Exothermic Effect Research Articles

A Fully Coupled Thermo-Hydro-Mechanical-Chemical Model for Methane Hydrate Bearing Sediments Considering the Effect of Ice

The ice generation is one of the challenges facing the methane hydrate depressurization, which, however, has not been fully addressed by existing numerical models for hydrate-bearing sediments (HBS). In this study, we develop a high-fidelity, fully coupled thermo-hydro-mechanical-chemical numerical model that incorporates the effect of ice. The model, developed using COMSOL, takes into account water–ice phase change, thermally induced cryogenic suction and constitutive relation in HBS. It is verified well against the temperature, pressure and cumulative gas production of Masuda’s experiment. The model is then employed to investigate multiphysical responses and gas/water production when ice generation is induced by setting a low outlet pressure. The results reveal that ice forms near the outlet boundary of the specimen center, leading to a reduction in intrinsic permeability and fluid velocity and an increase in the bulk modulus of ice-HBS. This enhanced bulk modulus results in higher porosity under axial load. Although the exothermic effect of ice generation promotes the hydrate dissociation, the effect on cumulative gas production is negligible after the ice melts. A negative correlation between ice saturation and water production rate is observed, indicating that a higher gas–water ratio can be achieved by adjusting the ice duration during hydrate production. The developed coupled model proves to be crucial for understanding the effect of ice on hydrate exploitation.

Thermal Stability of NASICON-Type Na3V2(PO4)3 and Na4VMn(PO4)3 as Cathode Materials for Sodium-ion Batteries

The thermal stability of NASICON-type cathode materials for sodium-ion batteries was studied using differential scanning calorimetry (DSC) and in situ high-temperature powder X-ray diffraction (HTPXRD) applied to the electrodes in a pristine or charged state. Na3V2(PO4)3 and Na4VMn(PO4)3 were analyzed for their peak temperatures and the exothermic effect values of their decomposition processes, as well as the phase transformations that took place upon heating. The obtained results indicate that Mn-substituted cathode material demonstrates much poorer thermal stability in the charged state, although pristine samples of both materials exhibit similar thermal behavior without any DSC peaks or temperature-induced phase transitions in the studied temperature range. The in situ HTPXRD revealed the amorphization of desodiated Na4VMn(PO4)3-based electrodes occurring at 150~250 °C.

Exothermic Reactions in AlNi Foils Produced by Rolling Powders

The possibility of manufacturing multilayer reaction foils of the Al-Ni system by rolling a powder mixture is considered. The sequence and temperatures of phase transformations during heating was established by the differential thermal analysis and X-ray phase analysis. The formation of the intermetallic compounds in the foils fabricated via rolling just mixed powder occurs only when a liquid phase appears (660°C). However, the foils fabricated from mechanically activated powders exhibit significant exothermic effect at temperature of 320°C unnecessarily for a liquid phase formation and can be proposed as a multilayer reactional foils for local heating in the technology of joining of various materials.

PHASE FORMATION DURING ALUMINOTHERMAL REDUCTION OF Ti, Nb, Gd (Y) FROM OXIDES

Alloys based on titanium and aluminum with additions of niobium and rare-earth metals have unique mechanical and heat-resistant properties, and also it likely that such alloys would have increased corrosion resistance. The method of thermodynamic modeling using the HSC program was used to study a system with aluminum consumption varying in the range from 0 to 100% of the mass of the initial charge. The features of phase formation in Al–[50TiO2–5Nb2O5–1Y2O3 (Gd2O3)] systems have been studied. The calculation of the heat balance of the process at 1600°C and 44% of Al was – 0.196 MJ per 1 kg of charge, which indicates the possibility of its occurrence with only the aluminothermic reactions. The reduction of titanium and niobium can proceed by reactions through the formation of their oxides of lower valency – TiO, NbO2, NbO. The aluminothermic reduction of gadolinium is thermodynamically possible only at temperatures below 1200°C. The reduction of yttrium through the interaction of Y2O3 with aluminum with the formation of AlY, Al2Y3 AlY2 compounds for the range of 1000–1800°C is thermodynamically impossible. The results of thermodynamic modeling of interactions correlated well with the data of differential thermal and X-ray phase analysis using STA 449 F3 Jupiter (NETZSCH) synchronous thermal analysis and XRD-7000 diffractometer (Shimadzu) with automatic program control, respectively. It was found that the process enters the active phase after the appearance of liquid aluminum and, apparently, is accompanied by exothermic effects with the formation of double and triple intermetallic compounds of aluminum with rare (Nb, Ti) and rare earth (Gd, Y) metals. Transformation of titanium dioxide and niobium pentoxide in the process of transformations is likely carried out through successive and parallel stages of formation of simple and complex oxides with low oxidation states. At the initial stages of the interaction of aluminum with oxides, niobium and titanium aluminides are mainly formed. At subsequent stages, the formation of more complex compounds is observed. At temperatures above 1300°C, ternary intermetallic compounds Al43Nb4Gd6, Ti4Al20Gd and Ti4Al3Y6, Al3Ti, Al0.23Nb0.07Ti0.7 are formed. Gadolinium and yttrium tend to form complex intermetallic compounds in such systems.

