Thermal Decomposition of PETN

Cook (Ref 1), in describing thermal decomposition of some HE s conducted in the quartz spring apparatus (described in Ref 1, p 175 and shown there in Figs 8.1a 8.1b), stated that PETN, RDX, Tetryl and to a small extent TNT decomposed autocatalyti-cally. EDNA followed the first-order decomposition law only until about 5% of the explosive had decomposed and then the reaction stabilized. The term autostabilization was applied here on the supposition that one of the condensed decomposition products of EDNA which accumulated in the explosive apparently tended to stabilize the bulk of expl and thus slow down the decomposition. After about 10% of the expl had decompd, however, the "autocatalysis developed. 

CA 43, 405 (1949) (Thermal decompn of PETN, NG, Ethylenediamine Dinitrate AN) l6)Ibid, TrFaradSoc 45, 85-93 (1949) CA 43, 5187 (1949) (Thermal decompn of RDX HMX) 17)A. J.B.Robertson, Third Symposium on Combustion and Flame and Explosion Phenomena , Williams Wilkins, Baltimore, Md (1949), 545 -51 (Thermal initiation of expln in liquid expls) I8)S. Livingston W.R.Tomlinson Jr, Fundamental Research on Explosives. Decomposition of Explosives at Elevated Temperatures , PAIR 1737 (1949) 19)Anon, Artillery Ammunition ,... 

Andreev and Kaidymov [134) published a teview on the thermal decomposition of FETN and a description of their own results. Their data for activation energy are given in Table 47. Tliey confirmed the results of T. Urbanski and co-workers (Vol. II, pp. 181-183) and similarly of Tonegutti [135) and Bourjol (136) that the addition of aromatic nitro compounds to PETN lowers [the stability of the latter. In all experiments it was shown that decomposition in Jthe liquid phase, that is, the molten system, engenders faster decomposition than [that of the solid phase. 

Because the technique relies on thermal decomposition of nitro-containing explosives, and no prior chromatographic separation is performed, no chemical information of the studied material is obtained. Currently, the unit will alarm on compounds such as RDX, PETN, TNT, urea nitrate, ammonium nitrate, nitroglycerine, EGDN and DMNB. 

Recently Lee et al (Ref 3) re-examined the behavior of PETN under 10 to 50 kbars of external pressure. They also find a reduction in decomposition rate with increasing applied pressure. HMX behaves similarly to PETN. TNT whose explosion products contain a high proportion of solid carbon, as expected from LeChatelier s Principle, shows little pressure effect on its thermal decomposition. Nitro-methane, however, appears to decompose more rapidly under an external pressure of 50 kbars than 10 kbars. This effect is not completely understood but Lee et al suggest that high pressure may favor the formation of the thermally less stable aci form of Nitromethane ... 

PETN and RDX in a special vacuum impact machine. Their.results showed that gases developed on impact approximate mote closely those developed on thermal decomposition chan those on deton. The results are in harmony with the hypothesis of a thermal origin of impact-initiated explns and with the slow initial burning velocities observed with the rotating drum camera... 

Pure PETN heated above its melting point explodes violently at 205-225°C. In. the primary stage of thermal decomposition, within the temperature range of 161-233°C, the activation energy E equals 47.0 kcal/mole, while logie B = 19.8, according to A. J. B. Robertson [26],... 

A study of the kinetics of thermal decomposition reactions using pentaerythritol tetranitrate(PETN), a high explosive, as the model substance was first conducted by SC-DSC. In this study, information was obtained that was relative to the characteristics of the DSC technique. However, the question as to how the results of analyses of this type were useful for practical work arose, and studies in this area were stopped. Subsequently, studies have proceeded on the evaluation of hazards by collecting as much data on self-reactive substances as possible. 

An enormous amount of material has been published on PETN. There are some 360 CA references since 1961 The older literature is also very voluminous (see Additional Refs). Consequently, the writer has chosen to emphasize modern work in this article, of course including important older studies. The article is divided into the following sections I. Physical Properties II. Solubility III. Chemical Properties IV. Specifications and Analytical V. Uses VI. Preparation VII. Detonation Characteristics VIII. Thermal Decomposition IX. Combustion DDT (deflagration-to-detonation transition) X. References. The major emphasis will be placed on Sections VII, VIII and IX... 

Pressure tends to increase the chemical reactivity of nitromethane as well as the rate of thermal decomposition. It was observed, quite accidentally, that a pressure-induced spontaneous explosion of single crystals of nitromethane at room temperature can occur. Further study revealed that single crystals grown from the liquid with the (111) and either the (001) or the (100) crystal faces perpendicular to the applied load direction in the DAG, if pressed rapidly to over 3 GPa, explode instantaneously accompanied by an audible snapping sound. The normally transparent sample becomes opaque instantly. Visual examination of the residue revealed a dark brown solid which was stable when heated to over 300 C. Subsequent x-ray analysis showed the material to be amorphous. Mass spectral analysis of the residue was inconclusive because no well defined spectra were observed. Because most of the sample is recovered as solid residue after the explosion and is stable to over 300°C, the material may be amorphous carbon. This stress-induced explosion occurs only in protonated nitromethane because similar attempts on the deuterated form did not result in explosion. Shock experiments on oriented pentaerythritol (PETN) crystals have shown similar type behavior [25]. In this case it was suggested that the sensitivity of shock pressures to crystal orientation is the result of the availability of slip planes or system of planes in the crystal to absorb the shock, thereby increasing the threshold to explosion. A similar explanation may be applicable to the nitromethane crystals as well. The deuteration effect must play a role in the initiation chemistry. An isotope effect has been observed previously in the sensitivity of HMX and RDX to shock and thermal conditions [23]. 

One analog of NHN is a substance with the nitrate group replaced by azide— nickel hydrazine azide (NHA). Only very limited information is available, including a preparation procedure which is practically the same as in the case of NHN. Aqueous solutions of the nickel salt and sodium azide are placed in a stirred reactor, acidity is adjusted by addition of acetic acid, the mixture is heated to 50-70 °C, and an aqueous solution of hydrazine hydrate is slowly added. NHA has green polycrystalline form with crystal density 2.12 g cm. Average particle size of product with good fluidity is around 80 pm and bulk density of such powder is 0.57-0.65 g cm . The thermal decomposition is a two-step process which starts at 165-206 °C (heating rates from 10 to 30 °C min ). The second step starts at 206 00 °C. NHA does not become dead pressed by 70 MPa, because it is less sensitive to impact but more to friction than PETN [19]. 

---