Si Composition Research Articles

Towards reconciling experimental and computational determinations of Earth's core thermal conductivity

The thermal conductivity (κ) of Earth's core is a critical parameter that controls predictions of core cooling rate, inner core age and the power available to the geodynamo. However, the values of core thermal conductivity inferred from recent studies span a wide range due to the challenges of extrapolating to the pressure-temperature-composition (P-T-C) conditions of the core liquid. In particular, extrapolations of κ from direct experimental determinations are lower than ab initio calculations conducted at core conditions. We have performed density functional theory (DFT) calculations to determine the thermal conductivity and resistivity (ρ) of solid FeSi alloys with two compositions, 4 mol % and 15 mol % Si, at a range of temperatures (850-4350 K) and pressures (60-144 GPa) for ease of comparison with recent directly measured κ values. In agreement with recent experiments, our calculations show that for the larger Si composition the resistivity of the mixture increases substantially, compared to pure Fe, reaching its saturated value already at the lowest temperature investigated. As a result, the thermal conductivity of the mixture is also correspondingly reduced. We also analysed the effect of possible errors in the DFT calculations due to the neglect of electron-electron scattering (EES) processes. Our results show that experimental and EES-corrected DFT calculations of κ are actually consistent within uncertainties when compared directly at overlapping P-T-C conditions. We present new core thermal history models using our EES-corrected estimates of κ=75−81 Wm−1K−1 at core-mantle boundary (CMB) conditions, which support previous determinations of late inner core formation around 400-700 Myrs ago and an early molten lower mantle.

Harvesting Si Nanostructures and C–Si Composites by Paired Electrolysis in Molten Salt: Implications for Lithium Storage

Harvesting Si Nanostructures and C–Si Composites by Paired Electrolysis in Molten Salt: Implications for Lithium Storage

Artificial silicide barrier coatings in titanium matrix composites

Abstract A continuous S2 silicide ([Ti,Zr] x Si y ) segregation layer was found in the fibre matrix interface of SCS6-SiC/Ti-5.8Al-4Sn-3.5Zr-0.7Nb-0.5Mo-0.35Si (IMI834) composites (composition in wt.%). The S2 layer separates completely the titanium matrix from the reaction layer. It was shown that the S2 layer stabilises the interface during thermal treatment. The thermal stability of composites was tested in which artificial coatings were introduced into the interface. For the artificial coatings a composition and structure of the S2 silicides were aspired. The interface of the composites was investigated with analytical transmission electron microscope in the as-processed condition and annealed at 700 °C for 3 000 h and at 800 °C for 1000 h. The coatings of the same composition and structure can be introduced into the interface of SiC-SCS6/IMI834 composites as those of the S2 silicide obtained by self-segregation. The composites with the artificial coatings have a similar interface stability at 700 °C as those obtained by self-segregation.

Fabrication and application of co-continuous Al2O3/Al composite by reactive infiltration of molten Al into the preform of SiO2 with cordierite addition

Abstract Interpenetration Al2O3/Al(Si) composites were fabricated by reactive infiltration of molten Al into the preforms with SiO2–4.6 mol.% cordierite at 1150 °C in air. The formation kinetics and microstructures of the composites were investigated. Experimental results show that the addition of cordierite in SiO2 is favorable for wetting of molten Al on the preform, leading to high growth rate of the composite (8.76 mm min –1). The growth rate of the composite was controlled by the infiltration of molten Al into the preform through the open pores and cracks formed during the preform fabrication or through microcracks created during the infiltration process. Since the addition of cordierite in SiO2 can lower the preform sintering temperature, one of its applications is used for ceramic – ceramic or ceramic – metal joints. A strong Al2O3–Al2O3 joint with a shear strength of 109 MPa was fabricated and investigated using the Al2O3/Al(Si) interlayer formed by this method.

SiAl composite feedhorn arrays for astrophysical applications: Cryogenic material properties.

A study investigating the physical properties and use of the SiAl composite Controlled Expansion 7 (CE7) for the packaging of silicon bolometric detectors for millimeter-wave astrophysical applications at cryogenic temperatures is presented. The existing interfaces to such detectors are typically made of either ductile metals or micro-machined silicon. As a composite of Si and Al, we find that CE7 exhibits properties of both in ways that may be advantageous for this application. This exploration of the physical properties of CE7 reveals: (a) superconductivity below a critical transition temperature, Tc ∼ 1.2K; (b) a thermal contraction profile much closer to Si than metal substrates; (c) the relatively low thermal conductivity anticipated for a superconductor, which can be improved by Au-plating; and (d) the feasibility of machining mechanical features with tolerances of ∼25 µm. We further discuss the use of CE7 in the cosmology large angular scale surveyor telescope array, which deployed CE7 in several of its detector focal planes.

