Enthalpy Of Decomposition Research Articles

Inorganic Halide Double Perovskites with Optoelectronic Properties Modulated by Sublattice Mixing.

All-inorganic halide double perovskites have emerged as a promising class of materials that are potentially more stable and less toxic than lead-containing hybrid organic-inorganic perovskite optoelectronic materials. In this work, 311 cesium chloride double perovskites (Cs2BB'Cl6) were selected from a set of 903 compounds as likely being stable on the basis of a statistically learned tolerance factor (τ) for perovskite stability. First-principles calculations on these 311 double perovskites were then performed to assess their stability and identify candidates with band gaps appropriate for optoelectronic applications. We predict that 261 of the 311 Cs2BB'Cl6 compounds are likely synthesizable on the basis of a thermodynamic analysis of their decomposition to competing compounds (decomposition enthalpy <0.05 eV/atom). Of these 261 likely synthesizable compounds, 47 contain no toxic elements and have direct or nearly direct (within 100 meV) band gaps between 1 and 3 eV, as computed with hybrid density functional theory (HSE06). Within this set, we identify the triple-alkali perovskites Cs2[Alk]+[TM]3+Cl6, where Alk is a group 1 alkali cation and TM is a transition-metal cation, as a class of Cs2BB'Cl6 double perovskites with remarkable optical properties, including large and tunable exciton binding energies as computed by the GW-Bethe-Salpeter equation (GW-BSE) method. We attribute the unusual electronic structure of these compounds to the mixing of the Alk-Cl and TM-Cl sublattices, leading to materials with small band gaps, large exciton binding energies, and absorption spectra that are strongly influenced by the identity of the transition metal. The role of the double-perovskite structure in enabling these unique properties is probed through an analysis of the electronic structures and chemical bonding of these compounds in comparison with other transition-metal and alkali transition-metal halides.

Heat capacity and decomposition of rimantadine hydrochloride

Heat capacities of the antiviral drug rimantadine hydrochloride in the crystalline state were measured by adiabatic calorimetry and differential scanning calorimetry in the temperature range from (7 to 453) K. A broad low-enthalpy solid-state phase anomaly was detected between (170 and 250) K. Thermodynamic functions for crystalline rimantadine hydrochloride were derived. Decomposition of the studied compound was probed by the Knudsen effusion method and thermogravimetry with the support of quantum chemical calculations. The enthalpy of decomposition of rimantadine hydrochloride into the corresponding amine and hydrogen chloride was estimated from those data. The thermodynamic functions of the corresponding amine in the ideal gaseous state, including enthalpy of formation, were obtained using statistical thermodynamics with the necessary molecular parameters computed using quantum chemical methods. The enthalpy of formation of crystalline rimantadine hydrochloride was estimated.

Significant decrease of hydride decomposition enthalpy in ordered Mg-In alloys induced by growing hydrogen concentration

Significant decrease of hydride decomposition enthalpy in ordered Mg-In alloys induced by growing hydrogen concentration

Significantly decreased stability of MgH2 in the Mg-In-C alloy system: Long-period-stacking-ordering as a new way how to improve performance of hydrogen storage alloys?

Hydrogen storage (HS) performance of Mg-In-CB alloys (CB – amorphous carbon) is studied. Indium concentration covers primary solid solution (Mg), two phase area (Mg) + β1 and also alloys containing ordered β structures. Seven Mg-In-CB alloys are prepared by ball-milling in hydrogen atmosphere. Kinetic curves and PCT isotherms are measured in the temperature interval from 200 °C to 375 °C. Hydrogen sorption experiments are done by the Sieverts method under the hydrogen gas pressure ranging from 0.1 MPa to 2.5 MPa. X-ray diffraction spectroscopy is used for structure investigation. Alloy with β’’ structure shows reversible amorphization during temperature cycling between about 100 °C and 350 °C. It is found that hydrogen sorption capacity varies between about 6 wt % H2 for (Mg) and 0.6 wt % H2 for β’’ structure. Hydride decomposition enthalpy calculated from desorption PCT experiments decreases to 54 ± 3 kJ × (mol H2)−1 and 57 ± 3 kJ × (mol H2)−1 for ordered alloys in the interval from 69 to 71 wt % In, and even down to 51.5 kJ × (mol H2)−1 for amorphous β’’ structure. Activation energy of desorption kinetics is also lowered in the ordered structure.

