Low Silicon Content Research Articles

Junction Characterization in a Functionally Graded Aluminum Part.

Aluminum alloys are widely used to produce automotive components, thanks to their great mechanical properties–to–density ratio. Engine components such as pistons are conventionally produced by casting of Al–Si eutectic alloys (Silumin alloys) such as EN AC 48000. Due to the harsh working conditions and the lower ductility if compared to aluminum–silicon alloys with lower silicon content, pistons made of this alloy are prone to fatigue failures in the skirt region. In order to overcome such limits, the use of a Functionally Graded Material (FGM) in the production of a piston is proposed. The adoption of a functionally graded architecture can maximize the properties of the component in specific areas. A higher level of thermal resistance in the crown of the piston can be achieved with EN AC 48000 (AlSi12CuNiMg), while higher elongation at rupture in the skirt region would be conferred by an EN AC 42100 (AlSi9Mg0.3). The FGM properties are strictly related to the metallurgical bonding between the alloys as well as to the presence of intermetallic phases in the alloys junction. In the present article, the characterization of gravity casted FGM samples based on Al–Si alloys with respect to microstructure and mechanical testing is presented, with a specific focus on the characterization by impact testing of the joint between the two alloys.

Preparation and adsorption properties of mesoporous material PS-MCM-41 with low-silicon content peanut shell ash as silicon source

The toxic and costly chemicals are usually used as the source of silicon for the synthesis of mesoporous materials. In this paper, the mesoporous material PS-MCM-41 was synthesized by hydrothermal synthesis, in which low-silicon content peanut shell ash is used as the silicon source. The properties of the obtained material were confirmed by N2 physical adsorption, X-ray diffraction (XRD), SEM, TEM, and FTIR. The adsorption performance was evaluated during the adsorption experiment of crystal violet dye and compared with that of the mesoporous material MCM-41. The results showed that the peanut shell ash as silicon source could be used to successfully synthesize the mesoporous material PS-MCM-41. The adsorption efficiency of PS-MCM-41 to 50 mg/L crystal violet solution reached 99.90%, and the adsorption efficiency of PS-MCM-41 to 800 mg/L crystal violet solution reached 84.2%. Compared with MCM-41 and other adsorbents, PS-MCM-41 exhibited excellent adsorption properties and adsorption capacity for crystal violet. The adsorption kinetic data showed that the pseudo-secondary equation could better explain the adsorption data of the adsorption crystal violet. The adsorption isotherm model was consistent with the Langmuir model (R2> 0.99) with maximum adsorption capacities of 1428.57 mg/g.

Silicon and reduced graphene oxide employed as additives to enhance the performances of artificial graphite anode for lithium-ion battery

In order to inherit the advantages of graphite anode and further to improve its capacity for practical applications regarding lithium-ion batteries (LIBs), a three-dimensional (3D) porous artificial graphite/silicon/reduced graphene oxide (G/Si/rGO) aerogel with low silicon content of 4.5 wt.% was fabricated. In this aerogel, artificial graphite (G) acted as a main component, and silicon (Si) nanoparticles and reduced graphene oxide (rGO) were employed as additives. As a result, G/Si/rGO anode was twice as high as the graphite anode regarding the reversible specific capacity after 100 cycling. Furthermore, the G/Si/rGO anode exhibited excellent rate-performance. The enhanced performances of the G/Si/rGO anode were attributed to its structure, in which the compatibility between Si and G was improved by introducing rGO as bridges, conductivity was enhanced and volume stress was released by the constructed 3D porous rGO frame. The systematically reported synthesis strategy may have practical significance for increasing capacity of the current graphite anode with only a small amount of Si.

