Wehrwissenschaftliches Institut für Werk- und Betriebsstoffe

1,5-Diamino-1H-tetrazole (2, DAT) can easily be protonated by reaction with strong mineral acids, yielding the poorly investigated 1,5-diaminotetrazolium nitrate (2a) and perchlorate (2b). A new synthesis for 2 is introduced that avoids lead azide as a hazardous byproduct. The reaction of 1,5-diamino-1H-tetrazole with iodomethane (7a) followed by the metathesis of the iodide (7a) with silver nitrate (7b), silver dinitramide (7c), or silver azide (7d) leads to a new family of heterocyclic-based salts. In all cases, stable salts were obtained and fully characterized by vibrational (IR, Raman) spectroscopy, multinuclear NMR spectroscopy, mass spectrometry, elemental analysis, X-ray structure determination, and initial safety testing (impact and friction sensitivity). Most of the salts exhibit good thermal stabilities, and both the perchlorate (2b) and the dinitramide (7c) have melting points well below 100 degrees C, yet high decomposition onsets, defining them as new (7c), highly energetic ionic liquids. Preliminary sensitivity testing of the crystalline compounds indicates rather low impact sensitivities for all compounds, the highest being that of the perchlorate (2b) and the dinitramide (7c) with a value of 7 J. In contrast, the friction sensitivities of the perchlorate (2b, 60 N) and the dinitramide (7c, 24 N) are relatively high. The enthalpies of combustion (Delta(c)H degrees ) of 7b-d were determined experimentally using oxygen bomb calorimetry: Delta(c)H degrees (7b) = -2456 cal g(-)(1), Delta(c)H degrees (7c) = -2135 cal g(-)(1), and Delta(c)H degrees (7d) = -3594 cal g(-)(1). The standard enthalpies of formation (Delta(f)H degrees ) of 7b-d were obtained on the basis of quantum chemical computations using the G2 (G3) method: Delta(f)H degrees (7b) = 41.7 (41.2) kcal mol(-)(1), Delta(f)H degrees (7c) = 92.1 (91.1) kcal mol(-)(1), and Delta(f)H degrees (7d) = 161.6 (161.5) kcal mol(-)(1). The detonation velocities (D) and detonation pressures (P) of 2b and 7b-d were calculated using the empirical equations of Kamlet and Jacobs: D(2b) = 8383 m s(-)(1), P(2b) = 32.2 GPa; D(7b) = 7682 m s(-)(1), P(7b) = 23.4 GPa; D(7c) = 8827 m s(-)(1), P(7c) = 33.6 GPa; and D(7d) = 7405 m s(-)(1), P(7d) = 20.8 GPa. For all compounds, a structure determination by single-crystal X-ray diffraction was performed. 2a and 2b crystallize in the monoclinic space groups C2/c and P2(1)/n, respectively. The salts of 7 crystallize in the orthorhombic space groups Pna2(1) (7a, 7d) and Fdd2 (7b). The hydrogen-bonded ring motifs are discussed in the formalism of graph-set analysis of hydrogen-bond patterns and compared in the case of 2a, 2b, and 7b.

Energetic salts of the 5,5‘-azotetrazolate anion with different guandidinium cations were investigated, including bis(guanidinium) 5,5‘-azotetrazolate (GZT), bis(aminoguanidinium) 5,5‘-azotetrazolate (AGZT), bis(aminoguanidinium) 5,5‘-azotetrazolate monohydrate (AGZTH), bis(diaminoguanidinium) 5,5‘-azotetrazolate (DAGZT), bis(triaminoguanidinium) 5,5‘-azotetrazolate (TAGZT), and bis(azidoformamidinium) 5,5‘-azotetrazolate (AFZT). AGZT was obtained according to the literature as the monohydrate (AGZTH), and DAGZT was synthesized for the first time. All salts were fully characterized by vibrational spectroscopy (IR, Raman), multinuclear NMR spectroscopy, and elemental analysis. Safety testing (impact and friction sensitivity) was performed to find safe handling procedures. The crystal structures of AFZT and AGZTH, which crystallize in the monoclinic space groups P21/n and C2/c, were determined. The thermal decomposition of the salts was monitored by differential scanning calorimetry, and the gaseous products of the explosions of all compounds were identified with mass spectrometry and IR spectroscopy.

