Wyniki wyszukiwania - BazTech

1

Nitro Groups vs. N-Oxide Linkages: Effects Upon Some Key Determinants of Detonation Performance

Politzer P., Murray J. S.

Central European Journal of Energetic Materials

|

2017

|

Vol. 14, no. 1

3--25

EN

Increasing the nitrogen/carbon ratios in the molecular frameworks of C,H,N,O explosives has attracted considerable attention because it tends to result in more positive heats of formation and often greater densities. In conjunction with this, there has been a growing interest in N-oxide linkages, N+ → O−, as another source of oxygen in these compounds, in addition to or even possibly replacing NO2 groups. In this study, for a series of polyazines and polyazoles, we have compared the effects of introducing a single N-oxide linkage or NO2 group upon key properties that affect detonation velocity and detonation pressure. We found that: (1) The heats of formation per gram of compound, which is what is relevant for this purpose, are almost always higher for the N-oxides. (2) The nitro derivatives have greater densities and detonation heat releases. In relation to the latter, it must be kept in mind that increasing detonation heat release tends to be accompanied by increasing sensitivity. (3) The N-oxides produce more moles of gaseous detonation products per gram of compound.

2

The Role of Product Composition in Determining Detonation Velocity and Detonation Pressure

Politzer P., Murray J. S.

Central European Journal of Energetic Materials

|

2014

|

Vol. 11, no. 4

459--474

EN

Four sets of rules for predicting the detonation product compositions of explosives have been investigated: the Kamlet-Jacobs, the KistiakowskyWilson, the modified Kistiakowsky-Wilson and the Springall-Roberts. These can result, for a given compound, in significantly differing detonation products and amounts of heat release. However the resulting detonation velocities D and detonation pressures P obtained for the compound using the Kamlet-Jacobs equations are generally quite similar, with the Kamlet-Jacobs rules leading to the D and P that are, on average, closest to the experimental. The fact that the variations among the D and P values are relatively small can be attributed to a balancing of opposing effects relating to the quantities of gaseous products and the heat releases. Accordingly, obtaining reasonable accuracy for D and P does not necessarily imply corresponding accuracy for the product composition and heat release that were used. The analysis presented explains the observations that D and P can be correlated with loading density alone, even though product compositions are known to change with density.

3

Tricyclic polyazine n-oxides as proposed energetic compounds

Politzer P., Lane P., Murray J. S.

Central European Journal of Energetic Materials

|

2013

|

Vol. 10, no. 3

305--323

EN

In designing proposed new explosives, we seek a balance between high detonation performance and low sensitivity. Accordingly we focus upon (1) planar molecules, for better packing efficiency and reduced shear strain upon impact/ shock, (2) high nitrogen content, for greater density and enthalpy of formation, (3) N→O linkages rather than NO2 or ONO2 groups as sources of oxygen, and (4) presence of NH2 groups, if possible, to increase density and diminish sensitivity. Here we report the results of a computational assessment of three tricyclic polyazine N-oxides that essentially satisfy these structural criteria. Their predicted crystal densities range from 1.96 to 2.03 g/cm3. The calculated solid phase enthalpies of formation are between 135 and 314 kcal/mol. The computed detonation velocities and detonation pressures are similar to HMX for two of the compounds and significantly greater for the third, exceeding even CL-20. Impact sensitivities were estimated on the basis of (1) the free space available in the respective crystal lattices, and (2) the molecular surface electrostatic potentials. All three compounds are expected to be less impact sensitive than both HMX and CL-20. One of the three in particular is suggested to represent the best balance between detonation performance and sensitivity.

4

Computational Characterization of Two Di-1,2,3,4-tetrazine Tetraoxides, DTTO and iso-DTTO, as Potential Energetic Compounds

Politzer P., Lane P., Murray J. S.

Central European Journal of Energetic Materials

|

2013

|

Vol. 10, no. 1

37--52

EN

Abstract: The isomeric di-1,2,3,4-tetrazine tetraoxides DTTO and iso-DTTO have aroused considerable interest in recent years as potential energetic compounds, due to their predicted high densities and heats of formation and superior detonation properties. While neither has yet been synthesized, it has been suggested that the N→O linkages on alternate nitrogens will have a stabilizing effect. In the present study, we have reassessed the expected properties of DTTO and iso-DTTO. We fnd their anticipated detonation velocities and detonation pressures to be improved over HMX and similar to CL-20. The molecular surface electrostatic potentials of DTTO and iso-DTTO are consistent with the proposed stabilizing infuence of the N→O bonds. Furthermore, estimates of the available free space in the crystal lattices indicate that DTTO and iso-DTTO may be signifcantly less sensitive to impact than either HMX or CL-20.

