Dynamic Oxidation Process Research Articles

Revealing Real Active Sites in Intricate Grain Boundaries Assemblies on Electroreduction of CO2 to C2+ Products

AbstractAlthough intricate structural assemblies contribute to enhancing the activity of electrocatalytic CO2 reduction (ECR) to C2+ products, blindly coupling multiple design strategies may not yield the expected results, and even inhibit the activity of intrinsic catalytic sites. Therefore, elucidating the promoting or inhibitory effects of each design strategy on the CO2‐to‐C2+ conversion to clarify the real active sites and dynamic oxidation processes is of paramount importance. Here, commonly used grain boundaries (GBs), oxidation states, and alloying strategies are focused on, constructing four different types of catalysts structures: original Cu GBs, oxygen‐enriched grain boundary oxidation (GBO), Ag‐enriched GBO, and Cu/Ag GBs. Multiple operando characterizations reveal that GBs and GBO strengthen the resistance of the oxidative Cu species to the electrochemical reduction. The in situ generated strongly oxidative hydroxyl radicals alter the local reaction environment on the catalyst surface, inducing and stabilizing oxidative Cuδ+ species. Catalytic activity comparisons indicate that the oxidation state of Cu plays a decisive role in the CO2‐to‐C2+ conversion, and the nanoalloy effect tends to favor the CH4 production in intricate GBs assemblies. Theoretical calculations suggest that weak CO adsorption on GBO structures facilitates hydrogenation, promoting C–C coupling toward C2+ products.

The oxidation of carbon nanostructures imaged by electron microscopy: Comparison between in-situ TEM and TGA experiments

The development of a model of carbon oxidation has engaged researchers for decades. Yet many outstanding questions remain due to the inability to experimentally study the details of the oxidation. Today, novel techniques such as environmental transmission electron microscopy (ETEM), allowing for in-situ nanoscale observations of the oxidation process, can help illuminate some of these questions. In this study of few layer graphene (FLG), multi-walled carbon nanotubes (MWCNTs), buckminsterfullerene (C60), and nanodiamonds (NDs) oxidizing in temperatures up to 1100 °C and we analyze the importance of nanostructure for the thermal stability of nanocarbons. The study was complemented with thermogravimetric analysis (TGA) and the experiments were in good agreement with oxidation rates increasing sharply with temperature and the thermal stability of the materials MWCNTs, FLG, C60 and NDs in descending order. Based on the direct nanoscale visualization obtained in the ETEM the materials can be divided into two overall categories: materials with low strain sp2-bonds (FLG and MWCNT); and materials with high strain sp2-bonds (C60) or sp3-bonds (NDs). For materials in the first category, it is possible to identify several different phenomena as their oxidation rate increases as a function of temperatures whereas materials in the second category appear to be more influenced by extrinsic factors such as the electron beam and by structural transformation upon heating. This study clearly shows the value of adding ETEM results to traditional TGA investigations since it gives both a complementary and more detailed information about the dynamic oxidation process.

Experimental study on oxidation and shell-breaking characteristics of individual aluminum particles at high temperature

Because of the significant contribution to energy release, aluminum nanoparticles (ANPs) are widely used as additives in propellants and explosives. To clarify the multiple changes of ANP during heating, the dynamic oxidation and shell-breaking processes of individual nanoparticles were obtained using in situ transmission electron microscopy. Results revealed that the changes of shell thickness were divided into three stages: initial oxidation, slow oxidation, and intense oxidation. The local thickness of the alumina shells increased dramatically after 650 °C and ruptured at the sharply thickened position within 770–780 °C. The active aluminum content of the ANP decreased by 23% before shell-breaking. Before 700 °C the particle diameter did not expand significantly, reaching a maximum value at 810 °C, and then rapidly decreasing. The results detailly revealed the oxidation phenomenon and reflected the oxidation mechanism of ANP, which will be helpful in improving both the energy release and particle safety.

Revealing Temperature-Dependent Oxidation Dynamics of Ni Nanoparticles via Ambient Pressure Transmission Electron Microscopy.