Co-axial fibrous silicon asymmetric membranes for high-capacity lithium-ion battery anode

Silicon as a promising candidate for the next-generation high-capacity lithium-ion battery anode is characterized by outstanding capacity, high abundance, low operational voltage, and environmental benignity. However, large volume changes during Si lithiation and de-lithiation can seriously impair its long-term cyclability. Although extensive research efforts have been made to improve the electrochemical performance of Si-based anodes, there is a lack of efficient fabrication methods that are low cost, scalable, and self-assembled. In this report, co-axial fibrous silicon asymmetric membrane has been synthesized using a scalable and straightforward phase inversion method combined with dip coating as inspired by the hollow fiber membrane technology that has been successfully commercialized over the last decades to provide billions of gallons of purified drinking water worldwide. We demonstrate that ~ 90% initial capacity of co-axial fibrous Si asymmetric membrane electrode can be maintained after 300 cycles applying a current density of 400 mA g−1. The diameter of fibers, size of silicon particles, type of polymers, and exterior coating have been identified as critical factors that can influence the electrode stability, initial capacity, and rate performance. Much enhanced electrochemical performance can be harvested from a sample that has thinner fiber diameter, smaller silicon particle, lower silicon content, and porous carbon coating. This efficient and scalable approach to prepare high-capacity silicon-based anode with outstanding cyclability is fully compatible with industrial roll-to-roll processing technology, thus bearing a great potential for its future commercialization.

Oxygen evolution behaviours of novel porous MnxSiy electrodes for metal electrowinning

In this study, three types of novel porous MnxSiy oxygen electrodes for metal electrowinning were prepared by elemental powders reactive synthesis. The electrocatalytic activity and corrosion resistance of the porous MnxSiy electrodes were evaluated. The results demonstrated that the electrodes with lower silicon content presented lower potential during a 24-h polarization period and that the corrosion resistance of MnxSiy electrodes was enhanced as the Si content increased. Among these prepared oxygen electrodes, the porous Mn5Si3 electrode exhibited the highest catalytic activity towards oxygen evolution reaction (OER) in 1.63 mol l−1 sulfuric acid solutions. The influence of the electrode active surface on electrocatalytic activity was also studied, and the results showed that large active surface greatly promoted the electrocatalytic performance of the electrodes. The porous MnxSiy electrodes were also tested in conditions which simulate industrial zinc electrowinning and compared to conventional Pb and Pb-Ag (0.8 wt%) anodes. The current efficiency of porous Mn5Si3 electrode reached 85.7%, which was comparable to that of Pb and Pb-Ag (0.8 wt%) anodes. Moreover, the zinc cathode exhibited much lower impurity content. Besides, the addition of Mn2+ ions was also found to result in blockage of pores and increase of potential.

Controlling acidity and external surface morphology of SAPO-34 and its improved performance for methanol to olefins reaction

Abstract Hollow SAPO-34 with thin-wall were successfully synthesized by mixed templates and varying the silicon content in the gel. The silicon enrichment at the surface of crystals occurs on both low silicon and high silicon samples. The cubic crystals of the molecular sieve transformed from hollow to dense phase with increase of silicon content. The surface of molecular sieve crystals turned from being abundant of macroporous openings to be integrated without visible macroporous cracks with the increase of silicon content in the gel. The thin-wall SAPO-34 with low acid density and Si(4Al) framework structure, synthesized from the low silicon content (nSiO2/nAl2O3 = 0.1) of the gel, presented the highest ethylene plus propylene selectivity. The hollow structure SAPO-34 with medium acid density obtained with medium silicon content (nSiO2/nAl2O3 = 0.26) in the gel possessed the longest lifetime.

Oxidation Behavior of Fe-Al, Fe-Si and Fe-Al-Si Intermetallics.

Iron aluminides are still deeply investigated materials for their use in power plants, automotive and chemical industry, and other sectors. This paper shows that it is possible to strongly improve their oxidation behavior by the addition of silicon. The description of the synergic effect of aluminum and silicon on the oxidation behavior of Fe–Al–Si alloys at 800 °C in air is presented. The oxidation rate, microstructure, phase, and chemical composition of these ternary alloys are compared with the binary Fe–Al and Fe–Si alloys. Results showed that the oxidation of Fe–Al–Si ternary alloys provides an oxide layer based on aluminum oxide with a low concentration of iron and silicon. Below this oxide layer, there is a layer of silicides formed as a result of depletion by aluminum, which forms a secondary oxidation protection.

