Exothermic Transformation Research Articles

Parameters of High-Voltage Electrochemical Explosion under Controlled Electrical Energy Supply

Under controlled electrical energy supply into the discharge channel of a high-voltage electrochemical explosion (HVECHE), the efficiency of exothermic reactions occurring in it was studied experimentally. The major factors that affect the efficiency of exothermic transformations in the discharge channel and that determine the HVECHE integral energy parameters in conditions of a controlled electrical energy supply were considered. The efficiency of the exothermic reactions occurring in the HVECHE discharge channel with electrical energy-controlled supply was first justified to determine, along with two electrophysical values (the electrical field intensity in the HVECHE discharge gap and specific electrical energy), the overall energy of the pulse current generator and the exothermic mass composition. It was established that the rational choice of the specific current energy, the modes of the energy supply, and mass of the exothermic composition makes it possible to increase the efficiency of the exothermic transformations in the HVECHE discharge channel by more than 2.5 times compared to the traditional energy supply.

Control of a high-voltage discharge-pulse installation when implementing technological modes of an electrochemical explosion

Studying the high-voltage electrochemical explosion as a control object has established a significant impact exerted by the modes of controlled energy input into a discharge channel on the efficiency of exothermal energy conversion. Dependence has been derived of the specific energy efficiency of the release of chemical energy by an exothermic mixture on the distribution of the total introduced electrical energy among successive discharge pulses. This has made it possible, based on the rules proposed here, to determine the initial conditions for the control algorithm of a discharge-pulse installation, which implements the high-voltage electrochemical explosion technological modes, providing maximum effectiveness of exothermal transformations.It has been shown that the considerable stochasticity of processes during exothermal transformations under a mode of explosive combustion does not make it possible to use control systems that regulate only the initial conditions for an electrochemical explosion. Such systems do not ensure the preset discharge modes at each implementation. The need for ongoing control over the process of exothermal transformations has been substantiated, in order to prevent the reduction of pressure in a discharge channel below the allowable value that maintains the exothermic reaction of explosive combustion. The performed correlation analysis of the relationship between the values of current pressure in a discharge channel and the discharge electrical characteristics has revealed that there is a dense enough information interrelation between them. Therefore, it has been proposed to use, as the information signals that indirectly determine the pressure in a discharge channel, the operationally defined electrical characteristics of a discharge.An algorithm has been built and a system has been developed to control a high-voltage discharge-pulse installation that implements a high-voltage electrochemical explosion. Control over the mode of energy input in the process of explosive transformation makes it possible to avoid the extinction of the exothermal reaction at an accidental, due to the stochasticity of the process, reduction in pressure to the maximum allowable value in the period between the discharge pulses. Due to this, the unproductive losses of an exothermic mixture are eliminated, the losses of chemical and electrical energy are reduced, and the amount of total energy released is increased, without increasing the introduced electric energy, at each implementation of a high-voltage electrochemical explosion

Development of theoretical foundations for the hot metal desulfurization with magnesium reduced by the heat from exothermal transformations

The process of hot metal desulfurization by magnesium, reduced by the heat from exothermic reactions, has been investigated. Our research into the thermodynamics of magnesium oxide reduction in line with various protocols has established that it is in principle possible to reduce magnesium oxide by carbon, silicon, manganese, iron, and aluminum. We have calculated starting temperatures for MgO reduction by iron, manganese, silicon, aluminum, and carbon, which are 2,956, 2,546, 2,313, 1,585 and 1,875 °C, respectively. It has been determined that the most rational method to reduce magnesium oxide is the process based on binding the products of reduction into a CaAl 2 O 4 compound. Based on the established rational conditions for magnesium oxide reduction, the exothermic mixture for hot metal desulfurization was calculated, %: MgO – 15.0; FeO – 56.0; CaO – 7.0; Al – 22.0. Experimental study has confirmed the most successful technical solution for the introduction of the calculated exothermic mixture to the melt aimed at desulfurization, which implies the application of a device for the introduction of active reagents into the melt, which is equipped with a chamber that collapses under the influence of the heat of liquid hot metal. Its use makes it possible to achieve the mean level of desulfurization of 65–70 %. We have performed, under industrial conditions, an experimental desulfurization of chromium hot metal using the designed exothermic mixture. According to the research conducted, the achieved degree of hot metal desulfurization in a ladle was at the level of 38 %; for the material of castings ‒ at the level of 45.7 %. Thus, there is a reason to argue about resource and energy savings when applying the proposed technology for the out-of-furnace hot metal desulfurization by reduced magnesium

Dysprosium Chlorocyanoanilate-Based 2D-Layered Coordination Polymers.

