Thermokinetic Properties Research Articles

A facile sunflower pectin gel foam for liquid fuel fire suppression with ReaxFF characterisation on its char-enhancing ability

A biomass fire suppression gel foam (FSGF) with outstanding thermal stability and fire resistance performance was synthesised to improve the flame retardancy of foam agents on liquid fuel fires. The foam comprehensive index, microstructure, thermal stability, fire resistance and extinguishing properties of the FSGF were benchmarked against aqueous film-forming foam (AFFF). Subsequently, reactive forcefield (ReaxFF) molecular dynamics (MD) simulations were performed on the FSGF to study the thermokinetic properties. Based on the experimental results, a porosity layer was found on the external film of FSGF, which enhanced the thermal stability of the foam. The gelling mechanism of the foam is the formation of an O–Ca–O bond. Through MD simulations it was discovered that the remained calcium oxide/hydroxide species when deposited on fuel surfaces would promote char formation as they capture H/O atoms via dehydration. Alternatively, the foam showed better thermal stability than that of AFFF due to a lower weight loss rate and longer collapse time. The extinguishing performance tests demonstrated that the fire extinguishing time and resistance time of FSGF respectively are 72 s and 801 s, showing a significant potential to suppress the re-ignition of tank fires.

In-Depth Study on Synergic Interactions and Thermo-Kinetic Analysis of (Wheat Straw and Woody Sawdust) Biomass Co-Pyrolysis over Mussel Shell-Derived CaO Catalyst Using Coats–Redfern Method

The behavior of wheat straw biomass (WS), woody sawdust biomass (WB), and their blends during catalytic co-pyrolysis are analyzed in the presence of CaO catalyst, which is obtained from the calcination of mussel shells. Synergy analysis of blends and pure materials is measured by studying the difference between theoretical and experimental values of wt.%/min, (RL%), and (WL%), which correspond to maximum weight loss rate, residue left, and weight loss, respectively. The Coats–Redfern method is utilized for evaluating the thermo-kinetic properties. The chemical reaction order model F1 is the best model that describes the Ea of 60.05 kJ/mol and ∆H, ∆G, and ∆S values of 55.03 kJ/mol, 162.26 kJ/mol, and −0.18 kJ/mol.K, respectively, for the optimum blend 80WS−20WB, reducing the thermo-kinetic properties. Model D3 showed better results for the Ea, ∆H, ∆G, and ∆S for the 5% CaO blend, which certified the viability of co-pyrolysis of WS and WB, while DTG indicated that exothermic and endothermic reactions occur together.

Experimental study on co-combustion of domestic garbage and sewage sludge: Evaluation of synergistic effect and thermo-kinetic behavior

A persistent increase in domestic garbage (DG) has become a significant worldwide issue due to its negative impact on the ecosystem. The co-combustion way of DG and sewage sludge (SS) in a garbage incineration plant has been deemed a viable option. The study aims to quantify co-combustion behaviors, interaction effects, and thermo-kinetic properties between DG and SS at isothermal conditions by a thermogravimetric analyzer. The results showed that co-combustion of DG with 20 % SS could boost the combustion performance indices, and exhibit the synergistic effect. In addition, at the various SS blending ratios (10, 20 and 35 %) under an air atmosphere, combustion performance indices gradually decreased with an increased SS blending ratio but the synergistic effects were inhibited with a 35 % SS blending ratio. Coat-Redfern method was used to determine the combustion kinetics and thermodynamic properties. The apparent activation energy in the DG-SS (80 %/20 %) blend exhibited a non-linear relationship but increased proportionally with higher SS blending ratio. The lowest activation energy (34.70 kJ/mol) was obtained at the DG-SS (90 %/10 %) blend. The results suggest that the co-combustion of DG and SS can improve the overall combustion performance with an optimal blending ratio of 20 % SS for the co-combustion application.

Crystal engineering of high explosives through lone pair-π interactions: Insights for improving thermal safety

In this high-risk/high-reward study, we prepared complexes of a high explosive anion (picrate) with potentially explosive s-tetrazine-based ligands with the sole purpose of advancing the understanding of one of the weakest supramolecular forces: the lone pair-π interaction. This is a proof-of-concept study showing how lone pair-π contacts can be effectively used in crystal engineering, even of high explosives, and how the supramolecular architecture of the resulting crystalline phases influences their experimental thermokinetic properties. Herein we present XRD structures of 4 novel detonating compounds, all showcasing lone pair-π interactions, their thermal characterization (DSC, TGA), including the correlation of experimental thermokinetic parameters with crystal packing, and in silico explosion properties. This last aspect is relevant for improving the safety of high-energy materials.

