Amorphous SiO2 Research Articles

Magnetron Sputter Deposition of Amorphous Silicon–SiO2 Quantized Nanolaminates

Quantization effects in nanolaminate structures of oxide materials are proposed and experimentally demonstrated only recently. Herein, the material combination of amorphous silicon and SiO2 deposited by magnetron sputtering is investigated and it is shown that the quantization effect can be observed indeed. Transmission electron microscopy characterization gives evidence of continuous layers of amorphous silicon and SiO2 with well‐defined interfaces. The deposition process is described and the tunability of the refractive index and the bandgap energy is demonstrated. By doing so, the advantages of this novel material over classical optical materials are shown and feasibility is proved. As an example, a longpass optical interference filter with edge at 720 nm is deposited using quantized nanolaminates as the high and SiO2 as the low refractive index material. This filter can be deposited successfully with close match to the design. It shows a blocking range throughout the visible spectrum whereas a comparable filter based on SiO2–TiO2 only blocks 500–700 nm.

Crystalline‐amorphous dual‐phase ceramic nanocomposites regulated by entropy engineering

AbstractSolid‐state reaction (SSR) is frequently used to fabricate bulk high‐entropy ceramics (HECs). However, a high temperature and a long dwelling time are typically required to allow the occurrence of SSR. Meanwhile, conventional HECs were typically composed of single‐phase solid solution with micrograins. It is of great interest to develop nanocrystalline dual‐phase HECs under mild conditions. Here, we fabricated entropy‐mediated crystalline‐amorphous dual‐phase ceramic nanocomposites, and the fabrication process showed significantly higher energy and time efficiency than the conventional SSR. The nanocomposites were composed of entropy‐mediated nanoparticles (EM‐NPs) embedded in an amorphous SiO2 matrix. The constituent elements were homogeneously distributed in the EM‐NPs at the atomic level. The EM‐NPs were dislocations‐free but with lattice strain, and they showed a strong coarsening tendency during annealing. The nanocomposites showed a significant solid solution hardening effect. The reported results would provide useful guidance to fabricate nanocrystalline HECs with crystalline‐amorphous dual‐phase microstructure.

The antioxidative protection mechanism of the ultra-high temperature radome composite material BNf/SiBN

In the study, a BNf/SiBN composite was fabricated through precursor infiltration and pyrolysis (PIP) method. The oxidation resistance of the composite was investigated at different oxidation temperatures, focusing on the micro-structure evolution, the phase composition and oxidation kinetics of bare fibers versus fibers protected by the matrix under various oxidation states. The result indicates that the BNf/SiBN composite remains stable at 1100 °C in air atmosphere, while the fibers protected by matrix maintain their complete structure even at 1500 °C. Furthermore, we elucidated the oxidation mechanism of SiBN matrix: SiBN matrix undergoes a prior oxidation stage and transforms into amorphous SiO2 and B2O3 at high temperatures to impede the oxygen attachment to fibers while preserving the integrity of internal structure. The emergence of ultra-high temperature resistant BNf/SiBN composite and along with the exploration of oxidation behavior has opened up new approach for advancing radome material development.

Stöber method to amorphous metal-organic frameworks and coordination polymers

The Stöber method is a widely-used sol-gel route for synthesizing amorphous SiO2 colloids and conformal coatings. However, the material systems compatible with this method are still limited. Herein, we have extended the approach to metal-organic frameworks (MOFs) and coordination polymers (CPs) by mimicking the Stöber method. We introduce a general synthesis route to amorphous MOFs or CPs by making use of a base-vapor diffusion method, which allows to precisely control the growth kinetics. Twenty-four different amorphous CPs colloids were successfully synthesized by selecting 12 metal ions and 17 organic ligands. Moreover, by introducing functional nanoparticles (NPs), a conformal amorphous MOFs coating with controllable thickness can be grown on NPs to form core-shell colloids. The versatility of this amorphous coating technology was demonstrated by synthesizing over 100 core-shell composites from 20 amorphous CPs shells and over 30 different NPs. Besides, various multifunctional nanostructures, such as conformal yolk-amorphous MOF shell, core@metal oxides, and core@carbon, can be obtained through one-step transformation of the core@amorphous MOFs. This work significantly enriches the Stöber method and introduces a platform, enabling the systematic design of colloids exhibiting different level of functionality and complexity.

