drgary wrote:To address aluminum boiler corrosion, you can also use a sacrificial zinc anode, as documented on page 2 of this old thread:

Aluminum Boilers, Care and Feeding

I somehow ended up here while searching for the best product for descaling an aluminum boiler. As someone with 2 degrees in metallurgy / metallurgical engineering I would caution against the use of a sacrificial zinc anode to protect an aluminum boiler. Cathodic protection is definitely not my specialty but I know enough about it to say it can be extremely complicated and is more art than science. I believe zinc acts as an anode to aluminum when the aluminum is coated with its natural protective oxide layer but the zinc becomes the cathode when the aluminum looses that oxide coating. So zinc will protect aluminum in some situations but will accelerate aluminum corrosion in others. I believe zinc anodes are used for aluminum hulled boats in seawater mainly to act as the sacrificial anode for the steel in the outboard motor so that the aluminum hull doesn't become the steel's sacrificial anode. The aluminum hull by itself (i.e. if there were no outboard motor) really doesn't need protecting because of its protective oxide layer. I suppose zinc could provide the same service in an aluminum / stainless steel espresso machine boiler? However, we don't make espresso with seawater and residential water chemistry is all over the map (very hard to very soft) so you could be making the situation worse with zinc - at higher pH the aluminum can become the sacrificial anode. Then there is temperature - I don't know how that factors into the equation? You also have fairly high electrical currents running through the heating element in or around the boiler which creates magnetic fields that might complicate things further. Someone in the old string suggested that magnesium would make a better sacrificial anode than zinc - looking at the galvanic series that makes sense but in practice the reaction between the magnesium and aluminum can create alkalies (high pH substances) that can corrode the aluminum (and presumably put a hole in your boiler). So bottom line - I'd stay away from trying to protect your aluminum boiler with a sacrificial anode. It might help, it might hurt, but my guess is that in most circumstances it would not do a thing. Anodizing, is a process that produces a thicker, harder oxide layer than the aluminum can make on it's own - if you really want corrosion protection of your boiler that might be the way to go - it's not difficult or complicated (I did it in high school chemistry lab) but it's a lot more trouble than I'd be prepared to go to - then again, I have relatively cheap espresso machines for which cheap replacement boilers are readily available - I suppose I might think differently if I had a $10,000 machine with a $1000 boiler.