"""...1)When i make the part anodic for a brief period and oxygen is liberated at the part surface.Doesn't the negative oxygen ions(O--)oxidize the part again and make the part surface to be copper oxide again(CuO)?
I know that the O-- ions give electron to the anode and become a gas,but what happens next,that cause the Cu++ ion to drop into the solution,rather than be connected with the oxygen ions in order to form CuO again?
Ok, so backing up, normally you would be using an alkaline cleaner for an electrocleaner. The normal process involves electrocleaning the part and then following up with an acid dip. Yes, through anodic cleaning, you will produce somewhat of an oxide film at the surface of the part, but a dip into acid will remove the oxide film because it has very low adhesion. The de-plating action of the anodic cleaning will help remove all other impurities on the surface, leaving you will a clean part surface and a very thin oxide layer, which as I said can be removed with an acid dip. This oxide layer can also be left on as a passivation layer that helps with corrosion resistance. However, it should not affect the appearance of the part.
2)When i make the part cathodic and the H+ ions take electrons from the copper oxide surface part and turns to bubbles gas,How does this action cause the oxygen from the part surface to be removed?
Also,when the oxygen is removed from the part surface in that process,the part is also being plated with Cu++ ions and with other loose ions in the solution,Isn't it disturb to the cleaning process?..."""
Water gets broken down at the part surface, which is where the hydrogen comes from. The hydrogen at the part surface is reducing the oxides and forming OH- ions. I would guess that if you check the pH of your cleaning solution after cathodic cleaning that the pH would be higher than when you started. I say guess because I've never used an acid for electrocleaning, it's just a thought.
The part will be plated with some ions, whether copper or anything else you have in the solution, but keep in mind that these we have very, very low adhesion. The scrubbing done by the hydrogen gas helps clean the surface and may help remove some of those plated ions. Keep in mind that the hydrogen evolution during cathodic cleaning is twice as high as the oxygen evolution during an anodic cleaning, so it is a pretty violent scrubbing action. But this is exactly why you do the anodic cleaning as the final step, because that will remove what was loosely plated. You should always end with anodic cleaning.