Investigation of scale formation and degeneration of silicide coating on Nb–Si based alloy in the temperature range from 1250 °C to 1560 °C

Nb silicide coatings modified with active elements have good oxidation resistance, but there is a lack of systematic research on their oxidation behavior at high temperatures above 1250 °C. The aim of this work is to investigate the oxidation behavior of an Al–Y modified silicide coating on Nb–Si based alloy in the temperature range from 1250 °C to 1560 °C. After oxidation at 1250 °C, the scale displays a typical layered structure consisting mainly of a TiO2 outer layer, an amorphous SiO2 matrix layer embedded with TiO2 and ZrSiO4, and an inner layer consisting of SiO2 and Cr2O3. Above 1350 °C, the evaporation reaction of Cr2O3 into CrO3 (g) is significantly accelerated and Cr2O3 disappeared gradually with temperature or time. The TiO2 layers covering on the scales formed at 1250–1500 °C grow along the crystallographic orientation of [100]. The micropores formed on the surface of TiO2 should be attributed to the further oxidation of Cr2O3 into volatile oxide CrO3 (g). The scales exhibit a similar structure consisting mainly of a SiO2 glass matrix embedded with ZrSiO4 and a surface TiO2 layer until 1500 °C. Above the eutectic temperature of SiO2–TiO2 system, the scale is mainly composed of a matrix layer of SiO2–TiO2 eutectic embedded with block TiO2 particles, and a thin SiO2 interface layer at 1560 °C. The degeneration path of the (Nb,X)Si2 coating is (Nb,X)Si2 → (Ti,Nb)5Si4 → γ-(Nb,X)5Si3.

Decomposition and migration behavior of Pt salt on Al2O3 and SiO2 upon calcination studied by XAFS and UV–visible spectroscopy using a laboratory-type spectrometer

Thermal decomposition behavior of two kinds of Pt salts, namely, H2PtCl6 and Pt(NH3)4Cl2, on amorphous SiO2 and γ-Al2O3 under air to prepare supported platinum catalysts up to 773 K was investigated by in-situ laboratory X-ray absorption fine structure (XANES/EXAFS) and UV–Vis spectroscopy. Changing the oxidation state of platinum species and the coordination environment, the migration to vacant sites or aggregation process on the surface were discussed. The supported H2PtCl6 was reduced to Pt2+ species under air flow around 573 K by eliminating Cl/O ligand atoms until 573 K. High-temperature treatment caused the re-oxidation of the supported Pt species on Al2O3, but it did not affect the oxidation state of SiO2-supported species. The formed platinum oxychloride on Al2O3 was stable under air, but it partly decomposed to atomic-like species above 673 K, followed by migration on the surface, trapping at the cation vacant site because of its defect spinel structure. The lattice oxygen atoms of Al2O3 adjacent to Pt atom captured might cause the re-oxidation, and molecular oxygen was not the oxidant. The partly formed atomic-like species migrates on the SiO2 surface, followed by aggregation to form metallic Pt particles above 573 K.

Stabilizing Cu0/Cu2+ interface by hydroxy-rich amorphous SiO2 for enhanced electrocatalytic CO2 reduction to ethylene

Constructing a stable Cu0/Cu2+ interface is critical for enhancing the C-C coupling during the process of CO2 electroreduction. However, the high-valence Cu species are unstable under the operating conditions. Herein, polyhedral-shaped CuO is coated with hydroxy-rich SiO2 nanoparticles (m-SiO2/CuO) to stabilize the Cu2+ species, enabling efficient CO2 reduction to the ethylene product. Significantly, the optimal m-SiO2/CuO catalyst exhibits an impressive Faradaic efficiency of 55.5 % and an industrial-level partial current density of 500 mA cm−2 toward ethylene. Fourier transform infrared spectra and X-ray photoelectron spectra reveal that the strong interfacial interaction between CuO and hydroxy-rich SiO2 is conducive to stabilizing the Cu2+ species. In-situ characterizations reveal that the Cu0/Cu2+ interface facilitates CO2 activation and the key intermediate *OCCHO, thus promoting the production of ethylene. This work paves the way for developing advanced electro-catalysts of producing ethylene.

Preparation and Characterization of Graphite-SiO2 Composites for Thermal Storage Cement-Based Materials.

