Si Interaction Research Articles

Stabilizing nanograined Fe-Cr alloy by Si-assisted grain boundary segregation

• Si promotes GB segregation of Cr in the NG Fe-8Cr-1Si treated by SMGT and annealing. • Cr segregation increases with the decrease of grain size, which is related to high- density GND. • NG Fe-8Cr-1Si has enhanced thermal stability and hardness due to Cr segregation. • Additions attractive to solute can stabilize NG binary alloys with weak segregation tendency. Intentional solute segregation at grain boundary (GB) can effectively stabilize the nanograined alloys by reducing the excess energy and mobility of GB, but it usually works for binary alloys with sufficient GB segregation tendency. Here, we found that the segregation of Cr can be enhanced in a nanostructured Fe-8Cr alloy with insufficient GB segregation tendency through the interaction of another solute Si (1.0 wt.%). After surface mechanical grinding treatment and subsequent annealing, the nanograined Fe-8Cr-1Si is more thermally stable than the nanograined Fe-8Cr, which is mainly attributed to the Si-enhanced Cr segregation as observed by Super-X energy-dispersive X-ray spectroscopy (EDS) mapping system. With the grain refinement to nanoscale, the thermal stability is further improved due to the increase of Cr content at GBs and the precipitates formed at appropriate high temperatures. The present finding provides guidance for the development of advanced nanostructured ternary alloys.

Novel polyhedral@SiO2 core–shell catalysts designed for Fischer–Tropsch synthesis

AbstractBackgroundFischer–Tropsch synthesis (FTS) has attracted much attention for converting syngas to liquid fuels. Enhanced catalytic stability and excellent product selectivity can be achieved by rational design of catalysts. However, the traditional SiO2‐supported Fe‐based catalysts display higher interaction between active metal and SiO2 support, thus resulting in a lower catalytic activity. Rational design of catalysts with weaker Fe–Si interaction promises excellent catalytic performances.ResultsNovel polyhedral@SiO2 core–shell catalysts with adjustable shell thickness were prepared. The incorporation of SiO2 shell with suitable thickness can maintain the integrity of the active structure, and thus promising excellent C5+ productivity combined with higher catalytic activity. On the other hand, the SiO2 layer can prolong the residence time of CnHm intermediates on the active surface of Fe particles that enhance the C–C coupling reaction, favoring chain growth for production of C5+ yield. However, excessive addition of tetraethyl orthosilicate cannot increase the shell thickness in the absence of ammonium hydroxide and can be responsible for a poor CO conversion. Si‐66 with shell thickness of 66 nm achieves an optimum C5+ yield of 2.23 × 10−3 gHC gFe−1 s−1 and a higher iron time yield value of 31.5 μmolCO gFe−1 s−1. Obviously, this C5+ yield is comparable to that for the Mn‐promoted FeSiMn catalyst (2.22 × 10−3 gHC gFe−1 s−1) reported in our previous work.ConclusionsThe introduction of SiO2 as shell can improve structural stability during FTS. Moreover, the novel polyhedral@SiO2 core–shell catalyst exhibits excellent C5+ yield, and which is 1.8 times higher than that for a spindle@SiO2 core–shell catalyst reported in our previous work. © 2022 Society of Chemical Industry (SCI).

Age hardening of Al-7Si-0.5Mg alloy: Role of Si size and distribution

The age-hardening behavior of the Al-7Si-0.5Mg alloy with different size and distribution of Si phase was investigated. The wedge-shaped mold was used to prepare specimens with different characteristics of Si. The specimen with fine and homogeneous Si showed accelerated age-hardening kinetics and higher peak hardness than the one with coarse and clustered Si due to the higher dislocation density resulted from the mismatch in the thermal contraction of Si and Al. The overlapping of the plastically-affected zone of the adjacent Si phase in the specimen with large and clustered Si led to a reduced volume fraction of the plastically-affected zone, lower dislocation density and lower age-hardening kinetics. The relationship between the radius of Si and the critical inter-particle spacing that minimize the interaction of adjacent Si to maximize the dislocation density and accelerate age-hardening kinetics was established.