Abstract The synthesis, NMR spectroscopic characterization and structure determination of highly explosive tetrazole azide, a very nitrogen‐rich material (88.3% N) is reported. Tetrazole azide was prepared in high yield from the diazotation reaction of aminotetrazole, followed by treatment of the formed diazonium salt with sodium azide. Synthesis in diethylether/methanol and recrystallization from diethylether afforded colorless cubes: CHN 7 ( 1 ): monoclinic, P1 2 1 /n 1 , a =1346.6(5), b =499.6(2), c =1360.9(5) pm, β =105.14(1) 0 , V =0.884(2) nm 3 , Z =8, ϱ =1.670 g cm −3 . The observed structural parameters (X‐ray) are in good accordance with the results from molecular orbital (MO) calculations. The computed electrostatic potential (B3LYP) suggests a pronounced shock and friction sensitivity which was confirmed experimentally. Quantitative valence bond (VB) calculations were performed for the most important 21 VB structures in order to obtain the structural weights and to obtain an assessment for the importance of the various individual VB structures considered.

To facilitate a less empirical approach to developing improved catalysts, it is important to correlate catalytic performance to surrogate properties that can be measured or predicted accurately and quickly, allowing experimental synthesis and testing of catalysts to focus on the most promising cases. Particularly hopeful is correlating catalysis performance to the electronic density of states (DOS). Indeed, there has been success in using just the center of the d-electron density, which in some cases correlates linearly with oxygen atom chemisorption energy, leading to a volcano plot for catalytic performance versus “d-band center”. To test such concepts we calculated the barriers and binding energies for the various reactions and intermediates involved in the oxygen reduction reaction (ORR) for all 12 transition metals in groups 8–11 (Fe–Cu columns). Our results show that the oxygen binding energy can serve as a useful parameter in describing the catalytic activity for pure metals, but it does not necessarily correlate with the d-band center. In addition, we find that the d-band center depends substantially on the calculation method or the experimental setup, making it a much less reliable indicator for ORR activity than the oxygen binding energy. We further examine several surfaces of the same pure metals to evaluate how the d-band center and oxygen binding energy depend on the surface.

Abstract 5‐Aminotetrazolium nitrate was synthesized in high yield and characterized using Raman and multinuclear NMR spectroscopy ( 1 H, 13 C, 15 N). The molecular structure of 5‐aminotetrazolium nitrate in the crystalline state was determined by X‐ray crystallography: monoclinic, P 2 1 / c, a =1.05493(8) nm, b =0.34556(4) nm, c =1.4606(1) nm, β=90.548(9)°, V =0.53244(8) nm 3 , Z =4, ϱ=1.847 g cm −3 , R 1 =0.034, wR 2 (all data)=0.090. The thermal stability of 5‐aminotetrazolium nitrate was determined using differential scanning calorimetry; the compound decomposes at 167 °C. The enthalpy of combustion (Δ comb H ) of 5‐aminotetrazolium nitrate ([CH 4 N 5 ] + [NO 3 ] − ) was determined experimentally using oxygen bomb calorimetry: Δ comb H ([CH 4 N 5 ] + [NO 3 ] − )=−6020±200 kJ kg −1 . The standard enthalpy of formation (Δ f H °) of [CH 4 N 5 ] + [NO 3 ] − was obtained on the basis of quantum chemical computations at the electron‐correlated ab initio MP2 (second order Møller‐Plesset perturbation theory) level of theory using a correlation consistent double‐zeta basis set (cc‐pVTZ): Δ f H °([CH 4 N 5 ] + [NO 3 ] − (s))=+87 kJ mol −1 =+586 kJ kg −1 . The detonation velocity ( D ) and the detonation pressure ( P ) of 5‐aminotetrazolium nitrate were calculated using the empirical equations by Kamlet and Jacobs: D ([CH 4 N 5 ] + [NO 3 ] − )=8.90 mm μs −1 and P ([CH 4 N 5 ] + [NO 3 ] − )=35.7 GPa.

Experimental and theoretical data for 5-azidotetrazole CHN7 and its phenyl derivative 5-azido-1-phenyltetrazole as well as tetrazolylpentazole are reported. We discuss their syntheses, their properties and the X-ray structures of 5-azidotetrazole and its phenyl derivative. The decomposition reactions of tetrazolylpentazole and 5-azidotetrazole were also investigated. We furthermore calculated the electrostatic potentials of 5-azidotetrazole, its methyl and phenyl derivatives and of tetrazolylpentazole to determine the relative sensitivity of these compounds.

