Kenkichi Ishigure

Pulse radiolysis study of concentrated sulfuric acid solutions. Formation mechanism, yield and reactivity of sulfate radicals

In the pulse radiolysis of concentrated sulfuric acid solutions, the absorption spectrum and the molar absorption coefficient (1600 dm3 mol–1 cm–1) of the sulfate radical are unchanged up to 10 mol dm–3 H2SO4, suggesting that the sulfate radical exists in the dissociated form (SO–4). Two formation processes for the sulfate radical have been directly demonstrated in sulfuric acid and hydrogensulfate solutions: a fast one completed in the duration of the electron pulse, and a slow one occurring over a microsecond time range. For sulfate solutions only the fast formation process is observed. In sulfuric acid solutions the slow formation process is OH + HSO–4→ H2O + SO–4(4.7 × 105 dm3 mol–1 s–1) and OH + H2SO4→ HSO4+ H2O → SO–4+ H3O+(1.4 × 107 dm3 mol–1 s–1), and the fast formation process is the direct action of radiation on sulfuric acid with a G value of (2.7 ± 0.4)× 10–2 molecule eV–1. The yields of (OH + SO–4) and H can be quantified as: G(OH + SO–4)= 2.9fw+ 2.7fs and G(H)= 3.7fw+ 2.7fs. The yields of SO–4 have also been evaluated and the decay kinetics and reactions of the sulfate radical studied.

Preparation and characterization of natural lower dimensional layered perovskite-type compounds

Abstract Thin films of layered perovskite compounds (CnH2n+1NH3)2(CH3NH3)m−1PbmBr3m+1 (m=1, 2 and 3) were prepared by the spin-coating method from their DMF (N,N-dimethylformamide) solutions. The control of the inorganic layer thickness in layered perovskites can be achieved by changing the ratio of the two amines (CnH2n+1NH3/CH3NH3). The layered perovskite films showed a strong, clear exciton absorption peak at room temperature due to their large exciton binding energy. With increasing numbers of inorganic layers, a red shift of the exciton absorption was observed due to the decrease in transfer energy. X-ray diffraction patterns clearly demonstrated that the spin-coated film was highly oriented normal to the surface, which is consistent with ‘mono’, ‘bi’, and ‘tri’ layer structures, respectively. The effect of the alkyl chain length of the organic part was also investigated.

Thermal decomposition of hydrogen peroxide and its effect on reactor water monitoring of boiling water reactors

AbstractThe thermal decomposition rate of hydrogen peroxide (H2O2) was measured in the aqueous phase at an elevated temperature. It was shown that the reaction follows first-order kinetics, and the...

Effects of structural defects on hole drift mobility in aryl-substituted polysilanes

Abstract The effects of a silicon-based structural defect on the hole transport properties of poly(methylphenylsilane) were studied by the DC time-of-flight technique. The defect was chemically introduced as silicon branching of the silicon backbone by copolymerizing methylphenyldichlorosilane and p-tolyltrichlorosilane with sodium. A good empirical relation was obtained between the hole drift mobility (μ E−0) at a zero electric field limit and the defect density. The value of μ E−0 decreased exponentially from 4 × 10−4 to 5 × 10−6cm2 V1 s−1 with an exponential increase in defect density from 0.0024 to 0.18. On the basis of Basslers disorder formalism, hole transport in the polymers was quantitatively analysed, revealing the different contributions of diagonal and off-diagonal disorder with the defect density. The degree of fluctuation in the density of state mainly determined the hole drift mobility in specimens with fewer defects, while intersite hopping distance controlled the mobility in the polymers...

γ-Radiolysis study of concentrated nitric acid solutions

The formation of nitrous acid has been studied in the 60Co-γ radiolysis of concentrated nitric acid solutions. The yields of nitrous acid are proportional to the electron fraction of nitric acid, on the basis of which, an additional reaction path, NO–3 [graphic omitted]→ O(3P)+ NO–2 with a primary yield of 0.16 µmol J–1, has been verified for the direct action of radiation on nitric acid.

Radiolysis of water at elevated temperatures—III. Simulation of radiolytic products at 25 and 250°C under the irradiation with γ-rays and fast neutrons

Abstract The G-values of water decomposition products under the irradiations with γ-rays and fast neutrons up to 250°C have been determined in previous studies. In order to clarify the characteristics of the determined G-values, computer simulations under the simplified conditions in nuclear reactors have been carried out. The recent G-values for γ-radiolysis reported by Elliot, Chenier and Quellete [(1990) Can. J. Chem. 68, 712; (1993) J. Chem. Soc. Faraday Trans. 89, 1193], Kent and Sims [(1992) Water Chemistry of Nuclear Reactor Systems 6, p. 153. BNES, London], and Sunaryo, Katsumura, Shirai, Hiroishi and Ishigure [(1994) Radiat. Phys. Chem. 44, 273] and Sunaryo, Katsumura, Hiroishi and Ishigure [(1995) Radiat. Phys. Chem. 45, 131] are almost equivalent from the point of simulations. On the contrary, G-values for fast neutron radiolysis give a significant influence to the result, which arises from the higher molecular yields and smaller radical yields of water decomposition in fast neutron radiolysis, and it has been revealed that the dose evaluation in the reactor is inevitably important. In addition, it was pointed out by the simulations that reverse reactions for H2+.OH→.H+H2O and eaq−+H+→.H, be neglected at room temperature, become important at higher temperatures.