Impact of chemical composition on precipitate morphology in an additively manufactured nickel base superalloy

Changes in the iron content within the allowable composition range in Inconel® 625 produce significant differences in the grain size and mechanical properties during laser-based directed energy deposition additive manufacturing. The resulting precipitate types and morphologies, which contribute to these different properties, originate from a complex interplay between iron, silicon, and titanium. While the addition of iron has traditionally been shown to promote Laves phase formation, thermodynamic calculations have shown that silicon contents in excess of 0.05 wt% are also required to promote its formation. For example, relatively low iron (1 wt%), low titanium (0.019 wt%), and high silicon (0.37 wt%) contents led to the formation of Laves phase. On the other hand, high iron (4 wt%), high titanium (0.19 wt%), and low silicon (0.035 wt%) contents produce MN nitrides and no Laves phase. By increasing the titanium concentration, the precipitation of nitrides rich in titanium and niobium is promoted in the liquid, and Laves phase formation is suppressed during solidification. After hot isostatic pressing, the precipitate distribution displayed minimal differences with that found in the as-deposited condition for both material chemistries. However, the precipitates in the as-deposited low iron material grew larger and developed a blocky morphology while the original Laves phase partially transformed to M2N nitrides rich in Nb, Cr, and Mo. In the high iron material, the MN nitrides became depleted in niobium and further enriched in titanium while maintaining a size similar to those in the as-deposited condition.

Tensile and fatigue properties, machinability and machined surface roughness of Al-Si-Cu alloys

In this paper, the aim was to determine if ASC91 (9 % Al, 1 % Cu) could be replaced with ASC73 (7 % Al, 3 % Cu) aluminium alloy, with presumably improved machinability due to lower silicon content (9 to 7 %) and retained mechanical properties due to a higher copper content (1 to 3 %). The test samples were excised from cylinder heads produced by the lost-foam casting technique in industrial conditions. The tensile properties (proof strength, ultimate tensile strength, elongation and modulus of elasticity), fatigue performance, microstructure and machinability of two as-cast aluminium alloys were examined. The results of the fatigue tests were statistically analyzed using the stair-case method described in the UNI 3964 standard. Tensile properties of the ASC91 were higher, while fatigue properties were higher in the ASC73 alloy. The resultant force was lower for the ASC73, while roughness was lower for the ASC73 alloy, if the feed per tooth is higher than 0.21 mm/t. Two main factors that influence such behaviour are the amount of eutectic silicon and the α-solid solution adhesion to the cutting tool. Keywords: aluminium cast alloys; tensile properties; fatigue; machinability; roughness.

Strain rate dependent dynamic mechanical response of bainitic multiphase steels

Bainitic steels, as a third generation of advanced high strength steels, are potential steel grades for automotive applications. Two grades of bainitic steels with low and high silicon content, with three different thermal treatments per grade and therefore different second phase constituents, are examined under quasi-static and high strain rate deformations. Microstructures are studied by advanced characterization techniques, including X-ray diffraction and scanning electron microscope equipped with an electron backscatter diffraction detector. Subsequently, the quasi-static and dynamic mechanical responses of the steels are correlated to the microstructures. A positive effect of the strain rate is observed for all the examined materials: when the strain rate is increased, both the tensile stress and deformation levels increase, thus also the energy absorption capacity. However, it is shown that the higher the fraction of second phase constituents, the lower the effect of strain rate becomes. In addition, the grain size directly correlates to the strain rate effect too. The phenomenological hardening model of Johnson-Cook is used to simulate the quasi-static and dynamic flow behaviors, allowing to quantify the strain rate sensitivity for each material. A comprehensive literature survey on the strain rate sensitivity of various steel grades reveals that steels with higher strength demonstrate a lower strain rate sensitivity factor. This trend can be approximated by a power law function which clearly is followed by the materials under consideration in this study.

