Research on Application of DCB Technology in Vacuum Interrupter Sealing Xu Sihua, Xu Chuanxi, Cui Xiufang (Institute of Electrical Insulation, Xi'an Jiaotong University, Xi'an 710049, China) 1203 ceramic copper f bonded specimens and stress diagrams, developed a new seal Research on the Technology of Sealing Vacuum Interrupter with DCB Technology . The sealing strength was studied and analyzed. It was found that the bonding strength of DCB bonding of Cu-Al23 porcelain with the oxygen content of Cu surface changed, and the influence of oxygen content on bond strength was studied in depth.
With the continuous improvement of science and technology, vacuum circuit breakers are widely used in power systems. Metal sealing is a problem in the vacuum interrupter manufacturing process. This requires that the seal between the cermet not only has high adhesion strength, but also has excellent sealing performance, thermal shock resistance, and environmental corrosion resistance. Sealing quality will directly affect the quality and service life of vacuum circuit breaker products. With the continuous development of new ceramic materials, the requirements for the sealing of cermets are also increasing. At present, the molybdenum-manganese metallization method is commonly used at home and abroad. Generally, it is performed in a hydrogen furnace or in a vacuum, and the cost is high. Therefore, the development of a metal-ceramics sealing process with high sealing strength, good mechanical resistance, and high efficiency and low cost is the main problem in the field of vacuum circuit breaker repair date: 2002-06-10. Here, a novel sealing process, a Cu-Al23 ceramic direct bonding technique (abbreviated as DCB technology), in which the copper copper and the ceramic are directly sintered together in an atmosphere at a high temperature is used as a research and development for the vacuum interrupter seal.
There are two main indicators to evaluate the quality of vacuum arc chamber sealing, namely sealing strength and hermeticity. The author first studied the sealing strength of Cu-Al23 porcelain DCB. Because the direct bonding of CuD cluster 3 is achieved through the combination of Cu2 and Al23 on the copper box surface to form CuAl2, the high strength bonding is achieved, and therefore, the oxygen content of the copper surface has a significant influence on its sealing strength. By controlling the oxygen content (the amount of Cu2 contained in the surface per square centimeter after pre-oxidation of the copper sheet), the authors studied the effect on the bonding strength of DCB and found out the regularity to obtain a high sealing strength.
Tests were performed using ASTM (American Materials Test Standard) W2X specifications. At high temperatures, a bonding reaction between the copper box and the ceramic takes place and the bonded samples are as shown.
2.2 Measurement of Oxygen Content A120, ceramic tensile strength test specimens It can be seen that the bond strength of Cu-Al23 porcelain begins to increase with the increase of oxygen content; at the beginning, the increase rate is faster, and then the increase rate is slowed down. , and gradually tends to saturation; when the oxygen content reaches a certain degree, the bonding strength decreases with increasing oxygen content. 3.2 Experimental analysis In a certain oxygen atmosphere at high temperature, the surface of the metal copper is oxidized to form a thin layer of Cu2. When the temperature is higher than the eutectic point, a Cu-Cu2 eutectic liquid phase appears. The Cu2 phase and the Al23 ceramic are good. The chemical affinity reduces the interfacial energy and allows the eutectic liquid phase to wet copper and ceramics well. At the same time, Cu2 in the liquid phase reacts with Al23 to form CuAl2. After cooling, it passes through the Cu-Al-O chemical bond, and Cu2 and the ceramic are firmly bonded together. As Cu2 is in contact with metallic copper, Cu2O is tightly connected to the copper layer by Cu-O ionic bonds, but the bonding force between Cu2O and H2O3 is smaller than that of Cu2O and H2O3. Therefore, in practice, the bonding strength between copper and ceramics is mainly determined by the bonding strength of the Cu-O ionic bond between the Cu2O crystal grains and the Cu-Cu2O eutectic formed on the copper surface. Therefore, the oxide layer on the surface of the copper box, especially the area and denseness of the area where Cu2O is formed, will directly affect the bonding strength of Cu-Al2O3 ceramic DCB.