Understanding the oxidation mechanism of metal nanoparticles under ambient pressure is extremely important to make the best use of them in a variety of applications. Through ambient pressure transmission electron microscopy, we in situ investigated the dynamic oxidation processes of Ni nanoparticles at different temperatures under atmospheric pressure, and a temperature-dependent oxidation behavior was revealed. At a relatively low temperature (e.g., 600 °C), the oxidation of Ni nanoparticles underwent a classic Kirkendall process, accompanied by the formation of oxide shells. In contrast, at a higher temperature (e.g., 800 °C), the oxidation began with a single crystal nucleus at the metal surface and then proceeded along the metal/oxide interface without voids formed during the whole process. Through our experiments and density functional theory calculations, a temperature-dependent oxidation mechanism based on Ni nanoparticles was proposed, which was derived from the discrepancy of gas adsorption and diffusion rates under different temperatures.

The Mechanisms of Oxygen Accelerated Low‐Temperature Bonding by Ag Nanoparticles

AbstractLow‐temperature bonding (≤300 o C) using Ag nanoparticles (Ag NPs) is considered to be the new generation of bonding technology in power electronics. The oxygen‐accelerated sintering has been observed by many researchers which is attributed to the decomposition of organics covered on Ag NPs. In this work, organic‐free Ag NPs are fabricated to eliminate the influence of organics, and it is found that the accelerated bonding process by oxygen is strongly correlated to the self‐confined amorphous Ag‐O compound shell on the surface of Ag NPs. In experiments, the sintering process is apparently accelerated by the elevating oxygen content, and the amorphous shell is observed after sintering, which do not grow thicker even in pure oxygen ambient for a long time while performing active chemical evolutions. In simulations, the results match well with the experiments and indicate that the amorphous shell performed the dynamic oxidation and decomposition process. This dynamic equilibrium is caused by the instability of silver oxides, which would enable the amorphous shell to activate the mobility of the surface mass flow and promote the surface diffusion. The shear strength of SiC chip increased by 354% when bonding in pure oxygen, targeting a broad variety of applications in electronic packaging.

Dynamic Collision Oxidation Behaviors of Ag Nanoparticles on Au Nano-Disk Electrodes and Nanopore Electrodes

The dynamic collision behaviors of single nanoparticles (NPs) using nano-sized electrodes in a confined space are highly desirable to be explored for revealing the intrinsic reaction mechanism that is masked in ensemble-averaged measurements. Herein, we illustrate the collision phenomena of silver NPs (Ag NPs) with different agglomeration degrees by using a gold nanodisk electrode (NDE) and a nanopore electrode (NPE). The dynamic collision behaviors of electro-oxidation of the Ag NPs at the single particle level and aggregation state were investigated on the gold NDE and NPE. The results show that the collision/oxidation events of single Ag NPs on the NDE usually lead to diffusion of NPs into the solution after the collision; thus, the degree of oxidation is low. On NPEs, the Ag NPs can hardly escape from the pore, so it shows more multi-peak phenomena and a higher oxidation charge. However, the oxidation collision of the aggregates of Ag NPs exhibits higher peak currents, longer relaxation times, and more obvious shoulder peaks on the Au NDEs and NPEs; the single collision event usually consists of a series of 1–10 discrete “sub-events” within an interval of approximately 5 ms. Compared with a single Ag NP collision, the aggregates of Ag NPs will disperse into smaller or even individual NPs after the first few collisions and then stochastic collisions will occur repeatedly. These findings can help us deeply understand the dynamic oxidation process of metal NPs and will benefit the applications in fundamental electrochemistry, electrocatalysis, and energy-related research.