Effect of the technological parameters of plasma-arc spraying of flux-cored wire on the structure and properties of intermetallide coatings based on Fe3Al

Existing techniques for applying intermetallide layers are characterized by low productivity, difficulties associated with the maintenance and operation of technological equipment, as well as significant costs for the purchase of materials for spraying. Therefore, modern science shows considerable interest in the development of new, highly effective technologies to form intermetallide coatings on the surface of articles. Such promising techniques include the technology of plasma-arc spraying (PAS) of flux-cored wires. This technique has a number of significant advantages, namely high performance, relative simplicity, as well as the affordability of equipment and materials for coating. This paper reports a study into the structure and properties of coatings obtained by flux-cored wire PAS, in which the steel sheath and aluminum powder filler interact when heated with the exothermic effect of Fe3Al synthesis. The influence of technological parameters of PAS process on the structure and properties of Fe-Al coatings was investigated by means of mathematical planning of the experiment. It was found that in all samples the main phase is an intermetallide of the Fe3Al type. Tests for gas-abrasive wear resistance at room temperature showed that the wear resistance of coatings exceeds the stability of steel S235 by an average of 2 times. As a result of studying the electrochemical properties in a 3-% aqueous solution of NaCl and in a 0.5-% solution of H2SO4, the score of corrosion resistance for these media was determined, which was, respectively, 4 and 5 (coatings belong to the group of "resistant"). In this regard, the practical use of coatings based on the Fe3Al intermetallide is recommended for protection against oxidation, corrosion, and gas-abrasive wear of components and assemblies in the heat power industry (heat exchanger pipes, catalytic converters, steam turbine blades, shut-off valves, etc.)

TG-DSC and TG-FTIR Studies of Annelated Triazinylacetic Acid Ethyl Esters-Potential Anticancer Agents.

To avoid problems associated with the storage and processing of newly developed potential medicines, there is a need to carry out thermal studies in the preclinical phase of drug development. The thermal behaviour and decomposition pathway of a whole novel class of patented potential molecular pharmaceutics, i.e., ethyl 2-[4-oxo-8-(R-phenyl)-4,6,7,8-tetrahydroimidazo[2,1-c][1,2,4]triazin-3-yl]acetates (1-6) were reported for the first time in inert and oxidative atmospheres. The experiments were conducted with the use of simultaneous thermogravimetry/differential scanning calorimetry (TG-DSC) and simultaneous thermogravimetry coupled with Fourier transform infrared spectroscopy (TG-FTIR). The decomposition pathways of compounds 1-6 were found to be different under oxidative and inert conditions. It was proven that the investigated molecules reveal higher thermal stability under a synthetic air atmosphere than under a nitrogen atmosphere, and their decomposition is preceded by the melting process. Among all the investigated compounds, only the meta-chloro derivative (4) was found to exhibit interesting polymorphic behaviour at a low heating rate (10 °C min-1). It was proven that the oxidative decomposition process of the studied molecules proceeds in three overlapping stages accompanied by strong exothermic effects. Additionally, it was concluded that the title compounds were stable up to a temperature of 195-216 °C in an atmosphere of synthetic air, and their thermal stability decreased in the order of R at the benzene ring: 4-CH3 > 3,4-Cl2 > 4-Cl > H > 2-OCH3 > 3-Cl.