1290! 1 h in the air; Sample n: Al2O3 + Cu2O + Cu (small amount) powders are dry pressed and shaped, and sintered in the same copper-ceramic bonding process (because of the sample in the raw materials and the manufacturing process and the DCB sample It is the same, therefore, the phase formed after sintering should also be consistent) for comparative X-ray diffraction (XRD) phase analysis. From the Cu2O-Al2O3 system phase diagram and know, 1169! At the same time, Cu2O-Al2O3 will form a eutectic and produce a new phase CuAlO2. XRD pattern of sample I. There are indeed many CuAlO2 peaks on (a) and there are also a few CuAl2O copper-ceramic bonding temperatures. Although far below 1 169! However, there is also a CuAlO2 peak on the XRD spectrum (b) of the sample. The phase is basically the same as that of Sample I, except that the height of the CuAlO2 peak is relatively low (that is, the CuAlO2 phase is formed less). It shows that when Cu-CuO co-melt infiltrates ceramics under bonding conditions, Cu2O forms chemical bonds with Al2O3, and new phases are formed. (a) and (b) are SEM micrographs of sample I, respectively, in which the dark phase is Al2O3 and the white phase is the Cu, Al, O compound. It can be seen that the volume of the white crystal phase in Sample I is much larger, and the peak of CuAlO2 is higher on the XRD spectrum. (c) is the XRD diffraction peak of the ceramic bonding surface after the copper is stripped. Analysis shows that "-Al2O3 has a strong diffraction peak, and also contains CuAlO2, CuAl2O4, and high-voltage electrical Cu20 phases. The diffraction peaks of these phases are Sample I and "were much weaker, because this layer is very thin. This further shows that the combination of copper and ceramic is formed by reacting C)2 with the ceramic.
Trial tff.ll cut-off from the experimental results of SFM photos can be obtained, Cu-A1203 ceramic DCB bonding strength of 6 ~ 12kN/cm2, can be achieved by the current molybdenum manganese metalization sealing strength.
From the point of view of Cu-Al23 ceramic bond strength variation with oxygen content, oxygen content is too low and too high, which is unfavorable for the Cu-Al23 ceramic bonding. By controlling the oxygen content of the copper surface and controlling the cooling rate and increasing the bonding point, the local stress of the sealing can be minimized, and the bonding strength can be increased.
In the experiment, most of the specimens were broken in the ceramic body. When the ceramic body itself was lower than the Cu-Al23 ceramic bonding strength, the fracture occurred in the ceramic body during the tensile test. However, it is also necessary to consider that in the process of cooling the seal 678, the stress caused by the difference between the thermal expansion coefficients of the copper and ceramic parts will reduce the tensile strength of the ceramic, and the cooling rate will also affect the sealing stress, and the cooling rate will be faster. The greater the joint stress, resulting in a substantial reduction in the ceramic body's own tensile strength, and the dispersion of the experimental results.
From the above analysis, we can see that due to the fracture occurred in the ceramic body, so the actual Cu-Al23 ceramic bonding strength is greater than the tensile test results, the average may reach 10kN/cm2 or more.
In addition, preliminary tests were also conducted on the airtightness of the samples produced using the DCB technique. According to the molybdenum-manganese gas tightness test method determined by Shaanxi Baoguang Plant Metallurgical Workshop, the specimens produced by DCB technology meet the requirements of sealing airtightness. To achieve the best airtight requirements, it needs further study.
4 Conclusions The bonding strength of DCB in Cu-Al23 ceramics is determined by the chemical combination of Cu and Al23 to form CuAl2, which is related to the oxygen content on the copper surface. Oxygen content should be controlled to obtain high bonding strength.
The bonding strength of DCB in Cu-Al2 porcelain reaches 9kN/cm2 in average in the plateau area, which is similar to the current sealing strength of Mo-Mn metallization. It solves the problem of the sealing strength of the cermet in the vacuum interrupter, and reaches the sealing gas after preliminary determination. The requirement for tightness provides a possibility for the sealing of vacuum interrupters.
In the tensile test, most of the bonded specimens occurred in the ceramic body at the time of fracture. The primary analysis was considered to be the sealing stress generated during the cooling process of the specimen, which reduced the tensile strength of the ceramic body itself. Therefore, the bonding strength of Cu-Al2 porcelain actually exceeds the measured value.
(4) DCB technology uses raw materials such as copper and alumina ceramics to reduce costs.
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