Thermochemical Analysis Research Articles

Determination of surface catalysis on copper oxide in a shock tube using thermochemical nonequilibrium CFD analysis

A numerical assessment of both oxygen and nitrogen catalytic recombination efficiency on copper oxide surface is conducted using a computational fluid dynamics (CFD) analysis. The numerical catalytic determination is performed based on the stagnation heat transfer measurement that is conducted in a shock tube facility. A two-temperature thermochemical nonequilibrium model with a partial catalytic wall boundary condition is applied in the numerical analysis. The partial catalytic wall boundary condition is modeled by considering the wall mass flux, which is due to the diffusion and surface catalytic recombination. Through the CFD analysis, the obtained heat transfer is compared to the heat transfer that is calculated from the literature using the Goulard heat transfer theory. The atomic recombination efficiency is estimated by comparing the calculated stagnation heat transfer with the one that is measured from the experiment. The computed recombination efficiency values for both the oxygen and the nitrogen atoms are later compared with the available literature data for the recombination efficiency. It is shown that the determination of surface catalytic efficiency from the heat transfer measurement in the shock tube through the Goulard heat transfer theory has some limitations. The numerical catalytic determination through a CFD analysis with the thermochemical nonequilibrium model should be considered in order to obtain a more reliable efficiency value.

Assessment of planar laminar flame speed of Hythane generated in-situ from non-thermal plasma reforming of Methane : Flame tube based experiments and thermo-chemical analysis

The article addresses the characterization of laminar flame speed of Hythane generated from non thermal plasma reforming of Methane using a dielectric barrier discharge reactor. Hythane with 5%, 10% and 15% Hydrogen fraction is generated by controlling the Methane residence time in the plasma zone. Planar laminar flame speed for the Hythane so generated is estimated using a flame tube and compared with flame speed of bottled Hythane over a range of operating stoichiometry. It is observed that Hythane from plasma reforming of Methane has substantially higher laminar flame speed as compared to bottled Hythane. At the peak flame speed equivalence ratio of ϕ=1.1, Hythane generated from plasma activation of Methane has laminar flame speed higher than corresponding bottled Hythane to the extent of 13.3%, 34.1% and 38.9% for 5%, 10% and 15% Hydrogen in Hythane respectively. It is also observed that flame speed difference is muted for lean mixtures as compared to rich mixtures. Thermo-chemical analysis indicates that the enhanced flame speed can neither be addressed based on thermal effects nor due to the presence of neutral intermediate species and non thermal reforming of Methane to generate Hythane potentially results in additional reaction kinetics influences which accelerate the combustion process. Such influences could arise from presence of long lived species formed (charged or otherwise) not detected in conventional analysis and changes to the energy levels of the reaction species, principally Methane and Hydrogen. In terms of terminal utility, non thermal plasma reforming of Methane can have path breaking influence considering that enhanced flame speeds can significantly improve the thermodynamic efficiency of a spark ignited engine with lower than pure thermo-chemical Hydrogen requirement in Hythane.

Thermochemical Analysis of Improvised Energetic Materials by Laser-Heating Calorimetry

Thermochemical Analysis of Improvised Energetic Materials by Laser-Heating Calorimetry

Thermo-chemo-mechanical characterization, modeling, and analysis of hydration of calcium-sulfoaluminate cement paste

The reaction kinetic of a commercial calcium sulfoaluminate (CSA) cement was characterized by heat flow calorimetry. Distinct behavior is observed whether tartaric acid is added as retarding agent or not. Employing the so-obtained calorimetric data, heat of hydration and chemical affinity of the investigated binder mixture was determined. Furthermore, continuous ultrasonic propagation velocity measurement gave access to the stiffness gain of paste samples. However, the ultrasonic test setup is characterized by a non-constant temperature history (temperature rise and fall). Modeling the temperature history and the history of the degree of hydration with a thermo-chemical analysis scheme, the intrinsic material function of the stiffness evolution of the investigated hydrating CSA paste was obtained. Furthermore, the robustness of the thermo-chemical analysis scheme was demonstrated by the comparison of the measured with the simulated temperature evolution. The versatility of the approach may contribute to a systematic assessment and optimization of the heat/mechanical evolution of CSA binder systems under various geometric, temporal, and thermal boundary condition.

