Preparation and Characterization of Nano‐TATB Explosive

Nano‐TATB was prepared by solvent/nonsolvent recrystallization with concentrated sulfuric acid as solvent and water as nonsolvent. Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) were used to characterize the appearance and the size of the particles. The results revealed that nano‐TATB particles have the shape of spheres or ellipsoids with a size of about 60 nm. Due to their small diameter and high surface energy, the particles tended to agglomerate. By using X‐ray powder diffraction (XRD), broadening of diffraction peaks and decreasing intensity were observed, when the particle sizes decreases to the nanometer size range. The corrected average particle size of nano‐TATB was estimated using the Scherrer equation and the size ranged from 27 nm to 41 nm. Furthermore, the specific surface area and pore diameter of nano‐TATB were determined by BET method. The values were 22 m²/g and 1.7 nm respectively. Thermogravimetric (TG) and Differential Scanning Calorimetric (DSC) curves revealed that thermal decomposition of nano‐TATB occurs in the range of 356.5 °C–376.5 °C and its weight loss takes place at about 230 °C. Furthermore, a slight increase in the weight loss was observed for nano‐TATB in comparison with micro‐TATB.     

Fractal Networks of Inter‐Granular Voids in Pressed TATB

Small‐angle neutron scattering techniques were used to study the evolution of void morphology with pressed density of the insensitive high explosive, TATB. Samples were studied as a loose powder and as pressed pellets, ranging in density from approx. 1 to 1.804 g cm⁻³. Inter‐granular voids in the loose powder were randomly arranged (non‐fractal) and had a surface defined mean size of 0.66 μm. Pressing was found to induce a fractal network of voids with fractally rough interfaces. The surface‐defined mean void size of the pressed samples was between 0.21–0.33 μm over the range of densities studied and was found to increase with pressed density up to 1.720 g cm⁻³, decreasing thereafter. The volume fractal dimension, indicative of the void arrangement, mirrored the changes in the mean void size. No systematic change in the surface fractal dimension was found. Surface area analysis allowed the average TATB grain size within the pressed samples to be quantified. An initial decrease of the mean grain size followed by an increase with pressed density suggests that the TATB grains behave in a brittle fashion at low densities and ductile at higher pressed densities.     

Preparation and Properties Study of Core‐Shell CL‐20/TATB Composites

The insensitive high explosive 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) was selected for coating and desensitization of hexanitrohexaazaisowurtzitane (CL‐20), another high explosive, after surface modification. About 2 wt‐% polymer binder was adopted in the preparation process to further maintain the coating strength and fill the voids among energetic particles. The structure, sensitivity, polymorph properties, and thermal behavior of CL‐20/TATB by coating and physical mixing were studied. Scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS) results indicate that submicrometer‐sized TATB was compactly coated onto the CL‐20 surface with coverage close to 100 %. The core‐shell structure of CL‐20/TATB was confirmed by observation of hollow TATB shell from the CL‐20 core dissolved sample. X‐ray diffraction (XRD) analysis revealed that the polymorph of CL‐20 maintained ε form during the whole preparing process. Thermal properties were studied by thermogravimetry (TG) and differential scanning calorimeter (DSC), showing effects of TATB coating on the polymorph thermal stability and exothermic decomposition of CL‐20. Both the impact and friction sensitivities were markedly reduced due to the cushioning and lubricating effects of TATB shell. The preparation of explosive composites with core‐shell structure provides an efficient route for the desensitization of high explosives, such as CL‐20 in this study.     

Correlation between Neutron Diffraction Measurements and Thermal Stresses in a Silicon Carbide/Alumina Composite

Sintering of Al₂O₃ powder and SiC fibers at high temperatures leads to a state of high internal stresses in the composite material at room temperature because of the difference in thermal contraction between both materials. These stresses are calcualted in this work using the scheme of the elastic elliposidal inclusion of Eshelby and regarding the fibers as prolate ellipsoids. The predicted strain in the fibers is used to calculate variations in the spacing of crystallographic planes and the results are compared against experimental measurements obtained with neutron diffraction by other authors. We show that in order to correlate the measurements with the actual stress state, it is necessary to account for the elastic anisotropy and the proper crystallographic structure of the fibers. We demonstrate that the interpretation also depends on the distribution of fiber orientations inside the matrix and that results can be substantially changed depending on the assumptions employed.     

