Glass Physics and Chemistry

, Volume 29, Issue 3, pp 243–253 | Cite as

Phase Separation and Crystallization in Glasses of the Na2O–K2O–Nb2O5–SiO2 System

  • G. T. Petrovskii
  • V. V. Golubkov
  • O. S. Dymshits
  • A. A. Zhilin
  • M. P. Shepilov

Abstract

The structure of initial glasses in the Na2O–K2O–Nb2O5–SiO2 system with an Nb2O5 content ranging from 5 to 39 mol % and their structural transformations in the course of isothermal treatments at different temperatures are investigated using small-angle X-ray scattering (SAXS) and X-ray powder diffraction. It is demonstrated that, in glasses containing 15 mol % Nb2O5 and more, the metastable phase separation is the primary process responsible for the formation of a microinhomogeneous structure. With further heat treatment of these glasses, NaNbO3 crystals precipitate in regions with a high Nb2O5 content. In this case, each region has a heterogeneous structure and consists of NaNbO3 microcrystals surrounded by layers of the high-silica matrix. These layers hinder transfer processes and, consequently, recrystallization, which ensures the stability of the heterogeneous structure and, correspondingly, constant sizes of microcrystals at temperatures up to 750–800°C. The intensity of light scattering is determined primarily by the sizes of regions formed upon phase separation. A decrease in their size with an increase in the niobium oxide content leads to a decrease in the light scattering loss and an increase in the transparency of heat-treated samples. The interference effects associated with the heterogeneous structure of high-niobate phase regions also favor an increase in the transparency of the prepared materials.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

REFERENCES

  1. 1.
    Rao, Bh.V., Neo-Ceramic Glasses and Their Structure, J. Glass Technol., 1964, vol. 5, no. 2, pp. 67–77.Google Scholar
  2. 2.
    Vernacotola, D.E. and Shelby, J.E., Potassium Niobium Silicate Glasses, Phys. Chem. Glasses, 1994, vol. 35, no. 4, pp. 153–159.Google Scholar
  3. 3.
    Golubkov, V.V., Zhilin, A.A., Chashchin, S.V., and Chuvaeva, T.I., A SAXS Study on Specific Features in the Crystallization of Na2O-Nb2O5-SiO2 Glasses, Fiz. Khim. Stekla, 1994, vol. 20, no. 1, pp. 58–67 [Glass Phys. Chem. (Engl. transl.), 1994, vol. 20, no. 1, pp. 38–43].Google Scholar
  4. 4.
    MacDowell, J.F. and Beall, G.H., Immiscibility and Crystallization in Al2O3-SiO2 Glasses, J. Am. Ceram. Soc., 1969, vol. 52, no. 1, pp. 17–25.Google Scholar
  5. 5.
    Aver'yanov, V.I., Areshev, M.P., Golubkov, V.V., and Doronina, L.A., Phase Separation in the Al2O3-SiO2 System, Fiz. Khim. Stekla, 1984, vol. 10, no. 3, pp. 257–265.Google Scholar
  6. 6.
    Andreev, N.S., Mazurin, O.V., Porai-Koshits, E.A., Roskova, G.P., and Filipovich, V.N., Yavleniya likvatsii v steklakh (Phase Separation in Glasses), Leningrad: Nauka, 1974.Google Scholar
  7. 7.
    Golubkov, V.V., The Structure of and Structural Transitions in Vitreous SiO2, Fiz. Khim. Stekla, 1992, vol. 18, no. 1, pp. 57–69 [Sov. J. Glass Phys. Chem. (Engl. transl.), 1992, vol. 18, no. 1, pp. 28–34].Google Scholar
  8. 8.
    Zarzycki, J. and Naudin, F., A Study of Kinetics of the Metastable Phase Separation in the PbO-B2O3 System by Small-Angle Scattering of X-rays, Phys. Chem. Glasses, 1976, vol. 8, no. 1, pp. 11–18.Google Scholar
  9. 9.
    Lipson, H. and Steeple, H., Interpretation of X-ray Powder Diffraction Patterns, London: Macmillan, 1970. Translated under the title Interpretatsiya poroshkovykh rentgenogramm, Moscow: Mir, 1972.Google Scholar

Copyright information

© MAIK “Nauka/Interperiodica” 2003

Authors and Affiliations

  • G. T. Petrovskii
    • 1
  • V. V. Golubkov
    • 2
  • O. S. Dymshits
    • 1
  • A. A. Zhilin
    • 1
  • M. P. Shepilov
    • 1
  1. 1.Vavilov State Optical Institute, All-Russian Research CenterResearch and Technological Institute of Optical Materials ScienceSt. PetersburgRussia
  2. 2.Grebenshchikov Institute of Silicate ChemistryRussian Academy of SciencesSt. PetersburgRussia

Personalised recommendations