Analysis of Selected Organophosphorus Compounds and Nano-Additives on Thermal, Smoke Properties and Quantities of CO and CO2 of Epoxy Materials.

Majority of anthropogenic air pollutants enter the atmosphere as a result of material combustion, industrial production and transport. Fires not only cause air pollution, but also disrupt ecosystems. Knowledge of the flammability parameters and proper flame-retardant modification of materials hinders the origin and spread of a fire, while also protecting against air pollution. The aim of this study was to obtain fire-retardant modifications of the epoxy resin, and then to analyse the effect of the introduced additives on the rate of heat release, the thermokinetic properties and the toxicity of volatile combustible products. The modifiers of the epoxy resin were organophosphorus compounds and aluminium and magnesium hydroxides, with a grain size of 10 nm. The introduced additives were found to be effective flame retardants as they reduced the rate of heat release and the amounts of toxic products of thermal decomposition and combustion. The HRRmax and HRRav values of all fire-retardant modifications were lower compared to the corresponding HRR values of the unmodified epoxy material.

Spectroscopic Characterization of an Atmospheric Pressure Plasma Jet Used for Cold Plasma Spraying

Cold plasma spray, a powder deposition method by means of an atmospheric pressure plasma jet is a promising coating technology for use on temperature sensitive surfaces. For further improvement of this coating process, a deeper understanding of its thermokinetic properties is required. By means of optical emission spectroscopy, the plasma effluent of an atmospheric pressure nitrogen arc jet is characterized by different distances from the nozzle and different gas flow rates of 35 Lmin−1 and 45 Lmin−1. A Boltzmann plot of N2+(B-X) was used to determine rotational temperatures, which were found to be around 4000 K at the nozzle exit. Excitation temperatures, analyzed using atomic nitrogen lines, were around 6000 K for all distances. Stark broadening of the Hα-line was too weak for determination of electron density for both gas flow rates. Overall no influence on gas flow rate was found.

Macromolecular and thermokinetic properties of a galactomannan from Sophora alopecuroides L. seeds: A study of molecular aggregation

The molecular aggregation of a galactomannan (NSAP-25) from Sophora alopecuroides L. seeds was investigated, where three polydisperse systems were confirmed during particle size analysis, indicating existence of different aggregates composed of random coil chains revealed by circular dichroism. Morphologically, NSAP-25 aggregate of various sizes (200–1200 nm) was possibly multi-stranded and formed by ellipsoid-like particles (20–60 nm) composed of compact coil chain, exhibiting extended amorphous structure with chain-like branches intertwined. Hence, NSAP-25 aggregation was inevitable, which exerted an unignorable effect on augmenting flexibility (β↓, γ↓, α↓ and Lp/ML↓) and compactness (ρ↓, df↑ and C∞↓) of branched random coil chain based on macromolecular analysis, especially when concentration increased. Moreover, it could be relevant to thermokinetic behavior of random nucleation and subsequent growth (A2 model and negative ΔS*) as well as good thermal stability (IPDT, ITS, t0.05, Tm and Tp), thus conferring potential applications for NSAP-25 in food and pharmaceutical industries.

Modelling of plutonium diffusion in (U,Pu)O2±x mixed oxide

The modelling of the thermo-kinetic properties of uranium-plutonium mixed oxide (MOX) is of utmost importance for optimizing its synthesis and for predicting its behaviour in Fast Breeder Reactors. Despite the stakes and likely because of experimental issues, little or no experimental data are available for the entire MOX system. We circumvent here the difficulties by developing a mobility database for plutonium using the DICTRA code. A well-established model of MOX formalized within the Compound Energy Formalism ensures the thermodynamic description. Rationalisation of the mobility parameters combined with the use of both cBΩ model and the few experimental data lead to a full and comprehensive description of plutonium self-diffusion in MOX for any plutonium content, O/M ratio and temperature. Additionally, we show that the observed plateau of the self-diffusion as a function of the oxygen to metal ratio (O/M) is related to the constant Pu3+ fraction for very low O/M ratio. Moreover, the observed minimum close to O/M = 2 is found for the lowest mobility of Pu4+.

