weeksie98
Harmless
Posts: 36
Registered: 24-10-2013
Location: England, UK
Member Is Offline
Mood: Pretty protic
|
|
Thermite - Nearly there!
I have acquired all of the materials for stage 1 of my preparation (the Fe(III)2O3). I have just one more question for you guys, then I'll get
started: Aluminium Powder. I have located a great source, kindly U2U'd to me. One thing I have picked up from numerous forums is the mesh size can be
a problem. I hear that ~#250-350 can cause disappointing results, however I can't get any lower than that in the UK unless I buy magnesium-aluminium
powder. Would I be better off buying the Mg-Al in a coarser mesh, or using regular ~#250-350 Al powder? Thanks guys!
|
|
|
woelen
Super Administrator
Posts: 8027
Registered: 20-8-2005
Location: Netherlands
Member Is Offline
Mood: interested
|
|
Mg/Al (magnalium) is more reactive than aluminium. I would not use that for a thermite, probably it burns too fiercely and it may become very
dangerous. Thermites usually need to be burned in somewhat larger quantities, and that is another reason to be very careful with it. Replacing one of
the components by a more reactive one can be really dangerous.
|
|
|
Metacelsus
International Hazard
Posts: 2539
Registered: 26-12-2012
Location: Boston, MA
Member Is Offline
Mood: Double, double, toil and trouble
|
|
In my experience, if you use coarser powder, it's harder to initiate, and burns somewhat more slowly, but is otherwise pretty much the same. If you
are making a small amount, go with the fine powder. Otherwise just use the coarse stuff, and be sure to use a strong ignition source.
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
If your purpose is to make metal rather than fireworks, that range of mesh is great.
Magnalium is an entirely different material altogether. For instance the MP of magnesia is 2,852 C, as opposed to the MP of alumina which is 'only'
2,072 C. This difference affects how the melt behaves and thus metal-slag separation. It's one of the reasons why magnesiothermic reactions with
oxides are rarely used.
Assuming it's metal you want to produce, you're best to include in your formulation about 10 % of a mineral flux like Fluorite (CaF2) or lime (CaO).
These reduce the viscosity of the alumina and promote metal-slag separation, thus increasing metal yield.
Quote: Originally posted by woelen  | | Thermites usually need to be burned in somewhat larger quantities, and that is another reason to be very careful with it. |
I've run many test charges of no more than 20 g of mixture, without problems. The trouble with thermites is that although it's easy in principle most
haven't got the foggiest clue on how to make them work (for metal preparation).
[Edited on 26-10-2013 by blogfast25]
|
|
|
weeksie98
Harmless
Posts: 36
Registered: 24-10-2013
Location: England, UK
Member Is Offline
Mood: Pretty protic
|
|
I see. Presumably I'd add that with the binder during heating?
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
Binder? There's no binder needed if you use the embedded design, that's a crucible with the thermite mixture embedded in a larger pot/bucket filled
with sand:
On this occasion the outer sand bucket could have done with filling up a little more with sand but it worked out well anyway. After the reaction and
cooling the 'crucible' (a cheap China tea mug) is badly cracked but can be hoisted out of the sand in one piece very easily. Then tapping the cracked
crucible and slag with a hammer you'll find the metal neatly at the bottom of the solidified slag puddle.
This is all in the assumption that you want to make metals with aluminothermy, not fireworks!
[Edited on 27-10-2013 by blogfast25]
|
|
|
Lambda-Eyde
National Hazard
Posts: 860
Registered: 20-11-2008
Location: Norway
Member Is Offline
Mood: Cleaved
|
|
Are you using disposable cups because ceramic crucibles (made for lab use) also have tendency to crack?
This just in: 95,5 % of the world population lives outside the USA
Please drop by our IRC channel: #sciencemadness @ irc.efnet.org
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
Yes. Specialist crucibles (but definitely not lab ceramic!) may survive the intense thermal shock but you'll probably still crack them getting the
post-reaction mix out of them. I've used anything from egg cups to 1 L terracotta plant pots as 'crucibles'.
With disposable crucibles you basically peel off the remains of the crucible and you're left with the solidified slag/metal puddle.
[Edited on 27-10-2013 by blogfast25]
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
