Influence of small additions of Li₂O raw materials on glass melting

Abstract

For a container glass composition up to 1 mol% of the alkali oxide was substituted by Li₂O in steps of ≈0.2 %. The lithia was added as Li₂CO₃ and as spodumene, respectively. As shown earlier Li₂O reduces the viscosity of the melts considerably, irrespective of the Li₂O source. However, melt formation, carbonate decomposidon, silicate and silicate melt formation processes during raw materials reactions are considerably accelerated by Li₂CO₃ addition only, whereas Li₂O in the spodumene silicate does not enhance these reactions. The fining of the melt and the corrosion behavior of refractories are strongly influenced also by the lower viscosity melts. Thus, the corrosion rate may be diminished by temperature reduction at constant viscosity. For technical purposes the glasses are very stable against crystallization, however, thermal analysis shows that the higher the Li₂O content is, the faster the crystal growth proceeds. The surface tension of the glass melts decreases and the water leach resistance of the solid glasses is enhanced with increasing Li₂O content. The Li⁺ ions are less polarizable and, due to their high Dietzel field strength, the glass structure is dghtened compared with that of Li₂O-free glass. In conclusion, the substitution of small amounts of Li₂O instead of Na₂O and/or K₂O shows several advantages. At low temperatures different raw materials reactions are accelerated and at high temperature the decrease in melt viscosity is decisive.