Exothermic Peak Research Articles

Investigations on physical properties of (Sm, Ni) co-doped LaFeO3 perovskite

Nano crystalline samples of LaFeO3 (LFO) and La0.9Sm0.1Fe0.9Ni0.1O3 have been successfully synthesized through the sol-gel process. X-ray diffraction patterns confirm the orthorhombic phase of standard LaFeO3. FTIR spectroscopy shows the existence of two active vibrational modes around 410 and 550 cm−1. Specific heat capacity (Cp) displays exothermic and endothermic peaks, related to evaporation of water vapor and phase transitions respectively. The Cp is seen to rise in the doped sample, which ensures its increased thermal stability. Magnetic studies reveal the increase in magnetization and the transition from antiferromagnetic to ferromagnetic state in doped sample. Magnetoelectric study confirmed the multiferroic nature of LFO.

Phase transition characteristics, electrical and optical properties of AgNbO<sub>3 </sub>crystals grown by flux method

<sec>AgNbO<sub>3</sub>, with the antiferroelectric ordering and huge polarization (>50 μC/cm<sup>2</sup>), has potential applications in smart electronic devices, such as energy storage dielectrics, large displacement actuators, and electrocaloric cooling device. Large electro-strain and excellent energy storage properties have been reported in AgNbO<sub>3</sub>-based ceramics. Nevertheless, the lack of systematic research on the AbNbO<sub>3</sub> single crystals increases the difficulty in further understanding their structure-property relationship.</sec><sec>In this work, <inline-formula><tex-math id="M3">\begin{document}${\left\langle {001} \right\rangle _c}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20230984_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20230984_M3.png"/></alternatives></inline-formula> oriented AgNbO<sub>3</sub> single crystals with a large size (maximum size 5 mm×4 mm×4 mm) and high quality are successfully grown by the flux method. The phase transition characteristics are studied by the X-ray diffraction, temperature dependence of dielectric data and AC impedance, polarized light microscope photos, and differential scanning calorimetry curves. The electrical and optical properties are studied by the ferroelectric response and electro-strain response, optical absorbance spectrum and photo-dielectric effect.</sec><sec>The AgNbO<sub>3</sub> single crystals with the <i>M</i> phase exhibit the same domain structure. When the structure changes from <i>M</i><sub>2</sub> to <i>M</i><sub>3</sub>, the contrast of the PLM image is darkened. Correspondingly, the conductivity and dielectric loss significantly increase, which relates to the dynamic behaviors of the carriers. Interestingly, neither exothermic peak nor endothermic peak relating to the <i>M</i><sub>2</sub>-<i>M</i><sub>3</sub> transition is observed. The active energy for the <i>M</i><sub>3</sub> phase AgNbO<sub>3</sub> single crystal is ~1.24 eV. When the structure changes from orthogonal <i>M</i><sub>3</sub> to paraelectric orthogonal <i>O</i>, the domain structure disappears and the contrast becomes darker. The finding indicates that the anisotropy of the crystals disappears. At the same time, an obvious thermal hysteresis observed in the DSC curve reveals that the <i>M</i><sub>3</sub>-<i>O</i> transition is first-order. At room temperature, the direct band gap of AgNbO<sub>3</sub> single crystal is ~2.73 eV, which is slightly narrower than that of AgNbO<sub>3</sub> ceramic. Below the critical electric field, AgNbO<sub>3</sub> single crystal shows an electro-strain of 0.076% under <i>E</i><sub>m</sub> = 130 kV/cm. The obtained electro-strain value is much higher than that of AgNbO<sub>3</sub> ceramic under the same electric field. The relative permittivity increases from 70 to 73 under the green laser irradiation, showing an apparent photo-dielectric effect. We believe that our study can assist in the further understanding of the phase transition characteristics and physical properties in AgNbO<sub>3</sub> single crystals.</sec>

