Computational Studies on Nitro,Nitramino, and Dinitramino Derivatives of 1‐Aminoazadiboridine as High Energetic Material

Computational studies were performed to determine the thermodynamic and explosive characteristics of high energy materials formed by placing explosophores such as nitro (−NO₂), nitramino (−NHNO₂), and dinitramino (−N(NO₂)₂) groups on 1‐aminoazadiboridine. G3 level calculations were made to determine the gas phase heat of formation of the designed species. In addition to the above, condensed phase heat of formation was also determined by evaluating the sublimation enthalpy. Crystal densities of title compounds were predicted with the help of a wave function analysis (WFA) program and were found to be in the range of 1.55–1.83 g cm⁻³. Bond dissociation energies of various possible bond rupture routes of the designed molecules were calculated at DFT‐B3LYP/6‐311G(d,p) level and attempt was made to identify the trigger linkage. Impact sensitivity was evaluated theoretically by employing a method based on statistical parameters determined from electrostatic potential data. Results show that the designed molecules are highly energetic and their corresponding detonation properties place them in the category of safe and high performance explosive materials.     

Estimated Detonation Velocities for TKX‐50, MAD‐X1, BDNAPM,BTNPM, TKX‐55, and DAAF using the Laser–induced Air Shock from Energetic Materials Technique

Since new energetic materials are initially produced in very small quantities for both safety and cost reasons, laboratory‐scale methods for characterizing their performance are essential for determining the most promising candidates for scale‐up. Laser‐induced air shock from energetic materials (LASEM) is a promising new method for estimating the detonation velocity of novel explosives using milligram amounts of material, while simultaneously investigating their high temperature chemical reactions. LASEM has been applied to 6 new explosives for the first time: TKX‐50, MAD−X1, BDNAPM, BTNPM, TKX‐55, and DAAF. Emission spectroscopy of the laser excited materials revealed the formation of the high pressure bands of C₂ during the ensuing exothermic reactions. The low thermal sensitivity of the materials also led to unusual laser‐material interactions, visualized with high‐speed video. The estimated detonation velocities for the 6 explosives were compared to predicted values from EXPLO5 and CHEETAH. The LASEM results suggest that TKX‐55, BDNAPM, and BTNPM have higher detonation velocities than predicted by the thermochemical codes, while the estimated detonation velocities for MAD−X1 and TKX‐50 are slightly lower than those predicted.     

On the Use of AMl and PM3 Methods on Energetic Compounds

Stewart's new semi-empirical method MNDO-PM3 (PM3) is compared with the well known Dewar's AMl method in the study of nitrosubstituted compounds, and some energetic materials. PM3 method shows better performances than the AMl one. Adjacent lone pair/lone pair repulsion are better described at PM3 level and the known systematic correction of about −9 kcal/mol for each C-NO₂ group of the AMl method becomes +3.5 kcal/mol at PM3 level. PM3 results for N-NO₂ containing compounds are directly comparable with experimental gas phase data.     

TATB thermal decomposition: Expanding the molecular profile with cryo-focused pyrolysis GC-MS

Understanding the molecular composition of high explosives during thermal decomposition is vital for predicting the sensitivity, safety, and performance of explosive materials. The thermal decomposition of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) has been linked to the formation of furazans through a series of dehydration reactions of the NO₂ and NH₂ groups on the phenyl ring, along with breakdown into small molecules (≤120 amu). Molecular identification of compounds formed in this transformation of the furazans to light gases has been lacking. To address this, we have applied a pseudo-confined sampling system in a cryo-focused pyrolysis gas chromatography-mass spectrometry (pyGC-MS) system to molecularly identify these intermediates. By design, sublimation of TATB, which has complicated MS analyses of thermal degradation, was significantly reduced and additional compounds were identified with potential structural information. In addition to the known furazan compounds, one of these compounds forms from the loss of oxygen from benzo-trifurazan (F₃) and produces an open ring structure that may be the first step in the formation of lower molecular weight furazan breakdown products. The loss of a nitro group from benzo-monofurazan (F₁) was also discovered and implicates the formation of oxidizing NO₂ gas in the thermal decomposition mechanism. These findings are vital for understanding the proper heat flow from energetic materials on a molecular level, necessary when measuring enthalpy and developing decomposition models based on kinetic parameters.     

