Yoshiaki Tsunawaki

Analysis of CaOSiO2 and CaOSiO2CaF2 glasses by Raman spectroscopy

Abstract Raman spectra of CaOSiO2 and CaOSiO2CaF2 glasses were measured to analyze three states of oxygen, i.e. bridging, non-bridging and free oxygen, in a similar way to the previous work on PbOSiO2 glasses. The stretching vibrational modes of the SiO bond in CaOSiO2 and CaOSiO2CaF2 glasses corresponded to the bands at 880, 920, 975 and 1050 cm−1. It is suggested from the comparison of the Raman spectra of the glasses with the Raman and infrared absorption spectra of crystalline silicates that these bands would arise from the SiO4 tetrahedron with four, three, two and one non-bridging oxygens, respectively. The fractions of bridging, non-bridging and free oxygens were calculated from the intensities of the four Raman bands and the composition of the glasses. They were in agreement with those obtained from the thermodynamical model for the CaOSiO2 glasses. When the content of CaF2 was smaller than 15–20 mol.% and the CaO SiO 2 ratio was smaller than unity, CaF2 contributed to the breakage of some SiO bonds.

Investigation of calcium-iron-silicate glasses by the Mössbauer method

Abstract The oxidation-reduction and coordination of iron atoms in calciumsilicate glasses has been studied as functions of the basic oxide content and partial oxygen pressure on the basis of Mossbauer spectra. It was found that the equilibrium concentration ratio NFe3+/NFe2+ increased as the CaO content or partial oxygen pressure increased. The coordination behavior of iron atoms was complicated. In the glasses containing a large amount of Fe2O3, the Fe2+ ion was always present in the octahedral site, while the Fe3+ ion showed amphoteric behaviour. The ratio in number of tetrahedrally coordinated to octahedrally coordinated ferric ions did not exhibit any remarkable variation for larger partial oxygen pressures (1 and 0.21 atm), but increased slightly with the CaO/SiO2 ratio for the small oxygen pressure (3 × 10−7 atm). In the glasses containing a small amount of Fe2O3, the Fe2+ ion was present in both tetrahedral and octahedral sites. However, the coordination state of the Fe3+ ion was not sufficiently clear in such glasses.

Self-diffusion of lithium in molten LiBeF3 and Li2BeF4

The self-diffusion coefficients of lithium in molten Li2BeF4 and LiBeF3 have been measured by the capillary reservoir technique using 6Li as a tracer. The concentration profiles of 6Li in a capillary were measured by an ion micro-mass-analyser and the self-diffusion coefficients D were calculated. The results can be described using the Arrhenius equation, D= 9.27 × 10–7 exp [(–32.5 ± 8.4)× 103/RT] standard error: ± 1.1 × 10–9(Li2BeF4) and D= 1.12 × 10–6 exp [(–38.9 ± 12.5)× 103/RT] standard error: ± 4.3 × 10–10(LiBeF3), where D is expressed in m2 s–1, R in J mol–1 K–1 and T in K. The activation energy for diffusion of lithium is much smaller than that of fluorine and slightly larger than that for electrical conductivity. These results suggest that the movement of fluorine does not involve electric current transfer and the mobility of lithium ions is much larger than that of the fluoroberyllate ion.The self-diffusion coefficients of lithium in molten LiBeF3 are smaller than those in molten Li2BeF4. However, the activation energies are similar in molten Li2BeF4 and LiBeF3.

Self-diffusion of lithium, sodium, potassium and fluorine in a molten LiF + NaF + KF eutectic mixture

The self-diffusion coefficients of lithium, sodium, potassium and fluorine in a molten LiF + NaF + KF (46.5 + 11.5 + 42.0 mol%: FLINAK) eutectic mixture have been measured by the capillary reservoir technique using the tracers 6Li, 24Na, 42K and 18F. The observed self-diffusion coefficients D(in m2 s–1) are expressed according to the Arrhenius equation as follows: DLi= 3.87 × 10–7 exp [–(37.2 ± 4.2)× 103/RT](480–663 °C), DNa= 4.28 × 10–7 exp [–(36.2 ± 7.1)× 103/RT](504–616 °C), DK= 2.05 × 10–7 exp [–(32.0 ± 7.5)× 103/RT](491–613 °C) and DF= 1.77 × 10–7 exp [–(30.8 ± 6.7)× 103/RT](480–663 °C), where R is the gas constant (in J mol–1K–1) and T the absolute temperature (in K). The observed self-diffusion coefficients of the ions in molten FLINAK give very similar values to each other and smaller values than given in the literature for other molten salts. These results are explained in terms of the interaction between cations and anions and the volume change on fusion.