Reaction Of Si Research Articles

Carbonatization and silicification of ophiolitic ultramafic rocks and formation of gold-bearing listvenites in the Arabian-Nubian shield: A case study from the Al-Barramiya district

Late Neoproterozoic mantle section in the Gabal Al-Barramiya area, the northwestern corner of the Arabian-Nubian Shield (ANS), contains variably serpentinized peridotites that are highly altered along shear zones and thrust planes to form gold-bearing listvenites. They can be categorized into carbonate listvenite, silica-carbonate listvenite and silica listvenite (birbirite). Carbonate listvenite is characterized by the presence of schistosity and deformation fabrics similar to the host serpentinites, but such fabrics are absent in the silica-carbonate and silica listvenites, suggesting that they postdate carbonate listvenite and serpentinization. The presence of listvenites along shears zones and the presence of relics of serpentine and Cr-spinel reflects their formation through metasomatism of ultramafic rocks by hydrothermal fluids circulating along the thrust faults. Silica-carbonate listvenite is characterized by the presence of fuchsite and is enriched in Zn, Pb, Cu, Ag, and Au. Rare earth element (REE) contents differ between the studied listvenites. Silica -carbonate listvenite has the lowest total REE (∑₌0.98–2.56 ppm), whereas the silica listvenite contains the highest total of REE (∑ ₌ 15.70–21.42 ppm). Based on the above, carbonate listvenite is the earliest to form by the infiltration of CO2–bearing fluids released during serpentinization of the original fore-arc peridotite slab, followed by formation of silica-carbonate listvenite due to the activities of SiO2–saturation and CO2-bearing fluids released during ophiolite obduction. Fuchsite in silica-carbonate listvenite formed as a result of metasomatic reactions of Si- and K-rich fluids with Cr-spinel due to hydrothermal alteration of serpentinized peridotite. Silica listvenite formed at the final stage by the silicification of the early formed silica-carbonate listvenite. Listvenitization of the mantle section of the Al-Barramiya ophiolite led to concentration of Au, Pb, Zn, Cu and Ag. The silica-carbonate listvenite contains higher concentration of gold (899–2199 ppb) than the carbonate listvenite (119–191 ppb) and silica listvenite (156–233 ppb).

Study on mechanical properties of ZnO/Si interface under thermal shock

Influence of thermal shock on ZnO/Si interfacial mechanical properties was studied through experiments, molecular dynamics simulations and machine learning prediction. ZnO films were deposited onto silicon wafers by radio frequency magnetron sputtering and then suffered different times of thermal shock. The experimental results show the adhesion strength of ZnO/Si interface is relatively stable under thermal shock. XRD and simulation illustrate the interfacial reactions of Si based films could experience strong interaction through Si, Zn and O atoms located at ZnO/Si interface during thermal shock, which could explain the stability of the interface. The machine learning prediction indicates the mechanical properties of ZnO/Si interface are still relatively stable after more thermal shocks. The obtained conclusions are hoped to be helpful for the understanding of ZnO/Si properties under thermal load and to guide the design of related devices in energy field.

Phase stability of W-containing high-entropy carbide with silicon addition at high temperatures

Reactive melt infiltration (RMI) is a typical method to produce carbon fiber-reinforced ultra-high temperature ceramic matrix composites (Cf/UHTCs), for which the molten Si is a very general and practical infiltrator. High-entropy carbide (HE-carbide) is a newly developed promising matrix phase of Cf/UHTCs. Understanding the phase equilibrium relation in the HE-carbide and Si reaction system can provide accurate guidance on designing the RMI process for preparing HE-carbide matrix composites with controlled phases and microstructure. This study systematically investigates W-containing HE-carbide and Si addition reactions at high temperatures. Samples with nominal starting compositions of (Ti0.2Zr0.2Hf0.2Ta0.2W0.2)C-xSi (HEC-xSi, x = 2.5, 5 and 10 wt%) are prepared by spark plasma sintering technique at 1500 °C and 1700 °C with an axial pressure of 40 MPa for 10 min. The results show that adding 2.5 wt% or 5 wt% Si removes carbon from the HEC matrix, forming SiC and stable equimolar (Ti0.2Zr0.2Hf0.2Ta0.2W0.2)C1-x phase with carbon deficiency at high temperatures. In contrast, besides the SiC phase, the addition of 10 wt% Si in the HEC matrix may form unstable transient phases of (Ti0.2Zr0.2Hf0.2Ta0.2W0.2)C1-x with supersaturated carbon deficiencies at high temperatures, which finally decomposes into non-equimolar HE-carbide (Ti0.2Zr0.2Hf0.2Ta0.2W0.2-y)C1-z and metal silicide WSi2 phases. The effects of the HEC and Si reactions on the microstructure evolution of the samples during sintering are discussed. Meanwhile, the mechanical properties of the samples with the reaction resulting microstructure are measured and briefly discussed.

