The copper gaskets are used in a system called CF-flanges, or con-flat, or conical-flat. The metal flange has a sharp, conical knife-edge that cuts into the copper to make a seal when the flange's bolts are tightened down. The flanges are almost always stainless steel, and require lots of bolts to generate a really high clamping pressure. Indium can be used with aluminum flanges that have smooth, flat faces. The clamping pressure is much lower because the indium is so soft.
Very interesting. Thanks Ben. I was wondering about issues with dissimilar metals in contact but, reading up on it, it doesn't look like there'll be a problem.
Silicone will work to seal things only relatively near to atmospheric pressures. At very high vacuum pressures the silicone will basically allow outside air to be pulled through the material. The best rubber like thing is Viton, but it has a pressure limit too.
At high vacuum levels (such as this system is designed to operate at), various chemical components in the silicone actually boil and get into the vacuum the silicone is trying to seal. Also, silicone will be slightly porous. Not enough to let water or anything through, but enough that it will reduce the maximum attainable vacuum level. Working with high-vacuum is weird. Basically any seal that's not completely metal, or a few select polymers will leak to some extent.
Even better! I got to spend about a year on an SEM and TEM in college. Lots of prep time goes into producing those whiz bang images. Hats off to Ben, my man cave is quite medieval in comparison.
Indium is very soft, non-toxic, and easily handled. It's actually fairly commonly used in high-vacuum applications. It has the downside that it's not really possible to do a high-temperature bake-out in a system that uses indium seals, as the indium will melt (at 156° C). Ultra-high vacuum systems use CF connections, that actually use pure copper as the gasket material. However, they also require the flanges to be made of steel (normally stainless), to handle the clamping pressures.
Vacuum penning gauges are used to meassure gas pressure. They are particularly well suited to meassure negative atmospheric pressure. Rather than traditional mechanical devices like a barometer a Penning gauge works by meassuring the decreased electrical conductivity of gasses at low preassure.
I love watching videos made by people smarter than me! I have no idea what the hell this thing is, but now I'm researching. And I had no idea that you could BUY a scanning electron microscope. What an awesome world we live in. Well, sometimes...
In my experience the crushable metal seal is usually indium wire, so good call. When I saw colouration like that it was usually titanium migration, but I worked with ion pumps.
Lead wire seals were traditionally used to seal the big chambers that were used to coat telescope. You can also use pure aluminum wire, it is dead soft. The one problem with indium is it tends to cold weld to everything, I mean everything. You can use it to solder glass to metal as well as ceramics. It is also in low temp solders used to solder laser diode bars down.
Also the rainbow colors you see there are thin films deposited. This is a result of gas molecules getting ionised by the spiraling electrons which in turn gain enough energy to sputter the cathode. the sputtered cathode reacts with the ambient gases it is exposed to in the vacuum environment forming those thin films. i have worked on sputter ion pumps for quite some time as part of my phd
Another common use of indium in vacuum systems is as a heat-transfer medium. The place I work has a few cryostats that run at ~4-20 K (that's kelvin, mind you!), and the thermal interface material is indium. Most heat-sink greases don't work at all at those temperatures, and most will outgas a LOT, which ruins your vacuum.
Crushing the lead took a lot more effort than it should. The parts wouldn't seal unless I really cranked down, and I was worried the aluminum would deform so much that making a good seal would not be possible.
aaahh that makes sense. The only time I've used crush seals was in a very large diesel engine (Navy). We used 16th inch copper gaskets, but the housing was made of steal so deformation wasn't an issue.
Nice video, good tip using the Indium wire for high vacuum seal. Keep the videos coming. What sort of range does that gauge have? What other gauges do you plan to use in your vacuum system? Is this new vacuum rig for a new project, linear accelerator perhaps?
