During the melting of glass, it is observed that at higher furnace temperature oxygen diffusivity into molten glass increases.
I have melted glass in using microwave energy, where atmosphere above the melt surface is less than that in conventional melting. It is found that oxygen penetration into the molten glass is less in microwave furnace. Whether oxygen diffusion in melt surface interface will be higher at higher temperature?
In general the diffusion constant D increases with increasing temperature T, its functional form depending however on the microscopic details, or the nature of transport. In a simple model of particles suspended in liquid, D increases linearly with T (see for instance Sec. 2.5 of the book Statistical Mechanics, by Huang); considering self-diffusion, for a gas of hard spheres D turns out to increase like T1/2 (see Sec. 11.G.2 in the book Modern Course in Statistical Physics, by Reichl). If transport is activated, then D depends exponentially on T, following the Arrhenius law (reaching its maximum at infinite T). For the latter, consult the attached lecture note.
http://web.utk.edu/~prack/mse201/Chapter%205%20Diffusion%20.pdf
Two ways to explain:
[A]The movement of O2 gas[or any cation] is directly related to the permeability,i.e. more the permeability, the more is the solubility or more will be the diffusivity.Now permeability is directly related to the number of vacant sites.The formation of vacancies in molten glass follow the swquence[i] At low temperatures, oxygen vacancy is controlled by impurities and an EXTRINSIC BEHAVIOUR is observed[ii] At intermediate temperatures, the oxygen vacancy concentration changes due to oxygen solubility with temperature. This is NONSTOICHIOMETRIC BEHAVIOUR[iii] At high temperatures, THERMAL VACANCIES BECOME VERY DOMINANT and thus more diffusion of O2.
[B]Diffusivity of a gas is analogous to its solubility. And the solubility of a gas ,beyond a certain temperature canincrease with temperature[ Arrhenius equation] because HEAT OF THE SOLUTION SERVES AS ENERGY OF ACTIVATION..[Just as N2 gas solubility in water decreases until about 70 C, and then begins to increase]
REFERNCE:
An Introduction to Materials Engineering and Science for Chemical and ...
By Brian S. Mitchell.PP-357-358.
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