Heavy Metal Azides Research Articles

Airborne metal nanoparticles released by azides detonation: determination and potential public exposure

Metal azides are highly energetic materials that release a large amount of gas upon detonation. They also release metal particles, generating an aerosol. The most common azide is sodium azide (NaN3), which is used nowadays in car airbags. If the decomposition is not complete, harmful azide particles might be inhaled. Heavy metal azides find application as a primary explosive (primer) in ammunition. Public health officials have raised concerns about heavy metal particles released during training in shooting ranges. We identify a lack of knowledge on airborne metal particles properties released from azide detonation and on the analytical methods applied to characterize them. As a case study, we detonated milligram amounts of silver azide, copper azide, and a mixture of them in a glove box. We then analyse the airborne particles with an ensemble analytical setup, able to measure real-time their particle size distribution and chemical composition. We detected spherical metal nanoparticles in the range of 2–500 nm. These findings and the developed analytical tools may allow identifying airborne nanoparticles the passenger compartments of vehicles after airbag activation as well as in indoor shooting ranges, contributing to the evaluation of public health risks.

ELECTRONIC STRUCTURE OF DIVALENT METAL AZIDES

Ion-molecular metal azides are well known because of their high reactivity, and nowadays they are widely used as energetic materials. Despite the large amount of experimental data exists on such kind compounds, the number of theoretical studies is still not so large. The aim of the present work is to study of the electronic structure of Me(N3)2 compounds, where Me=Sr, Ca, Cd, Hg. All the calculations have been carried out within the framework of the density functional theory with the use of the numerical pseudo-atomic orbitals basis. The results of the band structure calculations are presented in the work together with a maps of total and partial electronic density; the data on Cd(N3)2 and α-Hg(N3)2 are presented for the rst time. The values of band gaps calculated are in good agreement with those obtained by other authors or estimated in the experiments. The all the crystals under consideration, except of α-Hg(N3)2, are predominantly ionic compounds with a relatively small fraction of the covalent bonding. The overall structure of the valence band spectra, as well as the character of conduction band bottom, is similar to other heavy metal azides. The comparative analysis of the data on band gaps led to the conclusion about lesser stability of the heavy metal azides than that of the second group metal azides, what is also conrmed by the experimental data

Pressure-Induced Amorphization of Strontium Azide

Strontium azide (Sr(N3)2) has been studied by in situ high pressure X-ray diffraction at room temperature. Sr(N3)2 exhibits anisotropic compressibility due to the orientation and rotation of azide anions. The refinement results and spectra measurements reveal that Sr(N3)2 possesses bent azide ions at ambient conditions, differing from the linear azide ions of alkali azides. The bent azide ions further bend and rotate with increasing pressure. These unique properties of bent azide ions play a significant role in the process of electron orbit hybridization and greatly enhance the propensity of nitrogen polymerization. The bulk modulus of Sr(N3)2 is 49.1 GPa, which is larger than those of alkali azides and close to those of heavy metal azides. The larger bulk modulus is attributed to the partial covalent bonding character of Sr(N3)2. Sr(N3)2 transforms into an amorphous phase at relative low pressure compared with alkali azide. This property might induce that Sr(N3)2 transforms into polymeric nitrogen more readily than other inorganic azides.

Spectra of explosive glowing of heavy metal azides at initiation by high-current electron beam

Glowing spectra of products resulted by heavy metal azides explosive decomposition initiated by high-current electron beam were measured and identified. Intensive emission lines related to atoms of alkali metals were observed in spectra of samples under study. These atoms enter explosives during their preparation. Emission lines of elements being part of a sample holder were also presented in spectra of explosion.

Effect of the laser radiation wavelength on the energy threshold of initiation of heavy metal azides

The behavior of silver and lead azides (laminated and filiform crystals, pressed powders) with initiation of their explosive decomposition by a laser pulse is studied. The initiation energy thresholds are measured during irradiation at wavelengths of 1064, 532, 354.7, and 266 nm corresponding to four harmonics of laser radiation. Irradiation is performed under conditions with the sample surface being open or covered with a transparent dielectric (quartz plate) with a pressing force up to 5 · 108 N/m2. Surface covering does not exert any significant effect on the initiation energy threshold in the domain of transparency of the heavy metal azide matrix (first and second radiation harmonics). In the domain of bandgap absorption (fourth harmonic), the initiation threshold strongly depends on the surface conditions (open/covered). The results are discussed from the viewpoint of the influence of the transparent substrate on gas-dynamic unloading of the heat spot, which is formed in the domain of bandgap absorption owing to laser radiation absorption in a thin subsurface layer.

