Question

Question: “We wish to develop an expression for rate of tarnishing in terms of oxygen diffusivity through the oxide film, the densities of the metal and its oxide, and the stoichiometry of the reaction.”

reaction. Let co be the solubility of O, in the film, c, the molar density of the film, and z, the thickness of the film. Show that the film thickness is 2o. Mo, co (18B.12-1) This result, the so-called "quadratic law,"gives a satisfactory empirical correlation for a number of oxidation and other tarnishing reactions.? Most such reactions are, however, much more complex than the mechanism given above.

Answer 1

ven, tevms of oayren diffa rivily through the oxido film the donsty of the metat aud t oi de, auel the oichi onet ry of the Reactisn Accovlivg to the fcts, frst lau to the di fusion of oge R刊on tie-feKS (aco dlut solution of oxyVen is vilua ry s tay metal oid r This is mey he utgratad c for a reav-te eith the boundary Conto 2. eve) 근,ct) i s the slody vann7 oude film thickness at usteadty stl mass balake for the stale toe wi6 an ) auad (t+at) to acaount fox the planes and te altPuson endtion atition by

(t+a) 2, (4) IO4 tHere, Mos s ividy both sides by bt and effing At ao to 2eso Cox uaton for tho location 아-fic slowly mownej. Co 6Y)