Ted Mooney, P.E. RET
- Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Removal of copper oxide using cyanide
1999
My question relates to the removal of copper oxide from sterling silver parts using a mixture of sodium cyanide, water, and hydrogen peroxide. Sterling silver parts (92.5% silver and 7.5% copper) are soldered using a traditional soldering operation. A copper oxide forms on the parts. The copper oxide is removed using a three bath process.
- The first bath contains a mixture of:
- 100 mL dilute sodium cyanide (180 g/L NaCN)
- 1.5 L H20
- 100 mL hydrogen peroxide
- 1.5 L H20
- The second bath contains:
- 400 mL of dilute sodium cyanide (180 g/L NaCN)
- 3L H20
- The third bath contains only water.
Questions:
- 1. Exactly what is the chemical reaction that causes the copper oxide to be removed?
- 2. Does the hydrogen peroxide oxidize the sodium cyanide?
- 3. Is this process considered "chemical etching?"
- 4. What alternatives are available to replace the cyanide?
Any information/suggestions much appreciated.
kelley begin- boston, Massachusetts
It appears that you have oxidation-reduction reaction. Hydrogen peroxide is a mild oxidizing agent. So NaCN will be oxidized to NaOH or Na2CO3 and copper oxide is reduced to copper, removing oxide. As an alternative you my try 10% acetic acid ⇦this on eBay or Amazon [affil links] solution, preferably hot for a duration that will depend on oxide thickness.
Ram SinghSunnyvale, California
1999
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