my text says aluminium does not corrode much as a passive aluminium oxide layer is formed on it.Well other metals such as sodium adn potassium also form oxides. Why dont their oxides prevent further oxidation ?
sodium oxide and potassium oxide are water soluble aluminium oxide is not water soluble. the layer formed of oxide on the aluminium surface is coherent and adherent with no pores and stuck to the metal surface. the layer is also passive to most acids and alkalies except HCl and anti passive ions if present. sodium oxide and potassium oxide dissolve in any aqueous medium forming the corresponding alkalies NaOH and KOH leaving the fresh metal surface exposed to more corrosion. also the reaction of Na and K with aqueous media like water and acids is quite vigorous and fast unlike aluminium which is mu less reactive
Not sure. Maybe because Na K are more active than Aluminum.
