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watson.fawkes
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That could work, say, if only a closed end were in the furnace proper and the vacuum seal was outside it.
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blogfast25
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A *.pdf with some interesting illustrations of various Pidgeon process based reactors:
http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s...
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blogfast25
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Quote: Originally posted by aliced25  |
The best routes are through the respective oxides, in the case of Lithium & Sodium for example, these come from either decomposition of the
Carbonate at high-temperatures or formation and decomposition of the peroxide.
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Maybe but the oxides are hard to get/prepare.
Consider also NaF(s) + 1/2 Mg(l) === > Na(g) + 1/2 MgF2(s)
ΔHR298 K = +13.3 kJ/mol (NIST values)
For the equivalent reaction with KF, ΔHR298 K = + 6.5 kJ/mol
MgF2 is of course totally non-volatile: BP = 2260 C. NaF and KF also have high boiling points.
[Edited on 30-5-2013 by blogfast25]
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aliced25
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The oxides are extremely hard to get/prepare, but that is what the people looking to make this work elsewhere are using. I'm happy to try it out with
halides, but I suspect these people had some idea what they were doing.
You have read the preparation for BBr3 from AlBr3 and BF3 haven't you?
I also know the Pidgeon-type processes are used to make Titanium and pure Silicon from their halides, so I'm 50:50 on the idea. Let's work out how to
build a vacuum-retort that will fit in a propane/air heater, then we can imagine all sorts of things to make with the sucker.
Look up aluminothermic/calciothermic/silicothermic reductions on Google Scholar, there are a shitload of things that can be done using vacuum
metallurgy. Some use the halides, some the oxides. But there are limits, serious limits, on the materials that can be used with some of the compounds
(like molten lithium for instance), that will place restrictions on how this can be done.
A bottle of BBQ Gas, a propane furnace and then something to put in it, with a condenser (air cooled in all probability) and then someway to get the
reactive metals to the collection point and under paraffin so we can break the vacuum, to renew the charge or shut it down.
One major problem is that there will be reactive metals coating the inside of the entire system that have to be dealt with and removed, preferably
without scraping them off, which would be an absolute bitch in my view, perhaps running a meker burner along the sides to move them down to the
collection zone, or at least most of them?
The other part is the vacuum pump, the minute we start dealing with halides at high-temperature, shit can go wrong, as any stray halide/hydrohalide is
unlikely to condense before the pump. Oxygen, Carbon dioxide and the like, no drama (provided it is cooled).
[Edited on 30-5-2013 by aliced25]
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Endimion17
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Didn't we already have an identical thread?
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aliced25
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Yeah, I want it to be merged with unconventional sodium if possible.
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blogfast25
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| Quote: Originally posted by aliced25 | Look up aluminothermic/calciothermic/silicothermic reductions on Google Scholar, there are a shitload of things that can be done using vacuum
metallurgy. Some use the halides, some the oxides. But there are limits, serious limits, on the materials that can be used with some of the compounds
(like molten lithium for instance), that will place restrictions on how this can be done.
One major problem is that there will be reactive metals coating the inside of the entire system that have to be dealt with and removed, preferably
without scraping them off, which would be an absolute bitch in my view, perhaps running a meker burner along the sides to move them down to the
collection zone, or at least most of them?
[Edited on 30-5-2013 by aliced25] |
I think you're seeing obstacles where there are none. Have a good look at this thread (linked to from where it gets interesting):
http://www.sciencemadness.org/talk/viewthread.php?tid=6981&a...
None of this is easy but worrying about hot halides and vac pumps? Way before you get to the vac pump everything is at RT. I mean, why not worry about
metal getting into the vac pump too, huh? It's really just as unlikely.
In the case of fluorides, despite the mental association with fluorine that they conjure up, liquid fluorides are among the most stable, least
corrosive hot liquids known. See also their use in Molten Salts Nuclear Reactors.
[Edited on 30-5-2013 by blogfast25]
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aliced25
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Might I suggest you read the Kroll and Schlectern Paper I uploaded in the Unconventional Sodium Thread? Magnesium cannot be used in some processes as
it distills over at the temperatures needed for reaction (namely Lithium Fluoride), forming an alloy. Silicon doesn't, that is why they utilize it.
As to halides, halides at room temperature are still not something I particularly want in my vacuum oil, which will probably include a Diffusion Pump
for some materials, and still be at rather high vacuum (so RT is not STP). The metals will condense as they will be well under their boiling point,
even at high-vacuum. Halogens won't condense unless they are under positive pressure or we use a getter, or ultra-low temperature trap. Both are
additional concerns that needn't be worried about IMHO.
As to making the oxides, most of the oxides can be made by heating the carbonate to around 800-1,000C in a vacuum. That equipment is precisely what we
are making, more to the point, due to the fact that Calcium Oxide is needed to take up the Silica (if we use a silicon or if alumina if we use an
aluminum reductant), the carbonates can be mixed and heated, which is much more effective according to the literature.
As to Nuclear Reactors, we aren't going to be using Tungsten, Zircalloy or Titanium, or even 300 series Stainless Steels, we'll probably be using mild
steel (for ease of manipulation & welding - or cutting threads, etc., plus it copes better with high-temperatures than SS - have a look at SS
Mufflers next time you see a Harley, they are discoloured from the temperatures).