Experimental verification of double-four-ring-type aluminosilicate molecule as a single-source precursor for zeolite synthesis

Abstract While a variety of functional zeolites have been synthesized using hydrothermal methods with conventional discrete Al and Si sources, control of the composition, structure, and function of the targeted zeolites often involves expensive and time-consuming trial-and-error approaches. Despite ongoing efforts to manipulate zeolite formation by adjusting Al and Si sources and reaction conditions, limited attention has been given to studies on zeolite synthesis using molecular precursors (MPs) with preorganized Al–O–Si bonds. Here, we demonstrate the synthesis of LTA-type zeolites using [TMA]4[Al4Si4O12(OH)8]·13H2O ([MP]; TMA = tetramethylammonium cation) with a double-four-ring (D4R)-type core structure, which is known to be a secondary building unit in the LTA-type zeolite, as a MP. Here, we demonstrate the successful synthesis of LTA-type zeolites using [MP] under hydrothermal conditions at 100 to 200 °C in the presence of 1 equiv. of NaOH or NaCl. Notably, when discrete Al and Si sources were used instead of [MP] under otherwise identical conditions (the same Si/Al ratio, Na+ content, and temperature), GIS-, SOD-, and FAU-type zeolites lacking the D4R structure were obtained in addition to the LTA-type zeolites.

Feasibility analysis of the preparation of geopolymers from different types of coal based ash: Reaction, synthesis, and properties

This study compared the feasibility of circulating fluidized bed boiler fly ash (CFBFA), pulverized coal furnace fly ash (PCFA), and coal gasification slag (CGS) for the preparation of geopolymers by investigating the Si and Al dissolution reaction of the raw materials, product structure, and the development of the mechanical properties of the geopolymers. The results indicated that the reaction mechanism for preparing geopolymers were the same for the three kinds of coal based ash, i.e., the depolymerization and repolymerization of Si-O and Al-O bonds in raw materials. The loose and porous microstructure of CFBFA resulted in a high dissolution ratio of amorphous Si and Al, and its self-hardening properties generated ettringite crystals. This resulted in a high initial strength of the CFBFA based geopolymer (CFBFAG). The active Si and Al in PCFA and CGS were released slowly during the curing process, which was conducive to an enhanced compressive strength of the geopolymer in the later stage. The compressive strengths of the CGS based geopolymer (CGSG) after curing for 90 days reached 52.1 MPa, which was 139 % and 11.4 % higher than that of CFBFAG and PCFAG for the same curing time respectively. A microstructure analysis showed that the CGSG had a denser microstructure and more ordered geopolymer gel network than the other geoploymers. Compared with the CFBFA and PCFA, CGS was found to have a greater application potential in the preparation of geopolymers.

Phonon relaxation effect by regeneration of nano-inclusions in SiGe for ultralow thermal conductivity and enhanced thermoelectric performance

SiGe alloys exhibit high thermoelectric performance at mid to high temperatures, but their wide applications are hindered by intrinsically high thermal conductivity. Here, we report a new strategy for regenerating ultrafine nano phases of CrSi2 and SiO2 with an average grain size of approximate 130 nm by chemical reaction of Si and strong oxidizing CrO3 in a p-type SiGe matrix. Based on the Debye-Callaway calculation, the nano-sized second phase leads to a reduction in phonon relaxation time, thereby lowering the thermal conductivity to an ultralow value of 2.15 W m−1 K−1 at 873 K. The boundaries between the second phases (CrSi2) and the matrix (SiGe) establish potential barriers, allowing carrier filtering and phonon scattering, thus increasing the power factor. Eventually, the sample (CrO3)0.3-Si80Ge20B0.5 reaches a peak ZT of approximately 1.12 at 873 K, with an average ZT of approximately 0.62 from 323 K to 873 K, representing a 55.56% improvement compared with Si80Ge20B0.5. Our method provides a promising approach for enhancing the thermoelectric performance of SiGe.