Preparation and Thermal Decomposition Kinetics of Novel Silane Coupling Agent with Mercapto Group

Using carbon disulfide and 3-aminopropyltriethoxysilane as raw materials, a novel silane coupling agent with a terminal group was synthesized for the first time. The compound was synthesized in two steps in ethanol water solvent under the action of the catalyst triethylamine and a sulfhydryl-protecting agent. The product was characterized by FT-IR, 1H NMR, and mass spectra to determine and prove its structure. The best experimental scheme was explored by a single factor experiment: a thiol-protecting agent selected iodomethane, the total reaction time was 2 hours, the two-step reaction temperature was 15°C and 10°C, respectively, and ncarbon disulfide: n3−aminopropyl three ethoxysilane=1.4:1. Under these conditions, the product yield was up to 74.28%. Secondly, using the nonisothermal decomposition method, the thermal stability and thermal decomposition enthalpy of a thiohydrazide-iminopropyltriethoxysilane coupling agent were measured by a differential scanning calorimeter (DSC). Thereby, the thermal decomposition kinetic parameters and kinetic equations of the thiohydrazide-iminopropyltriethoxysilane coupling agent were derived.

Thermal Stability and Explosive Hazard Assessment of Diazo Compounds and Diazo Transfer Reagents.

Despite their wide use in academia as metal-carbene precursors, diazo compounds are often avoided in industry owing to concerns over their instability, exothermic decomposition, and potential explosive behavior. The stability of sulfonyl azides and other diazo transfer reagents is relatively well understood, but there is little reliable data available for diazo compounds. This work first collates available sensitivity and thermal analysis data for diazo transfer reagents and diazo compounds to act as an accessible reference resource. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and accelerating rate calorimetry (ARC) data for the model donor/acceptor diazo compound ethyl (phenyl)diazoacetate are presented. We also present a rigorous DSC dataset with 43 other diazo compounds, enabling direct comparison to other energetic materials to provide a clear reference work to the academic and industrial chemistry communities. Interestingly, there is a wide range of onset temperatures (Tonset) for this series of compounds, which varied between 75 and 160 °C. The thermal stability variation depends on the electronic effect of substituents and the amount of charge delocalization. A statistical model is demonstrated to predict the thermal stability of differently substituted phenyl diazoacetates. A maximum recommended process temperature (TD24) to avoid decomposition is estimated for selected diazo compounds. The average enthalpy of decomposition (ΔHD) for diazo compounds without other energetic functional groups is −102 kJ mol–1. Several diazo transfer reagents are analyzed using the same DSC protocol and found to have higher thermal stability, which is in general agreement with the reported values. For sulfonyl azide reagents, an average ΔHD of −201 kJ mol–1 is observed. High-quality thermal data from ARC experiments shows the initiation of decomposition for ethyl (phenyl)diazoacetate to be 60 °C, compared to that of 100 °C for the common diazo transfer reagent p-acetamidobenzenesulfonyl azide (p-ABSA). The Yoshida correlation is applied to DSC data for each diazo compound to provide an indication of both their impact sensitivity (IS) and explosivity. As a neat substance, none of the diazo compounds tested are predicted to be explosive, but many (particularly donor/acceptor diazo compounds) are predicted to be impact-sensitive. It is therefore recommended that manipulation, agitation, and other processing of neat diazo compounds are conducted with due care to avoid impacts, particularly in large quantities. The full dataset is presented to inform chemists of the nature and magnitude of hazards when using diazo compounds and diazo transfer reagents. Given the demonstrated potential for rapid heat generation and gas evolution, adequate temperature control and cautious addition of reagents that begin a reaction are strongly recommended when conducting reactions with diazo compounds.

