Mechanism of Oxygen Diffusion in Glassmelts Containing Variable-Valence Ions

A mechanism is proposed to describe the influence of redox reactions, which involve variable-valence ions, on the diffusional mass transport of molecular dissolved oxygen in glassmelts. The concentration profile for molecular dissolved oxygen in a melt with diffusional transport in one direction in a Cartesian coordinate system is described by a differential equation: ∂(O₂/∂ t = D_c (∂²[O₂]/∂ x ²), where D_c depends on the actual value of the diffusivity D of physically dissolved oxygen, the local molecular oxygen concentration, the concentration of variable-valence ions, and the equilibrium constant for the relevant redox reaction. This equation is applicable for diffusion into or outwards from the melt from or into the furnace atmosphere. It is shown here that the value of D_c is always less than D . Concentration profiles for diffusing oxygen in glassmelts with refining agents (containing variable-valence ions) are thus steeper than profiles in melts without refining agents. A decrease in temperature of a glassmelt with variable-valence ions generally leads to diffusion of oxygen into the melt. The flux of oxygen gas into (oxidation) or out (reduction) of the melt is proportional to ( D/D_c )^1/2 and is enhanced by the effect of variable-valence ions dissolved in the melt.