Alkali attack on light metals

In detail

Most metals are attacked by acids and left alone by alkalis. Aluminium and zinc are amphoteric — they react with both — and that single fact explains a large family of domestic damage that otherwise looks arbitrary. Four separate regulator fact sheets state it independently. Potassium hydroxide is corrosive in moist air to aluminium, zinc, tin and lead, forming flammable and explosive hydrogen gas. Trisodium phosphate in water solution reacts with aluminium, zinc and galvanised iron to produce hydrogen. Sodium hydroxide behaves the same way. And ammonium hydroxide carries a flat instruction not to use copper, aluminium or galvanised metals when handling it. Between them those cover oven cleaner, caustic drain products, sugar-soap and heavy-duty degreasers, ammonia-based cleaners, and automatic dishwasher detergent — which is why aluminium pans, moka pots, bakeware and trim come out of a dishwasher permanently dulled, pitted and grey. The damage is the metal being consumed, so it cannot be polished out. Anodised aluminium is not exempt: its oxide layer is finite, and a standards body warns that marks from mistreatment may be permanent.

Why

• Potassium hydroxide is explained by Alkali attack on light metals
• Trisodium phosphate is explained by Alkali attack on light metals
• Oven cleaner is explained by Alkali attack on light metals
• Dishwasher detergent is explained by Alkali attack on light metals
• Anodised aluminium is explained by Alkali attack on light metals
• Galvanised steel is explained by Alkali attack on light metals
• Aluminium is explained by Alkali attack on light metals
• Ammonia is explained by Alkali attack on light metals
• Alloy wheel is explained by Alkali attack on light metals
• Sugar soap is explained by Alkali attack on light metals
• Corrosion inhibitor is explained by Alkali attack on light metals