ABSTRACT: The corrosion behavior of Red Copper and its NACL salt deposit was studied at (80 ± 1) °C and (50 ± 1) °C, respectively, the samples were characterized by weightlessness, Olympus BX51M microscope and X-ray diffraction. The results show that the weight loss per unit area of red copper increases with the exposure time, but the corrosion rate decreases with the exposure time, and finally flattens. The corrosion rate of red copper increases with the increase of ambient temperature. The corrosion rate of the salt-deposited red copper is higher than that of the clean red copper, which shows that the chloride ion aggravates the corrosion of the red copper. The salt-deposited red copper corroded in the salt deposit area and expanded to the adjacent area with time. The determination of the structure of corrosion products showed that the corrosion products of copper exposed to the atmosphere were mainly composed of Cuprous oxide, while the corrosion products of copper after depositing salt were mainly composed of Cuprous oxide and basic copper chloride, so the corrosion is more severe. Keywords: Copper, corrosion behavior, high temperature, moderate temperature

TG172.3 literature identifier: a copper and its alloy materials have excellent conductivity, good chemical stability and mechanical properties, and occupy a very important position in electronic materials [1] . However, due to the small volume, high space density and small thickness of the metal layer of the electronic material, the slight corrosion may lead to the destruction of the electronic material, thus rendering the whole equipment invalid, it is of great significance to study the corrosion and protection of electronic materials. Copper is one of the most important metals commonly used as electronic materials, so it is of great significance to study its corrosion behavior. Atmospheric corrosion is the most common corrosion because metal products come into contact with the atmosphere all the time during processing, transportation, storage and storage, and there are many factors influencing atmospheric corrosion, it is very difficult to determine a reasonable atmospheric environmental corrosion evaluation system because of the complex function, the overlapping of the information and the variation of the regional and time conditions. According to many different experimental results, the atmospheric corrosion of Red Copper in different environment is very different, so it is not feasible to use a general atmospheric corrosion test to predict the performance of Red Copper in service condition. Therefore, the correct evaluation of atmospheric corrosion is a practical and theoretical significance of the research content. Based on the analysis of the failure conditions of Red Copper, the corrosion modes of red copper can be classified into three categories: temperature, humidity and polluted environment, it provides a reference for further research on the atmospheric corrosion mechanism of copper in electronic products.

1. Experiment 

1.1 the sample is 10mm 10mm 1mm red copper (main parameters are shown in Table 1) , which is polished by 240 # sandpaper, then polished by 600 # and 1000 # sandpaper, and polished by SIC polishing paste (particle size is 600 ~ 1000) The cleaned copper samples were washed with deionized water and then cleaned with acetone in an ultrasonic cleaning machine to remove oil. The cleaned copper samples were dried by a hair dryer and kept in a silica gel-sealed dryer for at least 24 hours The initial mass of the sample is weighed with the FA-2104 electronic balance to the fourth decimal place; the length, width and height of the sample are measured with the Vernier scale and the total surface area of each sample is recorded

To simulate the corrosion of copper in electronic products under relative humidity of 55% ~ 70% , the treated copper samples (pure copper and copper with 5% NaCl deposition) were placed in the 401B air thermal aging test chamber produced by Shanghai Experimental Instrument Factory, and the corrosion tests were carried out at different temperatures (80 °C and 50 °C) . According to Standard Gb/t 2423.51-2000, the sampling time is set as 3D, 7d, 14d and 21d. 1.2 The concentrated sulfuric acid with 1.84 G/ML by mass is prepared into a dilute sulfuric acid solution with 10% by mass, the residual NaCl on the sample is washed by distilled water and dried by hot air, and the sample is immersed in dilute sulfuric acid solution for 1 ~ 3 min, remove and rinse with distilled water, dry with hot air; weigh and record data. 1.3 the surface morphology of corroded red copper was analyzed by Olympus BX51M microscope. The corrosion products were identified by X-ray diffractometer, tested by Rigaku d/max-2400 diffractometer (Japan) and scanned by Cu Ka radiation.

Results and discussion

 2.1 corrosion kinetics

The corrosion rate of red copper is calculated according to the formula of corrosion rate V = w0-w1S T: V is the corrosion rate of Red Copper (G/(M2h)) , W0 is the mass before the corrosion of Red Copper (G) , W1 is the mass of Red Copper (G) after the corrosion product is removed; S is the surface area of copper exposed to corrosive environment (M2) , and t is the exposure time (h) . According to the kinetics law of corrosion layer, the curve follows power law: P = ATB: P is weight loss per unit area (g) ; a is constant; t is exposure time (h) ; B is constant. Fig. 1 shows the fitting relationship between mass loss per unit area of red copper and exposure time. It can be seen from the fitting curve that the mass loss of Red Copper increases non-linearly with the extension of exposure time, and the slope of the fitting curve is larger, which indicates that the protection of red copper corrosion products is weaker under different conditions, the constant values of the fitting curve are shown in Table 2

It can be seen from Fig. 1 that under the same exposure time, the mass loss of the deposited 5% NACL copper at 80 °C is the largest, followed by the mass loss of the deposited 5% NACL copper at 50 °C, and the mass loss of the undeposited salt copper at 80 °C, mass loss of non-depositing salt copper at 50 °C. In the same exposure time, the higher the temperature is, the greater the mass loss is, and the more serious the corrosion is. The FITTING FORMULA P = A3 & GT; A4A1 & GT; A2 in Ai Tbi shows that the higher the temperature and the higher the corrosion rate, the more serious the corrosion is when the copper is deposited by 5% NACL at the same exposure time, the higher the temperature, the higher the corrosion rate, the more serious the corrosion. That is, the higher the temperature, the heavier the corrosion of Red Copper. A3 and A4 are much larger than A1 and A2, which shows that the corrosion rate of red copper deposited by salt is higher than that of pure red copper. It also proves that the existence of Cl-aggravates the corrosion of red copper.

