On 02/08/2018 10:49, Thomas Prufer wrote:
On Wed, 1 Aug 2018 22:50:55 +0100, John Rumm
wrote:

DS3 is not HCL, but sulfamic acid (H3NSO3), generally safe on metals,
although may dull chrome on prolonged exposure.

Zinc gets eaten by pretty much everything, though.

I found a patent, including this language: "Even at room temperature Islamic
acid rapidly attacks zinc galvanize; in aqueous solution at concentrations as
low as 1.5% by weight, it is capable of completely dissolving a zinc galvanize
coating from a ferrous metal base in two to three hours. Repeated use of Islamic
acid even for short periods will severely corrode zinc galvanized equipment. The
corrosive effect of the acid on zinc increases with temperature, and galvanize
may be removed in less than 30 minutes at a temperature of 140 F."

And also this: "Weak acids such as citric acid, formic acid and sulphuric acid
are suitable for use with metals such as aluminum, zinc, copper and nickel.
Although these metals will be affected by these acids, this will be much less
severe."

A while back I asked a bunch of chemists with what to descale a pot with an
intact, thick layer of zinc -- and didn't get a useful answer. I ended up using
a wet stiff brush and elbow grease. This got rid of enough scale to be useful,
say 80%, and was surprisingly efficient. The removed scale formed a milky soup
that abraded the remaining scale very well...

In this case: if the zinc is gone, it won't be attacked. Just keep an eye on it,
OK?


Thomas Prufer

Interesting. IIRC the De Longhi coffee machine warns against sulphamic
acid, there may be zinc plated screws in there. Lactic acid, apparently:

https://www.delonghi.com/Global/coun...odecalk500.pdf