Sciencemadness Discussion Board

Urea nitrate issues

Chisholm - 18-4-2017 at 10:11

Urea nitrate is an attractive explosive from an economic perspective: urea is readily available, and the reaction with nitric acid occurs regardless of the concentration of the acid. The only negative impact of additional water is additional effort required to dry the urea nitrate (UNi).

Urea nitrate is a "tertiary explosive", i.e. one that usually requires a high explosive booster (PETN, tetryl, etc.) for initiation. Most tertiary explosives are AN + fuel mixtures, but pure urea nitrate also falls into this category (though experiments conducted by the FBI have produced detonation of UNi via blasting cap in unconfined charges as low as 500g in weight).

Pure UNi is also remarkably stable. It requires sudden heating to over 420ºC to initiate decomposition, as opposed to 358ºC for pure AN.

Its disadvantages are its corrosive nature, the difficulty of its initiation, and its inefficient mechanism of detonation. Some literature references give a TNT equivalence of 90%; this is incorrect for the reasons given in the next paragraph.

The rate of energy release from the explosive decomposition of pure UNi is insufficiently rapid for all of it to keep up with the shock front; this has an unusual effect on its RE factor. Near the blast seat, the RE can be as low as 15%, but at mid-range is as high as 75%. The integrated average works out to roughly 50%. (All data comes from the D-BREIE series of Dr. Kirk Yeager).

Normally, when the reaction zone of an explosion lags significantly behind the compression zone and even starts to bleed into the rarefaction zone, we call that a low explosive, and improving the performance is most easily accomplished via stronger confinement and finer particle size.

However, the shock front of UNi in even the loosely-packed state (0.7 g/cm3) is still traveling at least 3.5 km/s, and no pipe is containing that.

One remedy for low-VoD and low-efficiency explosives like AN + fuel mixtures is the addition of powdered aluminium; AN mixtures containing powdered aluminium produce less post-blast AN residue than non-aluminized charges, presumably due to the increase in the temperature of the reaction zone and the resulting increase in reaction rate. The use of aluminium in nitroguanidine-based charges indicates that the effect of aluminium can be beneficial even if the resulting mixture has a worse oxygen balance.

However, unlike AN, UNi readily attacks most metals; the uronium cation is a significantly weaker conjugate acid than ammonium, and consequently the compound is corrosive in the presence of even trace quantities of moisture. The nitric acid is only loosely bonded to the urea moiety, and mixtures of UNi with fuels such as sulfur or aluminium have occasionally produced violent chemical reactions.

I'm trying to think of ways to improve the performance (near-field blast pressure) of UNi without sacrificing too much in safety or economy. Does anyone have any ideas?

[Edited on 4-19-2017 by Chisholm]

Urea / TACN

Laboratory of Liptakov - 19-4-2017 at 01:29

Urea nitrate is outdated EM. Equal power and the detonation pressure can be achieved by a mixture TACN + 5% aluminum. This mixture is not hygroscopic and attack metal is negligible. Recrystallized TACN is stable throughout the years. Without the presence of aluminum. The most powerful compound is: TACN 88%, 7% cellulose dinitrate and aluminum bright color grade of 5%. recommend density 1,25 g/cm 3 for best strenght. Working of course from 0,6 g/cm3. For full kick enough only 300mg HMTD. Next advantage for TACN. And still save expensive HNO3. Thus if you have NH4NO3 from other sources, than from HNO3 + ammonia water.

Chisholm - 19-4-2017 at 03:25

Thank you for the information, but it wasn't what I was asking about.

JohnDoe13 - 19-4-2017 at 04:55

5 or 10 % nitromethane will do the trick.