Relations between the anionic structure and viscosity of silicate melts; a Raman spectroscopic study
Relations between the anionic structure and viscosity of silicate melts; a Raman spectroscopic study
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发表时间：
1980-08
影响因子：
3.1
通讯作者：
B. O. Mysen;D. Virgo;C. Scarfe
中科院分区：
文献类型：
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作者：
B. O. Mysen;D. Virgo;C. Scarfe
Raman spectroscopy of quenched silicate melts has been used to determine their anionic structure as a function of bulk composition and pressure. The structural results have been integrated with published data on physical and chemical properties of the melts. The structure of silicate melts on the joins NarO-SiOr, CaO-SiO2, CaO-MgO-SiO2, and probably other analogous binary joins, can b€ described in terms of anionic structural units ih"t, oo the average, have NBO/Si : 4, 3, 2, l, and 0 (NBO/Si: nonbridging oxygens per silicon). Distinct compositional regions involving only three of these structural units have been delineated. These compositional ranges (0--20, -20-50, and >50 moleVo metal oxide) coincide with compositional ranges defined by thermal expansivity data and data on the activation energy of viscous flow. Melts on the join NaAlOr-SiO, have a three-dimensional array of SiOo and AlOo tetra-hedra. Two three-dimensional units, which di-ffer in Si/(Si + Al), coexist' Both structural units become more aluminous as the bulk Si/(Si + Al) of the system decreases. The structure of these melts remains essentially unaffected as the pressure is increased to 38 kbar. At I atm, the viscosity of melts on this join decreases with increasing NaAlOz/SiOr. This decrease is related to the increased proportion of weaker Al-O relative to Si-O bonds in the three-dimensional structure. The decrease of the melt viscosity with increasing pressure is related to an increase in the number of nearest oxygen neighbors around the metal cations' We suggest that each Al-O bond in the structure is weakened as the result of this process, which results in the lowering of the melt viscosity. The Raman spectra of melts in the system NarO-AlzOr-SiO, with AllNa > I indicate that nonbridging oxygens are present in the melts. Some aluminum is, therefore, no longer in tet-rahedraicolrdination in the melt. This structural change is responsible for the observed decrease in viscosity and activation energy of viscous flow as Al/Na is increased above l.
