High Si Content Research Articles

Lamina-specific localization of silicon accumulation in two broadleaf tree species.

Silicon (Si) accumulation differs greatly among plant species, as revealed by an increasing number of studies reporting whole-leaf Si concentration for a wide range of land plants. Yet, we have limited knowledge about Si distribution across leaf parts (e.g., lamina vs. veins) within a leaf of eudicots. Here, we report how Si accumulation with leaf age differs among petiole, midrib, and lamina in two broad-leaved trees, Acer rufinerve and Ficus erecta. We marked a pair of neighboring leaves in each marked shoot and harvested one in May and the other in October to measure Si concentration. In both species, the lamina showed much higher Si concentration than the petiole and vein in both young and old leaves, and only the lamina showed clear increases in Si concentration from young to old leaves. Si accumulation rate correlated positively with shoot size and leaf production in F. erecta but not in A. rufinerve. These results strongly suggest that, in eudicot species, Si is deposited mostly in leaf lamina but in only a negligible amount in petioles and veins through which Si dissolved in water is transported. Future research on physiological regulations of Si accumulation in eudicot species should consider which specific cells in leaf lamina are responsible for such highly localized Si deposition.

On the Nb5Si3 Silicide in Metallic Ultra-High Temperature Materials

Refractory metal (RM) M5Si3 silicides are desirable intermetallics in metallic ultra-high temperature materials (UHTMs), owing to their creep properties and high Si content that benefits oxidation resistance. Of particular interest is the alloyed Nb5Si3 that forms in metallic UHTMs with Nb and Si addition. The choice of alloying elements and type of Nb5Si3 that is critical for achieving a balance of properties or meeting a property goal in a metallic UHTM is considered in this paper. Specifically, the different types of alloyed “normal” Nb5Si3 and Ti-rich Nb5Si3, namely “conventional”, “complex concentrated” (CC) or “high entropy” (HE) silicide, in metallic UHTMs with Nb and Si addition were studied. Advanced metallic UHTMs with additions of RMs, transition metals (TMs), Ge, Sn or Ge + Sn and with/without Al and with different Ti, Al, Cr, Si or Sn concentrations were investigated, considering that the motivation of this work was to support the design and development of metallic-UHTMs. The study of the alloyed silicides was based on the Nb/(Ti + Hf) ratio, which is key regarding creep, the parameters VEC and Δχ and relationships between them. The effect of alloying additions on the stability of “conventional”, CC or HE silicide was discussed. The creep and hardness of alloyed Nb5Si3 was considered. Relationships that link “conventional”, CC or HE bcc solid solution and Nb5Si3 in the alloy design methodology NICE (Niobium Intermetallic Composite Elaboration) were presented. For a given temperature and stress, the steady state creep rate of the alloyed silicide, in which TMs substituted Nb, and Al and B substituted Si, depended on its parameters VEC and Δχ and its Nb/(Ti + Hf) ratio, and increased with decreasing parameter and ratio value, compared with the unalloyed Nb5Si3. Types of alloyed Nb5Si3 with VEC and Δχ values closest to those of the unalloyed Nb5Si3 were identified in maps of alloyed Nb5Si3. Good agreement was shown between the calculated hardness and chemical composition of Nb5Si3 and experimental results.

Depositional and metamorphic events recorded in voluminous metasedimentary rocks from northwestern Vietnam: Tectonic implications for eastern Paleo-Tethys evolution, Tibetan Plateau

