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Thermodynamic Stability Analysis of Molybdenum Electrode in Molten Glass

The main component of the glass is SiO₂, Al₂O₃, CaO, MgO and K₂O and others. The main component of clarifying agent is As₂O₃ and Sb₂O₃. To learn the stability of molybdenum on these substances has an important significant for molybdenum electrodes in molten glass long-term stability operation.

Molybdenum at high temperature will oxidize to generate MoO₃ which is a self volatile gas. Table1 is chemical reaction between the glass components and molybdenum. Though thermodynamic stability analysis to calculate the free energy change between molybdenum and various glass components reaction, to understand the stability of molybdenum electrode in molten glass. If the free energy change is positive, i.e., △ G> 0, molybdenum electrode is stable in the molten glass, whereas if △ G <0, the molybdenum electrode will react with the glass components, which is instability in the glass molten. Experimental data found that molybdenum will not react with glass main component to occur oxidation, their reaction free energy is △ G> 0, but it will react with some other impurities and clarifying agents such as Sb₂O₃, As₂O₃, Fe₂O₃, which is △ G <0.

Further, through glass electric furnace scene observed found the electric melting furnace using Sb₂O₃ as a fining agent has many Sb-Mo eutectic ball with a diameter of up to 5mm on the botton of furnace. During lead glass production, lead glass solution will react with molybdenum electrode to deposit lead liquid in the bottom of the furnace. Using molybdenum electrode for the glass fiber production, when electrode current density is more than 1.5 ~ 2.0A / cm², the electrode surface will produce soybeans size bubbles. Besides it react with air will produce incandescent flash and to generate Na₂O powder. These phenomena all show that the actual operation is in line with the thermodynamic calculations. However, these fining agents content is low, so the reaction between it and electrode does not affect the life and stability of the electrodes. It can be seen, molybdenum electrodes can be stably used for a long time in the molten glass.

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