Tuning the thermal, mechanical, and combustion properties of NC-TEGDN-RDX propellants via incorporation of graphene nanoplates

ABSTRACT Graphene nanoplates (GNPs) were incorporated into a solid composite propellant (NC-TEGDN-RDX) to tune the thermal, mechanical, and combustion properties of the material. Physical, thermal, and combustion properties of NC-TEGDN-RDX with <2 wt% addition of GNPs were characterized using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), tensile/compressive/impact strength testing, and constant volume combustion experiments. Microstructure of the composite propellants examined using SEM demonstrated uniform dispersion of the GNPs at low-weight percent additives (<1 wt%), but began to show large agglomerations of the additives at higher additive content. Decomposition enthalpy of the propellant with 1 wt% GNPs increased by ~130 J/g compared to neat propellants. Moreover, the maximum burning rate was observed for samples containing 1 wt% GNPs, with values of 19 cm/s at 20°C and 17 cm/s at −40°C. Dynamic vivacity of the propellant achieved a maximum upon addition of 1 wt% GNPs. The pressure exponent of the propellant decreased with the addition of GNPs, as well. The mechanical properties including tensile, compressive, and impact strength were improved at 20°C and −40°C. These results demonstrate that the addition of GNPs may offer new methods by which to tune and improve thermal decomposition, thermal conductivity, combustion performance, and mechanical properties of the NC-TEGDN-RDX propellants.

Oxidative stability, thermal hazard analysis, and decomposition kinetics of 1-methylimidazolium nitrate via DSC, TGA, and GC/MS

Imidazolium-based ionic liquids are green solvents used as separation and electrolyte media in liquid–liquid extraction processes and electrochemical devices. However, they are volatile and flammable once they reach their thermal decomposition temperatures. In the present study, the oxidative stability, decomposition, and combustion reaction of 1-methylimidazolium nitrate [Mim][NO3] were investigated via thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). TG analysis revealed a single-stage mass loss between 117.6 and 230.2 °C with oxidative onset temperatures in the range of 126.6–163.2 °C with the increase in heating rate (1.0, 2.0, 4.0, and 8.0 °C min−1). DSC results indicated the degradation as exothermic with the average enthalpy of decomposition as 1610.4 J g−1. The estimated average value of apparent activation energy using isoconversional methods such as Kissinger, FWO, and Friedman was in the range of 106.1–114.2 kJ mol−1, and the reaction function (autocatalytic model) is expressed as: f(α) = (1 − α)1.42 (0.017 + α0.62) using multivariate nonlinear regression. The GC/MS analysis revealed the formation of methane isocyanate indicating the hazardous, toxic, corrosive, and carcinogenic nature of the decomposed gases. This research was aimed to develop a predictive model for oxidative degradation behavior and to provide the necessary basis for the design of precise safety systems.

Thermal stability of N-heterocycle-stabilized iodanes - a systematic investigation.

The thermal stability of pseudocyclic and cyclic N-heterocycle-stabilized (hydroxy)aryl- and mesityl(aryl)-λ3-iodanes (NHIs) through thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) is investigated. Peak decomposition temperatures (Tpeak) were observed within a wide range between 120 and 270 °C. Decomposition enthalpies (ΔHdec) varied from −29.81 to 141.13 kJ/mol. A direct comparison between pseudocyclic and cyclic NHIs revealed high Tpeak but also higher ΔHdec values for the latter ones. NHIs bearing N-heterocycles with a high N/C-ratio such as triazoles show among the lowest Tpeak and the highest ΔHdec values. A comparison of NHIs with known (pseudo)cyclic benziodoxolones is made and we further correlated their thermal stability with reactivity in a model oxygenation.

Interactions in N-[(2-hydroxyl)-propyl-3-trimethyl ammonium] chitosan chloride/sodium carboxymethyl cellulose based films