Low-temperature antiferromagnetism in quaternary Mn2FeSi0.5Al0.5 alloys

In this work, the quaternary Mn2FeSi0.5Al0.5 alloys are prepared for the first time in the form of cylinder-shaped ingots by traditional induction melting technique followed by homogenization annealing at 773 K for 100 h. The microstructural and magnetic properties of as-cast and annealed Mn2FeSi0.5Al0.5 samples are analyzed in detail and compared to the Mn2FeSi and Mn2FeAl ternary alloys. The Mn2FeSi0.5Al0.5 ingots are two-phase both before and after annealing, and their diffractograms correspond to the primitive cubic β-Mn structure. Obtained lattice constant of 0.6274 nm is only slightly lower than that of Mn2FeAl alloy (0.6339 nm) and different from Mn2FeSi (0.5672 nm). The existence of both phases enriched in Si at the expense of Al and Mn was confirmed by differential thermal analysis showing two endothermic and exothermic peaks at temperatures of 1363 K and 1407 K. The magnetic properties of both quaternary samples studied in wide temperature range from 5 K to 573 K indicate paramagnetic behavior at room and elevated temperatures. The annealed system has the values of Curie temperature and effective paramagnetic moment comparable to the ternary Mn2FeAl alloy. The transition to antiferromagnetic state occurring at Néel temperatures of 34 K (as-cast sample) and 37 K (annealed sample) is caused by strong geometric frustration of β-Mn structure. The magnetic transitions observed in both samples between Néel and room temperature are discussed in terms of the existence of Griffiths phase.

Nonlinear optical and spectroscopic properties, thermal analysis, and hemolytic capacity evaluation of quinoline-1,3-benzodioxole chalcone.

This article describes the synthesis, characterization (1H NMR, 13C NMR, FT-IR, HRMS and XRD), UV-Vis absorption and fluorescence spectra, theoretical analysis, evaluation of nonlinear optical properties (NLO), thermal analysis and determination of the hemolytic capacity of the compound (E)-N-(4-(3-(benzo[d][1,3]dioxol-5-yl)acryloyl)phenyl)quinoline-3-carboxamide (5). Radiological findings showed that compound 5 crystallized in space group Pca21. Furthermore, theoretical DFT studies performed with the B3LYP and M062X functionals showed good agreement with the experimental results and provided valuable information on the molecular and electronic structure, reactivity, polarizability, and kinematic stability of the compound. Besides, compound 5 did not show any hemolytic effect on human erythrocytes and exhibited strong NLO properties. The TG and DTA thermograms of quinoline-chalcone (5) revealed a multi-step thermal decomposition process with a total mass loss of 83.2%, including water content loss. The DTA curves exhibited endothermic peaks corresponding to decomposition steps, melting point, and thermochemical transition. Additionally, exothermic peaks in the DTA thermograms align with significant mass loss, confirming the compound's melting point and water content, as validated by X-ray diffraction analysis. These results contribute to the advancement of research on compounds with NLO properties and offer a promising avenue for the development of substances potentially applicable to optical devices in the biomedical field.

Синтез и строение сольвата бис[3,5-динитробензоата] трис(2-метокси)(5-бром)фенилсурьмы [C6H3(2-OMe)(5-Br)]3Sb[OC(O)C6H3(NO2)2-3,5]2 ∙ PhH ∙ ½ C8H18