Crystal and electronic structures of a new hexagonal silicide Sc38Co144Si97

Sc38Co144Si97 was prepared from the elements by arc melting under argon and subsequent annealing at 800 ​°C for 350 ​h. Single-crystal X-ray diffraction reveals Sc38Co144Si97 to crystallize in a new hexagonal structure type: Pearson's symbol hP279, space group P63/m, a ​= ​33.624(7), c ​= ​3.639(1) Å. The crystal structure of Sc38Co144Si97 can be considered as a 2D intergrowth of three kinds of fragments of simpler structure types: hexagons and quadrilaterals with the arrangements of the Sc6Co30Si19-type and triangles with the arrangement of the Gd4Co13(Si, P)9-type. Quantum chemical calculations have been performed to analyze the electronic structure and provide deeper insight into the structure-property relationships. The Extended Hückel (EH) calculation indicates that Co in Sc38Co144Si97 adopts close to a d10 configuration owing to the covalent interaction with Si. The Sc–Co and Sc–Si interactions are more ionic, and Co–Co and Co–Si bonds are more covalent interactions.

Nitrogen availability and plant-plant interactions drive leaf silicon concentration in wheat genotypes.

Estimating plasticity of leaf silicon (Si) in response to abiotic and biotic factors underpins our comprehension of plant defences and stress resistance in natural and agroecosystems. However, how nitrogen (N) addition and intraspecific plant-plant interactions affect Si concentration remains unclear.We grew 19 durum wheat genotypes (Triticum turgidum ssp. durum) in pots, either alone or in intra- or intergenotypic cultures of two individuals, and with or without N. Above-ground biomass, plant height and leaf [Si] were quantified at the beginning of the flowering stage.Nitrogen addition decreased leaf [Si] for most genotypes, proportionally to the biomass increase. Si plasticity to plant-plant interactions varied significantly among genotypes, with both increases and decreases in leaf [Si] when mixed with a neighbour, regardless of the mixture type (intra-/intergenotype). Besides, increased leaf [Si] in response to plant-plant interactions was associated with increased plant height.Our results suggest the occurrence of both facilitation and competition for Si uptake from the rhizosphere in wheat mixtures. Future research should identify which leaf and root traits characterise facilitating neighbours for Si acquisition. We also show that Si could be involved in height gain in response to intraspecific competition, possibly for increasing light capture. This important finding opens up new research directions on Si and plant-plant interactions in both natural ecosystems and agroecosystems. More generally, our results stress the need to explore leaf Si plasticity in responses to both abiotic and biotic factors to understand plant stress resistance. Read the free Plain Language Summary for this article on the Journal blog.

Effects of Potassium Loading over Iron–Silica Interaction, Phase Evolution and Catalytic Behavior of Precipitated Iron-Based Catalysts for Fischer-Tropsch Synthesis

Potassium (K) promoter and its loading contents were shown to have remarkable effects on the Fe–O–Si interaction of precipitated Fe/Cu/K/SiO2 catalysts for low-temperature Fischer-Tropsch synthesis (FTS). With the increase in K content from 2.3% (100 g Fe based) up to 7% in the calcined precursors, Fe–O–Si interaction was weakened, as reflected by ATR/FTIR, H2-TPR and XPS investigations. XRD results confirmed that the diffraction peak intensity from (510) facet of χ-Fe5C2 phase strengthened with increasing K loading, which indicates the crystallite size of χ-Fe5C2 increased with the increase in K contents either during the syngas reduction/carburization procedure or after FTS reaction. H2-TPH results indicated that more reactive surface carbon (alpha-carbon) was obtained over the higher K samples pre-carburized by syngas. Raman spectra illustrated that a greater proportion of graphitic carbon was accumulated over the surface of spent samples with higher K loading. At the same time, ATR-FTIR, XRD and Mössbauer spectra (MES) characterization results showed that a relatively higher level of bulk phase Fayalite (Fe2SiO4) species was observed discernibly in the lowest K loading sample (2.3 K%) in this work. The catalytic evaluation results showed that the CO conversion, CO2 selectivity and O/P (C2–C4) ratio increased progressively with the increasing K loading, whereas a monotonic decline in both CO conversion and O/P (C2–C4) ratio was observed on the highest K loading sample during c.a. 280 h of TOS.

