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topic 11476

HCl as a cleaning agent for some forms of copper corrosion?


Does HCl remove some normal surface contaminates from copper?

AL Hawes
US NAVY - Crane, IN, USA


Sure. It removes tarnish (copper oxides).

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


HCl will remove the copper oxides/hydroxides that build up when copper is left in air. It will not touch the base metal. For that you need an oxidising acid mix. It will not shift the oils or soils that might be on the surface for that you will need a cleaner.

Martin Trigg-Hogarth
Martin Trigg-Hogarth
surface treatment shop - Stroud, Glos, England


HCl will definitely dissolve copper and most copper alloys when exposed to air. An interesting demonstration of this is to take a new U.S. penny, nick the edge with a file to expose the zinc core, and drop it into some HCl. The zinc will act as a sacrificial anode and will offer galvanic protection to the copper until all of the zinc is reacted. If you watch the reaction carefully, you can actually remove the penny after the zinc is gone and you will have a thin copper "shell". If you don't watch the reaction carefully, the solution will turn blue and the entire penny will be gone; you will have a solution of HCl plus zinc and copper chloride.

If you are cleaning copper or brass with HCl, be sure to use acid diluted with distilled water and be sure to rinse completely after treatment. Also, HCl will etch brass, so be careful.

Dale Woika
Surface Conversion Sciences - Bellefonte, Pennsylvania, USA


I believe that there are better demonstrations of galvanic protection, the zinc is far more reactive than the copper, and the Metals Handbook says that the reaction of copper with acids depends largely on oxidizing conditions, so something else must be happening in your experiment.

pooky tom pullizi signature
Tom Pullizzi
Falls Township, Pennsylvania

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