High Si Content Research Articles

Laser induced reduction of iron ore by silicon

Iron ore powder accompanied by Si-powder as a reducing agent, was melted using a high-power laser beam. During laser melting of the two different powder beds placed next to each other, silicon merged and diffused into the iron ore, forming a ternary melt phase Fe-O-Si of around 30–60–10 at%. High speed imaging of the laser melting process as well as subsequent SEM-analysis of the generated nuggets showed the formation of droplets that merge with the surrounding Si- or ore-powder and form distinct domains. Under certain circumstances, the solidifying nuggets, of the order of 0.5–5 mm in size, generated numerous small domains, up to 25 µm, of high purity iron, 90 + at%, surrounded by a matrix of the above mentioned slag. Many of these Fe-domains were created in the vicinity of regions of high Si-content.

Microstructure and mechanical properties of in-situ Ti5Si3/TC4 composites via spark plasma sintering and hot rolling

In this study, low energy ball milling and spark plasma sintering techniques prepared the in-situ synthesized Ti5Si3 reinforced Ti-6Al-4V (TC4) matrix composites and then rolled them at high temperatures. In the composites with high Si content, the Ti5Si3 particles distributed at the interface of α-phase and β-phase agglomerated and then formed a quasi-continuous network structure, which will deteriorate the plasticity of the composites. After hot rolling, the grains of the composite were significantly refined, and more Ti5Si3 particles were precipitated. With the increase in Si content, the tensile strength of sintered composites increased slightly, but the elongation decreased greatly. After hot rolling, the tensile strength of the composite increased significantly with an increment of 359.4 MPa, among which the composite with 0.6 wt% Si achieved a synchronous increase in strength and plasticity. The strengthening mechanism of sintered composites included dislocation strengthening, solution strengthening, and grain refinement, among which dislocation strengthening and grain refinement were the main strengthening mechanisms. The strengthening mechanism of rolled composites was mainly the dislocation strengthening caused by rolling, the grain refinement, and the mismatch of thermal expansion coefficient.

Unexpected sluggish martensitic transformation in a strong and super-ductile high-entropy alloy of ultralow stacking fault energy

Displacive martensitic transformation usually prevails in face-centered cubic (FCC) steels and high-entropy alloys (HEAs) of low stacking fault energy (SFE; e.g., <15 mJ/m2) upon deformation. Here, we present and rationalize an unexpectedly sluggish and suppressed martensitic transformation behavior in a newly developed non-equiatomic HEA (Fe30Ni20Co20Cr20Si10, at.%) with an ultralow SFE, i.e., ∼7 mJ/m2 measured by weak-beam dark-field scanning transmission electron microscopy (STEM) at room temperature. The recrystallized FCC HEA with an average grain size of ∼14.9 µm shows an ultimate tensile strength of 903 MPa and a fracture elongation of ∼83.1 %. Plastic deformation of this alloy with ultralow SFE is characterized by the intensive formation of stacking faults (SFs), whereas the volume fraction of hexagonal close-packed (HCP) martensite is very low even at cold-rolled state with an equivalent strain of 1.85, i.e., < 8.3 % according to neutron diffraction analysis. Atomic-scale TEM observation demonstrates that chemical short-range order (CSRO) domains are present in the FCC solid solution. Apart from contributing to the high strength, the CSRO domains and atomic size misfit (2.36 %) promoted by the high content of Si are regarded to enhance the local barrier for the successive accumulation of SFs, hindering the formation of HCP martensite and mechanical twin. The uniform formation of SFs in the FCC matrix upon deformation effectively alleviates strain localization, contributing to the sustained strain-hardening ability and super-ductility. These insights suggest a strategy to design low-SFE alloys with excellent mechanical properties via manipulating the rate of martensitic transformation by CSROs and atomic size misfit.

