Intense Chemical Reactions Research Articles

CMAS corrosion characteristics of YSZ and Al2O3-YSZ thermal barrier coatings at 1250 °C–1350 °C

The calcium-magnesium-aluminum-silicate (CMAS) corrosion is now a great threat to thermal barrier coatings (TBCs), inducing coating spallation readily. The CMAS corrosion characteristics of both 7YSZ and 20 wt.%Al2O3-YSZ TBCs at a broad temperature range of 1250 °C to 1350 °C were investigated. 7YSZ coatings were completely degraded by CMAS at 1250 °C while the increased corrosion temperatures induced more serious destruction. This is due to that the viscosity of CMAS melt significantly decreased with corrosion temperature increasing, promoting melt fluidity and infiltration. The Al2O3-YSZ composite TBCs demonstrated superior resistance to CMAS corrosion at 1250°C-1350 °C. The intensive chemical reactions between Al2O3 and CMAS melt promoted the formation of anorthite products with either short rod-shaped or blocky morphologies. These products closely interconnected and stacked up to generate a dense layer, physically blocking CMAS melt infiltration and effectively improving the anti-CMAS corrosion properties of TBCs at higher temperatures. Furthermore, the corrosion temperatures critically influenced anorthite formation and present morphologies.

Ecological aspects in the use of soil enzymes as indicators of anthropogenic soil pollution

In the contemporary era, with rapid industrial growth and urbanisation, analysing the impact of human activities on soil enzyme activity becomes crucial. The purpose of this study is to assess the influence of anthropogenic pollution on enzyme activity in soil. Research on enzyme activity levels in the soil in the city of KaraBalta, Chuy Region, Kyrgyz Republic, was conducted using biochemical analyses and specific enzymatic tests. The results revealed significant diversity in catalase activity in different soil samples. Some samples exhibited high activity, while others showed low activity. These differences may be associated with oxidative stress and the ability of soil microorganisms to decompose hydrogen peroxide. Urease analysis indicated the highest activity in soil samples after 2 hours, particularly near the protective barrier of the tailings pond, suggesting intensive chemical reactions, especially near pollution sources. Research has also revealed the diversity of protease activity in soil ecosystems, where samples with high activity may more effectively break down proteins compared to samples with low activity. To achieve ecological stability of soil resources, it is necessary to develop a management strategy, including monitoring and restoring priority areas considering local characteristics, supporting biodiversity, applying sustainable agricultural methods, and combating soil erosion. Important steps also include forming a community emphasising the importance of soil resources, funding research, and collaborating with local authorities, scientists, and the business community. The results of the study can be used in developing strategies to prevent the negative consequences of soil pollution, contributing to improved ecological resilience, especially for environmental protection agencies

Types of Component Interfaces in Metal Matrix Composites on the Example of Magnesium Matrix Composites.

In this paper, a summary of investigations of the microstructure of cast magnesium matrix composites is presented. Analyses of the interfaces between the reinforcing particles and the magnesium alloy matrices were performed. Technically pure magnesium and four various alloys with aluminum and rare earth elements (RE) were chosen as the matrix. The composites were reinforced with SiC and Ti particles, as well as hollow aluminosilicate cenospheres. Microstructure analyses were carried out by light, scanning, and transmission electron microscopy. The composites with the matrix of magnesium and magnesium–aluminum alloys with SiC and Ti particles exhibited coherent interfaces between the components. In the composites based on ternary magnesium alloy with Al and RE with Ti particles, a high-melting Al2RE phase nucleated on the titanium. Different types of interfaces between the components were observed in the composites based on the magnesium–rare earth elements alloy with SiC particles, in which a chemical reaction between the components caused formation of the Re3Si2 phase. Intensive chemical reactions between the components were also observed in the composites with aluminosilicate cenospheres. Additionally, the influence of coatings created on the aluminosilicate cenospheres on the bond with the magnesium matrix was presented. A scheme of the types of interfaces between the components is proposed.