Electronic and optical properties of SixGe1−x−ySny alloys lattice-matched to Ge

We present a combined experimental and theoretical analysis of the evolution of the near-band gap electronic and optical properties of Si$_{x}$Ge$_{1-x-y}$Sn$_{y}$ alloys lattice-matched to Ge and GaAs substrates. We perform photoreflectance (PR) and photoluminescence (PL) measurements on Si$_{x}$Ge$_{1-x-y}$Sn$_{y}$ epitaxial layers grown via chemical vapour deposition, for Si (Sn) compositions up to $x =$ 9.6% ($y =$ 2.5%). Our measurements indicate the presence of an indirect fundamental band gap, with PL observed $\approx$ 200-250 meV lower in energy than the direct $E_0$ transition identified by PR measurements. The measured PL is Ge-like, suggesting that the alloy conduction band (CB) edge is primarily derived from the Ge L-point CB minimum. Interpretation of the PR and PL measurements is supported by atomistic electronic structure calculations. Effective alloy band structures calculated via density functional theory confirm the presence of an indirect fundamental band gap, and reveal the origin of the observed inhomogeneous broadening of the measured optical spectra as being alloy-induced band hybridisation occurring close in energy to the CB edge. To analyze the evolution of the band gap, semi-empirical tight-binding (TB) calculations are employed to enable calculations for large supercell sizes. TB calculations reveal that the alloy CB edge is hybridized in nature, consisting at low Si and Sn compositions of an admixture of Ge L-, $\Gamma$- and X-point CB edge states, and confirm that the alloy CB edge retains primarily Ge L-point CB edge character. Our experimental measurements and theoretical calculations confirm a direct transition energy close to 1 eV in magnitude for Si and Sn compositions $x =$ 6.8 - 9.6% and $y =$ 1.6 - 2.2%.

Высокотемпературные коррозионностойкие керамические композиционные материалы на основе соединений системы (Si – B – C – N) (обзор)

Based on the analysis of domestic and foreign scientific publications, a systematization of data on the results achieved in the development of promising materials based on two-, three- and four-component compounds of the system (Si – B – C – N), such as nitrides, carbides, borides, silicon carbonitrides and boron, silicoboron carbonitride. Information about their structure, physical and thermomechenical properties and methods of sintering are given. The dependence of the properties of fibers, bulk and composite materials on the chemical composition and structure of Si – B – C – N-compounds is considered. The results of testing finished products at high temperatures in an oxidizing environment are presented. The prospects for the use of materials of the system (Si – B – C – N) in industry and technology for the manufacture of parts and assemblies intended for operation at high temperatures under mechanical loading in corrosive media are described.

Volatile Organic Compound (VOC) Reduction from Face Mask Wastes via a Microwave Plasma Reactor

Since the outbreak of the COVID-19 pandemic, the driven of face masks as personal protective equipment has increased significantly. Thus, disposed face masks from users should be handled properly for preventing the contamination of medical waste and the potential spread of viruses to the environment. This study gives information for dealing with face masks and assessing the volatile organic compounds (VOCs) concentrations via an atmospheric-pressure microwave plasma reactor. Face mask samples were mixed with the flux agents, namely cullet/glass, Al2O3, SiO2 and CaCO3. Samples were compared with control (no addition of flux agents) and the addition of only cullet. Moreover, microwave power, gas flow rate and pyrolysis duration were controlled at 1000 W, 9 standard liter per minute (SLM) and 5 min, respectively. The total concentration of VOC with the absence of flux agents was 448.04 ppm. Furthermore, the fuse of cullet and SiO2-Al2O3-cullet in the mask reduced the concentration of VOCs by 314.77 ppm and 54.7 ppm, respectively. Furthermore, the combination of CaCO3-SiO2-Al2O3-cullet creates the vitrification of material with the presence of crystalline structure, where the compositions of Ca and Si were 13.55% and 19.12%, respectively. Moreover, the final composition of carbon from the flux agents was 17.92 ± 10.08%. This study confirms that the fuse of CaCO3-SiO2-Al2O3-glass/cullet reduced the VOC via plasma technology, which is a promising method to be implemented in order to reduce the concentration of VOC from the face mask waste.