Assessment of the benefits of 3D printing of advanced thermosetting composites using process simulation and numerical optimisation

3D printing of continuous fibre reinforced thermosetting matrix composites is set to revolutionise composite manufacturing practice. The potential of curing additively is anticipated to bring significant improvement in terms of increasing process speed, producing geometries that are inaccessible with current processing routes and eliminating detrimental exothermic effects during the process. This study presents a comparison between the curing stage of the 3D printing and standard batch processing for carbon fibre/epoxy components of varying thickness and size. An optimisation methodology links simulation of the cure using Finite Element solver Abaqus with a Genetic Algorithm capable of dealing with multi-objective problems. Optimal cure cycles to minimise both process time and temperature overshoot in 3D printing and batch processing are identified and the optimal trade-offs compared. The results highlight that temperature overshoot reduction up to 85 % is possible and that the intrinsic additive nature of the 3D printing allows eliminating the dependence of temperature overshoot on thicknesses and producing components with thicknesses that are very difficult to manufacture conventionally. A simplified procedure for the estimation of 3D printing process duration is proposed based on the results of finite element simulation. This is used for exploration of the limits of the process with respect to part size and for a generic comparison of process applicability against batch processing. The analysis shows that 3D printing is highly advantageous for small components, is efficient for mid-size components and can – on the basis of its scalability – offer a feasible route for producing large and very large components.

Effects of typical additives on the thermal stability of ammonium peroxydisulfate

Ammonium peroxydisulfate (APS), one of the most widely used inorganic peroxides in the process industries, is a thermally unstable peroxide and potent oxidizer due to the presence of peroxy bond in the molecule and is incompatible with most substances. To investigate the effect of typical additives on the thermal decomposition of APS, in this paper, diamine phosphate (DAP), monoamine phosphate (MAP), and aluminum hydroxide (AH) were selected as additives; pure APS and samples with 10 wt% and 20 wt% of additives were first tested by differential scanning calorimetry (DSC). The experiments and analysis showed that the samples with 10 wt% of additive had better thermal stability than those with 20 wt% of additive. After screening, the three groups of 10 wt% AH, 10 wt% MAP, and 20 wt% MAP additive conditions could be considered to have a better thermal stability effect on the thermal decomposition of APS. Four groups of samples were, in turn, tested by Phi-Tec II. The adiabatic results showed two discontinuous exothermic processes; 10 wt% AH promoted the weak exothermic effect in the first stage. In contrast, the three groups of additives in the main exothermic stage showed different degrees of inhibition, and the inhibiting effect was ranked as 10 wt% AH, 10 wt% MAP, and 20 wt% MAP in order. Finally, the self-accelerated decomposition temperature (SADT) was calculated under the 25 kg standard package. The adiabatic results, including SADT, were combined to render feasible recommendations for the use of additives, which provides references for the packaging and transportation of additives and their applications.

Структурная модификация высокодисперсных порошков вскрышных пород сапонитсодержащей бентонитовой глины

The kinetic regularities of the process of structural modification of highly dispersed powders of saponite-containing material after mechanical dispersion have been studied. As information criteria characterizing the restructuring of the crystal lattice of minerals, changes are used that occur with the specific surface of powders at different grinding times and the exothermic thermal effect (enthalpy change) in the temperature range of 810 – 820 °С. It has been determined that during mechanical grinding of a saponite-containing material for more than 20 minutes, intensive modification of saponite occurs, associated with its structural changes, leading to the formation of serpentine. It has been established that the traditionally used criterion for evaluating the process of mechanical grinding of raw materials by the specific surface of the powder in this case is not a sufficient information parameter when optimizing structural changes in experimental samples. The dominant parameter of this process is the enthalpy factor, which characterizes the thermal effect of the structural modification.

Features for obtaining of RuAl-based powder alloys

Refractory heat-resistant ruthenium monoaluminide β-RuAl is a promising material for operation in high-velocity gas oxidizing flows at temperatures above work temperatures and melt temperatures of nickel superalloys and refractory nickel and titanium aluminides. The possibilities of preparing high-quality powder materials from RuAl for the manufacture of compact samples are considered. Compact materials with minimum porosity and practically equilibrium phase composition can be obtained under conditions of high-temperature reaction alloying during three-stage hot isostatic pressing with intermediate homogenizing annealing. Preliminary treatment of mixtures of Ru and Al powders in an attritor for 15 h reduces the exothermic effect of RuAl formation and lowers the temperature at which the contact interaction begins.