Influence of Forest Combustible Material on the Characteristics and Conditions of Ignition of Bio-coal Water Fuels

ABSTRACT The results of the experimental studies of the particles ignition of bio-coal water fuels have been presented. The experiments have been carried out on the setup providing an error level of not more than 6.1% of the main recorded characteristics. The effect of the temperature of the oxidizing agent and the characteristic size of the fuel drops on the duration of the induction period of the fuel compositions has been studied. It has been established that the introduction of the additives from forest combustible materials of three typical tree species leads to an acceleration of the ignition process of substantially flooded particles of bio-coal water fuels. According to the results of a detailed analysis of the frames of the videogram, it has been shown that the duration of the intensive chemical reaction of the gaseous pyrolysis products with a high-temperature oxidizer is not more than 0.02% of the entire induction period. Colloquium. One of the possible promising directions for the development of the coal technologies in the energy sector and for reducing the negative anthropogenic impact of the thermal power plants that burn coal is the use of the composite fuels (coal- water (CWF), organ coal- water, etc.) based on coal. But a number of the technological problems significantly complicate the use of such fuels in the energy sector. This is evidenced by a significant increase (over the past 10 years) in the number of the publications devoted to the problems of carbonic fuels. The ignition process of CWF is quite long (ignition delay time (tign) up to 20 seconds). The use of fuel with such a large induction period in a real practice is practically impossible. One of the possible options for reducing the tign value of the liquid composite fuels is the introduction of biomass into their composition. This is a new composite bio-coal water fuel (Bio-CWF). At present, there are practically no publications devoted to the experimental and theoretical studies of the ignition of Bio -CWF particles under conditions corresponding to the furnaces of the typical boiler units of the thermal power plants. The duration of the characteristic stages of ignition of Bio-CWF particles (made on the basis of coal, water and various types of biomass) is an important characteristic necessary for carrying out the experimental design works on the development of new innovative boiler units burning bio-coal water fuel.

An experimental modelling and performance validation study: Top gas pressure tracking system in a blast furnace using soft computing methods

The blast furnace is a master iron-producing plant of iron and steel factories and affected by several process parameters as well as top gas pressure , which is a key process control phenomenon to maintain stability and operational productivity in such plants. Blast furnace operation is not tolerant to any interruption, unbalanced operations, momentary disturbances or loss of control due to its nature of intensive chemical reactions and heat balance requirements. Consequently, it is crucial to monitor and control top gas system components of the furnace with instrumentation measurements to maintain stable, efficient operation and system safety ongoing. In this study, a novel top gas pressure tracking system is developed using the chronologically obtained live process data of Erdemir BF#2 in Turkey. Eight process parameters are considered as input parameters as per the plant maintenance team's recommendations and soft computing methods, artificial neural networks and adaptive neuro fuzzy inference system are employed and a statistical regression tool, autoregressive integrated moving average, is also applied for comparison. Performance and success ratio analysis is carried out using coefficient of determination ( R2), mean absolute percentage error and root mean squared error terms. The best performing model output for the adaptive neuro fuzzy inference system is found to be 0.95, 1.21 and 0.023, and slightly lower performance is obtained for the artificial neural network model with the output values of 0.94, 0.029 and 1.32 against R2, mean absolute percentage error and root mean squared error terms, respectively. The maximum prediction error is found to be 9.85% and 10.2%, and the average prediction error is found to be 1.19% and 1.29% for adaptive neuro fuzzy inference system and ANN models, respectively, for optimum simulations. The proposed neuro-fuzzy-driven top gas pressure prediction system is unique in the literature and should be integrated into existing control systems to improve operational awareness and sustainability or can be used as input guidance for a possible future top gas recovery system.

How the Physicochemical Properties of the Bulk Material Affect the Ablation Crater Profile, Mass Balance, and Bubble Dynamics During Single-Pulse, Nanosecond Laser Ablation in Water.

