Chemical Phenomena Research Articles

Physical and Chemical Phenomena during the Production of Hydrogen in the Microwave Discharge Generated in Liquid Hydrocarbons with the Barbotage of Various Gases

The physical and chemical characteristics of the microwave discharge in petroleum solvent during hydrogen production processes involving Ar, He, and CO2 barbotage were studied. Gas chromatography, emission spectroscopy, high-speed photography, and shadow photography were used for diagnosis. The results demonstrated the dependence of hydrogen yield on the flow rates of Ar, He, and CO2. The maximum yield values of hydrogen were 791 mL/min and 811 mL/min, while the maximum energy efficiency reached 135.6 NL/kWh and 162.2 NL/kWh in Nefras with Ar and He barbotage, respectively. The dynamics of discharge structure and the rotational and vibrational temperatures of C2 molecules were studied.

Improvement of blast furnace production using digital technology

The role of mathematical models in the improvement of the blast furnace smelting technology is shown. Examples include the new developments of the Institute of Metallurgy of the Ural Branch of the Russian Academy of Sciences in the field of digital models of blast furnace production, in particular, two-dimensional and three-dimensional mathematical models of the thermal state of various zones of the blast furnace, including analysis and forecast of phe-nomena of gas dynamics, heat exchange, recovery in blast furnace using a complex of mathematical models; monitoring of refractory lining state and hearth filling using three-dimensional mathematical model of thermal processes; forecast of silicon content and other elements in cast iron and slag based on neural network technologies; optimization of the composition and improvement of metallurgical characteristics of iron ore agglomerate and coke in order to increase the efficiency of blast furnace melting and analysis of the efficiency of blast furnaces based on the calculation of the minimum consumption of coke. These models are based on the consideration of physical, chemical and thermal phenomena occurring in the blast furnace, taking into account their two-dimensional nature implicit in the problem statement. The developed complex of models includes balance (equilibrium) model, models of gas dynamics, heat exchange, reduction, cohesion zone. New developments in the field of analysis and control of thermophysical and physicochemical phenomena occurring in different zones of the blast furnace allow to raise the technology and methods of blast furnace melting to a fundamentally new level, which saves fuel and energy resources. The possibility of using a digital model in tempo with a process using sensor readings through the blast furnace department management system of the enterprise is shown.

Electronic-Level Insight into the Adsorption and Surface Diffusion Kinetics of a Simplified Glyphosate Model on a Goethite Surface.

The diffusive processes that occur in minerals involve chemical and physical surface phenomena of great interest that allow for understanding the mobility of different anions of environmental importance. One of them is glyphosate, which is widely used as a pesticide. In this work, we performed Hubbard-corrected density functional theory (DFT + U) calculations to study the adsorption and surface diffusion of methylphosphonic acid (MPA), as a model of glyphosate, on the (010) plane of goethite (GOT), one of the most important Fe(III) minerals in soils and sediments. In particular, the MPA adsorption was studied at the GOT-water interface, finding a strong covalent character in the bond. We also corroborated the occurrence of double proton transfer (MPA to GOT and GOT to GOT). Finally, activation energy barriers were calculated to estimate the half-lives for molecular diffusion, showing that MPA moves almost 3000 times slower than water at the GOT surface.

БЕЗАБРАЗИВНАЯ ЧИСТОВАЯ ОБРАБОТКА ДЕТАЛЕЙ МАШИН КОМБИНИРОВАННЫМИ МЕТОДАМИ

At the moment, traditional processing methods are deeply studied and fully implemented in all branches of mechanical engineering. Many experts believe that in the future we should not expect their large-scale development and new discoveries in this area, and if any appear, they will not be competitive enough. A new global method for the development of technological processes is considered to be the study and widespread introduction into the creation of new technological processes with the introduction of combined processing methods. They try to combine mechanical, chemical, thermal and similar phenomena. Their combined use can give a new breakthrough in the development of metalworking sequence design.

Vibrational polariton transport in disordered media.