To illuminate the interactions in N-[(2-hydroxyl)-propyl-3-trimethyl ammonium] chitosan chloride (HTCC)/sodium carboxymethyl cellulose (CMC) based films, the film-forming solutions were studied by rheology, and HTCC/CMC based films were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis. The HTCC/CMC based film-forming solutions with glycerol (polyvinyl alcohol (PVA) and anthocyanin) showed shear-thinning behavior. The apparent viscosity of the HTCC/CMC/glycerol (PVA and anthocyanin) film-forming solutions decreased slower than that of HTCC/CMC film-forming solution, due to the electrostatic interaction between HTCC and CMC, and hydrogen bonding interaction between the two biomacromolecules and glycerol, PVA and anthocyanin, which resulted in the formation of three-dimensional networks. The anthocyanin with rigid molecular structure formed different three-dimensional matrix with HTCC/CMC, resulted in viscosity dominated film-forming solution. The pH affected the electrostatic interaction between HTCC, CMC, and anthocyanin through neutralizing –COO− groups, and temperature showed a synergistic effect on both electrostatic interaction and hydrogen bonding. The inter-molecular interactions resulted in the red-shift of typical absorption peaks, and the increase of initial decomposition temperature and decomposition enthalpy of HTCC/CMC based films. The homogenous and smooth surface, and the compact texture of HTCC/CMC based films confirmed the intermolecular interaction between HTCC, CMC, and PVA (glycerol and anthocyanin).

Intensive investigation on hydrogen storage properties and reaction mechanism of the NaBH4-Li3AlH6 destabilized system

Notable effects of Li3AlH6 on the hydrogen storage properties of the NaBH4 are studied intensively. Li3AlH6 is synthesized by milling 2LiH-LiAlH4 mixture for 12 h. The best molar ratio of the NaBH4- Li3AlH6 destabilized system is 1:1 which has decomposed at two stages; Li3AlH6 decomposition stage at 170 °C and NaBH4decomposition stage at 400 °C. As no significant effect on the decomposition temperature between 1 h and 24 h of milling time can be observed, the 1-hour milling preparation method is selected for the characterization. Isothermal absorption has shown that the system is able to absorb 4.2 wt% and 6.1 wt% of hydrogen in 60 min at 330 °C and 420 °C under 30 atm of hydrogen pressure. In contrast, only about 3.4 wt% and 3.7 wt% of hydrogen can be absorbed by the milled NaBH4 under a similar condition. Meanwhile, the system is able to desorb 2.0 wt% and 4.1 wt% of hydrogen in 60 min at 330 °C and 420 °C in isothermal desorption while only 0.3 wt% and 2.1 wt% can be released by the milled NaBH4 under the similar condition. The decomposition activation energy and enthalpy of the NaBH4 stage are calculated to be 162.1 kJ/mol and 68.1 kJ/mol H2. Based on the X-ray diffraction analysis, Na, Al and AlB2 are formed during the dehydrogenation process. The formation of Al and AlB2 are the keys to the improvement of hydrogenation properties. It is concluded that Li3AlH6 is a good destabilizing agent for the NaBH4 system.

Origin of enhanced stability in thiocyanate substituted α-FAPbI3 analogues

In the past few years, hybrid perovskites have emerged as the most promising photovoltaic materials due to their excellent optoelectronic properties, and easy fabrication methods. However, the long-term stability is still the main obstacle for their commercial applications. Recently, thiocyanate-doped hybrid perovskites have shown enhanced stability and impressive efficiency, but the reason is still unknown. Herein, we discussed the enhanced stability of SCN-substituted pseudocubic FABX3 (B=Pb2+, Sn2+; X=I−, Br−, and Cl−) based on the density functional theory. Through a series of calculations of Bader charge transfer, vacancy formation energies of different kinds of vacancies, decomposition enthalpy, phonon density of states, and ab initio molecular dynamics simulation, we conclude that the incorporation of SCN− can stabilize pseudocubic FABX3, and attribute the enhanced stability mainly to two factors: (1) the strong interaction between Pb2+/Sn2+ and SCN−, as well as the strong hydrogen bonding between FA+ and X−/SCN−, and (2) the structural tilting induced by the incorporation of SCN−. These findings provide alternative method fortuning the poor stability of pseudocubic FABX3, as well as for obtaining high-performance solar cells.

Diazo-Transfer Reagent 2-Azido-4,6-dimethoxy-1,3,5-triazine Displays Highly Exothermic Decomposition Comparable to Tosyl Azide.