In the fabrication of fiber-reinforced plastics materials peel plies are commonly used as an additional layer on top of the laminates to sponge up the surplus resin and to create an activated surface for adhesive bonding or coating by peel ply removal. In theory, the peel ply removal results in a new and uncontaminated fracture surface that is activated by polymer chain scission. The peel ply method is often presented as being a good surface treatment for structural bonding. In this study carbon fiber-reinforced plastics (Hexcel® 8552/ IM7) were produced by the use of five different peel plies and a release foil made of polytetrafluorethylene (PTFE). The peel plies themselves and the surfaces on the CFRP created by peeling were examined by scanning electron microscopy (SEM), x-ray photo electron spectroscopy (XPS), energy-dispersive x-ray spectroscopy (EDX), infrared (IR) spectroscopy, atomic force microscopy (AFM), and contact angle measurements to characterize the surfaces produced. Furthermore, the bond strength of lap shear and floating roller peel samples was determined with and without additional plasma treatment. For bonding, a room temperature-curing two-component-epoxy adhesive (Hysol® 9395) was used to prove the applicability of different peel plies for structural adhesive bonding under repair conditions.

Abstract The enthalpies of combustion (Δ comb H ) of dinitrobiuret (DNB) and diaminotetrazolium nitrate (HDAT‐NO 3 ) were determined experimentally using oxygen bomb calorimetry: Δ comb H (DNB)=5195±200 kJ kg −1 , Δ comb H (HDAT‐NO 3 )=7900±300 kJ kg −1 . The standard enthalpies of formation (Δ f H °) of DNB and HDAT‐NO 3 were obtained on the basis of quantum chemical computations at the electron‐correlated ab initio MP2 (second order Møller‐Plesset perturbation theory) level of theory using a correlation consistent double‐zeta basis set (cc‐pVTZ): Δ f H °(DNB)=−353 kJ mol −1 , −1 829 kJ kg −1 ; Δ f H °(HDAT‐NO 3 )=+254 kJ mol −1 , +1 558 kJ kg −1 . The detonation velocities ( D ) and detonation pressures ( P ) of DNB and HDAT‐NO 3 were calculated using the empirical equations by Kamlet and Jacobs: D (DNB)=8.66 mm μs −1 , P (DNB)=33.9 GPa, D (HDAT‐NO 3 )=8.77 mm μs −1 , P (HDAT‐NO 3 )=33.3 GPa.

Abstract Additive Manufacturing (AM) becomes more and more focus of studies in the scientific community. Nevertheless, elastomers in 3D printing are still a relatively understudied topic despite their extensive use in machine components. The further understanding of the technologies and knowledge acquirement are fundamental steps towards the improvement of the printing process and the broadening of feasible applications of 3D printed elastomers. This work focused on thermoplastic polyurethanes printed with Fused Filament Fabrication (FFF) and investigated the effect of infill deposition angle and contour lines on the tensile and the stress relaxation behaviour. Samples were printed in alternating as well as unidirectional infill orientations, the latter without and with outlines. Tensile tests revealed that alternating orientations of 0°–90° and 45°–135° have a similar behaviour and benefit the integrity of the part. The fully unidirectional orientation at 90° hindered the tensile strength due to the absence of outlines and consequent delamination. All comparative analyses displayed a low influence of the raster angle at lower strains. Stress relaxation results showed similar behaviour for samples with outlines, without a clear effect of the infill orientations. In summary, contour lines are essential and an alternating orientation is recommended for better part integrity.

Novel polymeric flame retardants based on two acrylamides and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) or 5,5-dimethyl-[1,3,2]dioxaphosphinane-2-oxide (DDPO) are described for several applications in HexFlow® RTM6, a high-performance epoxy resin. Neat resin samples and carbon fiber-reinforced composites were tested for their glass transition temperatures (dynamic mechanical analysis), thermal stability (thermogravimetric analyses), flammability (UL94) and flame-retardant performance (Cone Calorimetry). Additionally, the fiber degradation occurring during combustion of carbon fiber-reinforced epoxy resins was observed by scanning electron microscopy to show the fiber protecting effect of these flame retardants. Whereas DOPO-containing polyacrylamides acting mainly in the gas phase showed the best flame retardant efficiency, DDPO-containing polyacrylamides acting mainly in the condensed phase showed the best fiber protection. A mixed polyacrylamide was synthesized to combine these effects. This thermoplastic is soluble in the resin and, therefore, suitable for injection molding processes. Interlaminar shear strength measurements showed no negative effect of the flame retardant. The versatility of these flame retardants is shown by investigations dealing with boehmite as synergist in neat resin samples.