A series of two-dimensional (2D)-layered coordination polymers (CPs) based on the heterosubstituted anilate ligand ClCNAn2- derived from 3-chloro-6-cyano-2,5-dihydroxybenzoquinone and DyIII are reported. By changes in the synthetic methods (layering technique, solvothermal or conventional one-pot reactions) and conditions (solvent, concentration, etc.), different types of 2D extended networks could be prepared and structurally characterized. Compounds 1 and 1', two polymorphs with the formula [Dy2(ClCNAn)3(DMSO)6]n·(H2O)x [x = 7 (1), 0 (1')], were prepared by a conventional one-pot reaction and recrystallized at different concentrations. Compound 2, formulated as [Dy2(ClCNAn)3(DMF)6]n, was prepared by a layering technique, while compound 3, formulated as {(Me2NH2)2[Dy2(ClCNAn)4(H2O)2]·(DMF)2·(H2O)5}n, was obtained by a solvothermal method. Compounds 1 and 2 are neutral 2D CPs of the ClCNAn2- ligand and DyIII ions, while 3 presents 2D anionic layers of [Dy2(ClCNAn)4(H2O)2]2- alternating with cationic layers of Me2NH2+ ions. These compounds show very diverse networks, with compound 1 forming 2D (8,3) and (4,3) topology with eight- and four-membered rings with square cavities, 1' and 2, respectively, a 2D (6,3) topology with six-membered rings (a rectangular cavity for 1' and a regular hexagonal cavity for 2), and 3 a 2D (4,4) topology with distorted square cavities. In this respect, 1 and 1' represent the first examples of polymorphism in the family of anilate-based CPs. Thermal analysis measurements (differential scanning calorimetry and thermogravimetry) show an exothermic polymorphic transformation from the kinetically stable 1' phase to the thermodynamically stable phase 1. The magnetic behavior of 1-3 very likely indicates depopulation of the mJ levels, while the presence of weak antiferromagnetic coupling between the DyIII centers mediated by the anilate bridge cannot be excluded.

Polymorphism with Conformational Isomerism and Incomplete Crystallization in Solid Ethanolamine

We employ calorimetry, Rietveld refinement of X-ray powder diffraction, broadband dielectric spectroscopy, and molecular dynamics simulations to investigate the phase behavior, crystal structure, dc conductivity, and dielectric response of the condensed phases of ethanolamine (EAM), an ethane derivative with two distinct hydrogen-bonding groups. EAM is found to exhibit, besides its stable crystal phase, a metastable crystalline phase obtained from the supercooled liquid. The metastable phase can only be maintained at low temperature; upon heating, an irreversible exothermic transformation to the stable crystal structure takes place at 210 K, with a low transition enthalpy of ca. 2.4 J/g. The observed polymorphism is accompanied by differences in the molecular conformation and degree of structural order. Each EAM molecule participates in six hydrogen bonds in both crystalline phases. While the stable phase is fully ordered, the metastable phase appears to be characterized by a statistical disorder in the p...