Tris(2-methoxy)(5-bromo)phenylantimony bis[3,5-dinitrobenzoate] (1) was obtained from 3,5-dinitrobenzoic acid by oxidative addition to triarylantimony in the presence of tertiary butyl hy-droperoxide in ether, and was isolated by recrystallization from a benzene-octane mixture in the form of a crystal solvate with benzene and octane molecules in its crystal lattice. The structure of solvate 1 was established by the IR spectroscopy and X-ray diffraction analysis (XRD). In the IR spectrum of complex 1, in addition to the absorption bands related to the stretching vibrations of the Sb–C, СAr–О–Ме, and carbonyl groups, there are bands corresponding to the stretching vibra-tions of the C–Br bonds (524 and 555 cm–1). The X-ray diffraction data show that the antimony at-oms in complex 1 have a distorted trigonal bipyramid coordination with carboxylate ligands in the axial position. The antimony atom and two oxygen atoms do not lie on the same straight line and are located in such a way that the OSbO angle is 170.79°. The O…Sb distances (2.134(4) and 2.110(5) Å) are close to the sum of the covalent radii of antimony and oxygen. In addition, accord-ing to the X-ray diffraction data, compound 1 crystallizes in the monoclinic crystal system, space group P21/n. The structural organization in the crystal is formed due to short contacts of oxygen atoms in the nitro groups of the carboxylate ligands with carbon and bromine atoms of the aryl lig-ands of neighboring molecules, as well as hydrogen O...H (2.524–2.715 Å) bonds. In addition, a certain contribution to the formation of the crystal structure is made by the p-p stacking between the aromatic rings of crystallization benzene and the methoxy-bromo-phenyl ligands. The aro-matic rings are displaced in relation to each other and the distance between them is 3.367 Å. Melt-ing point of solvate 1 is 172.6 °C, according to the thermal analysis data. However, further in-crease in temperature is accompanied by decomposition of compound 1, and therefore an exo-thermic peak is observed on the DSC curve at 255.7 °C, corresponding to a mass loss of 31 % ac-cording to the TGA data. Complete tables of atom coordinates, bond lengths, and valence angles are deposited at the Cambridge Crystallographic Data Center (No. 2060562, depos-it@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk/data_request/cif)

Quantification of crystallinity during indomethacin crystalline transformation from α- to γ-polymorphic forms and of the thermodynamic contribution to dissolution in aqueous buffer and solutions of solubilizer.

The thermodynamic properties and dissolution of indomethacin (INM) were analyzed as models for poorly water-soluble drugs. Physical mixtures of the most stable γ-form and metastable α-form of INM at various proportions were prepared, and their individual signal intensities proportional to their mole fractions were observed using X-ray powder diffraction and Fourier transform infrared spectrometry at standard temperature. The endothermic signals of the α-form, with a melting point of 426 K, and that of the γ-form, with a melting point of 433 K, were obtained by differential scanning calorimetry (DSC). Furthermore, an exothermic DSC peak of the α/γ-phase transition at approximately 428 K was obtained. As we computed the melting entropy of the α-form and that of its transformation, the frequency of the transition was quantitatively determined, which indicated the maximum of the α/γ-phase transition at an α-form proportion of 68%. Subsequently, the thermodynamic contributions of the α- and γ-forms were analyzed using a Van't Hoff plot for solubility in aqueous solutions at pH 6.8. The dissolution enthalpies for α- and γ-forms were 28.2 and 31.2 kJ mol-1, respectively, which are in agreement with the quantitative contribution predicted by the product of the temperature and melting entropy. The contribution of melting entropy was conserved in different dissolution processes with aqueous solvents containing lidocaine, diltiazem, l-carnosine, and aspartame as solubilizers; their γ-form Setschenow coefficients were -39.6, +82.9, -17.3, and +23.2, whereas those of the α-form were -39.7, +80.4, -16.7, and +22.7, respectively. We conclude that the dissolution ability of the solid state and solubilizers indicate their additivity independently.

Rapid microwave-assisted synthesis and characterization of a novel CuCoTe nanocomposite material for optoelectronic and dielectric applications.

In the realm of nanomaterial research, copper telluride and cobalt telluride have individually attracted considerable attention owing to their unique properties and potential applications. However, there exists a notable gap in the literature when it comes to the exploration of composite materials derived from these elements. From this point of view, a ternary CuCoTe nanocomposite was prepared using the microwave synthesis method. Various characterizations were performed by varying the power and irradiation time. X-Ray diffraction study and transmission electron microscopy analysis confirmed the polycrystalline nature of the material with Cu2Te and CoTe hexagonal phases. Field emission scanning electron microscopy images reveal nanoparticle-like morphology, which remains unchanged even when the time of irradiation increases. In addition, the nanoparticle size of the material lies in the range of 30-39 nm. The differential scanning calorimetry inferred various exothermic and endothermic peaks. Meanwhile, the optical analysis from the UV-visible study shows the red-shifted absorbance, enabling the material for semiconductor and photovoltaic devices. Furthermore, the optical bandgap of the material varies in the range from 2.45 to 3.61 eV, which reveals the tuneable bandgap desiring the material for various optoelectronic applications. The frequency-temperature-dependent dielectric study gives results for dielectric parameters, conductivity, and impedance behaviour. The material's dielectric constant, dielectric loss, and AC conductivity enhance with the increase in temperature. This behaviour of the material broadens the area of applicability in energy storage devices.