Understanding the key steps that drive the laser‐based synthesis of colloids is a prerequisite for learning how to optimize the ablation process in terms of nanoparticle output and functional design of the nanomaterials. Even though many studies focus on cavitation bubble formation using single‐pulse ablation conditions, the ablation efficiency and nanoparticle properties are typically investigated under prolonged ablation conditions with repetition rate lasers. Linking single‐pulse and multiple‐pulse ablation is difficult due to limitations induced by gas formation cross‐effects, which occur on longer timescales and depend on the target materials’ oxidation‐sensitivity. Therefore, this study investigates the ablation and cavitation bubble dynamics under nanosecond, single laser pulse conditions for six different bulk materials (Au, Ag, Cu, Fe, Ti, and Al). Also, the effective threshold fluences, ablation volumes, and penetration depths are quantified for these materials. The thermal and chemical properties of the corresponding bulk materials not only favor the formation of larger spot sizes but also lead to the highest molar ablation efficiencies for low melting materials such as aluminum. Furthermore, the concept of the cavitation bubble growth linked with the oxidation sensitivity of the ablated material is discussed. With this, evidence is provided that intensive chemical reactions occurring during the very early timescale of ablation are significantly enhanced by the bubble collapse.

Femtosecond Laser Processing Structural Surfaces of Zinc anodes for rechargeable zinc-air battery

Researches about renewable rechargeable battery have attracted the attention of many scholars, due to increasing demands of energy and global energy crisis. Zinc-air batteries are one of most promising energy sources, but the morphological changes and forming dendritic of zinc anodes greatly limit their cycle life during the charging-discharging process. In order to improve zinc-air batteries electrochemical performance and control dendritic growth, surface of zinc anodes is irradiated by femtosecond laser with different power. The electrochemical results indicate that zinc anodes of zinc-air batteries with different surface structures show different electrochemical properties. Due to the removing oxide layer on the surface of zinc anode, adding contact areas of zinc anodes and electrolytes, and restraining dendritic growth by femtosecond laser processing, first discharge time of zinc anodes with surface structures of zinc-air batteries is about 10 times than that of without processing. It is also found that more intense chemical reactions occur in the area treated by femtosecond laser.

Preparation of Few-Layer Porous Graphene by a Soft Mechanical Method with a Short Rolling Transfer Process.

Few-layer porous graphene is a promising material for a variety of fields. However, the synthesis of few-layer porous graphene is a great challenge. Here we report a feasible green path to produce few-layer porous graphene, which was exfoliated from high-pressure graphite balls onto microspheres with rough surfaces by a mild rolling transfer process. Ordinary ball milling equipment was adopted for the low-speed (100 rpm) ball-microsphere rolling transfer process. The rolling time (<10 min) was controlled to obtain porous graphene instead of graphene. The porous graphene on the exfoliating microspheres was then easily dispersed in solution by bath sonication. The product contains very few impure functional groups. The hole size and layer distribution of the few-layer porous graphene have been demonstrated to be 2.37±1.17 nm and 2.4±0.7 layers, respectively, and can be adjusted by redesigning the surface of the microspheres.

Marangoni convective nanofluid flow over an electromagnetic actuator in the presence of first‐order chemical reaction

AbstractThe present study aims to investigate Marangoni‐forced convective nanofluid flow over an electromagnetic actuator (Riga plate). A first‐order homogeneous chemical reaction is considered. The thermocapillary and solutocapillary Marangoni effect developed by the surface tension is considered as a driving force for the nanofluid. In addition, Grinberg‐term is accounted to involve the impact of Lorentz force impinged by the actuator in the model. A set of nonlinear ordinary differential equations is obtained via suitable transformations for a nonsimilar analysis. Series solutions are achieved through homotopy to discuss the behavior of the velocity field, thermal distribution, and concentration of the nanoparticles graphically. The variation in Nusselt and Sherwood numbers is discussed. The outcomes declared that the flow parallel to the surface of the plate is assisted by the Lorentz forces generated by electromagnetic bars of the actuator resulting in an enhancement in the fluid motion. Furthermore, the stronger Marangoni effect resulted in the declining trend of the temperature profile. The concentration of nanoparticles near the surface reduced intensive chemical reaction inside the nanofluid.

