Surface properties of tellurite and fluorotellurite glasses

The surface properties of some freshly cleaved, or polished, quaternary tellurite glasses (TeO₂-ZnO-Na₂O-Yb₂O₃and TeO₂-ZnO-Na₂O-GeO₂) and a proposed ternary fluorotellurite core/clad optical fiber pair (TeO₂-N a₂O-ZnF₂) were investigated by means of x-ray photoelectron spectroscopy and chemical durability. Semiquantitative chemical analysis of the x-ray photoelectron spectroscopy spectra of cleaved tungsten-tellurite and fluorotellurite glasses showed good agreement with the batched at.% values when taking into account the effects of processing (e.g., melt fluorine volatilization), and the samples seemed to exhibit negligible hydrolysis. However, spectra of polished surfaces did not yield useful data because of masking of the glass “signal” from organic contamination at the sample surface. The chemical durability of these glasses were studied; specifically, the glass resistance to the attack and the etchability of various acids (aqueous HF, H₂SO₄, and HCl), alkali (aqueous NaOH), and water at 15, 21, and 60 °C were obtained by simple mass loss experiments and optical microscopy. Based on the appearance of the glass surfaces after immersion in these solutions, aqueous HF was found to be the most promising etchant, however, infrared spectra showed that significant OH was introduced into the glass. Attack of the fluorotellurite glasses was found to proceed at a higher rate in water at 60 °C compared with room temperature, and at both temperatures was shown to be diffusion controlled, with an Arrhenian activation energy estimated as 57 kJ mol⁻¹.