Swede
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Methods of stabilization; NOx scavenging
I am particularly interested in the processes that can take a crude nitrated energetic material, contaminated, perhaps acidic, and turn it into a
compound with stability, purity, and a longer shelf life.
Nitrocellulose, the basis for smokeless powder, is a classic example. Without stabilizers like dephenylamine, it is prone to degradation, especially
if the temperatures are high.
The three basic NOx scavenging additives that I am aware of (no doubt there are more) are carbamide, diphenylamine, and betaine. Urea is easily used
due to its excellent solubility in water, and the fact that nitrated materials of interest are generally insoluble in water. Wash the material with a
solution of urea; drain, filter, or decant, allow to dry, and a hopefully adequate quantity of urea will be left behind. For this, I usually use a 5%
urea solution.
COPAE recommends diphenylamine, usually 1% to 2% by mass. I have finally found a source of this compound, but I am curious how the 1% is introduced
into, say, nitrocellulose. Diphenylamine is barely soluble in water.
Betaine, I have zero experience with.
Essentially, I am looking for techniques. How is diphenylamine at a good working mass % added to various nitrated esters? I assume it varies with
the energetic material, but if anyone could describe the basics, I would be very appreciative. A follow up topic would be home lab methods to
determine degradation, such as KI-starch paper and others.
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Rosco Bodine
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Dicyandiamide is another stabilizer better than urea and reportedly excellent for stabilizing MHN, probably for ETN also and some others.
Diphenylamine is definitely not any sort of "universal stabilizer" and neither are the others, certain ones are better for stabilizing specific
materials and not much good for others.
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Swede
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Can you elaborate a bit, Rosco? My understanding of the degradation of almost all nitrated energetics is that they evolve nitric oxides, which the
stabilizers scavenge over time. How are compounds like dicyandiamide and diphenylamine best incorporated, or does it vary too much with regards to
differing materials?
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Rosco Bodine
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The stabilizers are usually applied as a deliberate impurity coprecipitated during recrystallization or washing of the purified material to be
stabilized.
There are patent processes for the ways that have
been found to work best. And yeah the stabilizers
do work against the autocatalytic decomposition by
neutralizing the decomposition byproducts so that they do not accumulate. However, the reaction dynamic involved is very specific between the
stabilizer and
the thing being stabilized as a particular pairing, because the stabilizer, if the equilibrium is wrong can actually act to destabilize by virtue of
encouraging the
production of those byproducts it waits to neutralize,
if you can follow that, which is precisely why one stabilizer is not ideal with regards to all materials desired to be stabilized. Indeed some
materials will be more stable with no stabilizer at all, than with the wrong one applied. The optimum combinations are very specific pairings which
are tried and true.
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Swede
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Makes sense, thank you.
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Rosco Bodine
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Attached is the dicyandiamide related patent US2616920
It was first mentioned here
http://www.sciencemadness.org/talk/viewthread.php?tid=890&am...
Attachment: US2616920_Dicyandiamide_Stabilized_Nitromannite.pdf (191kB)
This file has been downloaded 878 times
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