Question

See in the photo . The point (c) is note is contradicting the point (d) Strain In Metals. Explain in detail that what is the logic ??
c. Presence of air and moisture . Air and moisture accelerate corrosion. Presence of gases such as SO₂ and CO₂ in air catalyze the process of corrosion. Iron when placed in vaccum does not rust.
d. Strains in metals. Electrolytes, if present, also increase the rate of corrosion. For example, iron rusts faster in saline water than in pure water.

Answer 1

Dear Student,

$$\begin{gathered} \mathrm{No},\mathrm{the}\mathrm{two}\mathrm{statements}\mathrm{donot}\mathrm{contradict}\mathrm{each}\mathrm{other}. \\ \mathrm{In}\left(\mathrm{c}\right)\mathrm{point}\mathrm{of}\mathrm{Notes},\mathrm{it}\mathrm{is}\mathrm{given}\mathrm{that}\mathrm{rusting}\mathrm{is}\mathrm{formed}\mathrm{at}\mathrm{sites}\mathrm{other}\mathrm{than}\mathrm{the}\mathrm{site}\mathrm{where}\mathrm{pitting}\mathrm{has}\mathrm{occurred}.\mathrm{Pitting}\mathrm{is}\mathrm{a}\mathrm{damaging}\mathrm{form}\mathrm{of}\mathrm{corrosion}\mathrm{which}\mathrm{degrades}\mathrm{the}\mathrm{metal}. \\ \mathrm{It}\mathrm{is}\mathrm{localised}\mathrm{rusting}\mathrm{which}\mathrm{leads}\mathrm{to}\mathrm{formation}\mathrm{of}\mathrm{cavity}\mathrm{or}\mathrm{pit}\mathrm{on}\mathrm{the}\mathrm{metal}.\mathrm{So},\mathrm{if}\mathrm{pitting}\mathrm{has}\mathrm{occurred}\mathrm{at}\mathrm{a}\mathrm{site},\mathrm{then}\mathrm{corrosion}\mathrm{will}\mathrm{not}\mathrm{occur}\mathrm{there}.\mathrm{It}\mathrm{will}\mathrm{occur}\mathrm{at}\mathrm{sites}\mathrm{different}\mathrm{than}\mathrm{the}\mathrm{pit}. \\ \mathrm{In}\left(\mathrm{d}\right)\mathrm{point}\mathrm{i}.\mathrm{e}.\mathrm{strains}\mathrm{in}\mathrm{metals},\mathrm{the}\mathrm{sites}\mathrm{i}.\mathrm{e}.\mathrm{bends},\mathrm{scrates},\mathrm{nicks}\mathrm{are}\mathrm{not}\mathrm{pits}.\mathrm{They}\mathrm{are}\mathrm{different}\mathrm{and}\mathrm{sites}\mathrm{where}\mathrm{corrosion}\mathrm{has}\mathrm{not}\mathrm{occured}. \end{gathered}$$