Thermal storage cement-based materials, formed by integrating phase change materials into cementitious materials, exhibit significant potential as energy storage materials. However, poor thermal conductivity severely limits the development and application of these materials. In this study, an amorphous SiO2 shell is encapsulated on a graphite surface to create a novel thermally modified admixture (C@SiO2). This material exhibits excellent thermal conductivity, and the surface-encapsulated amorphous SiO2 enhances its bond with cement. Further, C@SiO2 was added to the thermal storage cement-based materials at different volume ratios. The effects of C@SiO2 were evaluated by measuring the fluidity, thermal conductivity, phase change properties, temperature change, and compressive strength of various thermal storage cement-based materials. The results indicate that the newly designed thermal storage cement-based material with 10 vol% C@SiO2 increases the thermal conductivity coefficient by 63.6% and the latent heat of phase transition by 11.2% compared to common thermal storage cement-based materials. Moreover, C@SiO2 does not significantly impact the fluidity and compressive strength of the thermal storage cement-based material. This study suggests that C@SiO2 is a promising additive for enhancing thermal conductivity in thermal storage cement-based materials. The newly designed thermal storage cement-based material with 10 vol% C@SiO2 is a promising candidate for energy storage applications.

Light Promotion and Different Reaction Pathways Enhance Photothermocatalytic Syngas Production for Cellulose Steam Reforming Over Ni/θ‐Al2O3

AbstractThe photothermocatalytic cellulose steam reforming strategy has provided a sustainable approach, directly converting the largest renewable carbon resource (biomass), into syngas (H2 and CO) which are clean and high‐value‐added energy carriers. However, this strategy for achieving high catalytic efficiency inevitably produces char, resulting in rapid deactivation and difficult recovery of catalysts, impeding industrial application. Herein, the Ni NPs (nanoparticles) loaded on θ‐phase Al2O3 (Ni/θ‐Al2O3) catalyst enable efficient conversion of char generated during photothermocatalytic cellulose steam reforming process, thereby exhibiting high production rates of syngas (H2 3776.3 and CO 2028.1 mmol h−1) and excellent durability (no deactivation after 4 cycles). Compared with a reference catalyst of Ni NPs loaded on amorphous SiO2 (Ni/am‐SiO2), this study finds that the elementary step of char conversion with H2O to syngas can be enhanced on Ni/θ‐Al2O3. With an emphasis on the mechanism, a different pathway is discovered that surface hydroxyl groups participating in the formation of HCO* intermediates, further dissociating to syngas, significantly facilitate the conversion of char. Additionally, on Ni/θ‐Al2O3, the photoactivation effect enhances catalytic activity, particularly promoting the conversion of H2O with char to syngas, thus preventing deactivation caused by encapsulation of char.

Conversion of Phosphogypsum into Porous Calcium Silicate Hydrate for the Removal and Recycling of Pb(II) and Cd(II) from Wastewater.

The discharge of lead and cadmium wastewater, along with the pollution caused by phosphogypsum, represents a particularly urgent environmental issue. This study employed a straightforward hydrothermal method to convert phosphogypsum into porous calcium silicate hydrate (P-CSH), which was then used to remove and recover Pb(II) and Cd(II) from wastewater. The adsorption capacities of P-CSH for Pb(II) and Cd(II) were notably high at 989.3 mg/g and 290.3 mg/g, respectively. The adsorption processes adhered to the pseudo-second-order kinetics model and the Langmuir isotherm model. Due to identical adsorption sites on P-CSH for both Pb(II) and Cd(II), competitive interaction occurred when both ions were present simultaneously. Additionally, the adsorption efficacy was minimally impacted by the presence of common coexisting cations in wastewater. The dominant mechanisms for removing Pb(II) and Cd(II) via P-CSH were chemical precipitation and surface complexation. Moreover, the adsorbed heavy metals were efficiently separated and reclaimed from the wastewater through a stepwise desorption process. The primary components of the residue from stepwise desorption were quartz and amorphous SiO2. Following dissolution via pressurized alkaline leaching, this residue could be recycled for synthesizing P-CSH. This research offered a new strategy for the resourceful use of phosphogypsum and heavy metal wastewater.

