Small Amount Of Si Research Articles

Deposition behavior and mechanism of thermal sprayed SiC

AbstractIt is widely known that silicon carbide (SiC) is challenging to thermal spray. However, the nature of deposition and the underlying mechanisms are still not clearly understood. In the current work, the process of atmospheric plasma‐sprayed SiC was investigated in detail. SiC exhibits sublimation severely under the plasma spraying (PS). More than 65 mol.% SiC particles lost by sublimation during PS estimated by calculation. Due to the nonuniformity of temperature in plasma flame, a small amount of SiC particles was retained. Moreover, a small amount of Si and SiO2 was experimentally observed after deposition process from the single‐splat characterization. According to the first‐principles calculations, the detachment energy of C atom from the lattice (0.591 eV) is lower than that of Si atom (1.257 eV). The adsorption energies of an O atom on the Si‐ and C‐terminated surfaces are −9.549 and −7.631 eV, respectively. Therefore, C is more likely to form gaseous products after decomposition, and Si is more likely to be retained to form Si and SiO2. Mullite was found on the grain boundaries of molten Si, which was attributed to the rapid diffusion of the Al2O3 substrate along the grain boundaries of Si, promoting the spreading of molten splats. It is difficult to stack particles through self‐diffusion among SiC particles to form coatings. The discovery on thermal deposition mechanism of SiC in PS is helpful to promote the practical application of SiC coatings on preparation optimization and interfacial bonding improvement.

Facilitated fluorination and etching of 2D materials

Precise control of functionalization and etching have been required for surface modification and device fabrication of two-dimensional (2D) materials. Specifically, fluorination of graphene has been used to control the properties of graphene. Recently, xenon difluoride (XeF2) has been used for selective fluorination of graphene and etching of other 2D materials, such as hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMDs). However, there is a lack of studies on key factors that govern the XeF2 treatment, which results in inconsistent behaviors of fluorination and etching. Here, we report control over chemical reactions between XeF2 and 2D materials using a chemical mediator of Si. Even a small amount of Si can accelerate the dissociation of XeF2, leading to the formation of chemically reactive xenon fluoride (XeF) that enhances the fluorination and etching of 2D materials. Additionally, our findings show that defects in 2D materials serve as chemically unstable sites that facilitate the additional dissociation of XeF2, generating F single atoms that easily form covalent bonds on the surface of 2D materials. Our study suggests that Si can be utilized as a reaction mediator to regulate XeF2 treatment on 2D materials, which has important implications for the fabrication of 2D electronic devices.

High-Temperature Oxidation Behaviour of CrSi Coatings on 316 Austenitic Stainless Steel.

In this study, a closed-field unbalanced magnetron sputtering system, which is environmentally friendly and has high deposition efficiency, was used to deposit CrSi coatings on 316 austenitic stainless steel. This system utilised separate Cr and Si targets, and the appropriate content of Cr and Si of the coatings was adjusted by changing the currents applied to the targets. A series of CrSi coatings with different Si/Cr ratios were produced, and their oxidation behaviour at elevated temperatures was investigated. By analysing the weight gain, surface morphology and microstructure, composition and phase constituents, the oxidation behaviour at 600 °C, 700 °C and 800 °C was investigated and the optimized coating to protect the stainless steel has been identified. The outcome of the research indicated that a small amount of Si (between 4-7 at.%) in Cr coatings is effective in protecting the austenitic stainless steel against oxidation at high temperatures, while a high Si content (around 10 at.% or more) makes the coating more brittle and prone to cracking or delamination during oxidation at 800 °C.

