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Clean Nickel Silver
Enthalpy:
Hi dear friends!
Here are interrogation and observations about bicarbonate and aluminum cleaning nickel silver.
The item is my flute. It stayed some 40 years exposed to the air in a normally dry room, the last untouched 8 years were the worst. Supposedly banal nickel (or German) silver: variable Cu-Ni18-Zn27. Definitely no silver layer on it. The black patch is adhesive tape. The clean patches are unalloyed tin hold by unsupported acrylic tape, they look like new after 40 years. The covers where I put my fingers are the less corroded ones, so fingers clean nickel silver faster than they corrode it. The cleaner end at the headjoint (second longest joint) stayed fit in the main joint all the years.
The bath is what Internet rumours recommend for true silver:
* 1 litre boiling (microwave) water (tap).
* 2 tablespoons bicarbonate ("pure" from drugstore).
* A piece of aluminium foil (supermarket, usually Fe+Si 0.5% to 1%) at the bottom.
* Plastic container (feels and looks like polypropylene, meant for cereals).Observations:
* Aluminium fizzles in boiling bicarbonated water without the nickel silver, producing an odour known in electrochemistry.
* Bicarbonate poured in boiling water bubbles shortly, and then the alu foil doesn't fizzle. Supposedly, a decomposition cools the solution excessively. So, bicarbonate before heat.
* Action is within seconds, including from the foam. Dirtier places take longer, you guessed.
* The setup loses its efficiency quickly. The alu foil tarnishes, the bath gets less transparent, the temperature drops.
* Microwave and plastic container let re-heat easily. Wrapping paper and a lid conserve heat. An immersed resistor would help.
* Contact of nickel silver with aluminium makes no difference. For the small cleaned portion of the head joint, I avoided the contact.
* Aluminium is necessary.
* The used bath didn't etch my fingers. No strong NaOH concentration formed.
* Some places at nickel silver still needed short rubbing, which was inefficient before. A piece of old bedsheet worked with downpressure without any lotion.Can you propose a reaction? The usual "sacrifical anode" must be ba***cks. I vaguely suspect some aluminium hydroxide scavenges the corrosion layer at nickel silver. At heat, bicarbonate might etch aluminium like NaOH does. Or the bubbles do the job. They could be strongly reducing (hydrogen??), and somehow activated.
I must still clean the main joint and the keys (removed to clean the joints, reassembled, check the contrast) so I can experiment your suggestions. No lab here, not even a thermometer, that's home chemistry - but an ohmmeter yes.
Thank you!
Marc Schaefer, aka Enthalpy
AWK:
Sodium bicarbonate thermally decomposes at around 80°C and the solution becomes strongly alkaline (pH ~ 11.5).
Enthalpy:
--- Quote from: AWK on June 04, 2020, 05:09:29 AM ---Sodium bicarbonate thermally decomposes at around 80°C and the solution becomes strongly alkaline (pH ~ 11.5).
--- End quote ---
Yes. The only argument against this explanation is that I took no precautions at all and noticed no itch.
If I had 10g of NaHCO3 in 0.5L water, after full decomposition the pH could reach >13, but the amount of bubbles speaks against full decomposition.
I'll experiment a bit.
AWK:
NaHCO3 decomposes in hot water to Na2CO3.
Enthalpy:
--- Quote from: AWK on June 05, 2020, 10:00:09 AM ---NaHCO3 decomposes in hot water to Na2CO3.
--- End quote ---
I added beetroot juice to the water. It kept violet when the tap water boiled. Adding bicarbonate made little immediate difference, but after short renewed boiling the solution went yellow.
Complete conversion of 10g bicarbonate would have released 1L dioxide, so obviously the conversion to carbonate is very limited. My unprotected fingers don't itch.
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