YbPO4: A novel environmental barrier coating candidate with superior thermochemical stability

YbPO4 was synthesized to study thermomechanical and thermochemical stability as a novel EBC material candidate. Thermal expansion coefficients were measured by high temperature XRD and determined to be a = 5.4 ± 0.4 × 10−6 / °C, c = 7.3 ± 0.1 × 10−6 / °C for the tetragonal structure with a linear CTE = 6.0 ± 0.3 × 10−6 / °C for the 100 °C – 1200 °C temperature range. High-velocity water vapor exposure at 1400 °C for 60, 125, and 250 h resulted in the formation of Yb2O3 product layer at a rate of 8.7 µm2/h for the 80–200 m/s steam velocity range, which was a slower reaction rate than state of the art EBC Yb2Si2O7 under similar conditions. YbPO4 – molten CMAS exposures at 1300 °C for 4, 24, and 96 h resulted in a compositionally variant reaction product composed primarily of a continuous Ca8MgYb(PO4)7 layer that inhibited CMAS penetration into the bulk of the samples. YbPO4 was additionally found to be chemically stable in the presence of SiO2 at 1400 °C, which is important for compatibility with SiC/Si substrates at elevated temperatures. Initial thermomechanical and thermochemical analysis indicate that YbPO4 should be considered a viable material candidate for next-generation EBC systems.

High-Temperature Surface Oxide Growth Kinetics of Al–Si–Zr Bulk Alloys and Ribbons

A typical modification technique of the functional properties of Al–Si based alloys is the addition of some third element in trace level. In the present work, ternary Al–Si–Zr bulk and ribbon alloys have been prepared. The kinetics of high-temperature surface oxidation has been studied by thermogravimetric method. It was found that at the start of the experiment the chemical reaction velocity is rate-controlling while for longer times the (oxygen) diffusion is the rate-controlling process. Activation energy of the two stages of oxidation has been obtained. Additional studies such as thermochemical analysis, optical and electron microscopy, and microhardness tests have been done.

Combining Experimental and DFT Investigation of the Mechanism Involved in Thermal Etching of Titanium Nitride Using Alternate Exposures of NbF5 and CCl4, or CCl4 Only

AbstractThermally activated chemical vapor‐phase etching of titanium nitride (TiN) is studied by utilizing either alternate exposures of niobium pentafluoride (NbF5) and carbon tetrachloride (CCl4) or by using CCl4 alone. Nitrogen (N2) gas purge steps are carried out in between every reactant exposure. Titanium nitride is etched in a non‐self‐limiting way by NbF5–CCl4 based binary chemistry or by CCl4 at temperatures between 370 and 460 °C. Spectroscopic ellipsometry and a weight balance are used to calculate the etch per cycle. For the binary chemistry, an etch per cycle of ≈0.8 Å is obtained for 0.5 and 3 s long exposures of NbF5 and CCl4, respectively at 460 °C. On the contrary, under the same conditions, the etch process with CCl4 alone gives an etch per cycle of about 0.5 Å. In the CCl4‐only etch process, the thickness of TiN films removed at 460 °C varies linearly with the number of etch cycles. Furthermore, CCl4 alone is able to etch TiN selectively over other materials such as Al2O3, SiO2, and Si3N4. X‐ray photoelectron spectroscopy and bright field transmission electron microscopy are used for studying the post‐etch surfaces. To understand possible reaction products and energetics, first‐principles calculations are carried out with density functional theory. From thermochemical analysis of possible reaction models, it is found that NbF5 alone cannot etch TiN while CCl4 alone can etch it at high temperatures. The predicted byproducts of the reaction between the CCl4 gas molecules and TiN surface are TiCl3 and ClCN. Similarly, TiF4, NbFCl3, and ClCN are predicted to be the likely products when TiN is exposed to both NbF5 and CCl4. A more favorable etch reaction is predicted when TiN is exposed to both NbF5 and CCl4 (ΔG = −2.7 eV at 640 K) as compared to exposure to CCl4 only (ΔG = −2 eV at 640 K) process. This indicates that an enhanced etch rate is possible when TiN is exposed alternately to both NbF5 and CCl4, which is in close agreement with the experimental results.

