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Specialty steel for the core of power transformers must be loaded with silicon up to a prescribed content. This is accomplished by exposing a steel

Specialty steel for the core of power transformers must be loaded with silicon up to a prescribed
content. This is accomplished by exposing a steel sheet with negligible silicon content to an
atmosphere of SiCl4, which dissociates to Si(g) and Cl2(g) at high temperatures. The silicon gas
then dissolves into the steel. The treatment is carried out at atmospheric pressure and 1255K; at
this temperature the diffusivity of silicon in steel is 8.2*10-12m2s. The concentration of Si in the
bulk of the gas phase is 30 mole percent; at equilibrium this would result in a silicon concentration
in the steel of 2wt.%.
A) If a steel plate of 1mm thickness is exposed to the SiCl4 treatment on one side, while the
other side of the plate rests on an impermeable surface, determine how long it will take
before the bottom of the sheet reaches a silicon concentration of 1.5wt%. Assume
negligible surface resistance.
B) In reality, it turns out that it takes 1.5 times longer than calculated in A? to achieve the
desired concentration of 1.5wt.% at the bottom of the sheet due to the presence of surface
resistance. Estimate the value of the convective mass transfer coefficient under these
process conditions.
plz don;t use delta C/ delta x
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