Low‐temperature reactive hot‐pressing of Ta0.2Hf0.8C–SiC ceramics at 1700°C

AbstractTemperature above 2000°C and additional pressure is generally required to achieve the full densification of TaxHf1−xC‐based ceramics. This work proposed a novel method to fabricate dense Ta0.2Hf0.8C ceramics at relatively low temperature. Using a small amount of Si as a sintering aid, Ta0.2Hf0.8C was densified at 1700°C by reactive hot‐pressing (RHP), with SiC formed in situ. Microstructure evolution mechanisms of the ceramics during RHP were investigated. The effect of silicon content on the densification and mechanical properties of the ceramics was revealed. It is indicated that the apparent porosity of the Ta0.2Hf0.8C–SiC ceramics was as low as 0.5%, whereas bending strength and fracture toughness of the ceramics were as high as ∼637 MPa and 6.7 MPa m1/2, respectively, when the silicon content was 8 wt.%. This work provides a new idea for the low‐temperature densification of TaxHf1−xC and other ultrahigh temperature ceramics with high performance.

A novel (B4Cp+Gd)/Al6061 neutron absorber material with desirable mechanical properties

A novel (10 wt%B4Cp+3.6 wt%Gd)/Al6061 neutron absorber material having great potential commercial applications was designed by calculating equivalent B content (BEq) and its neutron absorber ability was evaluated based on an equivalent B areal density (EBAD) calculation as well as a Monte Carlo simulation. The designed material was successfully fabricated by ultrasound assisted casting method. The added B4C particles were distributed uniformly in the matrix and the newly formed large-sized Al3Gd particles existed along the grain boundaries (GBs) in the as-cast composite. It was found that a small amount of Si was solubilized in Al3Gd lattice and the solution behavior of Si was revealed using first-principles calculation. After hot extrusion (HE) and heat treatment (HT), the large-sized Al3Gd particles were broken into small ones and nano-sized βʺ phase was precipitated in the matrix. The mechanical properties of the modified composite were enhanced remarkably and the reason of which was mainly attributed to the following two aspects. On the one hand, HE induced the grain refinement and the fragmentation of large-sized Al3Gd particles as well as their more homogeneous distribution within grains from GBs were beneficial for the improvements in both strength and ductility of composite. On the other hand, HT induced the precipitation of βʺ phase could work as strengthening phase in the modified composite. The size and distribution of Al3Gd particles played an important role in improving the mechanical properties since cracking easily occurred on the large-sized Al3Gd particles which existed along GBs, leading to the severe degradation of mechanical properties of the as-cast composite. Furthermore, the related mechanism of cracking behavior of large-sized Al3Gd particles was discussed. This research provides a low-cost method to prepare easy-deform Al based neutron absorber material with desirable mechanical properties.

Synthesis of short-wave infrared Ge1−ySny semiconductors directly on Si(100) via ultralow temperature molecular routes for monolithic integration applications

We report the synthesis of Ge1−ySny films containing 6%–13% Sn directly on Si(100) for monolithic integration applications, circumventing the use of conventional Ge-buffer layers. The films are produced in a gas source molecular epitaxy chamber at ultralow temperatures of 185–210 °C and a pressure of 10−5 Torr by the reactions of pure vapor Ge4H10 and SnD4 or SnH4 without carrier gases. Very small amounts of Si, incorporated via the Si4H10 precursor, can be used to improve the structural properties. All samples were characterized by XRD, RBS, IR-ellipsometry, AFM, and TEM, indicating the formation of monocrystalline single-phase films with relatively low defectivity and flat surfaces. A notable highlight is that the residual strains of the alloy layers are much lower compared to those grown on Ge buffers and can be further reduced by rapid thermal annealing without decomposition, indicating that growth on bare silicon should produce bulklike, high Sn content alloys that cannot be accessed using Ge buffers. N-type analogs of the above samples doped with phosphorus were also produced using P(SiH3)3 as the in situ dopant precursor. The results collectively illustrate the potential of our chemistry-based method to generate good quality Ge1−ySny layers directly on large area Si wafers bypassing Ge buffers that typically lead to complications such as multiple hetero-interfaces and epitaxial breakdown at high Sn concentrations.