Degradation of polypropylene under gamma irradiation: protection effect of additives

Abstract The protection mechanism of antioxidants and an antirad agent dissolved in isotactic polypropylene (PP) irradiated under practical conditions has been investigated by the analysis of gas products and the measurement of mechanical properties. In vacuum radiolysis, protection operating through energy and charge-transfer processes, as observed in the model alkane liquids previously reported, results in the reduction of H2 evolution, in proportion to the number of benzene rings in the additive, and retardation of the film deterioration. Under oxygen atmosphere, G-values of more than 50 for oxygen uptake were measured in pure PP, which is attributable to a chain reaction. Although the uptake was significantly reduced by the addition of additives, the uptake recovered quickly after the consumption of additives at higher doses. In addition, it was found that the reduction of H2 evolution in the presence of additives decreases to nil under severe oxidation. The mechanism of the degradation of PP and the protection by additives is discussed by comparison with the results previously obtained in the model experiment by using liquid alkanes.

Effects of Hydrogen Peroxide on Intergranular Stress Corrosion Cracking of Stainless Steel in High Temperature Water, (IV) Effects of Oxide Film on Electrochemical Corrosion Potential

In order to determine the effects of hydrogen peroxide on electrochemical corrosion potential (ECP) of type 304 stainless steel (SUS304), ECPs were measured using a high temperature, high pressure water loop with polytetrafluoroethylene (PTFE) inner liner at controlled hydrogen peroxide concentration. It is observed that the ECP of SUS304 exposed to hydrogen peroxide is higher than that when exposed to oxygen at the same oxidant concentration. The ECP shows a hysteresis pattern for its concentration dependency. Those results were attributed mainly from the chemical form of oxide film on stainless steel specimens. The oxide film was affected by the corrosive circumstances. Hematite (α-Fe2 O3) was observed for the specimens exposed to hydrogen peroxide, while Fe3O4 was a main oxide when exposed to oxygen. The difference of the anodic polarization curves between O2 and H2O2 environments was caused by the difference of the stability between α-Fe2O3 and Fe3O4. Since the α-Fe2O3 is reduced to the Fe2+ when hydrogen is added to water, the ECP decreases with decreasing oxidant concentration without showing the hysteresis that keep the ECP higher value.

Effect of Gamma Radiation on the Release of Corrosion Products from Carbon Steel and Stainless Steel in High Temperature Water

The effect of gamma irradiation on the release of the soluble and insoluble corrosion products was investigated with carbon steel and austenitic Type 304 stainless steel at high temperature using a small experimental loop. It was found that gamma radiation enhances the release rates of insoluble corrosion products (crud) but does not enhance the release rates of soluble species under the experimental conditions. On the basis of the result, it was considered that the crud forms in the bulk water through the oxidation of ferrous ion by oxygen or radiolysis products.

Effects of Hydrogen Peroxide on Intergranular Stress Corrosion Cracking of Stainless Steel in High Temperature Water, (III): Crack Growth Rates in Corrosive Environment Determined by Hydrogen Peroxide

The stress corrosion cracking (SCC) of structural materials used in boiling water reactors has been studied at relatively low hydrogen peroxide (H2O2) concentrations, around lOppb, which was assumed to be representative of the corrosion environment formed in hydrogen water chemistry (HWC). The 1/4T compact tension specimen was used for measurement of crack growth rates (CGRs) of sensitized type 304 stainless steel in high temperature and high purity water. Crack length was monitored by a reversing direct current potential drop method. Since H2O2 is easily decomposed thermally, a polytetrafluoroethylene-lined autoclave was used to minimize its decomposition on the autoclave surface. The CGR in the H2O2 environment differed from that in the O2 environment even though the electrochemical corrosion potential (ECP) for both conditions was the same. The data implied that the ECP could not be used as a common environmental deterministic parameter for SCC behavior at higher potentials for different oxidant conditions. The corrosion current density was found to play an important role as an environmental index for SCC, which was given as just the current density at the ECP at a specific oxidant concentration. The CGRs were found to be written as CGR = (3.8±0.6)xl0-3 icor +(l-5±1.6) x 10-8mm/s using the calculated corrosion current density icorbelow 10-4 A-cm-2.