Thermodynamic analysis of gate-opening carbon dioxide adsorption behavior of metal-organic frameworks.

Thermodynamic analysis of gate-opening carbon dioxide (CO2) adsorption behavior of metal-organic frameworks (MOFs) was investigated using differential scanning calorimetry (DSC). Unlike measurements under nitrogen atmosphere, obvious exothermic and endothermic peaks were observed in DSC curves under CO2 flow. In situ heating X-ray diffraction and thermogravimetric analyses under CO2 revealed that reversible crystal structure and weight changes occurred upon CO2 adsorption/desorption. The thermodynamic parameters of the CO2 adsorption process by MOFs were determined by DSC analysis at various CO2 partial pressures.

Fabrication and energy release study of metastable intermolecular composite microspheres with enhanced combustion performance

Metastable intermolecular composites (MICs) are often used in military and aerospace applications because of their high energy density. However, the traditional preparation methods are either complicated and unsafe, or the prepared composites have incomplete combustion and low energy release rates. In this paper, a series of aluminum/metal oxide/nitrocellulose (AMxN) composite microspheres were prepared by spray drying technique. The field emission scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) results show that the prepared AMxN composite microspheres have regular morphology and uniform particle size, and nitrocellulose (NC) is successfully coated between fuel (Al) and oxidizers (CuO, MoO3, and Bi2O3). The thermal reactivity, energy, and combustion properties of AMxN were investigated and compared with physically mixed aluminum/metal oxide (AMx). The explosion heat of AMxN is higher than AMx, while the thermal reaction exothermic peak temperature is lower. Among them, the composite containing copper oxide has the highest explosive heat value (5034 J/g), and the composite containing bismuth oxide has the shortest burning time (2.8 ms). These results prove that NC as a binder shortens the reaction distance between the oxidizer and the fuel in the presence of spray drying. Different oxidizers can modulate the energy release rate of AMxN composites, which is beneficial for applying MICs in energetic materials.

Unravelling the thermal behavior and kinetics of unsaturated polyester resin supplemented with organo-nanoclay.

The integration of nanoclays within polymeric systems to develop high-performance materials is an emerging research field that has garnered significant attention. In this context, an organically modified montmorillonite (OMMT) is utilized as a reinforcing agent for unsaturated polyester resin (UPR) with loads of 1%, 3%, and 5 wt%. The modification of montmorillonite nanoclay (MMT) using a quaternary ammonium compound is performed through an effective repetitive modification process under reflux conditions. The curing behavior of the unsaturated polyester resin containing organically modified clay catalyzed with methyl ethyl ketone peroxide (MEKP) initiator and promoted by cobalt naphthenate accelerator is investigated using dynamic differential scanning calorimetry (DSC) followed by kinetic analysis using isoconversional methods. The dynamic DSC curing curves showed a bimodal exothermic peak, where two independent reactions, namely, redox and thermal decomposition of the initiator occurred. In this study, novel insights into the curing reaction of the studied UPR and UPR/OMMT systems have been revealed through the application of the Trache-Abdelaziz-Siwani (TAS) and Sbirrazzuoli (VYA/CE) isoconversional methods. These methods have enabled the elucidation of the intricate mechanisms and phenomena that impact the curing reaction, including the dilution effect in the redox reaction and the diffusion phenomenon at the end of the thermal decomposition reaction. The incorporation of nanoclay into unsaturated polyester resin (UPR) resulted in a reduction in the activation energy for both the redox and thermal reactions. Specifically, the energetic barrier decreased from 93.85 and 101.58 kJ mol-1 for pristine UPR to 60.71 and 72.93 kJ mol-1 for UPR/OMMT-5 in the redox and thermal reactions, respectively. The addition of OMMT caused a significant decrease in the pre-exponential factor. The values of UPR/OMMT-5 were 2.75 × 105 and 5.50 × 106 for the redox and thermal decomposition reactions, respectively, compared to 1.41 × 1012 and 5.13 × 1013 for UPR. The thermogravimetric analysis demonstrated that UPR/OMMT systems were more stable than UPR.