Metasedimentary rocks in the Son La area of northwestern Vietnam provide unique geochronological and metamorphic evidence for constraining Paleo-Tethys evolution. In this study, detrital zircons from the metasedimentary rocks in the Nam Co Complex were dated and yield ages between 2787 and 618 Ma. Their maximum depositional ages are constrained to ca. 870 Ma and ca. 835 Ma for the lower and upper formations, respectively. Similarly, the ages of detrital zircons from metasedimentary rocks in the Ta Khoa antiform cluster from 3280 to 749 Ma. The depositional ages of the metasandstone and gneisses are constrained at ca. 800 Ma and ca. 760 Ma, respectively. The age patterns and Hf isotope compositions of the Nam Co Complex and the Ta Khoa antiform are similar to those of the western Yangtze Block, suggesting that the metasedimentary rocks in northwestern Vietnam represent the southeastern extent of the western Yangtze Block.Metamorphic zircon and monazite from metasedimentary rocks in northwestern Vietnam constrain Triassic tectonic events at 247–240 Ma. The P-T conditions of the metasedimentary rocks from the Ta Khoa antiform were defined at P = ca. 7.0–7.5 kbar and T = ca. 685 °C. Additionally, mineral chemical analyses indicate that phengites occur in Grt-Ph schists from the Nam Co Complex. The phengites have high Si contents (up to 3.542p.f.u.), indicating that the Grt-Ph schist experienced a high-pressure metamorphic event. Previous studies have also reported that eclogites and granulites in the Jinshajiang, Ailaoshan, and Song Ma zones record Triassic high-pressure metamorphism with a clockwise P-T-t path. These results suggest that the Jinshajiang-Ailaoshan-Song Ma suture zone (JASSZ) is a Paleo-Tethyan ocean-continent subduction-collision orogenic belt. The spatial distribution and tectonic evolution of the metasedimentary rocks in the Son La area support the hypothesis of west-dipping subduction of the Yangtze Block beneath the Indochina Block along the JASSZ.

Tracing Water–Rock–Gas Reactions in Shallow Productive Mud Chambers of Active Mud Volcanoes in the Caspian Sea Region (Azerbaijan)

We present geochemical and mineralogical datasets for five new mud volcanoes in continental Azerbaijan (Hamamdagh and Bendovan) and the adjacent Caspian Sea (Khara-Zire, Garasu and Sangi-Mughan). The fluid ejects have a Na–Cl-type composition and are generated by the mixing of evaporated Caspian seawater and low- to high-salinity pore waters, as indicated by Br–B and Cl–B systematics and Na–K and SiO2 geo-thermometers. The fluids contain high concentrations of As, Ba, Cu, Si, Li, Sr and Zn (60 to 26,300 ppm), which are caused by surface evaporation, pyrite oxidation, ion exchange reactions and hydrocarbon maturation in Oligocene-Miocene ‘Maykop’ shales. The solid ejects comprise liquid, oily and brecciated mud, mud/claystones and sandstones. The mud heterogeneity of the volcanoes is related to the geological age and different sedimentological strata of the host rocks that the mud volcanoes pass through during their ascent. All ejects show evidence of chemical alterations via water–rock–gas reactions, such as feldspar weathering, smectite illitization and the precipitation of Fe-(hydr)oxides, calcite, calcian dolomite, kaolinite and smectite. The studied localities have petrographic similarities to northern extending mud volcano systems located on Bahar and Zenbil islands, which suggests that mud volcanoes in the Caspian Sea region are sourced from giant shallow mud chambers (~1–4 km depth) located in Productive Series strata. Our results document the complex architecture of the South Caspian Basin—the most prolific hydrocarbon region in the world.

Toughening ultrastrong low-density steel by textured δ-ferrite lamellas

By both the Charpy V-notched impact and the projectile tests, we here investigated the dynamic fracture behavior of a recently developed ultrastrong lightweight steel comprising a hierarchical martensitic matrix, dispersed ultra-fine-retained austenite grains and oriented δ-ferrite lamellas, the latter being due to high Al and Si contents employed for low-density design. This steel shows a superior combination of specific ultimate tensile strength and impact toughness to other ultrastrong steels and has successfully arrested a real steel-cored bullet shot. These are attributed to the densely textured δ-ferrite lamellas that can deflect the propagating cracks until they are trapped and enclosed besides austenite-to-martensite transformation crack closure, leading to more energy consumed before failure. These results suggest a new pathway for toughening ultrastrong lightweight steels.

