Reason and treatment of red copper oxidation

Reason and treatment of red copper oxidation

 

Red copper oxidation causes and red copper anti oxidation treatment? The blackening of red copper is the performance of copper oxidation. There are many reasons for copper oxidation. In order to prevent copper oxidation, we can take relevant measures. At present, there are many anti oxidation measures for red copper. It is very important to oxidize copper from different aspects

The definition of copper oxidation can be divided into narrow definition and broad definition. The narrow definition of copper oxidation: the chemical reaction between oxygen element and copper, which is called oxidation, is also an important chemical unit process; the broad definition of copper oxidation refers to the process of copper loss of electrons (increase of oxidation number). Knowing the definition of red copper oxidation, this paper introduces the reasons of red copper oxidation and its anti oxidation treatment.

 

1、 The chemical reaction formula of copper oxidation is as follows

2Cu+O2==2CuO

4cu + O2 = = 2cu2o (insufficient oxygen, or temperature above 1000 ℃)

2Cu+O2+H2O+CO2=Cu2(OH)2CO2

 

2、 Color of red copper after oxidation

1. Red copper may also be oxidized to cuprous oxide (Cu2O), which is brick red.

2. Red copper is black after being heated and oxidized, which is copper oxide (CuO).

3. Red copper will turn green (copper green) in humid environment for a long time, that is, basic copper carbonate (Cu2 (OH) 2co2).

 

3、 Reason of copper oxidation

1. The reason of copper surface oxidation: the surface discoloration of copper is related to the humidity of atmosphere, the pollution of copper surface and the impurity gas in the environment.

① Surface pollution: the surface pollution has a great influence on the oxidation discoloration of copper surface. Even slight pollution such as fingerprints can make the copper surface discolor quickly. The reason is that the saturated vapor pressure of the polluted area decreases, which is conducive to the formation of water film. At the same time, the conductivity of the water film is improved and the electrochemical corrosion process is accelerated.

 

② The surface condition of red copper before exposure: the surface condition of red copper before exposure has great influence on the discoloration of red copper after exposure. For example, the anti tarnish ability of the red copper pickled with sulfuric acid containing potassium dichromate is stronger than that of acid pickling with dilute sulfuric acid only, which is mainly due to the formation of protective chromium film on the surface of red copper by the former.

 

③ Atmospheric humidity: atmospheric humidity has a great promoting effect on the oxidation discoloration of copper surface. The growth rate of oxide film under high humidity is much faster than that in dry air, and the density of oxide film formed is more than half of that in dry air. It can be inferred that the oxide film formed in humid atmosphere has similar porous internal defects. This defect reduces the compactness of the oxide film and the protection to the matrix. In humid atmosphere, even if the surface of copper is not dewed, it is easy to form a liquid film on the wet surface, which produces the same electrochemical reaction as immersion in water to form an oxide film with chemical composition of Cu2O (it should be noted that the oxide film formed by immersion of copper in water contains both Cu2O and CuO).

 

④ Impurity gas in the environment: the impurity gas in the environment is also the main factor to promote discoloration. The test shows that when the content of SO2 in the atmosphere is less than 100 × 10-6, as long as the atmospheric relative humidity is less than 60%, the color of copper surface has no great change; however, when the humidity is greater than 60%, the corrosion rate is obviously accelerated. The effect of hydrogen sulfide is more obvious, even if the content of hydrogen sulfide is 1 × 10-6, the color of copper surface will change quickly. In coastal and industrial urban areas, the discoloration degree of red copper specimens is more serious than that in mountainous areas. The corrosion products near the sea contain more elements such as chlorine and sodium, while the corrosion products in industrial areas contain more elements such as s, Si and al.

 

2. The internal surface oxidation reason of red copper was as follows

① During annealing, the protective gas in the furnace is unqualified and the cleanliness of furnace gas is not enough.

② The cleaning process before or after annealing is not careful, and a large amount of cleaning fluid remains on the inner surface.

③ The process of blowing protective gas into the tube before annealing does not meet the requirements. For the coil without internal purging process in annealing process, if the protective gas blowing into the tube before annealing does not meet the requirements and oxygen or water gas is left in the pipe, the inner surface of the pipe is easy to be oxidized and discolored after annealing, such as insufficient pressure and time during blowing, leakage of blowing pipeline and joint, unqualified protective gas for blowing, not timely entering the furnace after blowing or unsealed at both ends Air is replaced by external air. The blackening in the coil caused by this reason is shown as blackening at one end or both ends; sometimes it is shown as a bright section in the middle section and a blackening section in the interval, which is generally difficult to check and find out, which is often found by users in the process of use. During annealing, the protective gas in the furnace can reduce the inner surface of a section near the ends of the coil, and only the inner surface of the middle layer (local) of the coil appears black.

④ The internal lubricating oil used for drawing has too high sulfur content and forms cus (black) after annealing.

⑤ During the annealing process of internally grooved tube, the internal purging process is not operated properly or the purging gas is unqualified.

⑥ Copper drawing or finishing layer winding (or rewinding) is not careful, occasionally there are external oil or cleaning agent inhaled on the inner surface of pipe head and tail, and residual oil and carbon black on the inner surface after annealing.

