Effect of the initial stages of leaching on the surface of alkaline earth sodium silicate glasses

The effect of the nature of the alkaline earth cation R (R = Mg, Ca, Sr or Ba) on the chemical composition, structure and mechanical propel ties of th e surface of leached (RO)(15) (Na2O)(15) (SiO2)(70) glasses has been invest igated during the initial stages of interaction with water. The glasses wer e leached by immersion in deionized water, at near neutral pH, at different temperatures, and for different periods of time. Compositional analysis wa s carried out using several depth profiling techniques, viz., RES. ERD and SIMS. The chemical bonding state of the glass was investigated using Fourie r-transform infrared (FTIR) reflection spectroscopy. UV-VIS reflection spec troscopy was used to study the optical properties of the glass surface. The Ba and Ca glasses were subjected to Vickers indentation at different loads to study the effect of leaching on the mechanical properties of the glass surface. For all glasses, the H penetration depth after leaching is shown t o be approximately equal to the depletion depth of Na. The Na depletion and H penetration depths generally increase with leaching temperature and time . For Ba and Sr glasses, Ba and Sr cations are depleted to the same extent as Na. However, for Ca and Mg glasses, depletion of Ca and Mg is shown to b e negligible as compared to Na depletion. The Na depletion depth is similar for the Sr, Ca and Mg glasses while much larger for Ba glass. In addition. Ba glass indented after immersion yields a larger indentation diagonal len gth and a lower corresponding Vickers hardness in comparison with Ba glass indented before immersion. Moreover, Ba glass exhibits a larger increase in radial crack size after immersion in water in comparison with Ca glass. On this basis, it is inferred that the mechanical properties of the Ba glass surface after leaching are controlled by the Ba and Na depletion depth. (C) 2000 Elsevier Science B.V. All rights reserved.