Chemical reactions and energy transport phenomena have been experimentally reported to be significantly affected by strong light-matter interactions and vibrational polariton formation. These quasiparticles exhibit nontrivial transport phenomena due to the long-range correlations induced by the photonic system and elastic and inelastic scattering processes driven by matter disorder. In this article, we employ the Ioffe-Regel criterion to obtain vibrational polariton mobility edges and to identify distinct regimes of delocalization and transport under variable experimental conditions of light-matter detuning, disorder, and interaction strength. Correlations between the obtained trends and recent observations of polariton effects on reactivity are discussed, and essential differences between transport phenomena in organic electronic exciton and vibrational polaritons are highlighted. Our transport diagrams show the rich diversity of transport phenomena under vibrational strong coupling and indicate that macroscopic delocalization is favored at negative detuning and large light-matter interaction strength. We also find the surprising feature that, despite the presence of dephasing-induced inelastic scattering processes, macroscopic lower polariton delocalization and wave transport are expected to persist experimentally, even in modes with small photonic weight.

Influence of Ion Nitriding on Microstructure and Properties of Haynes 282 Nickel Superalloy Specimens Produced Using DMLS Technique.

The paper investigates the influence of the ion-nitriding process on the microstructure, corrosion resistance, and tensile strength at elevated temperatures of Haynes 282 nickel superalloy specimens produced by the Direct Metal Laser Sintering (DMLS) technique. The study was performed for two conditions, i.e., as-built by DMLS method and as-built by DMLS method + covered by a layer containing CrN + Cr2N phases. An analysis of the surface morphology revealed that the ion-nitriding process significantly affects the physical and chemical phenomena occurring on the specimen's surface. The XRD measurement of the specimens showed that preparing them with the DMLS method as well as following a nitriding process produced residual tensile stresses. Based on the measurement of the nanohardness distribution through the layer approximatively of 7 μm in width and the superalloys substrate, the results of the nanohardness showed the maximum values of 27 GPa and 13.5 GPa for the nitrided layer and the substrate, respectively. The surface protection from the nitrided layer proved a positive effect on the corrosion resistance of the DMLS specimens in the solution of 0.1 M Na2SO4 + 0.1 M NaCl at room temperature. The results of the tensile tests at 750 °C showed that the ion-nitriding process did not significantly affect the elevated-temperature tensile strength of the superalloy specimens produced with the DMLS technique.

Apparecchiando la Tavola: l’ordine degli elementi

The periodic table of the chemical elements, published in 1869 by Dmitri Mendeleev, is actually the destination of an exciting journey that lasted over 3000 years, which will be broken down into key steps and briefly discussed herein. To this journey, driven mainly by the innate curiosity of scientists and philosophers to understand the structure and composition of the world around us, the greatest minds of chemistry and natural philosophy, from Empedocles, to Priestley, to Lavoisier, to Davy, have contributed with essential individual pieces that combined into the solution of such a majestic jigsaw puzzle by Mendeleev. Although the periodic table is a milestone of chemistry and one of the greatest triumphs of scientific knowledge, it is continuously evolving and it is still nowadays one of the most useful and versatile tools for the understanding and rationalizing a broad range of chemical and physical phenomena.

SERS as a Probe of Surface Chemistry Enabled by Surface-Accessible Plasmonic Nanomaterials.

