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<SpeedEvil>
whitequark: On direct coagulation... - a number of vendors on alibaba seem to have AlO polish in the 0.3um range.
<SpeedEvil>
whitequark: I have not properly investigated if this is a typo for 0.3mm, though it seems plausible that it is not in at least some cases.
<Noxz>
Al2O3 ?
<SpeedEvil>
yes
<Noxz>
shouldn't that be just about any aluminum powder, as it will oxidize in air?
<SpeedEvil>
fine aluminium will not burn/oxidise into a homogenous powder
<SpeedEvil>
this process - I think - wants a hard dense blob
<Noxz>
hrm
<SpeedEvil>
which - happily - are also the properties you want for an abrasive
<Noxz>
cheaper than diamond paste?
<whitequark>
SpeedEvil: no, this process requires powder with very high surface area
<whitequark>
well, polishing either, really, mirror finish is under 1 micron
<SpeedEvil>
yes - 10m^3 is equal to that particle diameter of 'square' particles
<SpeedEvil>
unless I screwed up on the dimensions
<SpeedEvil>
^cubic
<whitequark>
yep
<whitequark>
vendors on alibaba probably do have it in 0.3 micron range.
<whitequark>
that would be just fumed alumina
<whitequark>
burning some compound of aluminium in oxygen. I don't remember which. organoaluminium, maybe
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<whitequark>
another way to get is to find 'linde a' gem polishing powder
<whitequark>
but that's expensive as hell
<whitequark>
i have an ounce of linde a.
<SpeedEvil>
I might have some. I have way too much from an old rock shops stock
<whitequark>
oh cool
<whitequark>
how much
<SpeedEvil>
~100kg of various SiC/SnO/CeO/...
<SpeedEvil>
Poorly catalogued
<whitequark>
holy fuck
<whitequark>
actually that sounds interesting even from a polishing perspective
<whitequark>
ceria, mmmmmm
<_Sync_>
polishing shits cheap usually in bulk
<SpeedEvil>
yeah.
<SpeedEvil>
I was seeing prices of $1/kg
<SpeedEvil>
(@10 tons FOB)
<SpeedEvil>
I wonder if there is an analogous process for SiC
<whitequark>
I think SiC is done by, well, melting Si with C
<whitequark>
at least that's what USSR did
<SpeedEvil>
I was meaning a low-energyish near-net-shape process
<whitequark>
oh
<whitequark>
no deason DCC can't work for SiC
<whitequark>
reason
<SpeedEvil>
If you can call a process where you sinter for a day at 1700C low energy
<whitequark>
a vacuum induction oven!
<SpeedEvil>
I want to make a vacuum furnace.
<whitequark>
I *am* making one
<SpeedEvil>
I think the key to making it easy is to seperate the two parts.
<whitequark>
the what and what?
<SpeedEvil>
the vacuum and the furnace.
<whitequark>
er.
<SpeedEvil>
That is - the vacuum structure remains 'cold' - and the furnace is just several layers of radiation shielding with no forces on it
<whitequark>
yes, that was my idea as well.
<whitequark>
use Mo or Ta sheets.
<whitequark>
I'm told six or so are enough.
<_Sync_>
you don't need Mo or Ta in the later shields
<whitequark>
Mo is cheap enough you could just make the entire thing out of it
<_Sync_>
the trick is to have very low thermal conductivity between the shields
<whitequark>
spot-weld it to a Mo C-beam on which the crucible will stand
<_Sync_>
because at those temperatures conduction is not relevant
<SpeedEvil>
It would be nice if medium vacuum would work for vacuum insulation
<SpeedEvil>
Well - without fumed silica or something in the way
<_Sync_>
why would you put any insulation in there?
<_Sync_>
there is no need
<_Sync_>
calculate the mean free path
<SpeedEvil>
yes - mean free path means it needs to get well under a pascal for anything to happen.
<SpeedEvil>
This - while fine in a nice pumped enclosure - isn't ideal in - for example - a vacuum insulation panel
<_Sync_>
well, imho vacuum insulation panels for houses are not a really good idea
<_Sync_>
I'd rather see aerogels
<SpeedEvil>
You can combine them for more fun
<SpeedEvil>
And yes - aerogels are awesome.
<whitequark>
have you seen what happens to a marshmallow under vacuum
<SpeedEvil>
I've been wondering about making quite a lot in a scaffolding tube.
<_Sync_>
0o
<SpeedEvil>
It can handle the pressure easily
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<_Sync_>
well, they are also pretty small
<SpeedEvil>
Well 'lot' as in several litres at a time.
<SpeedEvil>
1m^3@250C/500PSI or whatever would be harder