Structure and dissolution of CaO–ZrO 2–TiO 2–Al 2O 3–B 2O 3–SiO 2 glass (II)

Abstract

The purpose of this study is to determine the structure and dissolution resistance of the CaO–ZrO 2–TiO 2–Al 2O 3–B 2O 3–SiO 2 glass fabricated in Part (I). Vibrational spectroscopy indicated the structure units of the glass are SiO 4, TiO 4, BO 4 and their groupings for thermal exposure up to 750°C. The surface of an etched sample contained amorphous-phase-separated droplets which developed in multiple stages and clustered upon heating near the glass transition temperature, T g (ca. 640°C). Room temperature (30±1°C) dissolution of glass powders in aqueous solutions (pH=0, 1, 3, 5, 10 and 12) showed size-dependent leaching of cations Ca, Al, Ti and Zr, with Zr the most dissolution-resistant component. The leaching of the cations Ca and Al was linear with time in the initial dissolution stage and each had a logarithmic dissolution rate versus pH dependence; the slope being negative in acidic while positive in basic condition with a minimum dissolution rate in the pH range of 6.5 to 8.5. Dissolution of a partially devitrified glass slab under acidic (pH=0) or basic (pH=12) conditions indicated that glass/crystal (ZrO 2 derived) interfaces were preferentially dissolved with the crystals being more resistant. An Al-depleted layer and ridge-free hillocks developed on the glass surface at pH=12 and 0, respectively.