The 1991 explosive Hudson volcanic eruption as a geochronological marker for the Northern Antarctic Peninsula

It is estimated that the explosive Hudson volcano eruption in Southern Chile injected approximately 2.7 km3 of basalt and trachyandesite tephra into the troposphere between August 8-15, 1991. The Hudson signal has been detected in Antarctica at the eastern sector and in South Pole snow. In this work, we track the Hudson volcanic plume using a dispersion model, remote sensing, and a re-analysis of a high-resolution ice core analysis from the Detroit Plateau in the Antarctic Peninsula and sedimentary records from shallow lakes from King George Island (KGI). The Hudson eruption imprint in these records is confirmed by using a weekly resolved aerosol concentration database from KGI demonstrating that the regional impact of Hudson eruption predominates over the Mount Pinatubo/Phillippines volcanic signal, dated from June 1991, in terms of particulate matter depositions. The aerosol elemental composition of Ca, Fe, Ti, Si, Al, Zn, and Pb increases from 2 to 3 orders of magnitude in background level during the days following the eruption of the Hudson volcano.

Investigation of Magnetic Behavior of Non-Stoichiometric Co1.75mn0.5fe0.75si and Co1.5mnfe0.5si Compositions Associated with Their Co2fesi and Co2mnsi Parent Alloys

Investigation of Magnetic Behavior of Non-Stoichiometric Co1.75mn0.5fe0.75si and Co1.5mnfe0.5si Compositions Associated with Their Co2fesi and Co2mnsi Parent Alloys

Effect of co-addition of WC and MoSi2 on the microstructure of ZrB2–SiC–Si composites

In this paper, ZrB2–SiC–Si-based ceramic composites with WC and MoSi2 additives were fabricated using SPS method and their densification behavior was investigated by phase and microstructural studies. During the SPS process and according to the prevailing conditions, WC and MoSi2 additives reacted with the surface oxide impurities of the main raw materials. As a result of these reactions and the decomposition of some raw materials, a series of oxide liquid phases formed, which were often Si-based, and due to their good fluidity, undissolved and free elements such as Zr, Mo and W moved to open porosities and grain boundaries. According to the established thermodynamic conditions, binary solid solutions and new phases such as MoB, ZrC and WB formed. The synthesis of such phases boosted the densification of the composites due to the fact that they formed in porosities or voids between the main grains. The results showed that the sample doped with 2.5 vol% WC and 2.5 vol% MoSi2 had the highest relative density (about 99%). Meanwhile, microstructural studies showed that homogeneous and dense parts can be achieved by SPS technology.

Li and Si isotopes reveal authigenic clay formation in a palaeo-delta

Marine authigenic clay formation has long been postulated as a major process to explain the mass budgets of some elements in seawater, and might act a reverse reaction for the neutralization of atmospheric acidity by soil forming reactions on land. Nevertheless, to date, a handful of studies have directly investigated the effect of reverse weathering due to the challenges associated with sampling complexity. Deltas are thought to be one of the possible environments where reverse weathering reactions may occur because of the abundant influx of weathering derived materials and dynamic activities. In this study, we use a unique combination of three isotope systems (Si, Li, and Nd) as evidence of authigenic clay formation using sediments collected from a ∼40 Ma-old delta complex (Ainsa Basin, Spain). Sediments were collected along the land to sea depositional continuum, from alluvial and coastal plains to marine environments. Direct comparison between alluvial, coastal, and marine sediments allows for observing the potential effect of reverse weathering. Systematic differences in Si and Li isotope composition exist between marine and continental sediments, revealing the formation of an authigenic phase sequestrating light Li and Si as associated with the diagenesis of Fe in reducing deltaic environments. Finally, this study proposes a geochemical tool for helping distinguishing marine and continental origins of sedimentary rocks when lithofacies and biofacies prove to be ineffective.