Regional gain and global loss of 5-hydroxymethylcytosine coexist in genitourinary cancers and regulate different oncogenic pathways

BackgroundDNA 5-hydroxymethylcytosine (5hmC) is produced by dynamic 5mC oxidation process contributing to tissue specification, and loss of 5hmC has been reported in multiple cancers including genitourinary cancers. However, 5hmC is also cell-type specific, and its variability may exist between differentiated tumor cells and cancer stem cells. Thus, cancer-associated changes in 5hmC may be contributed by distinct sets of tumor cells within the tumor tissues.ResultsHere, we applied a sensitive immunoprecipitation-based method (hMeDIP-seq) to analyze 5hmC changes during genitourinary carcinogenesis (including prostate, urothelial and kidney). We confirmed the tissue-specific distribution of 5hmC in genitourinary tissues and identified regional gain and global loss of 5hmC coexisting in genitourinary cancers. The genes with gain of 5hmC during tumorigenesis were functionally enriched in regulating stemness and hypoxia, whereas were associated with poor clinical prognosis irrespective of their differences in tumor type. We identified that gain of 5hmC occurred in soft fibrin gel-induced 3D tumor spheres with a tumor-repopulating phenotype in two prostate cancer cell lines, 22RV1 and PC3, compared with conventional two-dimensional (2D) rigid dishes. Then, we defined a malignant signature derived from the differentially hydroxymethylated regions affected genes of cancer stem-like cells, which could predict a worse clinical outcome and identified phenotypically malignant populations of cells from prostate cancer tumors. Notably, an oxidation-resistant vitamin C derivative, ascorbyl phosphate magnesium, restored 5hmC and killed the cancer stem cell-like cells leading to apoptosis in prostate cancer cell lines.ConclusionsCollectively, our study dissects the regional gain of 5hmC in maintaining cancer stem-like cells and related to poor prognosis, which provides proof of concept for an epigenetic differentiation therapy with vitamin C by 5hmC reprogramming.Graphic

Dynamic monitoring oxidation process of nut oils through Raman technology combined with PLSR and RF-PLSR model

During preservation of nuts, nut oils are easily oxidized; hence, peroxide value (PV) is an important evaluation index. In this study, a novel method for the determination of the PV of nuts based on partial-least-square regression (PLSR) and Forest random PLSR (RF-PLSR) model was established. Meanwhile, the Raman spectrum was processed by 24 spectral pretreatment methods to transform the whole Raman band, and the best band was selected by RF method. Among the whole bands, 36 wavenumbers were selected to establish the PLSR model. The R-square of the correction set (R2c) and prediction set (R2p) of the optimal Standard normal variate transformation + first Derivative-PLSR model and RF-PLSR were 0.9552, 0.8672, 0.8048, and 0.7927, while the root-mean-square error of calibration (RMSEC) and prediction (RMSEP) were 0.067, 0.1100, 0.1514, and 0.1547, respectively. These results showed that Raman spectroscopy combined with chemometrics could be used to establish a rapid, nondestructive, and precise method for the determination of oil oxidation index.

In Situ Observation of Reaction Fronts During the Initial Stages of Iron Surface Oxidation at 1150 °C

This study focuses on the initial stages of iron surface oxidation, studied by confocal scanning laser microscopy. Pure iron cubes were prepared and polished for in situ observation. Samples were oxidized for 2–60 s by dry air at 1150 °C. A dynamic oxidation process was observed, with two reaction fronts that moved from the sample edge to the center at around 20–30- and around 40–50-s oxidation, respectively. Scanning electron microscopy (SEM) was used to characterize the iron oxide surface morphology. Pyramidal features appeared first on the surface, and then the surface became flatter with time. X-ray diffraction was used to characterize the phases of the outermost oxide layer. Overall, the content of wustite decreased and hematite content increased with oxidation time. SEM with a backscattered electron detector was used to measure the oxide layer thicknesses, and it was found that the oxide thickness increased parabolically with time. The different oxide layers within the scale were identified by an optical microscope with a polarized light source. Even after 2-s oxidation, an obvious magnetite layer was found on the wustite layer, and after 10-s oxidation, an obvious hematite layer was observed on the magnetite layer. A thicker hematite layer was observed at the sample edge. The reasons for the morphology changes are discussed.