Solution chemistry mechanisms of exogenous silicon influencing the speciation and bioavailability of cadmium in alkaline paddy soil

The mechanism of silicon (Si) influencing cadmium (Cd) speciation and bioavailability in alkaline paddy soil solution remains unclear. Therefore, this study sought to elucidate the effect of Si on Cd by combining chemical analysis and rice pot experiments. In this work, the effects of Na2SiO3 alkalinity and the differences in Na+ were eliminated in all treatments, and the Cd speciation in soil solutions was determined in-situ using a Field-Donnan membrane technology (DMT) cell. Additionally, rice yields and the Cd content in various parts of the rice plant were studied. The results showed that Si application significantly increased rice biomass by 32% (P < 0.05) while significantly reduced the Cd content in brown rice by 52% (P < 0.01) and the free Cd2+ concentration in the soil solution. Further analysis of the interaction of Si and Cd using Fourier transform-infrared spectroscopy (FT-IR), Raman, and X-ray photoelectron spectroscopy (XPS) indicated that a Si-Cd complex was formed by Cd and Si-O groups. In summary, Si changed the chemical speciation of Cd in the alkaline soil solution and formed a water-soluble Si-Cd complex that the rice could not absorb, consequently reducing Cd bioavailability.

Mo–Si–B alloys for ultra-high-temperature space and ground applications: liquid-assisted fabrication under various temperature and time conditions

Boron-doped molybdenum silicides have been already recognized as attractive candidates for space and ground ultra-high-temperature applications far beyond limits of state-of-the-art nickel-based superalloys. In this work, we are exploring a new method for fabricating Mo–Si–B alloys (as coatings or small bulk components) by utilizing a pressure-less reactive melt infiltration approach. The basic assumption of this approach is a synthesis of binary and/or ternary and complex intermetallic phases (silicides, borides, borosilicides), through a direct interaction of Si–B melt with molybdenum. The main purpose of this work was to examine the effect of temperature and time of Si–B melt interaction on the structure and morphology of the formed reaction products. For this purpose, sessile drop experiments were carried out on the eutectic Si–3.2B (wt%) alloy/Mo couples at temperature varying between 1385 and 1550 °C and holding time between 10 and 30 min. The solidified sessile drop couples were subjected to microstructural characterization by means of light microscopy and scanning electron microscopy analyses performed both at “top-view” and cross-sectioned interfaces. The phases formed within the interaction zone were identified by using TEM/SAED and XRD techniques. It was documented that a thickness of both main product layer (MoSi2 + Mo5Si3) and boron-rich interlayer increases with raising temperature and time of the Si–B melt interaction with Mo substrates.

Coupling effects of mineral components on arsenic transformation during coal combustion

Exploring arsenic (As) transformation during coal combustion is beneficial for reducing its pollution. Herein, combustion experiments were developed at 1100–1300 °C in a fixed-bed experimental system with 25 types of coal samples. The occurrences of As in coal and combustion products were characterized. All the original forms of As in coal were found to be unstable during combustion. As retained in ash existed as water-soluble and ion-exchangeable and residual forms, but only as residual form at combustion temperature above 1200 °C. The distribution of As in gaseous and solid combustion products varied widely by coal types, which resulted from the coupling effects of multi-minerals in coal. Co-combustion experiments were conducted using As model compounds and pure minerals, by which the interaction of Ca, Fe, Si and Al minerals to retain As was elucidated. The As transformation during coal combustion was primarily attributed to the coupling action of Ca, Fe, Si and Al minerals in coal. As a result, As was retained as Ca–Si–Al–As and Fe–Si–Al–As composite salts in the ash, which have little environmental hazard. Utilizing the coupling effects of multi-minerals during combustion help reduce As pollution from coal-fired plants.