Phase separation in alumina-rich glasses to increase glass reactivity for low-CO2 alkali-activated cements

Ways to reduce cement-related carbon emissions are actively sought. One possible solution is partial substitution of Portland cement by alkali-reactive glass. We report on low-CO2 glass compositions that have high alkali solubility derived from industrial basaltic stone wool compositions. We found that highly alkali-soluble glasses can be formed with glass compositions that in principle can be made using silicate minerals which have no raw material-related CO2 emissions. The reason behind the reactivity of these glasses is thought to be caused by the dilution of the main network-forming species, silicon, which is further enhanced by phase separation, forming phases with high-silicon and low-silicon concentrations. Phase separation in alumina-rich samples is further studied and occurs at moderate cooling rates. The effect of glass-glass phase separation is discussed in the context of reactive glasses in cementitious systems. The results indicate that controlled phase separation could decouple CO2 emissions from the reactivity of glassy supplementary cementitious materials.

Deposition of polysiloxane coatings by runaway electrons preionized diffuse discharge in nitrogen flow

A deposition of polysiloxane coating on titanium substrate by means of atmospheric pressure plasma enhanced chemical vapor deposition (PECVD) in a runaway electron preionized diffuse discharge (REP DD) has been investigated. The coating was produced from vapor of hexomethyldisiloxane (HMDSO) diluted in nitrogen at a flow rate of 1 nl/min. After deposition, the mechanical properties of the coatings have been measured by means of a nanoidentation. The maximum nanohardness of the coating with 3 μm thickness was 4.7 GPa. Energy dispersive analysis has shown that the coatings contain a significant content of carbon and titanium (about 52 at. %, 32 at. %, respectively) and a low content of silicon (about 16 at. %). In the FTIR spectrum, high intensity bands corresponding to stretching vibrations of the Si-O-Si, the Si(CH3)x and CH3 groups are observed, that indicates the organic and inorganic coating structure. Carbon free coating can be produced by REP DD plasma treatment of the deposited SiOxCyHz film, when REP DD operated only in nitrogen.

Effects of silicon content on the separation and purification of primary silicon from hypereutectic aluminum–silicon alloy by alternating electromagnetic directional solidification

Hypereutectic aluminum (Al)–silicon (Si) alloys with different Si contents were used to evaluate the effects of Si content on separation and purification by alternating electromagnetic directional solidification (AEM–DS) at 3 kHz. A relatively high pulling speed of 40 µm/s was used for improved energy efficiency. After cooling, samples underwent AEM–DS, and efficient separation was obtained. The Si content in Si-rich areas exceeded 85 wt.% (considerably higher than the content in others) and exhibited not a slight relevance with the original Si contents in the hypereutectic Al–Si alloy. With regard to purification, impurities— particularly metallic impurities (Fe, Ti, and Ca)—can be removed to a low level. Electron probe microanalysis (EPMA) indicated that B content was lower in the Si-rich area than in the Al–Si alloy, suggesting that the segregation of B in solid primary Si was higher than that in Al–Si melt during AEM–DS. Moreover, the contents of metallic impurities (Fe, Ti, and Ca) and B decreased when the initial Si content in the Al–Si melt decreased. This finding was attributed to a lower silicon content, which indicated a lower melt temperature, thus allowing segregation at a lower temperature.

