Chemical Transformation of Octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX) Induced by Low Energy Electron Beam Irradiation

The effects of 8.0×10⁻¹⁷ J (500 eV) and 3.2×10⁻¹⁹ J (2 eV) electrons on chemical structure of octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX) were studied in situ, under ultra‐high vacuum conditions using a combination of X‐ray photoelectron spectroscopy (XPS) and quadrupole mass spectrometry. XPS data indicated that electrons impact by 8.0×10⁻¹⁷ J for 30 s caused a decrease in nitro group concentration, and a little shift in the binding energy of the nitrogen 1s peak. Such a phenomenon was found at very low kinetic energy (3.2×10⁻¹⁹ J) with time evolution. Quadrupole mass spectrometry detected gas desorption after electron irradiation included H₂O and H₂ mostly. Microscopy‐IR spectroscopic investigations also proved that the intensity of nitro groups of HMX after irradiation decreased compared with those of the pristine HMX. We attributed the structure changes obtained by XPS and IR spectroscopy result in a chemical transformation, which was associated with low‐energy dissociative electron attachment (DEA) of surface contaminants followed by deoxidization reactions to form the product molecules.     

Coefficient of Thermal Expansion of the Beta and Delta Polymorphs of HMX

Dimensional changes related to temperature cycling of the β and δ polymorphs of HMX (octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine) are important for a variety of applications. The coefficient of thermal expansion (CTE) of β and δ phases are measured over a temperature range of −20 °C to 215 °C by thermo‐mechanical analysis (TMA). Dimensional changes associated with the phase transition were also measured, and the time‐temperature dependence of the dimensional change is consistent with phase transition kinetics measured earlier by differential scanning calorimetry (DSC). One HMX sample measured by TMA during its initial heating and again three days later during a second heating showed the β‐to‐δ phase transition a second time, thereby indicating back conversion from δ‐to‐β phase HMX during those three days. DSC was used to measure kinetics of the δ‐to‐β back conversion. The most successful approach was to first heat the material to create the δ phase, then after a given period at room temperature, measure the heat absorbed during a second pass through the β‐to‐δ phase transition. Back conversion at room temperature follows nucleation‐growth kinetics.     

Synthesis and Electrochemical Properties of BaFe1−xCuxO3−δ Perovskite Oxide for IT‐SOFC Cathode

A series of iron‐based perovskite oxides BaFe_1−xCu_xO_3−δ (x = 0.10, 0.15, 0.20 and 0.25, abbreviated as BFC‐10, BFC‐15, BFC‐20 and BFC‐25, respectively) as cathode materials have been prepared via a combined EDTA‐citrate complexing sol‐gel method. The effects of Cu contents on the crystal structure, chemical stability, electrical conductivity, thermal expansion coefficient (TEC) and electrochemical properties of BFC‐x materials have been studied. All the BFC‐x samples exhibit the cubic phase with a space group Pm3m (221). The electrical conductivity decreases with increasing Cu content. The maximum electrical conductivity is 60.9 ± 0.9 S cm⁻¹ for BFC‐20 at 600 °C. Substitution of Fe by Cu increases the thermal expansion coefficient. The average TEC increases from 20.6 × 10⁻⁶ K⁻¹ for BFC‐10 to 23.7 × 10⁻⁶ K⁻¹ for BFC‐25 at the temperature range of 30–850 °C. Among the samples, BFC‐20 shows the best electrochemical performance. The area specific resistance (ASR) of BFC‐20 on SDC electrolyte is 0.014 Ω cm² at 800 °C. The single fuel cell with the configguration of BFC‐20/SDC/NiO‐SDC delivers the highest power density of 0.57 W cm⁻² at 800 °C. The favorable electrochemical activities can be attributed to the cubic lattice structure and the high oxygen vacancy concentration caused by Cu doping.     

Investigation on the Thermal Expansion and Theoretical Density of 1,3,5‐Trinitro‐1,3,5‐Triazacyclohexane

The CTE and the theoretical density are important properties for energetic materials. To obtain the CTE and the theoretical density of 1,3,5‐trinitro‐1,3,5‐triazacyclohexane (RDX), XRD, and Rietveld refinement are employed to estimate the dimensional changes, within the temperature range from 30 to 170 °C. The CTE of a, b, c axis and volume are obtained as 3.07×10⁻⁵ K⁻¹, 8.28×10⁻⁵ K⁻¹, 9.19×10⁻⁵ K⁻¹, and 20.7×10⁻⁵ K⁻¹, respectively. Calculated from the refined cell parameters, the theoretical density at the given temperature can be obtained. The theoretical density at 20 °C (1.7994 g cm⁻³) is in close match with the RDX single‐crystal density (1.7990 g cm⁻³) measured by density gradient method. It is suggested that the CTE measured by XRD could perfectly meet with the thermal expansion of RDX.     