ConspectusWhen the size of materials is reduced, their volume decreases much faster than their surface area, which in the most extreme case leads to 2D nanomaterials which are "all surface". Since atoms at the surface have free energies, electronic states, and mobility which are very different from bulk atoms, nanomaterials that have large surface-to-volume ratios can display remarkable new properties compared to their bulk counterparts. More generally, the surface is where nanomaterials interact with their environment, which in turn places surface chemistry at the heart of catalysis, nanotechnology, and sensing applications. Understanding and utilizing nanosurfaces are not possible without appropriate spectroscopic and microscopic characterization techniques. An emerging technique in this area is surface-enhanced Raman spectroscopy (SERS), which utilizes the interaction between plasmonic nanoparticles and light to enhance the Raman signals of molecules near the nanoparticles' surfaces. SERS has the great advantage that it can provide detailed in situ information on surface orientation and binding between molecules and the nanosurface. A long-standing dilemma that has limited the applications of SERS in surface chemistry studies is the choice between surface-accessibility and plasmonic activity. More specifically, the synthesis of metal nanomaterials with strong plasmonic and SERS-enhancing properties typically involves the use of strongly adsorbing modifier molecules, but these modifiers also passivate the surface of the product material, which prevents the general application of SERS in the analysis of weaker molecule-metal interactions.In this Account, we discuss our efforts in the development of modifier-free synthetic approaches to synthesize surface-accessible, plasmonic nanomaterials for SERS. We start by discussing the definition of "modifiers" and "surface-accessibility", especially in the context of surface chemistry studies in SERS. As a general rule of thumb, the chemical ligands on surface-accessible nanomaterials should be easily displaceable by a wide range of target molecules relevant to potential applications. We then introduce modifier-free approaches for the bottom-up synthesis of colloidal nanoparticles, which are the basic building blocks for nanotechnology. Following this, we introduce modifier-free interfacial self-assembly approaches developed by our group that allow the creation of multidimensional plasmonic nanoparticle arrays from different types of nanoparticle-building blocks. These multidimensional arrays can be further combined with different types of functional materials to form surface-accessible multifunctional hybrid plasmonic materials. Finally, we demonstrate applications for surface-accessible nanomaterials as plasmonic substrates for SERS studies of surface chemistry. Importantly, our studies revealed that the removal of modifiers led to not only significantly enhanced properties but also the observation of new surface chemistry phenomena that had been previously overlooked or misunderstood in the literature. Realizing the current limitations of modifier-based approaches provides new perspectives in manipulating molecule-metal interactions in nanotechnology and can have significant implications in the design and synthesis of the next generation of nanomaterials.

Sub-picosecond collapse of molecular polaritons to pure molecular transition in plasmonic photoswitch-nanoantennas

Molecular polaritons are hybrid light-matter states that emerge when a molecular transition strongly interacts with photons in a resonator. At optical frequencies, this interaction unlocks a way to explore and control new chemical phenomena at the nanoscale. Achieving such control at ultrafast timescales, however, is an outstanding challenge, as it requires a deep understanding of the dynamics of the collectively coupled molecular excitation and the light modes. Here, we investigate the dynamics of collective polariton states, realized by coupling molecular photoswitches to optically anisotropic plasmonic nanoantennas. Pump-probe experiments reveal an ultrafast collapse of polaritons to pure molecular transition triggered by femtosecond-pulse excitation at room temperature. Through a synergistic combination of experiments and quantum mechanical modelling, we show that the response of the system is governed by intramolecular dynamics, occurring one order of magnitude faster with respect to the uncoupled excited molecule relaxation to the ground state.

Human Olfactory Receptor Sensor for Odor Reconstitution.

Among the five human senses, light, sound, and force perceived by the eye, ear, and skin, respectively are physical phenomena, and therefore can be easily measured and expressed as objective, univocal, and simple digital data with physical quantity. However, as taste and odor molecules perceived by the tongue and nose are chemical phenomena, it has been difficult to express them as objective and univocal digital data, since no reference chemicals can be defined. Therefore, while the recording, saving, transmitting to remote locations, and replaying of human visual, auditory, and tactile information as digital data in digital devices have been realized (this series of data flow is defined as DX (digital transformation) in this review), the DX of human taste and odor information is not yet in the realization stage. Particularly, since there are at least 400,000 types of odor molecules and an infinite number of complex odors that are mixtures of these molecules, it has been considered extremely difficult to realize "human olfactory DX" by converting all odors perceived by human olfaction into digital data. In this review, we discuss the current status and future prospects of the development of "human olfactory DX", which we believe can be realized by utilizing odor sensors that employ the olfactory receptors (ORs) that support human olfaction as sensing molecules (i.e., human OR sensor).

Analysis of Chemical Representations in the Physical Sciences Textbooks for Grade 12 Learners in South Africa

Textbooks play a prominent role in the teaching and learning of chemistry. It is the major organiser and the intended curriculum teachers adapt for their instructional practices. Although chemistry is abstract in nature, the use of visuals or images in textbooks to depict chemical phenomena at different levels remains a meaningful approach to help facilitate students’ understanding of chemistry. Therefore, this study analysed chemical representations in the chemistry components of the Physical Sciences textbooks for grade 12 learners in South Africa. Three textbooks were selected and analysed using the five criteria developed by Gkitzia, Salta and Tzougraki (2011). The findings revealed that the chemical representations in the textbooks were largely at the macroscopic and hybrid levels, with surface features that are ambiguous or explicit and representations that are unlinked to text. In addition, there were few sub-microscopic, multiple, and mixed representations in the textbooks. An interesting result is that a majority of the chemical representations had appropriate captions. The implications of these findings for textbook authors or publishers were discussed.