Systematic study of ionic conduction in silver iodide/mesoporous alumina composites 2: effects of silver bromide doping.

In our preceding paper (Y. Fukui et al., Phys. Chem. Chem. Phys., 2023, 25, 25594-25602), we reported a systematic study of the Ag+-ion conducting behaviour of silver iodide (AgI)-loaded mesoporous aluminas (MPAs) with different pore diameters and AgI-loading ratios. By optimising the control parameters, the Ag+-ion conductivity has reached 7.2 × 10-4 S cm-1 at room temperature, which is more than three orders of magnitude higher than that of bulk AgI. In the present study, the effect of silver bromide (AgBr)-doping in the AgI/MPA composites on Ag+-ion conductivity is systematically investigated for the first time, using variable-temperature powder X-ray diffraction, differential scanning calorimetry, and electrochemical impedance spectroscopy measurements. The AgBr-doped AgI/MPA composites, AgI-AgBr/MPA, formed a homogeneous β/γ-AgI-structured solid solution (β/γ-AgIss) for the composites with AgBr ≤ 10 mol%, above which the composites underwent a phase separation into β/γ-AgIss and face-centred cubic AgBr solid solutions (AgBrss). The onset temperature of the exothermic peaks attributed to the transition from α-AgI-structured solid-solution phase to β/γ-AgIss or AgBrss decreased with increasing the AgBr-doping ratio. The room-temperature ionic conductivity of the AgI-AgBr/MPA composites exhibited a volcano-type dependence on the AgBr-doping ratio with the highest value (1.6 × 10-3 S cm-1) when the AgBr content was 10 mol%. This value is more than twice as high as that of the highest conducting AgI/MPA found in our previous study.

Limestone powder-based alkali-activated materials: Influence of activator type

Limestone powder (LP)-based cementitious materials with four types of alkali activators: NaAlO2, NaOH+Al(OH)3, NaOH, and Na2SiO3, were investigated at ambient temperature. The NaAlO2 and NaOH+Al(OH)3 groups produced crystalline monocarboaluminate (Mc, 3CaO∙Al2O3∙CaCO3∙11H2O), which was associated with the second exothermic peak. TEM observations revealed that AH3 (Al2O3·3H2O) generated in the NaAlO2 group was a microcrystalline phase. This microcrystal enabled cementing LP and lamellar-shaped Mc for forming compacted microstructure. However, unreacted gibbsite (Al(OH)3) in the NaOH+Al(OH)3 group did not have such effects. Thus, the 28-day compressive strength of the NaAlO2 group (20.90 MPa) considerably surpassed that of the NaOH+Al(OH)3 group (0.81 MPa). No strength appeared in the NaOH group due to the limited cementitious properties of the newly-formed gaylussite (CaNa2(CO3)2·5H2O) and pirssonite (CaNa2(CO3)2·2H2O). The Na2SiO3 group tended to generate calcium silicate hydrate (CSH) gels, resulting in a 28-day compressive strength of 8.20 MPa. NaAlO2 was more efficient in activating LP than other activators.