Graphene Aerogel-encapsulated Silicon Nanoparticles Mechanofused on Graphite without Prelithiation for Cylindrical Ni-rich NMC811 Li-ion Batteries

Silicon (Si), one of the promising anodes, provides a high theoretical specific capacity of ca. 3500 mAh g−1 at room temperature. It experiences many drastic issues, such as cost-effectiveness, large volume expansion, and unstable thick solid–electrolyte interfaces (SEI), leading to poor cycling stability. A small amount of Si has recently been added to graphite and used as the anode for commercial Li-ion batteries. Nevertheless, the intrinsic issues of Si still occur. Herein, we encapsulated Si nanoparticles with reduced graphene oxide (RGO) aerogel and graphite to obtain Si-RGO@Graphite using a dry surface coating technique so-called mechanofusion. This technique enhances the strong binding between these materials. We also demonstrated the practical use of the as-prepared Si-RGO@Graphite (9.9:0.1:90.0 wt% of Si:RGO:Graphite) anode coupling with Ni-rich NMC811 cathode at a 18650 cylindrical cell level. In this attempt, we avoid using an expensive vacuum-required prelithiation process, which currently inhibits the practical and commercial use of the Si-based anode. We believe this new composite material may be useful for high-energy LIBs in the future.

A combinatorial study of SiGeAsTe thin films for application as an Ovonic threshold switch selector

In this paper, we investigate the thermal stability of a wide range of ternary and quaternary (Si)GeAsTe alloy thin films. These type of materials are reported to show Ovonic threshold switching, which means they conduct the current above a specific threshold voltage and are not conducting at lower voltages, making them ideal as a selector element for crosspoint memory devices. For threshold switching to occur in these chalcogenides, the amorphous state of the material is crucial, and hence the material may not crystallize below 400°C to be compatible with temperatures used in device process flows. A combinatorial deposition technique is used to create a thin film library of 36 different compositions, and in situ X-ray diffraction and X-ray fluorescence spectroscopy is used to investigate the thermal stability of the films. We show that Si doping of GeAsTe improves the thermal stability by increasing the crystallization temperature and small amounts of Si (i.e.5at%) decreases the tendency to lose material by sublimation. Also capping the films with a W cap avoids material loss if the capping layer does not show cracking under annealing. An optimal chalcogenide composition, being As50Te20Ge20Si10 combined with a W electrode is identified and is integrated in 65nm mushroom type devices for electrical characterization. The material shows threshold switching and excellent endurance with over 108 cycles.

Microstructure and mechanical properties of Si and YN doped powder metallurgical tantalum

Abstract Tantalum has a wide range of applications due to its high melting temperature, its corrosion resistance and its mechanical and electrical properties. One of these applications are fine wires which are needed for Ta-capacitors. During fabrication of such components, the wires are exposed to high temperatures and, thus, grain growth combined with embrittlement becomes a major problem. In the present work, the effects of doping with small amounts of Si and YN on microstructure and mechanical properties of annealed Ta-wires have been investigated. Doped samples show a higher hardness and strength than samples of pure powder metallurgical (PM) Ta; however, the grain growth kinetics are very similar. Samples doped with Si and samples doped with both Si and YN exhibit almost identical properties.

Effect of silicon content on the microstructure evolution, mechanical properties, and biocompatibility of β-type TiNbZrTa alloys fabricated by laser powder bed fusion