Selective Extraction of N‐Heterocyclic Precursors of 1,3,5,7‐Tetranitro‐1,3,5,7‐tetraazacyclooctane (HMX) Using Molecularly Imprinted Polymers

N‐heterocyclic compounds are key nitration precursors for some high energy density explosives such as 1,3,5,7‐tetranitro‐1,3,5,7‐tetraazacyclooctane (HMX). Nitration of 1,3,5,7‐tetraacetyl‐1,3,5,7‐tetraazacyclooctane (TAT) yields HMX in high yields and purity. However, the analogue 1,3,5‐triacetyl‐1,3,5‐triazacyclohexane (TRAT) is easily co‐produced via the condensation of acetonitrile and 1,3,5‐trioxan. To selectively extract TAT from a mixture of TAT and TRAT, the molecular imprinting technology (MIT) was developed in this study. The capacity of the dry polymer is 16 mg g⁻¹ and the recovery surpasses 75 %.     

Low‐Temperature Sintering of β‐Spodumene Ceramics Using Li2O–GeO2 as a Sintering Additive

Low‐temperature sintering of β‐spodumene ceramics with low coefficient of thermal expansion (CTE) was attained using Li₂O–GeO₂ sintering additive. Single‐phase β‐spodumene ceramics could be synthesized by heat treatment at 1000°C using highly pure and fine amorphous silica, α‐alumina, and lithium carbonate powders mixture via the solid‐state reaction route. The mixture was calcined at 950°C, finely pulverized, compacted, and finally sintered with or without the sintering additive at 800°C–1400°C for 2 h. The relative density reached 98% for the sample sintered with 3 mass% Li₂O–GeO₂ additive at 1000°C. Its Young's modulus was 167 GPa and flexural strength was 115 MPa. Its CTE (from R.T. to 800°C) was 0.7 × 10^?6 K^?1 and dielectric constant was 6.8 with loss tangent of 0.9% at 5 MHz. These properties were excellent or comparative compared with those previously reported for the samples sintered at around 1300°C–1400°C via melt‐quenching routes. As a result, β‐spodumene ceramics with single phase and sufficient properties were obtained at about 300°C lower sintering temperature by adding Li₂O–GeO₂ sintering additive via the conventional solid‐state reaction route. These results suggest that β‐spodumene ceramics sintered with Li₂O–GeO₂ sintering additive has a potential use as LTCC for multichip modules.     

β‐Galactosidase immobilization into poly(hydroxyethyl methacrylate) membrane and performance in a continuous system

The activity of β‐galactosidase immobilized into a poly(2‐hydroxyethyl methacrylate) (pHEMA) membrane increased from 1.5 to 10.8 U/g pHEMA upon increase in enzyme loading. The K_m values for the free and the entrapped enzyme were found to be 0.26 and 0.81 mM, respectively. The optimum reaction temperatures for the free and the entrapped β‐galactosidase were both found to be 50°C. Similarly, the optimum reaction pH was 7.5 for both the free and the entrapped enzyme. The immobilized β‐galactosidase was characterized in a continuous system during lactose hydrolysis and the operational inactivation rate constant (k_iop) of the entrapped enzyme was found to be 3.1 × 10⁻⁵ min⁻¹. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1367–1373, 1999     

First principles investigation on mechanical and thermal properties of α‐ and β‐YAlB4 ultra‐high temperature ceramics

Ultra‐high temperature ceramics (UHTCs) exhibit a unique combination of excellent properties that makes them promising candidates for applications in extreme environments. Various UHTCs are needed due to diverse harsh conditions that UHTCs are faced with in different applications. Due to structural similarity to ZrB₂, possible high melting point and possible protective oxide scale formed in oxygen rich and water vapor environments, REAlB₄ (RE: rare‐earth) is suggested a good candidate for UHTCs. In the present work, temperature‐dependent mechanical and thermal properties of both α‐YAlB₄ (YCrB₄ type, space group Pbam) and β‐YAlB₄ (ThMoB₄ type, space group Cmmm) were investigated by first principles calculations in combination with quasi‐harmonic approach. Due to the structural similarity between α‐YAlB₄ and β‐YAlB₄, their properties are very similar to each other, which are approximately transverse isotropic with properties in (001) plane being almost the same and differing from properties out of (001) plane. The results reveal that resistance to normal strain in (001) plane (~460 GPa) is higher than that along [001] direction (~320 GPa) and thermal expansion in (001) plane (~10 × 10^?6 K^?1) is lower than that along [001] direction (~17 × 10^?6 K^?1), which is because the stiff boron networks are parallel to (001) plane. The average thermal expansion coefficient is around 12 × 10^?6 K^?1, which is fairly high among UHTCs and compatible with metallic frameworks. The combination of high thermal expansion coefficient and protective oxidation scale forming ability suggest that REAlB₄ is promising for practical applications not only as high‐temperature structural ceramic but also as oxidation resistant coating for alloys.     