5

Some Perspectives on Estimating Detonation Properties of C, H, N, O Compounds

Politzer P., Murray J. S.

Central European Journal of Energetic Materials

|

2011

|

Vol. 8, nr 3

209-220

EN

We have explored various aspects of the Kamlet-Jacobs equations for estimating detonation velocities and pressures. While the loading density of the explosive compound is certainly an important determinant of these properties, its effect can sometimes be overridden by other factors, such as the detonation heat release and/or the number of moles of gaseous products. Using a gas phase rather than solid phase enthalpy of formation in obtaining a compound's heat release can produce a signifcant error in the calculated detonation velocity. However a negative enthalpy of formation is not necessarily incompatible with excellent detonation properties. Additional evidence is presented to support Kamlet and Jacobs' conclusion that, for C, H, N, O explosives, assuming the detonation product composition to be N2(g)/H2O(g)/CO2(g)/C(s) gives overall quite satisfactory results.

6

Computational Characterization of a Potential Energetic Compound: 1,3,5,7-Tetranitro-2,4,6,8-tetraazacubane

Politzer P., Lane P., Murray J. S.

Central European Journal of Energetic Materials

|

2011

|

Vol. 8, nr 1

39-52

EN

The high densities and (strain-induced) enthalpies of formation of cage-type molecules have drawn attention to their polynitro derivatives as potential energetic materials. Several such compounds have been synthesized, including octanitrocubane and hexanitrohexaazaisowurtzitane. One that has not yet been prepared but has evoked continuing interest is 1,3,5,7-tetranitro-2,4,6,8- tetraazacubane. Some years ago, on the basis of a very high estimated density (about 2.19 g/cm3), it was predicted to have detonation properties greatly superior to those of HMX. We have now used computational procedures developed since that time to reassess the expected detonation performance of this compound. We find: density, 1.940 g/cm3; solid phase enthalpy of formation at 298 K, 757 cal/g; detonation velocity, 9.8 mm/µs; detonation pressure, 444 kbar; impact sensitivity, h50 ∼ 40 cm. These are all better than the corresponding values for HMX, but not by as much as had been estimated earlier.

7

Computational Investigation of Amine Complexes of 2,4,6-Trinitrotoluene

Politzer P., Murray J. S., Koppes W. M., Concha M. C., Lane P.

Central European Journal of Energetic Materials

|

2009

|

Vol. 6, nr 2

167-182

EN

Using the B3PW91/6-31G(d) computational procedure, we fnd two types of complexes to be formed between aliphatic amines and 2,4,6-trinitrotoluene (TNT). Type 1 are noncovalent, primarily electrostatic interactions that occur in the vicinities of the NO2 groups; Type 2 are δ-adducts, at carbons 1, 3 and 5. In Type 1, the TNT framework is very little affected. In Type 2, however, the site of the complex becomes quasi-tetrahedral, with longer bonds to its neighbors in the ring; the C-NO2 bonds are shortened. The Type 1 complexes have weakly negative (attractive) interaction enthalpies. For one of them, utilizing a chargetransfer formalism, we obtained a wave length for an electronic transition to a low-lying dative excited state that is in good agreement with observed values. The Type 2 interaction enthalpies are near-zero or even positive; however all of the complexes correspond to energy minima (no imaginary frequencies). For one of the Type 2, a transition state to a nitronic acid was found, with an activation enthalpy of only 5.6 kcal/mole. This indicates a possible route for amine-induced decomposition of TNT.

8

Effects of Electric Fields Upon Energetic Molecules: Nitromethane and Dimethylnitramine

Politzer P., Murray J. S., Concha M. C., Lane P.

Central European Journal of Energetic Materials

|

2007

|

Vol. 4, nr 4

3-21

EN

We have investigated computationally (B3PW91/6-31G**) the effects of electric fields upon certain properties - dipole moments, energies, geometries and electrostatic potentials – of two prototypical energetic molecules, nitromethane and dimethylnitramine. Fields of various strengths and in different directions were considered. The stronger fields significantly polarized the molecular charge distributions, especially when applied parallel to the C-NO2 and the N-NO2 bonds. These directions correspond to the principal polarities of the ground-state molecules, which these parallel fields either reinforce or counteract. With respect to geometries, the changes are primarily conformational, e.g. rotation of the methyl groups or inversion of the pyramidal nitrogen in (H3C)2N-NO2.