Glass-to-Metal Seal

Would this be for an aquarium?

No this is for making xray tubes where there are a bunch of lead wires and a glass wafer. that are joined together. We currently have to do a step to oxidize are lead wires. But i heard there is way that some people can do it without oxidising

You really should read a book on glass to metal seals. A good one is "Materials and Techniques for Electron Tubes" by Walter H. Kohl. The answer to your question is, yes, there are many techniques for providing vacuum tight feedthrus, that don't involve oxidation of the feedthru wire.

Field's metal. Fuses to glass. Alloy of bismuth, tin and indium.

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Dow corning (I really feel they must make me their marketing man) has a number of silicones - also GE and Loctite have them - of different temperature - they are used at our places to stick - of course not glass but ceramics to metals. Only they are not transparent and temperature should be less than 250 deg C

Adhesion is very good as I have seen (the machine has a high vibration and the tiles do not fall down)

Do not have any exposeure to your application area (X Ray tubes) except when I go to Hospitals or our NDT deptt (there too mostly are radio isotopes so..

Kovar is a metal that is used for glass to metal seals. There are several problems actually making the seal but for an X-ray tube it is done every day. These joints must be mass spectrometer leak tight and withstand a wide range of temperatures. Kovar and Invar both have thermal coefficients of expansion close to glass so they work. The actual mechanism of it I do not know but I do know that these materials are used almost exclusively.

Silicones, epoxies and other adhesives will not work. I suspect that if you find a publication on the manufacture of cathode ray tubes, a good (old) experimental physics ( they tend to have how to sections), or a book on manufacture of vaccum tubes would give you help. These glass to metal seals are commercially available.

Good Luck and don't try to re-invnt the wheel.

in searching the web there is a company that claims they have found a way to do this. I know the glass and metal have to be close in cte. We have been doing it sucessfully for years. But are just trying to cut costs by trying to cut out some steps.Glass-to-Metal Seal, Hermetic Seals & Hermetic Feedthrough Custom Manufacturer: Tekna Seal, Inc.

When you study glass to metal seals, you will find something called a compression seal. Compression seals are based on a purpose expansion (cte) mismatch between the glass and the metal. If the concept lent itself to a few words ofexplanation, I would provide it. The fact is that you really should study conventional techniques before you attempt to invent new ones. You will then be standing on the backs of giants.

invar is what I am familiar with.

http://en.wikipedia.org/wiki/Invar

http://www.phynicx.com/site/

milo

Hi,

there is the very old MnMo process where the metal is oxidised but you don't see it.

There is the Cu on glass or ceramic process where the 10ppm water or oxygen content in the "inert gas" nitrogen is responsible for buildup of a very thin CuO layer that is attaching to other oxides and an the other side to copper.

And there is the vacuum brazing with active braze materials (Ti or Zr are partially oxidised).

Commercial furnaces are very expensive so I built one myself, not too cheap but much less than commercial ones.

Here an example from diamond to carbide brazing.

RHABE

we purchased a furnace and are getting ready to put it to the test. Right now we are doing everything with torches and molds. Guess it will be interesting trying to figure out the profiles.

Do you use inert gas in your vacuum chamber? Or do you have negative atmospheres?

Hi,

no inert gas, as this will boost the convective heat transfer to the walls, thus much more power and cooling will be needed.

Pressure will be down to below 10^-4 mbar, better 10^-5 mbar.

To achieve this a prepump and a high vacuum pump (turbomolecular for example) will be necessary.

RHABE

I've seen and had some interesting disasters trying to weld magnesium using vacuum chambers.

As stated elsewhere, thermal-expansion driven glass-to-wire compression seals can work fine - but we either need the glass to cool down from a melt where it contacts the wires so that it conforms to their shape and then contract to compress the wires, or we need to use a glass preform that has a close fit to the wires and rely on elasticity/ductility of the wires. If you also require the lead-through to be soldered/brazed to a metal wall, a hot metal ring can be placed around the bead and allowed to cool into place in a similar way.

For systems where there will be significant temperature cycling, it is generally thought preferable to have a reasonable expansion match and to rely on a chemical-bond between metal and glass.

Pre-oxidation is not generally necessary in either case (though it may make life easier in the way that it effects the flow of molten glass along the metal), but cleanliness is always essential, and oxidation is one way in which it may be achieved.

A point to note: as-drawn wire often has sub-surface creases along the axis of the wire, which can be permeable to light gases and to silicones. Often these are removed by etching the wire, which also leaves a clean surface.

http://www.dumet.net/glass_to_metal_seal.html

Hi,

what happened?

Molten magnesium can be pretty dangerous if a glass-window or a seal is failing.

Molten aluminum is not so bad, hot titanium may/will ignite!

Do not try water! But sand or any other oxide or gypsum will be a good idea!

I broke two windows. Both 50mm diameter and 8 to 12 mm thick. Hot at inner side, a tiny scratch at the inner surface, stress in tension at the inner side from outside atmosphere and inside nearly no pressure. All this added up to slowly developing and growing cracks. Until sudden failure, turbopump stops with overload, o-rings damaged but nothing else because no igniting material inside. Heater has no interlock for vacuum good or bad! Should have one.

RHABE

oh, nothing much happened. Birds stopped singing for a week. Windows imploded. Neighbours moved away. Lots of fire engines and police cars.

Catastrophic failure of large glass cylinder at -10/9mmb.

So far it looks like some pretty interesting ideas. We are just trying to keep up in these hard times. Not an easy thing to do.

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Indium foil is ideal for creating cryogenic vacuum seals. If there is any interest, feel free to contact me for more details and pricing.