Question

How is highly alkaline nature corrosive

Answer 1

A corrosive substance is one that will destroy and damage other substances with which it comes into contact. It may attack a great variety of materials, including metals and various organic compounds, but people are mostly concerned with its effects on living tissue: it causes chemical burns on contact. Metals typically develop a passivation layer in moderately alkaline (high pH) solutions, which lowers the corrosion rate as compared to acidic (low pH) solutions. The passivation layer provides a measure of immunity to further corrosion (e.g. Ti, Ta).