Structures and Properties Prediction of HMX/TATB Co‐Crystal

In this study, a new co‐crystal explosive of 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane (HMX)/1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) (molar ratio 1 : 1) was designed based on crystal engineering. The crystal structure was predicted using the polymorph predictor (PP) method. The main properties of co‐crystal consisting of mechanical properties, stability, and interaction formats were simulated through molecular dynamics methods. Simulated results indicate that the crystal structure of the HMX/TATB co‐crystal may belong to the P , P2₁2₁2₁ or P2₁/c space group. The calculations of the binding energy and the analysis for radial distribution function show that the two components are connected through electrostatic hydrogen bonding and strong van der Waals interactions. The new co‐crystal has better mechanical properties with the moduli systematically decreased. With the appearance of the new crystal, the trigger bond N NO₂ has little change.     

Structural Defect Evolution of TATB‐Based Compounds Induced by Processing Operations and Thermal Treatments

2,4,6‐Triamino‐1,3,5‐trinitrobenzene (TATB) compounds are commonly used in high performance explosives because of their thermal stability and high detonation velocities compared to other materials. The insensitivity and mechanical properties are related to the stability of their crystalline structure. Crystallographic structure and structural defects evolution of TATB and TATB‐based compounds were studied by X‐ray diffraction for powders, molding powders, and pressed compounds, using Rietveld refinement. The effects of synthesis conditions, thermal treatments, coating and pressing operations on the structure of TATB compounds were evaluated. The results show that the pressing operation results in anisotropic crystallite size, leading to an increase of the structural defects density. It could be due to the anisotropic mechanical response of the TATB crystal under pressure, possibly plasticity. Finally, it is shown that increasing thermal treatment temperature on TATB powders decreases the structural defects density.     

Experimental Study and DEM Simulation of Micro–Macro Behavior of TATB Granules During Compaction Using X‐ray Tomography

In this study, a noninvasive experimental method and a discrete element method (DEM) model were used to investigate the micro–macro behavior of TATB granules including global deformations, contact forces, stress distributions, local coordination number, local pore ratio, particle kinematics, and granule displacement during compacting process. The TATB granule deformation and structural evolution during compaction process were studied by X‐ray tomography and the deformation characteristics of deformable material. The size and number of granules with different sizes were determined from the CT images. The digital microstructure can be directly used for the numerical simulation setup. The DEM method was used for the numerical simulation of TATB granules during compaction. The contact forces and displacement vectors in compaction process were obtained. The behaviors and stress distributions at different pressures were also derived from the simulation. This study evaluated the possibility to better describe the behaviors of TATB granules.     

Temperature‐Dependent Deformation and Dislocation Density in SrTiO3 (001) Single Crystals

This study evaluates the change of flow stress as related to dislocation density in SrTiO₃ single crystals in order to provide guidance for later electrical studies. The key parameters varied are temperature and loading rate during the deformation. It is found that in <100>‐oriented SrTiO₃ single crystals, the dislocation density is enhanced by plastic deformation, more so at higher temperature as compared to room temperature. The experimental approach of quantifying the dislocation density through a determination of ex situ X‐ray diffraction rocking curves was successfully applied over the upper temperatures region of the lower temperature ductility zone for strontium titanate, i.e., in the so‐called “A‐regime”. For 1.0% deformed samples deformed at 300°C, a fourfold increase in dislocation density to 1.4 × 10¹³ m^?1 was found as compared to the nondeformed state (3.7 × 10¹² m^?1). Cross‐section techniques confirmed that the observed dislocation densities measured at the surfaces were identical to those seen in the core of the crystals. The use of rapid changes in loading rate provided an estimate for activation volume of the dislocation core for both 25°C and 300°C.     

Time‐ and Temperature‐Dependent Fracture Mechanics of Polymers: General Aspects at Monotonic Quasi‐Static and Impact Loading Conditions

Well‐defined correlations exist between the maxima in mechanical loss factor and the local maxima in temperature‐ or loading‐speed‐dependent fracture toughness. The non‐linear viscoelastic fracture processes and small‐strain deformations are characterised by the same Arrhenius‐type activation enthalpies. The local increase in toughness is linearly correlated with the relaxation strength of molecular relaxation processes. Stable crack propagation can be understood as a three‐phase process resulting in steady‐state stable crack growth. The normalised steady‐state crack‐tip‐opening displacement is independent of matrix material, temperature and loading speed.