2-Azido-4,6-dimethoxy-1,3,5-triazine (ADT) was reported recently as a new "intrinsically safe" diazo-transfer reagent. This assessment was based on differential scanning calorimetry data indicating that ADT exhibits endothermic decomposition. We present DSC data on ADT that show exothermic decomposition with an initiation temperature ( Tinit) of 159 °C and an enthalpy of decomposition (Δ HD) of -1135 J g-1 (-207 kJ mol-1). We conclude that ADT is potentially explosive and must be treated with caution, being of comparable exothermic magnitude to tosyl azide (TsN3). A maximum recommended process temperature for ADT is 55 °C.

Preparation and characterization of ethane-1,2-diaminium trinitromethanide as a novel energetic ionic liquid

In the present research, ethane-1,2-diaminium trinitromethanide ([NH3C2H4NH3][C(NO2)3]2) as a novel energetic dicationic ionic liquid (EDIL) was synthesized in a simple manner. The synthesized [NH3C2H4NH3][C(NO2)3]2 was characterized using FT-IR, Mass, 1H NMR, 13C NMR and DSC analysis. [NH3C2H4NH3][C(NO2)3]2 showed good thermal stability and decomposition enthalpy, which is significant compared to traditional energetic materials such as 1,3,5-Trinitro-1,3,5-triazinane (RDX) and 1,3,5,7-Tetranitro-1,3,5,7-tetrazocane (HMX). Also, a number of computational approaches such as electrostatic maps, electron density properties, enthalpy of formation and volumetric for [NH3C2H4NH3][C(NO2)3]2 were explored. The interaction energy and structural parameters of the prepared DIL is estimated at M06-2X/6–311++G (2d,2p) level of theory.

Changes in phase composition of soderites of the bakal deposit at heating

The article presents the results of a study of formation mechanism of magnesia-ferrite when heated siderites of the Bakal deposit with different iron oxide content in an inert and oxidizing atmosphere. It was established that in the case of firing in an inert atmosphere, the decomposition of siderite with high iron content begins at a lower temperature and the enthalpy of such decomposition is less. This effect can be explained by the different phase composition of the samples. The main phases formed under conditions of oxidative firing are hematite and magnesia-ferrite. The amount of hematite and magnesia-ferrite produced in the samples with different iron oxide content during firing in an oxidizing atmosphere is different. Siderite with high content of iron oxides contains more hematite in the firing products than magnesia-ferrite, and siderite with a low content of iron oxides contains more magnesia-ferrite in the firing products than hematite. Formed under conditions of oxidative firing magnesia-ferrites are solid solutions and differ in the degree of substitution of iron and magnesium ions. In siderites with high content of iron oxides, the degree of substitution of magnesium ions with iron ions is greater than in samples with a low content of iron oxides. Since the siderites of the Bakal deposit are poor ore formations, the considerable amount of magnesia-ferrite formed in them during firing makes it difficult to separate silicate and iron-oxide firing products by traditional enrichment methods. Wustite in the products of oxidative firing is not detected, because under these conditions it is in a metastable state and in the presence of a weakly oxidizing atmosphere is converted into magnetite. The scientific novelty is the explanation of the mechanism of siderite decomposition and the description of products of such decomposition. Understanding of the mechanism of decomposition of siderite from the Bakal deposit made it possible to develop the technology of reductive firing of siderite to facilitate separation of its products, and which consists in the regulation of the phase composition of silicate products of reductive firing, ensuring the collapse of magnesia-ferrite and output of iron oxide in a separate phase. The developed technology can be used to provide high-quality enrichment of siderite from the Bakal deposit.

Influence of Carbon Nanofibers on Thermal and Mechanical Properties of NC‐TEGDN‐RDX Triple‐Base Gun Propellants

AbstractTriple‐base gun propellants composed of nitrocellulose (NC), triethylene glycol dinitrate (TEGDN) and cyclotrimethylenetrinitramine (RDX) with carbon nanofibers (CNFs) were studied to explore the effects of CNFs on the thermal and mechanical properties. The results indicated that CNFs with less than 0.50 wt % were evenly and randomly dispersed in the propellant, otherwise there existed obvious aggregation. Temperatures of initial decomposition and exothermic peak reduced with the increase of NCFs from 0.00 to 3.00 wt %. Decomposition enthalpy of the composites with 0.50 wt % NCFs was 1214.6 J g−1, increased by ∼131.4 J g−1 compared to that of NC‐TEGDN‐RDX propellants. Moreover, the mechanical properties were effectively tailored by varying the amount of CNFs added to the composition. Decomposition enthalpy of the propellant with 0.25 wt % CNFs were hardly compromised for achieving enhancement in the compressive and impact properties, while the tensile strengths decreased slightly compared to that of the propellants.