Mesopore silica effect on chemical, thermal and tribological properties of polyimide composites

Abstract In this experimental study, the effects of mesoporous silica filler content on the chemical, thermal and tribological properties of polyimide composites were investigated. For that purpose, Pi/mesoporous silica composites were produced by in situ polymerization with various mesoporous silicas. After fabrication, thermal stability and chemical characterization were determined using TGA and FTIR. Morphological alterations were monitored with a scanning electron microscope (SEM). Texture structure (pore size and pore volume) were determined by the BJH method. Friction and wear properties were investigated by using a pin-on-disc arrangement. At the end of the study, minor shifts of Pi/mesoporous silica composites were observed. Thermal stability, as well as pore size and pore volume, was decreased with mesoporous silica. The coefficient of friction and specific wear rate decreased with the addition of mesoporous silica. Abrasive wear behaviors were seen for both neat Pi and Pi–Si composites. Hence, this study evidenced that the properties of Pi are influenced by mesoporous dimensions and content of Si employed.

Correlated iron isotopes and silicon contents in aubrite metals reveal structure of their asteroidal parent body

Iron isotopes record the physical parameters, such as temperature and redox conditions, during differentiation processes on rocky bodies. Here we report the results of a correlated investigation of iron isotope compositions and silicon contents of silicon-bearing metal grains from several aubritic meteorites. Based on their Fe isotopic and elemental Si compositions and thermal modelling, we show that these aubrite metals equilibrated with silicates at temperatures ranging from ~ 1430 to ~ 1640 K and likely sampled different depths within their asteroidal parent body. The highest temperature in this range corresponds to their equilibration at a minimum depth of up to ~ 35 km from the surface of the aubrite parent body, followed by brecciation and excavation by impacts within the first ~ 4 Myr of Solar System history.

Nano Silicon Composite with Gelatin/Melamine Derived N-doped Carbon as an Efficient Anode Material for Li-ion Batteries

Silicon (Si) has a high theoretical capacity and low working potential vs. Li/Li<sup>+</sup>, and has been investigated as the most capable negative electrode material for lithium-ion batteries (LIBs). However, Si undergoes significant volume changes during the Li<sup>+ </sup>alloying/ dealloying processes, leading to unstable cycle life and limiting its practical applicability in anodes. Introducing carbon into the Si anodes can effectively address the Si drawbacks, while providing advantages of improved conductivity and structural stability. In this study we choose gelatin/ melamine combination as an eco-friendly and cost-effective source for nitrogendoped carbon to make a Si composite. The prepared composite was studied as an anode material for LIBs, and it delivered excellent cyclability with 2175 mAh g<sup>-1</sup> capacity after 50 cycles with 86% capacity retention at 200 mA g<sup>-1</sup>. The composite exhibited superior rate capability and improved Li<sup>+</sup> diffusion properties compared with bare Si nanoparticles (Si NP). The significant enhancement could be attributed to the structural stability and conductivity provided by the nitrogen-doped carbon matrix. This work promotes emerging batteries with low-cost materials as a promising solution for increasing energy storage requirements.

Microstructure characteristics and enhanced properties of network-structured TiB/(TA15-Si) composites via rolling deformation at different temperatures

Discontinuously reinforced titanium matrix composites (DRTMCs) with network structure have attracted much attention in recent years due to their superior strengthening effect and ductility. To figure out their microstructure characteristics of the as-rolled network-structured composites under different rolling temperatures, hot rolling deformation processes at α+β region, upper α+β region, β region were performed on a series of TiB whiskers reinforced Ti–6.5Al–2Zr–1Mo–1V–0.3Si (TA15) composites (TiB/TA15–Si). The results showed that with the increase of rolling temperature, primary α (αp) phases and silicides gradually decreased, while transformed β (βT) phases, secondary α (αs) phases and TiB aspect ratio gradually increased, which is attributed to the phase transformation, Si dissolution and lower deformation resistance. And the silicides were fractured into several parts at 900 °C due to the low solid solubility and excessive growth. Besides, the composite rolled at α+β region exhibited dominant dynamic recrystallization (DRX) of α phase, while the composite rolled at β region presented an elongated deformation of prior β phase inside the network and DRX behavior near the network. With the increasing rolling temperature, the composites showed an increasing trend in strength and a decreasing trend in ductility. The composite rolled at 1100 °C can obtain better overall ultimate tensile strengths of 1260 MPa (at RT), 843 MPa (at 600 °C), 729 MPa (at 650 °C) and 595 MPa (at 700 °C), which increased by 13.4%, 38.2%, 36.3%, 21.9% compared with those of the as-sintered composite, respectively. The superior strengthening mechanism of the as-rolled composites can be mainly attributed to grain refining of the matrix and load transfer of TiB.

