Diffusion equations expressed in molar fractions: Theory and application to ionic diffusion and demixing

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Engineering

Background:

• Molar quantities and reduced molar quantities are often used interchangeably in diffusion kinetics.
• Current diffusion equations using molar fractions lack consistency with the molar fraction normalization condition.
• This inconsistency arises because diffusion fluxes depend on material properties.

Purpose of the Study:

• To develop a diffusion kinetics framework consistent with the molar fraction normalization condition.
• To address the inconsistency in diffusion equations when using molar fractions.
• To provide a more accurate method for modeling diffusion phenomena.

Main Methods:

• Developed a novel set of diffusion kinetics equations.
• Ensured the equations adhere to the molar fraction normalization condition.
• Applied the method to diffusion with total reduced flux, including external or flow fields.

Main Results:

• The developed diffusion kinetics are consistent with the molar fraction normalization condition.
• The new method accurately models diffusion processes where molar quantities are used.
• Demonstrated applicability to ionic diffusion in electrolytes and ionic demixing in semiconductor oxides.

Conclusions:

• The developed diffusion kinetics provide a consistent and accurate framework for modeling diffusion.
• This method is particularly useful for systems with total reduced flux, such as electrolytes and oxides.
• The findings advance the understanding and application of diffusion kinetics in various scientific fields.