(material transport by atoms motion,
movement of atoms from site to site, requires sufficient
vibration energy, can change structure in solids)
-atoms of one molecule diffuse into another,
concentration changes w/ time
– all atoms
exchanging positions are the same type, no change in
concentration, ex. metals.
flux does not change with time.
D(ΔC/Δx), D-const of proportionality [m
concentration gradient [kg/m
], x-distance [m], J-diffusion
=surface concentration, C
=concentration at depth ‘x’,
erf()=Gaussian error function.
Erf(1)=0.85, x=2sqrt(Dt), C~15%.
– species & temperature.
increases when T rises, atomic size, structure (activation
energy), phase change, cold work.
=temp-independent preexponential [m
energy [J/mol], R=gas const., T=abs temp.
movement of atoms;
– ion pairs move to preserve
electroneutality (long-term), single point defects may not
exist, cations diffuse quicker than anions;