Adiabatic Heating of Austenitic Stainless Steels at Different Strain Rates

This work focuses on the effect of strain rate on the mechanical response and adiabatic heating of two austenitic stainless steels. Tensile tests were carried out over a wide range of strain rates from quasi-static to dynamic conditions, using a hydraulic load frame and a device that allowed testing at intermediate strain rates. The full-field strains of the deforming specimens were obtained with digital image correlation, while the full field temperatures were measured with infrared thermography. The image acquisition for the strain and temperature images was synchronized to calculate the Taylor–Quinney coefficient (β). The Taylor–Quinney coefficient of both materials is below 0.9 for all the investigated strain rates. The metastable AISI 301 steel undergoes an exothermic phase transformation from austenite to α’-martensite during the deformation, which results in a higher value of β at any given strain, compared to the value obtained for the more stable AISI 316 steel at the same strain rate. For the metastable 301 steel, the value of β with respect to strain depends strongly on the strain rate. At strain rate of 85 s−1, the β factor increases from 0.69 to 0.82 throughout uniform elongation. At strain rate of 10−1 s−1, however, β increases during uniform deformation from 0.71 to a maximum of 0.95 and then decreases to 0.91 at the start of necking.

Microstructure and mechanical behavior of Al92Fe3Cr2X3 (X = Ce, Mn, Ti, and V) alloys processed by centrifugal force casting

Microstructural and mechanical characterization of Al92Fe3Cr2X3 (X=Ce, Mn, Ti, and V) alloys were performed. The alloys were processed by a method that uses centrifugal force to cast the samples into a rotating copper mold. Microstructural characterization was carried out by means of x-ray diffraction, scanning electron microscopy, and differential scanning calorimetry. Compressive tests at room and at 300°C were performed in selected samples to evaluate their mechanical properties. Microstructural characterization showed the formation of quasicrystalline phases as well as other intermetallic phases embedded within an Al-FCC matrix. The Ce-containing alloy exhibited promising results regarding quasicrystalline phase formation and stability as well as with respect to its mechanical properties at high temperatures. The quasicrystalline phase of this alloy appears to be stable up to 545°C when the DSC reveals an exothermic transformation. In addition, the presence of a eutectic structure surrounding the Al-FCC grains enhanced the mechanical strength of this alloy. At 300°C, the Ce-containing alloy showed yield strength and ultimate tensile strength of 180MPa and 360MPa, respectively. If compared to a commercial aluminum alloy 2024 at the T6 condition, close to 300°C, the alloy studied here showed an increase of more than 4 times in the yield strength, and almost 7 times in the ultimate tensile strength. The high thermal stability and mechanical properties at high temperatures of this alloy open interesting possibilities for further studies and future applications of this Al-Fe-Cr-Ce alloy.

Modeling and thermodynamic properties of soybean cultivar BRS257 hydration

AbstractThe hydration kinetics were carried out at 30, 40, 50 and 60°C for 510 min. The maximum absorption (389%) was obtained at 50°C after 8 hr and the equilibrium moisture (62.26%) after only 3 hr. The diffusion model exhibited a good fit with to the experimental data R2 > 0.98, p < 4.94% and Def ranged from 0.71 to 2.75 × 10−9 m2/s, demonstrating the dependence of this parameter on temperature. The hydration experiments with colorants indicated a greater water absorption by diffusion at 100 min, the colorant solution reached the center of the grain at 290 min and the equilibrium moisture at 510 min. The SEM analysis showed changes in the conformation of the cells and protein networks. The thermodynamics properties demonstrated that the soybean hydration is associated with exothermic transformations, non spontaneous, temperature sensitive and does not result in a significant increase in the disorder of the system.Practical applicationsThe approach presented in this paper is useful for describing the kinetics and the regime of water absorption during hydration. The mathematical modeling and the study of the mechanism of the water absorption by diffusion, shows new approaches to the development of hydration models, contributing to the development and optimization of the industrial process.

From new geological paradigm to the problems of regional geological-geophysical survey

