Buckit - chemistry query - PolyTech Forum

Bill H 15 years ago

Decided to do my good deed for the day and put a mixture of cinder ashes and a bit of rock salt along the wheel ruts. Since the ashes were still hot from yesterday I used our galvanised steel bucket instead of the uusal plastic one.

Imagine my horror to find, after a happy hour sprinkling this mixture, that the bottom of the bucket had turned to lace. This bucket has been used for years for moving ash between the fire and the galvanised dustbin we put it in to cool; so plain ash usually takes a while to wreck it.

Clearly the salt has had a major effect. Can anyone explain the likely chemical mix going on that produces such a corrosive mixture?

Obligatory model engineering bit - I feel a riveting job coming on. Bill H Derby

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David Littlewood 15 years ago

In article , Bill H writes

Bill,

As Jim said, I don't think and caustic alkali would attack iron (though it does attack zinc).

Two other possibilities. First, sodium chloride in solution is itself pretty corrosive towards iron; I doubt though that it would rust through

*that* quickly. Second, some sulphur-containing coals will produce a fair amount of sulphur dioxide and trioxide on burning. This will result in some sulphuric acid, or other strong acids, which will react with NaCl to give HCl - hydrogen chloride, the anhydrous form of hydrochloric acid. Now this will be able to migrate rapidly through the ash and corrode the iron quite swiftly.

This may seem quite contradictory to Rusty's KOH hypothesis; I don't know the answer, but although I know wood ash is indeed rich in strong alkali (especially KOH) I have never hear that coal is similar in this respect.

Any good hypothesis should be capable of testing. To do this, place the same brew in a plastic bucket with some steel object suspended above it, but not touching the solids, and preferably with a lid. Since the only likely gaseous products would be SOx and HCL, the appearance of corrosion would tend to support my hypothesis.

David

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Bill H 15 years ago

Will have a go. It is coal ash not wood ash. It was the speed of destruction that amazed me. Bill H Derby

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