Morphology Of Si Research Articles

Mechanism of boron removal of primary Si phases and morphology evolution of impurity phases during slow cooling solidification refining of Al-30wt.%Si alloy with Zr additions

This work combines the control of kinetic factors and the addition of a small amount of Zr element in Al-Si solvent refining process to obtain a super high B removal rate. Impurity removal of primary Si phases in Al-30wt.%Si alloy is evaluated by solvent refining with slow cooling rates of 0.4, 2, 10, and 50 mK ⋅s−1, and Zr addition contents of 0, 330, 1000, and 3000 ppmw, respectively. With a 3000 ppmw Zr addition, the removal fraction of B in the primary Si is all over 93% and the best value reaches 99.36%. The P content is more sensitive to the cooling rate but does not change significantly with the increase of Zr. By morphology observation and ICP-OES analysis of the primary Si phases, the interaction between Zr, B, and Si, and the morphology evolution of ZrB2 and ZrSi2 phases are revealed. Based on theoretical calculations, the formation temperature of ZrB2 in the Al-Si melt is evaluated and a competitive reaction mechanism is discovered. Due to the excessive Zr addition, Zr first reacts with B and forms ZrB2 before the primary Si phase growth, which causes a decrease of the B content in the melt and contributes to the high B removal fraction. The remaining Zr in the melt combines with Si to form ZrSi2 phases. A model is established to describe the different trapping/ engulfing/ pushing situations of ZrB2 and ZrSi2 phases, which determine the final impurity content in the refined primary Si phases.

Experimental investigation of hot tensile properties of Al-8Si-0.4 Mg alloy with varying Ni addition

An examination was carried out to decide the impact of Ni expansion and differing test temperature on the hot tensile properties of the cast Al-0.4 Mg-8Si alloy. The Al-0.4 Mg-8Si combination was softened in an electric furnace and Ni was added to the liquefy. The liquefy was cast in a metal mould. The cast samples were solutionised at 537 °C for 12 hrs and after that aged for 100 hrs. The hot tensile properties were resolved at 200, 250, 300 and 350 °C. The microstructure was observed utilizing an optical magnifying lens and the stages displayed in the microstructure were distinguished utilizing SEM, energy dispersive spectroscopy (EDS), XRD and TEM. The eutectic Si morphology was refined and a transitional stage Al3Ni was observed. Ultimate tensile strength (UTS) and yield strength (YS) expanded and %elongation (%El) expanded imperceptibly with expanding Ni expansion, though UTS and YS diminished and %El expanded insignificantly with expanding test temperature. It is reasoned that the Ni expansion altogether enhances the hot tensile properties of the base Al-8Si-0.4 Mg alloy and hot elasticity diminishes with expanding test temperature.

Research on Distribution and Morphology of Primary Si Under the Effect of Direct Current

Research on Distribution and Morphology of Primary Si Under the Effect of Direct Current

High temperature wettability and oxidation behavior of TiN, Ti–Al–N and Ti–Si–N PVD film

In aluminium cutting and die casting, tools are exposed to Built UP Edge (BUE) and Built Up Layer (BUL) and erosion due to the frequent contact of the tool surface to the aluminum alloy, to oxidation due to high temperatures. For this reason, the susceptibility to reaction with liquid aluminum and stability of TiN, Ti–Al–N and Ti–Si–N films were investigated using wetting test, high temperature oxidation experiment and complementary differential scanning calorimetry. The results show that the type of chemical bond affects the surface tension, tool steel with metal bonds is most easily wetted, after being wetted and cooled by molten Al at 725 °C, the contact angle is approximately 0°. Because the maximum temperature of the experiment has reached the decomposition temperature of TiN film, therefore, the contact angle of TiN film with ionic bond is 35.3°, slightly larger than tool steel. However, there are complex ionic bond compounds Ti3AlN and covalent bond compounds Si3N4 in Ti–Al–N and Ti–Si–N films, which significantly reduce the wettability of the film with molten aluminum. The contact angles are 78° and 71°, respectively. During the oxidation process, due to Ti–Al–N and Ti–Si–N films contain Al and Si elements, the phase and morphology did not change until 800 °C, this indicates that the effects of different chemical bonds caused by alloying elements on oxidation resistance and wetting resistance have a similar relationship.