Coefficient of thermal expansion for Twaron® fibers using crystallographic data

The effect of in situ heating on the unit cell dimensions of crystalline aramid fiber (Twaron® fibers) has been studied in the temperature range 20–280°C. The changes in the unit cell dimensions have been used to estimate the coefficients of thermal expansion along the axial directions. On heating, the a and b axes expand, the coefficients of thermal expansion being α_a = 35.84 × 10⁻⁶/°C and α_b = 38 × 10⁻⁶/°C at room temperature. The c-axis contracts on heating, giving negative coefficient of thermal expansion α_c = −5.38 × 10⁻⁶/°C at room temperature. Volume coefficient of thermal expansion α_V however is positive, being 101.22 × 10⁻⁶/°C. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers     

In Situ Diffraction from Levitated Solids Under Extreme Conditions—Structure and Thermal Expansion in the Eu2O3–ZrO2 System

The accurate determination of structure and thermal expansion of refractory materials at temperatures above 1500°C is challenging. Here, for the first time, we demonstrate the ability to reliably refine the structure and thermal expansion coefficient of oxides at temperatures to 2200°C using in situ synchrotron diffraction coupled with aerodynamic levitation. Solid solutions in the Eu₂O₃–ZrO₂ binary system were investigated, including the high‐temperature order–disorder transformation in Eu₂Zr₂O₇. The disordered fluorite phase is found to be stable above 1900°C, and a reversible phase transition to the pyrochlore phase is noticed during cooling. Site occupancies in Eu₂Zr₂O₇ show a gradual increase in disorder on both cation and anion sublattices with increasing temperature. The thermal expansion coefficients of all cubic solid solutions are relatively similar, falling in the range 8.6–12.0 × 10^?6 C^?1. These studies open new vistas for in situ exploration of complex structural changes in high‐temperature materials.     

A Layered Perovskite EuBaCo2O5+δ for Intermediate‐Temperature Solid Oxide Fuel Cell Cathode

A layered perovskite EuBaCo₂O_5+δ (EBCO) has been prepared by a solid‐state reaction, and evaluated as potential cathode for intermediate‐temperature solid oxide fuel cells. Structural characterizations are determined at room temperature using powder X‐ray diffraction and transmission electron microscopy technique. The good fits to the XRD data by Rietveld refinement method are obtained in the orthorhombic space group (Pmmm). The lower average thermal expansion coefficient, 14.9 × 10^–6 °C^–1 between 100 and 800 °C, indicates its better thermal expansion compatibility with conventional electrolytes, compared with the other cobalt‐containing cathode materials. The high electrical conductivity and large oxygen nonstoichiometry at intermediate temperatures suggest the effective charge transfer reactions including electron conduction and oxide‐ion motion in cathode. As a result, a highly electrochemical activity towards the oxygen reduction reaction is achieved between 600 and 700 °C, as evidenced by low area‐specific resistances, e.g. 0.14–0.5 Ω cm². In addition, cathodic overpotential and oxygen reduction kinetics of the EBCO cathode have also been studied.     

A novel β‐nucleating agent for isotactic polypropylene

The nucleating ability of p‐cyclohexylamide carboxybenzene (β‐NA) towards isotactic polypropylene (iPP) was investigated by differential scanning calorimetry, X‐ray diffraction, polarized optical microscopy and scanning electron microscopy. β‐NA is identified to have dual nucleating ability for α‐iPP and β‐iPP under appropriate kinetic conditions. The formation of β‐iPP is dependent on the content of β‐NA. The content of β‐phase can reach as high as 96.96% with the addition of only 0.05 wt% β‐NA. Under non‐isothermal crystallization the content of β‐iPP increases with increasing cooling rate. The maximum β‐crystal content is obtained at a cooling rate of 40 °C min^–1. The supermolecular structure of the β‐iPP is identified as a leaf‐like transcrystalline structure with an ordered lamellae arrangement perpendicular to the special surface of β‐NA. Under isothermal crystallization β‐crystals can be formed in the temperature range 80–140 °C. The content of β‐crystals reaches its maximum value at a crystallization temperature of 130 °C. © 2012 Society of Chemical Industry     