2.2 corrosion morphology

Fig. 2 is a photomicrograph of copper deposited with 5% NACL at different temperatures. As can be seen from Fig. 2, the corrosion of Red Copper was the most serious after 21 days and the least after 3 days at 80 °C and 5% NACL. With the extension of exposure time, the corrosion of red copper becomes more and more serious. With the extension of the exposure time, the corrosion product layer was formed on the surface of the sample. With the further extension of the exposure time, the color of the corrosion product darkened and a little green product adhered to the surface, the green corrosion product increased continuously, finally, the whole surface is covered with green corrosion products, and the corrosion pits are visible. Under the condition of 5% NACL deposition, corrosion of the exposed product of Red Copper begins along the salt deposit area, and with the further extension of the exposure time, the corrosion extends to the adjacent area. Therefore, there are still some areas not corroded at the beginning of corrosion in the salt deposit area. It can also be seen from Fig. 2 that the surface of the copper is heavily corroded, covered with blue-green corrosion products, and that pits on the surface of the corrosion products can be seen. The reaction process may be that Cl-first adsorbed on the metal surface, when the copper surface film was formed, some Cl-first arrived at some positions of the interface of the copper preferential decomposition, resulting in local preferential destruction.

2.3 Structure Analysis

 Fig. 3 is the XRD of pure copper corrosion product at 80 °C. it can be seen that there is a characteristic peak of Cuprous oxide. Therefore, the corrosion product of copper at 80 °C is mainly Cuprous oxide.

Figure 4 shows the XRD pattern of corrosion products of the deposited salt samples at medium and high temperatures. It can be seen that the characteristic peaks of Cuprous oxide and basic copper chloride also appear on the surface of the samples. Therefore, the corrosion products of copper in medium containing chloride ions at medium and high temperatures are mainly Cuprous oxide and basic copper chloride. As can be seen from figures 3 and 4, the corrosion product of clean copper at medium and high temperatures is copper(I) chloride, and basic copper chloride is formed when chloride ions are present, and the higher the temperature, the stronger the basic copper chloride is, that is, the more basic copper chloride is produced. Cu (OH) Cl was formed in the corrosion products of red copper at low temperature (50 °C) and 5% NACL deposition.

2.4 Corrosion Mechanism

 Cu2o is the most common corrosion product in Verdigris, and Cu2o is also the first corrosion product of copper exposed to the atmosphere. CU2O has a highly symmetrical cubic structure, with two oxygen atoms around each metal atom, each surrounded by a copper tetrahedron, and CU2O is insoluble in water and slightly soluble in acid. CU2O layers are protective, and the protective properties of CU2O decrease gradually due to the deposition of corrosive gases and atmospheric particles

CU2O can be converted into other substances under certain conditions. The study of Strandberg [13] shows that CU2O can react with NaCl in moist air to form basic copper chloride. CU2O is dissolved to form Cu + , and then Cu2Cl (OH)3[14] is formed by the steps of dissolution, ion pairing and redeposition. Copper semi-precious metal has a positive potential compared with equilibrium hydrogen electrode, but a negative potential compared with oxygen electrode, so the CATHODIC oxygen uptake corrosion may be carried out under most corrosion conditions. ANODIC reaction, in which copper enters the electrolyte in the form of Ions and leaves electrons in the metal, and the electrons flow from the anode to the Cathode, i. e. Cu * Cu + e-cathodic reaction, oxygen is formed by diffusion or convection to the cathode surface to absorb the remaining electrons in the metal, i. e. , 12O2 + H2o + 2e * 2OH-the corrosion product of the clean copper is Cu2O, and the corrosion product of the hydroxide is Cu2O, that is: 2Cu + OH-* Cuoh 2CuOH * Cu2o + H2O deposition of sodium chloride copper in sodium chloride dissociation at the same time formed Cu (OH)-cl and Cu2Cl (OH)3 corrosion products, that is: 2Cu2 + + CL-+ 3oh-* Cu2cl (OH)3cu2 + + + Cl-OH-Cu (OH) Cl Cl has a very small radius and is easy to penetrate through the corrosion product layer on the metal surface, causing corrosion of the inner metal and gradually forming soluble metal chloride, eventually, it reaches a point where it Dynamic equilibrium at a certain rate of corrosion.

3. Conclusion

 (1) at 50 °C and 80 °C, the higher the temperature and the higher the corrosion rate, the more serious the corrosion is. BY NONLINEAR FITTING THE MASS LOSS OF RED copper in the simulation experiment and the exposure time, it can be seen that the mass loss of red copper increases non-linearly with the exposure time, and the slope of the fitting curve is larger, the corrosion product of red copper has weak protection. The corrosion rate of red copper after salt deposition is higher than that of pure red copper, which indicates that the existence of Cl-aggravates the corrosion of red copper. 

(2) XRD analysis shows that the corrosion products of pure copper at 50 °C and 80 °C are Cuprous oxide, and the corrosion products of copper in the medium containing chloride ion are mainly Cuprous oxide and basic copper chloride. 

Source: Chinanews.com, by WAN ye