Increasing Silicon Content Research Articles

Calendering of Silicon-Containing Electrodes and Their Influence on the Mechanical and Electrochemical Properties

The process chain of electrode production includes calendering as a crucial process step to enhance the volumetric energy density as well as to influence the particle-pore-structure and simultaneously the mechanical and electrochemical properties of the electrode coating. A further way to improve the volumetric energy density is the usage of other materials with higher specific capacity, such as silicon instead of graphite as the active material for anodes. In this study, both opportunities, calendering and using silicon-containing composites, are combined to investigate the relations between material, process and performance. The applied line loads for the compaction are correlated with the silicon mass fraction and lead to a silicon-dependent mathematical model to estimate further line loads for silicon-graphite-composite electrodes. On the basis of established analyzing methods for adhesion strength and deformation behavior, it is shown that with increasing silicon content, the elastic deformation of the electrode coating rises. In addition, the overall porosity of the electrodes is less affected by silicon than the pore size distribution compared to graphite electrodes. Furthermore, the electrical conductivity decreases at higher silicon contents independent of coating density. Moreover, the long-term electrochemical stability deteriorates with increasing silicon content and coating density.

Effect of silicon addition on phosphorus segregation at grain boundary and temper embrittlement of Fe-C-Mn-xSi steels

In this study, the influences silicon content on phosphorus segregation at grain boundary and temper embrittlement in Fe-C-Mn-(0.33 ∼ 2.07 wt%) Si low alloy steels are elucidated based on microstructural and mechanical characterizations. Our results demonstrate that the increase of silicon content in steels improves the ductility of the material by inhibiting the precipitation of carbides during tempered at 550 °C, but promotes the degree of phosphorus segregation at grain boundaries since the repulsive interaction of silicon and phosphorous, which is the main reason for the deterioration of impact toughness. The experimental results provide new insights into the temper embrittlement in steels with high silicon content.

Solids retention time dependent, tunable diatom hierarchical micro/nanostructures and their effect on nutrient removal

The hierarchical three-dimensional (3D) micro/nanostructures of diatoms make them a promising biomaterial for fabricating nanomaterials, producing bioactive pharmaceuticals or nutraceuticals, and removing micropollutants. For diatom production in a continuous flow system, little is known how bioreactor operating parameters, especially solids retention time (SRT), affect the 3D structures of diatoms. This study demonstrated that tunable diatom micro/nanostructures could be produced by varying the SRT of membrane bioreactors (MBRs). A diatom strain (Stephanodiscus hantzschii) was cultivated in two identical MBRs with a fixed hydraulic retention time (HRT) of 24 h and staged SRTs from 5, to 10, and to 20 d. As SRTs increased from 5 to 20 d, important characteristics of diatom micro/nanostructures showed linear decreases: the diameters of foramina on the areola layer decreased from 170 ± 10 to 130 ± 12 nm, the numbers of nanopores per cribrum layer decreased from 20 ± 3 to 12 ± 2, and the specific surface areas of the diatoms decreased from 36.01 ± 1.27 to 12.67 ± 2.45 m2·g−1. However, the average diatom heights increased from 2.9 ± 0.3 to 3.9 ± 0.4 µm, while diatom cell diameter (5 µm) and nanopore size (20 nm) remained unchanged. The silicon content of diatoms also linearly increased with SRT. The decrease in diatom porosity and increase in silicon content were probably due to the reduced diatom growth rates (likely resulting in less pores) at increasing SRTs, which also facilitated silica deposition as the overall diatom population stayed longer in the MBRs. As the SRTs increased from 5 to 10, and to 20 d, the nitrate (NO3−) removal efficiency decreased from 75% to 70%, and to 60%, respectively, whereas phosphorus (P) removal efficiency increased from 74% to 80%, and to 90%, respectively. The opposite trends in efficiencies were because NO3−-N was removed by cellular uptake and biomass waste whereas P was mainly removed through diatom-assisted chemical precipitation.

