Sealed shut!!!!!
Oct. 30th, 2009 07:35 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
kareinaI welded it! I welded it! That capsule is SHUT! Totally air tight, and there is no shadow of doubt about it whatsoever! I've been struggling with this skill for a while now. Step one in setting up my experiments has become routine--take a piece of gold tubing 2mm in diameter and cut off a 7 mm length of it, pinch one end shut into a triple-junction, and weld that shut. But the next part, which involves adding a measured amount of water (and putting the holder + capsule + water onto the scale and making note of the combined mass), then adding the powder (again making note of the combined mass) such that the water is 5% of the total, then adding a sliver of graphite (again taking note of the mass) and then carefully cleaning the end of the gold tube so that not one speck of the powder nor any other contaminant remains, and then pinching it shut and welding it has been a problem.
In part because this second weld needs to be done with the capsule "cooled" during the process. This means that we set a small beaker full of water under it, and carefully arrange wet tissue paper fore and aft, in contact with the full part of the capsule, so that the welding process doesn't cause the internal water to boil out before it is sealed shut. In part because I've had problems getting the voltage exactly the correct setting on our old, jury-rigged, welding system, and in part because the bad welds I'd been doing have required carefully trimming of the end of the capsule, and trying again, which, if all isn't well, can cause the part I'm welding to be low enough in the capsule that some of the powder is caught between the pinched parts of the area I'm trying to seal, causing the melting to get down to that level, and the whole thing to open up to reveal the now molten powder. This happened again tonight, on my first attempt.
But I resolved to try once more, and pulled out a second ready to fill capsule. I added the water. Check. Added the powder. Check. Not quite enough powder, add a bit more. Check. Added the graphite. Check. Thought about it, and after very, very careful packing down of the powder and cleaning of the top portion of the capsule I moved the pliers lower than I had been, so that a millimeter or two stuck out above the width of the pliers. Then I carefully pinched the tube shut, confidant that the powder is located at least the full width of the pliers away from the end of the tube. Then I took the capsule to the large clamp and very carefully placed only the outermost bit of the pinched end of the tube into it and cranked it shut. This is called a cold-weld, and some labs stop here, not caring if their capsule is truly sealed. But we care here. So then I very carefully trimmed the very end of it off, making an even tighter, narrower end to weld. Then I applied the welder. I still don't have the hand-eye coordination to do the whole length of the weld at once (I think I'm still jumping back away from it when the flash of light and noise of the welding happens), but the first pass sealed one end with a beautiful bead. Try again from the other end. Another beautiful bead. But the middle is still un-melted. Oops, they recommend always working from the end towards the middle. Oh well, one last try, and it worked! The whole end of the capsule is a beautiful bead, totally smooth and looking exactly like it should! I was so pleased that I literally broke into song, making up a tune to the words "It's shut! I welded it", and variations thereof. Now I'm going to celebrate by heading home early (it is only 8pm!), and in the morning I'm off to the Alps for a gentle hike with some new friends.
In part because this second weld needs to be done with the capsule "cooled" during the process. This means that we set a small beaker full of water under it, and carefully arrange wet tissue paper fore and aft, in contact with the full part of the capsule, so that the welding process doesn't cause the internal water to boil out before it is sealed shut. In part because I've had problems getting the voltage exactly the correct setting on our old, jury-rigged, welding system, and in part because the bad welds I'd been doing have required carefully trimming of the end of the capsule, and trying again, which, if all isn't well, can cause the part I'm welding to be low enough in the capsule that some of the powder is caught between the pinched parts of the area I'm trying to seal, causing the melting to get down to that level, and the whole thing to open up to reveal the now molten powder. This happened again tonight, on my first attempt.
But I resolved to try once more, and pulled out a second ready to fill capsule. I added the water. Check. Added the powder. Check. Not quite enough powder, add a bit more. Check. Added the graphite. Check. Thought about it, and after very, very careful packing down of the powder and cleaning of the top portion of the capsule I moved the pliers lower than I had been, so that a millimeter or two stuck out above the width of the pliers. Then I carefully pinched the tube shut, confidant that the powder is located at least the full width of the pliers away from the end of the tube. Then I took the capsule to the large clamp and very carefully placed only the outermost bit of the pinched end of the tube into it and cranked it shut. This is called a cold-weld, and some labs stop here, not caring if their capsule is truly sealed. But we care here. So then I very carefully trimmed the very end of it off, making an even tighter, narrower end to weld. Then I applied the welder. I still don't have the hand-eye coordination to do the whole length of the weld at once (I think I'm still jumping back away from it when the flash of light and noise of the welding happens), but the first pass sealed one end with a beautiful bead. Try again from the other end. Another beautiful bead. But the middle is still un-melted. Oops, they recommend always working from the end towards the middle. Oh well, one last try, and it worked! The whole end of the capsule is a beautiful bead, totally smooth and looking exactly like it should! I was so pleased that I literally broke into song, making up a tune to the words "It's shut! I welded it", and variations thereof. Now I'm going to celebrate by heading home early (it is only 8pm!), and in the morning I'm off to the Alps for a gentle hike with some new friends.
![[identity profile]](https://www.dreamwidth.org/img/silk/identity/openid.png){kind=small}
(no subject)
Date: 2009-10-30 07:16 pm (UTC)(no subject)
Date: 2009-10-31 07:55 am (UTC)The short answer is "experimental petrology" :-)
Date: 2009-10-31 05:25 pm (UTC)Re: The short answer is "experimental petrology" :-)
Date: 2009-11-01 08:48 am (UTC)