Wood biomass fly ash ameliorates acidic, low-nutrient hydromorphic soil & reduces metal accumulation in maize

Biomass-fuelled facilities generate alkaline and mineral-/nutrient-enriched co-product (ash) that has to be appropriately managed, and preferably reused. The assumption that wood biomass fly ash (BFA) could be used in chemical amelioration of soil acidity and fertility was tested by: i) physicochemical characterisation of BFA and ii) bioassay with maize grown in acidic (pHKCl 4.68) hydromorphic soil amended with BFA (0–10% w/w). Scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction revealed non-homogeneous (ir)regular spherical/porous agglomerated particle morphology and distinctive distribution of Si-/Ca-/K-based minerals, while secondary ion mass spectrometry, for the first time, confirmed their isotopic (six Ca, three Si/Mg and two K isotopes) diversity. BFA addition strongly shifted soil pHKCl (up to 9.1), raised salinity (by > 8.2-fold) and the content of most phytonutrients (up to 5.4-fold); however, BFA amendments at >1.25% restricted the maize root and shoot growth, likely due to alkaline stress as indicated by necrotic/chlorotic symptoms at >5.0% rate. The BFA amendments increased total concentration of metals in soil (without exceeding the levels recognised as contamination); however, phytoextraction of Cd, Zn, Mn, Cu and Mo was significantly supressed (Cd by almost 12-fold), confirming that BFA improved soil-plant metal immobilisation, shifting rhizosphere biogeochemistry towards chemisorption/precipitation reactions. Even though results revealed a strong liming and P–K–Ca–Mg–Zn–Mn–Cu enrichment potential of BFA, to avoid possible negative environmental implications (saline/alkaline stress, metal contamination, adverse effects on soil microbiome), quantitative and qualitative ex ante evaluation of the BFA/soil matrix combinations is essential before application to ameliorate suboptimal (acidic, low-nutrient) or metal-contaminated soils.

Formation of Hierarchical Pyramid-structured Si with Nanoholes by Using Thermally Dewetted Ag Thin Films

Si surface texturing generally requires an etching process to improve the anti-reflection and the self-cleaning properties of the surface. Among the various etching techniques for surface texturing, the wet etching method has been widely adopted as a relatively simple and inexpensive manufacturing method. In this study, we report the effects of hierarchical pyramid-structured Si with nanoholes formed using a chemical wet etching process with thermally dewetted Ag thin films. First, alkaline etching was performed on a Si wafer to fabricate micrometer-sized random pyramid structures. Then, Ag thin film was thermally grown on the pyramid-structured Si. Finally, nanopores were formed on the random pyramid structure via metal-assisted chemical etching. The final morphology of Si was a hierarchical random pyramid structure with nanoholes, exhibiting both anti-reflection and superhydrophobicity. The average reflectance decreased to ∼4%, and the contact angle increased to 170.5°, allowing these surfaces to be used in various wettability-controlled optoelectronic devices, such as Si solar cells for where light trapping and self-cleaning are essential.

Heterogeneous microstructure and voids dependence of tensile deformation in a selective laser melted AlSi10Mg alloy

Microstructure and voids evolution of a selective laser melted (SLM) AlSi10Mg alloy during tension were systematically investigated. The SLM AlSi10Mg sample is featured with a multi-level heterogeneous microstructure that is composed of melt pools (MPs), columnar Al grains and sub-cells. According to the Si morphologies and thermal history, the MP could be divided into three regions, including the fine structure zone (FSZ), remelted zone (RMZ) and heat-affected zone (HAZ), respectively. The Si segregation phenomenon on sub-cells boundaries is observed and may attributed to the constitutional supercooling. The tensile deformation behaviors of the vertical sample (V-sample) vary from the horizontal sample (H-sample) for that heterogeneous microstructure arises strain localization in V-sample. In addition, the voids have no obvious effect on the uniform plastic deformation, while they may affect the non-uniform deformation during tension. The combined effects of strain localization and void contribute to the earlier break in V-samples than in H-samples.