Influence of Graphite-Phase Parameters on the Mechanical Properties of High-Silicon Ductile Iron

High silicon solid solution-strengthened ductile iron exhibits advantageous combinations of static strength and ductility due to elevated silicon contents. However, the Charpy impact toughness decreases rapidly with increasing silicon content. In particular, the transition temperature between ductile and brittle fracture behaviour is shifted significantly to higher temperatures. Therefore, the optimum adjustment of the graphite phase is of major importance in order to achieve sufficient toughness properties. So far, little is known about the influence of the graphite phase on the toughness properties of high-silicon ductile iron. In the present study, the graphite particle distribution was therefore systematically varied for ductile iron grade EN-GJS-500-14. The effect of the graphite nodule count in the range from 77 to 273 1/mm2, and the influence of the average particle size and particle distance on the Charpy impact energy and the characteristics of the resulting transition curves were investigated by means of statistical analyses. The results that were obtained indicate that the ductile-to-brittle transition temperature in Charpy impact tests can be reduced by about 22 °C by increasing the average nodule count by 100 1/mm2. Additionally, both the lower and upper shelf energies are raised by increasing the nodule count by 100 1/mm2. Based on these results, it becomes apparent to producers that the inoculation technology for toughness-stressed components needs to be specifically considered and adapted.

The effect of cooling rate on the structure and selected properties of AlCoCrFeNiSix (x = 0; 0.25; 0.5; 0.75) high entropy alloys

High entropy alloys with variable silicon content were prepared by two different methods to determine the influence of the cooling rate and chemical composition on the structure and properties of the alloys. First, the structure of the alloys was investigated using X-ray diffractometry and electron microscopy and compared with Mössbauer spectra to obtain a comprehensive description of the atom arrangement. The formation ability of the BCC and B2 phases was confirmed. The magnetic properties were examined using a vibrating sample magnetometer and Mössbauer spectroscopy. The corrosion resistance behavior was studied by electrochemical testing. Our results show that the saturation magnetization tends to decrease with increasing silicon content and that the lowest coercive force was noted for rapidly cooled plates. The highest corrosion resistance in a 3.5% NaCl solution characterizes the AlCoCrFeNiSi0.75 alloy in the form of plates. For which Ecorr and jcorr was equal to − 0.155 V and 0.17 μA/cm2. The addition of Si led to an increase in the hardness of the ingots and plates. For example, AlCoCrFeNiSi0.75 shows 859 HV for the ingot and 727 HV for the plate.

Improvement of growth of maize by application of silicon through its suppressing effect on sodium uptake under salt stress condition

An experiment was conducted with three levels of salinity (0, 60, and 120 mM NaCl) and four levels of silicon (0, 5, 10, and 20 mM) in petridish. All the growth parameters were decreased gradually with increasing salt concentration, whereas increasing silicon concentration progressively increased the parameters up to 10 mM Si across all the salt concentrations. The beneficial role of Si was noticed both in saline and non-saline conditions. Silicon application in the growth medium dramatically reduced shoot Na content, making plants tolerant to salt stress. J. Bangladesh Acad. Sci. 45(2); 251-253: December 2021

Microstructural and Mechanical Evaluation of NbMoTiVSix(x = 0, 0.25) Refractory High‐Entropy Alloys at High Temperature

The novel refractory NbMoTiVSix(x = 0,0.25) refractory high‐entropy alloys (RHEAs) with both high strength and good ductility simultaneously by vacuum arc melting are developed. The microstructure evolution, compressive mechanical properties, and strengthening mechanism of the RHEAs with the addition of silicon at 1000 °C are analyzed and discussed. Microstructure observation shows that the NbMoTiV RHEA comprises of a single body‐centered cubic (BCC) phase, whereas the NbMoTiVSi0.25 RHEA consists of a BCC phase and simple multi‐component M5Si3 (M = Nb, Mo, Ti, V) phases. Compressive tests show that the yield and ultimate strength of the NbMoTiVSix(x = 0,0.25) RHEAs at 1000 °C increases from 590 to 931 MPa and from 682 to 1090 MPa with increasing silicon content. The improvement of strength is caused by the dipolar dislocation walls, the pinning effect of the diphasic interface, and a large amount of nano‐silicides phase particles in BCC phase, all of them are the result of silicide formation.

