Chemistry Reference
In-Depth Information
is assumed to be related to the partial pressure of the oxidant in the gas by Henry's
law:
Henry's law holds in the absence of dissociation or association of the oxidants at the
outer surface, implying the oxidant to be and in the cases of dry and wet oxygen
oxidation. The flux of the oxidant across the oxide layer is assumed to follow Fick's
law:
with
the effective diffusion coefficient. Since at a steady state
must be the same
at any points within the film, meaning
Eq. (3.14) reduces to
where
is the concentration near the
interface. The reaction flux at the inter-
face is assumed to be first order:
Considering the situation under diffusion control with
and
and com-
bining Eqs. (3.12), (3.13), (3.15), and (3.16), we obtain
where is the rate of growth and the number of oxidant molecules incorporated
into the unit volume of the oxide layer. Integration of Eq. (3.17) with an initial condi-
tion
at
t =
0 yields