Crystallization profile and morphological study of SAPO-5 templated by imidazolium cations of different functional groups

1-Propyl-2,3-dimethyl-1H-imidazole-3-ium ([pmIm] + ), 3-(2,3-dihydroxypropyl)-1,2-dimethyl-1H-imidazole-3-ium ([dhmIm] + ) and 1-benzyl-2,3-dimethyl-1H-imidazole-3-ium ([bzmIm] + ) cations were used as organic templates for crystallizing SAPO-5 with AFI microporous framework. The physico-chemical influences of the functional groups of the templates (e.g. polarity/hydrophilicity, molecular dimension and size) on SAPO-5 formation were investigated. The results revealed that the crystallization rate, crystallinity and solid yield could be enhanced by increasing the polarity/hydrophilicity of the templates. In addition, the isomorphous Si substitution, morphology and particle size of the resulted SAPO-5 were also affected by the substituted groups of the imidazolium templates. The thermogravimetry results further supported that the selection of organic template with proper polarity/hydrophilicity could be crucial to obtain SAPO-5 with high porosity (S BET , S mic , S ext and V total ) as high polar/hydrophilic template exhibited stronger chemical interaction with the AFI framework during template removal process via calcination process. • SAPO-5 is synthesized using imidazolium-based templates. • Template's functional group affects crystallization and morphological profiles. • Proper hydrophobicity is essential to control host-guest chemical interactions. • Polar template interacts strongly with SAPO-5, hence high temperature calcination is needed.

Well-dispersed double carbon layers coated on Si nanoparticles and the enhanced electrochemical performance for lithium ion batteries

The amorphous carbon was coated on the surface of the nano-silicon with citric acid by a simple mechanical stirring in water bath method and high temperature pyrolysis method, and then the carbon-coated silicon composite material(Si@C) was coated with polyvinyl alcohol by the secondary mechanical stirring and high temperature pyrolysis to obtain double carbon layer-coated silicon composite material (Si@C@C). The microstructure and surface morphology of Si@C@C were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of Si@C@C were investigated by constant current charge–discharge, cyclic voltammetry, and electrochemical impedance spectra techniques. The study found that the first reversible specific capacity of Si@C@C was 1669 mAh/g at the current density of 0.1 C. The specific capacity remained at 1300 mAh/g, while the capacity retention rate was 77.9% after 200 cycles. The cyclic stability of Si@C@C was higher than that of Si@C, which greatly improved the electrochemical performance of silicon-based materials as anode materials for lithium ion batteries.

Understanding the formation mechanism of supersonic atmospheric plasma sprayed in-situ hypereutectic Al-25 wt%Si coating with nanostructured coupled eutectic: From powder, in-flight droplet, splat to coating

A comprehensive study on the formation mechanism of supersonic atmospheric plasma sprayed hypereutectic Al-25 wt%Si coating was performed by investigating microstructural evolution from powder, in-flight droplet, splat, to coating. Results show that feedstock Al-20 wt%Si powder exhibits sub-micron eutectic and micro-sized primary Si. Elements loss, surface oxidation, breakup and chemical diffusion occur when in-flight droplets are exposed to plasma jet. The splat exhibits an ideal structure of nano-sized coupled eutectic. The coating consists of featureless (~84.7 vol%) and ultrafine (~14.2 vol%) zones. Four Si morphologies coexist in the coating from scale of angstrom to sub-micron: Si atoms/clusters in supersaturated solid solution; round/rod-shape Si precipitations (~6.23 nm); nano-Si particulates (~34.37 nm) in featureless zone; and sub-micron Si particulates (~107.32 nm) in ultrafine zone. Further, physical/chemical changes mechanisms of in-flight droplets, rapid solidification mechanisms of splat and coating, formation mechanisms of featureless and ultrafine zones, precipitation and growth mechanisms of Si phase are extensively elucidated. Accordingly, the coating demonstrates ultra-high hardness (~259.8 HV0.1, better than previously reported values of hypereutectic Al-Si alloys with similar silicon content), and superior wear resistance. The unique microstructure with solid solution and grain refinement strengthening mechanisms, and in-situ fabricating higher Si-content Al-Si alloys contribute to the exceptional mechanical properties.