Vacuum dynamic oxidation process for separating Pb-Sb alloy

Up to now, separating Pb-Sb alloy obtained from jamesonite by conventional pyrometallurgy processes has many drawbacks such as long technological process, high energy consumption, and unsatisfactory separation efficiency. Thinking about the facts that antimony is used mainly in the form of Sb2O3, and separation of Sb2O3 with good volatility from the lead melt is very easy under vacuum, vacuum dynamic oxidation process, a new and effective process for separating lead and antimony from Pb-Sb alloy, was developed in this work. Experimental results revealed that the content of antimony in Pb-Sb alloy decreased from 42% to 0.30%, that the removal percent of antimony reached 99.59%, and that the PbO content in the distillate was 0.12% under melt temperature of 953 K, vacuum treatment time of 210 min, and air flow rate of 3 L/min, corresponding to the system pressure of 14 kPa. This study is of significance for separating Pb-Sb alloy obtained from jamesonite.

Imaging Dynamic Collision and Oxidation of Single Silver Nanoparticles at the Electrode/Solution Interface.

The electrochemical interface is an ultrathin interfacial region between the electrode surface and the electrolyte solution and is often characterized by numerous dynamic processes, such as solvation and desolvation, heterogeneous electron transfer, molecular adsorption and desorption, diffusion, and surface rearrangement. Many of these processes are driven and modulated by the presence of a large interfacial potential gradient. The study and better understanding of the electrochemical interface is important for designing better electrochemical systems where their applications may include batteries, fuel cells, electrocatalytic water splitting, corrosion protection, and electroplating. This, however, has proved to be a challenging analytical task due to the ultracompact and dynamic evolving nature of the electrochemical interface. Here, we describe the use of an electrochemical nanocell to image the dynamic collision and oxidation process of single silver nanoparticles at the surface of a platinum nanoelectrode. A nanocell is prepared by depositing a platinum nanoparticle at the tip of a quartz nanopipette forming a bipolar nanoelectrode. The compact size of the nanocell confines the motion of the silver nanoparticle in a 1-D space. The highly dynamic process of nanoparticle collision and oxidation is imaged by single-particle fluorescence microscopy. Our results demonstrate that silver nanoparticle collision and oxidation is highly dynamic and likely controlled by a strong electrostatic effect at the electrode/solution interface. We believe that the use of a platinum nanocell and single molecule/nanoparticle fluorescence microscopy can be extended to other systems to yield highly dynamic information about the electrochemical interface.

Anodic Oxidation of Carbon Fiber Surfaces: Influence of Static and Dynamic Process Conditions

We investigate the effects of static and dynamic anodic oxidation treatment on the surface chemical composition and functionality of carbon fibers. During static treatment, the electrolytic surface oxidation process is performed on a spatially fixed carbon fiber bundle, while in the dynamic process a moving, continuous carbon fiber tow is oxidized. In both treatment modes electrolytic current density and treatment time were varied. Surface chemical composition and functionality of the resulting carbon fibers were analyzed by x-ray photoelectron spectroscopy. A good agreement between the chemical composition and the functionality of fibers from static and dynamic anodic oxidation treatment is found. This suggests that results from static fiber treatment in a variable, easy to handle laboratory setup can be applied to dynamic anodic oxidation process conditions on a large scale.

Visualizing the Cu/Cu2(O) Interface Transition in Nanoparticles with Environmental Scanning Transmission Electron Microscopy.

Understanding the oxidation and reduction mechanisms of catalytically active transition metal nanoparticles is important to improve their application in a variety of chemical processes. In nanocatalysis the nanoparticles can undergo oxidation or reduction in situ, and thus the redox species are not what are observed before and after reactions. We have used the novel environmental scanning transmission electron microscope (ESTEM) with 0.1 nm resolution in systematic studies of complex dynamic oxidation and reduction mechanisms of copper nanoparticles. The oxidation of copper has previously been reported to be dependent on its crystallography and its interaction with the substrate. By following the dynamic oxidation process in situ in real time with high-angle annular dark-field imaging in the ESTEM, we use conditions ideal to track the oxidation front as it progresses across a copper nanoparticle by following the changes in the atomic number (Z) contrast with time. The oxidation occurs via the nucleation of the oxide phase (Cu2O) from one area of the nanoparticle which then progresses unidirectionally across the particle, with the Cu-to-Cu2O interface having a relationship of Cu{111}//Cu2O{111}. The oxidation kinetics are related to the temperature and oxygen pressure. When the process is reversed in hydrogen, the reduction process is observed to be similar to the oxidation, with the same crystallographic relationship between the two phases. The dynamic observations provide unique insights into redox mechanisms which are important to understanding and controlling the oxidation and reduction of copper-based nanoparticles.