Which pump? A high-vacuum system (Like Ben's) actually uses several, in series. The roughing pump is usually a rotary vane pump, and will get to ~0.01-10 torr, depending on quality. After that you have a diffusion pump (what Ben has), or a turbomolecular pump. That will get you ~10^−5 - ~10^−10, depending usually on how well you have cleaned the vacuum chamber. There are a lot of variables, and it depends a lot on the particular setup.
Ben, it looked like your loop of wire was not placed to allow for the expansion. On the long ends of the chamber you have the sealing wire very close to the edge. Much of the wire will end up in the chamber. The seal there will be narrow and the chamber may be contaminated by the wire. Why not space the sealing wire an even distance from the chamber, or at least a minimum at the closest points to the chamber edge?
Ben, Towards the end of the video, when looking inside the re-assembled unit, It looks an awful lot like you got the seal in too close to the openning. Gonna redo that?
Ben awesome videos !!! i was wondering if you know if one could substitute a 524-2 varian penning gauge on a CVC GPH320C gauge meter . I m assuming the voltage that are used in the unit, maybe the same as in 2kv but not sure about the gap and calibration of the different settings. Any ideas or information would be very helpful! Thanks!!!
Yeah, High-vacuum is weird. For the really, REALLY high vacuum systems (10^-12 torr), the ENTIRE vacuum enclosure is generally stainless steel, ceramic, and uses copper gaskets for the seals. Then, when they're pumping the system down, they heat the entire sealed system to several hundred degrees to bake any volatile compounds that may have crept into the chamber out, and turn them into gas, so they can be pumped away. Just the oil from a single finger-print can ruin the vacuum.
My leak detector is getting contaminated by whatever volatiles get in there off the surfaces of pipes and moisture from sorption capsule charcoal. Then the dust from mechanical pump seals among other things finishes off the mess. Could I somehow purge or flush the system? My equipment are getting to quite a sorry state. Any ideas appreciated.
Hi Ben, nice video. I read on a page that penning tubes are not appropriate for diffusion pump systems since they leave a film of silicon in the gauge. It is beacause the HV attracts oil molecules. Could that be the rainbow pattern you see? Search for tubecrafter_006.htm to find the page.
He BUILT an SEM. Go watch the rest of his channel. I guarantee it will leave you astounded and feeling like an ineffectual chump. But in a good way. :)
negative atmospheric pressure doesn't pertain to a negative number less than 0. Units are irrelevant, But if you must: How about the equivalent of stacked elephants per square furlong. You'll have to do the math yourself.
From Wikipedia: "Indium has no biological role, though its compounds are somewhat toxic when injected into the bloodstream. Most occupational exposure is through ingestion, from which indium compounds are not absorbed well, and inhalation, from which they are moderately absorbed." The isotope Indium-111 is injected directly into the human body as a radiotracer in nuclear medicine.
The copper gaskets are used in a system called CF-flanges, or con-flat, or conical-flat. The metal flange has a sharp, conical knife-edge that cuts into the copper to make a seal when the flange's bolts are tightened down. The flanges are almost always stainless steel, and require lots of bolts to generate a really high clamping pressure. Indium can be used with aluminum flanges that have smooth, flat faces. The clamping pressure is much lower because the indium is so soft.
Ben does not always add content, but when he does its always worth watching. Keep up the great videos!
i have no idea what your videos are about but I still watch them cause you make them sound interesting
Very interesting. Thanks Ben. I was wondering about issues with dissimilar metals in contact but, reading up on it, it doesn't look like there'll be a problem.
Silicone will work to seal things only relatively near to atmospheric pressures. At very high vacuum pressures the silicone will basically allow outside air to be pulled through the material. The best rubber like thing is Viton, but it has a pressure limit too.
At high vacuum levels (such as this system is designed to operate at), various chemical components in the silicone actually boil and get into the vacuum the silicone is trying to seal.
Also, silicone will be slightly porous. Not enough to let water or anything through, but enough that it will reduce the maximum attainable vacuum level.
Working with high-vacuum is weird. Basically any seal that's not completely metal, or a few select polymers will leak to some extent.
