title: Identification of solvated species present in concentrated and dilute sodium silicate solutions by combined 29Si NMR and SAXS studies.
abstract: Both concentrated and diluted sodium silicate solutions have been investigated by combining (29)Si NMR spectroscopy and SAXS experiments. The chemical nature of the entities responsible for the high siliceous species solubility observed in such alkaline concentrated sodium silicate solutions and their evolution according to dilution have been identified. For the most concentrated solution ([Si]=7 mol/l; pH=11.56; Si/Na atomic ratio=1.71), the results evidence the preponderant presence of neutral Si(7)O(18)H(4)Na(4) complexes, which behave like colloids of about 0.6-0.8 nm able to form very small aggregates with an average size lower than 3 nm. Addition of distilled water to this initial concentrated solution leads, on one hand, to a doubling of the colloid size, i.e. 1.2-1.5 nm, and, on the other hand, to a progressive decrease of the aggregate size until their total disappearance. Such a behavior could be explained by considering, first, the dissociation of the neutral Si(7)O(18)H(4)Na(4) complexes present in the concentrated solution into Na(+) ions and charged (Si(7)O(18)H(4)Na(4-n))(n-) complexes (with 1 ≤ n ≤ 4) and, second, the condensation of these siliceous charged species in order to form larger (Si(7y)O(18y-z)H(4y-2z)Na((4-n)y))(ny-) colloids. The mean size of these colloids suggests that the condensation occurs between 2 and 8 (Si(7)O(18)H(4)Na(4-n))(n-) groups.
authors.affiliation: Groupe d'Etude des Matériaux Hétérogènes (GEMH E.A. 3278), CEC, Ecole Nationale Supérieure de Céramiques Industrielles, 12 rue de l'Atlantis, 87068 Limoges Cedex, France.
authors.forename: Monique Tohoué
authors.initials: MT
authors.lastname: Tognonvi
authors.forename: Dominique
authors.initials: D
authors.lastname: Massiot
authors.forename: André
authors.initials: A
authors.lastname: Lecomte
authors.forename: Sylvie
authors.initials: S
authors.lastname: Rossignol
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Bonnet
mesh_terms: D007554:Isotopes; D009682:Magnetic Resonance Spectroscopy / Q000592:standards; D010316:Particle Size; D012015:Reference Standards; D053838:Scattering, Small Angle; D017640:Silicates / Q000737:chemistry*; D012825:Silicon / Q000737:chemistry*; D012996:Solutions; D013499:Surface Properties; D014961:X-Ray Diffraction
chemical_list: D007554:Isotopes; D017640:Silicates; D012996:Solutions; C005691:sodium silicate; D012825:Silicon