Start thinking of how to build a simple reactor, preferably out of a straight section of pipe with a flange at the end so we can introduce the
briquettes and vacuum seal it. Probably needs a flange at the other end too, so we can remove the product and disassemble it for cleaning. A propane
kiln/furnace can be controlled to some extent, by reducing the introduction of forced air and the amount of propane (ie. mixture control). Only one
part of the furnace has to be heated.
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12AX7
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Stainless does up to 600C or so in air, while maintaining useful strength and corrosion resistance. Discoloration is superficial only, due to a
thickening of the chrome oxide layer. Mild steel isn't rated for any temperatures and will turn to oxides rapidly at 600C and up. (Obviously, steel
parts can handle some temperature, but this depends on environment, alloy and heat treating. Steel quickly tarnishes in air above 150C, and even with
protective oil or whatever, metallurgical changes take place that may be undesirable. Car engine parts don't operate much over 100C, and the parts
that get the hottest (valves, exhaust manifold, turbocharger impeller and housing) are made from alloy, stainless, cast iron, or aluminized steel.
Stainless may not be the most pleasant to cut ("three oh four is a whore") but if you need it, you need it.
Tim
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blogfast25
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Aliced:
With LiF you’re picking an extreme example, as Li is the least volatile of Group I. Silicon wouldn’t work there either, as SiF4 would be formed.
Which thread are you referring to?
Re. nuclear reactors, you wouldn’t need fancy alloys for reducing NaF or KF with Mg in vacuo. For one, you’d react molten Mg with the solid
fluoride. In MSRs the exposure of tubing to the eutectic fluorde is very prolonged and under mild pressure, quite different.
Any reason why copper couldn’t be used for the reactors?
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aliced25
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Stainless is not fun to cut, I too am talking from experience here, it will puddle, splatter and if it gets down your welding gloves you'll do the
dance of "ohfukithurts", where possible threads are your friend.
What we are talking about here is temperatures up to 1,300C from the high-temperature self-sustaining combustion synthesis (http://en.wikipedia.org/wiki/Self-propagating_high-temperatu...), initiated by the SiC heating the metal to ignition point - ie. MW ignited
thermites buring in a solid-flame under vacuum. I don't know that SS or even MS will cut it, it might be worthwhile looking at putting a tungsten
(formed by the same type of synthesis) or tungsten carbide, or silicon carbide end in the hot bit - it is just whether or not they'll hold a decent
vacuum.
There is examples where commercial microwave ovens have been modified, but not to vacuum configuration. I'd remove the turntable entirely, put the
refractory floor down on the base of the microwave, cut a hole in the top for the crucibles to come through (down to the base with the outer crucible
- so it is supported) and have it so that only the metal container/crucible inside the susceptor (ie. not subject to MW Heating as such) is under
vacuum, with a gas take-off at the top.
Attachment: Peng.Binner.MW.Ignited.Combustion.Synthesis.of.Aluminium.Nitride.pdf (715kB)
This file has been downloaded 594 times
Attachment: Rosa.etal.MW.Ignited.Combustion.Synthesis.as.a.Joining.Technique.for.Dissimilar.Metals.pdf (528kB)
This file has been downloaded 1481 times
Attachment: Microwaves.and.Metals.Appendix.A.Experimental.Techniques.in.MW.Processing.pdf (1.6MB)
This file has been downloaded 1460 times
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blogfast25
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You’ve lost me now.
For (e.g.) Na2O + ½ Si → 2 Na + ½ SiO2 the Standard Heat of Enthalpy is a mere – 34.5 kJ/mol, barely exothermic. Assuming you have lime in
there, then add the Enthalpy for CaO + SiO2 → CaSiO3, also quite pitiful I’d imagine. That’s not a lot of heat to keep this going and
without constant removal of the Na vapour not too much is actually going to happen. I wouldn’t call that ‘self-sustaining’.
Also where does the SiC come into it?
You mention thermites in that context. Well, the heat-starved aluminothermic reduction of TiO2:
TiO2 + 4/3 Al → Ti + 2/3 Al2O3
... has a Standard Heat of Reaction of – 178 kJ/mol and could work in these MW ignited conditions. But – 178 kJ/mol is
already worlds apart from – 35 kJ/mol.
As regards microwave heating, I think on a small scale temperature control isn't going to be easy. Contrast that with a 'static' propane or electrical
furnace...
[Edited on 1-6-2013 by blogfast25]
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aliced25
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Temperature control is going to be easy enough with a MW, on or off as needed.
Now, with the salts we are after, rather than Beryllium (Fluoride - reduction with Mg), Hafnium (Iodide process deposition off a Tungsten Alloy) or
Potassium (the Chloride is reduced by Aluminumsilicon Alloy), the oxides look like a good place to start.
Now you mention the MW Ignited methods, the heat comes from the SiC, once it reaches a certain temperature, the thermite ignites. As to
self-sustaining reactions, the only thing I've seen that will reduce Na is Mg and that is hellishly self-sustaining if it can be done in atmospheric
oxygen. Various metallic/semi-metallic reductants are used for various products, silico/alumino/magnesiothermic reactions are utilized depending upon
their reducing power. Might I suggest you actually read the literature, there is a shitload online for fuck all (dtic.mil has a lot).
http://www.sciencemadness.org/talk/viewthread.php?tid=2105&a... - is where the thread should be moved.
[Edited on 3-6-2013 by aliced25]
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