Прогнозна оцінка фізико-хімічних властивостей нових композицій хромовмістних феросплавів

The aim of the work was to predict the most significant physicochemical characteristics (melting temperature and density) of new chromium-containing ferroalloys with reduced chromium content and increased silicon content. The applied methodology and criteria for quantitative assessment took into account microheterogeneity of multicomponent metal melts, melting temperature and density. Information about these characteristics is necessary for studying the kinetics of melting, assimilation of the leading elements of ferroalloys by the metal melt, and determining the efficiency of their use. An original approach is used to solve the modeling tasks, which is based on the concept of physicochemical modeling of interatomic interaction processes in melts, developed under the leadership of Professor E. V. Prykhodko. According to the developed concept, metal melts are considered as chemically unified systems, and a change in their composition affects a complex of physical and chemical properties caused by a change in the parameters of their electronic structure. To evaluate and take into account the influence of the microheterogeneity of the structure of melts of ferroalloy systems, the method of calculating criteria (ΔZy and Δd) was used, characterizing the degree of difference in the electronic and structural state of the melt as a chemically unified system, as opposed to a mechanical mixture of their initial components. Using these criteria and experimental ones, the values of the most important physicochemical characteristics of new compositions of chromium-containing ferroalloys, which are missing in the literature, were obtained. The results of the calculation of these properties can be used to change and improve the characteristics of chromium-containing ferroalloys in order to develop their rational compositions.

Increasing Silicon Concentration and Doping Heteroatom to Successfully Realize High HER Catalytic Activity in 2D Metal-Free BSi n (n = 1–4) Structures: A First-Principles Study

Under the DFT calculations, the graphene-like two-dimensional (2D) BSi n (n = 1–4) nanostructures are stable in terms of energy, kinetics and thermal aspects, and can possess metallic conductivity, which are advantageous to their catalytic activities for hydrogen evolution reaction (HER). Our computed results reveal that they can uniformly exhibit high HER catalytic activity. With increasing the Si/B atomic ratio, higher HER activity can be achieved, due to the change from weak aromaticity to strong anti-aromaticity for the correlative BxSiy six-membered rings. Moreover, by doping P, S, Ge and C atoms with the different electronegativity, the HER activity of the studied systems can be further improved because the electron transfer induced by these dopants can effectively activates the relevant B and Si atoms. In addition, in view of more active sites, increasing the Si concentration can also generally increase the HER activity of doped systems. For all BSi n systems studied, the Si–Si bridge sites or Si-sites can uniformly serve as the most active sites. This study not only represents the first application of 2D metal-free BSi n in HER catalysis, but also provides new strategies for designing high-efficient and low-cost HER electrocatalysts based on Si/B or even other Si-containing materials.

Appearance of phenotypic plasticity of leaves in psammophyte Corynephorus canescens during flooding

The results of the study of the leaf structure in psammophyte Corynephorus canescens, which grew under controlled conditions and flooding using the methods of light microscopy, scanning electron microscopy, and laser confocal microscopy, are presented. This study revealed common and distinctive signs of morphological and anatomical parameters of C. canescens leaves in the phase of vegetative growth. Among the common features were the shape and size of the leaf laminas, hypostomatic type of the leaf, isolateral structure of the parenchyma, the thick-walled epidermis, and the bilayered hypodermis. Among the distinctive features were the signs of the destruction of cells in the photosynthetic parenchyma, change in their shape with the formation of protuberances at the cells’ poles, and almost doubling area of the aerenchyma in C. canescens leaves under flooding conditions. Scanning electron microscopy showed the similarity of ultrastructure and density of trichomes on the adaxial surface, excepting the formation of cuticular wax structures on the epidermal surface of the leaves in flooded plants. The subcellular localization of silicon inclusions was studied for the first time. The presence of amorphous and small crystalline silicon inclusions in the periclinal walls of the main epidermal cells and amorphous silicon inclusions in leaf trichomes was established. An increase in the relative silicon content along the trichomes in the leaves’ epidermis after flooding was revealed. It was assumed that the phenotypic plasticity of C. canescens, is realized through the increasing area of aerenchyma in leaves and increasing silicon content in trichomes. Such plasticity helps to optimize both the oxygen balance of plants and water balance in flooded plants, thus increasing the species’ resistance to prolonged flooding.

