Glass Batch Modification to Improve the Weathering Resistance in Soda-Lime Silicate Glass

Abstract

The soda bloom - white stain on the glass surface – is an issue concerned in the glass manufacturing. It is because of high humidity and warm weather especially in the tropical region. The aim of this study was to modify glass batch to increase the weathering resistance for soda-lime glass. The weathering resistance of glass was measured by using the sodium (Na) leach technique according to the ISO 719. In principle, the strength of glass structure decreases with increasing Na content. The reactions start when free Na+ions moving to the glass surface and react with moisture from the surroundings. From this reason, the soda bloom occurs during storage lifetime. Two samples of glasses as described in Table 1 were modified with dolomite (CaMg (CO3)2) or alumina (Al2O3) to reduce the sodium free ion on the glass surface and increase the strength of glass structure Table 1: The glasses compositions All glasses were melted at 1500oC for 3 hours and annealed at 570°C. In glass structure, magnesium (Mg) and aluminium (Al) are network modifiers that can improve the structural strength and the weathering resistance of glass. The weathering resistance is in the inverse relationship with the weight of Na2O in mg per 50 ml of water according to theISO 719. The results showed that the weathering resistance increased with increasing dolomite or alumina contents. The experiments of increasing dolomite from 0 to 18 wt.% in a replacement of calcite showed the result that indicated the weight of Na2O in mg per 50 ml of water decreased from 0.53 to 0.41 mg, and the glass with increasing alumina from 0 to 1 wt.% showed that the weight of Na2O in mg per 50 ml of water decreased from 0.80 to 0.39 mg. According to the weathering chamber test under the cyclic atmospheric conditions of 60% and 80% relative humidity, and the cyclic temperatures of 20°C and 32 °C for 14 days, the glasses with more than 12 wt.% dolomite or more than 1 wt.% alumina did not generate the white stains on the surface. This process can be applied in the glass production. The satisfied result was found in the glass sample with 12 wt.% dolomite and 1 wt.% alumina. The weight of Na2O per 50 ml H2O reduced to 0.43 and 0.41mg, respectively, and the storage time increased from 3 months to 6 months without soda bloom.