Analysis of the latest scientific achievements in different areas of geological and geophysical research showed that investigation of deep Earth degassing from its core up to the surface and atmosphere acquires status of the mainstream in the Earth sciences. Of great fundamental and applied significance is identification of the most energetically active and powerful sub-vertical upward degassing processes, which generate trans-geosphere and cross-formational systems and are localized in the form of a hierarchy of different-sized degassing pipes — from the base plume to the elementary near-surface channel. Existence of this system is ensured by a series of successive exothermic transformations of elementary recovered gases into oxide substances. As a result of given chemical reactions these substances consistently receive new portions of energy sufficient for the gradual upward breakthrough of the mantle and crust internal substance. Interpretation of mantle plumes as the basic degassing mega-tubes allows us to unite the main aspects of endogenous ore formation, naphtidogenesis in the lithosphere and ecological processes in the earth’s crust and atmosphere. The cross-formational systems serve as the structural-geological basis of degassing pipes. Given systems are the basic concentrates of the naphtides upward migration and accumulation in the multi-layered deposits. The relationship between diapirism and mega-plumes derivatives — degassing pipes becomes increasingly clear. The degassing energy is the main factor of diapirism. The locations of possible anomalous degassing in Ukraine were identified based on the analysis of geophysical and other signs of modern activation. An assumption is made of possible commercial production of natural hydrogen in some of these locations. Ecological risks of deep Earth degassing, in particular, catastrophic degassing through super volcanoes are considered. Possible directions of counteraction against these risks with the help of purposeful efforts of the progressive humanity are also discussed. There is a need to revise the strategy and methodology of further development of geological and geophysical researches in general and, in particular, the major applied research areas, such as complex geological survey, mapping, prospecting of mineral resources and geo-ecology.

FEATURES OF THE FORMATION OF STEEL-ALUMINUM COMPOSITE MATERIAL STRUCTURE

The initiation of the process of decreasing the solubility of Fe in the direction of Al comes from the structural state of iron at the time of the exothermic phase transformation in the interval 450-550 ° C. Experimental curves for the thermal analysis of steel St0 have been constructed. Correlation of the eff ects between the heating rate function and the diff erential thermal analysis plot is established. According to the data obtained the thermal parameters of materials with an unconventional approach to research are more pronounced. In the compound of technical iron (C

Propagation of Cellular Modes of Combustion of Porous Media under Nonadiabatic Conditions

The formation and propagation of cellular combustion of porous media under near-critical combustion existence conditions were investigated. The sizes and structure of cells in which the condensed component reacted with the gas depended nonlinearly on the heat loss to the environment. With increasing heat loss, the oscillation frequency of the cellular front, its average propagation velocity, and the intensity of the exothermic transformation of the condensed phase increased, and the cell sizes decreased. Cellular combustion was extinguished only when the transformation of the condensed component within a cell was completed.

Kinetics of isochronal crystallization in a Fe-based amorphous alloy

In this paper, the kinetics of isochronal differential scanning calorimetry of Fe48Cr15Mo14Y2C15B6 amorphous alloy was analyzed to understand the mechanism of crystallization. The crystallization process constituted of overlapping exothermic transformations occurring from 900 to 1100 K with activation energies from 369 to 437 kJmol−1. Analysis of the mechanism of crystallization under the theoretical framework of the Johnson-Mehl-Avrami-Kolmogorov model revealed that these transformations occurred by three-dimensional growth with either a decreasing nucleation rate or from nuclei that have already been formed. A comparison of the kinetic parameters of nucleation and growth of this alloy with that of Fe50Cr15Mo14C15B6 amorphous alloy showed the effect of yttrium on the increase of thermal stability and impediment of atomic diffusivity leading to decreased nucleation rate in the alloy.

Alternating-Magnetic-Field-Mediated Wireless Manipulations of a Liquid Metal for Therapeutic Bioengineering

SummaryAs emergent multifunctional materials, room temperature liquid metals (LMs) display many unique properties. Here we show that applying an external alternating magnetic field (AMF) to an LM induces various physical phenomena, such as exothermic behavior, controlled locomotion, electromagnetic levitation, and transformations of the LMs between different morphologies and configurations, in a non-contact manner. Additional interesting therapeutic bioengineering applications of LMs demonstrated herein include in vitro and in vivo effective cancer magnetic hyperthermia via wireless AMF, remote manipulation of a pill-shaped microdevice based on an LM/hydrogel composite, and spatiotemporal controlled release of drug molecules from the microdevice. Overall, as an innovative therapeutic bioengineering technology, this platform and the described performance traits of LMs enable the development of biocompatible smart devices with a wide range of dynamic components that can be wirelessly controlled in a manner that solves issues related to the powering of devices and biocompatibility.