The Nitrolysis Mechanism of 3,7‐Dinitro‐1,3,5,7‐tetraazabicyclo[3,3,1]nonane

Two intermediates, 1,5‐dinitroso‐3,7‐dinitro‐1,3,5,7‐tetraazacyclooctane (DNDS) and 1‐nitroso‐3,5,7‐trinitro‐1,3,5,7‐tetraazacyclooctane (MNX), were isolated and characterized in the synthesis of 1,3,5,7‐tetranitro‐1,3,5,7‐tetraazacyclooctane (HMX) from the nitrolysis of 3,7‐dinitro‐1,3,5,7‐tetraazabicyclo[3,3,1]nonane (DPT) for the first time. When the nitrolysis of DPT was slowed down, two intermediates were detected with HPLC. It was proposed that electrophilic NO₂⁺ and NO⁺ from HNO₃ and N₂O₄ might attack nitrogen atoms at positions 3 and 7 of DPT to form the cations of the intermediates, then nucleophilic H₂O attacked the bridge carbon atoms of DPT to produce the intermediates, which were oxidized to form HMX.     

Synthesis,Crystal Structure,and Thermal Behaviors of 3‐Nitro‐1,5‐bis(4,4′‐dimethylazide)‐1,2,3‐triazolyl‐3‐azapentane (NDTAP)

The energetic material, 3‐nitro‐1,5‐bis(4,4′‐dimethyl azide)‐1,2,3‐triazolyl‐3‐azapentane (NDTAP), was firstly synthesized by means of Click Chemistry using 1,5‐diazido‐3‐nitrazapentane as main material. The structure of NDTAP was confirmed by IR, ¹H NMR, and ¹³C NMR spectroscopy; mass spectrometry, and elemental analysis. The crystal structure of NDTAP was determined by X‐ray diffraction. It belongs to monoclinic system, space group C2/c with crystal parameters a=1.7285(8) nm, b=0.6061(3) nm, c=1.6712(8) nm, β=104.846(8)°, V=1.6924(13) nm³, Z=8, μ=0.109 mm⁻¹, F(000)=752, and D_c=1.422 g cm⁻³. The thermal behavior and non‐isothermal decomposition kinetics of NDTAP were studied with DSC and TG‐DTG methods. The self‐accelerating decomposition temperature and critical temperature of thermal explosion are 195.5 and 208.2 °C, respectively. NDTAP presents good thermal stability and is insensitive.     

The Synthesis and Energetic Properties of 5,7‐Dinitrobenzo‐1,2,3,4‐tetrazine‐1,3‐dioxide (DNBTDO)

Energetic tetrazine‐1,3‐dioxide, 5,7‐dinitrobenzo‐1,2,3,4‐tetrazine‐1,3‐dioxide ( DNBTDO ), was synthesized in 45 % yield. DNBTDO was characterized as an energetic material in terms of performance (V_det 8411 m s⁻¹; p_{C J} 3.3×10¹⁰ Pa at a density of 1.868 g cm⁻³), mechanical sensitivity (impact and friction as a function of grain size), and thermal stability (T_dec 204 °C). DNBTDO exhibits a sensitivity slightly higher than that of RDX , and a performance slightly lower (96 % of RDX ).     

Thermal stability and dynamic mechanical behavior of exfoliated graphite nanoplatelets‐LLDPE nanocomposites

The objective of this research was to investigate thermal stability and dynamic mechanical behavior of Exfoliated graphite nanoplatelets (xGnP™)‐Linear Low‐Density Poly Ethylene (LLDPE) nanocomposites with different xGnP loading content. The xGnP‐LLDPE nanocomposites were fabricated by solution and melt mixing in various screw rotating systems such as co‐, counter‐, and modified‐corotating. The storage modulus (E′) of the composites at the starting point of −50°C increased as xGnP contents increased. E′ of the nanocomposite with only 7 wt% of xGnP was 2.5 times higher than that of the control LLDPE. Thermal expansion and the coefficient of thermal expansion of xGnP‐loaded composites were much lower than those of the control LLDPE in the range of 45–80°C (299.8 × 10⁻⁶/°C) and 85–100°C (365.3 × 10⁻⁶/°C). Thermal stability of the composites was also affected by xGnP dispersion in LLDPE matrix. The xGnP‐LLDPE nanocomposites by counter‐rotating screw system showed higher thermal stability than ones by co‐rotating and modified‐co‐rotating system at 5 wt% and 12 wt% of xGnP. xGnP had a great effect on high thermal stability of xGnP‐LLDPE composites to be applied as tube and film for electrical materials. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Poly‐α,β‐(3‐hydroxypropyl)‐DL‐aspartamide: A new drug carrier

