The Study On Medium Temperature Metallization Formula For 95% Alumina Ceramics Of Vacuum Switch Tubes

Vacuum switch tube is the core component of medium and high voltage power switch.Ceramic metallization is needed in the manufacturing process in order to seal with metal parts.Isostatic pressing alumina ceramics has been accepted by more and more manufacturers due to its excellent performance.However,compared with traditional hot-die-casting ceramics,isostatic pressing ceramics need higher metallization temperature.At present,the commonly used metallization formula to isostatic pressing ceramics is required to be sintered at more than 1500?.However,the rise of sintering temperature will lead to a series of problems such as cracking of products,deformation,flow of glaze and so on.The energy consumption and cost of products is accordingly increased.Therefore,it is important to design a medium temperature metallizing formula,to meet the need of the isostatic pressing alumina ceramics.In this paper,the metallization of isostatic pressing 95%alumina ceramics for vacuum switch tubes was studied.The ball milling process of metallized raw materials was improved by activating Mo-Mn method.According to the phase diagram of MnO-Al₂O₃-SiO₂,16 compositions of activator formula and Mo powder proportions were designed by using five ratios of MnO/SiO₂ and isotherms at three temperatures.The effects of different activator formulations and Mo powder content on the mechanical properties and microstructures of the metallized layer were studied by tensile strength test,XRD phase detection,SEM and EDS element analysis.The experimental results show that the new ball milling process can greatly reduce the particle size of metallized raw materials,effectively reduce the number of aggregates of Mo powder,and the metallized layer is uniform and compact,and the glass phase distribution is uniform.It can effectively improve the tensile strength and consistency of the metallized layer,and the fracture mode is?fully bonded porcelain?.Different phases were detected by sintering different activator formulations at metallization temperatures.MnAl₂O₄ was detected in the MnO:SiO₂ activator with MnO:SiO₂ as 2:1 and 1.5:1.Completely melts was found,however,to form for the formula with MnO:SiO₂ as 1:1,1:1.5 and 1:2 respectivlely.Under the same isotherm,with the decrease of MnO:SiO₂,the tensile strength of metallized layer increases first and then decreases.When the activating agent composition is MnO:SiO₂=1:1 and 1:1.5,and the isotherms are at 1200?and1300?,the average tensile strength of the metallized layer is over 430 MPa.Among them,the average tensile strength of the metallized layer manufactured by No.9activator formula with MnO:SiO₂=1:1.5 and isotherm at 1300?can reach to 488.33MPa,which is the best mechanical property of all the formulations.And the fracture mode is?fully sticky porcelain?.With the increase of Mo powder content,the tensile strength of the metallized layer increases first and then decreases,showing moderate Mo content is needed in the formula.When the content of Mo powder is 75%,the metallized layer is uniform and compact,the tensile strength is the highest,the average value is 494 MPa,and the fracture mode is?fully sticky porcelain?.Finally M-75 formula was found to be best suitable for isostatic pressing ceramic metallizing.