Dany
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Thermal analysis predict a half-life of 12 millions years for PETN
An important paper published in 1982 by H.N.Vaulltrauer, came up with important result for PETN. PETN is far mor stable than we thought. In a
collaboration with the Laurence Livermore National Lab (LLNL), a thermal study is realized on two sample of PETN (prepared in LLNL) having different
surface area. In the experiment, the author heat the samples of PETN at different temperature, ranging between 53-120 degree Celsius, at the same time
the gaseous NOx emitted from decomposing samples were analyzed and quantified using a chemiluminescence analyzer. Extrapolating data (from
fig.2 in the article) down to 30 degree Celsius, yield a half-time of 12 million years which mean that PETN decompose very very slowly at this
temperature and thus PETN is very stable (in term of thermal decomposition) in storage at room temperature. Another significant conclusion is that
finer PETN (PETN with highest surface area) is two time faster in decomposition than the coarser one at a given temperature. Compared to
Nitrocellulose, PETN gives 1000 time less NOx emission at 30 degree Celsius.
i will upload the original paper of Vaulltrauer and another important revue on PETN aging which gives a lot of informations on PETN chemical and
physical properties.
Dany.
Attachment: Real time low temperature decomposition of explosives - PETN.pdf (201kB)
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Attachment: The aging of PETN.pdf (952kB)
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papaya
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Yes, must be a great dating tool for future antropologists 
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killswitch
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However unlike atomic nuclei molecular substances can be attacked by biological processes. If a microbe is synthetically engineered for passive mine
disposal and subsequently evolves beyond its design parameters, there will be nothing for the intelligent radiation-resistant raccoons or
anthropomorphic ravens to uncover.
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Dany
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Hello Killswitch,
the half-life of 12 millions years should only be given to the purified PETN materials. Unfortunately, the study of Vaulltrauer say nothing about the
presence of impurity (e.g., acid residue from synthesis). impure explosives will decompose faster when heated. The impurity will probably act in most
of case as catalyst for the degradation.
Dany.
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papaya
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Quote: Originally posted by killswitch  | | If a microbe is synthetically engineered for passive mine disposal and subsequently evolves beyond its design parameters... |
<offtopic> I want to see a synthetically engineered microbe that will defecate PETN just from sweet water and air!  </offtopic>
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Dany
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Additional important articles on thermal analysis:
https://e-reports-ext.llnl.gov/pdf/388335.pdf (for the ODTX test)
Dany.
Attachment: The effect of molecular structure on thermal stability, decomposition kinetics and reaction models of nitric esters.pdf (1.3MB)
This file has been downloaded 681 times
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AndersHoveland
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That is probably because pentaerythritol does not consist of any secondary alcohol groups. These secondary alcohol groups, as in the case of
isopropanol or the central alcohol group in glycerin, are much more vulnerable to oxidation than the other classes of alcohols. And being in solid
(non-porous) form likely helps with long-term chemical stability also, since the acidic degredation products are not free to float around and catalyze
further hydrolysis of the nitrate ester.
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caterpillar
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Nice news. We may sleep well...
Women are more perilous sometimes, than any hi explosive.
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Ral123
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12 million huh? But the decomposition is autocatalytic, it's exponential. May be the figure would be close to reality if the material doesn't keep any
decomposition products. How about EGDN? How will cast material store compared to pressed crystaline?
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Dany
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Hello Ral 123,
Maybe the decomposition of PETN is autocatalytic but don't forget that the predicted half-life of 12 millions years is based on an extrapolated
kinetic data to approximately room temperature. At room temperature the decomposition of PETN is very slow and the concentration of decomposition
product are extremely low, so virtually no autocatalysis is observed at room temperatue. But as i already mentioned in one of the comment above, the
study is realized on a pure sample of PETN, the presence of impurity like formate or oxalate anion (see https://e-reports-ext.llnl.gov/pdf/244673.pdf for mor informations) is expected to accelerate decomposition.
It is difficult to say how a pressed solid explosive will behave thermally compared to a cast charge, but taking the aggregate state of each
explosive it is obvious the cast explosive are nearly voidless so there are much less space for the accumulation of decomposition products which may
act as catalyst for decomposition.
the state of material influence the decomposition temperature. It has been shown using the one dimensional time to explosion test (ODTX), that fine
particle TATB (5 microns) decompose faster than coarser one (52 micron).
the ODTX study is posted above your comment in this thread.
Dany.
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Ral123
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I feel that in the pressed form, the "rotten stuff" will condense in micro bubbles with less surface area. In the cast from wouldn't they be more
finely mixed? Do you think adding recrystalised urea is a good idea for these materials? Do you have data on TNP and RDX?
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