Foundations of plasma enhanced chemical vapor deposition of functional coatings

Since decades, the PECVD (‘plasma enhanced chemical vapor deposition’) processes have emerged as one of the most convenient and versatile approaches to synthesize either organic or inorganic thin films on many types of substrates, including complex shapes. As a consequence, PECVD is today utilized in many fields of application ranging from microelectronic circuit fabrication to optics/photonics, biotechnology, energy, smart textiles, and many others. Nevertheless, owing to the complexity of the process including numerous gas phase and surface reactions, the fabrication of tailor-made materials for a given application is still a major challenge in the field making it obvious that mastery of the technique can only be achieved through the fundamental understanding of the chemical and physical phenomena involved in the film formation. In this context, the aim of this foundation paper is to share with the readers our perception and understanding of the basic principles behind the formation of PECVD layers considering the co-existence of different reaction pathways that can be tailored by controlling the energy dissipated in the gas phase and/or at the growing surface. We demonstrate that the key parameters controlling the functional properties of the PECVD films are similar whether they are inorganic- or organic-like (plasma polymers) in nature, thus supporting a unified description of the PECVD process. Several concrete examples of the gas phase processes and the film behavior illustrate our vision. To complete the document, we also discuss the present and future trends in the development of the PECVD processes and provide examples of important industrial applications using this powerful and versatile technology.

Grain-level residual stress distribution at dwell fatigue crack tips in a nickel-based superalloy

Dwell fatigue crack growth in nickel-based superalloys is influenced by a complex interplay between mechanical and chemical phenomena. The stress distribution at the crack tip is closely related to these phenomena and to the local microstructure. In this study we evaluate experimentally the microscale residual stress distribution ahead of crack tips in RR1000 alloy samples after interrupted high temperature dwell fatigue testing. In the crack opening direction the results show a compressive residual stress zone, the extent of which is linked to the plastic zone size and crack growth retardation behaviour. In the direction of crack propagation the residual stress is also influenced by crystallographic grain orientation. The results demonstrate a novel approach of experimentally evaluating crack tip stress distribution via focused ion beam – digital image correlation (FIB-DIC) ring-core measurements at the grain-level. This provides new insights into fatigue crack growth in microstructurally heterogeneous materials.

Ultrafast Electronic Coupling Estimators: Neural Networks versus Physics-Based Approaches.

Fast and accurate estimation of electronic coupling matrix elements between molecules is essential for the simulation of charge transfer phenomena in chemistry, materials science, and biology. Here we investigate neural-network-based coupling estimators combined with different protocols for sampling reference data (random, farthest point, and query by committee) and compare their performance to the physics-based analytic overlap method (AOM), introduced previously. We find that neural network approaches can give smaller errors than AOM, in particular smaller maximum errors, while they require an order of magnitude more reference data than AOM, typically one hundred to several hundred training points, down from several thousand required in previous ML works. A Δ-ML approach taking AOM as a baseline is found to give the best overall performance at a relatively small computational overhead of about a factor of 2. Highly flexible π-conjugated organic molecules like non-fullerene acceptors are found to be a particularly challenging case for ML because of the varying (de)localization of the frontier orbitals for different intramolecular geometries sampled along molecular dynamics trajectories. Here the local symmetry functions used in ML are insufficient, and long-range descriptors are expected to give improved performance.