The new nanocapsule structure and cyclic tribological properties of Mo2N/Ag/Si3N4 nanocomposite film

Nanostructured films present versatile properties in the area of friction. This paper introduced a adaptive nanostructured film with multiple cycle service capability. Based on the concept of capsule sustained-release, a series of Mo2N/Ag/Si3N4 composite films with different Si contents were prepared. The results show that the films were mainly composed of fcc-Mo2N, fcc-Ag and Si3N4, presenting a “capsule structure” with the encapsulation of Mo2N/Ag by Si3N4. The crystalline Si3N4 wrap the Mo2N to form a co-extended growth structure, when the Si content is lower than 6.3 at. %. However, the coherent interface could be destroyed for the film with higher content of Si (>6.3 at. %), owing to the transforming to an amorphous phase of Si3N4. When annealed at 500 °C, the growth of Ag content on the surface is higher for film with 6.3 at. % Si than that of film with 11.4 at. % Si, indicating that the capsule structure with amorphous Si3N4 can hinder the diffusion of Ag. With the increase of Si content, the hardness of the film increases firstly and then decreases gradually. The maximum hardness value of 34.3 GPa can be obtained for the film with 6.3 at. % Si. The average friction coefficient of Mo2N/Ag/Si3N4 composite films with 6.3 and 11.4 at.% Si contents decreased from 0.48 to 0.33 and from 0.42 to 0.31 respectively with the increase of friction temperature from 200 °C to 700 °C under friction test. At the same temperature, the friction coefficient for film with 6.3 at.% Si is always lower than that of film with 11.4 at.% Si, but the wear rate is always slightly higher. The temperature-cycling friction times of nanocomposite films consisting of amorphous Si3N4 capsule structure with11.4 at.% Si is twice that of crystalline Si3N4 with 6.3 at % Si. The amorphous “capsule” structure can improve the multi-cycle serviceability of the film.

Development of FeSi steel with increased Si content by laser powder bed fusion technology for ferromagnetic cores application: Microstructure and properties

Additive manufacturing technology like laser powder bed fusion represents a valid alternative for the production of ferromagnetic cores. In this study, two grades of steel were considered, with standard (3.0 wt%) and high (6.5 wt%) Si content. The study is aimed at optimizing the process parameters in order to obtain components suitable for magnetic applications. Moreover, the effect of post-production annealing heat treatment on the microstructure evolution is investigated. The investigation included microstructural analysis by optical microscope, dynamic scanning calorimetry analysis and electro-magnetic measurements on samples with optimized geometry. Results shows that both types of steel can be produced free from defects. Even if the magnetic behaviour of FeSi6.5 samples by AM do not fully reproduces that obtained on electrical steels manufactured by standard process, it appears quite promising. In this framework the optimization of post-production processes represents a promising challenge to meet market demands.Graphical abstract

Effect of Si content on the microstructure and properties of CrSi coatings for ATF cladding

Microstructure, mechanical properties, corrosion resistance and high-temperature oxidation resistance of four CrSi coatings with different Si content ranging from 0 at% to 67 at% were investigated. With increasing Si content from 11 at% to 67 at%, the main forms of Si exist the coatings were detected to be Cr3Si, Cr5Si3 and CrSi2, respectively. All the CrSi coatings own higher nano-hardness due to the formation of intermetallic. For Si content ≤33 at%, the CrSi coatings showed good corrosion resistance in static pure water of high temperature and pressure. However, the higher Si content (67 at%) led to the dissolution of Si in the form of [Si(OH)]4, as well as insufficient Cr to form a continuous Cr2O3 layer. The high-temperature oxidation tests showed that the coating with 11 at% Si content exhibited the best oxidation resistance than other coatings, due to the formation of outermost Cr2O3 layer, stable Cr3Si phase and inner Zr2Si. Our study indicates that the coating with 11 at% Si content displays good comprehensive properties and could be used as a candidate material for ATF coatings.