Catastrophic processes in dielectrics in irradiation by high-current electron beams

The results of the research in explosive decomposition of heavy metal azides initiated by electric (“streamer”) charges induced by high-current electron beam have been considered. A physical model for initiation of heavy metal azides explosive decomposition by electron beam has been suggested. The model suggests formation of strong electric field in the sample and its neutralization by ultrasound anode charges. The streamer front generates “hot spots” which start the formation of explosive decomposition sites in a condensed reactive material.

Initiating the explosive decomposition of heavy metal azides by electron-beam-induced electric discharge

The explosive decomposition of heavy metal azides (HMAs) initiated by the electric (streamer) discharge induced by a nanosecond electron beam has been experimentally studied. A physical model is proposed that describes the initiation of an electron-beam-induced HMA explosion, which involves the formation of a strong electric field in a sample and its neutralization by a supersonic anode discharge. The propagating streamer front generates hot spots in a condensed reactive substance, from which the foci of explosive decomposition are formed.

A diffusion model of chain-branching reaction of the explosive decomposition of heavy metal azides

A diffusion model of a solid-phase chain reaction of explosive decomposition of heavy metal azides was developed. The dimensional effects of initiation of the reaction were examined: the dependence of the critical fluence of initiation on the microcrystal size H(R) and on the irradiated zone diameter H(d). It was demonstrated that the diffusion model of the chain reaction closely describes the measured H(R) dependence at diffusion coefficients of D ∼ 0.2–0.3 cm2/s, values that correspond to experimentally measured mobility of electronic charge carriers of μ ∼ 10 cm2/(V s). To account for the measured H(d) dependence and the reaction front propagation velocity (V = 1.2 km/s), it is necessary that the diffusion coefficient be three orders of magnitude higher than the experimentally determined value. That the H(R) and H(d) dependences cannot be quantitatively described simultaneously is indicative of the underlying mechanisms of energy transfer being different.

Effect of radiation treatment on the explosive conduction kinetics of heavy metal azides

A study is performed of the effect of preliminary irradiation on the explosive conduction kinetics of whisker crystals of silver and lead azides under laser initiation. The rate of explosive decomposition of lead azide is shown to be a nonmonotonic function of the radiation dose, exhibiting a rise at low doses (tens of thousands of radians) and a fall at high doses (hundreds of thousands of radians). The results are analyzed using the previously proposed model of charge exchange of reaction centers during initiation. It is concluded that this model can be used to describe the effect of radiation treatment on the early stages of explosive decomposition.

Ab initio study of electronic structure and optical properties of heavy‐metal azides: TlN3, AgN3, and CuN3

Detailed ab initio studies on the electronic structure and optical properties of the heavy-metal azides have been performed using density functional theory within the generalized gradient approximation. An analysis of band structure, density of states, charge transfer, and bond order shows that the heavy-metal azides are ionic compounds but have covalent character. The valence bands of AgN3 and CuN3 are strongly dominated by Ag- and Cu-d, respectively, but that of TlN3 arises from the contributions of Tl-s and terminal N-p and not from Tl-d. The real and imaginary parts of the dielectric function, adsorption coefficient, and electron energy-loss spectra are calculated and compared with available experimental data.

Deformation mechanism of the explosive degradation of heavy metal azides under pulsed treatments

The experimental results on the kinetics of explosive degradation of heavy metal azides by the action of nanosecond laser and electron-beam pulses and by the impact of accelerated microparticles are reported. It was found that, basically, the kinetics of the processes was qualitatively and quantitatively similar under the action of all the above factors. A local lattice deformation was the overall result of initiation by all the above factors. A theoretical analysis of the dependence of the electronic structure and electron density of a crystal on the degree of lattice deformation demonstrated that the lattice deformation resulted in a redistribution of bonds between atoms within the anion and between atoms of neighboring anions. A possible structural mechanism for the initiation of the primary reaction is discussed.