Surface preparation and double layer effect for silane application on electrogalvanized steel

Abstract Silanes are an alternative to replace pretreatments based on Cr(VI) for electrogalvanized steel (ES). As the interaction between the silane and the metal is important to ensure pretreatment efficiency, surface preparation is a critical step. In this sense, the presence of OH groups on the metal surface is essential. In this paper, the surface preparation of ES and a single/double layer application on the corrosion protection afforded by 3-aminopropyltriethoxy silane was studied. The metal surface was cleaned by polishing, electrochemically (employing anodic or cathodic current) or by chemical oxidation. The electrochemical behavior of the cleaned surfaces was analyzed by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Afterwards, the hydrolyzed silane was applied in a single or double layer. Coatings were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy, EIS and by exposure to the humidity chamber. Coatings applied on ES cleaned by electrochemical anodic processes or chemical oxidation provided the best protective performance due to a lower surface of zinc exposed to the high humidity environment. Double layer coatings improved protection due to more homogeneous and higher Si content, sealing defects and increasing the thickness of the one-layer protection, enhancing the barrier protection of the silane.

Determination of Corrosion Resistance of High-Silicon Ductile Iron Alloyed with Nb

In this study, the effects of Nb on the microstructural characteristics, hardness, and corrosion resistance of high-silicon ductile cast iron (HSDI)-3.6 wt.% Si were investigated. Samples from different castings with 0–0.9 wt.% Nb were obtained and compared to a commercial ductile iron. Microstructures showed that the amount of ferrite in the matrix increased with increasing Nb content, from 34% for unalloyed HSDI to 88% for HSDI-0.9 wt.% Nb. The presence of randomly distributed NbC carbides was identified by EDX for all the samples alloyed with Nb, and the hardness of the HSDI increased with the Nb content. To evaluate the influence of the Nb content on the corrosion resistance of HSDI, potentiodynamic tests were carried out in a solution of H2SO4. The highest corrosion rate on HSDI was obtained for the HSDI-0.3 wt.% Nb sample, with 2802 mills per year, due to the amount of pearlite present and the lowest presence of NbC carbides, compared to the HSDI-0.9 wt.% Nb, with 986 mills per year. This behavior was attributed to the ferrite matrix obtained because of a high Si content in the DI, which delayed the anodic dissolution of the alloy and suppressed the pearlitizing effect of Nb for contents greater than 0.3 wt.%, as well as to the effect of NbC carbides, which acted as inhibitors.

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.

Climate‐induced organic matter enrichment in lacustrine basin: Insights from the Palaeogene–Neogene oil shale in the Lunpola Basin (Tibet, China)

Lacustrine rift basins are ideal continental settings for understanding organic matter (OM) accumulation mechanisms, because lacustrine deposits are most sensitive to variable climatic and palaeoenvironmental conditions. The Lunpola Basin is a Cenozoic lacustrine rift basin with widespread oil shale depositions that provide a valuable example of triggering factors that controlled OM accumulation. In the investigated interval of the basin, high Si, Ti, Zr, Th, Al and rare earth element concentrations suggest high clastic fluxes during the oil shale deposition. These high clastic fluxes could be attributed to warm and humid climates due to high values of ln(Al2O3/Na2O) and C‐value (Ʃ (Fe + Mn + Cr + Ni + V + Co)/Ʃ (Ca + Mg + Sr + Ba + K + Na)). The Lunpola shales and oil shales were deposited in saltwater environments under enhanced dysoxic to anoxic conditions with high palaeoproductivity. In the Lunpola Basin, climate warming can be subdivided into two different stages based on C‐value and ln(Al2O3/Na2O) variations. Each stage is consistent with an increase in the primary productivity of the palaeolake. Thus, a model for climate‐induced OM enrichment in lacustrine rift basins is proposed, which indicates that climate and primary productivity are the key factors controlling OM accumulation.