A review on computational modeling of instability and degradation issues of halide perovskite photovoltaic materials

AbstractHybrid halide perovskite solar cells have been recognized as one of the most promising future photovoltaic technologies due to their demonstrated high‐power conversion efficiency, versatile stoichiometry and low cost. However, degradation caused by environmental exposure and structural instability due to ionic defect migration hinders the commercialization of this technology. While the experimental studies try to understand the phenomenology of the degradation mechanisms and devise practical measures to improve the stability of these materials, theoretical studies have attempted to bridge the gaps in our understanding of the fundamental degradation mechanisms at different time and length scales. A deeper understanding of the physical and chemical phenomena at an atomic level through multiscale materials modeling is going to be crucial for the knowledge‐based prognosis and design of future halide perovskites. There have been increased efforts in this direction in the last few years. However, the instability fundamentals explored through atomistic modeling and simulation methods have not been reviewed comprehensively in the literature yet. Therefore, this paper is an attempt to present a critical review, while identifying the existing gaps and opportunities in the investigation of the degradation and instability issues of the halide perovskites using computational methods. The review will primarily focus on the instability caused due to the intrinsic ionic defect migration and degradation due to thermal, moisture and light exposure. The findings from the simulation studies conducted primarily using density functional theory, ab initio molecular dynamics, classical molecular dynamics and machine learning methods will be presented.This article is categorized under: Software > Molecular Modeling Structure and Mechanism > Computational Materials Science Data Science > Artificial Intelligence/Machine Learning

Unsaturated hydro-mechanical-electro-chemical coupling based on mixture-coupling theory: a unified model

Electro-kinetic remediation and electro-kinetic consolidation play an important role in soil reinforcement and remediation. Although they are interrelated in mechanism, modeling of the two technologies is often separated due to the knowledge and multiple-scale gap between geomechanics and electro-chemistry, including electro-osmosis, hydraulic-osmosis, chemical osmosis, and mechanical deformation. This paper develops a unified hydro-mechanical-electro-chemical (HMEC) constitutive model for unsaturated soil by using a non-equilibrium thermodynamics-based approach, mixture-coupling theory, to study the two technologies in one framework. Entropy production during the dissipative process is considered, and Helmholtz free energy is used to bridge the interactions between mechanical deformation at the macroscale scale and electro-chemical transport at the molecular scale. A new term, electric-induced stress coefficient, has been introduced into the stress-strain relationship to reflect the effects of electric field on the solid matrix. Meanwhile, the classic Darcy's law has been fundamentally extended to consider the electro and chemical osmosis phenomena. The model is verified by comparing with existing equations and models. Finally, parameter analyses and case studies show that chemical transport and mechanical deformation are significantly influenced by electrical parameters and physical-chemical properties. In the unsaturated state, the chemical concentration distribution is affected by the coupling effects between electro-osmosis consolidation and chemical osmosis.

High-order pump-probe and high-order two-dimensional electronic spectroscopy on the example of squaraine oligomers.

Time-resolved spectroscopy is commonly used to study diverse phenomena in chemistry, biology, and physics. Pump-probe experiments and coherent two-dimensional (2D) spectroscopy have resolved site-to-site energy transfer, visualized electronic couplings, and much more. In both techniques, the lowest-order signal, in a perturbative expansion of the polarization, is of third order in the electric field, which we call a one-quantum (1Q) signal because in 2D spectroscopy it oscillates in the coherence time with the excitation frequency. There is also a two-quantum (2Q) signal that oscillates in the coherence time at twice the fundamental frequency and is fifth order in the electric field. We demonstrate that the appearance of the 2Q signal guarantees that the 1Q signal is contaminated by non-negligible fifth-order interactions. We derive an analytical connection between an nQ signal and (2n + 1)th-order contaminations of an rQ (with r < n) signal by studying Feynman diagrams of all contributions. We demonstrate that by performing partial integrations along the excitation axis in 2D spectra, we can obtain clean rQ signals free of higher-order artifacts. We exemplify the technique using optical 2D spectroscopy on squaraine oligomers, showing clean extraction of the third-order signal. We further demonstrate the analytical connection with higher-order pump-probe spectroscopy and compare both techniques experimentally. Our approach demonstrates the full power of higher-order pump-probe and 2D spectroscopy to investigate multi-particle interactions in coupled systems.