Beta-type titanium alloys are excellent candidates for biomedical applications because of their very low elastic modulus, excellent corrosion resistance, and biocompatibility. However, many traditional β-type titanium alloys exhibit low yield strength. In this study, a small amount of Si (3 and 5 at.%) was added to a Ti-35Nb-7Zr-5Ta (wt%, TNZT) biomedical alloy prepared via laser powder bed fusion (LPBF) to increase its yield strength. The Si addition resulted in a significant increase in the compression yield strength of the alloy (from 802 to 1282 MPa). Meanwhile, the elastic moduli of the TNZT alloys (48.7–60.6 GPa) with 3 and 5 at.% Si were much lower than that of the Ti-6Al-4 V alloy (110 GPa), which is used extensively in clinical applications. The microstructural analyses indicated that the ultrahigh-strength of the TNZT alloy containing Si was due to the presence of ultrafine (Ti, Nb, Zr)5Si3 (S1) grains in the β-Ti matrix. In addition, thin shell-shaped S1 and (Ti, Nb, Zr)2Si (S2) grains precipitated along the columnar β-Ti grain boundaries in the TNZT alloys containing 3 and 5 at.% Si, respectively. Moreover, the introduction of Si to the TNZT alloy significantly refined the grains, weakened the cubic texture, decreased surface roughness, and improved Vickers hardness. The ultrahigh strength of the Si-containing TNZT alloys was due to grain boundary strengthening and precipitation strengthening. In addition, in vitro studies with MC3T3-E1 cells revealed that the cytocompatibilities of the LPBF-fabricated TNZT and Si-containing TNZT alloys were equivalent and were better than that of the LPBF-fabricated Ti-6Al-4 V alloy. In particular, the TNZT alloy with 3 at.% Si showed the best elastic modulus (48.7 ± 1.0 GPa), yield strength (1151 ± 17 MPa), and cell biological response among all the alloys investigated in this study, and hence was found to be a suitable candidate for application in load-bearing bone implants.

Модифицирование наноразмерными частицами нитрида кремния материалов на основе системы Ti – B – Fe, полученных методом СВС-экструзии

Compact ceramic SHS-electrode materials based on titanium diboride modified with silicon nitride nanoparticles have been obtained by SHS-extrusion. The phase composition, structure, and physicomechanical properties of the obtained materials have been studied. The results of scanning electron microscopy showed that, in the modified samples, grain refinement of the main phase of titanium diboride is observed, as well as a change in the phase composition of the material. With the introduction of 5 wt. % nanosized particles of silicon nitride, in addition to the main wear-resistant phase TiB2, the formation of phases is observed: TiN, Fe2B and TiSi2 located in the FeTi intermetallic matrix. The average grain sizes of TiB2 and TiN are 0.5 – 2 mm and 2 mm, respectively. With the addition of 10 wt. % Si3N4, the structure of the material consists of TiB2 and TiN phases uniformly distributed in the FeTi intermetallic matrix, and a small amount of Si and B solid solutions. The TiB2 grain size does not exceed 0.5 – 1 mm, and the TiN phase has an average grain size about 0.5 – 1.5 mm. It is shown that the obtained modified ceramic SHS-electrode materials have higher microhardness and hardness compared to the material without Si3N4 additives.

Microstructure and Properties of FeCoNiCuSix High Entropy Alloys

The microstructure morphology, hardness, corrosion resistance and magnetic properties of FeCoNiCuSix high entropy alloys prepared by vacuum arc melting at different Si content were studied. Found by multiple testing methods, the crystal structure of the FeCoNiCuSix high entropy alloy without Si has both FCC and BCC structures. After adding Si, all the structure of the alloy transforms to FCC, and there are differences between the alloys after adding Si, which mainly concentrates in the interdendritic areas and dendritic edges. At the same time, because of the addition of Si, the overall hardness of the alloy very significantly improves. When the content of Si < 0.2, the overall compressive property of the alloy decreases, but when the content of Si > 0.2, the alloy has a certain ductility and compressive strength. Due to the enrichment of Cu, the alloy is easy to form a primary cell at the enrichment of Cu, which reduces the corrosion resistance of the alloy. Meanwhile, a small amount of Si can form a solid solution in the Cu enrichment area, reduce the galvanic effect, and improve the corrosion resistance of the alloy. However, with the increase of Si content in the FeCoNiCuSix high entropy alloy, the corrosion resistance of the alloy will deteriorate and the corrosion rate will accelerate. At the same time, the addition of Si will also have a negative effect on the magnetic properties of the alloy.

