PNNL

Abstract

While various glass alteration layer formation mechanisms have been debated in recent years, it is generally agreed upon that more information on physical properties of the alteration layers is needed to further the understanding of their impacts on overall glass alteration. In this work, pore volumes and solid structures of glass alteration layers formed in solutions of various pH conditions are evaluated with positron annihilation spectroscopy and small angle X-ray scattering. Pore volumes of alteration layers formed at pH 9 were found to be at their lowest near the surfaces of the alteration layers. Solid structures of alteration layers are compared to those of synthetic aerogels of comparable compositions produced under various pH conditions. Alteration layers formed at pH 11 were shown to contain large structures (>10 nm) similar to synthetic aerogels created under neutral and basic conditions whereas alteration layers formed at pH 9 did not. The large structures formed at pH 11 are proposed to be caused by excessive free Si species through Ostwald Ripening.