Rheology, mechanical properties, and hydration of synergistically activated coal gasification slag with three typical solid wastes

The utilization of multiple solid-waste-activated slags to prepare clinker-free binders has garnered considerable interest due to their environmental friendliness and low cost. In this study, a novel binder was developed by incorporating multiple solid wastes, namely red mud (RM), carbide slag (CS), phosphogypsum (PG), and coal gasification slag (CGS). RM, CS, and PG were used as activators to synergistically activate two kinds of ultra-fine CGS precursors with median particle sizes of 5.2 μm and 6.1 μm, respectively. The effects of parameters including precursor fineness and activator dosage were systematically investigated. The hydration products were then characterized to elucidate the activation mechanism. The results showed that the rheology of the pastes fitted well with Herschel-Bulkley model, exhibiting shear thinning behavior regardless of the proportion of the activators. The low CGS fineness and high PG dosage reduced viscosity, yield stress, and shear stress of the pastes. Fine CGS particles were found to shorten the hydration dormancy period and accelerate the appearance of the second exothermic peak, thus promoting strength development. CGS with small particles facilitated the formation of ettringite but restricted hydrotalcite generation. This study reported a binder utilizing full solid wastes and confirmed its feasibility as a sustainable alternative in construction applications.

Modeling the curing kinetics of two thermoset adhesives under varying temperature conditions

AbstractThis paper presents detailed curing kinetics models for two thermoset adhesives. The cure kinetics were characterized using differential scanning calorimetry in both anisothermal and isothermal modes. The Sestak–Berggren autocatalytic model was applied to describe the anisothermal cure kinetics of the two adhesives with the Malek and undetermined coefficients methods determining their kinetic parameters. The Kamal autocatalytic model was adopted for the isothermal curing processes with the Kenny analytical‐graphical method determining the kinetic parameters. A modified Kamal model was developed by introducing a concept of the maximum degree of cure (DOC) and temperature‐depended kinetic parameters to describe the isothermal cure kinetics of the adhesive with a typical exothermic peak, and an extended Kamal model was further proposed by adding an initial‐phase‐control term to the modified Kamal model to describe the isothermal cure kinetics of the adhesive with two exothermic peaks. The results showed that the presented curing kinetics models with the determined parameters can precisely predict the evolutions of the DOC of the two thermoset adhesives in both anisothermal and isothermal modes.

The Investigation of the Production of Salt-Added Polyethylene Oxide/Chitosan Nanofibers.

The influence of different concentrations of salt-added polyethylene oxide (PEO) on the spinnability of chitosan (CS)/PEO + NaCl blends that could be used as a component part of filters for water treatment or nanofiber membranes as well as for medical applications was investigated in this study. The morphological properties of manufactured nanofibers were analyzed as well. It was determined that an increase of PEO concentration resulted mostly in thin and round nanofibers formed during electrospinning, but the manufacturing process became complex, because many wet fibers reached the collector while spinning. Also, it was noticed that the salt was not dissolved completely in the polymer solutions and some crystals were seen in the SEM images of manufactured fiber mats. However, the addition of salt resulted in lower viscosity and better conductivity of solution and fiber mats as well. The opposite effect was observed as the concentration of PEO was increased. The orientation of produced nanofibers as well as their diameter were analyzed with commercially available software. It was determined that the results obtained by software and microscopically are repeatable. The difference among the results of diameter calculated with software and taken by microscope varied from 0% to approximately 12%. The FTIR analyses indicated that alterations in polymer concentrations or the addition of salt did not induce any discernible changes in the chemical composition or nature of the materials under investigation. The sodium chloride present in the solutions enhanced electrical properties and increased conductivity values more than 50 times for PEO solutions and six times for CS/PEO blend solutions, compared to conductivity values of solutions without salt. To assess the thermal characteristics of the PEO/CS blend nanofibers, measurements using a differential scanning calorimeter (DSC) to determine melting (Tm) and crystallization (Tc) temperatures, as well as specific heat capacities were conducted. These parameters were derived from the analysis of endothermic and exothermic peaks observed in the DSC data. It showed that all produced nanofibers were semicrystalline.

