3 ms·
I attended a talk at Nat Geo by the engineers who built the drop probes enclosed by glass spheres. A few interesting bits as I recall them: The glass is made i
by snowwrestler 5y ago
I attended a talk at Nat Geo by the engineers who built the drop probes enclosed by glass spheres. A few interesting bits as I recall them:
The glass is made in two hemispheres and the contact surface is ground flat. There’s no glue or mechanical attachment; the hemispheres are carefully lined up by hand and then they pull vacuum. Atmospheric pressure alone keeps them mated prior to submersion. Then of course they are pushed together harder and harder as they descend.
The engineers talked a university into letting them use their hyperbaric chamber for testing. One of the prototypes failed at high pressure, which sounded like a bomb going off. The glass was reduced to tiny slivers, which the university was still finding in nooks and crannies years later. (The Nat Geo team was not allowed back after that.)
The probes were timed on the bottom by using thin steel wire to attach the weight. Basically the wire would rust until it broke, then the globe would float to the surface and start broadcasting a radio beacon for pickup. They adjusted the time by varying the thickness of wire.
They also stuffed the globes with LED lights and used them as “sun-like” sources of illumination for underwater cave photography.
- rhn_mk1 5y ago> the hemispheres are carefully lined up by hand and then they pull vacuum. I'm guessing it was not very close to vacuum? The article mentions air explicitly: > As the instrument's glass collapsed under the weight of five miles of water, it released a pocket of air that oscillated under pressure before splintering into a veil of tiny bubbles.
- snowwrestler 5y agoYes, sorry, I meant they created a pressure differential by sucking out some air; that is called pulling vacuum even if you don’t remove all the matter (hard vaccum).
- dan-robertson 5y agoYou don’t need to pull a vacuum for this. If the glass is sufficiently flat and clean, the pieces can be attached with a process called ‘contact bonding’ where the surfaces are close enough to be attracted by Van der Waals forces.
- wereHamster 5y agoIs this similar to cold welding that may happen in space (where surfaces don't oxidate)?
- dan-robertson 5y agoIt feels more similar to wringing gauge blocks (or other very flat surfaces) together, though it is more disputed how that works. You can separate the two objects if you pull them apart with a reasonable force (or more typically shearing and some leverage) and if you imagine the atomic scale structure of the surface, the crystal lattice will break down as atoms on the edge have bonds going into the material rather than free electrons hanging out waiting for another atom to bond to. I don’t know if cold welding is really welding but contact bonding is certainly not like welding.
- wereHamster 5y agoAFAIU cold welding is like welding in that the two materials which were separate atomic matrices become one, as atoms from one 'object' do not care if their neighbours are from a different 'object', if they are close enough to be attracted to each other. It only works if the material does not have an oxide layer at it's surface, which is why it's been observed to happen in space (and apparently caused issues with joints no longer being able to move, or something like that).
- deleted 5y ago[deleted]
- snowwrestler 5y agoTo be clear, this wasn’t my project, I just posted what I remembered from the talk.