MODELING OF STRUCTURE FORMATION PROCESS IN INTERMETALLIC NiAl ALLOYS DURING THERMOCHEMICAL PRESSING

Mathematical model aimed at obtaining NiAl alloys with a given structure and properties is proposed and implemented, based on the use of data on the features of the physical modeling of the thermochemical pressing process. For a mathematical description of the process of extrusion of a high-temperature synthesis product, it is necessary to determine a system of equations that takes into account the distribution of the thermo-kinetic and rheological properties of the synthesis product in a mold and caliber. High-temperature synthesis of intermetallic compound NiAl in a powder mixture of pure elements in the conditions of thermochemical pressing allows to obtain an intermetallic alloy with an average grain size of ~ 40—50 microns.

Multivariable control of ball-milled reactive material composition and structure

In reactive bimetallic compounds such as Ni–Al multilayers, desirable thermo-kinetic properties upon ignition require simultaneously controlled geometric microstructure and material composition. This article establishes fundamental dynamical models of plastic deformation and material diffusion in ball milling processing of particulates from Ni and Al powders, for the purpose of designing and implementing feedback control strategies for process control. The role of heat dissipation from plastic yield and friction slip in affecting compressibility and diffusivity of the material is elucidated. The different sensitivity of compressibility and diffusivity to thermal power is exploited by introducing multivariable control of both bilayer thickness and penetration depth simultaneously, using a real-time computational model as an observer with adaptation informed by infrared measurements of external vial temperature. The proposed control scheme is tested on a laboratory low-energy ball milling system and demonstrated to effectively modulate power intensity and process duration to obtain the desired microstructure and material composition.

Synthesis of a Valen Schiff-base bismuth(III) complex and its thermokinetic studies on the growth metabolism of S. pombe

A Valen Schiff-base ligand [1,5-bis(2-hydroxy-3-methoxybenzylidene)thiocarbonohydrazide] and its bismuth(III) complex were synthesized. The compositions and structures of two compounds were characterized by elemental analysis, spectrometry (1HNMR, MS, FT-IR, and UV-visible), chemical analysis, molar conductivity, and TG–DTA analysis. The results showed that the molecular formula of Schiff base and its bismuth(III) complex was C17H18O4N4S (abbreviated as H2L, L = C17H16O4N4S) and [Bi(C17H16O4N4S)Cl·H2O] (abbreviated as [Bi(L)Cl·H2O]), respectively. Furthermore, the thermokinetic properties of the action of Schiff base and its bismuth(III) complex on the growth metabolism of S. pombe were studied by bio-microcalorimetry at 305.15 K. The growth rate constant (k), maximum heat power, generation time, inhibition ratio (I) and half inhibition concentration (IC50), and their quantitative relationship with the concentration were calculated, respectively. Experimental results indicated that both Schiff base and its bismuth(III) complex could inhibit the growth of S. pombe, but the inhibitory effect of Schiff base was stronger than that of the complex. The half inhibition concentrations of Schiff base and its bismuth(III) complex were found to be 4.17 × 10−3 mol L−1 and 6.13 × 10−3 mol L−1, respectively.

Evaluation of thermo-kinetic and absorption characteristics of pure desiccants and desiccant mixtures

Air conditioning systems are used to control the air dry-bulb temperature and humidity level for human thermal comfort. In order to control the humidity level, air dry-bulb temperature needs to be brought down below its dew point temperature to condense out the moisture from the air. This eventually consumes a significant amount of total building energy in terms of electricity. Therefore, to minimize the energy consumption, researchers are stimulating their study towards an alternative latent heat load control system. In this regard, desiccant based sorption technologies are more effective compared to the conventional vapor compression system. Therefore, it is necessary to analyze the different desiccants' individual properties and their physical behavior in material perspective. In this study, an effort is devoted to explore the thermo-kinetic properties of pure LiBr, CaCl2, as well as their mixtures (LiBr:CaCl2 of 90:10; 85:15; 80:20 and 75:25) by X-ray diffraction (XRD), thermo-gravimetric (TG) and absorption rate, analyzes through numerous control experiments. The XRD study confirmed that peaks of CaCl2 and LiBr were shifted slightly for LiBr and CaCl2 mixtures due to interaction effects. The results of present investigation elucidated that mixtures of LiBr and CaCl2 showed less moisture regeneration cost than pure CaCl2 and all the mixtures revealed more rate of moisture absorption than pure LiBr and CaCl2. Further, 85:15 mixture of LiBr:CaCl2 showed higher rate of moisture absorption when compared to other prepared samples.