For structures made of carbon fiber-reinforced plastics (CFRP), fast, robust, and reliable repair technologies are mandatory for economical usage. In this paper, the authors explain their strategy and experiences. An automated process is proposed to achieve the challenging goals. A general overview on the origin, effects, and analysis of contaminants in CFRP structures and the relationship to the achievable strength of adhesive bonds are given. For the repair of composite structures using adhesive bonding, surface pretreatment is a key factor in terms of reliability and strength. Different surface treatment processes such as grinding, grit blasting, plasma and pulsed lasers treatments are discussed. Furthermore, the possibilities and technical implementation of an automated milling process for the repair of composite structures are presented. This change from manual production to automation tremendously improved the quality and duration of the repair and allows the creation of a uniform surface for adhesive bonding. Further integration of novel technologies is discussed and will further support and enhance the repair in the near future.

Abstract The applicability of Additive Manufacturing for operational parts expands with the availability of new materials with specific properties. For elastomeric components produced with Fused Filament Fabrication, challenges associated with the printing process due to the nature of the material are faced. This paper investigates the effect of under-extrusion in this process regarding the feeding system and, predominantly, the moisture for thermoplastic polyurethanes with 3D printing experiments and thermomechanical testing. In particular, the filament flow control with a Bowden extruder provides a challenge. A microscopic analysis reveals the signs of under-extrusion, along with the influence of material drying to reduce the moisture content. The drying may depend not only on time and temperature, but also on mass and surface effects. Water uptake measurements exhibit absorptions up to 1.89% in weight, most of which take place during the first 24 h of the experiments. Tensile tests performed on samples with different moisture contents show their influence in the ultimate stresses. The moisture in the material causes under-extrusion induced failures. Those failures are less likely to happen at lower moisture levels, resulting in occasional higher tensile strengths. Overall, the importance of proper storage of the material throughout printing is verified, even under moderate humidity conditions due to its hygroscopic nature.

Triazidotrinitro benzene, 1,3,5-(N3)3-2,4,6-(NO2)3C6 (1) was synthesized by nitration of triazidodinitro benzene, 1,3,5-(N3)3-2,4-(NO2)2C6H with either a mixture of fuming nitric and concentrated sulfuric acid (HNO3/H2SO4) or with N2O5. Crystals were obtained by the slow evaporation of an acetone/acetic acid mixture at room temperature over a period of 2 weeks and characterized by single crystal X-ray diffraction: monoclinic, P 21/c (no. 14), a=0.54256(4), b=1.8552(1), c=1.2129(1) nm, β=94.91(1)°, V=1.2163(2) nm3, Z=4, ϱ=1.836 g⋅cm−3, Rall =0.069. Triazidotrinitro benzene has a remarkably high density (1.84 g⋅cm−3). The standard heat of formation of compound 1 was computed at B3LYP/6-31G(d, p) level of theory to be ΔH°f=765.8 kJ⋅mol−1 which translates to 2278.0 kJ⋅kg−1. The expected detonation properties of compound 1 were calculated using the semi-empirical equations suggested by Kamlet and Jacobs: detonation pressure, P=18.4 GPa and detonation velocity, D=8100 m⋅s−1.

Abstract The structure and bonding in 2‐diazo‐4,6‐dinitrophenol (DDNP) is discussed on the basis of quantitative molecular orbital (MO) calculations at the density functional theory (DFT) level using the natural bond orbital analysis (NBO). Qualitative valence bond theory (VB) was used to generate an increased VB structure for DDNP. The increased‐valence structure is better in accordance with the computed and observed (X‐ray) geometry than is the NBO analysis.

SUMMARY The influence of the orientation of carbon fibres on the reaction‐to‐fire characteristics of a layered composite has been investigated in detail. 8552/IM7 prepregs were laid up to give unidirectional and quasi‐isotropic laminates. Specimen thickness (0.25 to 8.0 mm) and heat flux (15 to 80 kW/m 2 ) were varied for irradiation. Fundamental reaction‐to‐fire properties of this composite are interpreted on the basis of the matrix components: epoxy resin and polyethersulfone. Cone calorimetry and temperature distributions through the laminate showed that the velocity and degree of combustion are dominated by fibre orientation for a given resin. In general, a quasi‐isotropic fibre orientation leads to faster ignition, because of preferred delaminations, but retards combustion processes more effectively than a unidirectional lay‐up. Migration velocities of the pyrolysis zone were measured. Copyright © 2011 John Wiley & Sons, Ltd.