Extraction of Al and rare earths (Ce, Gd, Sc, Y) from red mud by aerobic and anaerobic bi-stage bioleaching

Red mud (RM) is a typical mass quantity of solid waste generated from industrial alumina production and usually consists of valuable metals such as Al and rare earths (REs). This work mainly investigated the extraction of Al and REs from RM via aerobic and anaerobic bi-stage bioleaching by Acidianus manzaensis with the addition of pyrite, by monitoring the morphology, phase and speciation transformations of Al, Si, S and Fe using primarily SEM-EDS, XRD, XPS, and XANES. The results showed that during the aerobic bioleaching stage with increase in mass ratios of pyrite/RM, the extraction rates of Al and REs increased; the highest rates for Al (85.1%), Ce (82.4%), Gd (86.8%), Y (85.3%) and Sc (78.6%) were achieved at pyrite/RM mass ratio 2:1 after 22 d of bioleaching. A slight decrease then occurred because that the complexes formed from jarosites, hematite, diaspore and SiO2-gel can adsorb small amounts of the dissolved elements. Under anaerobic conditions, the additive S0 gradually oxidized to sulfate, and the jarosites gradually dissolved into Fe2+ and disappeared at day 10 with maximal bioleaching rate for Al, Ce, Gd, Y and Sc as 52.5%, 86.3%, 93.7%, 90.2% and 74.9%, indicating that the residues from the first stage were dissolved with the dissimilatory reduction of jarosites by A. manzaensis using S0 as an electron donor. These results suggested a new method for the efficient recovery of valuable metals from RM.

Tailoring microstructure and its effect on wear behavior of an Al–7Si alloy reinforced with in situ formed Al3Ti particulates

The microstructure and wear behavior of an Al–7Si alloy reinforced with in situ Al3Ti particulates were studied. The effects of Sr modification and heat treatment were also investigated. Sr and Al3Ti particulates had clear effects on modifying the morphology of eutectic Si and the microstructure of the Al–Si alloy, playing a key role in improving the hardness and wear properties of the Al3Ti/Al–7Si–Sr composite. T6 heat treatment was performed to spheroidized coarse eutectic Si, reducing stress concentration and further improving the hardness and wear properties of the composites. Among them, the Al3Ti/Al–7Si–Sr composite displayed the highest hardness and the lowest friction coefficient in both as-cast and T6 heat treated states attributed to the combined effects of Sr modification and Al3Ti reinforcement.

Effect of morphology of nanoparticles on performance of transparent display

Nanoparticles based transparent display is one of the most successful methods to realize transparent monitors. Also, an array of nanoparticles, especially aperiodic arrangements, plays an important role in this case. Normally, when one talks about nanoparticles, the spherical morphology appears in mind, in which it is possible to implement different morphology for nanoparticles. In this paper, six different classes of morphologies with various arrangements, such as periodic array and deterministic aperiodic arrays, have been investigated to propose a high-performance transparent display. We compare different morphologies of Si–SiO2 nanoparticles at RGB (Red, Green, Blue) wavelengths in different types of arrays to find the highest scattering cross-section. Our calculations and figure of merit depending on the optical properties of nanoparticles, such as the resonance wavelength, the extinction, scattering and absorption cross-section, and the scattering to absorption ratio (SAR). We will show that in the proposed structures, there are suitable parameters to provide higher scattering cross-section as well as narrow bandwidth in which that is equivalent to introduce the maximum transparency and contrast ratio of transparent monitor. We use the Finite-Difference Time-Domain (FDTD) numerical method to simulate and calculate the deterministic aperiodic and periodic arrays of nanoparticles. Finally, we obtain the absorption and scattering cross-sections for six classes of nanoparticles: Cube, Sphere, Disk, Oblate ellipse, Prolate ellipse, and Pyramid into aperiodic and periodic arrays.

