Other
Scientific paper
Nov 1985
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985gecoa..49.2289d&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 49, Issue 11, pp.2289-2296
Other
16
Scientific paper
The solubility of rutile has been determined in a series of compositions in the K 2 O-Al 2 O 3 -SiO 2 system ( K * = K 2 O /( K 2 O + Al 2 O 3 ) = 0.38-0.90), and the CaO-Al 2 O 3 -SiO 2 system ( C * = CaO /( CaO + Al 2 O 3 ) = 0.47-0.59). Isothermal results in the KAS system at 1325°C, 1400°C, and 1475°C show rutile solubility to be a strong function of the K * ratio. For example, at 1475°C the amount of TiO 2 required for rutile saturation varies from 9.5 wt% ( K * = 0.38) to 11.5 wt% ( K * = 0.48) to 41.2 wt% ( K * = 0.90). In the CAS system at 1475°C, rutile solubility is not a strong function of C * . The amount of TiO 2 required for saturation varies from 14 wt% ( C * = 0.48) to 16.2 wt% ( C * = 0.59). The solubility changes in KAS melts are interpreted to be due to the formation of strong complexes between Ti and K + in excess of that needed to charge balance Al 3+ . The suggested stoichiometry of this complex is K 2 Ti 2 O 5 or K 2 Ti 3 O 7 . In CAS melts, the data suggest that Ca 2+ in excess of A1 3+ is not as effective at complexing with Ti as is K + . The greater solubility of rutile in CAS melts when C * is less than 0.54 compared to KAS melts of equal K * ratio results primarily from competition between Ti and Al for complexing cations (Ca vs . K). TiK x-ray emission spectra of KAS glasses ( K * = 0.43-0.60) with 7 mole% added TiO 2 , rutile, and Ba 2 TiO 4 , demonstrate that the average Ti-O bond length in these glasses is equal to that of rutile rather than Ba 2 TiO 4 , implying that Ti in these compositions is 6-fold rather than 4-fold coordinated. Re-examination of published spectroscopic data in light of these results and the solubility data, suggests that the 6-fold coordination polyhedron of Ti is highly distorted, with at least one Ti-O bond grossly undersatisfied in terms of Pauling's rules.
Dickinson James E. Jr.
Hess Paul C.
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