     

Small‐Angle Neutron Scattering and Contrast Variation Measurement of the Interfacial Surface Area in PBX 9501 as a Function of Pressing Intensity

Small‐angle neutron scattering with contrast variation was used to measure the interfacial surface area in a composite high explosive formulated with a deuterated binder. Continuing our work on the effect of varying the pressing intensity on void and binder size distribution, the effect of pressing intensity on the three interfaces (HMX‐binder, HMX‐voids and binder‐voids) of the PBX 9501 microstructure was studied. Formulation of PBX 9501 with a deuterated binder allowed the neutron scattering length density contrast to be varied and thus allowed differentiation of the three interfaces. Porod analysis was used to measure the surface area. The surface area at the interfaces of HMX and binder was found to increase with increasing pressing intensity, while the surface area between HMX and voids may have decreased slightly. No evidence was found for voids within the binder at any pressing intensity.     

Flameless Combustion Synthesis of Ni and Ag Nanoparticles in Ballasted Systems: A Time‐Resolved X‐ray Diffraction Study

The combustion of cellulose nitrate in ballasted mixtures containing an organic binder and nickel hydroxycarbonate or silver carbonate as precursors resulted Ni or Ag nanoparticles. The formation of Ni and Ag nanoparticles from flameless combustion of cellulose nitrate was monitored by time‐resolved X‐ray diffraction. During the formation of the Ag nanoparticles, the diffraction patterns exhibited only signals from decreasing amounts of the precursor and newly simultaneously formed 20–30 nm silver particles. It was detected that in the systems with Ni precursor the formation of the Ni 5–10 nm crystals proceeded by some 2–3 s diffraction‐silent intermediate states of the whole system.     

Laser Doppler Measurements of Turbulent Parameters in Different Multiple‐Propeller Systems

In this study, laser Doppler anemometry (LDA) measurements in the r‐z plane are obtained in two stirred tanks equipped with two downward pumping propellers in the turbulent and the transient flow domains. A new approach of the hydrodynamics generated by this system consists of determining the one‐dimensional energy spectrum and the autocorrelation coefficient function at different locations in each vessel. In the turbulent flow, the integral scales, the Taylor microscales, and the Kolmogorov microscale have been determined. The dissipation rate is obtained with two methods: from the semi‐empirical expression ϵ = A k^3/2/D and from the frequency spectrum. Results show the influence of the rheological properties on the flow patterns, the influence of the blade passage frequency on the frequency spectrum, and the apparition of a low frequency characterizing the production of macro‐instabilities. Comparison of the turbulent characteristics with the values reported in the literature shows that our combination of propellers produces larger eddies than a Rushton turbine.     

Aging of Standard and Insensitive RDX Crystals Investigated by Means of X‐Ray Diffraction

Coarse particles of the high explosive RDX in different qualities (S‐RDX, I‐RDX, VI‐RDX) were aged artificially in air and argon, equivalent up to 25 years at 25 °C. The samples were investigated by means of X‐ray diffraction and rocking curves, revealing the behavior of microstrain during the artificial aging. The investigations revealed that the improved crystal quality of RDX survives artificial aging in contrast to a standard quality, where aging increases microstrain significantly. Besides aging details and mechanisms on a crystal level are described and discussed, such as eutectic mixtures with HMX impurities, crystal growth, defect healing, surface diffusion and smoothing, and reconstruction of crystal faces, edges and corners in rounded particles.     

In Situ X‐Ray Diffraction and Stress Analysis of Solid Oxide Fuel Cells

To increase the long term stability and performance of solid oxide fuel cell (SOFC) materials, it is important to understand the main degradation processes in their functional layers. In this work, the interface between electrolyte and anode material was investigated by in situ X‐ray diffraction (XRD) stress and phase analysis. It has been found that the determining process for the initial degradation of SOFC is the reduction of the anode material with hydrogen. During this process a tensile strength of 600–700 MPa is measured. These stresses are induced in the electrolyte material and produce crack networks. The reduction from nickel oxide to pure nickel was monitored by in situ phase analysis. This reaction induces tensile stress at the interface between electrolyte and anode. The stress produced in the electrolyte material was also confirmed by the observation of crack networks detected using scanning electron microscopy (SEM). Finally, the reducing process was optimized using different process gases, decreasing the destructive tensile stress level.     