The Use of Coke Ash Residue as Power Generating Fuel at Thermal Power Facilities

The aim of the study is to preliminarily estimate the possibility of using coke-ash residue as power generating fuel. Coke-ash residue is obtained in the process of gasifying the Balakhta brown coal from the Kansk–Achinsk coal basin in the technological process of obtaining producer gas used as fuel for boilers. To achieve the formulated aim, a technical and elemental analysis of the fuel was carried out. Using the thermogravimetric method at three different heating rates in air flow, the temperature intervals of the main stages included in the combustion process are established, and typical combustion characteristics are determined. By applying the scanning electron microscopy method, a qualitative analysis of the fuel particle surfaces for the presence of pores, cracks, and channels was carried out. Using the curve crossing method, the coke residue ignition and burnout temperatures were determined. The average ignition and burnout and burnout temperatures were found to be 466°C and 685°C, respectively. Based on the mass loss curve profiles, the percentage reduction in the fuel mass at all stages of the combustion process was determined. Proceeding from the mass variation rate curve profiles, the maximum reaction rate was established for all heating rates. By using differential scanning calorimetry, the endothermic and exothermic effects at different heating rates were established, and the maximum heat flux intensity was determined. The obtained results are recommended to be used in designing the generating devices and systems at thermal power facilities. Coke-ash residue with a calorific value of 15.1 MJ/kg and a volatile matter content of 11.8% can be used as a smokeless power generating fuel.

Reconsidering autoignition in the context of modern process safety: Literature review and experimental analysis

Autoignition is regarded as the spontaneous combustion of a fuel without an apparent ignition source. With respect to fires and explosions in the process industries, the autoignition hazard is one that requires management and consideration. Despite the importance of understanding the autoignition hazard, the literature on the topic is often disappointingly sparse and inconsistent. Experimental methods don't adequately represent real-world conditions and are complicated by experimental error, invoking the need for a reconsideration of autoignition as it pertains to process safety. This work utilized the ASTM E659 method to study potential experimental error for the purpose of improving the process safety community's understanding of autoignition phenomena. Of interest to this study were effects of humidity and suspected occurrences of cool flames, two sources of error which have not been fully explained in the literature. For the fuels tested, results show that humidity has only a slight effect on overall autoignition behavior. However, this study's examination of cool flames suggests that they could be a common occurrence in this testing method. Analysis of these experiments show that cool flames can feature significant exothermic effects and are thus of concern from a perspective of risk management. In addition, this work proposes a novel criterion for a more conservative assessment of autoignition experiments, which results in less subjectivity of analysis.

STUDY OF THE HEAT OF DEHYDRATION OF D–FRUCTOSE SOLUTION

The heat of evaporation of water is the main component of the consumption during the drying of bio raw materials. Its share in the consumption depends not only on the initial moisture content of the drying object. As our previous studies have shown, the state of water in the material affects the total heat consumption. The state of water is determined by its chemical composition and structure. Drying objects rich in sugars deserve special attention. Sugars have a high tendency to hydration, are concentrated in the juice and determine both the kinetics and heat of dehydration. The most reliable data on glucose and fructose hydration are analyzed and presented. Measurement of the specific heat of evaporation of water r from fructose solutions with an initial concentration of 12.5 wt. % was performed in the evaporation calorimeter. Continuous registration of changes in heat flows and mass of the sample was ensured during the measurement process. The dependence of the reduced specific heat of evaporation of water (R = r/rtab) on the concentration of fructose was obtained in the isothermal mode at 40, 60 and 80 °C. The presented curves reflect the thermal processes occurring in the solution during water removal. The processes are characterized by an endothermic period of dehydration and an exothermic period of simultaneous dehydration and spontaneous homogeneous crystallization of fructose. It was found that the change in the degree of hydration of fructose in solution from 12.5 to 5 mol/mol occurs with increasing, almost linear, specific heat consumption. Removal of water from the first coordination sphere, when the degree of hydration decreases to values <5, the increase in specific heat of evaporation is steeper and reaches the excess over the tabular values of heat of evaporation of pure water rtab by 6 – 7 %. The heat of spontaneous crystallization of fructose has a power greater than the power of endothermic heat consumption for dehydration, therefore, a general exothermic effect is recorded. It is shown that the measured specific heat of water evaporation increases with increasing concentration of solutions despite a decrease in the degree of hydration of fructose. It was established that water has a strong hydrogen bond with sugar in solutions in which the degree of hydration of fructose is less than ~5. Assumptions about strongly and weakly bound hydrated water in solutions of monosaccharides are substantiated.

