During the resistance brazing of silver and copper alloys, copper oxide forms on the surface of pure copper due to an increase in the alloy's temperature, and copper reacts with oxygen to form copper oxide on the surface of the alloys. If oxide removes by any wet method, then bolding between copper and silver brake. And paper polish method properly works but takes a lot of time for a larger quantity of alloys and also damages the human skin during polishing.
I mean, you could try heating it in a hydrogen atmosphere, but why exactly does it have to be dry? What speaks against using wet electrochemistry for your application?
This is a bi-metal electrical contact rivet, the bottom is pure copper, and the head is silver alloy. As a requirement, contact rivets are made by these two alloys and joined by resistance brazing with filler Metal (braze alloys). If the rivet size is small, go for the cold forging method. But the rivet size was large; then used in resistance welding methods, the during resistance welding temperature of the rivet increased, and copper reacted with the atmosphere and formed copper oxide. Remove copper oxide on the surface of copper by the wet method, and then it is more chance that silver alloys and copper alloys will separate, bobble formation between the two-layer. And wet methods rivet fail during operation.
A simple dry method to clean any metallic surface, is by sand blasting.
K. Sreenivas thanks for answering. it is possible for small size of sample. ?
The answer is yes. Question how small an object.
Well in my sputtering system, many metallic component, shields, target clamping rings, metallic substrate holders etc., use to get coated with sputtered films, which were very hard to remove. Chemical, wet cleaning and abrasion were not convenient, because the components had complicated shapes and edges.
During my post doc research, I found the sand blasting machine in the mechanical workshop very convenient. It used to save my day, and keep my sputtering chamber always very clean, and allowed me to achieve a good vacuum.
It is like a glove box, with a thick transparent window (you can see through it. Keep the components to be cleaned inside, close the door, start the machine, and there were gloves, into which we insert our hands. With one hand we used to hold the sand blasting gun with a trigger, and the component to be cleaned with the other hand. Fine micron sized sand particles would should out from the gun as the trigger is pressed. You can have different nozzles.
So if your object to be cleaned can be held firmly with your fingers, you can easily sand blast it gently to skim off the rusted, or oxide layers very easily.
You will find these machine in a typical well equipped mechanical workshop.
At least in foreign countries it was a standard facility.
K. Sreenivas . Thanks sir. best solution for this problem is copper oxide heat with ammonia gas at 320 degree.
Reaction of copper (II) oxide with Ammonia gas at above 300 °C temperature
3CuO (s)+ 2NH3(g) → 3Cu(s) + 3H2O(g) + N2(g)
This alternate method you have found also seems to be quite interesting, especially for small Cu components which can be inserted into a tube furnace conveniently, and can get cleaned up. It is worth trying.
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