Revealing time-dependent behavior of asphalt binder at low-temperature by crystallization kinetics

To gain deeper insights into the influence of thermal history on wax crystallization and thermoreversible aging for enhanced asphalt pavement durability, this study employed the extended bending beam rheometer (ExBBR) test and modulated differential scanning calorimetry (MDSC) analysis. These techniques were utilized to analyze the crystallization kinetics of diverse asphalt binders under both isothermal and non-isothermal conditions. The ExBBR test results demonstrated that the cold-temperature performance of asphalt binders experiences continuous degradation with an increasing grade loss during conditioning. The Avrami isothermal crystallization kinetic theory proved to be an accurate descriptor of the thermoreversible aging tendency in asphalt binders. MDSC test findings revealed that distinct cooling rates exert an influence solely on specific asphalt varieties, with discrepancies in thermal signals arising from diverse oil sources. The Ozawa exponent, determined through the endothermic background area selected from the baseline, serves as a reliable guide for assessing the degree of thermoreversible aging in different asphalt binders. Crucially, the appearance of crystallizable fractions in asphalt binders with varying thermal histories can be effectively modeled using both isothermal Avrami and non-isothermal Ozawa theoretical frameworks. To conclude, the study undertook the separation of four components of asphalt, analyzing the microstructural evolution of these components under identical test conditions. The contribution of each component to the asphalt crystallization process is comprehensively expounded through considerations of glass transition temperatures, as well as endothermic and exothermic peaks associated with distinct components.

One‐pot synthesis, thermal analysis, and density functional theory study of methyl urotropine perchlorate

AbstractAn energetic material methyl urotropine perchlorate (MUTP) was synthesized from urotropine, perchloric acid, and triethylenediamine. The single crystal structure of the energetic salt was characterized by X‐ray single crystal diffractometer. The results show that the single crystal of MUTP is an orthogonal crystal system with Pnma space group. The thermal decomposition process of MUTP was studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) technology. There were two exothermic peaks in TGA and DSC test, and the peak temperatures (Tp) were 261.61°C and 366.75°C, respectively. The thermal stability of MUTP was up to 247.10°C. Geometric optimization, frontier molecular orbitals, electrostatic potential (ESP), and weak interaction were explored by density functional theory using Gaussian 16. It is found that MUTP has a large energy gap (5.94 eV), which is larger than that of HMX (5.84 eV). The results of reduced density gradient method show that there are dense hydrogen bond interactions in MUTP with high electron density and intensity. In addition, a strong spatial repulsion is formed at the center of the cage.

Application of an industrialized ultrafine composite powder in cement-based materials: Hydration characteristics, microstructure, and corrosion resistance

To reduce the reliance on cement clinker, employing ultrafine powders as supplementary cementitious materials (SCMs) is gradually gaining importance. This study investigated the effect of an ultrafine composite powder (UCP) having a specific surface area of approximately 730 m²/kg, produced by industrial ball milling ordinary blast furnace slag and fly ash at a 1:1 ratio, on cement hydration and its durability. The ultrafine composite powder was characterized by X-ray fluorescence spectrometer (XRF), X-Ray diffraction (XRD), particle size analyzer, and scanning electron microscope (SEM). The effects of ultrafine composite powder on the macroscopic properties of cement-based materials were assessed through flowability tests, setting time tests, and mechanical properties tests. Then, the hydration heat release, hydration products and microstructures of the pastes were characterized using isothermal calorimetry, XRD, thermogravimetric (TG), SEM and mercury intrusion porosimetry (MIP). Finally, the effects of ultrafine composite powder on the durability of cement-based materials were evaluated by electrical flux, chloride diffusion coefficient, and mechanical properties tests. The results showed that ultrafine composite powder enhanced the flowability of cement paste under the synergistic effect of superplasticizer. However, the setting time was prolonged due to the dilution of cement by ultrafine composite powder. The ultrafine composite powder significantly improved the early mechanical properties of the mortar, and the mechanical properties after 28-days was equivalent to that of the control. The ultrafine composite powder could significantly decrease the cumulative heat release of cement paste. Due to the high SO3 content, an additional exothermic peak representing ettringite formation was observed. As the hydration time extends, the hydration products in the paste changed, especially the transformation from ettringite to kuzite, and the formation of hemicarbonate and monocarbonate. As the ultrafine composite powder content increases, the proportion of gel micro-pores increased, whereas the proportion of middle and large capillary pores decreased. Consequently, the total pores in the paste also decreased. The addition of ultrafine composite powder enhanced the durability of the cement-based materials, making it an ideal choice for use in coastal engineering projects.