Molecular Dynamics Simulations of an Initial Chemical Reaction Mechanism of Shocked CL-20 Crystals Containing Nanovoids

To understand the initial chemical reaction mechanism of the heterogeneous explosive hexanitrohexaazaisowurtzitane (CL-20), it is necessary to study the shock initiation mechanism of this nanovoid-containing crystal. In this paper, supercells of CL-20 with different void sizes were constructed. The chemical reactions induced by different impact velocities were calculated using molecular dynamics based on the ReaxFF-lg reactive force field. The effects of impact velocities and void sizes on the chemical reactions of the CL-20 crystal were discussed. The initial reaction of CL-20 molecules around the voids was analyzed, and the evolution of the formation and breakage of chemical bonds as well as the elementary reactions were also obtained. It is found that under an impact, the CL-20 molecules around the voids first undergo polymerization of the N–O bonds and then breakage of the C–N, N–N, and C–H bonds occurs. Increased void size and impact velocity lead to higher temperature “hot spots” and more intense chemical reactions, but have little effect on the breaking sequence of chemical bonds in the CL-20 molecules.

Diamond photochemistry with visible light

This project demonstrates diamond-based photochemistry using visible light. Diamond has the unique property of having a widely tunable electrochemical surface, with hydrogen terminated diamond known to have a negative electron affinity. This property enables the emission of electrons from the surface of the diamond. In this work, electrons are emitted into an aqueous solution, creating a reservoir of free, solvated electrons, that can be used to initiate energy intensive chemical reactions. We demonstrate that visible light incident on thin films of diamond on molybdenum substrates can be used to reduce nitrogen gas to ammonia via the photogenerated electrons.

Optimal Temperature for Human Life Activity

The optimal temperature for the human life activity has been determined, by assuming that this parameter corresponds to the most intensive oxygen transport in arteries and the most intensive chemical reactions in the cells. The oxygen transport is found to be mainly governed by the blood saturation with oxygen and the blood plasma viscosity, with the both parameters depending on the temperature and the acid-base balance in blood. Additional parameters affecting the erythrocyte volume and, accordingly, the temperature of the most intensive oxygen transport are also taken into account. Erythrocytes are assumed to affect the shear viscosity of blood in the same way, as impurity particles change the suspension viscosity. It is shown that theoptimal temperature equals 36.6 ∘C under normal environmental conditions. The dependence of the optimal temperature for the human life activity on the acid-base index is discussed.

Theoretical analysis of lithium‐ion battery failure characteristics under different states of charge

SummaryLithium‐ion batteries (LIBs) are extensively applied in various portable electronic equipment because of their high energy density power. However, accidents related to LIBs frequently occur. This study focuses on failure results, characteristics, and phenomena. Lithium‐ion batteries under different states of charge (SOCs) (0%, 30%, 50%, 80%, 100%, and 120%) at high temperatures have been investigated with the thermal abuse test. During the experiments, several typical failure processes were captured. According to the phenomena, 2 failure modes (smoke and jet fire) and 3 stages (primary reaction, tempestuous reaction in the middle time period, and extinguishing reaction in the final stage) were observed. A substantial amount of gas was vented, and jet fire was detected in the middle period. Only gas vented when the SOC was lower than 50%, whereas vented gas and jet fire were detected simultaneously when the SOC exceeded 50%. The results indicated combustible behaviors and exothermic reactions related to the SOC. An increase in the SOC caused a decrease in the thermal runaway initial temperature and the maximum increase in temperature. A higher SOC determined intense chemical reactions in the cell at higher temperatures, which caused a significant amount of materials to spew out of the batteries as well as additional mass loss. Relationships between failure characteristics and internal reactions were analyzed. The SOC should be lower than 50% in transportation or storage. The intercalated lithium capacities were the main reason for the series of domino reactions, which caused runaway in the terminal. These studies can serve as a reference for safety applications, transportation, and loss prevention in LIBs.