Nonpassivated Silicon Anode Surface.

A stable solid electrolyte interphase (SEI) has been proven to be a key enabler to most advanced battery chemistries, where the reactivity between the electrolyte and the anode operating beyond the electrolyte stability limits must be kinetically suppressed by such SEIs. The graphite anode used in state-of-the-art Li-ion batteries presents the most representative SEI example. Because of similar operation potentials between graphite and silicon (Si), a similar passivation mechanism has been thought to apply on the Si anode when using the same carbonate-based electrolytes. In this work, we found that the chemical formation process of a proto-SEI on Si is closely entangled with incessant SEI decomposition, detachment, and reparation, which lead to continuous lithium consumption. Using a special galvanostatic protocol designed to observe the SEI formation prior to Si lithiation, we were able to deconvolute the electrochemical formation of such dynamic SEI from the morphology and mechanical complexities of Si and showed that a pristine Si anode could not be fully passivated in carbonate-based electrolytes.

Effects of solution heat treatment time on the as-quenched microstructure, hardness and electrical conductivity of B319 aluminum alloy

Abstract In Al-Si-Cu alloys, solution heat treatment promotes several microstructural transformations that influence both hardness and conductivity. Dissolution, spheroidization and coarsening processes can occur concurrently with heat treatment time, directly impacting material properties. However, the absence of time-dependent as-quenched data in the literature impedes distinction of their individual effects. This research aimed to clarify the solution heat treatment kinetics and identify the competing mechanisms controlling electron flow in industrial Al alloys. Samples of automotive B319 alloy were cast in the unmodified and strontium-modified conditions with two solidification rates. After solution treatment at 500 °C for up to 48 h, the Rockwell hardness and electrical conductivity of the samples were measured in the as-quenched condition. Quantitative image analysis revealed a co-dependence between casting prehistory and heat treatment time on the microstructure. Gradual decreases in as-quenched hardness were observed after long treatment times. Yet, clear electrical conductivity trends suggested that there were two distinctive stages in the progression of solution heat treatment of B319 alloy. Initially, Al2Cu dissolution into the supersaturated aluminum solid solution caused transient conductivity reductions. Nonetheless, the eutectic Si spheroidization and coarsening processes promoted subsequent conductivity increases by up to 10%, relative to the as-cast condition. This research elucidates the role of Si morphology in enhancing electron transfer, and it supports the optimization of component performance, manufacturing costs and lead times.

Effect of Strontium Modification on the Morphology of Primary Si in Hypereutectic Al-Si Alloys

In the present study, hypereutectic Al-Si alloys were modified by strontium and the effect of the strontium content and holding time on the morphology of primary Si was investigated. Primary Si is modified to imperfect octahedron with primary dendrites or secondary dendrites when the amount of Sr exceeds 0.04wt.%. With extending the holding time, there is no significant difference with the morphology of primary Si. However, the size of primary Si decreases remarkably when the holding time prolongs to 120min. Further analysis reveals that the Sr content has a considerable impact on the morphology of primary Si due to growth mechanism influence, while the modifying time mainly influences the size of primary Si.

Effects of Bi addition on Si features, tensile properties and wear resistance of hypereutectic Al-15Si alloy

Al-Si alloys are very important in the automotive industry. This is thanks to their high strength to weight ratio, suitable fluidity, good corrosion resistance and high productivity. The shape of the eutectic Silicon (Si) has been widely studied since it is considered an index of quality regarding many application properties. Understanding the effects of alloy additions on the morphology of Si has drawn researcher’s attention. One of these elements of interest is Bismuth (Bi), which may be part of the composition of Al-Si alloys either as an addictive or a contamination. Hence, the microstructure aspects related to the presence of Bi are important requiring further consideration. In the present study, Al-15wt% Si hypereutectic alloy is modified with 1.0 wt% Bi. The goal is to compare the effect of this addition on the morphology of the phases forming the microstructure and on tensile/wear properties. In order to pursue that comparison, previously available data for the binary Al-15wt% Si alloy will be used. Various samples characterized by distinct cooling rates were generated by transient directional solidification of the ternary Al-Si-Bi alloy. The experimental variations of the eutectic spacing will be compared to each other based on their trends. It was found that the addition of minor Bi content (∼1%) permitted tensile strength and ductility of 195 MPa and 14%. Furthermore, wear resistance was improved thanks to Bi. The reasons for that will be outlined.