Heat treatment effect on microstructure evolution of two Si steels manufactured by laser powder bed fusion

Additive manufacturing technology represents a valid alternative for the production of ferromagnetic components in Si steels (FeSi) with high Si content. In this work the effect of heat treatments on microstructural evolution of two steels with standard (3.0 wt.% - FeSi3) and high (6.5 wt.% - FeSi6.5) Si content manufactured by Laser Powder Bed Fusion (L-PBF) was investigated. Four different temperatures ranging from 900 °C up to 1150 °C (soaking time of 1 h) were tested for each steel.In as-built condition, all the grains of FeSi3 are columnar with the [100] direction parallel to the building direction (BD) whereas in the case of FeSi6.5 there is a mix of columnar and equiaxed grains. The average grain size of FeSi6.5 (11.3 ± 0.6 μm) is about one order of magnitude lower than that of FeSi3 (103.1 ± 5.2 μm). EBSD analysis revealed that there is a prevalence of low-angle boundaries (LABs) in FeSi3 and of high-angle boundaries (HABs) in FeSi6.5. The different initial microstructure affects the response to heat treatments of the two alloys: grain size and shape of FeSi3 do not remarkably change, on the contrary significant grain growth takes place in FeSi6.5 without a weakening of the [100] texture. No brittle ordered phases were detected in as-built and heat treated samples of both materials. The results indicate that heat treatments at high temperature can be exploited to improve the magnetic characteristics of printed FeSi6.5 and reach similar properties of commercial steels.

The effect of rice residue management on rice paddy Si, Fe, As, and methane biogeochemistry

Rice production results in residues of straw and husk, and the management of these residues has implications for the sustainability of the rice agroecosystem. Rice straw is typically incorporated into soil either as fresh residue or is burned prior to incorporation. Rice husk is not typically returned to rice fields. However, rice husk contains high levels of silicon, which has been shown to decrease rice accumulation of arsenic. In this work, we studied the resulting biogeochemical changes in rice paddy soils when paddies were amended with either straw or burned straw and either no husk, husk, or burned husk over two years. Using a full-factorial design, we observed that the higher lability of rice straw carbon controlled redox-sensitive processes despite the application of husk and straw at similar carbon rates. Amending paddies with straw, rather than burned straw, increased porewater Fe and As, plant As, and methane emissions regardless of husk amendment. Husk addition provided insignificant Si to the plant despite its high concentration of Si, suggesting limited short-term mobility of Si and that long-term additions of husk or higher rates may need to be studied.

Elemental composition and material properties of radular teeth in the heterobranch snail Gastropteron rubrum (Mollusca, Gastropoda, Cephalaspidea) foraging on hard organisms.

The molluscan feeding structure is the radula, a chitinous membrane with teeth, which are highly adapted to the food and the substrate to which the food is attached. In Polyplacophora and Patellogastropoda, the handling of hard ingesta can be facilitated by high content of chemical compounds containing Fe or Si in the tooth cusps. Other taxa, however, possess teeth that are less mineralized, even though animals have to avoid structural failure or high wear during feeding as well. Here, we investigated the gastropod Gastropteron rubrum, feeding on hard Foraminifera, diatoms and Porifera. Tooth morphologies and wear were documented by scanning electron microscopy and their mechanical properties were tested by nanoindentation. We determined that gradients of hard- and stiffness run along each tooth, decreasing from cusp to basis. We also found that inner lateral teeth were harder and stiffer than the outer ones. These findings allowed us to propose hypotheses about the radula-ingesta interaction. In search for the origins of the gradients, teeth were visualized using confocal laser scanning microscopy, to determine the degree of tanning, and analyzed with energy-dispersive X-ray spectroscopy, to test the elemental composition. We found that the mechanical gradients did not have their origins in the elemental content, as the teeth did not contain high proportions of metals or other minerals. This indicates that their origin might be the degree of tanning. However, in the tooth surfaces that interact with the ingesta high Si and Ca contents were determined, which is likely an adaptation to reduce wear.

Tectonic Transition from Passive to Active Continental Margin of Nenjiang Ocean: Insight from the Middle Devonian-Early Carboniferous Granitic Rocks in Northern Great Xing’an Range, NE China

