Particularly with regard to problems in diffusion I find that the factor Dt is generally taken constant to solve certain lengthy and difficult looking problems.If possibly can anyone give me an insight into the fact why this is taken into consideration.
D is dependent on the diffusion system and on the temperature of the system.
The diffusion coefficient in solids at different temperatures is generally found to be well predicted by the Arrhenius equation.
See: https://en.wikipedia.org/wiki/Mass_diffusivity
Dear Mr. Koyal,
The concept of Dt as the time-depended characteristic was forwarded in the 60s to describe the ANOMALOUS diffusion in polymer glasses and thermodynamically nonequilibrium systems. From diffusivity point of view, there are two fundamental paradigms to interpret the absence of the classical square-root-of-time dependence. A) the nonequilibrium condition at the boundary of polymer specimen. For us the second case (B) is most important, namely D(t) i.e. diffusion coefficient is function of time. Such the physic formalism suggests that in any point of the matrix, where diffusion occurs, polymer characteristics (e.g. density, segmental mobility etc) are changed with the rate that is compared with the rate of diffusion.
At this situation, the mathematics of diffusion becomes relatively complicated but such approach, nevertheless, has reasonable perspectives for Brownian moving of particles, non-Fickian anomalous features, in metallurgy, electronic transport, sun cell development, drug release therapy ..
Best regards,
Prof. Alexey Iordanskii
The diffusion coefficient can also change because of a changing temperature and associated viscosity of the medium
or viscosity change by a reaction of diffusing solvent and solution
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science