Effect of beryllium addition and heat treatment on the microstructure and mechanical properties of the 15%Mg2Si/Al-8Si composite

In the present work, the effect of beryllium (Be) addition (0, 0.3, 0.6, 1.0, 1.5 and 2.0 wt%) on the microstructure and mechanical properties of the 15%Mg2Si/Al-8Si composite has been investigated. With the addition of Be, the morphology of the primary Mg2Si particles changed from dendritic to regular, the eutectic Si phase was refined remarkably, and the size of the Mg2Si phase was decreased evidently. With addition of 1.5%Be, the mean grain size of α-Al decreased from ~24 μm to ~13 μm and the finest eutectic Si phase were obtained, in the meantime, the Mg2Si particles were present in fully modified square to spherical. In addition, it was proposed that the according to the microstructure analysis, the BeO phases might be responsible for the modification of Mg2Si phases. With addition of 1.5%Be, the maximum improvement of the mechanical properties was achieved, and the corresponding Be-modified alloys in T6 heat treated condition obtained the best tensile properties compared with other experimental alloys, with the corresponding yield strength(YS), ultimate tensile strength(UTS) and elongation(EL) values being 178.2 MPa, 282.0 MPa and 5.1%, respectively. Meanwhile, the shear properties of 1.5% Be-modified and T6 heat treated is improved compared with the un-modified alloy, with the corresponding shear stress (SS) and deformation rate(DR) being 161.0 MPa and 36.3%. Furthermore, the 1.5% Be-modified and T6 heat treated is improved compared with the un-modified alloy, the wear amount and friction coefficient decrease to 0.55mm3 and 0.5, suggesting it can be a good candidate for the commercial applications.

Hexagonal Si-Ge Class of Semiconducting Alloys Prepared by Using Pressure and Temperature.

Multi-anvil and laser-heated diamond anvil methods have been used to subject Ge and Si mixtures to pressures and temperatures of between 12 and 17 GPa and 1500-1800 K, respectively. Synchrotron angle dispersive X-ray diffraction, precession electron diffraction and chemical analysis using electron microscopy, reveal recovery at ambient pressure of hexagonal Ge-Si solid solutions (P63 /mmc). Taken together, the multi-anvil and diamond anvil results reveal that hexagonal solid solutions can be prepared for all Ge-Si compositions. This hexagonal class of solid solutions constitutes a significant expansion of the bulk Ge-Si solid solution family, and is of interest for optoelectronic applications.

Coupled artificial mixed conductor interfaces boosts excess Li-storage capability and ultra-long cycle durability in Si composite

It is a critical challenge for silicon to achieve fast lithium storage for the intrinsic sluggish kinetics in spite of an attractive theoretic capacity up to 4200 mAh g−1. In this study, mixed conductor double layers composed of heterogeneous SnO: carbon and Si: carbon interfaces are conceived and configured successfully on the surface of silicon to construct SnO/C@Si composite. Amazing excess Li-storage on interface combined with bulk storage is thus strategically obtained by the coupled job-sharing modes in the artificial interfaces. Outstanding surfacial pseudocapacitive effect, which is hardly mentioned in the modification of silicon electrode materials, is demonstrated in the constructed SnO/C@Si composite. The approach demonstrates that constructing artificial interfaces with coupled job-sharing mode opens a feasible way for alloy-type materials to meet the requirement of fast kinetics and capacity enhancement.

Evaluation of Vickers Hardness Number of Al-Si Alloy Under Heat Treated Conditions

The paper deal with the hardness property assessment of various Al-Si alloys under heat treated conditions. The tested specimens have the compositions of Si with percentages such as 12 18 and 24. The fabrication of the selected composition is carried out by melting the material to the melting temperature of around 800°C. The material is subjected to solutionised heat treatment for 3 hours at 500°C, 520°C and 535°C and quenched in water. Further aging is carried out at 155°C for 2 hours, 5 hours and 8 hours respectively for 500°C, 520°C and 535°C of solution heat treatment condition. The hardness property is evaluated using Vickers Hardness tester as per the standards of ASTM- E92. Thorough comparison of Vickers hardness number is performed among the as- cast and various heat treated environment. Desirable properties of alloy are observed at 520°C solutionised heat treatment & 5 hours of precipitation hardening at 155°C for 18% of Silicon composition. The hardness value decreases due to the increase in percentage of silicon and the values are observed.