Northeast China occupies the majority of the eastern Central Asian Orogenic Belt, which mainly consists of continental blocks and accretionary terranes. The Devonian was a tectonic quiet period in the NE China region due to a lack of tectono-magmatism, but the tectonic background of this period has been unclear, especially for the Hegenshan-Heihe Suture between Xing’an and Songliao accretionary terranes, which represents the Paleozoic Nenjiang Ocean (a branch ocean of the eastern Paleo-Asian Ocean). Here we report granitic rocks from the Woluohe area, Northern Great Xing’an Range, NE China, to constrain the tectonic process of the transition from the Devonian quiet period to the Early Carboniferous active tectonic period. Three granitic rock samples produce zircon U-Pb ages of 389 Ma, 368 Ma, and 351 Ma, belonging to the Middle and Late Devonian and Early Carboniferous, respectively. They have high Si, Al, K, and Na contents, but with low Mg, Fe, and Ti contents, together with positive Hf isotopic features and low molar Al2O3/(MgO+FeOT) ratios, we suggest that they were derived from partial melting of lower crustal igneous rocks. Meanwhile, the narrow major element variation at odd with the fractionation process and their negative Nb and Ta anomalies imply the obvious contribution of crustal. Comprehensive tectonic setting analysis shows all samples are in calc-alkali magmatic series with rightward fractionated REE and trace element patterns that are enriched in LREE and LILE and depleted in HREE and HFS, indicating a subduction-related magmatic arc setting. Considering the regional tectonic setting and the small scale of the Devonian plutons, we suggest a limited subduction tectonic setting during the quiet period of the northern Great Xing’an Range, which might indicate the beginning of an initial northwestward subduction of the Nenjiang Oceanic lithosphere beneath the Xing’an Accretionary Terrane in the Middle Devonian, accelerated subduction in the Late Devonian, and bidirectional subduction in the Early Carboniferous.

Microchemistry evolution during industrial DC casting and subsequent homogenization of aluminum alloy AlMn0.5Mg0.5 (AA 3105)

The properties of non-heat treatable Al wrought alloys are influenced by the materials microchemistry in terms of the portion of alloying elements either in solid solution or in precipitated form. In the present study we analyze the phase selection during solidification as well as the changes in solute level and particle state during subsequent homogenization of the Al-Mn alloy AA 3105 (ISO AlMn0.5Mg0.5). Characterization of the microchemistry reactions is performed by a combination of optical and scanning electron microscopy with differential scanning calorimetry and measurements of thermoelectric power as well as specific electrical resistivity. The results are underpinned by CALPHAD simulations of the second-phase particles in the as-cast state, while the changes in solute level as well as volume, size and type of second-phase particles during homogenization are tracked with a statistical microchemistry simulation tool named ClaNG. Owing to the high Si content of the present alloy the as-cast state is dominated by α-Al(Fe,Mn)Si phase constituent particles together with a few Al6(Mn,Fe) and Mg2Si phases. Homogenization is characterized by the formation and redissolution of Mg2Si and, at higher temperatures, dispersoids of the α-Al(Fe,Mn)Si phase.

Fruitful TEM Analysis of Hot-dip Galvanized Industrial Steels with Low and High Si Content: Challenges and Solutions.

Fruitful TEM Analysis of Hot-dip Galvanized Industrial Steels with Low and High Si Content: Challenges and Solutions.

Cultivation of carbohydrate-rich microalgae with great settling properties using cooling tower wastewater

Wastewater treatment and simultaneous production of value-added products with microalgae represent a sustainable alternative. Industrial wastewater, characterized by high C/N molar ratios, can naturally improve the carbohydrate content in microalgae without the need for any external source of carbon while degrading the organic matter, macro-nutrients, and micro-nutrients. This study aimed to understand the treatment, reuse, and valorization mechanisms of real cooling tower wastewater (CWW) from a cement-processing industry mixed with domestic wastewater (DW) to produce microalgal biomass with potential for synthesis of biofuels or other value-added products. For this purpose, three photobioreactors with different hydraulic retention times (HRT) were inoculated simultaneously using the CWW-DW mixture. Macro- and micro-nutrient consumption and accumulation, organic matter removal, algae growth, and carbohydrate content were monitored for 55 days. High COD (> 80%) and macronutrient removals (> 80% of N and P) were achieved in all the photoreactors, with heavy metals below the limits established by local standards. The best results showed maximum algal growth of 1.02 g SSV L−1 and 54% carbohydrate accumulation with a C/N ratio of 31.24 mol mol−1. Additionally, the harvested biomass presented a high Ca and Si content, ranging from 11 to 26% and 2 to 4%, respectively. Remarkably, big flocs were produced during microalgae growth, which enhanced natural settling for easy biomass harvesting. Overall, this process represents a sustainable alternative for CWW treatment and valorization, as well as a green tool for generating carbohydrate-rich biomass with the potential to produce biofuels and fertilizers.

