The so called “Mo-Mn process” and “Mo process” are the methods for forming ceramic-to-metal hermetic seals by metallizing, nickel plating and successive hard-soldering.
Author has reported in his previous paper on alumina ceramic-to-metal seals by the Mo-Mn process. In this research, high alumina ceramic discs containing MnO (92 wt% Al
2O
3) were sealed to Kovar parts by the Mo process. Tensile strengths of sealed layers and vacuum tightness of the seals were studied.
The layers were examined by optical and scanning type electron microscope and by electron probe microanalyzer.
Quartz glass-Mo foil seal was additionally observed, in order to achieve an insight on the sealing mechanism of the Mo process.
The results were as follows:
1) Seal strength was the highest and the best vacuum tightness was obtained when the ceramics were metallized at 1450°C-1500°C for 60 minutes.
2) The sealing layers were consisted of multiple layers which were arranged in the following order; Ceramic-Metallizing layer-Ni plating layer-Hard solder-Ni plating layer-Kovar
In the seals by Mo-Mn process, the intermediate layer was observed between ceramic and metallizing layer. However, no intermediate layer was recognized in the seals by the Mo process.
3) In the seal of quartz glass-Mo foil, the surface layer of Mo metal was oxidized and Mo oxide thus formed diffused in to the quartz glass forming a transition layer, which was quite useful in reducing sealing stress and in improving adhesion.
4) Pores in the Mo metallizing layer were filled with glassy phase in the system SiO
2-MnO-Al
2O
3 and nickel; the former came out from ceramic body and the latter from nickel plating layer. Infiltration and interdiffusion of these materials gave strong and vacuum-tight sealing layers.
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