Thermicity of the Decomposition of Oxygen Functional Groups on Cellulose-Derived Chars.

The evolution of oxygen functional groups (OFGs) and the associated thermic effects upon heat treatment up to 800 °C were investigated experimentally as well as by theoretical calculations. A synthetic carbon with a carbonaceous structure close to that of natural chars, yet mineral-free, was derived from cellulose and oxidized by HNO3 vapor at different temperatures and for varied durations in order to generate char samples with different concentrations and distributions of OFGs. The functionalized samples were subjected to calorimetric temperature-programmed desorption measurements in correlation with an extensive effluent gas analysis, thereby focusing on the specific heat effects of individual OFG evolution. Interpretation of the experimental results was aided by density functional theory (DFT) calculations which allowed one to infer the thermal stability of different OFGs and the reaction energy associated with their evolution upon heating. Results showed that, with increasing temperature, H2O was released due to the loss of physisorbed water, the decomposition of clusters bound to carboxylic acids, and condensation reactions. The associated heat uptake amounted to about 100 kJ mol-1. Contrarily, the release of CO2, attributed to the decomposition of condensed acids, carboxylic acids, anhydrides, and lactones, resulted in a heat release of about 40 kJ mol-1. The most strongly pronounced thermic effects were detected for the release of CO, comprising highly exothermic effects due to the decomposition of condensed acids and carbonyls/quinones as well as endothermic effects attributed to anhydrides and phenols/ethers. Notably, anhydrides can be formed during the oxidative treatment as well as during heating by condensation of adjacent carboxylic acids. In the latter case, the two-step decomposition is overall highly exothermic, indicating the associated occurrence of pronounced carbon matrix rearrangements. DFT investigations suggest that these rearrangements not only affect the immediate OFG proximity but also involve several carbon sheets.

Use of Industrial Waste in the Development of Ceramic Mass Compositions

The compositions of ceramic masses for facing slabs based on Angren secondary kaolin and clay were developed, using metallurgical waste–iron–containing dust from the gas cleaning of “Uzmetkombinat” JSC and sandy waste from the Toytepe fluorite enrichment plant. With the help of differential thermal and X–ray phase analysis, the chemical–mineralogical compositions, exothermic and endothermic effects of the used components of ceramic masses were determined during their heat treatment. Thus, the suitability of using these wastes for the development of the composition of ceramic masses has been established.

Debinding of additively manufactured parts from spinel powders with particle sizes below 200 nm

The widespread application of additive manufacturing in ceramics is still hindered by recurrent cracking issues during debinding. To date, the various strategies that have been attempted to reduce this problem often fail upon particle size reduction. Indeed, a reduction in particle size affects the diffusion rates (e.g. pore network) such that even slow heating rates and long dwell times during debinding may not prevent crack formation. In this study, the analysis of the curing and debinding behavior of magnesium aluminate spinel in different acrylates and one methacrylate was performed. Crack formation was analyzed by combining thermal effects with FTIR and dilatometry data. The strategy to reduce exothermal effects through the addition of propylene carbonate (i.e. non-reactive diluent) was evaluated.

Multi-signal information increment sensing system for point-of-care testing of NADH based on cobalt oxyhydroxide nanoflakes