Numerical Simulation of Heat Transfer Using Cooling Roof Panels

Roof cooling can be used in coffered roofs, acoustic panels, as active cooling plasterboard attached to a standard metal structure designed for lowered roofs, or as a system of cooling register under the plaster. The roof cooling system works on the principle of heat transfer through a large active area and there is no unpleasant air flow than with conventional air conditioning. For technological reasons, very often pipes with a heat transfer medium are attached to a sheet metal of various materials, the thermokinetic properties of which significantly influence the intensity of the heat flux dissipated by the cooling system. The paper presents a numerical analysis of heat transport using stainless steel and aluminium sheets as the supporting sheet, as well as the influence of different ways of installing large panels under the roof.

First-principles molecular dynamics simulations on the local structure and thermo-kinetic properties of molten magnesium chloride

MgCl2 is a salt of considerable interest for the concentrating solar thermal power (CSP) system with advantages of high operating temperature and low cost. While the value of first-principles molecular dynamics (FPMD) simulations in investigating molten salt has been illustrated in many studies, there have been very few studies on molten MgCl2 from a first-principles method. In this work, FPMD simulations are employed to investigate the local coordination structure, as well as its structural dynamics, and thermo-kinetic properties of molten MgCl2. The basic thermo-kinetic properties of density, diffusivity, and ion conductivity are calculated for pure MgCl2 at multiple temperatures. The partial radial distribution function, partial structure factor, probability distribution of coordination numbers, and bond angle distribution are also derived from FPMD simulations. FPMD simulations are found to give satisfactory structural and transport characteristics compared with experiments. This study shows that the four-fold coordinated Mg2+ cations exist in pure MgCl2 and the Mg2+ first coordination shell has more octahedral geometry with anion vacancies. In conclusion, this work shows that FPMD simulations provide an effective method for exploring molten salts, which can be used in future research on Mg-based salts.

Energy estimation and modeling solid thermal explosion containment on reactor for three organic peroxides by calorimetric technique

In this paper, we describe thermokinetic properties and decomposition characteristics of benzoyl peroxide, dicumyl peroxide, and lauroyl peroxide, which are widely used in the polymerization process as energy boosters. In the past, many accidents occurred that involved overpressure and runaway excursion of the process and thermal explosion. One reason for accidents is because of the peroxy group (–O–O–) of organic peroxides (OPs) due to its thermal instability and high sensitivity when exposing to heat. Apparent activation energy and pre-exponential factor were obtained during decomposition via non-isothermal well-recognized kinetic equation, fitting curve tests, and approximate solution to design safer reaction conditions when OPs are used as fuel. Moreover, the storage conditions were investigated for the simulation of thermal explosion in a 24-kg cubic box package and a 400-kg barrel reactor for commercial application. Experimental results established the novel features of solid explosion hazard of OPs.

Study of thermo-kinetic properties of graphite micro-platelet-enriched vinyl ester composites

In this study, graphite-enriched vinyl ester resin (GVER) composites were prepared with 1, 3 and 5% of graphite micro-platelets (GMPs) to investigate thermo-mechanical and thermo-kinetic properties of composites. The thermal degradation behavior of GVER composites has been studied by thermo-gravimetric analysis under non-isothermal conditions in inert nitrogen atmosphere. Different iso-conversional methods such as Kissinger, Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose and Tang method were applied for this study. The apparent activation energy (E a) calculated from Kissinger’s method was found to be increased from 117.2 (neat vinyl ester) to 147.3, 150.5 and 155.8 kJ mol−1 for composites containing 1, 3 and 5% GMPs, respectively. The elastic modulus values were found to be increased 83.8, 107 and 71% for composites containing 1, 3 and 5% GMPs, respectively. The glass transition temperature values were increased 23.8% for 1% GMPs and 21.1% for 3 and 5% GMPs.

