Fast dynamics of H2O in hydrous aluminosilicate glasses studied with quasielastic neutron scattering
Fast dynamics of H2O in hydrous aluminosilicate glasses studied with quasielastic neutron scattering
复制标题
用准弹性中子散射研究水合铝硅酸盐玻璃中 H2O 的快速动力学
DOI：
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
B. Frick
中科院分区：
文献类型：
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作者：
S. Indris;P. Heitjans;H. Behrens;R. Zorn;B. Frick
We studied the dynamics of dissolved water in aluminosilicate glasses with the compositions ${mathrm{NaAlSi}}_{3}{mathrm{O}}_{8}ifmmodecdotelse extperiodcenteredfi{}0.3{mathrm{H}}_{2}mathrm{O}$, ${mathrm{NaAlSi}}_{3}{mathrm{O}}_{8}ifmmodecdotelse extperiodcenteredfi{}1.3{mathrm{H}}_{2}mathrm{O}$ and ${mathrm{Ca}}_{0.5}{mathrm{AlSi}}_{3}{mathrm{O}}_{8}ifmmodecdotelse extperiodcenteredfi{}1.3{mathrm{H}}_{2}mathrm{O}$ using quasielastic neutron scattering. As shown by near-infrared spectroscopy on these samples, ${mathrm{H}}_{2}mathrm{O}$ molecules are the predominant hydrous species in the water-rich glasses whereas $mathrm{OH}$ groups bound to tetrahedrally coordinated cations are predominant at low water contents. Backscattering and time-of-flight methods were combined to investigate motional correlation times in the range between $0.2phantom{
ule{0.3em}{0ex}}mathrm{ps}$ and $2phantom{
ule{0.3em}{0ex}}mathrm{ns}$. For the water-rich glasses an elastic scan between $2phantom{
ule{0.3em}{0ex}}mathrm{K}$ and $420phantom{
ule{0.3em}{0ex}}mathrm{K}$ shows that the dynamical processes set in at lower temperatures in the $mathrm{Ca}$-bearing glass than in the $mathrm{Na}$-bearing glass. This is corroborated by the broadening of the inelastic spectra $S(Q,ensuremath{omega})$. The shape of the scattering function $S(Q,t)$ suggests a distribution of activation barriers for the motion of hydrous species in the disordered structure of the glass. The distribution is narrower and the average activation energy is smaller in the $mathrm{Ca}$-bearing glass than in the $mathrm{Na}$-bearing glass. No indication for dynamics of hydrous species was found at temperatures up to $520phantom{
ule{0.3em}{0ex}}mathrm{K}$ in the water-poor glass ${mathrm{NaAlSi}}_{3}{mathrm{O}}_{8}ifmmodecdotelse extperiodcenteredfi{}0.3{mathrm{H}}_{2}mathrm{O}$ containing dissolved water mainly in the form of $mathrm{OH}$ groups. It is concluded that ${mathrm{H}}_{2}mathrm{O}$ molecules are the dynamic species in the above-mentioned time regime in the water-rich glasses. The dynamic process is probably a rotation of ${mathrm{H}}_{2}mathrm{O}$ molecules around their bisector axis.
We studied the dynamics of dissolved water in aluminosilicate glasses with the compositions ${mathrm{NaAlSi}}_{3}{mathrm{O}}_{8}ifmmodecdotelse extperiodcenteredfi{}0.3{mathrm{H}}_{2}mathrm{O}$, ${mathrm{NaAlSi}}_{3}{mathrm{O}}_{8}ifmmodecdotelse extperiodcenteredfi{}1.3{mathrm{H}}_{2}mathrm{O}$ and ${mathrm{Ca}}_{0.5}{mathrm{AlSi}}_{3}{mathrm{O}}_{8}ifmmodecdotelse extperiodcenteredfi{}1.3{mathrm{H}}_{2}mathrm{O}$ using quasielastic neutron scattering. As shown by near-infrared spectroscopy on these samples, ${mathrm{H}}_{2}mathrm{O}$ molecules are the predominant hydrous species in the water-rich glasses whereas $mathrm{OH}$ groups bound to tetrahedrally coordinated cations are predominant at low water contents. Backscattering and time-of-flight methods were combined to investigate motional correlation times in the range between $0.2phantom{
ule{0.3em}{0ex}}mathrm{ps}$ and $2phantom{
ule{0.3em}{0ex}}mathrm{ns}$. For the water-rich glasses an elastic scan between $2phantom{
ule{0.3em}{0ex}}mathrm{K}$ and $420phantom{
ule{0.3em}{0ex}}mathrm{K}$ shows that the dynamical processes set in at lower temperatures in the $mathrm{Ca}$-bearing glass than in the $mathrm{Na}$-bearing glass. This is corroborated by the broadening of the inelastic spectra $S(Q,ensuremath{omega})$. The shape of the scattering function $S(Q,t)$ suggests a distribution of activation barriers for the motion of hydrous species in the disordered structure of the glass. The distribution is narrower and the average activation energy is smaller in the $mathrm{Ca}$-bearing glass than in the $mathrm{Na}$-bearing glass. No indication for dynamics of hydrous species was found at temperatures up to $520phantom{
ule{0.3em}{0ex}}mathrm{K}$ in the water-poor glass ${mathrm{NaAlSi}}_{3}{mathrm{O}}_{8}ifmmodecdotelse extperiodcenteredfi{}0.3{mathrm{H}}_{2}mathrm{O}$ containing dissolved water mainly in the form of $mathrm{OH}$ groups. It is concluded that ${mathrm{H}}_{2}mathrm{O}$ molecules are the dynamic species in the above-mentioned time regime in the water-rich glasses. The dynamic process is probably a rotation of ${mathrm{H}}_{2}mathrm{O}$ molecules around their bisector axis.