Assessment of structural order indices in kaolinites: A multi-technique study including EXAFS

This work presents a study of the structural properties on four representative kaolinite samples. Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Thermochemical Analyses (DTA/TGA), and X-ray Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy measurements were carried out, and different empirical indices that quantify the structural order were assessed. Also, XRD patterns and EXAFS signals were compared to those corresponding to idealized defect-free structures calculated theoretically, to analyze the effects related to the structural disorder on real samples. The structural order at different scales (crystallographic, superficial, and local) was comprehensively examined for the four samples, and correlations between the order indices were performed and discussed, including the Debye-Waller factor obtained from Si K-edge EXAFS measurements. The proposed methodology shows that EXAFS is a suitable complementary technique that can provide valuable information about the Si local environments in natural kaolinites.

Density functional theory-based analyses on selective gas separation by β-PVDF-supported ionic liquid membranes

Finding proper candidates for polymer-supported ionic liquid (IL)-based gas separating membranes is a challenge. The current article elucidates the quantum chemical perspective of the selective gas adsorption efficiency, from a mixture of CO2, CO, CH4, and H2, of α- and β-polyvinylidene fluoride (PVDF)-supported imidazolium- and pyridinium-based six ionic liquid membranes. Although IL-based membrane efficiency mainly depends on the gas solubility of ILs, IL/support binding and gas adsorption on the support material are also studied to describe the overall gas adsorption properties of the PVDF/IL complexes. β-PVDF exhibits better binding with the ILs, and better gas affinity, thus, qualified as a more suitable membrane component as compared to α-PVDF. Dispersion-corrected density functional calculations are performed to provide a detailed insight into the energetic interactions, nonbonding intermolecular interactions based on symmetry adapted perturbation theory (SAPT), natural bond orbitals (NBO), Bader's quantum theory of atoms in molecules (QTAIM), reduced density gradient (RDG), frontier orbital interactions, density of states (DOS), and thermochemical analyses of the gas-adsorbed systems. Gas molecules interact with the membrane components through weak hydrogen bonds and exhibit low interaction energies, indicating physisorption of the gases. Gas adsorption energies are more negative than the mutual interaction energies of the gas molecules, ensuring effective gas adsorption by the membrane components. All the β-PVDF/IL systems have shown the highest and lowest affinity for CO2 and H2, respectively, leading to effective separation of CO2 and H2 from the other gases.

A machine learning framework for real-time inverse modeling and multi-objective process optimization of composites for active manufacturing control

For manufacturing of aerospace composites, several parts may be processed simultaneously using convective heating in an autoclave. Due to uncertainties including tool placement, convective Boundary Conditions (BCs) vary in each run. As a result, temperature histories in some of the parts may not conform to process specifications due to under-curing or over-heating. Thermochemical analysis using Finite Element (FE) simulations are typically conducted prior to fabrication based on assumed range of BCs. This, however, introduces unnecessary constraints on the design. To monitor the process, thermocouples (TCs) are placed under tools near critical locations. The TC data may be used to back-calculate BCs using trial-and-error FE analysis. However, since the inverse heat transfer problem is ill-posed, many solutions are obtained for given TC data. In this study, a novel machine learning (ML) framework is presented capable of optimizing air temperature cycle in real-time based on TC data from multiple parts, for active control of manufacturing. The framework consists of two recurrent Neural Networks (NN) for inverse modeling of the ill-posed curing problem at the speed of 300 simulations/second, and a classification NN for multi-objective optimization of the air temperature at the speed of 35,000 simulations/second. A virtual demonstration of the framework for process optimization of three composite parts with data from three TCs is presented.