Summary Fundamental aspects for the thermal decomposition and formation of respirable fragments of carbon fibers are investigated to assess the health hazard of carbon fiber reinforced plastic material after a fire. The influence of temperature (600°C‐900°C)/heat flux (30‐80 kW/m 2 ), time of thermal load (up to 20 minutes), and oxygen exposure is analyzed by means of mass loss and fiber diameter of intermediate modulus and high tenacity fibers with initial diameters of 5 to 7 μm. Various types and concentrations of flame retardants were tested with respect to fiber protection. Epoxy‐based composite specimens (RTM6/G0939) additionally containing aluminum or magnesium hydroxide and/or zinc borate (1‐25 wt% per resin) were analyzed by cone calorimetry. Carbon fiber decomposition increases with combustion/irradiation time and temperature/heat flux, after a threshold temperature (ca 600°C) is exceeded. Critical fiber diameters below 3 μm are reached within minutes and are predominantly observed close to the panel surface in contact with air. Effective fiber protection is achieved by flame retardants acting beyond 600°C, forming thermally resistant layers such as zinc borate. A new field of research is opened identifying flame retardants, which protect carbon fibers in carbon fiber reinforced plastic.

An atmospheric-pressure plasma jet (APPJ)-based surface treatment process was investigated for the structural (τB > 15 MPa) adhesive bonding of polyamide 6 (PA6) composites. The treated surfaces were examined by contact angle measurement, X-ray photoelectron spectroscopy, and atomic force microscopy (AFM). Additionally, the shear strengths of single lap specimens were determined as a function of different plasma intensities and polyurethane adhesives. Our results show that APPJ leads to an increase of the surface free energy, oxygen concentration, and number of functional groups. Furthermore, the topography of the surface was significantly modified by exposure to APPJ. AFM measurements show that special attention has to be paid to the intensity of the plasma treatment to avoid melting and flattening of the PA6 surface on the nanometer scale. With optimized multiple APPJ treatments, lap shear strength of 20 MPa was achieved for the first time for this material system, allowing the material system to be employed in future automobile applications.

The production of spare parts using Additive Manufacturing (AM) is an emerging area that impacts the supply chain management. To give designers a way to proceed at the moment of redesign and produce a spare part using AM, this contribution presents a methodology for the design and manufacturing of digital spare parts using AM in decentralized facilities. The re-design of the spare parts is tackled by giving design considerations based on agile hardware development practices to improve the quality of the spare parts and reduce the lead time. Since this methodology is derived from different case studies of the military over two years, the approach is suited for the defence industry but can be adapted to other industries that operate reduced facilities abroad. Additionally, three different use cases following the methodology are presented. The weaknesses of the processes are highlighted and some recommendations for production engineers and designers are given.

The aim of this work was to predict composition and nine selected physicochemical properties of fossil/synthetic aviation fuel blends by chemometric analysis of mid-infrared spectra. Therefore, infrared spectra of various mixtures with six different synthetic hydrocarbon fuels were recorded and comprehensively interpreted, supported by data from comprehensive two-dimensional gas chromatography–mass spectrometry analysis of these fuels. Deep insight has been gained on how individual blend components are differentiated in principal component analysis and how they influence physicochemical properties by means of partial least squares regression. A chemometric model has been established to determine the amount of an individual synthetic fuel in a blend with a precision of <1 vol % and a detection limit of <2 vol %. The quality of prediction of physicochemical properties is good enough to compete with results obtained by established test methods.

Abstract In this paper we present an approach where ultrasonic testing data (UT) is linked with its spatial coordinates and direction vector to the examined specimen. Doing so, the processed nondestructive testing (NDT) results can be visualized directly on the sample in real-time using augmented or virtual reality. To enable the link between NDT data and physical object, a 3D-tracking system is used. Spatial coordinates and NDT sensor data are stored together. For visualization, texture mapping was applied on a 3D model. The testing process consists of data recording, processing and visualization. All three steps are performed in real-time. The data is recorded by an UT-USB interface, processed on a PC workstation and displayed using a Mixed-Reality-system (MR). Our system allows real-time 3D visualization of ultrasonic NDT data, which is directly drawn into the virtual representation. Therefore, the possibility arises to assist the operator during the manual testing process. This new approach results in a much more intuitive testing process and a data set optimally prepared to be saved in a digital twin environment. The size of the samples is not limited to a laboratory scale, but also works for larger objects, e.g. a helicopter fuselage. Our approach is inspired by concepts of NDE 4.0 to create a new kind of smart inspection systems.