TY - JOUR

T1 - Transition elements in water-bearing silicate glasses/melts. Part II. Ni in water-bearing glasses

AU - Farges, François

AU - Munoz, Manuel

AU - Siewert, Ralf

AU - Malavergne, Valérie

AU - Brown, Gordon E.

AU - Behrens, Harald

AU - Nowak, Marcus

AU - Petit, Pierre Emmanuel

N1 - Funding Information: The authors thank A. Manceau (CNRS, Grenoble, France) for donating the nepouite sample, F. Martin (Toulouse 3) for donating the Ni-talc XAFS spectrum, B. Reynard (ENS Lyon, France) and S. Rossano (LMCP, Paris 7, now at Marne la Vallée) for their help with Raman scattering and ultraviolet-Vis-NIR data collection, G. Calas and L. Galoisy (LMCP, Paris, France) for fruitful discussions, Max Wilke (formerly at Universität Hannover, now at Universität Potsdam, Germany) for the synthesis of the hydrous NS3 glass with 2 wt.% Ni. The paper benefited from constructive reviews from C.M.B. Henderson (University of Manchester, UK) and B. Mysen (Geophysical Laboratory). This work was supported by the EEC TMR network “In-situ properties of water in silicates melts” (http://www.inhydromel.net) (FF, RS, VM) and by National Science Foundation Grant EAR-9725899 (G.E.B.). The Stanford Synchrotron Radiation Laboratory is supported by the Department of Energy, Office of Basic Energy Sciences, and National Institutes of Health, Biotechnology Resource Program, Division of Research Resources.

PY - 2001/5/15

Y1 - 2001/5/15

N2 - The local coordination environment around Ni(II) in a series of sodium trisilicate (NS3) and albitic (ALB) glasses has been evaluated by using high-resolution XANES and anharmonic EXAFS spectroscopies. The glasses contain e1 1000 to 4000 ppm of Ni and from 0 to 8.2 wt.% water. They were synthesized at pressures between 2.2 and 5 kbars and temperatures between 1050 and 1350. K. The bulk glasses were characterized by using X-ray diffraction, transmission electron microscopy. Raman, and ultraviolet-Vis-NIR spectroscopies. Both hydrous NS3 and ALB glasses show dominant amounts of Ni(II) in relatively regular 6-coordinated environments, in contrast with their anhydrous counterparts, where 5-coordinated Ni dominates. There are also significant differences in the average medium-range environment (2-3.5 Å) around Ni between the anhydrous and hydrous glasses. In the ALB glasses, the pressence of water in amounts > 2 wt.% induces the formation of nanocrystallites, with an average diameter of e140 Å and an atomic arrangement similar to that of nepouite ([6]Ni3Si2O5(OH)4) or Ni-talc nanophases are difficult to detect by using conventional characterization methods and can cause misleading interpretations of the glass structure if not detected. In contrast, there is no evidence for Ni-rich, nanocrystalline domains in NS3 glasses containing high water contents (up to 8.2 wt.%); instead, two to three Si second neighbors are observed around Ni in all NS3 glasses (and in ALB glasses with water contents <4 wt.%). The bonding of Ni to oxygens in the tetrahedral framework is inconsistent with the presence of large amounts of Ni(H2O)26+ complexes in these glasses. However, Ni(II) may form Ni(OH)n O(4 + n) 6 -n - (n ~ 6) complexes in hydrous glasses. Our results for Ni combined with results from other studies of 3-d divalent transition metal cations in hydrous silicate glasses suggest that water in silicate melts helps these cations form their preferred coordination environment [6-coordinated for Mn(II), Fe(11), and Ni(II), Ni(II) may occur in natural hydrous silicate melts dominantly in 6-coordinated environments, rather than dominantly in 4-coordinated environments, as in anhydrous melts and supercritical aqueous fluids, explaining the compatible behavior of Ni in magmas. However, in situ experiments are required to test this suggestion.

AB - The local coordination environment around Ni(II) in a series of sodium trisilicate (NS3) and albitic (ALB) glasses has been evaluated by using high-resolution XANES and anharmonic EXAFS spectroscopies. The glasses contain e1 1000 to 4000 ppm of Ni and from 0 to 8.2 wt.% water. They were synthesized at pressures between 2.2 and 5 kbars and temperatures between 1050 and 1350. K. The bulk glasses were characterized by using X-ray diffraction, transmission electron microscopy. Raman, and ultraviolet-Vis-NIR spectroscopies. Both hydrous NS3 and ALB glasses show dominant amounts of Ni(II) in relatively regular 6-coordinated environments, in contrast with their anhydrous counterparts, where 5-coordinated Ni dominates. There are also significant differences in the average medium-range environment (2-3.5 Å) around Ni between the anhydrous and hydrous glasses. In the ALB glasses, the pressence of water in amounts > 2 wt.% induces the formation of nanocrystallites, with an average diameter of e140 Å and an atomic arrangement similar to that of nepouite ([6]Ni3Si2O5(OH)4) or Ni-talc nanophases are difficult to detect by using conventional characterization methods and can cause misleading interpretations of the glass structure if not detected. In contrast, there is no evidence for Ni-rich, nanocrystalline domains in NS3 glasses containing high water contents (up to 8.2 wt.%); instead, two to three Si second neighbors are observed around Ni in all NS3 glasses (and in ALB glasses with water contents <4 wt.%). The bonding of Ni to oxygens in the tetrahedral framework is inconsistent with the presence of large amounts of Ni(H2O)26+ complexes in these glasses. However, Ni(II) may form Ni(OH)n O(4 + n) 6 -n - (n ~ 6) complexes in hydrous glasses. Our results for Ni combined with results from other studies of 3-d divalent transition metal cations in hydrous silicate glasses suggest that water in silicate melts helps these cations form their preferred coordination environment [6-coordinated for Mn(II), Fe(11), and Ni(II), Ni(II) may occur in natural hydrous silicate melts dominantly in 6-coordinated environments, rather than dominantly in 4-coordinated environments, as in anhydrous melts and supercritical aqueous fluids, explaining the compatible behavior of Ni in magmas. However, in situ experiments are required to test this suggestion.

UR - http://www.scopus.com/inward/record.url?scp=0034997080&partnerID=8YFLogxK

U2 - 10.1016/S0016-7037(00)00624-4

DO - 10.1016/S0016-7037(00)00624-4

M3 - Article

AN - SCOPUS:0034997080

VL - 65

SP - 1679

EP - 1693

JO - Geochimica et cosmochimica acta

JF - Geochimica et cosmochimica acta

SN - 0016-7037

IS - 10

ER -