Yoshimasa Takashima

Mössbauer spectroscopic study of the formation of non-bridging oxygen in the potassium borate glasses

Abstract Mossbauer spectroscopic study was performed to investigate the formation of non-bridging oxygen in the potassium borate glasses denoted by the formula of x K 2 O(100 − x ) B 2 O 3 · 7 Fe 2 O 3 (0 ⩽ x ⩽ 40 mol%). In the range of alkali content higher than 20 mol%, the quadrupole splitting for Fe 3+ decreased continuously with the concentration of the alkali oxide in the glass, showing the increase of the symmetry around the Fe 3+ ions. The isomer shift value also decreased in almost the same x region. The drastic decrease of Mossbauer parameters was attributed to the formation of non-bridging oxygen at the adjacent site of the Fe 3+ ions. In the region of lower alkali content (less than 10 mol%), Mossbauer spectra only showed the absorption due to α-Fe 2 O 3 . X-ray powder diffraction patterns also displayed the existence of α-Fe 2 O 3 , together with the microcrystal of potassium borate.

Mössbauer and ESR studies of non-bridging oxygens in potassium phosphate glasses

Abstract Mossbauer spectroscopic study was performed to investigate the behavior of non-bridging oxygens in the potassium phosphate glasses denoted by a formula of x K 2 O(100− x )P 2 O 5 7 Fe 2 O 3 . The quadrupole splitting values for Fe 2+ and Fe 3+ ions decreased continuously with the alkali content of the glasses in the alkali region of 0–30 mol.%, and increased in the higher alkali region. On the other hand, the Mossbauer absorption area for Fe 2+ increased continuously in the same alkali region ( x = 0–30 mol.%), and then decreased in the higher alkali region. The continuous decrease of the quadrupole splitting, i.e., the increase of the symmetry around the iron and the increase of the absorption area for the Fe 2+ ions are discussed in connection with the increase of non-bridging oxygens at site adjacent to the iron. ESR measurements for the γ-ray irradiated potassium phosphate glasses free from iron were also carried out to confirm the formation of the non-bridging oxygens in the glasses by observing PO 4 2− radicals produced by γ-ray irradiations. We conclude that the ESR absorption intensity for the PO 4 2− radicals linearly increases with the alkali content of the glasses, which was ascribed to the linear increase of non-bridging oxygens in the PO 4 tetrahedra.

Mössbauer study of the fraction of non-bridging oxygens in potassium borate glasses☆

Abstract A Mossbauer study was performed to find the fraction of non-bridging oxygens in potassium borate glasses containing a small amount of iron. The borate glasses with alkali contents of 15, 20, 25, 30 and 40 mol% were irradiated with 60 Co-γ rays at room temperature in a nitrogen atmosphere. The Mossbauer absorption area for the irradiation-induced Fe 2+ increased with the total γ-ray dose in the range of 1 × 10 6 −2 × 10 8 R, and became constant after irradiation ranging from 2 × 10 8 R − 1 × 10 9 R. The absorption area for the Fe 2+ at the saturated region was correlated with the difference in the glass structure, i.e., the fraction of the non-bridging oxygens was estimated from the increased absorption area for the Fe 2+ as a function of the alkali content of the glasses. The fraction of the non-bridging oxygen increased with the alkali content of the glasses in the alkali region above 20 mol%, and about 14% of the fraction was obtained for an alkali content of 40 mol%.

Mössbauer spectroscopic study of potassium borate glasses at low temperatures

Abstract Mossbauer studies of potassium borate glasses containing a small amount of iron were performed at dry ice and liquid nitrogen temperatures in order to investigate the physical properties of non-bridging oxygens in the glasses. The Mossbauer spectra at the temperature of dry ice were almost the same as those at room temperature. On the other hand, the spectra at the temperature of liquid nitrogen consisted of quadrupole doublet and hyperfine structure due to Fe 3+ ions with tetrahedral symmetry. Magnetic suceptibility measurements revealed that the hyperfine structure was observed because of a paramagnetic relaxation effect. Isomer shift values for both the quadrupole doublet and the hyperfine structure were constant in the alkali region below 20 mol.%, and continuously decreased when the alkali content of the glasses was in the region ⩾ 20 mol.%. The absorption areas for the hyperfine structure were also constant in the alkali region below 20 mol.%, and linearly decreased with alkali content in the region ⩾ 20 mol.%. The internal magnetic field for the hyperfine structure also showed the same tendency as the absorption area. These results were attributed to the formation of non-bridging oxygen at the site adjacent to the iron, and the decrease of the absorption area for the hyperfine structure seemed to be directly related to the fraction of non-bridging oxygen in the oxygens constituting FeO 4 tetrahedra.

