Fining and refining, when bubbles are removed from the glass melt, is an important step in glass manufacturing to reach the quality demands. It is well known that the refining does not always work properly if the composition in the glass is altered. There are still questions concerning the mechanisms of refining with Sb2O3, which typically is used in glass industries where the furnaces have limited process temperature.
This study is done to monitor how changes in glass composition affect the fining efficiency and the oxygen activity of the melt. The specific number of bubbles was determined in the glasses in order to evaluate the fining efficiency. The oxygen activity measurement is a way to in situ monitor the fining characteristics and it has been measured electrochemically at 1400 C in some of the glass melts.
In this work 20NaO2-10RxOy-70SiO2 glasses were used. RxOy is CaO, BaO, MgO, ZnO, SrO or a mix of CaO with BaO, MgO, ZnO, SrO, B2O3, Al2O3 or TiO2. Nitrate and 0,2 mol% Sb2O3 were used as refining agent. In the glasses with a combination of CaO and B2O3 the number of bubbles was lower compared to the glass with only CaO. In all other glasses the amount of bubbles was higher. A maximum number of bubbles were found in the glass containing a combination of CaO and SrO. The oxygen activity was measured at 1400C in glass melts with SrO, CaO+SrO, CaO+BaO and with CaO+B2O3.