Simulation of Ladle Refining Reactions in Si–Mn‐Killed Steel

Steel quality, to a large extent, is controlled by ladle refining reactions. The understanding of such reactions can help to prevent the formation of unwanted phases and improve the overall high‐temperature process control. A new approach, namely, the multioxide inclusion kinetic model has been recently developed to simulate steel–inclusion reactions in liquid steel. The coupling of this kinetic model with a multicomponent, multiphase steel–slag reaction interface model leads to an overall model framework to predict the evolution of steel, slag, and inclusion composition. The current work shows the application of the model to simultaneous deoxidation and desulphurization during ladle refining of Si–Mn‐killed steel. The model shows good performance with industrial data. It is demonstrated that for ladle refining practices, silica‐rich slags should be strictly used with basicity (CaO/SiO2) between 1 and 1.2 and with Al2O3 content less than 5 wt%. Additional simulations are also carried out to reveal the capability of the model to aid in online process control. Finally, certain limitations of the current model are discussed.

Thermodynamic and experimental study on carbothermal reduction of JSC-1A lunar regolith simulant for metal and metalloid production

The carbothermal reduction of JSC-1A lunar simulant with activated carbon was investigated for producing metals and metalloids. Chemical equilibrium compositions were examined using Gibb’s free energy minimization to identify favorable operating temperatures at 0.1, 10-8, and 3 × 10-15 bar for Fe and Si production. Complete conversion of Fe2O3 to Fe(g) was predicted at temperatures above 850 °C and about 90 % conversion of SiO2 to Si(g) was predicted at temperatures above 1000 °C for lunar surface pressure of 3 × 10-15 bar. Thermogravimetry was used to examine the reactions with mixtures of JSC-1A and stoichiometric activated carbon in 100 % Ar up to 1500 °C, and comparisons between temporal mass losses and CO evolution were used to estimate volatile production. The results were compared to ultra-high vacuum experiments at ∼ 10-12 bar with temporal CO measured. Solid-state surface material characterization was performed using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray diffractometry, and transmission electron microscopy to identify elemental distributions and particle morphology of sample surface before and after experiment as well as chemical compositions present after experiment. Changes in elemental distributions and morphologies of Si-, Fe-, and Ti- in the sample before and after the experiment provided strong evidence of reactions of Si-, Fe-, and Ti- compounds in JSC-1A. Characterization of the loose sample after TGA confirmed the presence of crystalline SiC, Si, and Fe. Deposits collected on Cu foils mounted above the sample in the ultra-high vacuum experiments were found to contain Fe-, Al-, Mg-, and Si- volatiles.

Fast cycling of lithium metal in solid-state batteries by constriction-susceptible anode materials.

Interface reaction between lithium (Li) and materials at the anode is not well understood in an all-solid environment. This paper unveils a new phenomenon of constriction susceptibility for materials at such an interface, the utilization of which helps facilitate the design of an active three-dimensional scaffold to host rapid plating and stripping of a significant amount of a thick Li metal layer. Here we focus on the well-known anode material silicon (Si) to demonstrate that, rather than strong Li-Si alloying at the conventional solid-liquid interface, the lithiation reaction of micrometre-sized Si can be significantly constricted at the solid-solid interface so that it occurs only at thin surface sites of Si particles due to a reaction-induced, diffusion-limiting process. The dynamic interaction between surface lithiation and Li plating of a family of anode materials, as predicted by our constrained ensemble computational approach and represented by Si, silver (Ag) and alloys of magnesium (Mg), can thus more homogeneously distribute current densities for the rapid cycling of Li metal at high areal capacity, which is important in regard to solid-state battery application.

Medium-temperature calcination and acid pressure leaching extract the Al2O3 from coal gangue: activation mechanism and kinetic analysis.

Bauxite is an important strategic resource, and it is facing with the problem of balance between high demand of bauxite ore and low resource of bauxite reserves in China. This research takes the Fuxin coal gangue as the object and extracts Al2O3 by medium-temperature calcination and acid pressure leaching process. The results show that at a calcination temperature of 650 °C, calcination time of 2 h, acid pressure leaching temperature of 160 °C and acid pressure leaching time of 6 h, the extraction ratio of Al2O3 reaches 80.19%. Furthermore, the research finding that the complete activation temperatures of kaolinite and muscovite are 650 °C and 850 °C, respectively, and the decomposition reactions of active Si, active Al, and metakaolinite occur above 800 °C, which leads to a low extraction ratio of Al2O3. The acid pressure leaching process can directly destroy the muscovite structure at a calcination temperature of 650 °C. The acid pressure leaching kinetic equations are studied by three kinetic models, and the apparent activation energies of the reactions are calculated by the Arrhenius formula. The results show that acid pressure leaching is subject to solid residue in-layer diffusion control, and the kinetic equation is "". The apparent activation energy is 13.48 kJ mol-1.