Damping Behaviour of High Silicon Nodular Cast Iron

This work focused on producing and characterizing high silicon cast irons (microstructural analysis, tensile properties, damping capacity, elastic properties). Moreover, it also evaluated the influence of RE alloying on damping capacity. The samples present a step-casting geometry to verify the cooling rate’s impact on their microstructures and, consequently, on the mechanical properties. The high Si SGI presented a fully ferritic matrix (i.e. pearlite < 5%) with uniform dispersed graphite nodules; however, those also RE alloyed showed a lower nodularity. The results show an average increase, relative to the base SGI, of 33% for tensile strength and 55% for yield strength (section thicknesses between 45 and 25 mm). A damping capacity increase was observed, reaching a maximum increase of 32% with the addition of RE. The beneficial impact lies in the possibility of increasing the damping capacity of SGI, without compromising its tensile strength, by balancing the graphite degeneration (induced by RE alloying) and strengthening the ferritic matrix (promoted by the high Si content).

Mechanical Properties of Polymer-Infiltrated Fluorapatite Glass Ceramics Fabricated from Clam Shell and Soda Lime Silicate Glass

Can polymer-infiltrated florapatite glass ceramic produced from waste materials, such as clam shell and soda lime silicate glass, be used in prosthetic rehabilitation? The purpose of this study is to investigate the effect of Si/Ca ratio on the mechanical properties of Nb-Bi-Ce doped polymer-infiltrated fluorapatite ceramic networks (PICNs) produced from clam shell (CS) and soda lime silicate (SLS) glass by conventional melt-quench technique, used as a dental ceramic. PICNs comprising Si/Ca at four different weight percentage ratios: 1.27% (PICN-1), 2.15% (PICN-2), 4.12% (PICN-3) and 12.6% (PICN-4) were prepared (n=10). The powder mixtures in four different ratios were compressed in a rectangular prism shaped mold and subjected to equal pressure from all sides in a cold isostatic press, followed by heat treatment at 750C for 3 h. Then complete vacuum infiltration was done with a polymer mixture then low temperature firing was applied leading to the formation of the PICNs. Wear behavior and 3-point bending properties were evaluated and specimens were analyzed using scanning electron microscopy (SEM). The friction and wear properties were determined by means of a pin-on-disk tribotester. Since the flexural strength test did not show normal distribution, Kruskal Wallis test was performed in independent groups, p[0.05. There is a significant difference of flexural strength values between the groups (p=0.032), it was determined that the difference was between the PICN-1 and PICN-4 groups (p=0.037). In the analysis of wear scar, abrasion grooves were also observed. The results of this study showed that high Ca and Si content in CS and SLS glass, respectively, encourages the use of waste materials in the production of PICNs intended to be used in prosthetic rehabilitation. The composition of PICNs produced from waste materials affected flexural strength and wear behavior. Increasing the Si/Ca ratio was found to support the mechanical properties of experimental PICN and that experimental PICNs can be considered as high potential candidates for dental applications.

Modes of occurrence of lithium in black shale in the Nandan area, Guangxi, SW China: Implications for clay-type resources

Lithium is used in rechargeable batteries due to its high electrochemical potential, and the rapid development of electric vehicles is exerting increasing pressure on reserves. Currently, pegmatites and brine deposits are the two main Li sources, although volcanic clay-type and carbonate-hosted clay-type that formed mainly in continental or coastal basins are receiving increasing attention due to their large size and potential as future Li sources. However, mechanisms of clay Li enrichment are still debated. Marine black shale at the top of the upper Carboniferous-lower Permian Maping Formation in the Nandan area, northern Guangxi, SW China, is enriched in Li to levels of ∼1000 ppm. Knowledge of its genetic mechanism would contribute to understanding the geochemical behaviour and enrichment mechanisms of Li in surface environments. The different geological features of the shale, relative to the above clay types, suggest that the Nandan shale is a new type of Li-rich sedimentary rock. Its whole-rock Li contents are positively correlated with K2O and illite contents, indicating that illite (K0.7Al2[(Si,Al)4O10](OH)2) is the carrier of Li in the shale, as supported by high shale Al, Si, K, and Li contents in the in situ images. Mineralogical studies have revealed that the Li-rich illite is of detrital origin and was formed during continental weathering. The widespread occurrence of framboidal pyrite and high contents of TOC in the shale indicate that Li-rich shales formed under anoxic depositional conditions. Our findings may provide reference material for the study of the genesis of clay-type Li resources.

