What is Slagomite

Many of the benefits of using Slagomite , including improved melting efficiency, reduced process CO₂ emissions and improved color stabilization are always achieved when Slagomite is used. Other benefits can be maximized depending on the specific priorities of the glassmaker at the time, for example reducing energy consumption or improving glass quality.

Slagomite increases the melting rate of the batch, thereby allowing furnace temperatures or energy consumption to be reduced without affecting glass quality. The glass melting process is, in effect, a series of reactions rather than a true melting process. In the glass tank, a large number of these reactions will be occurring simultaneously, depending on the small local variations in composition, temperature and atmosphere that will inevitably occur within the furnace. There is a number of ways in which Slagomite is believed to influence the melting process.

As the batch is heated, liquid phases start to form at around 750-800ºC, which then coat the raw material grains, enhancing the reactions within the melt. This initial liquid phase will include Na₂CO₃, either from direct melting or reaction with other batch materials. This liquid reacts with the sand grains, forming sodium silicates, by reactions such as:

Na₂CO₃ + Si0₂ = Na₂0 • SiO₂

Na₂0 • Si0₂ = NaO • 2SiO₂

As the temperature increases, other batch materials will react to become part of the liquid. Limestone and dolomite decompose at 800-900ºC, through an endothermic reaction releasing CO₂ and CaO and MgO that react and form part of the melt. However, it is known that limestone and CaO are poorly wetted by the primary melt.

The use of Slagomite provides between 15% and 40% of the CaO in the new glass from the batch. As the Slagomite is glassy and, therefore, liquid at glass melting temperatures, it is available to take part in the batch reactions at lower temperatures than the decomposition of limestone and dolomite. This improves the homogenization of the batch and also reduces the endothermic effect associated with the decomposition of the carbonates.

The final stage in the melting process is the dissolution of residual sand grains. As the sand grains dissolve, a SiO₂rich boundary layer will form in the melt around the sand grain. The rate of dissolution will depend on the solubility of SiO₂ in the melt and the rate of diffusion of SiO₂ away from the sand grain into the melt. Slagomite has a lower concentration of SiO₂ than the glass melt, along with a tendency to wet the sand grains. This results in a SiO₂ concentration gradient that encourages dissolution of the sand grains into the melt, thereby increasing the melting rate.