Mössbauer studies of FeNiP and related compounds

Abstract Phosphides of the type FeMeP, where Me is a transition metal, have been studied by Mossbauer spectroscopy. This work is mainly concerned with the site preference of metal atoms in many ternary systems in which Me is Ni, Co, Mn, Cr, Zr, Nb and Ta. Iron atoms in alloys FeMnP, FeCrP, FeNbP, FeTaP and FeZrP occupy the smaller lattice position exclusively. Iron atoms in FeCoP are randomly distributed among the available sites. A temperature dependence of site preference in the disordered system, (Fe, Ni) 2 P, was not observed.

Correlation between the structure and glass transition temperature of potassium, magnesium and barium tellurite glasses

The Mössbauer spectrum of tellurite glasses, containing 5 mol% Fe2O3 as a probe, consists of a paramagnetic quadrupole doublet with an isomer shift of 0.39 ± 0.01 mmsec−1. This indicates that Fe3+ ions are present at substitutional sites of Te4+ ions constituting distorted TeO4 trigonal bipyramids, each of which has one oxygen vacancy at an equatorial site. On increasing the K2O content from O to 35 mol%, the quadrupole splitting (Λ) for potassium tellurite glasses decreases continuously from 0.76 to 0.44 mm sec−1. On the other hand, Λ for magnesium and barium tellurite glasses increases with increasing MgO and BaO content, respectively. When the alkali or alkaline earth oxide contents are the same as each other, Λ increases in proportion to the ionic potential (Z/r) of the alkali or alkaline earth metal ion. These results suggest that the glass matrices of alkaliv and alkaline earth tellurite glasses are continuously changed into a chain and a three-dimensional network structure, respectively. Differential thermal analysis studies reveal that there exists a linear relationship between the glass transition temperatureTg and the quadrupole splitting, indicating thatTg is primarily determined by the magnitude of the distortion of TeO4 trigonal bipyramids. This relationship is also applicable to several oxide glasses.

Mössbauer spectroscopic study of gamma-ray irradiated potassium phosphate glasses

Abstract A Mossbauer spectroscopic study was performed to investigate the effect of γ-ray irradiation on the formation of non-bridging oxygens in the potassium phosphate glasses denoted by the formula x K 2 O · (100 − x )P 2 O 5 · 7 Fe 2 O 3 (0 ⩽ x ⩽ 50 mol.%). Mossbauer spectra for these glass samples consisted of two kinds of doublets due to Fe 2+ and Fe 3+ ions of octahedral symmetries. Only small changes occurred in the Mossbauer parameters as a result of irradiation at room temperature in a dry nitrogen atmosphere, except for the decrease in the absorption area for the Fe 2+ ions. The decrease in the absorption area was attributed to the electron transfer from the Fe 2+ ions to the neighboring oxygens. Thermal annealing experiments for a few non-irradiated glass samples indicated that the decrease in the absorption area was confirmed to be due to γ-rays rather than heating during the irradiation.

Tritium in pine needles and its significant sources in the environment

Abstract Tissue-free water tritium (TFWT) and tissue-bound tritium (TBT) were analyzed in pine needles collected at 21 locations of the general environment in Japan. The TFWT was recovered by freeze-drying and the TBT was obtained in the form of water by combustion of dried samples. Tritium was measured by liquid scintillation counting. The concentrations of TFWT were comparable with those in natural waters in Japan. The concentration of TBT, however, was higher than that of TFWT. This excess TBT may be attributed to direct assimilation of HT that is present in the atmosphere with extremely high specific activity.

Determination of chromium(vi) in natural waters by the sorption of chromium-diphenylcarbazone with xad-2 resin.

The sorption of the chromium(III)-diphenylcarbazone complex (Cr-DPC) with XAD-2 has been investigated, for use in the separation of Cr(VI) from Cr(III) species in natural waters. Cr-DPC is formed from the reaction of Cr(VI) with diphenylcarbazide, but Cr(III) species give no reaction in aqueous solution. The addition of sodium chloride or sodium beta-naphthalenesulphonate markedly enhances the sorption. The Cr-DPC sorbed on XAD-2 can be almost completely eluted with organic solvents, especially methanol, but about 5% of it is irreversibly sorbed and cannot be eluted. The excess of diphenylcarbazide and some of the organic matter in natural waters are also sorbed on XAD-2 but most of this can also be eluted with methanol. Organic matter which interferes with measurement of the absorbance of Cr-DPC can almost all be removed by extraction with chloroform. By use of these techniques, Cr(VI) in sea-water has been determined by the standard-addition method. Although about 50 litres of sea-water are necessary for the analysis, organic and colloidal Cr(III) species do not interfere.

Annealing of fission tracks in zircons

Abstract Etching conditions and thermal annealing effects have been studied for fission tracks in four kinds of zircons. The observation of fission tracks under an optical microscope was made with respect to the mean pit length as well as the mean pit density. Apparent rate constants were obtained by substituting the isochronal (60 minutes) annealing data into the ordinary equation of the rate constant. The order of reaction (almost 3rd or 4th) and the activation energy (1.7–2.9 eV) of annealing were determined from the Arrhenius plot of the apparent rate constants.