Composition-structure-property effects of antimony in soda-lime-silica glasses

Float glass-type SiO2-Na2O-CaO glasses with 0 – 10 mol% Sb2O3 were melted and their compositional, structural, thermal and optical properties characterised. All glasses were X-ray amorphous and increasing Sb2O3 content progressively decreased glass transition temperature (Tg) and dilatometric softening point (Td), despite increases in Al2O3 content from greater crucible corrosion. 121Sb Mössbauer spectroscopy confirmed that Sb was predominantly incorporated as Sb3+ (Sb3+/ΣSb ~ 0.9) and Raman spectroscopy showed that Sb substantially decreased average (Si, Al)-O Q n speciation. Both techniques confirmed that Sb3+ ions were incorporated in trigonal pyramidal [:SbO3] polyhedra. XRF and Raman spectroscopies confirmed that SO3 content decreased with increasing Sb2O3 content. TGA analysis showed, as a linear function of Sb2O3 content, mass gain commencing at 700°C, reaching a maximum at 1175°C, then mass loss above 1175°C, consistent with oxidation (Sb3+ → Sb5+) then reduction (Sb5+ → Sb3+). The TGA samples were shown to have attained or approached Sb redox equilibrium during measurement. Optical absorption spectroscopy (UV-Vis-nIR) showed red-shifts of the UV absorption edge with increasing Sb2O3 content, consistent with increasing intensity of far-UV absorption bands from Sb3+ and Sb5+ s→p transitions. UV-Vis-nIR fluorescence spectroscopy evidenced a broad luminescence band centred at ~25,000 cm-1 , attributed to the 3P1→1S0 transition of Sb3+ , which is Stokes shifted by ~15,000 cm-1 from the 1S0→3P1 absorption at ~40,000 cm-1 . The most intense emission occurred at 0.5 mol% Sb2O3, with concentration quenching reducing luminescence intensities at higher Sb2O3 contents. Additions of Sb2O3 to float-type soda-lime-silica glasses could thus enable lower melting energies and/or new solar energy applications.