Effects and phenomena in filamentary heavy-metal azide crystals exposed to heat, light, and electric and magnetic fields

Heavy-metal azides (lead, silver, and thallium azides) attract attention of scientists not only because they are common initiating explosives whose nature of explosion is still discussed, but also because their properties are close (on a number of parameters) to those of halogenides whose physical properties are well studied. In the present work, based on the analysis and correlations of polarization-and magnetostrictive effects found in heavy-metal azides, an attempt is made to substantiate the physical-chemical mechanism of detonation initiation as ionization induced by the electric field.

Effect of preliminary irradiation on the detonation sensitivity of lead azide

The effect of preliminary irradiation on the probability of lead azide detonation has been studied. It is established that the detonation probability is a nonmonotonic function of the irradiation dose, which grows in the region of small doses, exhibits a maximum, and then drops at large doses. The obtained experimental data agree with a divacancy model of the initiation of heavy metal azides.

Kinetics and Mechanism of Explosive Decomposition of Heavy Metal Azides

The explosive decomposition of heavy metal azides initiated by a laser pulse was studied experimentally over a broad range of action levels (from the threshold values to those exceeding the threshold ignition energy by a factor of 100) and in the time interval including the induction period, and rapid explosive decomposition, and the expansion of detonation products. The explosive glow and expansion dynamics of the decomposition products in air and vacuum were investigated, and the velocities of the explosive decomposition front, the compression pulse, and the expansion of the explosion products were measured. Based on the results obtained, the possibility of the occurrence of preexplosion phenomena is discussed and the mechanism of laser initiation of heavy metal azides is analyzed.

Local structure of the chemical bond in metal azides calculated in a basis set of Wannier functions

The local structure of the chemical bond in molecular ion crystals of alkaline and heavy metal azides (MN3, M = Li, Tl, Ag) is discussed in terms of Wannier functions. Various schemes of localization are considered in relation to the peculiarities of electronic structure, and hybridization effects, leading to anion-cation complexes in compounds with covalent bonds, are analyzed.

Effect of Temperature on the Growth Rate of Pre-Explosion Luminescence in Silver Azide

The effect of temperature on the growth rate of pre-explosion luminescence in AgN3 crystals is examined. It is found in experiments that the reaction rate of the explosive decomposition at 300 K is higher than at 80 K. It can be inferred from here that the limiting stage for the chain reaction is electron capture on a neutral center (divacancy). The data obtained agree well, both qualitatively and quantitatively, with the previously reported model of initiation in heavy metal azides, thus providing support to the divacancy model.

Initial Processes of Explosive Decomposition of Heavy Metal Azides Exposured to Pulsed Radiation

Results of experimental investigations into the kinetics of explosive decomposition of heavy metal azides excited by laser pulses and pulsed electron beams of nanosecond duration as well as in the course of a decomposition reaction initiated by accelerated particles are presented. It is demonstrated that the kinetics of such excitation processes differs only by the presence of a burst of cathode luminescence. It is established that the decomposition reaction is initiated by impacts of accelerated particles of micron sizes. The structural mechanism of initial reaction initiation is suggested.

The physical nature of the optical emission and absorption accompanying explosive decomposition of heavy metal azides

The kinetics and spatial characteristics of the optical emission and absorption have been studied in the course of explosive decomposition of silver azide initiated by a pulsed electron beam. The emission and absorption observed after the induction period reflect the process of formation and expansion of the products of chemical decomposition of silver azide.

Electronic structure of heavy-metal azides

Calculations of the electronic crystal structure in the basis of pseudoatomic orbitals are used to investigate major heavy-metal azides AgN3 and TlN3. Special features and composition of the energy bands are analyzed for two cases: with allowance for spin-orbit interaction and without it. The chemical bond structure determined by the electron-density distribution is also examined.

Explosive Glow of Heavy Metal Azides under Pulsed Initiation by Laser and Electron Beams

New experimental results were obtained on the kinetics of explosive glow of heavy metal azides with initiation of explosion by a laser pulse and an electron beam. The results were used to identify the nature of the explosive‐decomposition process.