From silicon to silicones without dimethyldichlorosilane: direct green mechanochemical synthesis of methylmethoxysilanes from silicon and dimethyl ether

First gram-scale synthesis of methylmethoxysilanes via mechanochemical direct reaction of Si with dimethyl ether, achieving nearly 100% silicon conversion and high selectivity for dimethylsilyl-containing products.

Evaporation residue cross-section measurements for 30Si+142Ce system

Evaporation residue (ER) cross-sections were measured for 30Si+142Ce reaction at laboratory energies in the range of 105 - 132 MeV using the HYbrid Recoil mass Analyzer (HYRA) at IUAC, New Delhi. The transmission efficiency of the HYRA was estimated using the calibration reaction 28Si+142Ce. Sub-barrier fusion enhancement was observed when compared with the one-dimensional barrier penetration model predictions for the present system. To explore the phenomena responsible for sub-barrier fusion enhancement, coupled-channels calculations were performed using the CCFULL code. The effect of couplings and the role of positive Q-value neutron transfer (PQNT) channels on sub-barrier fusion cross-sections were investigated. Coupled-channels calculations were able to reproduce the data by including the coupling in both projectile and target nucleus along with two neutron-transfer channels having positive Q-value. The measured ER cross-sections were compared with the nearby systems to explore the role of deformation of the colliding nuclei.

Nanostructure of Si-Sn Thick-Film Electrodes to Improve the Energy Density of Oxide-Based All-Solid-State Lithium-Ion Batteries

Charge and discharge characteristics of Si-Sn composite thick-film electrodes on a garnet-type solid electrolyte were studied systematically. Charge/discharge cycle performance of 0.1 μm-thick Si-Sn thin-film electrodes simply depended on the Si:Sn composition ratio, while the thick-film electrodes with a thickness of 1 μm delivered the most outstanding performance at a specific Si/Sn atomic ratio of 7:3. The Si7-Sn3 composite film had a unique nanostructure to promote the charge/discharge reactions of Si and to maintain the interfacial contact with the solid electrolyte. These results can provide a clue to the design of Si-based negative electrodes for all-solid-state lithium ion batteries with high energy density.

Spray drying as a one-step production method of SiC-based granulates for direct reactive laser sintering of Reaction Bonded Silicon Carbide (RBSiC)

This research is focused on the development and production of SiC-based granulates for reactive laser sintering. Ceramic slurries with different compositions of SiC, Si, C powders, and PVA binder were subjected to spray drying. Carbon source in form of latex was proposed to avoid a reaction of Si with H2O in alkalic pH caused by the presence of carbon in the slurry. It was observed that the latex was beneficial for improvement of the flowability. Selected granulates were subjected to laser processing using two different methods. The first one where SiC-based granulates were spray deposited on a SiC substrate and laser treated with single pulse working of the laser. The second method where a pressed green sample of SiC were processed by the continuous working mode of the laser. Results revealed that the use of the continuous work mode during laser processing allowed to produce Reaction Sintered SiC (RBSiC).

High-Performance Silicon-Rich Microparticle Anodes for Lithium-Ion Batteries Enabled by Internal Stress Mitigation

HighlightsThe Sn and Sb incorporation boosts the electronic conductivity and lithium diffusivity of Si anodes, thereby reducing the stress due to lithium concentration gradient.The lithiation of modified electrode mimics isotropic solid solution reaction, rather than the original anisotropic two-phase reaction of Si, effectively weakening the stress concentration.The silicon-rich particles exhibit a capacity of over 1.9 Ah g−1 after 100 cycles at 0.1 A g−1 and maintain the excellent cyclic stability at 3 A g−1.