Thermochemical analysis of intermolecular interactions of L-carnosine with isonicotinic acid in aqueous solutions

Thermochemical analysis of intermolecular interactions of L-carnosine with isonicotinic acid in aqueous solutions

Methane Adsorption on Heteroatom-Modified Maquettes of Porous Carbon Surfaces.

Experimental and theoretical studies disagree on the energetics of methane adsorption on carbon materials. However, this information is critical for the rational design and optimization of the structure and composition of adsorbents for natural gas storage. The delicate nature of dispersion interactions, polarization of both the adsorbent and the adsorbate, interplay between H-bonding and tetrel bonding, and induced dipole/Coulomb interactions inherent to methane physisorption require computational treatment at the highest possible level of theory. In this study, we employed the smallest reasonable computational model, a maquette of porous carbon surfaces with a central site for substitution and methane binding. The most accurate predictions of methane adsorption energetics were achieved by electron-correlated molecular orbital theory CCSD(T) and hybrid density functional theory MN15 calculations employing a saturated, all-electron basis set. The characteristic geometry of methane adsorption on a carbon surface ("lander approach") arises due to bonding interactions of the adsorbent π-system with the proximal H-C bonds of methane, in addition to tetrel bonding between the antibonding orbital of the distal C-H bond and the central atom of the maquette (C, B, or N). The polarization of the electron density, structural deformations, and the comprehensive energetic analysis clearly indicate a ∼3 kJ mol-1 preference for methane binding on the N-substituted maquette. The B-substituted maquette showed a comparable or lower binding energy than the unsubstituted, pure C model, depending on the level of theory employed. The calculated thermodynamic results indicate a strategy for incorporating electron-enriched substitutions (e.g., N) into carbon materials as a way to increase methane storage capacity over electron-deficient (e.g., B) modifications. The thermochemical analysis was revised for establishing a conceptual agreement between the experimental isosteric heat of adsorption and the binding enthalpies from statistical thermodynamics principles.

INVESTIGATION OF RESIDUAL STRESSES AND DEFORMATIONS OF A PULTRUDED THIN BEAM PROFILE

In the present study, a coupled 3D transient thermo-chemical analysis together with 2D plane strain mechanical analysis is carried out for the pultrusion process. For the mechanical analysis, a cure hardening instantaneous linear elastic (CHILE) approach is used of a thin beam profile made of glass fibre and epoxy resin. The applied approach is efficient and fast to investigate the residual stresses and deformations together with the distributions of temperature and degree of cure obtained from the thermo-chemical analysis.

Synthesis, Spectroscopic Characterization (FT-IR, NMR, UV), NPA, NBO, NLO, Thermochemical Analysis and Molecular Docking Studies of 2-((4-hydroxyphenyl)(piperidin-1-yl)methyl)phenol

In this study, a new alkylaminophenol compound was synthesized and characterized by spectroscopic techniques (FT-IR, NMR, UV). The optimized molecular geometry and the vibrational wavenumbers were calculated using density functional theory (DFT) B3LYP/WB97XD and HF methods with 6-311++ G([Formula: see text], [Formula: see text]) basis set. Thus, theoretical data were compared within themselves before comparing with experimental data. The detailed interpretation of the vibrational spectra has been carried out by VEDA program.1H-NMR and [Formula: see text]C-NMR chemical shifts of the compound were calculated using GIAO/IEFPCM method in CDCl3. Using time-dependent (TD-DFT) approach electronic properties such as HOMO and LUMO energies, the electronic spectrum of the title compound has been studied and reported. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Linear polarizability, anisotropic linear polarizability and hyperpolarizability values of the title compound were found to be higher than the values of the pNA compound that are used as a standard substance in the NLO analysis. Molecular electrostatic potential (MEP), the thermodynamic properties (heat capacity, entropy and enthalpy) were calculated. Also, to investigate the biological properties of the title compound, molecular docking was done with DNA(PDB ID: 414D). It has been observed that the effective interaction is hydrogen bonds.

