Decomposition temperature of sulfates

Above 1288°C, the thermal decomposition of Na2SO4 (in the presence of glass) begins to become significant. As the decomposition proceeds, the decomposition products (Na2O, SO2, O2) are dissolved in the glass melt; they are transported into the glass at the interface between the undecomposed liquid sulfate and the glass. This material transfer disrupts the interfacial tension, releasing a large amount of energy, thereby causing intense turbulence in the melt at the interface. At around 1428°C, the partial pressure of the sulfate decomposition products reached one atmosphere, causing bubbles to form in the glass. As these bubbles rise, they transport sodium from the glass regions with high sodium content to the upper parts of the melt where the sodium content is lower, thereby further homogenizing the glass. The bubbles that remain without being exhausted dissolve back into the melt as the glass cools.

The calculation of the thermal decomposition temperature of sulfates is mainly based on the theory of ionic polarization; there are certain calculation formulas, but no unified one. A paper has been posted in the shared area; it contains a formula as well as the thermal decomposition temperatures of some sulfates for reference.