Effect of Si Content on the Properties of A356 Aluminum Alloy

The effects of different Si contents on the microstructure and mechanical properties of A356 aluminum alloy were studied by metallographic microscope analysis and tensile property test. The results show that when the silicon content is between 7% and 11 %, with the increase of silicon content, the eutectic silicon in the matrix increases, and the tensile strength and elongation decrease. When the silicon content increased to 13%, the primary silicon structure appeared in A356 aluminum alloy, and its mechanical properties increased.

Influence of silicon on the structure and properties of high-strength cast aluminum alloy AZ5NF

The phase composition and the mechanical properties of the AZ5NF with various contents of silicon impurities alloy were investigated by both calculation and experimental methods. For evaluation of the alloy phase composition and the effect of the chemical composition, CALPHAD method integrated in Thermo-Calc software was applied. Further scanning electron microscopy technique a significant increase of the volume fraction of Mg2Si phase with an increase of silicon content from 0.1% to 0.3%. It is shown that in case of silicon content higher than 0,2 wt.% Mg2Si phase starts forming during equilibrium crystallization. This phase forms as the thin layers at the grain boundaries. This leads to brittle intergranular fracture and significant reduction of the alloy ductility both in the as-cast state and in T6 temper. Based on this limits for the silicon content in AZ5NF have been proven. It is shown that dissolution of Mg2Si phase (full or partial depending on silicon content) requires solid solution treatment. Following quenching and artificial ageing provide high strength and ductility.

Reversible kinetics and rapid tunnelling characteristics of silicon doped magnesium-titanium nanocomposites prepared by mechanical alloying route for nickel-metal hydride batteries

Magnesium-Titanium-Silicon (Mg-Ti-Si) hybrid nanocomposites have been synthesized by using high energy ball milling. Magnesium, titanium and silicon powder mixtures are taken in the stoichiometric molar ratio of Mg0.8-xTi0.2Six (x = 0, 0.10, 0.15, 0.20 and 0.25) and mechanically milled for 30 h. The phase transformation, micro-strain and microstructural changes during mechanical alloying are examined by X-ray diffraction (XRD) and scanning electron microscope (SEM). Band gap engineering is a process done by high energy ball milling of Mg0.8Ti0.2, Mg0.8-xTi0.2Six powders, which have been tailored from 0.629 to 1.685 eV, which are obtained from the optical absorption spectra. The band gap energy is the most substantial parameter to understand the electrochemical charge-discharge activation behaviour. The high planar diffusion with high reversible reaction has been occurred only for the 30 h ball milled Mg0.70Ti0.20Si0.10 and Mg0.65Ti0.20Si0.15 powders. During the oxidation behaviour, they have been gained the higher diffusion coefficient (1.87 × 10−08 cm2 s−1 and 1.53 × 10−08 cm2 s−1), high exchange ion current density (1841 mA g−1 and 1113 mA g−1), the patronizing maximum discharge capacity (329 mAh g−1 and 307 mAh g−1), maximum energy density (0.265 Wh g−1 and 0.219 Wh g−1) with high quasi-reversible coulombic efficiency (65.80% and 61.40%) and high cyclic stability (87.23% and 82.08%) respectively. The addition of silicon concentration increases (i.e. x = 0.10–0.25) in magnesium-titanium based ball milled powders enhance the activation behaviour and robustly reduce the Gibbs free energy from −127 to −64 kJ mol−1.