Superior high-temperature oxidation resistance of nanocrystalline 304 austenitic stainless steel containing a small amount of Si

Improving the high-temperature oxidation resistance of steels by excessive Si addition to form a continuous silica healing layer would deteriorate the mechanical, welding and irradiation properties. Here, we report a thermally stable nanocrystalline 304 (NC-304) austenitic stainless steel with a low Si content (less than 1 wt.%) and superior high-temperature oxidation resistance. The segregated Si at the grain boundaries (GBs) of NC-304 presets a nanoscale Si-enriched network for the formation of a continuous SiO2 GB network during the high-temperature oxidation. Besides, the high-density La-Si-O-rich nanoprecipitates can serve as heterogeneous formation sites for SiO2, promoting the formation of a continuous SiO2 phase along the GB network. The unique nanocrystalline microstructure and element distribution feature of Si in NC-304 accelerate the construction of a continuous SiO2 healing layer, which effectively eliminates the breakaway oxidation found in coarse-grained 304 counterpart and significantly reduces the high-temperature oxidation rate at least to 1000 °C.

Large tunneling magneto-dielectric enhancement in Co(Fe)−MgF2 granular films by minor addition of Si

We report a large enhancement of the tunneling magneto-dielectric (TMD) effect in Co−MgF2 granular films induced by doping using a small amount of Si. This minor addition of Si is dispersed uniformly in the MgF2 matrix and acts by inhibiting the interdiffusion between the Co and MgF2 phases, thus enhancing the magnetization when compared with the case of the corresponding undoped Co−MgF2 films; this consequently results in a greatly enhanced peak dielectric variation (TMD ratio, Δε′/ε′), as indicated by theoretical fittings. Extension of this Si doping effect to CoFe−MgF2 films led to a record-high Δε′/ε′ of 4.3% at 10 kHz and 8.5% at 200 kHz under the application of a magnetic field (H) of 10 kOe, while remaining as high as 2.1% even under H = 1 kOe. This study presents a simple but highly effective approach to enhance the TMD effect in granular nanocomposites, thus opening up the prospect of development of high-performance magnetoelectric devices.

Aluminium nitride layers prepared by nitrogen arc discharge on Al-Si alloy substrate

AlN strengthening layers were prepared on the surface of the Al-Si alloy substrate by nitrogen arc discharge at various currents. The strengthening layer is mainly composed of AlN, Al and a small amount of Si. In the nitriding process, the melt from the melting region transports upward to form the layer and Si works as the catalyst. In this method, the nitriding reaction is rapid and stable, which is virtually not affected by the oxygen partial pressure. The nitride layer can greatly improve the wear resistant of the sample. As the nitride current increases, the volume loss of the frictional wear test under lubricant condition decreases first and then increases. The volume loss reaches its lowest value at 90 A, which is only about 1/38 that of the substrate.

First principles density functional theory calculations on the elastic properties of Mo-Si based solid solutions

The alloy system Mo-Si-B gained a lot of attention, as it showed superior elastic properties than currently used Ni based superalloys at elevated temperatures. In the Mo-Si-B alloy system, Mo based solid solutions play an important role as a compound and one can observe a solid solution with small amounts of Si and tiny, almost negligible, amounts of B. To improve the ductility of this alloy at higher temperatures, titanium is added and as a result Mo-Si-Ti solid solutions are formed. To get an idea of the elastic properties of new Mo based solid solutions, first principles density functional theory calculations serve as a powerful method for the prediction and qualitative, often almost quantitative results for the elastic moduli are achieved. Here we show the elastic properties like bulk, shear and Young’s modulus as well as the Vickers hardness, calculated with first principles density functional theory (DFT), of Mo-Si-B-Ti based solid solutions with approximated atom concentrations Mo-1 at.% Si, Mo-3 at.% Si, Mo-2 at.% Si-1 at.% Ti, Mo-3 at.% Si-1 at.% B and Mo-3 at.% Si-1 at.% Ti.