Development of Gas Generators for Fire Extinguishing

Gas producing materials are widely used in military or space applications as solid rocket and gun propellants. The chemical formulations of these propellants cannot be directly transferred to other applications as their product gases are optimized on high power, producing high amounts of CO and toxic trace constituents not acceptable in industrial applications. Beneath small scale applications in inflating bag boats or ejecting pilots of aircrafts etc. the gas generators for airbag inflation became a standard equipment of cars and improved safety of drivers and passengers substantially. Recently, systematic investigations started to realize the idea of using gases or aerosols produced by solid energetic or pyrotechnique materials for fire extinguishing. The actually introduced chemical gas generator formulations are based on the experience of pyrotechnics and solid propellants. Sodium azide and nitrocellulose containing mixtures cover most requirements on mass products. Despite their high level of technical development both formulations exhibit strong disadvantages. The work reported considers organic formulations for fire extinguishing, which produce gases composed of N₂ and CO₂. The gasgenerants described consist of non-toxic chemicals including fuel, oxidant, catalyst and cooling agent for thermal process control. The formulations show higher gas output per mass, can be recycled environmentally friendly and are of low costs. The results comprise thermochemical properties governing the time dependent gas output, characterization of the constituents and trace species of the product gas, safety and stability aspects. From selected gas generants the following data were measured: Estimation of thermal stability using DSC methods and mass-loss tests; Pressure/time curves in the ballistic bomb; Rate of product gases by means of gaschromatography.     

Recent Developments for Prediction of Power of Aromatic and Non‐Aromatic Energetic Materials along with a Novel Computer Code for Prediction of Their Power

The explosive power or strength of an energetic material shows its capacity for doing useful work. This work reviews recent developments for prediction of power of energetic compounds. A new user‐friendly computer code is also introduced to predict the relative power of a desired energetic compound as compared to 2,4,6‐trinitrotoluene (TNT). It is based on the best available methods, which can be used for different types of energetic compounds including nitroaromatics, nitroaliphatics, nitramines, and nitrate esters. The computed relative powers are consistent with the measured data for some new materials containing complex molecular structures.     

Influence of surface acid–base properties of zirconia and titania based catalysts on the product selectivity in gas phase dehydration of glycerol

Acid–base properties of zirconia and titania based materials were investigated by adsorption microcalorimetry of NH₃ and SO₂ probe molecules. Catalytic performance of the catalysts was also tested in the gas phase dehydration of glycerol with the intention of finding correlations between catalytic activity and surface acid–base features. Results show that the number of basic sites directly affects the selectivity in gas phase dehydration of glycerol to produce acrolein. Therefore, in order to realize the target reaction it is necessary to control not only the strength and the amount of the desired sites (acidic ones), but also to hinder as much as possible the number/strength/action of the undesired ones (basic ones).     

A New Computer Code for Prediction of Enthalpy of Fusion and Melting Point of Energetic Materials

The prediction of phase change properties of energetic materials is important for the assessment of hazardous energetic materials. A novel user‐friendly computer code, written in Visual Basic, is introduced to predict the melting point and the enthalpy of fusion of energetic materials by only using their molecular structure parameters. It can be used for different types of energetic compounds including polynitro arenes, polynitro heteroarenes, acyclic and cyclic nitramines, nitrate esters, and nitroaliphatic. The predicted results were compared with several of the best available methods, which confirmed the higher reliability of the new computer code for some new and well‐known energetic compounds with complex molecular structures. This code can be used for designing of energetic compounds with desirable phase change properties.     

Properties of Gas‐Generating Mixtures Related to Different Fuel and Oxidizer Compositions

This work focuses on solid energetic materials designed to produce high‐pressure gas for pressurizing or inflating devices. In small gas generators sodium azide is often used. Unfortunately, this chemical exhibits drawbacks concerning toxicity and yield of gas. Other classical gas‐generating agents are double base propellants. However, they deliver toxic and reactive gases and their combustion temperatures are high. In previous work a series of alternative gas‐generating compositions have been proposed, fuelled with double base propellants, azodicarbonamide, nitroguanidine or guanidine nitrate and oxidized with potassium nitrate or potassium perchlorate. They were theoretically and experimentally evaluated on a series of combustion properties, such as ignition delay, burning rate, vivacity, specific energy, etc. The purpose of this paper is to experimentally examine the gas production of the previously proposed compositions. The yield of gas is determined through static pressure measurements after a closed vessel test, while the composition of the combustion gases is investigated through gas analysis. The addition of an oxidizer causes a significant drop in the yield of gas, but avoids the formation of hazardous gases, such as H₂ and CO, in most of the studied cases. The only exception is the mixture of a double base propellant with potassium nitrate: potassium nitrate does not fully react with the double base propellant and therefore the formation of CO and H₂ is not prevented.     