Deformation from Formation Until End of Life: Micro X-ray Computed Tomography of Silicon Alloy Containing 18650 Li-Ion Cells

The use of Si-containing negative electrodes is one of the most promising options to increase the energy density of Li-ion batteries. Nonetheless, increasing the Si content in the anode above 5–10 weight % is still a challenge because of the expansion/contraction behavior of the Si upon lithiation/de-lithiation. Due to a 2 to 3 fold volume increase of Si during charging, it is paramount to understand and manage structural changes from the formation until the end of life. This applies not only at electrode, but also at cell level and specifically for cells with high electrode loadings close to mass production format. To this aim, we report here on the structural changes in Si-blended anode/manganese nickel cobalt oxide (NMC) 622 cathode 18650 format cells from production through formation until end of life by means of micro X-ray computed tomography (CT). We constructed specially designed 18650 cells in which the jelly roll does not fill the full volume of the case. The volume change without external constraint led to the identification of three main deformation mechanisms at the jelly roll level and shed some light on the effect of the cell geometry on the use and performance of anodes with high Si-content.

Formation of Nitrogen-Rich Hot Springs in the Water–Granite and Water–Porphyrite Systems

The processes of evolutionary transformation of solutions in crystalline rocks of different composition under formation parameters of nitrogen-bearing hot springs have been studied using physicochemical modeling. It has been established that the fundamental factor in the formation of solutions that correspond to modern nitrogen hot springs in composition is the presence of elements that produce anions in the host rocks in appropriate concentrations. They create a characteristic geochemical environment that controls their concentrations and speciation in the solutions and the crystallization/dissolution timing and amounts of secondary minerals at each step of changing the value of the rock/water ratio. Both cations and anions clearly maintain the sequence of their presence in the solution in accordance to their concentration in the rock until the time when the crystallization of secondary minerals modifies the trends of component concentrations in the solution. The reasons for low and very low mineralization of nitrogen hot springs, low concentrations of Mg, Ca, and K and high contents of Na and Si are elucidated. Modern nitrogen terms cannot be formed in rocks containing elements that form anions in an amount corresponding to their average values. Based on the revealed high discreteness of the distribution of these elements in space and their extremely poor understanding, it is concluded that the successful study of hydrogeochemical processes is impossible without taking into account the geological heterogeneity, which is a key problem of hydrogeochemistry and is not taken into account when the processes of interaction in the water/rock system are studied.

Gold endowment and unloading along pathway for giant gold mineralization: Insights from spatiotemporal variations of in-situ pyrite geochemistry and gold fineness from the Jiaodong gold deposits, north China Craton