Electron Microscopy Investigation of Rice Husk-Derived Silicon-Tin/Nitrogen-Doped Graphene Composites Nanostructure

Nowadays, there is an increasing of the demanding in high energy density lithium-ion batteries (LIBs) due to the growing of energy storage needs for electronic vehicles and portable devices. Silicon (Si) and Tin (Sn) are the promising anode materials for LIBs due to their high theoretical capacity of 4200 mAh/g and 994 mAh/g. Moreover, Si can be derived from rice husk which is the main agricultural product in Thailand. However, the using of Si and Sn encounters with the huge volume expansion during lithiation and delithiation process. To alleviate this problem, Nitrogen-doped graphene (NrGO), carbon supporter, is used as composite with these metals to buffer the volume change and increase the electrical conductivity of composites. This work aims to synthesis Si/NrGO and SiSn/NrGO nanocomposites and Si used in these composites is derived from rice husk. All products were characterized by X-rays diffraction (XRD), Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. XRD results showed that the composites contained phases of Si, Sn and carbon. The electron microscopy techniques were the main part to clarify the morphology and distribution of Si and Sn particles on NrGO. SEM and TEM results confirm that there were small sized particles of Si and Sn dispersed and covered on NrGO surface. Furthermore, the electrochemical properties of prepared composites were measured to confirm their efficiency as anode materials in lithium-ion batteries by coin cell assembly. The composite with 10 percent Si and 10 percent Sn on NrGO could deliver a high capacity around 480 mAh/g over 100 cycles and expected to use as anode materials in the next generation lithium-ion batteries.

Influence of Solution Treatment on Microstructure and Electrical Conductivity of Wrought Al-15Si Alloy

In the present work, the microstructures and electrical conductivity of Al-15Si alloy in casting, extruding and solution treatment conditions were investigated. The results indicate that the extruded Al-15Si alloy has higher electrical conductivity. It has been revealed that the morphology of Si, iron element and grain boundary impact on electrical conductivity of the Al-Si alloy. With the revolution of the microstructure, these factors which lead to the changing electrical conductivity of the alloy are discussed in detail.

Achievement of High Strength and Ductility in Al-Si-Cu-Mg Alloys by Intermediate Phase Optimization in As-Cast and Heat Treatment Conditions.

In order to obtain high-strength and high-ductility Al–Si–Cu–Mg alloys, the present research is focused on optimizing the composition of soluble phases, the structure and morphology of insoluble phases, and artificial ageing processes. The results show that the best matches, 0.4 wt% Mg and 1.2 wt% Cu in the Al–9Si alloy, avoided the toxic effect of the blocky Al2Cu on the mechanical properties of the alloy. The addition of 0.6 wt% Zn modified the morphology of eutectic Si from coarse particles to fine fibrous particles and the texture of Fe-rich phases from acicular β-Fe to blocky π-Fe in the Al–9Si–1.2Cu–0.4Mg-based alloy. With the optimization of the heat treatment parameters, the spherical eutectic Si and the fully fused β-Fe dramatically improved the ultimate tensile strength and elongation to fracture. Compared with the Al–9Si–1.2Cu–0.4Mg-based alloy, the 0.6 wt% Zn modified alloy not only increased the ultimate tensile strength and elongation to fracture of peak ageing but also reduced the time of peak ageing. The following improved combination of higher tensile strength and higher elongation was achieved for 0.6 wt% Zn modified alloy by double-stage ageing: 100 °C × 3 h + 180 °C × 7 h, with mechanical properties of ultimate tensile strength (UTS) of ~371 MPa, yield strength (YS) of ~291 MPa, and elongation to fracture (E%) of ~5.6%.