Gasification of municipal refuse-derived fuel as an alternative to waste disposal: Process efficiency and thermochemical analysis

This is the first study to investigate the use of municipal refuse-derived fuel for gasification in pilot plant scale aiming at urban waste treatment and energy generation. Energy and mass balances were applied to the thermochemical reactor based on the experimental data obtained during pilot scale operation to calculate thermal efficiency associated to the process. Volumetric composition, lower heating value, and density of the resulting syngas were determined using calorimetric tests and chromatographic analyses. The pilot plant gasification system processed 7.1 tonnes day−1 of municipal refuse-derived fuel producing 16.9 tonnes day−1 of syngas with a lower heating value of 4.6 MJ kg−1, along with 26 wt.% ash. No tar was generated during the process. According to results of this study, the pilot plant is able to generate sufficient electricity for nearly 800 small houses if connected to a steam power cycle. Pollutants emitted from syngas combustion (performed by accredited agencies) were analyzed and levels were below legal standards established in Brazil and in the United States, thus demonstrating the feasibility of this technology for conversion of municipal solid waste into a renewable energy source.

Substitution Reactions in the Pyrolysis of Acetone Revealed through a Modeling, Experiment, Theory Paradigm

The development of high-fidelity mechanisms for chemically reactive systems is a challenging process that requires the compilation of rate descriptions for a large and somewhat ill-defined set of reactions. The present unified combination of modeling, experiment, and theory provides a paradigm for improving such mechanism development efforts. Here we combine broadband rotational spectroscopy with detailed chemical modeling based on rate constants obtained from automated ab initio transition state theory-based master equation calculations and high-level thermochemical parametrizations. Broadband rotational spectroscopy offers quantitative and isomer-specific detection by which branching ratios of polar reaction products may be obtained. Using this technique, we observe and characterize products arising from H atom substitution reactions in the flash pyrolysis of acetone (CH3C(O)CH3) at a nominal temperature of 1800 K. The major product observed is ketene (CH2CO). Minor products identified include acetaldehyde (CH3CHO), propyne (CH3CCH), propene (CH2CHCH3), and water (HDO). Literature mechanisms for the pyrolysis of acetone do not adequately describe the minor products. The inclusion of a variety of substitution reactions, with rate constants and thermochemistry obtained from automated ab initio kinetics predictions and Active Thermochemical Tables analyses, demonstrates an important role for such processes. The pathway to acetaldehyde is shown to be a direct result of substitution of acetone's methyl group by a free H atom, while propene formation arises from OH substitution in the enol form of acetone by a free H atom.

Power Generation from Melon Seed Husk Biochar Using Fuel Cell

Melon seed husk (MSH) biochar was used in a single cell direct carbon fuel cell (DCFC) as an alternative biofuel. The DCFCs belong to a generation of energy conversion devices that are characterised with higher efficiencies, lower emission of pollutants and MSH biochar as the fuel. Several analytical techniques (proximate, ultimate and thermo-chemical analysis) were employed to analyse the characteristics of the biomass fuel, their effects on the cell’s performance, and the electrochemical reactions between the fuel and the electrolyte in the system. High carbon content and calorific values are some of the parameters responsible for good performances. The performance of a lab-scale DCFC made of ceramic tubes using molten carbonate electrolyte was investigated. Binary carbonates mixture (Na2CO3-K2CO3, 38-62 mol.%) was used as electrolyte and the waste MSH carbonised at 450oC as biofuel. A practical evaluation of the fuel used in the DCFC system was conducted, for varying temperature of 100 - 800oC. The maximum open circuit voltage (OCV) was 0.71 V. With an applied load resistance and active surface area of 5.73 cm2 the maximum power density was 5.50 mWcm-2 and the current density was 29.67 mAcm-2 at 800oC.