Differences in the Triplechem Learning Model with Balinese Local Wisdom and the Discovery Learning Model in Influencing Students' Visual Literacy and Mental Models about Acid-Base Solutions

This study intends to investigate the differences in the effect of the TripleChem learning model with Balinese local wisdom and the Discovery Learning model on students' visual literacy and chemical mental models about acid-base solutions. The research was designed using a quantitative approach and classified as quasi-experimental. The research design used was a pretest-posttest non-equivalent control group design. The population of this study was 206 junior high school students with Balinese cultural backgrounds with various beliefs (religions), namely Hindus, Muslims, and Christians. Cultural content will cause learning to be more contextual, more interesting, and bring students closer to their own culture. The sampling was done using a simple random sampling technique, and obtained two sample classes, one class as the experimental group, and the other as the control group. The experimental group was taught using the TripleChem learning model containing Balinese local wisdom, while the control group was taught using the Discovery Learning model. The dependent variable in this research was visual literacy and students' mental models of chemistry. Data collection was carried out using a visual literacy test (10 items in total; item validity between 0.520 – 0.893; and test reliability coefficient of 0.895) and a chemical mental model test (8 items in total; item validity between 0.669 – 0.878; and test reliability coefficient of 0.922). Data analysis was carried out descriptively and MANCOVA. The results show that the TripleChem learning model is more effective to be applied to improve students' visual literacy and mental models about acid-base solutions compared to the Discovery Learning model. This condition is caused by the syntax of the TripleChem learning model which is more sequential and structured to build students' visual literacy and chemistry mental models. The application of the TripleChem learning model in chemistry learning needs to be supported by laboratory facilities to display chemical macroscopic phenomena and animated media to explain these phenomena at the level of matter particles.

Calculating of square-wave voltammograms—a practical on-line simulation platform

Square-wave voltammetry (SWV) is a widely used technique for getting insight into mechanistic and kinetic aspects of various electrochemical reactions. To date, this pulse-voltammetric technique has been utilized in numerous electrochemical studies and it remains one of the most sophisticated electrochemical methods available. As a result of its higher sensitivity and its potential to provide insights similar to cyclic voltammetry for electrode mechanisms characterization, the SWV is increasingly being included in undergraduate electrochemistry laboratory curriculums. The features of experimental SW voltammograms are affected by various factors, such as kinetics of charge transfer, diffusion, adsorption phenomena, and chemical reactions coupled to electron transfer step. To understand some of the physical and chemical phenomena hidden in a single experimental SW voltammogram, it is inevitable to get a help of computer simulations. The purpose of this article is to offer a basic introduction to SWV written in a simple language, intended to engage students and familiarize them with the fundamentals of this technique. The ultimate objective is to provide the aspiring young electrochemists with a simulation procedure using the MATHCAD software, which can be employed to compute SW voltammograms following a rather easy simulation approach. A detailed tutorial on simulating SW voltammograms with MATHCAD software is presented. The simple tutorial offers a step-by-step breakdown of the simulation process of a square-wave voltammogram. Additionally, a MATHCAD ready-to-use file for simulation of a common electrode mechanism is provided. The current work aims to assist undergraduate students in learning about electrochemical simulations that serve as a corner stone to more advanced studies in SWV.

Adsorption Efficiency of Bentonite Clay and Parrotia persica During Acid Mine Drainage Treatment for the Removal of Turbid Material

We conducted jar tests on the efficacy of using various mixtures of pulverized bentonite clay and Parrotia persica plant to treat AMD from a mine in Mogale City, South Africa without adding alkalinity. Two nearly identical sets of experiments were conducted using the same materials after they were rinsed using distilled and potable waters, respectively, to remove impurities, and then dried in an oven at 60 °C for 24 h, after which they were pulverized again. The pH, electrical conductivity, oxidation reduction potential, turbidity, and metal concentrations were measured before and after the experiments. The samples were treated in a jar test using standard procedures, i.e. rapid and slow mixing and settling for 1 h. The results showed that increasing the concentration of P. persica relative to the bentonite improved treatment effectiveness and that the highest turbidity removal (> 96.8%) was produced by rinsing the mixtures with potable water, drying them, and then pulverizing them again. Potentially toxic metals were removed by more than 93.7%. The morphological structure of the SEM micrographs indicate that the removal mechanism involves both physical and chemical phenomena and that the clay and P. persica are both important, particularly to the physical aspects.