Improving toughness and strain-hardening of a silicon-enriched ferritic/martensitic (F/M) steel via an austenite isothermal hot-rolling (AIHR) process

Si-enriched ferritic/martensitic (F/M) heat resistance steels are emerged as structural materials in advanced thermal and nuclear power stations attributed to their satisfactory corrosion resistance to coolants. However, the low toughness from high Si content over 0.5 wt% due to the formation of weaking δ-ferrite phase and the weak bonding between ferrite and martensite has been a tough trouble for application. Long time annealing at austenitizing temperature could alleviate ferrite phase but at the sacrifice of coarsening carbides and grains. Here we present an austenite isothermal hot-rolling (AIHR) strategy in which multi-pass rolling and limited annealing time are conducted at isothermal states above the austenitizing temperature. This increased toughness by almost 700% (from 7 to 56 J/cm2) meanwhile the same yield strength (787 MPa) compared to the normal quenching + tempering treatment (NT, 757 MPa). The control of element diffusion and dynamic recrystallization (DRX) by AIHR accelerated the dissolution of ferrite within short process time, coupled with the reduced {100} cleavage plane & texture and the reduction of grain size and M23C6 phases, which are responsible for the improved toughness. Besides, higher strain hardening exponent accompanying refined microstructure and primary dislocation density implies deformation stability of the steel via AIHR process. These results provided a possible way of tailoring both the strength/toughness trade-off and the hardening ability on a Si-enriched F/M steel.

Microstructural Evolutions and Strengthening Mechanism according to the Aging Temperatures of a High Si Cast Aluminum Alloy

A356 cast aluminum alloy contains 7 at.% Si and 0.3 at.% Mg, producing an approximately 50% eutectic microstructure. This high Si content and various casting conditions play a significant role in strengthening A356 alloy, by controlling the eutectic morphology and precipitates of other intermetallic compounds. Understanding how Si-related precipitates and clusters are soluble in the α-matrix is necessary to provide high strength and fatigue resistance to A356 alloys. The aging heat-treatment temperature in the A356 alloy most likely promotes the formation of these precipitates and clusters. The A356 samples were differently aged at temperatures of 110 oC and 130 oC for 2 h, and were labeled 110A, and 130A, respectively. 110A was found to have improved mechanical properties, such as high strength and elongation, compared to 130A, which may be attributed to the formation of secondary phases in the α-phase matrix. Scanning and transmission electron microscopy and atom probe tomography analyses demonstrated Ti2Si precipitation and various-sized cluster formations in 110A. In contrast, 130A had fewer clusters than 110A. Therefore, different aging heat-treatment temperatures relate to a change in the behavior of atoms, affecting the mechanical properties.

Comparative study on effects of annealing temperature on microstructures and mechanical properties of high-Al low-Si steel

We elucidate here profound effects of quenching and partitioning process after partial (IQP) or full austenitization (FQP) on the microstructure and mechanical properties of high strength hot-dip galvanized steel with high Al and low Si content. The results showed that the FQP steel contains 3.38% vol.% retained austenite with mainly film-like morphology, while the IQP steel mainly consists of 6.44–8.13 vol.% retained austenite with block shape. Additionally, retained austenite in the IQP sample transforms into martensite more easily duo to higher nucleation rate, which means lower austenite stability. A combination of various austenite grain size and morphology make the TRIP effect throughout the whole deformation process and increased the elongation for IQP sample. When the steel was treated by annealing temperature of 967 °C, partitioning temperature and time of 460 °C and 100 s respectively, the steel exhibited excellent mechanical properties with tensile strength of 754 MPa, total elongation of 27% and the product of strength and ductility exceeds 20 GPa%. The proposed content in the present study demonstrates compatibility with the continuous hot-dip galvanizing process.