Effect of the type and quality of antioxidant additions on properties of materials of the system Al2O3-SiC-C

Results are presented for a study of the apparent density and ultimate strength in compression of developed materials of the system Al₂O₃-SiC-C, modified by introduction of phosphate addition and complex antioxidant (Al + Si + phosphate addition). It is established that introduction of a phosphate addition together with a complex antioxidant (Al + Si) to the composition of corundum-graphite SiC-containing refractory based on an ethyl silicate binder leads to compaction of the structure and formation of materials of prescribed phase composition with increased oxidation resistance. Translated from Novye Ogneupory, No. 5, pp. 28–31, May 2008.     

Production of titanium-containing metal-ceramic composites based on boron carbide in the nanocrystalline state

ABSTRACT

The results of the study of the production technology, phase composition, structure and physico-mechanical properties of metal-ceramic materials based on boron carbide and their components are presented. Boron carbide was obtained by direct synthesis from chemical elements using amorphous boron and carbon black. By mechanical dispersion, solid reagents were converted into an ultrafine state. Using a chemical method, nanoscale (70–80?nm) boron carbide was synthesised from suspension solutions of amorphous boron and liquid hydrocarbons. Boron carbide-based metal-ceramic composite powder B₄C–(Co–Ni–Ti) was obtained by mechanical dispersion of the constituent components. Based on results of studying of the temperature-dependence of wetting angle of boron carbide with Co–Ni–Ti metallic alloy, the compacting modes of metal-ceramic composite powders by plasma-spark sintering and hot pressing have been developed. The influence of the component content of the binder metal (alloy) on some physico-mechanical properties (linear expansion coefficient, hardness, and bending strength) of hardmetal-ceramic materials based on boron carbide was studied. It was found that the optimum content of the metal component in the composite is ～ 25?wt-%. In the temperature range 300–600°C, the materials obtained are characterised by stable dimensional factors, since in this temperature range the thermal conductivity coefficient does not depend much on temperature. At room temperature, their bending strength is about 1?GPa. A new method of chemical synthesis of nanocrystalline ceramic compositions of boron carbide and titanium diboride using suspension solutions for the preparation of powders and their spark plasma sintering was also developed to obtain a compacted material of composition B₄C+30?wt-%TiB₂, which has a high hardness of 95 HRA (with maximum microhardness 45.6?GPa) and sufficient strength (with a bending strength of 834?MPa).     

Estimation and prediction of the heats of formation for non-aromatic polynitro compounds on the basis of the QSPR approach

The analysis of “Quantitative Structure-Property Relationship”(QSPR), concerning the heat of formation in the condensed state, is performed for non-aromatic polynitrocompounds. The QSPR approach and our original computer program “EMMA”(Efficient Modelling of Molecular Activity) are used. This approach is based on the construction of optimal linear regression models involving physical-chemical, topological, informational, and substructural indices; it can be used as an alternative to traditional additive schemes for evaluating physical-chemical characteristics of energetic materials. On the basis of the QSPR method, the “structure-heat of formation (ΔH°_f)” relationship is revealed for a data base of non-aromatic polynitrocompounds, and ΔH°_f is predicted for some hypothetic substances.     

Stationary Phases 45(1). Chromatographic Separation of High Energetic Materials with C60-Fullerene Stationary Phase

A method for the chromatographic separation of nitroaromatic high energetic materials on C₆₀-fullerene stationary phase is discussed. Special selectivity on this phase using methanol/water(80/20) as mobile phase leads to have a wider separating space so that its retention power is much greater than that of a commercial RP-18 phase. This advantage can be used to identify the isomers of some nitroaromatic high energetic materials.     

A New Method for Determining Gas Phase Heat of Formation of Aromatic Energetic Compounds

A new correlation is introduced for desk calculation of gas phase heat of formation of aromatic energetic compounds that contain the elements of carbon, hydrogen, nitrogen and oxygen. Predicted gas phase heats of formation for 26 energetic compounds have a root mean square of deviation from experiment of 20.67 kJ/mol, which is in good agreement with respect to measured values of oxygen‐lean and oxygen‐rich aromatic energetic compounds.     