A Comparative Study of the Very Early Age Cement Hydration Monitoring Using Compressive and Shear Mode Smart Aggregates

The load-bearing capacity of concrete is highly influenced by the initial cement hydration process, especially in its very early age (0–48 h). Due to the rapid and intense chemical reactions between the cement and the water in the very early hydration process, it is still a challenge to monitor the cement hydration process in real time. In this paper, we investigated a stress wave-based active sensing method to monitor the cement hydration process using piezoceramic-based transducers, called smart aggregates. Using different types of the embedded piezoceramic patches, including $\text{d}_{33}$ and $\text{d}_{15}$ modes, smart aggregates can function as both the compressive and shear wave transmitters and receivers. In each mode of the smart aggregate, the active sensing approach that uses a pair of smart aggregates, one as a wave transmitter and the other one as a wave receiver, was employed. A comparative study was conducted to investigate the performance of monitoring the very early age cement hydration process by using compressive wave (P-wave) and shear wave (S-wave). A frequency domain analysis of the received signal was performed during the very early age cement hydration process. Experimental results reveal the differences of the received signal strength, valid monitoring period, and the effective frequency range by using both P-wave and S-wave.

Effect of fuel composition and differential diffusion on flame stabilization in reacting syngas jets in turbulent cross-flow

Three-dimensional direct numerical simulation results of a transverse syngas fuel jet in turbulent cross-flow of air are analyzed to study the influence of varying volume fractions of CO relative to H2 in the fuel composition on the near field flame stabilization. The mean flame stabilizes at a similar location for CO-lean and CO-rich cases despite the trend suggested by their laminar flame speed, which is higher for the CO-lean condition. To identify local mixtures having favorable mixture conditions for flame stabilization, explosive zones are defined using a chemical explosive mode timescale. The explosive zones related to flame stabilization are located in relatively low velocity regions. The explosive zones are characterized by excess hydrogen transported solely by differential diffusion, in the absence of intense turbulent mixing or scalar dissipation rate. The conditional averages show that differential diffusion is negatively correlated with turbulent mixing. Moreover, the local turbulent Reynolds number is insufficient to estimate the magnitude of the differential diffusion effect. Alternatively, the Karlovitz number provides a better indicator of the importance of differential diffusion. A comparison of the variations of differential diffusion, turbulent mixing, heat release rate and probability of encountering explosive zones demonstrates that differential diffusion predominantly plays an important role for mixture preparation and initiation of chemical reactions, closely followed by intense chemical reactions sustained by sufficient downstream turbulent mixing. The mechanism by which differential diffusion contributes to mixture preparation is investigated using the Takeno Flame Index. The mean Flame Index, based on the combined fuel species, shows that the overall extent of premixing is not intense in the upstream regions. However, the Flame Index computed based on individual contribution of H2 or CO species reveals that hydrogen contributes significantly to premixing, particularly in explosive zones in the upstream leeward region, i.e. at the preferred flame stabilization location. Therefore, a small amount of H2 diffuses much faster than CO, creating relatively homogeneous mixture pockets depending on the competition with turbulent mixing. These pockets, together with high H2 reactivity, contribute to stabilizing the flame at a consistent location regardless of the CO concentration in the fuel for the present range of DNS conditions.

The role of persistence in chemical evaluations.

The initial stage in the assessment and priority setting of chemicals for their potential to cause harm to humans and the environment is usually a hazard assessment employing metrics for persistence, bioaccumulation, and inherent toxicity. This hazard assessment is followed, when necessary, by the more demanding task of risk assessment. Hazard assessment of data and processes influencing persistence are discussed, leading to a number of suggestions for more effective evaluation. These include 1) an initial focus on accurate data for intensive chemical partitioning and reaction half-life properties that are universally applicable as distinct from extensive properties that can be included later on a location-specific basis; 2) separate treatments of near-field and far-field exposures; 3) a focus on persistence and its effect on levels of exposure, especially for substances for which "time to exposure" is less than "time to degradation" and have been termed "pseudo-persistent." We show that "continuously present" is a better descriptor of this concern. Case studies illustrate and support these suggestions. Data on the intensive properties and on exposure pathways are best combined in evaluative multimedia mass balance models that can provide a clear depiction of the likely chemical fate, exposure routes, and levels. The information generated by the mass balance models can serve to justify and direct a full risk assessment that includes region-specific information on chemical quantities, estimates of exposure, and potential for adverse effects.