Combined effect of silicon and non-thermal plasma treatments on yield, mineral content, and nutraceutical proprieties of edible flowers of Begonia cucullata

Edible flowers are becoming popular as a nutraceutical and functional food that can contribute to human nutrition with high antioxidant molecules and mineral elements. While comparative studies between different flower species have been performed, less is known about the best agronomical practices to increase yield and nutraceutical proprieties of blooms. Silicon stimulates plant resistance against stress and promotes plant growth while non-thermal plasma (NTP) technology has been applied for the disinfection and decontamination of water, as well as for increasing plant production and quality. The application of silicon and NTP technology through nutrient solution and spraying was investigated in edible flowers given that the combination of these treatments may play a role in promoting their nutritional and nutraceutical proprieties. The treatments were applied on two varieties of Begonia cucullata Willd. (white and red flowers) to explore their effects on different flower pigmentations. Plants with red flowers showed higher nutraceutical proprieties than the white ones but yielded a lower flower number. While the NTP treatment did not improve flower yield and quality, the silicon treatment increased anthocyanins and dry weight percentage in red flowers. NTP treatment increased zinc concentration, while it decreased potassium, magnesium, and manganese, and increased silicon concentration in white flowers. The combination of silicon and NTP showed negative effects on some nutraceutical proprieties of red flowers thus highlighting that the two treatments cannot be combined in edible flower production. In conclusion, the positive effect of silicon use in edible flower production has been demonstrated while the NTP technology showed contrasting results and its use should be explored in greater depth, including a consideration of its role in biotic attack prevention and reduced chemical input.

The Effect of Dust Transport on the Concentration of Chlorophyll-A in the Surface Layer of the Black Sea

This paper focuses on the atmospheric dust transport effect on the changes in chlorophyll-A concentration in the Black Sea surface layer. In order to assess the input of nutrients with atmospheric precipitations at the Crimean coast of the Black Sea, the collected samples were analyzed for the content of inorganic nitrogen, phosphates, and silicon. The samples were taken into a wet-only sampler and into a permanently open one, to assess the effect of dust on the nutrients concentration in dry depositions. Cases of multi-fold excess of the nutrients content in the open sampler collected precipitation over that in the wet-only sampler were identified. For such high concentration cases, the 7-day back-trajectories analyses was carried out using the model of the international network AERONET and the HYSPLIT model. The results of our research showed that the influx of nutrients with the atmospheric depositions can result in increasing of chlorophyll-A concentration in 11–36% in the surface layer of the Black Sea. After atmospheric depositions, concentration of phosphates in the surface layer can increase more than five times compared with the background concentration. The increase of silicon concentration can reach 30%. The influx of atmospheric precipitation containing significant amounts of nutrients into the bay can shifts the Redfield ratio compared with background value up to three times.

Investigation of selective oxidation during cooling of hot-rolled iron-manganese-silicon alloys

The kinetics of selective oxidation in iron-manganese-silicon alloys of varying silicon contents was examined at 700°C and oxygen partial pressure of 2.9×10−22 bar for up to 2 h. The investigation revealed a linear mass gain over time, suggesting oxygen uptake as the rate-controlling step of reaction. Internal oxidation depth particularly along grain boundaries increased considerably with increasing silicon content. Differences in microstructure and near-surface chemistry of the alloys as a function of the silicon content are discoursed on. The results point to the crucial role of a thin oxide layer, a solid solution between FeO and MnO, in the oxidation process.

Influence of Strain Rate, Temperature and Chemical Composition on High Silicon Ductile Iron

Today, the use of solution hardened ductile iron is limited by brittleness under certain conditions. If chassis components are subjected to loads having high strain rates exceeding those imposed during tensile testing at sub-zero temperatures, unexpected failure can occur. Therefore, it is the purpose of this review to discuss three main mechanisms, which have been related to brittle failure in high silicon irons: intercritical embrittlement, the integrity of the ferritic matrix and deformation mechanisms in the graphite. Intercritical embrittlement is mainly attributed to the formation of Mg- and S-rich grain boundary films. The formation of these films is suppressed if the amount of free Mg- and MgS-rich inclusions is limited by avoiding excess Mg and/or by the passivation of free Mg with P. If the grain boundary film is not suppressed, the high silicon iron has very low elongations in the shakeout temperature regime: 300 to 500 °C. The integrity and strength of the ferrite are limited by the reduced ordering of the silicumferrite with increasing silicon content, once the “ordinary” ferrite is saturated at 3% silicon, depending on the cooling conditions. Finally, the graphite damaging mechanisms are what dictate the properties most at low temperatures (sub −20 °C).