ACE2-Fc fusion protein overcomes viral escape by potently neutralizing SARS-CoV-2 variants of concern

COVID-19, an infectious disease caused by the SARS-CoV-2 virus, emerged globally in early 2020 and has remained a serious public health issue. To date, although several preventative vaccines have been approved by FDA and EMA, vaccinated individuals increasingly suffer from breakthrough infections. Therapeutic antibodies may provide an alternative strategy to neutralize viral infection and treat serious cases; however, the clinical data and our experiments show that some FDA-approved monoclonal antibodies lose function against COVID-19 variants such as Omicron. Therefore, in this study, we present a novel therapeutic agent, SI–F019, an ACE2-Fc fusion protein whose neutralization efficiency is not compromised, but actually strengthened, by the mutations of dominant variants including Omicron. Comprehensive biophysical analyses revealed the mechanism of increased inhibition to be enhanced interaction of SI–F019 with all the tested spike variants, in contrast to monoclonal antibodies which tended to show weaker binding to some variants. The results imply that SI–F019 may be a broadly useful agent for treatment of COVID-19.

Theoretical Study on Si−Cl Bond Activation in Pd‐Catalyzed Cross‐Coupling of Chlorosilanes with Organoaluminum

AbstractThe catalytic cross‐coupling of chlorosilanes has recently emerged as an efficient method for the synthesis of organic silicon compounds. Direct Si−Cl bond activation by transition metals is a key elementary reaction in these methods. This theoretical study aimed to elucidate the mechanism of activation of the strong Si−Cl bond in Pd‐catalyzed coupling reaction to gain insights for rational catalyst design. Our results suggest two plausible pathways for the bond activation: (i) trans‐oxidative addition and (ii) SN2‐type oxidative addition assisted by a Lewis acid. With an increase in Cl substituents of chlorosilanes, trans‐oxidative addition highly feasible due to their higher Lewis acidities, in which the facile formation of the Pd→Si interaction enables the smooth activation of the Si−Cl bond. The general mechanism of direct Si−Cl bond activation presented here may prove useful for the rational design of catalysis in the future.

Metal complexes containing silicon‐based pincer ligands: Reactivity and application in small molecule activation

AbstractThis review highlights the chemical properties of metal complexes supported by silicon‐based tridentate ligands. Silicon donors coordinated to a metal exhibit unique characteristics such as a strong trans influence, σ‐SiH interaction, and metal–ligand cooperativity. Thus, this type of donors ensures distinct reactivity toward various substrates. In particular, the σ‐SiH interaction and mechanism of SiH bond cleavage are discussed. Several attempts to exploit silyl metal complexes for the activation of small molecules, including dinitrogen, carbon dioxide, dihydrogen, and dioxygen, have been reported. This review summarizes recently reported reactions of silyl pincer complexes with small molecules and provides new insights into the possibility of adapting silicon‐based ligands to model the chemistry of biological catalytic systems.

Understanding the interaction mechanism of iron and calcium during Zhundong high-iron coal combustion by the experimental study and molecular dynamics simulation

In order to obtain widespread applications for Zhundong high-iron coal, the interaction characteristics of calcium and iron during the Zhundong high-iron coal combustion were investigated experimentally in one-dimensional furnace and further explored via molecular dynamics (MD) simulation. The properties of raw coal and formed ash deposition were analyzed by XPS, ICP-OES, XRD and SEM-EDX, and MD simulations were mainly employed to dig the microstructural characteristics and viscosities of the slag systems. The results indicated that the main forms of iron in Zhundong high-iron raw coal are sulfide iron, carbonate iron and silicate iron, which account for about 46.6%, 34.5% and 18.9%, respectively. The spherical and irregular lumpy deposited samples will bond with the increase of the temperature, signifying that more iron-containing minerals in the flue gas begin to melt and react with other minerals to form a low-temperature eutectic. The hollow ash spheres are produced during the combustion process, due to the decomposition of anhydrite under higher temperatures. Meanwhile, the interaction of Fe, Ca, Al, and Si for forming a low-temperature eutectic can result in the enhanced smoothness of ash deposited surface. The MD simulations results indicated that the reaction between iron and calcium is one chemical interaction, and the appearance of multiple peaks verifies the occurrence of the slag melting phenomenon. In addition, the viscosity of Zhundong high-iron coal is relatively lower, and decreases with the increase of the temperature. The slag body burning Zhundong high-iron coal can exhibit a good fluidity, aggravating ash deposition issues.