Oxidation Kinetics and Oxygen Capacity of Ti-Bearing Blast Furnace Slag under Dynamic Oxidation Conditions

The oxidation kinetics of low valence titanium and iron in Ti-bearing blast furnace slag were investigated, the activation energies were calculated, which are 461.1 and 437.3 kJ/mol, respectively. The results illustrate that the oxidation process of Ti3+ in the slag is controlled by chemical reactions. However, the chemical reaction between oxygen and iron, between slag and gas, is the determining step of the iron oxidation process. The effects of the isothermal oxidation on the content of Fe2O3, FeM, FeO, and FeT in the slag are discussed. The Fe2+ and Ti3+ in the molten slag were oxidized at high temperatures. Oxygen affinity of the slag can be described using oxygen capacity. The oxygen capacity of Ti-bearing blast furnace slag was investigated during the dynamic oxidation process, the results indicates that the oxygen capacity of the slag decreased with increasing oxidation time during the dynamic oxidation process.

Understanding the stability and reactivity of ultrathin tellurium nanowires in solution: An emerging platform for chemical transformation and material design

The stability and reactivity of nanomaterials are of crucial importance for their application, but the long-term effects of stability and reactivity of nanomaterials under practical conditions are still not well understood. In this study, we first established a comprehensive strategy to investigate the stability of a highly reactive nanomaterial from the viewpoint of reaction kinetics with ultrathin tellurium nanowires (TeNWs) as a model material in aqueous solution through an accelerated oxidation process. This allowed us to propose a new approach for the design and synthesis of other unique one-dimensional nanostructures by a chemical transformation process using the intermediate nanostructures “captured” during the dynamic oxidation process under different conditions. In essence, the oxidation of ultrathin TeNWs is a gas-solid reaction which involves liquid, gas and solid phases. It has been demonstrated that the oxidation process of ultrathin TeNWs in aqueous solution can be divided into three stages, namely oxygen limiting, ultrathin TeNWs limiting and mass transfer resistance limiting stages. The apparent oxidation kinetics for ultrathin TeNWs is approximately in accord with a first order reaction kinetics model and has an apparent activation energy as low as 13.53 kJ·mol−1, indicating that ultrathin TeNWs are thermodynamically unstable. However, the unstable nature of ultrathin TeNWs is actually an advantage since it can act as an excellent platform to help us synthesize and design one-dimensional functional nanomaterials-with special structures and distinctive properties-which are difficult to obtain by a direct synthesis method.

Fabrication of Al/AlOx/Al Josephson junctions and superconducting quantum circuits by shadow evaporation and a dynamic oxidation process

Besides serving as promising candidates for realizing quantum computing, superconducting quantum circuits are one of a few macroscopic physical systems in which fundamental quantum phenomena can be directly demonstrated and tested, giving rise to a vast field of intensive research work both theoretically and experimentally. In this paper we report our work on the fabrication of superconducting quantum circuits, starting from its building blocks: Al/AlOx/Al Josephson junctions. By using electron beam lithography patterning and shadow evaporation, we have fabricated aluminum Josephson junctions with a controllable critical current density (jc) and wide range of junction sizes from 0.01 μm2 up to 1 μm2. We have carried out systematical studies on the oxidation process in fabricating Al/AlOx/Al Josephson junctions suitable for superconducting flux qubits. Furthermore, we have also fabricated superconducting quantum circuits such as superconducting flux qubits and charge-flux qubits.