Over 5000 tonnes of gold were accumulated in the Jiaodong Peninsula at the early Cretaceous, the sources and critical ore-forming processes of which are still controversial. Here, we conducted comprehensive in-situ textural, elemental and isotopic analyses on pyrite and gold grains from the different mineralization styles, hydrothermal stages and depths for three representative gold deposits (Linglong, Xiadian and Jiangjiayao) from the northwestern Jiaodong Peninsula, with the aim to exactly constrain the sources and ore-forming processes. Three groups of δ34Spyrite were identified in the studied deposits, of which the Group 1 shows stable and low δ34S (4.8–7.6‰) throughout the hydrothermal evolution while the Group 2 has elevated δ34S (6.0–12.8‰) coupled with increasing As and Au concentrations. The Group 3 shows moderate δ34S (5.2–9.8‰) accompanied by high Al and Si concentrations. The Group 1 suggests a low-δ34S primary auriferous fluid derived from a mantle-related source, whereas the Group 2 indicates the primary auriferous fluid leaching additional S, As and Au from the Precambrian metasedimentary rocks along pathway. The Group 3 is petrographically coupled with numerous silicate inclusions, indicating enhanced fluid-rock interaction between the auriferous fluids and the granitic wallrcoks. Gold fineness decreases from the early to the late hydrothermal stages, combined with increasing deposition of polymetallic sulfides, suggesting an increase of pH resulting in efficient Au deposition. Gold fineness and Bi concentrations in pyrite decrease with shallowing, suggesting that cooling affected Au deposition as well. Bismuth-Te-S minerals were identified in the deep depths, combined with the well correlated Bi and Ag, implying that Bi-Te complexes might play a role in transporting Au and Ag at high-temperature conditions. The above results corroborate that multiple sources and ore-forming processes were responsible for the giant gold mineralization, of which the gold endowment from Precambrian wallrocks needs to be further concerned.

Origins of Electrical Compensation in Si‐Doped HVPE GaN

Herein, the results of positron lifetime and X‐ray absorption spectroscopy obtained in Si‐doped GaN crystals, grown by the hydride vapor phase epitaxy (HVPE), are reported. Pushing the Si doping to high concentrations leads to surprisingly strong compensation effects. Positron experiments show that the concentrations of Ga vacancies are not high enough to be efficient compensation centers. Other acceptor‐like impurities are present in concentrations orders of magnitude lower than the Si content in the samples. X‐ray absorption shows that the local environment of Si dopants in compensated samples is different from the fully activated case. Simulated spectra of X‐ray absorption near edge structure strongly suggest that in compensated spectra Si is likely to have more Si atoms in the nearest local environment. Hence, autocompensation of Si dopants appears as a likely compensation mechanism at high Si contents GaN samples grown by HVPE.

Core origin of seismic velocity anomalies at Earth's core-mantle boundary.

Seismic studies have found fine-scale anomalies at the core-mantle boundary (CMB), such as ultralow velocity zones (ULVZs)1,2 and the core rigidity zone3,4. ULVZs have been attributed to mantle-related processes5-10, but little is known about a possible core origin. The precipitation of light elements in the outer core has been proposed to explain the core rigidity zone3, but it remains unclear what processes can lead to such precipitation. Despite its importance for the outer core11, the melting behaviour of Fe-Si-H at relevant pressure-temperature conditions is not well understood. Here we report observations of the crystallization of B2 FeSi from Fe-9wt%Si melted in the presence of hydrogen up to 125 GPa and 3,700 K by using laser-heated diamond anvil cells. Hydrogen dramatically increases the Si concentration in the B2 crystals to a molar ratio ofSi:Fe ≈ 1, whereas it mostly remains in the coexisting Fe liquid. The high Si content in the B2 phase makes it stable in a solid form at the outermost core temperatures and less dense than the surrounding liquids. Consequently, the Si-rich crystallites could form, float and be sedimented to the underside of the CMB interface, and that well explains the core side rigidity anomalies3,4. If a small amount of the FeSi crystals can be incorporated into the mantle, they would form dense low-velocity structures above the CMB, which may account for some ULVZs10. The B2 FeSi precipitation promoted by H in the outermost core provides a single core-driven origin for two types of anomalies at the CMB. Such a scenario could also explain the core-like tungsten isotope signatures in ocean island basalts12, after the materials equilibrated with the precipitates are entrained to the uppermost mantle by the mantle plumes connected to ULVZs.

Silicon Nanoparticles Embedded in Chemical-Expanded Graphite through Electrostatic Attraction for High-Performance Lithium-Ion Batteries.