 

3. The causes of copper surface oxidation in actual production are as follows

(1) surface pollution: the following factors easily cause copper surface pollution and oxidation and discoloration: a copper surface is wetted by (rain) water; B residual emulsion or liquid after cleaning is spattered on the surface of copper; C occasionally contaminate other surfaces contaminating copper surfaces (such as overhead car lubricants plus too much drip); D bare hands contact copper; e packaging has corrosive properties.

② Wet weather: the weather in southern China is relatively humid, and oxidation blackening occurs during the production process.

③ Improper control of process parameters: insufficient exhaust gas during annealing, unclean atmosphere in the furnace, high temperature of furnace, etc. will lead to more unqualified products with discoloration and blackening.

④ Annealing equipment failure: during copper annealing, the lower the oxygen potential of protective atmosphere in furnace is, the better. The oxygen content of protective atmosphere in furnace is required to be only 10-6 grade, and it is better to have slight reducibility. However, the continuous roller hearth annealing furnace used in our factory is relatively backward. In the actual production (especially bell type furnace and well type furnace), the oxidation discoloration caused by furnace liner crack, pipeline and valve leakage accounts for a certain proportion.

 

4、 Anti oxidation treatment of red copper

 

1. Anti oxidation treatment of copper surface:

① Strengthen the management of production plan in wet season, when the intermediate annealing semi-hard coil drawing finished product passes, try to cool the copper tube in the drawing process, and finish the winding as soon as possible after drawing to avoid surface oxidation and discoloration.

② Strengthen the detection and monitoring of annealing protective atmosphere. The annealing equipment is equipped with furnace atmosphere on-line detection. The production personnel should monitor the furnace atmosphere detection results during the annealing process. If there is any abnormality or alarm, the cause should be found out and corrected as soon as possible. The relevant products produced under the conditions of process factors change should be identified, isolated and properly handled.

③ According to the equipment level of different annealing equipment, measures should be taken to ensure that the annealed copper tube is packaged in dry environment immediately or after it is reduced to appropriate temperature in dry environment according to the equipment level of different annealing equipment.

During the production process, the surface contamination should be prevented. It is strictly forbidden to touch the copper tube with bare hands, prevent the rain from wetting, and spoil the residual emulsion or liquid after cleaning. During the whole process from drawing to semi-finished products to finishing, annealing, packaging, warehousing and delivery, surface contamination shall be prevented. Products with surface contamination shall be identified, isolated and properly treated.

⑤ To improve the control level of annealing process and equipment, on the one hand, select reasonable process methods to make the residual oil on the inner and outer surface of copper pipe be removed timely and fully in the annealing process; on the other hand, regularly inspect the annealing equipment to prevent cracks and leakage of furnace liner and furnace seat, leakage of valves and pipelines, and formulate corresponding measures as soon as possible and implement them.

 

2. Anti oxidation treatment for inner surface of red copper:

① Check the inner surface quality of annealed copper tube.

② Strengthen the standard operation and management of cleaning process.

③ Prevent the copper pipe from sucking in the external oil, isolate and deal with the abnormal situation.

④ Ensure that the annealing protective atmosphere is qualified, and strengthen the online detection, inspection and control of the protective atmosphere.

⑤ Formulate appropriate internal purging process system of annealed pipe to eliminate oil contamination in pipe timely and fully.

⑥ The sulfur content of internal lubricating oil for drawing shall be strictly controlled to prevent unqualified internal lubricating oil from being put into production.

⑦ Ensure the sealing of the blowing joint and pipeline to prevent gas leakage; ensure that the pipe is filled with protective gas before annealing or the gas in the pipe is not replaced by air after blowing.

⑧ Ensure the quality of gas used for blowing; strengthen the blowing process before annealing of products of different specifications to ensure sufficient blowing to prevent pressure and time shortage, and set relevant detection or alarm devices when necessary.

 

5、 Red copper oxidation post-treatment:

 

1. Clean with dilute sulfuric acid, only CuO on the surface.

2. If the articles are not afraid of corrosion, you can use dilute hydrochloric acid, put rusty items in dilute hydrochloric acid, and then take them out.

3. However, if you are a little afraid of corrosion, you can use dilute hydrochloric acid to smear on rusty articles. Be careful, and you can wipe it off once. Because the main components of copper rust are basic copper carbonate, copper hydroxide and copper oxide, all soluble in acid.

 

6、 Precautions for anti oxidation treatment of red copper

 

1. The influencing factors of oxidation discoloration in actual production are dynamic, which need to be studied continuously. Corresponding measures should be taken to control and improve the main problems in different periods.

2. Oxidation discoloration is a common quality defect in the production of red copper, which can be divided into internal and external surface oxidation discoloration or blackening. The main causes of oxidation discoloration are high temperature, high humidity, residual oil on the inner and outer surface of copper tube, annealing equipment and protective atmosphere are not effectively controlled.

3. In order to prevent copper tube from oxidation discoloration, it is necessary to strengthen the monitoring of relevant links in the production process. The key is to formulate appropriate annealing process system (including aeration and internal purging process) under the premise of ensuring the quality of annealing equipment and protective atmosphere, so as to achieve clean production and dry packaging (that is, packaging under appropriate temperature and humidity to prevent moisture absorption). All measures are implemented in actual production.

Reason and treatment of red copper oxidation