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Aluminium anodizing (eloxal or Electrolytic Oxidation of Aluminium) [12] is usually performed in an acidic solution, typically sulphuric acid or chromic acid, which slowly dissolves the aluminium oxide. The acid action is balanced with the oxidation rate to form a coating with nanopores, 10–150 nm in diameter. [6]
A current passes from the anode, where metal on the surface is oxidised and dissolved in the electrolyte, to the cathode. At the cathode, a reduction reaction occurs, which normally produces hydrogen. Electrolytes used for electropolishing are most often concentrated acid solutions such as mixtures of sulfuric acid and phosphoric acid.
Chemical coloring of metals is the process of changing the color of metal surfaces with different chemical solutions. The chemical coloring of metals can be split into three types: electroplating – coating the metal surface with another metal using electrolysis. patination – chemically reacting the metal surface to form a colored oxide or ...
An electrolyte of 100 g of litharge dissolved in 0.5 l of water can also be used in which 100 g of NaOH is dissolved. Becquerel used a solution of 200 parts water, 20 potassium hydroxide and 15 litharge. A. Roseleur used a much milder solution of 200 parts of water, 10 parts of potassium hydroxide and 1 part of litharge. [21]
Hexavalent chromium plating solution is used for both decorative and hard plating, as well as bright dipping of copper alloys, chromic acid anodizing, and chromate conversion coating. [2] A typical hexavalent chromium plating process is: Activation bath; Chromium bath; Rinse; Second rinse
Porous AAO is formed by electrochemical oxidation (anodization) of aluminum in acid electrolytes in the conditions that balance the growth and the AAO films are formed with limited thickness. Anodizing aluminum has been widely used since early last century for corrosion protection and decorative purposes.
A phosphate coating is usually obtained by applying to the steel part a dilute solution of phosphoric acid, possibly with soluble iron, zinc, and/or manganese salts. The solution may be applied by sponging, spraying, or immersion. [6] Phosphate conversion coatings can also be used on aluminium, zinc, cadmium, silver and tin. [7] [8]
The NaOH (caustic soda) and elevated temperature cause Fe 3 O 4 (black oxide) to form on the surface of the metal instead of Fe 2 O 3 (red oxide; rust). While it is physically denser than red oxide, the fresh black oxide is porous, so oil is then applied as post treatment to the heated part, which seals it by "sinking" into it.
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