Even better! I got to spend about a year on an SEM and TEM in college. Lots of prep time goes into producing those whiz bang images. Hats off to Ben, my man cave is quite medieval in comparison.
Indium is very soft, non-toxic, and easily handled.
It's actually fairly commonly used in high-vacuum applications.
It has the downside that it's not really possible to do a high-temperature bake-out in a system that uses indium seals, as the indium will melt (at 156° C). Ultra-high vacuum systems use CF connections, that actually use pure copper as the gasket material. However, they also require the flanges to be made of steel (normally stainless), to handle the clamping pressures.
I am impressed that rosin core solder worked as well as it did.
Vacuum penning gauges are used to meassure gas pressure. They are particularly well suited to meassure negative atmospheric pressure.
Rather than traditional mechanical devices like a barometer a Penning gauge works by meassuring the decreased electrical conductivity of gasses at low preassure.
I love watching videos made by people smarter than me! I have no idea what the hell this thing is, but now I'm researching. And I had no idea that you could BUY a scanning electron microscope. What an awesome world we live in. Well, sometimes...
In my experience the crushable metal seal is usually indium wire, so good call. When I saw colouration like that it was usually titanium migration, but I worked with ion pumps.
Lead wire seals were traditionally used to seal the big chambers that were used to coat telescope. You can also use pure aluminum wire, it is dead soft. The one problem with indium is it tends to cold weld to everything, I mean everything. You can use it to solder glass to metal as well as ceramics. It is also in low temp solders used to solder laser diode bars down.
Also the rainbow colors you see there are thin films deposited. This is a result of gas molecules getting ionised by the spiraling electrons which in turn gain enough energy to sputter the cathode. the sputtered cathode reacts with the ambient gases it is exposed to in the vacuum environment forming those thin films. i have worked on sputter ion pumps for quite some time as part of my phd
First time I heard of someone using indium. For UHV usually copper gaskets are pretty standard and probably also cheaper.
Another common use of indium in vacuum systems is as a heat-transfer medium. The place I work has a few cryostats that run at ~4-20 K (that's kelvin, mind you!), and the thermal interface material is indium. Most heat-sink greases don't work at all at those temperatures, and most will outgas a LOT, which ruins your vacuum.
Crushing the lead took a lot more effort than it should. The parts wouldn't seal unless I really cranked down, and I was worried the aluminum would deform so much that making a good seal would not be possible.
aaahh that makes sense. The only time I've used crush seals was in a very large diesel engine (Navy). We used 16th inch copper gaskets, but the housing was made of steal so deformation wasn't an issue.
Nice video, good tip using the Indium wire for high vacuum seal. Keep the videos coming.
What sort of range does that gauge have?
What other gauges do you plan to use in your vacuum system?
Is this new vacuum rig for a new project, linear accelerator perhaps?
Which pump? A high-vacuum system (Like Ben's) actually uses several, in series.
The roughing pump is usually a rotary vane pump, and will get to ~0.01-10 torr, depending on quality.
After that you have a diffusion pump (what Ben has), or a turbomolecular pump. That will get you ~10^−5 - ~10^−10, depending usually on how well you have cleaned the vacuum chamber.
There are a lot of variables, and it depends a lot on the particular setup.
Your own SEM? Seriously dude? Why aren't you my neighbor? Gotta love America!
What are you using as your base plate for your bell jar? Can you elaborate on the surface finish? Thanks!
Ben, it looked like your loop of wire was not placed to allow for the expansion. On the long ends of the chamber you have the sealing wire very close to the edge. Much of the wire will end up in the chamber. The seal there will be narrow and the chamber may be contaminated by the wire. Why not space the sealing wire an even distance from the chamber, or at least a minimum at the closest points to the chamber edge?
Also I measured the HV on the output of the CVC GPH320C is about 2Kv out.
Ben,
Towards the end of the video, when looking inside the re-assembled unit, It looks an awful lot like you got the seal in too close to the openning. Gonna redo that?
very cool. i hope to have a nice shop someday to do activities like this in
I had the same question. Thanks for explaining it to us
Very interesting and clearly presented.
