The solution behavior of H2O in peralkaline aluminosilicate melts at high pressure with implications for properties of hydrous melts

Details The solution behavior of H2O in peralkaline aluminosilicate melts at high pressure with implications for properties of hydrous melts The solution behavior of H2O in peralkaline aluminosilicate melts at high pressure with implications for properties of hydrous melts

Apr 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007gecoa..71.1820m&link_type=abstract

Geochimica et Cosmochimica Acta, Volume 71, Issue 7, p. 1820-1834.

Computer Science

4

Scientific paper

Solubility and solution mechanisms of H2O in depolymerized melts in the system Na2O Al2O3 SiO2 were deduced from spectroscopic data of glasses quenched from melts at 1100 °C at 0.8 2.0 GPa. Data were obtained along a join with fixed nominal NBO/T = 0.5 of the anhydrous materials [Na2Si4O9 Na2(NaAl)4O9] with Al/(Al+Si) = 0.00 0.25. The H2O solubility was fitted to the expression, XO=0.20+0.0020fO-0.7X+0.9(X), where XO is the mole fraction of H2O (calculated with O = 1), fO the fugacity of H2O, and XAl = Al/(Al+Si). Partial molar volume of H2O in the melts, VHOmelt¯, calculated from the H2O-solulbility data assuming ideal mixing of melt H2O solutions, is 12.5 cm3/mol for Al-free melts and decreases linearly to 8.9 cm3/mol for melts with Al/(Al+Si) ˜ 0.25. However, if recent suggestion that VHOmelt¯ is composition-independent is applied to constrain activity composition relations of the hydrous melts, the activity coefficient of H2O, γHOmelt, increases with Al/(Al+Si). Solution mechanisms of H2O were obtained by combining Raman and 29Si NMR spectroscopic data. Degree of melt depolymerization, NBO/T, increases with H2O content. The rate of NBO/T-change with H2O is negatively correlated with H2O and positively correlated with Al/(Al+Si). The main depolymerization reaction involves breakage of oxygen bridges in Q4-species to form Q2 species. Steric hindrance appears to restrict bonding of H+ with nonbridging oxygen in Q3 species. The presence of Al3+ does not affect the water solution mechanisms significantly.

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