Thermomechanical Studies of Yielding and Strain Localization Phenomena of Gum Metal under Tension.

This paper presents results of investigation of multifunctional β-Ti alloy Gum Metal subjected to tension at various strain rates. Digital image correlation was used to determine strain distributions and stress-strain curves, while infrared camera allowed for us to obtain the related temperature characteristics of the specimen during deformation. The mechanical curves completed by the temperature changes were applied to analyze the subsequent stages of the alloy loading. Elastic limit, recoverable strain, and development of the strain localization were studied. It was found that the maximal drop in temperature, which corresponds to the yield limit of solid materials, was referred to a significantly lower strain value in the case of Gum Metal in contrast to its large recoverable strain. The temperature increase proves a dissipative character of the process and is related to presence of ω and α″ phases induced during the alloy fabrication and their exothermic phase transformations activated under loading. During plastic deformation, both the strain and temperature distributions demonstrate that strain localization for higher strain rates starts nucleating just after the yield limit leading to specimen necking and rupture. Macroscopically, it is exhibited as softening of the stress-strain curve in contrast to the strain hardening observed at lower strain rates.

Review of Ayurvedic herbs with Kesharanjana Property in the Management of Caniites (Palitya)

Greying of hair according to age is common phenomenon. But in modern era due to different kind of stress and changing life style Canities (Palitya) occur in early age. According to W.H.O in India, its incidence is high in the age group of 20-30 years. In Ayurveda premature greying of hair is called as Akala palitya (premature gray hair). According to Ayurveda grey hair is mainly due to the vitiation of Pitta dosha (biological entity related to exothermic reactions or transformation) & reference of Palitya is directly mentioned only in Pitta Prakruti (inherent constitution of an individual). The use of purification procedures of panchakarma (detoxifying therapy) has prime importance in the remedies mentioned for premature greying. Nasya karma (nasal medication) is one of the major rejuvenative treatments. Palliative external & internal medicaments measures like Shiro dhara (pouring oil on head), Shoro pichu (cloth dipped in oil kept on head), Shiro basti (oil is kept on head with an apparatus), Shiro lepa (application of medicated paste over head), Shiro abhyanga (oil massage to head) helps in speedy recovery. The chemical components in the herbs responsible for hair dyeing are discussed

Quasi-Hydrostatic Model of the Combustion of Compositions Forming Molten Reaction Products in the Presence of Centrifugal Forces

A mathematical model of the exothermic chemical transformation of a high-calorie mixture in the presence of centrifugal forces is considered. The process is studied for the 3NiO + (2 + α)Al → Al2O3 + (3 − α)Ni + αNiAl thermite composition, as an example. Such processes are used in high-temperature synthesis for the production of target products in the combustion wave propagating through the initial mixture. This technological process represents a combination of high-temperature combustion with the formation of liquid products, their separation, and subsequent cooling. A distinctive feature of the proposed model is the use of a “through” description, which makes it possible to examine the mutual influence of the individual stages on the dynamics of the process. This feature provides a more realistic description of the actual process.

О возникновении пожаров в лесах из-за возгорания лесного опада

Fires in forests cause great environmental damage to our country due to loss of wood, destruction and damage to residential and industrial buildings and structures. Often fires in forests are accompanied by death of people. Large fires affect the pollution of the atmosphere, climate change in a certain area, generally have a negative impact on the environment of the affected regions, increase incidence and mortality rates of the population, create social tension in society. The paper analyzes the causes of anthropogenic and natural origin of fires. The main attention is paid to the conditions of spontaneous combustion of forest litter (litter) in coniferous forests, which can occur under certain conditions, even in winter, after snowfall. A physicochemical justification for the process of spontaneous combustion of forest litter is presented, and corresponding thermophysical calculations are made. It is shown that in the layer of litter of a certain thickness, a process of self-heating takes place and an increase in temperature due to an exothermic reaction, because of which the temperature rises in the litter - up to the temperature of spontaneous combustion. Such a picture will be observed until a certain self-heating temperature is reached at which the exothermic transformations in the material (decomposition, oxidation) begin, leading to self-heating of the material. When a certain temperature is reached, selfignition of the forest litter may occur. Specific examples of spontaneous combustion of forest litter in coniferous forests of the Voronezh region in the beginning of winter under a layer of snow and possible causes of spontaneous combustion of coniferous litter in forests during the summer are considered. It is shown that the process of spontaneous combustion can occur when certain climatic conditions are combined, as well as factors such as thickness, humidity and dispersed state, and the thermophysical characteristics of the litter, temperature and mobility of the atmosphere. Based on the solution of the equation of non-stationary Fourier thermal conductivity with an internal heat source, it is planned to determine the conditions for heat exchange on the surface and the thickness of the fallen layer of litter, in which a selfignition process may occur.