Method for the modification of graphite subsurface layer to a solid mixture of SiC and graphite

We studied the interaction of molten Si and graphite surface during annealing in different atmospheres (CO, vacuum, Ar). The studies have shown that during annealing in CO atmosphere a composite material of SiC and graphite in a thick subsurface layer of the graphite is being formed, whereas at vacuum and Ar atmosphere the modified layer is either thin or absent. The composition and structure of both the composite material itself and the interface between the composite material and the graphite matrix were investigated using the methods of scanning electron microscopy and Raman spectroscopy. Studies have shown that the composite material obtained by this method has a branched fibrous structure consisting of small tubular layers of silicon carbide interspersed with large monocrystalline grains of silicon carbide of the cubic polytype, which leads to significant strengthening of the material. Thus the proposed method can be used to form a thermal protective, chemically resistant coating on graphite surface.

Different Reactivities of (5-Ph2P-Ace-6-)2MeSiH toward the Rhodium(I) Chlorides [(C2H4)2RhCl]2 and [(CO)2RhCl]2. Hirshfeld Atom Refinement of a Rh–H···Si Interaction

The reaction of (5-Ph2P-Ace-6-)2MeSiH with [(C2H4)2RhCl]2 proceeded via elimination of ethylene and oxidative addition of the Si–H bond at rhodium and provided the rhodium(III) complex (5-Ph2P-Ace-6-)2MeSiRh(H)Cl (1) possessing a reverse agostic interaction of the type Rh–H···Si, which was characterized by Hirshfeld atom refinement (HAR) of single-crystal X-ray diffraction data. This technique allows the precise and accurate determination of hydrogen positions also for heavier transition-metal hydrides. The bonding situation in the Rh–H···Si interaction was further analyzed using a set of complementary bonding indicators, such as the compliance matrix analysis or real-space bonding indicators derived from the electron and electron pair densities. The reaction of (5-Ph2P-Ace-6-)2MeSiH with [(CO)2RhCl]2 occurred via elimination of hydrogen chloride and produced the rhodium(I) complex (5-Ph2P-Ace-6-)2MeSiRh(CO)2 (2).

Mitigation of climate change and environmental hazards in plants: Potential role of the beneficial metalloid silicon

In the last decades, the concentration of atmospheric CO2 and the average temperature have been increasing, and this trend is expected to become more severe in the near future. Additionally, environmental stresses including drought, salinity, UV-radiation, heavy metals, and toxic elements exposure represent a threat for ecosystems and agriculture. Climate and environmental changes negatively affect plant growth, biomass and yield production, and also enhance plant susceptibility to pests and diseases. Silicon (Si), as a beneficial element for plants, is involved in plant tolerance and/or resistance to various abiotic and biotic stresses. The beneficial role of Si has been shown in various plant species and its accumulation relies on the root's uptake capacity. However, Si uptake in plants depends on many biogeochemical factors that may be substantially altered in the future, affecting its functional role in plant protection. At present, it is not clear whether Si accumulation in plants will be positively or negatively affected by changing climate and environmental conditions. In this review, we focused on Si interaction with the most important factors of global change and environmental hazards in plants, discussing the potential role of its application as an alleviation strategy for climate and environmental hazards based on current knowledge.

Interaction of Si and Al and Its Effect on AlN Precipitation in Ferritic Fe at 1373 K to 1473 K

To investigate the effect of Si on Al and AlN precipitation in ferritic Fe, high-temperature thermochemical equilibrium experiments were conducted on Fe-Si-Al foils and Ag-Si-Al alloys at 1373 K, 1423 K, and 1473 K. Using the activity coefficient in the infinite dilute solution and the self-interaction parameter of Si in ferritic Fe, the interaction parameter between Si and Al in solidified ferritic Fe was found to be a positive value, which corresponds to a repulsive relationship. And its temperature dependence could be also determined as follows. $$ e_{\text{Al}}^{\text{Si}} = \frac{3025}{T} - 1.73 $$ Considering the effect of Si on the activity coefficient of Al, the solubility of AlN in ferrite Fe was investigated and compared with the conventional estimation. It could be confirmed that the stable region of AlN formation becomes larger due to the repulsive relationship between Si and Al in the present research.