You can still get lead solder? (I have some stockpiled here, next to my stash of incandescent light bulbs!)
sweet stuff !!could you use 24k gold wire or shim instead of indium ??
You said the magnets are meant to make the path of ions longer, but why does the path need to be long? What is wrong with a short path?
Why indium? I have right on my desk a spool of soldering wire that's just tin and lead (no flux) and wasn't hard to find at all.
Why wouldn't silicone work for the sealer? Not enough space?
Ben awesome videos !!! i was wondering if you know if one could substitute a 524-2 varian penning gauge on a CVC GPH320C gauge meter . I m assuming the voltage that are used in the unit, maybe the same as in 2kv but not sure about the gap and calibration of the different settings. Any ideas or information would be very helpful! Thanks!!!
Yeah, High-vacuum is weird.
For the really, REALLY high vacuum systems (10^-12 torr), the ENTIRE vacuum enclosure is generally stainless steel, ceramic, and uses copper gaskets for the seals.
Then, when they're pumping the system down, they heat the entire sealed system to several hundred degrees to bake any volatile compounds that may have crept into the chamber out, and turn them into gas, so they can be pumped away. Just the oil from a single finger-print can ruin the vacuum.
What kind of pressures can you get with that vacuum pump?
What kind of output does the sensor have? I mean could I use it with a standard 3.3v or 5v microcontroller? Thanks
My leak detector is getting contaminated by whatever volatiles get in there off the surfaces of pipes and moisture from sorption capsule charcoal. Then the dust from mechanical pump seals among other things finishes off the mess. Could I somehow purge or flush the system? My equipment are getting to quite a sorry state. Any ideas appreciated.
thanks for that bit of knowledge!
Rosin is solid resin, well at least it is when speaking about tree resins and rosins.
I thought the very same thing when I saw it... lets hope the best.
Nevertheless a very nicely made and interesting video...
Got a Penning gauge head to clean up. I'll probably use plain lead wire.
What is it used for?
Negative atmospheric pressure as in: less than 101.325 kPa, the average air pressure at sea level.
I would say extremely low...I wouldn't know exactly how low, but since that is a turbomolecular pump it's pretty much as low as it gets.
Negative in what unit?
Interesting. Thank you!
Thanks
hello ben, can you teach me how to measure vacuum in these gauges. for a class i need to measure 70 mTorr and 7x10-5 Torr. Please help thank you.
im sorry meant to say read vaccum
Hi Ben, nice video. I read on a page that penning tubes are not appropriate for diffusion pump systems since they leave a film of silicon in the gauge. It is beacause the HV attracts oil molecules. Could that be the rainbow pattern you see?
Search for tubecrafter_006.htm to find the page.
Negative atmospheric pressure? I thought gases could only go down to zero atmospheres...
He BUILT an SEM. Go watch the rest of his channel. I guarantee it will leave you astounded and feeling like an ineffectual chump. But in a good way. :)
With luck you'll show us the gauge in action.
Whoops, I meant 10^-9
Thats McGuyver on steroids!
negative atmospheric pressure doesn't pertain to a negative number less than 0. Units are irrelevant, But if you must: How about the equivalent of stacked elephants per square furlong. You'll have to do the math yourself.
Make more videos!
As far as I know Indium is very toxic and rather daungerous in contact with the skin. It is better not to touch it with the bare hands.
From Wikipedia: "Indium has no biological role, though its compounds are somewhat toxic when injected into the bloodstream. Most occupational exposure is through ingestion, from which indium compounds are not absorbed well, and inhalation, from which they are moderately absorbed."
The isotope Indium-111 is injected directly into the human body as a radiotracer in nuclear medicine.
Cool! Does this mean we'll be seeing a super-sonic ping pong ball gun any time soon? youtu be / I9zBGgpzl0I
If you tight on money you can buy solder without resin.