Phase-formation processes in the Al2O3-ZrO2-SiO2 system in heating

The specifics of the phase-formation processes and material structure formation based on Al₂O₃, ZrO₂, and Si₂O₂ are investigated. The possibility of using these materials to protect various construction materials from gas corrosion at high temperatures is demonstrated.     

Influence of heat treatment temperature on the properties of the lithium disilicate-fluorcanasite glass-ceramics

This study aims to investigate the influence of heat treatment temperatures on the mechanical properties and chemical solubility (CS) of lithium disilicate-fluorcanasite glass-ceramics and to develop new dental materials. The glasses and glass-ceramics were prepared using CaF₂-SiO₂-CaO-K₂O-Na₂O-Li₂O-Al₂O₃-P₂O₅-based glass system using a conventional melt quenching method followed by a two-stage crystallization process. This two-stage method involves two heating temperature steps: first at a constant temperature (T_S1) of 600°C and second step at varying temperatures (T_S2) of 650, 700, 750, and 800°C. The crystallization behavior, phase formation, microstructure, translucency characteristic, density, hardness, fracture strength, and CS were investigated. It was found that the lithium disilicate crystal acted as the main crystalline phase, and the crystalline phase of fluorcanasite occurred at the heat treatment temperatures of 750 and 800°C. In addition, it was found that density, hardness, fracture strength, and CS increased while the translucency values decreased with increasing heat treatment temperatures. Furthermore, the CS increased dramatically when the fluorcanasite phases occurred in the glass-ceramic samples. The maximum density values, Vickers hardness, fracture toughness, and flexural strength are 2.56 g/cm³, 6.73 GPa, 3.38 MPa.m^1/2, and 259 MPa, respectively. These results may offer a possibility to design a new material for dental applications based on lithium disilicate-fluorcanasite glass-ceramics.     

Simulation study on the liquid‐crystalline ordering and fluidity of energetic diblock copolymers based on poly[3,3‐bis(azidomethyl) oxetane]

The liquid‐crystalline ordering and fluidity of energetic diblock copolymers based on poly[3,3‐bis(azidomethyl) oxetane] (BAMO) and 3‐nitratomethyl‐3′‐methyloxetane (NMMO) were investigated by the dissipative particle dynamics method. The results show that these copolymers, with moderate BAMO block lengths (x's), experienced the disorder, nematic, and smectic phases with decreasing temperature. The nematic phase was suppressed when the rod length was too long or short. After the formation of the smectic phase, the fluidity had a sharp decline. The temperature forming the smectic phase was defined as the order–disorder transition temperature (T_ODT) and depended strongly on x. A simple scaling rule, T_ODT ≈ e^?x, between T_ODT and x was constructed. The effect of the soft NMMO block fraction on the fluidity emerged before the formation of the smectic phase. These results can help researchers design and synthesize new energetic copolymers with an appropriate melting temperature range for use as binders of solid propellants. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

New refractory concretes and binding systems: Basic trends of development, production, and use of refractories in the 21st century. Part II. Ceramic binders and castables

A brief review of recently obtained and studied ceramic binding systems and castables based on them is presented. It is shown that corundum ceramic castables (Al₂O₃>95%) and ceramic castables based on aluminomagnesia spinel can be produced in principle. New molding methods that employ static pressing, ramming (vibroramming), and centrifugal shaping are described. The centrifugal method was used to produce ceramic castables (d _max≤5 mm) with an initial porosity of 13–14%. The method of vibroramming from molding systems with a moisture content of 3.4–4.0% was used to produce mullite-corundum ceramic castables with an elevated density and strength. The high efficiency of use of ceramic castables in metallurgy is due to the superfine porous structure of their matrix (binding) phase. The predominant pore size in various binders is 0.01–1.0 μm. In service, materials with such a structure are not impregnated by slag or metal. A principle for increasing the endurance of refractories produced from conventional raw materials using a new technology is suggested. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 3, pp. 15–24, March, 1998. For the beginning of the article see No. 2, 1998.     

Nitroureas II. Synthesis of Bicyclic Mono- and Dinitrourea Compounds

We report the synthesis and characterization of several bicyclic mono- and dinitrourea compounds as energetic materials and discuss their use as precursors to other energetic compounds. The new nitrolyzing reagent, trifluoromethanesulfonic acid anhydride/20% N₂O₅/nitric acid, will also be described.