![]() ![]() Iron oxides in carbon steel Vs Chromium oxides stainless steel Above 18%, Chromium gives a continuous protective chromium oxide layer. The ratio 1/8 = 12.5 at% corresponds to practical findings, where the corrosion rate is found to drop significantly at an alloy content of about 12%. In a solid solution of iron and chromium, one needs at least 1 atom in 8 to be chromium to form a continuous network of chromium in the metal matrix. ![]() In a BCC lattice, like iron, every atom has eight nearest neighbours. The inner part is a compact layer consisting of mainly Cr2O3 and an outer hydroxide layer. Passivation by chromium involves oxygen combining with chromium to create a film of chromium oxide (Cr2O3) on the surface. Passivation and corrosion protection by chromium How strong a metal bond would be would depend on how many free electrons the atom possesses to form metal.Ĭoming back to why Chromium is so hard, the reason is chromium has five unpaired delocalized electrons moving freely throughout the crystal structure of chromium forming a sea of electrons around chromium atoms holding chromium ions by strong attractive forces. Literally, atoms are enveloped within a sea of electrons, please see the left side image. The electrons and the positive ions in the metal have a strong attractive force between them and that gives strength to metallic bonds. ![]() Delocalized electrons are not associated with a particular nucleus of metal, instead, they are free to move throughout the whole crystalline structure forming a "sea" of electrons. Therefore, the valence electrons are delocalized throughout the metals. ![]()
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