Investigation of fluctuation behavior in viscosity of coal slags used in entrained-flow gasifiers

Entrained-flow gasification has attracted extensive attention because of its clean and efficient utilization of coal as well as flexible application in industry for power generation and chemical production. Numerous theoretical and experimental investigations on slag flow in entrained-flow gasifiers have been performed to ensure a smooth operation, but an unscheduled shutdown due to slag tap blockage remains an ongoing challenge. A fluctuation phenomenon of slag viscosity gives a rise in the risk of slag tap blockage. In this work, three Chinese coal slags with low silicon content and high iron content were used to investigate the viscosity fluctuation phenomenon. It was found that the crystalline phases and suspended bubbles can cause the fluctuation phenomenon. The fluctuation degree is related to the volume fraction of crystalline phases and the crystallization rate. In the search for the mechanism of the viscosity fluctuation, an in-situ observation using a high temperature stage microscope system (HTSM) in combination with XRD and SEM analyses was carried out. In addition, the viscosity of investigated slags with the suppression of solid phases as well as the phase distribution at high temperatures was calculated. Based on a comprehensive analysis of the results, a possible mechanism has been proposed that the viscosity fluctuation is attributed to an instant local change in the macrostructure such as the deformation of suspended bubbles, the change of the orientation of acicular crystals and the interaction of the acicular crystals and suspended bubbles.

Additive Manufactured A357.0 Samples Using the Laser Powder Bed Fusion Technique: Shear and Tensile Performance

New aluminium alloys, with lower silicon content than in the first-developed formulations, have recently been introduced in the field of Additive Manufacturing and are dedicated to automotive applications. As they are relatively new, mechanical characterization under standard protocols of the automotive field are of utmost scientific as well as industrial relevance. The paper addresses the mechanical properties and microstructure of A357.0. Static tensile and shear tests of samples built by Laser Powder Bed Fusion, with different orientations in the machine work volume, have been performed. The aim was to identify possible anisotropy in the tensile and shear behaviour of this innovative alloy. Particularly for shear, the effect of adhesion between the layers onto shear strength was studied. Results analysis, by means of statistical tools, allows for the affirmation that no tensile modulus or yield strength anisotropy is observed. Instead, a small (yet statistically significant) increase in both shear- and tensile strength and a decrease in ductility are obtained as the direction of the specimens approaches the growth direction. Scanning Electron Microscope (SEM) observation of the failure mechanisms assisted in the interpretation of the results, by relating different failure modes to the relative orientation of loads versus the directions of inherent anisotropy in Laser Powder Bed Fusion processes.

Impact of silica deposition on the performance of gas-fired domestic appliances caused by the combustion of siloxanes in the fuel

Abstract The effects of silica deposition resulting from the combustion of siloxane-containing biomethane on the performance of seven domestic appliances have been studied. The results show that silica deposition increases the flow resistance across the heat exchangers, which consequently reduces the air intake from the surroundings. For the flow-through hot water heater studied, the reduction in air intake in the appliance results in a substantial increase in the CO emission with time, ultimately resulting in a safety risk for the end user. For the fully premixed boilers examined, the increased flow resistance reduces the thermal input, and thus the thermal output, of the appliance. The extent of the reduction in thermal input is seen to depend strongly upon the concentration silicon in the fuel, and the configuration and material of the heat exchanger. For the boilers studied, the ion current measured by the flame safety device decreases with time because silica deposits on the probe used to measure the current in the flame; this ultimately results in boiler failure. Based on the results, extrapolation methods are proposed that can be used to assess the impact of low silicon concentrations in biomethane on appliance performance and safety with time.

Evolution of Microstructure and Texture with the Low-Silicon in Non-Oriented Silicon Steel

Microstructure, texture, the second phase and magnetic were studied with different silicon content in non-oriented electrical steel. The results showed that: microstructure of the products in cold rolling non-oriented electrical was recrystallization of equiaxed ferrite. With the increase of silicon content, the grain size of the finished product increased; the iron loss and magnetic induction value reduced. Hot-rolled electrical steel coil without normalization treated after cold rolling deformation formed a strong {111} surface texture in finished products. After cold rolling and continuous annealing process, grain orientation is not big changes. The {100} and {Goss} texture enhancement and the {111} texture weakening in cold-rolled oriented electrical steel with low silicon, after the normalization process. In low silicon content, the square TiMnS and AlTiN as the second phase particles formed in the hot rolling austenitic area. Because without normalization process, the particles of polymer composition did not change; however, that finished product after the normalization process, the second phase exists in the form of AlN and MnS precipitates. The experimental results showed that Ti has a strong affinity with Mn, S, N and Al in high temperature; Polymer TiMnS and AlTiN can't change after the cold rolling and annealing process.