Laser welding of dual-phase steels with different silicon contents: Phase evolutions, microstructural observations, mechanical properties, and fracture behavior

Abstract This paper reports an investigation into the effect of silicon content on phase transformations, microstructural evolutions, and mechanical behavior of Nd:YAG laser welded dual-phase steels. The experimental investigation was conducted on laboratory-processed 0.15 C-1.7 Mn steels with different silicon contents. The heat treatment cycle to develop a dual-phase structure consisted of austenitization at 790 °C for 15 min followed by water quenching. The fabricated steels were welded in a butt joint configuration to obtain a fully-penetrated weld joint. Optical microscopy, scanning electron microscopy, and uniaxial tensile test were performed to evaluate microstructural changes, phase transitions, and mechanical properties, respectively. The fracture behavior of the welded joints was also investigated using a scanning electron microscope. The results showed that the volume fraction of martensite was increased with an increase in silicon content. The samples with higher silicon content also had a finer structure, which was due to the higher driving force created during previous cold working. All welded joints were found to consist of a nearly fully martensitic structure, and the heat-affected zone (HAZ) contained a low-temperature region (with partially or fully tempered martensite) and a high-temperature region (with newly-formed martensite). The specimen with the lowest silicon content had the minimum elongation and toughness modulus owing to an incomplete tempering process in HAZ. The specimens containing higher amounts of silicon were fractured in the base metals because of the presence of the martensite phase as a major micro-constituent in the fusion zone. The fracture mechanism of the laser-welded dual-phase steels with a low-volume fraction of martensite and small ferrite grain size was micro-void formation whilst the separation and de-cohesion were observed in dual-phase steels that had a high-volume fraction of martensite.

Is it possible to reactivate hydrotreating catalyst poisoned by silicon?

The feasibility of the reactivation of CoMo/Al2O3 hydrotreating catalysts poisoned by Si compounds has been studied. CoMo/Al2O3 catalysts poisoned with 3, 4 and 5 wt.% of silicon were obtained during hydrotreating of diesel fraction contaminated with decamethylcyclopentasiloxane. Catalysts poisoned by different amount of silicon were regenerated by oxidative treatment and subsequently reactivated using citric acid solution. The catalysts were studied by nitrogen adsorption-desorption method, CHNS analysis, UV–vis, thermal analysis, SEM, HRTEM, XPS. It was shown that the hydrodesulfurization activity of regenerated catalysts decreased with increasing silicon content. According to UV–vis results, the increase in Si content on the spent catalyst leads to the formation of CoOx oxides after oxidative regeneration. Probably, cobalt oxides do not promote MoS2 slabs during sulfidation, convert to inactive Co species and decrease hydrodesulfurization activity. After reactivation procedure, there was the increase in active component particles dispersion, while catalytic activity in hydrodesulfurization of dibenzothiophene and hydrodenitrogenation of quinoline increased. It was established that hydrodesulfurization and hydrodenitrogenation activities of CoMo/Al2O3 catalyst with less than 3 wt.% of Si could be completely restored by reactivation.

Silicon-content-dependent microstructures and mechanical behavior of (AlCrTiZrMo)-Six-N high-entropy alloy nitride films

The multi-component (AlCrTiZrMo)-Six-N high-entropy films with different silicon contents were deposited on the silicon substrate by magnetron sputtering. The influence of silicon contents on the structures and properties of the films was studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), electron probe microanalyzer (EPMA) and nanoindentation. The results show that the (AlCrTiZrMo)N film without silicon has columnar crystals and the (200)-preferred direction. With the increase of the silicon content, the films gradually change from columnar grains with a (200) preferential orientation to structures with amorphous phases (amorphous phases are the state of near order and long disorder in the arrangement of atoms in a solid state) containing nanocrystals (nanocrystallites are single-phase (AlCrTiZrMo)N of grains with a size of 5–10 nm) with finer grains. As the silicon content increases, the mechanical properties of the films first increase then decrease. Thus, when the silicon content is 4.5 atomic percent (at.%), the film obtained possessed comprehensive mechanical properties with the maximum hardness and modulus values of 28.5 GPa and 325.4 GPa, respectively. The results show that the improvement of hardness and modulus is mainly attributed to the microstructures of the films.