Evaluation of the Physical and Chemical Properties of Eyjafjallajökull Volcanic Plume Using a Cloud-Resolving Model

The Eyjafjallajokull volcanic eruption, which occurred on April 14, 2010, caused many environmental, air traffic and health problems. An attempt has been made to demonstrate for the first time that certain improvements could be made in the quantitative prediction of the volcanic ash parameters, and in the accounting of the processes in the immediate vicinity of the volcano, using a cloud-resolving model. This type of explicit modeling by treatment of volcanic ash and sulfate chemistry parameterization, with input of a number parameters describing the volcanic source, is the way forward for understanding the complex processes in plumes and in the future plume dispersion modeling. Results imply that the most significant microphysical processes are those related to accretion of cloud water, cloud ice and rainwater by snow, and accretion of rain and snow by hail. The dominant chemical conversion rates that give a great contribution to the sulfate budget are nucleation and dynamic scavenging and oxidation processes. A three-dimensional numerical experiment has shown a very realistic simulation of volcanic ash and other chemical compounds evolution, with a sloping structure strongly influenced by the meteorological conditions. In-cloud oxidation by H2O2 is the dominant pathway for SO2 oxidation and allows sulfate to be produced within the SO2 source region. The averaged cloud water pH of about 5.8 and rainwater pH of 4.5 over simulation time show quantitatively how the oxidation may strongly influence the sulfate budget and acidity of volcanic cloud. Compared to observations, model results are close in many aspects. Information on the near field volcanic plume behavior is essential for early preparedness and evacuation. This approach demonstrates a potential improvement in quantitative predictions regarding the volcanic plume distribution at different altitudes. It could be a useful tool for modeling volcanic plumes for better emergency measures planning.

Simulation of the oxidation pathway on Si(100) using high‐resolution EELS

AbstractWe compute high‐resolution electron energy loss spectra (HREELS) of possible structural motifs that form during the dynamic oxidation process on Si(100), including the important metastable precursor silanone and an adjacent‐dimer bridge (ADB) structure that may seed oxide formation. Spectroscopic fingerprints of single site, silanone, and “seed” structures are identified and related to changes in the surface bandstructure of the clean surface. Incorporation of oxygen into the silicon lattice through adsorption and dissociation of water is also examined. Results are compared to available HREELS spectra and surface optical data, which are closely related. Our simulations confirm that HREELS offers complementary evidence to surface optical spectroscopy, and show that its high sensitivity allows it to distinguish between energetically and structurally similar oxidation models.

Study of the oxidation dynamics of ethyl cysteinate dimer in solution by ultra‐performance liquid chromatography with tandem mass spectrometry

Diaminodithiol (N2S2)-type compounds readily oxidize to produce disulfides. We found that some ligands failed to produce a prospective protonated molecular ion peak but gave a peak of [M-2+H]+, whereas others produced both [M+H]+ and [M-2+H]+ peaks in electrospray ionization mass spectra. In this study, an important N2S2 ligand, the ethyl cysteinate dimer (ECD), was investigated with high-resolution accurate mass measurements and tandem mass spectrometric analysis. The elemental compositions of ECD and its oxidized product were analyzed. The oxidation of ECD was confirmed. An ultra-performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) method in multiple reaction monitoring mode was developed, and ECD and its oxidized product were quantitated in solution. The dynamic oxidation process of ECD in solution was studied in detail. The full time course of the decrease in ECD and the increase in its oxide was observed; the oxidation procedure followed first-order kinetics, and the half-life time of ECD was 51 min.

Precipitation selectivity of perovskite phase from Ti-bearing blast furnace slag under dynamic oxidation conditions

The effects of dynamic oxidations on the crystal morphology and the precipitation behavior of the perovskite phase from Ti-bearing blast furnace slag were investigated. Air was blown into the molten slag as an oxygen source through a lance during the dynamic oxidation process. It was found that the dispersed Ti components were selectively taken into the perovskite phase (CaTiO 3), and the perovskite phase could be selectively precipitated and grown. Oxidation of molten slag produced a large amount of heat, which not only increased the temperature of the slag, but also promoted the precipitation and growth of the perovskite phase. It was confirmed by isothermal experiments and non-isothermal pilot experiments that the precipitation of the perovskite (CaTiO 3) in molten slag is obviously affected by operation factors such as oxidizing time, and slag temperature. The perovskite phase precipitation kinetics and mechanisms from molten slag during the dynamic oxidation processes were also investigated.