Oxidation and carburizing behaviors of HP40Nb tube after 100,000h service in pyrolysis furnace

The behaviors of the oxidation and carburizing of the HP40Nb furnace tube after 100,000 h service in high temperature and strong carburizing environment were analyzed in this study. The results show that there are three zones including surface oxide layer, intercrystalline oxidation zone and carburizing zone from inwall to center of the tube. The oxidation behavior of the furnace tube consists of outer oxide layer and internal oxidation. Because of standard free energies of the reactions of Cr and Si with per mole of O2 varies with the diffusion depth of oxygen, initial stage of the internal oxidation Cr is reflected first and SiO2 is closer to the interior of the alloy. Excess activated carbon atoms are precipitated in the form of Cr23C6 in the central region of the alloy, forming the carburizing zone. The severe depletion of Cr in the intercrystalline oxidation zone leads to an increase of the critical carbon concentration of Cr carbide in this region, resulting in only a small amount of NbC distribution in this region. The intercrystalline carbide is coarsened into the form of coarse chain and block.

Significantly enhanced performance of Li-storage via in-situ oxidation of silicon particles by zinc oxide

The synthesis of Si-based composite material can be realized via the reduction of ZnO by excess Si during ball milling. X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy analysis confirmed the presence of the reacted products Zn and SiOx (0 <x < 2) in the Si matrix. The composite material was coated with carbon by a high-temperature carburizing process. The carbon-coated composite material shows excellent cycling stability at 0.2 C by demonstrating a capacity retention rate of 78.05 % after 300 cycles with a charging-specific capacity of 697 mA h/g. These results indicate that the nanocrystalline Zn and amorphous SiOx products from the solid-state reaction of cheap Si and ZnO are very effective in improving the cycling stability of Si-based composite material.

Carbonization-driven motion of Si islands on epitaxial graphene

We investigate structural changes in Si islands deposited at room temperature on epitaxial few-layer graphene on SiC(0001) during subsequent annealing. Annealing causes the Si islands move on epitaxial graphene thicker than monolayer with monolayer-deep trenches left behind. In contrast, Si islands do not form trenches on monolayer graphene, but the Si atoms are intercalated to form quasifreestanding bilayer graphene. The islands which terminated their motion are made of SiC. During annealing, Si islands are carbonized into SiC islands by incorporating carbon atoms from graphene, resulting in the etching of graphene. The carbonization reaction of Si is a driving force of the motion of the Si islands.

Core–shell spherical graphite@SiC attenuating agent for AlN-based microwave attenuating ceramics with high–efficiency thermal conduction and microwave absorption abilities

A core–shell structured spherical graphite (SG)@SiC attenuating agent with a tunable silicon carbide (SiC) shell thickness was synthesized via in-situ solid-liquid reaction of SG and Si. Then, fully dense 10 wt%SG@SiC/AlN microwave attenuating composite ceramics were prepared through hot-pressing sintering, and the morphology of SG@SiC particle was well maintained. By moderately modulating the thickness of the SiC shell with relatively low complex permittivity and thermal conductivity, an effectively inhibited solid solution of SiC into AlN, weakened dipole and electron polarization, enhanced conduction loss, and an improved impedance matching, thermal conductivity and microwave loss capacity were simultaneously achieved. Thus, the SG@SiC/AlN composite exhibit excellent and impressive thermal conductivity of 63.92 W m−1·K−1 and minimum reflection loss of −34.2 dB. The outstanding performance of SG@SiC/AlN composite indicates that the composite is promising microwave attenuating ceramic with excellent thermal conduction and microwave absorption ability. This work opens up a new core–shell structure strategy for designing and developing a high-efficiency attenuating agent and microwave attenuating ceramic.

Mechanisms and Thermochemistry of Reactions of SiO and Si2O2 with OH and H2O.

This paper reports on computational studies of gas-phase reactions of SiO and Si2O2. The oxidation of SiO can initiate efficient formation of silica or silicate dust particles in a wide range of environments. Both OH radicals and H2O molecules are often present in these environments, and their reactions with SiO and the smallest SiO cluster, Si2O2, affect the efficiency of eventual dust formation. Density functional theory calculations on these reactions, benchmarked against accurate coupled cluster calculations, indicate that the Si2O2 + OH reaction should be faster than SiO + OH. The reaction SiO + H2O → SiO2 + H2 is both endothermic and has high activation energies to reaction. Instead, the formation of molecular complexes is efficient. The reaction of Si2O2 with H2O, which has been suggested as efficient for producing Si2O3, might not be as efficient as previously thought. If the H2O molecules dissociate to form OH radicals, oxidation of SiO and Si2O2 could be accelerated instead.