Why Bronze disease hides - a new argument for cleaning

[bruce61813]

Here goes, and this is really going to stir things a bit. I have been redoing my old articulate on Bronze Disease for publication, and have several things to add.

1. Bronze disease is a misnomer, if you actually look at my original paper, BD should be called Copper Disease. It is present in all the copper alloys, not just bronze.

2. Copper II [ that is the reduced form of copper,  and is the trouble maker] is not just the cyan color we have associated with BD. the cyan color is the fully hydrated form of Copper II, in it's anhydrous form it is a dark brown, and depending on the relative humidity, it can go from anhydrous to a saturated form in as little as 8 days. for a full visual see -  http://www.amazingrust.com/Experiments/background_knowledge/CuCl2.html for pictures of a 6 day change in color.

I am working on my own set of pictures, but i need to get a hygrometer so i can track the real relative humidity as i photo graph the change in color. But to start with, the attached photo shows the dry [anhydrous] form of copper II and the fully wet form [not dissolved].

As you can see, the copper disease can hide in dirt and in small encrustations and crevasses in the coins matrix, just waiting for atmospheric moisture or and other form of water. Once it has reach the cyan color it begins converting copper to copper II in a complex cycle, and if NaCl is present, into CuCl2 .

this should add to the discussions.



Bruce-of-the-many-numbers

[SC]

Bruce,

I look forward to the updated article.

Is your research shed any light on the dark-red brown colour that seems related but is itself hard and solid?

Also the question of the boils that sometimes appear as part of (?) or with BD?

Shawn

[bruce61813]

The red-brown is probably pure copper left after the copper II has become neutralize, with some advanced analysis I can't tell. Unfortunately I don't have the equipment.

Added  information:

What Happens and To An Extent Why.
    Copper in moist air slowly acquires a dull green coating, called Verdigris, because its top layer has oxidizes with the air. Some architects use this material on rooftops for this interesting color. The simple chemistry is as follows:

The green material is a 1:1 mole mixture of Cu(OH)2 and CuCO3.
2 Cu(s) + H2O + CO2 + O2 → Cu(OH)2 + CuCO3(s)
Malachite is (Cu2(OH)2CO3). Copper II can  be generated by treatment of the hydroxide, oxide, or copper(II) carbonate with hydrochloric acid. In many cases it is the simple formation of Hydrochloric acid from Sodium chloride [NaCl] and water [H2O].
NaCl + H2O → NaOH + HCl

2NaOH + 2HCl + CuCO3(s) = NaCO3  + CuCl2  + 2H2O
Why is it so hard to detect?
   Anhydrous Copper II Chloride may appear in color from a dark brown to the cyan green, depend on the amount of atmospheric moisture that is absorbed. If it was in a desert region with very low relative humidity and dry air, it may never be seen. In moist or very humid areas, it changes color rapidly and starts to work on the solid copper.



Bruce