Thermally induced metallurgical processes in Cr3C2-NiCr thermal spray coatings as a function of carbide dissolution

Cr3C2-NiCr thermal spray coatings are widely used to mitigate wear and corrosion at high temperatures. The aim of this work was to determine what minimum treatment temperature is required to transform the non-equilibrium as–sprayed coating composition back to an equilibrium composition, with the aim to improve the wear resistance. Cr3C2-NiCr coatings were sprayed using two HVOF techniques and a shrouded plasma spraying technique to produce samples with a broad spectrum of carbide dissolution and peritectic decomposition of Cr3C2. Shrouded plasma spraying was found to be highly effective in decreasing the carbon loss and the oxygen uptake. Differential scanning calorimetry (DSC) was used to characterize the exothermic solid-state phase transformations within the coatings. For the HVOF coatings, one main exothermic peak was observed, which was attributed to the crystallization of the metastable Ni binder material. In the plasma spray coating an additional higher temperature peak was also observed. This was attributed to the transformation of (Cr,Ni)7C3 and a high Cr content Ni phase, into the equilibrium phases Cr3C2 and a low Cr content Ni binder.

Phase-transformation-induced lubrication of earthquake sliding.

Frictional failure is not possible at depth in Earth, hence earthquakes deeper than 30-50 km cannot initiate by overcoming dry friction. Moreover, the frequency distribution of earthquakes with depth is bimodal, suggesting another change of mechanism at about 350 km. Here I suggest that the change at 30-50 km is from overcoming dry friction to reduction of effective stress by dehydration embrittlement and that the change at 350 km is due to desiccation of slabs and initiation by phase-transformation-induced faulting. High-speed friction experiments at low pressure indicate that exceeding dry friction provokes shear heating that leads to endothermic reactions and pronounced weakening. Higher-pressure studies show nanocrystalline gouge accompanying dehydration and the highest pressure experiments initiate by exothermic polymorphic phase transformation. Here I discuss the characteristic nanostructures of experiments on high-speed friction and high-pressure faulting and show that all simulated earthquake systems yield very weak transformation-induced lubrication, most commonly nanometric gouge or melt. I also show that phase-transformation-induced faulting of olivine to spinel can propagate into material previously transformed to spinel, apparently by triggering melting analogous to high-speed friction studies at low pressure. These experiments taken as a whole suggest that earthquakes at all depths slide at low frictional resistance by a self-healing pulse mechanism with rapid strength recovery.This article is part of the themed issue 'Faulting, friction and weakening: from slow to fast motion'.

Modeling the hydration step of the rice (Oryza sativa) parboiling process

This work deals with the thermal, morphological, and kinetic characteristics of rice during hydration, as well as the modeling of the process. Rice grains were subjected to different hydrothermal conditions and showed no degradation, but presented an endothermic transition corresponding to gelatinization at 53.8 °C. During hydration, the water absorption rate increased with temperature and grain morphological changes were observed only after gelatinization. There was a good agreement between the predictions of the theoretical model based on Fick’s second law and the experimental results (maximum error of 2.067%); the phenomenological model built numerically was able to represent (3D and 2D) moisture transfer into the grain with an error of 1.708%. The parameters adjusted to the different models confirmed the effect of temperature on the process, and the thermodynamic properties (enthalpy, entropy, and Gibbs free energy) determined showed that hydration happened with non-spontaneous exothermic transformations.