutral and alkaline pH at 25°C by an undersaturation method. No influence of the formation of polynuclear and colloidal species on the apparent solubility was observed in the case of the ZrO2. By using the solubility data of the ZrO2 and by considering the contributions of the mononuclear species, Zr4+, ZrOH3+ and Zr(OH)4(aq), to the solubility curve in the lower pH region, the solubility product was obtained to be log K°sp = --62.46 ± 0.10. In the case of the Zr(OH)4, no equilibrium was observed during the experimental period up to four months.

Hydrolysis Constant and Coordination Geometry of Zirconium(IV)

The solubility of zirconium was studied by comparing recent experimental data with predictions using an electrostatic hard sphere model. In the model, an antiprismatic structure was assumed for a mononuclear hydrolysis species of zirconium, and the formation of an oligomeric species such as Zr4(OH)8 8+ was considered by combining antiprismatic structure units, which was supported by the theoretical approach. By taking the known values of the solubility products, the hydrolysis constants of these mononuclear and polynuclear species were evaluated and were found to be consistent with the experimental solubility data of amorphous Zr(OH)4 and crystalline ZrO2.

Hydrolysis constants and complexation of Th(IV) with carboxylates

Abstract The hydrolysis constants of Th(IV) were determined using the solvent extraction method in a NaClO4 solution at I=0.1 and 25 °C. A trace amount of thorium below the solubility limit was used in order to avoid the formation of polynuclear species and colloids in the experiment. The values were compared with the literature data. Considering the effect of competitive hydrolysis reactions under weak acid conditions, the complexation constants of Th(IV) with a series of dicarboxylic acids containing different alkyl chain lengths were determined.

Systematics of Hydrolysis Constants of Tetravalent Actinide Ions

Systematic trends of mononuclear and polynuclear hydrolysis constants of tetravalent actinide ions were analyzed by using an electrostatic hard sphere model. The effective charges of actinide ions were introduced into the model by considering possible contributions of non-electrostatic interactions of actinide ions in addition to those of ordinary electrostatic ones. The systematic trends of hydrolysis constants were well fitted by the present model, and the parameter values such as the effective charges of actinide ions were determined. Some predictions were made and discussed in comparison with the solubility curves of tetravalent actinides.

Zirconium Solubility in Ternary Aqueous System of Zr(IV)-OH-Carboxylates

The solubility of zirconium(IV) hydroxide in the presence of oxalic and malonic acids was measured for a wide range of pH values and organic acid solutions prepared by the oversaturation method. In nearneutral pH solutions, the apparent solubility increased with the concentration of the organic acid due to the formation of soluble carboxylate complexes. On the other hand, under acidic conditions, a precipitate of carboxylate salts was formed and the solubility was controlled by the precipitate. The complex formation constants and solubility products of zirconium oxalate and malonate were obtained by analysis of the solubility results.

Experiment on atomic hydrogen reflection by use of a permeation probe

Experiments on reflection behavior of atomic hydrogen with lower energies were conducted by use of a palladium membrane as a probe for detecting atomic hydrogen. The palladium membrane was exposed to a deuterium rf-plasma, and reflectors were located between them. Hydrogen atoms easily permeated through palladium, which acted as a window for hydrogen atoms. By changing the arrangement of the reflectors of nickel, graphite, glass, tungsten and polytetrafluoroethylene, the corresponding permeation flux was observed, and from which the relative value of the incident atoms to the membrane was estimated. The incident atoms reflected at least once by nickel were nearly the same as those which were reflected more than twice. This indicated that an atomic reflection was very significant. The other reflector materials also showed high atomic reflection. These results may mean that atomic hydrogen is transported for a long distance in openings of structures in fusion devices.

Analysis of Sorption Behavior of Cesium Ion on Mineral Components of Granite

The influence of pH and ionic strength on the sorption of Cs by quartz, biotite, and microcline was investigated to understand the Cs sorption process onto the granite host rock. Cesium sorption by each mineral increased with increasing pH, and reached a constant value at high pH. The Cs sorption decreased in the presence of sodium perchlorate as a matrix ion, and the apparent Kd decreased with an increasing initial concentration of Cs. In the analysis, a two-site model either giving or not giving consideration to the presence of the triple layer was applied to the results of each mineral, and the model parameters were determined. By taking the obtained parameters, the model was used to predict the distribution coefficient Kd of cesium on granite. The simulated Kd values were discussed by comparing themselves with the reference ones for granite.

Production behavior of irradiation defects in vitreous silica under ion beam irradiation

Abstract The production behavior of irradiation defects in vitreous silica was studied by an in situ luminescence measurement technique under ion beam irradiation of H + and He + . No apparent difference was observed in the luminescence spectra of specimens of different OH contents. The temperature dependence of the luminescence intensity at 280 and 460 nm was measured, and analyzed by considering the production mechanisms and kinetics of the irradiation defects of oxygen deficiency centers.

Influence of hydrogen surface coverage on atomic particle reflection

Atomic reflection of deuterium on metal samples of nickel, palladium and type 304 stainless steel (SS-304) was observed by use of a permeation probe. The surface densities of deuterium on the sample materials, which were continuously irradiated by atomic deuterium particles, were measured by the nuclear reaction analysis (NRA). As a result, for each sample, the amount of reflected deuterium decreased with increasing the sample temperature and temperature dependence of the amount was very similar to that of the surface density of deuterium. This would be explained by the fact that atomic hydrogen is reflected as being atoms with a significant probability on hydrogen-covered surface but not reflected on hydrogen-free surface.