[that mad man (OP)]

I have recently been doing a lot of electronics design and have been etching printed circuit boards using sodium persulphate.

This is the first time in using it as I have used ferric chloride etchant in the past.

The solution starts out clear and over time the build up of dissolved copper in it turns it a nice blue colour.



Sodium Persulphate after some use.



I have to add that this is NOT the bottle it is stored in but just used for the photo because it was clear.

Now, I had a mark on a bit of copper board and decided to help the etch by scraping the surface of the board with a steel blade.

This happened to the blade after a few minutes.



As you can see, it has been coated with copper!

The copper coating builds up easily and can be peeled off into a deposit.



Once the copper is peeled off the blade looks black.



But after dipping in the etchant the copper builds up and can be scraped off again.



This I would think is not electroplating as that uses current and electrodes, so what is happening.

It must be some chemical reaction but does anyone know what?

The more copper dissolved in the solution make the solution weaker so, If I keep doing this and recover the copper would I be right to suggest that the solution would get stronger?

If so then this could be an economical way of copper recovery on "old" circuit boards, or perhaps its already used?

Taps head and thinks for a change......

 []

Bee

PS sorry, I hope the photos are not too big!

[lightarrow]

I have recently been doing a lot of electronics design and have been etching printed circuit boards using sodium persulphate.

This is the first time in using it as I have used ferric chloride etchant in the past.

The solution starts out clear and over time the build up of dissolved copper in it turns it a nice blue colour.



Sodium Persulphate after some use.



I have to add that this is NOT the bottle it is stored in but just used for the photo because it was clear.

Now, I had a mark on a bit of copper board and decided to help the etch by scraping the surface of the board with a steel blade.

This happened to the blade after a few minutes.



As you can see, it has been coated with copper!

The copper coating builds up easily and can be peeled off into a deposit.



Once the copper is peeled off the blade looks black.



But after dipping in the etchant the copper builds up and can be scraped off again.



This I would think is not electroplating as that uses current and electrodes, so what is happening.

It must be some chemical reaction but does anyone know what?

The more copper dissolved in the solution make the solution weaker so, If I keep doing this and recover the copper would I be right to suggest that the solution would get stronger?

If so then this could be an economical way of copper recovery on "old" circuit boards, or perhaps its already used?

Taps head and thinks for a change......

 []

Bee

PS sorry, I hope the photos are not too big!

Nice photos.
The effect is very simple: Fe + Cu⁺⁺ --> Fe⁺⁺ + Cu
So copper(II) oxides iron reducing itself to copper iron, which deposit on the blade and iron goes in solution. You can have the same effect potentially with all the metals which reduction potential is lower than that of copper.
If you do it with powdered zinc, for example, the reaction is so exothermic that you can see the solution to boil.

[that mad man (OP)]

Thanks for the explanation lightarrow. []

My mistake was assuming that you needed electrodes and a current flow for that to happen as in electroplating.

What surprised me was how quick the reaction occurred and how easily the copper deposited.

Now I have to find out if the iron build up in the solution will affect its ability to dissolve copper.

Some controlled experimenting me thinks.  []

Bee

[lightarrow]

Thanks for the explanation lightarrow. []

My mistake was assuming that you needed electrodes and a current flow for that to happen as in electroplating.

What surprised me was how quick the reaction occurred and how easily the copper deposited.

Now I have to find out if the iron build up in the solution will affect its ability to dissolve copper.

Some controlled experimenting me thinks.  []

Bee

Sometimes chemistry is amazing, and fascinating, isnt'it?

[that mad man (OP)]

To me it definitely is.

Something I have never had any schooling in, not that I had much schooling anyway....  [:I]

[lightarrow]

To me it definitely is.

Something I have never had any schooling in, not that I had much schooling anyway....  [:I]

Make me know the results of your future experiments!