The physical mechanism of AZS refractory brick and bubble formation
The molten AZS brick contains a lot of pores inside, and the inside of these pores is filled with gas. The composition of the gas is roughly the same as that of air, that is, it is mainly nitrogen, oxygen, and a small amount of carbon dioxide gas. As the contact time between AZS bricks and glass liquid increases, due to the erosion of the brick surface, the internal voids will be exposed, and the gas filled inside will be released at the same time to form bubbles.
The chemical mechanism of AZS refractory and bubble formation
The molten AZS refractory contains impurity elements that can be oxidized to form gas, such as carbon, sulfur, zirconium carbide, nitride, nitrogen oxide, etc. When the AZS refractory brick is heated to above 1400℃, these impurity elements will undergo oxidation reaction to form corresponding nitrogen, carbon monoxide, carbon dioxide, sulfur dioxide and other gases.
When the molten AZS brick is cooled and heated again, oxygen bubbles and secondary bubbles are generally generated at the contact point between the glass liquid and the molten AZS brick. This is because, in general, cast AZS bricks contain a small amount (<0.3% (mass fraction)) of variable valence elements, such as iron (Fe, Fe) or titanium (Ti, Ti). These variable valence elements can change their valence state with the change of temperature, thereby completing the role of absorbing or releasing oxygen.
When the temperature decreases, the reaction equation proceeds in the positive direction, which is conducive to the formation of Fe3+. When the temperature increases, the reaction equation proceeds in the opposite direction (reverse reaction), which is conducive to the formation of O2.
Another reason for the generation of oxygen is the electrochemical reaction between the glass melt and the AZS refractory brick, or the "remote" electrochemical reaction when the glass melt and the AZS refractories are not in contact. Alkali metal or alkaline earth metal ions are responsible for electron transfer. In this battery reaction, oxygen ions (O2-) in the glass melt are oxidized to oxygen (O2).
The glass melt is in contact with the cast AZS brick. The concentration of alkali metal or alkaline earth metal ions in the glass melt is much greater than that in the refractory. In addition, due to the infiltration of the glass phase, these metal ions Mn+ will diffuse into the refractory. The result is that it neutralizes the electrons diffused into the AZS refractory material, maintaining electrical neutrality.
