The effect of atmospheric moisture: Japan Koizumi and Roy, etc., respectively, the use of cathodic reduction method and electrodynamic measurement technology, studied the effect of moisture on the oxidation of copper surface. Today, GNEE will share with you the four main factors of oxidative discoloration on the surface of copper pipe.
Their experiments consistently illustrate that humidity has a great role in promoting the formation of the surface film, the growth rate of the oxide film in high humidity is much greater than in dry air, the density of the formed oxide film is more than half of the small. It was deduced that the oxide film formed under humid atmospheres has internal defects similar to porous ones, and that such defects make the oxide film less dense and less protective of the basic.
Koizumi further pointed out that in a humid atmosphere, even if the copper surface does not condense, a humid surface liquid film is easily formed. Under this liquid film the same electrochemical reaction will occur as when immersed in water:
Anodic reaction: Cu → Cu + e
Cathode reaction: 2H2O+O2+4e→4OH-
It should be noted that: in the humid atmosphere generated by the oxide film is Cu2O, and copper in the water when immersed in the oxide film generated at the same time contains Cu2O and CuO, which indicates that the degree of oxidation in the humid atmosphere is relatively low.
The impact of surface pollution: surface pollution on the surface of the copper tube surface oxidation reaction is great, even if the fingerprints of a class of minor pollution, but also the surface of the copper tube will soon change color. This is mainly due to pollution at the saturated vapor pressure drop, conducive to the formation of water film, while the pollutants so that the conductivity of the water film has been greatly improved to accelerate the process of electrochemical corrosion, that is, to accelerate the rate of oxidation of the copper surface discoloration.
Impurity gases in the environment: impurity gases in the environment is also one of the main factors contributing to the oxidative discoloration of copper surface. Tests show that the content of So2 in the atmosphere ≤ 100PPM, as long as the relative humidity of the atmosphere RH <60%, the discoloration does not have much effect, but when the RH> 60%, it is obvious to accelerate the corrosion rate. Hydrogen sulfide (H2S) effect is more obvious, even in 1PPM micro-content will quickly change the copper surface color. It not only reacts directly and generates copper sulfide, but also catalyzes the oxidation of copper, production of Cu2O. in China, especially in coastal areas, due to industrial development, air pollution is serious, sulfur in the air, chlorine and other impurity gases, the environment on the surface of the copper tube oxidation and discoloration of the impact is more prominent.
Copper coil annealing out of the surface conditions before the impact: copper coil annealing out of the surface conditions before the discoloration of the copper tube is very important for the future impact. For example, air conditioning parts manufacturers with potassium dichromate containing sulfuric acid pickling of copper tubes than simply with sulfuric acid pickling of copper tubes, the ability to resist discoloration is stronger. Mainly due to the former in the copper tube surface to form a protective chromium film.
