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Galvanic plating

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Forum » In General » Galvanic plating
           
Maciej Bialecki
 
 
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24.Nov.09 18:32

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Dear friends,

What kind of galvanic plating it is? This shell was often used for example by Philips. After many years at chassis appear greenish-yellow precipitate (oxide, sulphide, sulphate?) After polishing, it looks like chrome. Was this chassis chromed or cadmium plating or is it another type of shell?

Sorry for my English, I am still learning :)

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This article was edited 24.Nov.09 18:40 by Maciej Bialecki .

Nikolaus Löwe
Nikolaus Löwe
 
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24.Nov.09 19:59

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Dear Maciej,

the green stuff is zinc oxide. It can hardly be mistaken because of its lime green colour. The carrier material is probably iron. Try not to polish too much, the zinc surface is porous and may wear off. I use a mild solvent/cleaning oil named WD40 and a cloth to take off the green zinc oxide and at the same time clean the surface from grease and remains of adhesives or rubber.

Yours,

Nikolaus

Löwe

Maciej Bialecki
 
 
PL  Articles: 12
Schem.: 42
Pict.: 4
25.Nov.09 14:25

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Thank you for reply. But I am not sure if it is zinc oxide (ZnO). As I know zinc oxide is white not lime green colour. ZnO is used for example in Pharmacy ( cream ). What is more Zn sulphate (ZnS) and  Zn sulphide (ZnSO4) is also white. Lime green colour has for example: Cr oxide (Cr2O3)

But what is important. When I put chassis in to “rust remover” which contains phosphoric acid (H3PO4) it smell hydrogen sulfide (H2S ). In my opinion it is sulphide or sulphate because oxides do not smells hydrogen sulphide (H2S ).

I can be wrong of course. Does anyone have any idea?

 Ps.I must remove old surface and apply new one. 

Rüdiger Walz
Rüdiger Walz
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26.Nov.09 21:08

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Only very few radio chassis have been Zinc plated. The only example I know is Lorenz Music-Center 5001. Here the frames for the printed circuit boards are Zinc plated. Zinc becomes dark grey within time.

The parts you show in your photographs are Cadmium (Cd) electro-plated. Cadmium keeps its silvery look much longer than Zinc and can be welded easier than Zinc. Because of that is has been used in Radio Industry.

The yellow colour is Cadmiumsulfide (CdS) or Cadmiumoxide (CdO). CdS is bright yellow and CdO is brownish, in thin layers also green-yellowish.

As you polished the iron parts you removed the thin Cd layers and got a nicely polished iron which will rust within short time without any protection. In my long collector's career I have see several such chassis cleaned up by collectors.

Later laquers containing Aluminium-powder (Al) have been used to protect the chassis. You can remove these organic coatings with organic solvents e.g. like white spirit.

To restore such a chassis I would recoment a modern Al-containing laquer also used for car wheels. You can buy it in do-it-yourself stores in spray cans. If you spray in thin layers you will get a little bit rough surface like the original look.

By the way: Be careful in polishing or cleaning Cd coated iron parts. Cd is hazardous. Use gloves and do not inhale the dust. See also safety data sheets for Cadmiumoxide or Cadmiumsufide in the www.

Rüdiger Walz

This article was edited 26.Nov.09 21:18 by Rüdiger Walz .

Maciej Bialecki
 
 
PL  Articles: 12
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Pict.: 4
27.Nov.09 19:39

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You are right. Now I am 100% sure it is Cd. Thank you for the confirmation of my conjecture. Of course, I took appropriate measures of protection, before started working with it.

Maciej Bialecki

  
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