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anodized aluminum product Article Contents: Aluminum Anodizing Practice Aluminum Anodizing Steps Electropolishing Alkaline Solution ...

July 8, 2008

Degreasing Metallic Article

Degreasing metallic article prior to electroplating is therefore accomplished by immersing them for some time in a tank containing the hot, mixed alkaline solution. The typical formulation is given in the table below:


Chemicals
Formula
Heavy Duty
Oz/gal (g/l)
Medium Duty
Oz/gal (g/l)
Light Duty
Oz/gal (g/l)
Caustic Soda
NaOH
6 (37.5)
2 (12.5)
-
Sodium Carbonate
Na2CO3*
4 (25)
4 (25)
-
Trisodium Phosphate
Na2PO4.12H2O
1 (6.2)
2 (12.5)
4 (25)
Sodium Metasilicate
Na2SIO2.5H2O
-
2 (12.5)
4 (25)
Sodium Cyanide
NaCN
-
-
2 (12.5)**
Wetting Agent

0.25 (1.5)
0.12 (0.75)
0.12 (0.75)
  • * Anhydrous sodium carbonate, commercially known as soda ash. The decahydrate Na2CO3.10 H2O, known as washing soda, may be used in proportionately greater amount.
  • ** Sodium cyanide optional, but particularly valuable with copper alloys.

The stronger and harsher alkalis are the most effective for saponification, but not necessary for emulsification; they also tend to stain iron and steel, and attack zinc and aluminum. Potassium hydroxide is even stronger and harsher than sodium hydroxide and is much more expensive. Caustic alkalis rapidly absorb carbon dioxide from the air; they are also not compatible with many useful synthetic detergents. For these reasons most degreasing solutions today are formulated from the milder alkalis, such as sodium carbonate, sodium silicate and sodium phosphate. Sodium cyanide is often also included in cleaners for copper alloys and other non-ferrous metals as it dissolves oxide and sulphide stains chemically.

Alkaline degreasing solutions can conventionally be contained in mild steel tanks, which are not attacked by alkalis. Such tanks are cheap and can easily be heated by external flames or internal steam coils. Handling the articles themselves after the degreasing operation would be likely to re-contaminate them, so it is universal practice first of all to fasten the articles onto wires or jigs of convenient design, by means of which they can be handled and supported in the various tanks, not only for degreasing but throughout the electroplating processes.