Alkali attack on light metals
Aluminium, zinc and their alloys are dissolved by strong alkalis as readily as by acids, and the reaction gives off hydrogen.
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 regulator fact sheets in this register say 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
Sources for this page
Sources
Right to Know Hazardous Substance Fact Sheet: Potassium Hydroxide (RTK 1571)
New Jersey Department of Health, 2010 · Government or regulator
Relied on for: That potassium hydroxide is corrosive in moist air to aluminium, zinc, tin and lead, forming flammable and explosive hydrogen gas. (states this directly)
Verification: a person has read the passage relied on.
Read on — The 'Description and Use' paragraph and the 'Handling and Storage' reactivity list. Supports the claim as stated. Completes the caustic pair, and the aluminium statement is the evidential basis for warning against caustic oven products on aluminium bakeware and trim, which had rested on the sodium hydroxide record alone.
Right to Know Hazardous Substance Fact Sheet: Sodium Phosphate, Tribasic (RTK 1724)
New Jersey Department of Health · Government or regulator
Relied on for: That trisodium phosphate solutions react with aluminium, zinc and galvanised iron to produce flammable hydrogen gas. (states this directly)
Verification: a person has read the passage relied on.
Read on — The 'IDENTIFICATION' paragraph and the 'HANDLING AND STORAGE' reactivity list. Supports the claim as stated. Adds the alkaline builder family to the agent records, and gives the catalogue a fourth independent regulator statement that alkalis attack aluminium — which is now sourced from sodium hydroxide, potassium hydroxide, trisodium phosphate and sodium carbonate rather than from one sheet.
AAMA 609 & 610-02: Cleaning and Maintenance Guide for Architecturally Finished Aluminum
American Architectural Manufacturers Association (AAMA), 2002 · Standards body
Relied on for: That aggressive alkaline cleaners must never be used on aluminium finishes and that marks from mistreatment may be permanent. (states this directly)
Verification: a person has read the passage relied on.
Read on — Read in full. Sections 3 General, 4.1 light surface soil, 4.3 organic coatings, and 5 Cleaning Precautions. Supports the claim as stated.
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