Finite temperature effects on the structural stability of Si-doped HfO2 using first-principles calculations

The structural stabilities of the monoclinic and tetragonal phases of Si-doped HfO2 at finite temperatures were analyzed using a computational scheme to assess the effects of impurity doping. We proposed a method that the finite temperature effects, i.e., lattice vibration and impurity configuration effects, are considered. The results show that 6% Si doping stabilizes the tetragonal phase at room temperature, although a higher concentration of Si is required to stabilize the tetragonal phase at zero temperature. These data indicate that lattice vibration and impurity configuration effects are important factors determining structural stability at finite temperatures.

Enhanced mechanical properties of a near-α titanium alloy by tailoring the silicide precipitation behavior through severe plastic deformation

The microstructure evolution, tensile properties, and strengthening mechanisms of a near-α high-temperature titanium alloy with high Zr and Si content during isothermal multi-dimensional forging (IMDF) at the β-phase region were systematically investigated. The results show that the alloys exhibit a basket-weave microstructure after IMDF, with the silicides diffusely distributed in the matrix. As the forging temperature decreased, the intragranular primary α laths became more refined and the volume fraction of silicides increased, while the average size of silicides gradually decreased. The dynamic spheroidization of α laths occurs preferentially at the prior β grain boundary and extends into the grains as the deformation temperature decreases. The IMDF-1100 alloy possesses excellent high-temperature tensile properties and moderate room-temperature tensile properties, with ultimate tensile strengths (UTS) of 738.4 MPa and 1124.8 MPa at 650 °C and room temperature, respectively, which makes the alloy have tremendous potential for aerospace applications. The strengthening of the alloy at room temperature is primarily attributed to microstructure refinement and the thermal mismatch between silicide and matrix. However, owing to the weakening of grain boundaries at 650 °C, grain refinement leads to a decrease in tensile strengths. When tensile at 650 °C, the fragmentation and decohesion of large-size silicides tend to cause premature fracture of the alloy, and the microstructure with small-size silicide distribution presents better ductility.

Recycling silicon scrap for spherical Si–C composite as high-performance lithium-ion battery anodes

The growth of the semiconductor and solar industry has been exponential in the last two decades due to the computing and energy demands of the world. Silicon (Si) is one of the main constituents for both sectors and, thus, is used in large quantities. As a result, a lot of Si waste is generated mainly by these two industries. For a sustainable world, the circular economy is the key; thus, the waste produced must be upcycled/recycled/reused to complete the circular chain. Herein, we show that an upcycled/recycled Si can be used with carbon as a composite anode material, with high Si content (∼40 wt%) and loading of 3–4 mAh/cm2 for practical use in lithium-ion batteries. The unique spherical jackfruit-like structure of the Si–C composite can minimize the total lithium inventory loss compared to the conventional Si–C composite and pure Si, resulting in superior electrochemical performance. The superior electrochemical performance of Si–C composites enables the cell energy density of ∼325 Wh kg−1 (with NMC cathode) and ∼260 Wh kg−1(with LFP cathode), respectively. The results demonstrate that Si-based industrial waste can be upcycled for high-performance Li-ion battery anodes through a controllable, scalable, and energy-efficient route.

Lamina-specific localization of silicon accumulation in two broadleaf tree species.

Silicon (Si) accumulation differs greatly among plant species, as revealed by an increasing number of studies reporting whole-leaf Si concentration for a wide range of land plants. Yet, we have limited knowledge about Si distribution across leaf parts (e.g., lamina vs. veins) within a leaf of eudicots. Here, we report how Si accumulation with leaf age differs among petiole, midrib, and lamina in two broad-leaved trees, Acer rufinerve and Ficus erecta. We marked a pair of neighboring leaves in each marked shoot and harvested one in May and the other in October to measure Si concentration. In both species, the lamina showed much higher Si concentration than the petiole and vein in both young and old leaves, and only the lamina showed clear increases in Si concentration from young to old leaves. Si accumulation rate correlated positively with shoot size and leaf production in F. erecta but not in A. rufinerve. These results strongly suggest that, in eudicot species, Si is deposited mostly in leaf lamina but in only a negligible amount in petioles and veins through which Si dissolved in water is transported. Future research on physiological regulations of Si accumulation in eudicot species should consider which specific cells in leaf lamina are responsible for such highly localized Si deposition.