The Study On Al₂O₃ Ceramic Metallizing For Electrical Vacuum Device In Low Temperature

With the continuous development of science and technology, vacuum electronics entered the field of high power, uhf, and long life, the traditional glass and ceramic seal has not been able to reach the requirement of the vacuum tube production. Therefore, another kind of sealing technology, ceramic-metal seal technology arises. Among them, the alumina ceramic metallization technology is the basis of the alumina ceramic application in the field of vacuum electronics, the technology has been gradually maturing. But in the preparation process of alumina ceramics metallization, as the result of the high sintering temperature of metallizing, the product quality is not stable and the qualified rate is low. In this paper, a metallization formula is designed. This formula can finish the ceramic metallization at a lower temperature, and meet the requirements to apply to the vacuum device. This research not only can contribute to the energy conservation, emissions reduction and low carbon economy, but also can improve the level of technology, product quality and market competitiveness, and is one of the key technologies to promote the development of vacuum electronic devices.Based on the 95% alumina ceramic surface metal as the research object, by adding activators to the present preparation techniques, a suitable metallization formula is designed. Sintering temperature control in 1300-1360 ℃, tensile strength > 100 MPa. Design principles considered the "three elements" and the "three features", at the same time, combined with the sealing mechanism of the activation method of Mo-Mn. On the basis of Mo- Mn method, add activator Ca O to the formula, designing several different proportion, analysis and comparison of its impact on the metallization process.By the means of analysis, the main factors influencing the metallized layer surface condition are: particle size of powder, coating thickness, solid phase compositioncontent, sintering temperature and heat preservation time, etc. By comparing, the best technological parameters is: the median particle size of Mo powder is 1.6μm; The sintering temperature is 1350 ℃; The heat preservation time is 20 minutes. Under this condition of alumina ceramic metallization, the metallized layer shows a compact structure covers a continuous Ni layer and the surface is smooth. When Ca O content is 2%, the effect of metal has a lower sintering temperature, the tensile strength of sealing sample of more than 300 MPa, and uniform porcelain phenomena appear.Analyzing the activator’s influence on alumina ceramic metallization surface condition and the influence of the metallized layer. Using scanning electron microscope and energy spectrometer, etc., analyze microstructure and composition of the metallized layer. The results show that under the optimum condition, the metallized layer has porcelain phenomena and a good tensile strength.