Crystallization of Enantiomerically Pure Proteins from Quasi‐Racemic Mixtures: Structure Determination by X‐Ray Diffraction of Isotope‐Labeled Ester Insulin and Human Insulin

As a part of a program aimed towards the study of the dynamics of human insulin‐protein dimer formation using two‐dimensional infrared spectroscopy, we used total chemical synthesis to prepare stable isotope labeled [(1‐¹³C=¹⁸O)Phe^B24)] human insulin, via [(1‐¹³C=¹⁸O)Phe^B24)] ester insulin as a key intermediate product that facilitates folding of the synthetic protein molecule (see preceding article). Here, we describe the crystal structure of the synthetic isotope‐labeled ester insulin intermediate and the product synthetic human insulin. Additionally, we present our observations on hexamer formation with these two proteins in the absence of phenol derivatives and/or Zn metal ions. We also describe and discuss the fractional crystallization of quasi‐racemic protein mixtures containing each of these two synthetic proteins.     

High‐Temperature Neutron Diffraction,Raman Spectroscopy,and First‐Principles Calculations of Ti3SnC2 and Ti2SnC

Herein, we report—for the first time—on the additive‐free bulk synthesis of Ti₃SnC₂. A detailed experimental study of the structure of the latter together with a secondary phase, Ti₂SnC, is presented through the use of X‐ray diffraction (XRD), and high‐resolution transmission microscopy (HRTEM). A previous sample of Ti₃SnC₂, made using Fe as an additive and Ti₂SnC as a secondary phase, was studied by high‐temperature neutron diffraction (HTND) and XRD. The room‐temperature crystallographic parameters of the two MAX phases in the two samples are quite similar. Based on Rietveld analysis of the HTND data, the average linear thermal expansion coefficients of Ti₃SnC₂ in the a and c directions were found to be 8.5 (2)·10^?6 K^?1 and 8.9 (1)·10^?6 K^?1, respectively. The respective values for the Ti₂SnC phase are 10.1 (3)·10^?6 K^?1 and 10.8 (6)·10^?6 K^?1. Unlike other MAX phases, the atomic displacement parameters of the Sn atoms in Ti₃SnC₂ are comparable to those of the Ti and C atoms. When the predictions of the atomic displacement parameters obtained from density functional theory are compared to the experimental results, good quantitative agreement is found for the Sn atoms. In the case of the Ti and C atoms, the agreement is more qualitative. We also used first principles to calculate the elastic properties of both Ti₂SnC and Ti₃SnC₂ and their Raman active modes. The latter are compared to experiment and the agreement was found to be good.     

Progress in the Field of Water‐ and/or Temperature‐Triggered Polymer Actuators

Water‐ and/or temperature‐triggered polymer actuators have great potential in robotics, microfabrication and micromanipulation, cell culture, artificial scaffolds, muscles, and motors. In the past few years, a large amount of work has been carried out, and several innovative concepts have been proposed to address challenges such as actuation with large‐scale displacement in a very short time, actuation of large‐sized samples, complex 3D shaping, directional control, multiresponsive actuation, and strong actuators. Herein, the progress made in the field of actuators triggered by water, temperature, and a combination of both is presented, emphasizing the new concepts of fast and direction‐controlled actuation, the corresponding mechanisms, the associated challenges, and future tasks and perspectives.     

Direct Internal Reformation and Mass Transport in the Solid Oxide Fuel Cell Anode: A Pore‐scale Lattice Boltzmann Study with Detailed Reaction Kinetics

The solid oxide fuel cell (SOFC) allows the conversion of chemical energy that is stored in a given fuel, including light hydrocarbons, to electrical power. Hydrocarbon fuels, such as methane, are logistically favourable and provide high energy densities. However, the use of these fuels often results in a decreased efficiency and life. An improved understanding of the reactive flow in the SOFC anode can help address these issues. In this study, the transport and heterogeneous internal reformation of a methane based fuel is addressed. The effect of the SOFC anode's complex structure on transport and reactions is shown to exhibit a complicated interplay between the local molar concentrations and the anode structure. Strong coupling between the phenomenological microstructures and local reformation reaction rates are recognised in this study, suggesting the extension to actual microstructures may provide new insights into the reformation processes.