Can somebody suggest a high temperature (723 K) vacuum sealing method to join metal to ceramic. The joint should sustain a vacuum of 10-3 mbar at 723 K.
For such tasks you can either look for metallic solder or glass solder, as polymer adhesive for 450°C does not exist.
To recommend a suitable solder more information is necessary:
Hi Dr. Vadmin,
The following is the information you required
Ceramic is alumina (Al2O3), shape is 1.6 mm OD and thickness of 0.1 mm tubular, thermal expansion 8x10-6/C
Joining metal is stainless steel tube 1.8 mm ID and 3 mm OD. Thermal expansion is 18.2x10-6/C
Joining is face to face as per drawing
Please suggest some
Hi Subhasis,
The task is very complex, because when cooling of soldered tubes, very high stresses form in ceramic tubes. The most dangerous point is at the exit of ceramic tube from the steel tube, at this point there are tensile stresses in ceramic, which can lead to breakage. Much better and safer would be the case where the ceramic tube is completely inside steel tube itself. In such case, ceramic is loaded by pure compressive stresses.
As for the solder, you can try as well as different silver braze as also a glass solder. In your place, I would have started with slightly meltable enamels for steels. These glasses are quite fluid at 800-850°C, wet both materials in air atmosphere very well and fill quite wide gaps. For brazing with glass solder you do not need a vacuum or protective gas furnace, but a simple electric furnace (air, max 900°C).
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