Enhanced combustion reaction and energy output of Al based energetic materials through introducing perfluorocarbon

Introducing additional oxidizers in aluminized explosives is an effective way to improve energy performance by enhancing the secondary combustion reaction. In this work, perfluorocarbon as oxidizer has been introduced into TATB/Al based energetic materials to improve combustion reaction and energy output performance. The uniform TATB/Al/perfluorocarbon composites are prepared through acoustic resonance mixed technology, and the energy and pressure output performance are fully studied in air blast and underwater explosion. A significantly exothermic peak derived from the reaction between fluorine and Al is observed between 540 ℃ and 580 ℃ for TATB/Al/perfluorocarbon. The heat of explosion of TATB/Al/perfluorocarbon is increased first and then decreased with F/Al ratio from 0 to 0.608. The highest heat of explosion is 6021 J/g for TATB/Al/perfluorocarbon with F/Al ratio of 0.274. Furthermore, the enhanced working capacity, the significantly enlarged fireball and relatively high overpressure are obtained for TATB/Al/perfluorocarbon. More importantly, the shock impulse and first bubble oscillation time of TATB/Al/perfluorocarbon have been increased by 23.2% and 21.18% during underwater explosion, respectively. The results further illustrate that adding perfluorocarbon is a feasible approach to enhance energy output due to combustion reaction between fluorine and Al, which can be applied in explosives and propellants.

Development of porous asphalt mixture based on the synthesis of PTEMG and MDI polyurethane asphalt

Polyurethane-modified asphalt (PA) stands out as an environmentally sustainable road material, renowned for its exceptional performance that significantly extends road surface lifespans while reducing maintenance costs. This study focuses on the preparation of PA using a single-component blending method that incorporates polyether polyol PTEMG (Poly-(tetra methylene ether glycol)) and isocyanate MDI (4,4′-diphenylmethane diisocyanate) as primary raw materials. Various analytical techniques, including Fluorescence Microscopy, Fourier-transform Infrared Spectroscopy (FTIR), Thermogravimetric analysis (TG), Differential Scanning Calorimetry (DSC), Viscosity Testing, Tensile Testing, and Bending Beam Rheometer (BBR), were employed to investigate PA's microstructure, modification mechanism, thermal properties, viscosity characteristics, curing properties, and low-temperature stability. A porous polyurethane-modified asphalt mixture, targeting a void content of 20%, was designed and compared to a high-viscosity modified asphalt mixture with the same void content in terms of performance. The results indicate a combination of chemical and physical processes in PA modification. Through TG and DSC experiments, it was ascertained that polyurethane-modified asphalt commences decomposition at 252 °C, exhibiting an exothermic peak within the temperature range of − 19.98–2.73 °C. The introduction of polyurethane substantially enhances the thermal performance and cryogenic stability of the asphalt binder. Viscosity tests and tensile experiments indicate that the curing reaction of polyurethane-modified asphalt is protracted and irreversible. Consequently, it is recommended to prepare polyurethane-modified asphalt mixtures employing a compaction temperature of 175 °C and a maximum resting time of 100 min. Additionally, specimens should rest at room temperature for at least 3 days. Comparatively, the porous asphalt incorporating polyurethane exhibits notable advantages over the high-viscosity modified asphalt mixture. It demonstrates superior high-temperature stability, excellent resistance to low-temperature cracking, reduced sensitivity to strains, prolonged fatigue life, and improved flexibility. However, its fatigue resistance and resistance to dynamic loads are slightly inferior. This study offers valuable insights into the use of polyurethane in porous asphalt mixtures, making it a promising option for sustainable road construction.