Silicon (Si) is a promising next-generation anode for high-energy-density lithium-ion batteries. The application of silicon/carbon (Si/C) composites with high Si content is hindered by the huge volume change and insecure electrochemical interface of the Si anode. Herein, chemical-expanded graphite (CEG) is used as a carbon matrix to form Si@CEG/C composites with an embedded structure. CEG with an abundant pore structure and electropositivity can well disperse and accommodate a mass of Si nanoparticles (Si NPs). With the flexibility and porosity of CEG, the embedded structure of Si NPs fixed in an expanded graphite layer can adopt the volume change of Si NPs and offer the abundant path of diffusion of lithium-ion, which leads to a moderate cycle and rate performance. Si@CEG/C exhibits a high reversible capacity of 1232.4 mA h g-1 at a current density of 0.5 A g-1 and with a capacity retention rate of 87% after 200 cycles. This embedded structure of Si/C composites built by CEG is meaningful for the structure design of the Si-based anode with higher specific capacity, active material utilization, and satisfactory cycle stability.

Towards a dependable TEM characterization of hot-dip galvanized steels with low and high Si content

Designing Advanced High-Strength Steels assumes fine-tuning of alloying elements to enhance performance properties. This affects the kinetics of Fe-Zn interaction during further galvannealing. A key role here belongs to the inhibition layer at the steel/coating interface. Applying mutually-reinforcing TEM techniques, we traced the evolution of Zn-Fe phases in low- and high-Si steels during galvannealing. It has been shown that conventional room temperature Ga FIB for TEM sample preparation is applicable only to annealed low-Si steel, a coating of which comprises equilibrium Zn-Fe compounds. The phases were validated via electron microscopy and diffraction methods. In contrast, even relatively long annealing of the high-Si steel was not sufficient to form stable Zn-Fe phases pointing to a hampering of the interphase reactions. As-galvanized and annealed high-Si specimens contain almost pure Zn and are affected by Ga via a eutectic reaction during FIB preparation. Thus, low-temperature FIB has been applied for reliable Zn-coated steel preparation. We refined with HRTEM the inhibition layer structures specific for low- and high-Si steel grades. While the typical Fe2Al5-xZnx interface layer has been found in the low-Si samples, for high-Si ones the formation of a quite stable Si-Mn mixed oxide membrane, which drastically hinders Fe-Al reaction, has been disclosed.

Carbon-Coated Si Nanoparticles Anchored on Three-Dimensional Carbon Nanotube Matrix for High-Energy Stable Lithium-Ion Batteries

An easy and scalable synthetic route was proposed for synthesis of a high-energy stable anode material composed of carbon-coated Si nanoparticles (NPs, 80 nm) confined in a three-dimensional (3D) network-structured conductive carbon nanotube (CNT) matrix (Si/CNT@C). The Si/CNT@C composite was fabricated via in situ polymerization of resorcinol formaldehyde (RF) resin in the co-existence of Si NPs and CNTs, followed by carbonization at 700 °C. The RF resin-derived carbon shell (~10 nm) was wrapped on the Si NPs and CNTs surface, welding the Si NPs to the sidewall of the interconnected CNTs matrix to avoid Si NP agglomeration. The unique 3D architecture provides a highway for Li+ ion diffusion and electron transportation to allow the fast lithiation/delithiation of the Si NPs; buffers the volume fluctuation of Si NPs; and stabilizes solid–electrolyte interphase film. As expected, the obtained Si/CNT@C hybrid exhibited excellent lithium storage performances. An initial discharge capacity of 1925 mAh g−1 was achieved at 0.1 A g−1 and retained as 1106 mAh g−1 after 200 cycles at 0.1 A g−1. The reversible capacity was retained at 827 mAh g−1 when the current density was increased to 1 A g−1. The Si/CNT@C possessed a high Si content of 62.8 wt%, facilitating its commercial application. Accordingly, this work provides a promising exploration of Si-based anode materials for high-energy stable lithium-ion batteries.