Functional Dependence of Thermodynamic and Thermokinetic Parameters of Refrigerants Used in Mine Air Refrigerators. Part 1 – Refrigerant R407C

Abstract The authors of this article dealt with the issue of modeling the thermodynamic and thermokinetic properties (parameters) of refrigerants. The knowledge of these parameters is essential to design refrigeration equipment, to perform their energy efficiency analysis, or to compare the efficiency of air refrigerators using different refrigerants. One of the refrigerants used in mine air compression refrigerators is R407C. For this refrigerant, 23 dependencies were developed, determining its thermodynamic and thermokinetic parameters in the states of saturated liquid, dry saturated vapour, superheated vapor, subcooled liquid, and in the two-phase region. The created formulas have been presented in Tables 2, 5, 8, 10 and 12, respectively. It should be noted that the scope of application of these formulas is wider than the range of changes of that refrigerant during the normal operation of mine refrigeration equipment. The article ends with the statistical verification of the developed dependencies. For this purpose, for each model correlation coefficients and coefficients of determination were calculated, as well as absolute and relative deviations between the given values from the program REFPROP 7 (Lemmon et al., 2002) and the calculated ones. The results of these calculations have been contained in Tables 14 and 15.

Oxygen diffusion model of the mixed (U,Pu)O2 ± x: Assessment and application

The uranium-plutonium (U,Pu)O2 ± x mixed oxide (MOX) is used as a nuclear fuel in some light water reactors and considered for future reactor generations. To gain insight into fuel restructuring, which occurs during the fuel lifetime as well as possible accident scenarios understanding of the thermodynamic and kinetic behavior is crucial. A comprehensive evaluation of thermo-kinetic properties is incorporated in a computational CALPHAD type model. The present DICTRA based model describes oxygen diffusion across the whole range of plutonium, uranium and oxygen compositions and temperatures by incorporating vacancy and interstitial migration pathways for oxygen. The self and chemical diffusion coefficients are assessed for the binary UO2 ± x and PuO2 − x systems and the description is extended to the ternary mixed oxide (U,Pu)O2 ± x by extrapolation. A simulation to validate the applicability of this model is considered.

Research and development of heat flux sensor for ablative thermal protection of spacecrafts

The objective of this paper is to estimate heat fluxes on the surface of advanced materials with known thermal and thermokinetic properties using the approach based on inverse methods. In many practical situations it is impossible to measure directly heat fluxes on the surfaces of analyzed composite structures (in particular a thermal protection systems (TPS) of spacecraft) especially in the case of thermokinetic processes inside materials. The only way that can often be used to overcome these difficulties is indirect measurements. This type of measurements is usually formulated as the solution of inverse heat transfer problems. By solving such inverse problems, the boundary conditions and unsteady temperature distribution are reconstructed using interior temperature measurements in structures. Such problems are ill-posed in mathematical sense and their main feature shows itself in the solution instabilities. The general method of iterative regularization is concerned with application to the estimation of external heat flux for thermal protection of spacecraft.

Transitional grain boundary structures and the influence on thermal, mechanical and energy properties from molecular dynamics simulations

The thermo-kinetic characteristics that dictate the activation of atomistic crystal defects significantly influence the mechanical properties of crystalline materials. Grain boundaries (GBs) primarily influence the plastic deformation of FCC metals through their interaction with mobile dislocation defects. The activation thresholds and atomic mechanisms that dictate the thermo-kinetic properties of grain boundaries have been difficult to study due to complex and highly variable GB structure. This paper presents a new approach for modelling GBs which is based on a systematic structural analysis of metastable and stable GBs. GB structural transformation accommodates defect interactions at the interface. The activation energy for such structural transformations was evaluated with nudged elastic band analysis of bi-crystals with several metastable 0 K grain boundary structures in pure FCC Aluminium (Al). The resultant activation energy was used to evaluate the thermal stability of the metastable grain boundary structures, with predictions of transition time based on transition state theory. The predictions are in very good agreement with the minimum time for irreversible structure transformation at 300 K obtained with molecular dynamics simulations. Analytical methods were used to evaluate the activation volume, which in turn was used to predict and explain the influence of stress and strain rate on the thermal and mechanical properties. Results of molecular dynamics simulations show that the GB structure is more closely related to the elastic strength at 0 K than the GB energy. Furthermore, the thermal instability of the GB structure directly influences the relationship between bi-crystal strength, temperature and strain rate. Hence, theoretically consistent models are established on the basis of activation criteria, and used to make predictions of temperature-dependent yield stress at a low strain rate, in agreement with experimental results.