Correlation between mixing enthalpy and structural order in liquid Mg−Si system

The mixing enthalpies and structural order in liquid Mg−Si system were investigated via ab-initio molecular dynamics at 1773 K. By calculating the transferred charges and electron density differences, the dominance of Si−Si interactions in the chemical environments around Si was demonstrated, which determined that the mixing enthalpy reached the minimum on Mg-rich side. In terms of Honeycutt and Anderson (HA) bond pairs based on the partial pair correlation functions, the attraction between Si−Si pairs and Mg atoms was revealed, and the evolution of structural order with Si content was characterized as a process of constituting frame structures by Si−Si pairs that dispersed Mg atoms. Focusing on tetrahedral order of local Si-configurations, a correlation between the mixing enthalpy and structural order was uncovered ultimately, which provided a new perspective combining the energetics with geometry to understand the liquid Mg−Si binary system.

Interactions, space presentations, blocks and cross products

Physics counts four basic forces, the electromagnetic EMI, weak WI, strong SI interactions and gravity GR. The first three are provided with a unified theory which partly needs revision and has the symmetry U(1)xSU(2)xSU(3). In this article their space presentations are described in order to inlcude a theory for gravity which cannot be added directly to the standrd model. There are many instances of gravitational actions which are different from the other three interactions. Gravity uses geometrical models beside spactime, often projective, including stereographic and spiralic orthogonal subspace projections. Real and complex cross products, symmetries which belong to the complex Moebius transformation subgroups, complex cross ratios, Gleason frame GF measures, dihedrals nth roots of unity with symmetris are some new tools (figure 14) for a new gravity model. The basic vector space is 8-dimensional, but beside the usual vector addition and calculus there are different multiplications added. The author uses complex multiplications in the complex 4-dimensional space C4 for calculus. The SU (3) multiplication of GellMann 3x3-matrices is used for C³ and its three 4-dimensional C² projections. Projective spaces are CP² for nucleons and a GR Higgs plane P² and projective measuring GF‘s which have 3-dimensional, orthogonal base vectors like spin. The doubling of quaternionic spacetime to octonians has a different multiplication and seven GF‘s which partly occur in physics as cross product equations. Beside the real, the complex cross product extends the spacetime dimensions from 4 to 8. Consequences are that there are many 3-dimensional, many 4-dimensional, some 6-dimensional and also projective 5-dimensional spaces in which the actions of gravity can then be described. Spacetime is for this not sufficient. No symmetry can be muliplied to the standard model since the new symmetries belong to different geometries and are not directly related to a set of field quantums like one photon for EMI, three weak bosons (or four) for WI, eight gluons for SI. GR has graviton waves similar to EMI waves and in quasiparticle form rgb-graviton whirls, for mass Higgs bosons, maybe also solitons (density as mass per volume changing). They attribute to a distance metric between two points (kept fixed) an amplitude density (operator} which changes the metrical diameter of the volume, but not the mass.

The intricacy of silicon, plant growth regulators and other signaling molecules for abiotic stress tolerance: An entrancing crosstalk between stress alleviators

Unfavorable environmental conditions are the critical inimical to the sustainable agriculture. Among various novel strategies designed to protect plants from abiotic stress threats, use of mineral elements as ‘stress mitigators’ has emerged as the most crucial and interesting aspect. Silicon (Si) is a quasi-essential nutrient that mediates plant growth and development and interacts with plant growth regulators (PGRs) and signaling molecules to combat abiotic stress induced adversities in plants and increase stress tolerance. PGRs are one of the most important chemical messengers that mediate plant growth and development during stressful conditions. However, the individual roles of Si and PGRs have extensively defined but their exquisite crosstalk with each other to mediate plant stress responses is still indiscernible. The present review is an upfront effort to delineate an intricate crosstalk/interaction between Si and PGRs to reduce abiotic stress adversities. The combined effects of interaction of Si with other signaling molecules such as reactive oxygen species (ROS), nitric oxide (NO) and calcium (Ca2+) for the survival of plants under stress and optimal conditions are also discussed.