The tectonometamorphic evolution of the Uppermost Unit south of the Dikti Mountains, Crete

AbstractWe present a new geological map and new structural, petrographical and geochronological data from the Uppermost Unit of the Cretan nappe pile exposed south of the Dikti Mountains in eastern Crete (Greece). Based on these data, the Uppermost Unit in the study area can be subdivided (from bottom to top) into the Arvi Unit, Theodorii Greenschist and Asterousia Crystalline Complex (ACC)-type rocks. The ACC-type rocks have been affected by polyphase deformation (D1–D3) and metamorphism. Relics of the D1phase are preserved as internal foliation in garnet porphyroblasts. D2top-to-the SE shearing under upper amphibolite facies conditions led to the dominant foliation. After post-D2exhumation, parts of the ACC-type rocks were affected by contact metamorphism of a non-exposed pluton, which intruded at a depth below 10 km during Campanian time (74±2Ma; laser ablation inductively coupled plasma mass spectrometry on zircon). This age, obtained from zircon of chiastolite hornfels, is in line with intrusion ages of ACC-type (meta)granitoids exposed on Crete and on Anafi. The S2-foliation of the ACC-type rocks was reactivated during the late phase of contact metamorphism by D3top-to-the SE shearing. Latest Cretaceous cross-mica with low silicon content post-dates this shearing event. During middle Paleocene time, the ACC was thrust on top of the Theodorii Greenschist. This thrusting event as well as subsequent brittle thrusting of the greenschists and the ACC-type rocks on top of the prehnite-pumpellyite facies metamorphic Arvi Unit was still accommodated by top-to-the SE kinematics, which is the dominant kinematics of the Uppermost Unit on Crete and on Anafi.

Direct laser sintering of reaction bonded silicon carbide with low residual silicon content

Additive manufacturing (AM) techniques are promising manufacturing methods for the production of complex parts in small series. In this work, laser sintering (LS) was used to fabricate reaction bonded silicon carbide (RBSC) parts. First, silicon carbide (SiC) and silicon (Si) powders were mixed in order to obtain a homogeneous powder. This powder mixture was subsequently laser sintered, where the Si melts and re-solidifies to bind the primary SiC particles. Afterwards, these SiSiC preforms were impregnated with a phenolic resin. This phenolic resin was pyrolysed yielding porous carbon, which was transformed into secondary reaction formed SiC when the preforms were infiltrated with molten silicon in the final step. This resulted in fully dense RBSC parts with up to 84 vol% SiC. The optimized SiSiC combined a Vickers hardness of 2045 HV, an electrical conductivity of 5.3 × 103 S/m, a Young's modulus of 285 GPa and a 4-point bending strength of 162 MPa.

From science to application: field demonstrations to enhance sustainable rice production in the north of Vietnam—lessons from the LEGATO project

Two major human-made problems in rice production systems in the north of Vietnam concern the low plant-available silicon content of soils and the low biodiversity. The results of the LEGATO project suggest a change to an environmentally friendly rice production system that will help to recover biodiversity. We propose here a framework for a demonstration and dissemination model that will be exemplary for the farmers once it has been successfully realized. We advocate local-option models in different districts to demonstrate to farmers. The methods should be adapted to local and ecoregional differences in climate and land-use tradition, and they explicitly take into account soil care, organic fertilizer, manual weeding, native nectar-rich plant bunds, manual pest snail collection, hymenopteran nesting aids, and biodiversity and yield monitoring.