Poly‐α,β‐(3‐hydroxypropyl)‐DL ‐aspartamide (PHPA) was synthesized by the ring‐open reaction of polysuccinimide (PSI) and 3‐hydroxypropylamine. The polymer was characterized by ¹H‐NMR, ¹³C‐NMR, FTIR, and GPC. Mark–Houwink coefficients were obtained from viscometry and GPC measurements, K = 5.53 × 10⁻³ and α = 0.78 in water. The acute toxicity of PHPA was examined and it revealed no death in ICR mice up to the dose treated of 15.3 kg/kg, and hematological parameters showed no significant difference between treated and control animals. The potential use of PHPA as a drug carrier was also investigated. In a typical case, a contraceptive drug, norethindrone (NET), was bonded to PHPA, and the drug sustained released as long as 120 days an in vitro test. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2411–2417, 2000     

High-pressure structural stability,equation of state,and thermal expansion behavior of cubic HfO2

The structural stability, equation of state, and thermal expansion behavior of nanocrystalline cubic HfO₂, an ultra-high-temperature ceramic, have been investigated using X-ray diffraction at extreme conditions of pressures and temperatures. High-pressure studies show that the cubic structure is stable up to 26.2 GPa, while the high-temperature studies show the stability of the cubic structure up to 600°C. The Rietveld structure refinement of the high-pressure data reveals the progressive transition of secondary monoclinic phase to the cubic phase at higher pressures. The phase progression is accompanied by incompressibility along the b axis and a large compressibility along the c axis of the monoclinic structure. The second-order Birch-Murnaghan equation of state fit to the unit cell volume data yielded a bulk modulus of 242(16) GPa for the cubic structure. A linear thermal expansion value of α_a(c) = 8.80(15) × 10⁻⁶°C⁻¹ and a volume thermal expansion value of α_v = 26.5(4) × 10⁻⁶°C⁻¹ have been determined from the in situ high-temperature X-ray diffraction studies. The results are discussed by comparing with the high-pressure and high-temperature behavior of isostructural ZrO₂. To the best of our knowledge, this is the first experimental report on the structural stability of cubic HfO₂ at high pressures.     

Synthesis,characterization and thermal degradation of poly[2‐(3‐p‐bromophenyl‐3‐methylcyclobutyl)‐2‐hydroxyethylmethacrylate]

In this work, 2‐(3‐p‐bromophenyl‐3‐methylcyclobutyl)‐2‐hydroxyethylmethacrylate (BPHEMA) [monomer] was synthesized by the addition of methacrylic acid to 1‐epoxyethyl‐3‐bromophenyl‐3‐methyl cyclobutane. The monomer and poly(BPHEMA) were characterized by FT‐IR and [¹H] and [¹³C]NMR. Average molecular weight, glass transition temperature, solubility parameter, and density of the polymer were also determined. Thermal degradation of poly[BPHEMA] was studied by thermogravimetry (TG), FT‐IR. Programmed heating was carried out at 10 °C min⁻¹ from room temperature to 500 °C. The partially degraded polymer was examined by FT‐IR spectroscopy. The degradation products were identified by using FT‐IR, [¹H] and [¹³C]NMR and GC‐MS techniques. Depolymerization is the main reaction in thermal degradation of the polymer up to about 300 °C. Percentage of the monomer in CRF (Cold Ring Fraction) was estimated at 33% in the peak area of the GC curve. Intramolecular cyclization and cyclic anhydride type structures were observed at temperatures above 300 °C. The liquid products of the degradation, formation of anhydride ring structures and mechanism of degradation are discussed. © 1999 Society of Chemical Industry     

A Combined Experimental and Theoretical Study of HMX (Octogen,Octahydro‐1,3,5,7‐Tetranitro‐1,3,5,7‐Tetrazocine) in the Gas Phase

The structures of α‐ and β‐HMX were fully optimized and the vibrational frequencies computed at the hybrid DFT B3LYP/6‐31G(d, p) level of theory. The DCI+mass spectrum of HMX using ammonia (NH₃) as a “soft” ionising gas is reported. Field desorption mass spectrometry (FD) was used because of the high molecular intensities and low fragmentation. The FD spectrum shows only one significant peak at m/e 297 due to the protonated molecular ion [M+H]⁺. These observations clearly establish that under the conditions of CI and FD mass spectrometry experiments HMX is present in the gas phase (without decomposition) prior to the chemical ionisation.