Part 2. Structure, mechanical and thermophysical properties of consolidated ceramics based on (Hf,Ta)B2

(Hf,Ta)B2-based ceramics were produced by hot pressing (HP) and spark plasma sintering of powders obtained by combustion synthesis in Hf-Ta-B system. The dense ceramics possess exceptionally high hardness (60–70 GPa) and Young's modulus (584 GPa). The thermal conductivity is 30.3–52.9 W/m K depending on the phase composition. Plasma torch testing of the single- and two-phase (Hf,Ta)B2-based ceramics at 1500–2500 °C demonstrated the formation of a protective multi-layer oxide film with good adhesion to the ceramic, which increases the enthalpy of decomposition of ceramics up to 390 kJ/g.

Mechanical properties and ablation behaviour of nuclear sacrificial materials containing graphene sulfonate nanosheets

Graphene and its derivatives have been attracting the widespread interest of researchers because of their capability to improve several properties (e.g. mechanical properties, durability, anti-corrosion) of cementitious composites. This paper presents an experimental study on the influence of graphene sulfonate nanosheets (GSNSs) on mechanical properties and ablation behaviour of ferro-siliceous sacrificial cement paste and mortar, including flexural strength, compressive strength, microstructure, porosity, and thermal properties. Based on the results of differential scanning calorimetry and decomposition temperatures, the decomposition enthalpy of ferro-siliceous sacrificial cement paste and mortar was determined. It was found that, (1) the flexural strength and compressive strength of ferro-siliceous sacrificial mortar were increased by 16.22% and 24.44% respectively with the addition of 0.1 wt% GSNSs; (2) the decomposition enthalpy of ferro-siliceous sacrificial mortar was increased by 14.65%, 101.33%, and 135.15%, when adding 0.03 wt%, 0.1 wt%, and 0.3 wt% GSNSs, respectively; (3) the optimum GSNSs content was 0.1 wt% considering the mechanical strength, microstructure, and ablation rate of ferro-siliceous sacrificial cement paste and mortar. These findings can guide the design of ferro-siliceous sacrificial composites, e.g., cement paste, mortar, and even concrete containing GSNSs.

EFECTO DE LA MODIFICACIÓN QUÍMICA DE LAS PARTÍCULAS DE DIÓXIDO DE TITANIO MEDIANTE SILANIZACIÓN SOBRE LAS PROPIEDADES DE LAS PELÍCULAS DE CHITOSAN/ALMIDÓN DE PAPA

In this work we present a simple way to improve the dispersion of titanium dioxide (TiO2) particles inside chitosan/potato-starch films by chemical modification of the surface of these nanoparticles via silanization. The films increased in luminosity due to the modified particles, in addition to the fact that the water activity remained within the acceptable values ​​for microbial non-proliferation. The thermal analyzes indicated that the addition of TiO2 increases the glass transition temperature in the film, and the addition of functional groups such as those of the silane, give mobility to the polymer chains during the rise in temperature. The mobility of the polymer is related to a decrease in the value of the temperature necessary to reach a vitreous state in the films that contains silanized particles. The most important result was that the existence of these functional groups reduced the enthalpy of decomposition of the films making them more stable for thermal degradation. The photo-oxidation results suggested the passivate of TiO2 thanks to the presence of silane, which implies that it is a more stable film against UV radiation, avoiding the negative effect of unmodified TiO2 particles.

Small Organic Azides as High Energy Materials: Perazidoacetylene, ‐ethylene, and ‐allene

AbstractCompounds containing the azide group are already being used as primary explosives or energetic polymers/plasticizers. Here we present a short survey of the energy content of three small organic molecules that have been fully derivatized by N3 groups. Calculated thermodynamic and molecular properties indicate that their specific enthalpies of decomposition and combustion are in the range of those for current high energy‐density materials.