Improvement of CoCr Alloy Characteristics by Ti-Based Carbonitride Coatings Used in Orthopedic Applications

The response of the human body to implanted biomaterials involves several complex reactions. The potential success of implantation depends on the knowledge of the interaction between the biomaterials and the corrosive environment prior to the implantation. Thus, in the present study, the in vitro corrosion behavior of biocompatible carbonitride-based coatings are discussed, based on microstructure, mechanical properties, roughness and morphology. TiCN and TiSiCN coatings were prepared by the cathodic arc deposition method and were analyzed as a possible solution for load bearing implants. It was found that both coatings have an almost stoichiometric structure, being solid solutions, which consist of a mixture of TiC and TiN, with a face-centered cubic (FCC) structure. The crystallite size decreased with the addition of Si into the TiCN matrix: the crystallite size of TiCN was 16.4 nm, while TiSiCN was 14.6 nm. The addition of Si into TiCN resulted in smaller Ra roughness values, indicating a beneficial effect of Si. All investigated surfaces have positive skewness, being adequate for the load bearing implants, which work in a corrosive environment. The hardness of the TiCN coating was 36.6 ± 2.9 GPa and was significantly increased to 47.4 ± 1 GPa when small amounts of Si were added into the TiCN layer structure. A sharp increase in resistance to plastic deformation (H3/E2 ratio) from 0.63 to 1.1 was found after the addition of Si into the TiCN matrix. The most electropositive value of corrosion potential was found for the TiSiCN coating (−14 mV), as well as the smallest value of corrosion current density (49.6 nA cm2), indicating good corrosion resistance in 90% DMEM + 10% FBS, at 37 ± 0.5 °C.

Genesis of authigenic kaolinite and its indicative significance to secondary pores in petroliferous basins: A case study in the Dongying Sag, Bohai Bay Basin, Eastern China

Porosity of sandstone generally declines as the formation burial depth rises, during which transformation of unstable minerals (e.g. feldspar) in sandstone significantly contributes to abnormally high porosity zones. It is still controversial that whether transformation of feldspar being massive in sandstone can lead to formation of considerable secondary pores. As the main diagenetic product of feldspar transformation, namely authigenic kaolinite, in terms of the physical and chemical features, acts as indicators of the transformation process of feldspar and the consequent formation of secondary pores. In this study, a series of analyses are implemented on sandstone samples collected from the Dongying Sag, Bohai Bay Basin, Eastern China, including microscopic observation, SEM, EDX, XRD, isotope, and fluid inclusion analysis, with specific attention to genesis and formation process of authigenic kaolinite as well as their indicative significance to secondary pores. It is demonstrated that there are mainly three types of authigenic kaolinite (denoted as K1, K2, and K3), the occurrence and geochemical characteristics of which are greatly different. Based on contact relationship between authigenic kaolinite and other diagenetic products, the three authigenic kaolinite are distinguished into two stages, namely the first-stage K1and the second-stage K2 and K3, which are of obviously different genesis. Specifically, K1 is formed under the effect of acidic fluids that are rich in carboxylic acids. In contrast, K2 and K3 are formed under the effect of acidic fluids that are rich in CO2. During formation of K1, plagioclase dissolution pores are formed and well preserved, and carbonate cements get well preserved, showing no sign of dissolution. During formation of K2 and K3, K-feldspar is kaolinitized as K2, and a small amount of Si and Al elements migrates with short-distance and precipitates as K3 in the vicinity of K2. During this process, K-feldspar is transformed into kaolinite, accompanied by dissolution of carbonate cements and massive formation of secondary pores.

Effect of Si Content on Melt Infiltration Method of SiCf/SiC-Ti3SiC2

SiCf/SiC composites have attracted wide attention as thermo-structural materials owing to its extraordinary properties at elevated temperature. To further improve the toughness of SiCf/SiC, Ti3SiC2 is used as the reinforcement of SiC matrix. In this study, the effect of Si content on the formation of Ti3SiC2 was discussed. The melt Si infiltration method was used to prepare the SiC matrix, whichTi3SiC2phase was in-situ formed from the reaction between TiC, C and Si during the infiltration process. X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were determined to characterize the phase constitution and microstructure of the matrix. The results demonstrate that the synthesis of Ti3SiC2 was depended on the amount of Si during the molten Si infiltration. The small amount of Si could resulted in the incomplete infiltration reaction. TiSi2 was obtained at the presence of excessive Si. Thus appropriate amount of Si promotes the formation of Ti3SiC2 and improves the purity.

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.