Microwave Discharge as an Effective Tool for Surface Treatment of Small Samples

Plasma created in different gases using conventional microwave (MW) discharge is presented. The discharge chamber is a quartz tube mounted into a rectangular waveguide. Standing-wave conditions established in the MW cavity allow for creation of plasma in a small volume. The discharge power up to 1200 W allows for treatment of small samples with rather intense plasma. Samples mounted on sample holders with poor thermal contact with cold materials are heated to elevated temperature that allows for intensive surface chemical reactions. Plasma color depends on the type of gas and impurities released from samples as a result of plasma treatment.

Combustion-assisted plasma in fuel conversion

The long history of plasma application for fuel conversion shows that reasonably low specific energy requirement has been achieved in most cases using non-equilibrium systems with relatively high local temperature (‘warm’ plasmas). Analysis of reasons for this trend presented in this paper indicates that transitional warm plasma discharge systems are optimal for large-scale fuel processing. This analysis also reveals one specific feature of warm discharges that was not discussed earlier: warm discharge-based plasma-chemical systems are very sensitive to gas temperature and chemical reactions. When temperature reaches the level that is high enough to support chemical reactions in a particular system (ignition temperature), chemical reactions produce high concentration of excited molecules, and these molecules form a basis for stepwise ionization. This results in a significant drop in the energy necessary to support electric discharge in the system for two reasons. First, stepwise ionization that requires relatively low electron energy overcomes direct ionization that is typical for low-temperature non-equilibrium plasmas and requires much higher ionization energy. Second, high temperature of surrounding gas reduces heat losses from the discharge channel, while a significant portion of the discharge energy in warm plasma systems should be spent to compensate these losses. Thus, an intensive chemical reaction, e.g. combustion, supports the existence of a warm electric discharge.

Flame propagation characteristics and flame structures of zirconium particle cloud in a small-scale chamber

Flame propagating through zirconium particle cloud in a small-scale vertical rectangle chamber was investigated experimentally. In the experiments, the zirconium quoted 99% purity was used and the diameter of particles was distributed 1–22 μm. The zirconium dust was dispersed into the chamber by air flow and ignited by an electrode spark. A high-speed video camera was used to record the images of the propagating flame. Micro-thermocouples, schlieren optical system and microscopic lens were used to obtain temperature profiles and flame structure, respectively. Based on the experimental results, flame propagation characteristics and flame structure of zirconium particle cloud were analyzed. The propagation velocity of the flame is quite slow in the initial 14 ms and then accelerates to maximum value. Subsequently, the propagation velocity of the flame almost keeps constant. The combustion zone width of zirconium particle cloud is 5–6 mm. Smaller particles burn mainly at the leading edge of combustion zone in the width of 1.4 mm followed by larger particles burning 1.4–6 mm behind the leading edge of the combustion zone. Gas phase flame is not seen in zirconium particle cloud and the combustion time of single zirconium particle is 1–5 ms, which depends on its original size. The preheated zone is 7–8 mm thickness ahead of the combustion zone and intensive chemical reaction takes place at 490 K. The maximum flame temperature increases at lower concentrations, reaches the maximum value, and then decreases slightly at higher concentrations.

Simple Channel Geometry for Enhancement of Chemical Reactions in Microchannels

The mixing of different fluids or chemical species flowing through a microchannel is of great concern in many microfluidic applications, especially microchannel reactors. Flows in a microchannel are generally laminar, and mixing occurs due to molecular diffusion, which is a slow process. Mixing of solutions as a phenomenon is driven by the diffusion itself, but change of the channel shape results in the change of the mixing properties of particular microfluidic structure. This paper presents an experimental and theoretical investigation into the effect of channel axial cross-section shape on mixing and chemical reaction in microchannels. Three microchannels with uniform, converging, and diverging axial cross-sections were used to perform a liquid−liquid acid−base reaction that produces CO2 gas. Flow visualization demonstrated that the most intense chemical reactions (enhanced bubble formation) occurred in the diverging microchannel. Results of both qualitative mixing experiments using two reactive solutions and theoretical analysis indicated that the flow deceleration effect in the diverging microchannel significantly enhanced diffusive mixing in the lateral direction and, consequently, chemical reactions. From these results, it is concluded that a microchannel with a simple diverging cross-section can be used to develop microfluidic devices such as microchannel reactors.