Herein, an innovative multi-signal information increment sensor was proposed to achieve sensitive and immediate detection of NADH (POCT) by measuring a series of values such as pressure, temperature and weight without the need for complex instrumentation. Hydrogen peroxide (H 2 O 2 ) can be decomposed to O 2 by cobalt hydroxide (CoOOH) nanosheets in a sealed bottle, accompanied by a significant pressure and a significant temperature increase due to the exothermic effect of the reaction (ΔH = -98.2 kJ/mol). The increase in pressure forces a certain amount of H 2 O to spill out from the drainage bottle into the water collection bottle pre-filled with ammonium chloride (NH 4 Cl), resulting in a significant decrease in the bottle temperature due to the good heat absorption effect of NH 4 Cl (ΔH=14.8 kJ/mol). In contrast, NADH can significantly inhibit the catalytic activity of CoOOH and a significant decrease in the pressure, overflow water weight, and temperature response was observed. The changes in response signal can be easily obtained by barometer, electronic balance and thermometer. Importantly, signal amplification is achieved by coupled superposition of incremental and decremental temperature signals to improve the sensitivity of the platform. The obtained barometric pressure difference, temperature difference, weight change and NADH concentration showed good linearity. With a linearity range of 0.9-19 mg mL –1 and a sensor detection limit of 0.26 mg mL –1 NADH, the quantification results of this multi-signal sensor were consistent with those of High-Performance Liquid Chromatography (HPLC).

The Role of Graphene Oxide in the Exothermic Mechanism of Al/CuO Nanocomposites.

Metastable intermixed composites (MICs) have received increasing attention in the field of energy materials in recent years due to their high energy and good combustion performance. The exploration of ways of improving their potential release of heat is still underway. In this study, Al-CuO/graphene oxide (GO) nanocomposites were prepared using a combination of the self-assembly and in-suit synthesis methods. The formulation and experimental conditions were also optimized to maximize the exothermic heat. The DSC analysis shows that the addition of the GO made a significant contribution to the exothermic effect of the nanothermite. Compared with the Al-CuO nanothermite, the exothermic heat of the Al-CuO/GO nanocomposites increase by 306.9-1166.3 J/g and the peak temperatures dropped by 7.9-26.4 °C with different GO content. The reaction mechanism of the nanocomposite was investigated using a DSC and thermal reaction kinetics analysis. It was found that, compared with typical thermite reactions, the addition of the GO changed the reaction pathway of the nanothermite. The reaction products included CuAlO2. Moreover, the combustion properties of nanocomposite were investigated. This work reveals the unique mechanism of GO in thermite reactions, which may promote the application of carbon materials in nanothermite.

Inhibiting Effects of Inhibitors on Different Temperature Oxidation of Sulfide Ores

ABSTRACT To control spontaneous combustion of sulfide ores, the compound inhibitor was prepared by selecting physical resistance raw materials(Na2CO3), chemical resistance raw materials(Melatonin), Cetyltrimethylammonium bromide(CTMAB) and hydroxyethyl cellulose(HEC). With the help of the simultaneous thermal analyzer, different concentrations of inhibitors were prepared and the thermal behavior of the ore samples with 10, 15, and 20 wt% inhibitor at four heating rates of 5, 10, 15, and 20 K/min was determined. The Flynn-Wall-Ozawa method was applied to calculate the activation energy of sulfide ores with different concentrations. The results showed that: Gradually increasing the heating rate will increase the reaction intensity of each ore sample in the first weight loss stage of thermal decomposition, and then reduce the mass of the ore samples involved in the second weight loss stage; The thermal stability of each resisted ore sample is better than that of the original ore sample; The increase in the concentration of inhibitor can inert the reaction process of ore samples in the thermal decomposition stage, weakening the exothermic effect of ore samples; The inhibitor with 15 wt% had a better effect on preventing spontaneous combustion of sulfide ores, and its property value is higher than other concentrations.

Enhancement of Thermoelectric Performance of Donor-Doped ZnO Ceramics by Involving an In Situ Aluminothermic Reaction during Processing

This work explores the possibility of involving aluminothermy in processing donor-doped zinc oxide-based thermoelectrics by relying on local, strong exothermic effects developed during sintering, with a potential positive impact on the electrical and thermal transport properties. The strategy was exemplified by using aluminium as a dopant, due to its recognized ability to generate additional, available charge carriers in ZnO, and by using two different metallic Al powders and conventional Al2O3 as precursors. Nanosized aluminium powder was involved in order to evaluate the possible desirable effects of the particles size, as compared to aluminium micropowder. A significant enhancement of the electrical and thermoelectric performance of the samples prepared via metallic Al precursors was observed and discussed in terms of the potential impacts provided by the aluminothermic reaction on the microstructure, charge carrier concentration and mobility during sintering. Although the presented results are the first to show evidence of how aluminothermic reactions can be used for boosting the thermoelectric performance of zinc oxide materials, the detailed mechanisms behind the observed enhancements are yet to be understood.