Thermo-chemical analysis and modeling of combustion of waste pyrolysis gaseous products

The results of the study of joint pyrolysis of various types of waste (municipal solid waste, plastic waste, etc.) are presented. Preliminarily crushed and dried wastes were fed into the pyrolysis chamber of the model experimental setup. Thermal energy required for heating raw materials and carrying out their thermal destruction was obtained by burning a part of the pyrolysis gases. The rest of these gases were removed from the pyrolysis chamber and cooled. The temperature in the pyrolysis zone was about 650 °C. Plant productivity was up to 500 kg/h. The target product was the liquid phase, which is a mixture of hydrocarbon compounds. When organizing the processes, the yield of solid carbon residue was minimized. The obtained mass ratio of the final gas/liquid products was approximately equal to 1/6. Experimental results of the analysis of the chemical composition of the gas and liquid fractions are presented. The results of modeling the combustion of pyrolysis products at different amounts of supplied air are also shown. The operating parameters at which the optimum temperature level in the pyrolysis zone is maintained are numerically determined and recommended.

Temperature and Solvent Effects on H2 Splitting and Hydricity: Ramifications on CO2 Hydrogenation by a Rhenium Pincer Catalyst.

The catalytic hydrogenation of carbon dioxide holds immense promise for applications in sustainable fuel synthesis and hydrogen storage. Mechanistic studies that connect thermodynamic parameters with the kinetics of catalysis can provide new understanding and guide predictive design of improved catalysts. Reported here are thermochemical and kinetic analyses of a new pincer-ligated rhenium complex (tBuPOCOP)Re(CO)2 (tBuPOCOP = 2,6-bis(di-tert-butylphosphinito)phenyl) that catalyzes CO2 hydrogenation to formate with faster rates at lower temperatures. Because the catalyst follows the prototypical "outer sphere" hydrogenation mechanism, comprehensive studies of temperature and solvent effects on the H2 splitting and hydride transfer steps are expected to be relevant to many other catalysts. Strikingly large entropy associated with cleavage of H2 results in a strong temperature dependence on the concentration of [(tBuPOCOP)Re(CO)2H]- present during catalysis, which is further impacted by changing the solvent from toluene to tetrahydrofuran to acetonitrile. New methods for determining the hydricity of metal hydrides and formate at temperatures other than 298 K are developed, providing insight into how temperature can influence the favorability of hydride transfer during catalysis. These thermochemical insights guided the selection of conditions for CO2 hydrogenation to formate with high activity (up to 364 h-1 at 1 atm or 3330 h-1 at 20 atm of 1:1 H2:CO2). In cases where hydride transfer is the highest individual kinetic barrier, entropic contributions to outer sphere H2 splitting lead to a unique temperature dependence: catalytic activity increases as temperature decreases in tetrahydrofuran (200-fold increase upon cooling from 50 to 0 °C) and toluene (4-fold increase upon cooling from 100 to 50 °C). Ramifications on catalyst structure-function relationships are discussed, including comparisons between "outer sphere" mechanisms and "metal-ligand cooperation" mechanisms.

Non-covalent interactions in molecular systems: thermodynamic evaluation of the hydrogen bond strength in aminoalcohols.

In molecules with two functional groups that form hydrogen bonds, the structure-property relationship can depend significantly on the strength of intra-molecular hydrogen bonding. This bonding can cause a substantial conformational change that is accompanied by a frequency shift in the infrared spectrum, which provides the basis for experimental studies. Despite its great importance in biological systems, the available literature data for the strength of this bonding are scarce and not in agreement. In this work, we present the results of four thermodynamic methods for the determination of the strength of intramolecular hydrogen bonds. Comprehensive thermochemical analysis of 1-amino-2-alcohols and 2-amino-1-alcohols was performed with Fourier-transform infrared spectroscopy, high-level G4 quantum-chemical calculations, the homomorph scheme with enthalpies of vaporization and a group contribution method. With the combination of these four thermodynamic methods, the strength of intramolecular hydrogen bonding in 1,2-aminoalcohols and 2,1-aminoalcohols was evaluated quantitatively. The results were correlated with NBO parameters to find an explanation for the different strengths of intramolecular hydrogen bonds in total charge transfer and second order stabilization energies.