Effects of amorphous phase and yttrium on flash sintering and microstructures of ZrO2–SiO2 ceramic nanocomposites

AbstractFlash sintering has been used to consolidate a wide range of ceramics and ceramic composites. However, flash sintering of ceramic nanocomposite with a substantial amorphous phase is rarely studied. Meanwhile, the effects of yttrium addition on the flash sintering behaviors and microstructures of ZrO2‐based ceramic nanocomposite remain unknown. Herein, ZrO2‐SiO2 crystalline‐amorphous ceramic nanocomposites (CACNs) with different contents of amorphous phase and two types of yttrium dopants were sintered by flash sintering. Results showed that the content of amorphous phase (SiO2) had significant effects on the flash sintering behavior. The CACN with 65 mol% SiO2 was nonflash sinterable due to the high electric resistivity of SiO2, whereas, the CACN with 45 mol% SiO2 can be flash sintered to high densification within 35 seconds. The flash‐sintered CACNs consisted of ZrO2 nanocrystallites distributed in an amorphous SiO2 matrix. Flash sintering enhanced the tetragonal‐to‐monoclinic phase transformation of ZrO2. In addition, influences of yttrium dopant on CACNs were also investigated. Yttrium dopants can rapidly dissolve in ZrO2 lattices and show a tetragonal phase stabilization effect during flash sintering. Firework‐like ZrO2 microcrystallites formed by dendritic growth were observed close to the cathode region, which was attributed to athermal electric field effects and the formation and aggregation of oxygen vacancies at the cathode region. The results would provide guidance for fabricating CACNs via flash sintering.

Construction of sub micro-nano-structured silicon based anode for lithium-ion batteries

The significant volume change experienced by silicon (Si) anodes during lithiation/delithiation cycles often triggers mechanical-electrochemical failures, undermining their utility in high-energy-density lithium-ion batteries (LIBs). Herein, we propose a sub micro-nano-structured Si based material to address the persistent challenge of mechanic-electrochemical coupling issue during cycling. The mesoporous Si-based composite submicrospheres (M-Si/SiO2/CS) with a high Si/SiO2 content of 84.6 wt.% is prepared by magnesiothermic reduction of mesoporous SiO2 submicrospheres followed by carbon coating process. M-Si/SiO2/CS anode can maintain a high specific capacity of 740 mAh g−1 at 0.5 A g−1 after 100 cycles with a lower electrode thickness swelling rate of 63%, and exhibits a good long-term cycling stability of 570 mAh g−1 at 1 A g−1 after 250 cycles. This remarkable Li-storage performance can be attributed to the synergistic effects of the hierarchical structure and SiO2 frameworks. The spherical structure mitigates stress/strain caused by the lithiation/delithiation, while the internal mesopores provide buffer space for Si expansion and obviously shorten the diffusion path for electrolyte/ions. Additionally, the amorphous SiO2 matrix not only servers as support for structure stability, but also facilitates the rapid formation of a stable solid electrolyte interphase layer. This unique architecture offers a potential model for designing high-performance Si-based anode for LIBs.

Effect of changes in organo-silicon electrolyte concentration and composition on SiO2 ceramic coating prepared by plasma electrolytic oxidation on 6061 aluminum alloy

An amorphous SiO2 ceramic coating with a thickness of ∼72 μm is prepared within 13 min in organo-silicon electrolyte, which is stable in strong acid solutions, reducing corrosion current density of 6061 aluminum alloy by 3 orders of magnitude. With the aim to reveal influence of the electrolyte concentration, NaOH content and additive (NaPO3)6 on microstructure and corrosion resistance of the coatings, SEM/EDS, XRD, electrochemical tests were used to characterize their thickness, surface and cross-sectional morphology and structure, and corrosion performance prepared by using different electrolytes under the same electric control parameters. The results show that they significantly affect the surface morphology, structure and corrosion resistance of the coatings. Dilution of the electrolyte results in a significant decrease in coating thickness and surface porosity, reduction of NaOH content leads to coating thinning, increased porosity but reduced pore size. Coatings with lower porosity or smaller pore sizes are more effective in resisting corrosive media penetration for long term immersion. Whereas, the additive (NaPO3)6 promotes coating thickening, widening of the transition layer, which helpfully improves the corrosion resistance of the coating.

Ablation behavior of Csf/SiC‐BN composites with polyborosilazane as sintering aids: High‐temperature damage mechanism

AbstractMicrostructural evolution and high‐temperature ablative damage mechanism of Csf/SiC‐BN composites with and without polyborosilazane (PBSZ) as sintering aids that can convert to polymer‐derived SiBCN ceramics (PDCs‐SiBCN) by cross‐linking and pyrolysis during sintering were studied. The density of Csf/SiC‐BN composites increases from 2.17 to 2.25 g/cm3 with 10 wt.% sintering aids because PBSZ promotes rearrangement and redistribution of raw materials by pyrolysis during the sintering process. With the increase of carbon fiber content, ablation performance (mass ablation rate: 15.25 mg/s; linear ablation rate: 0.100 mm/s) negligibly decreases, compared to counterparts with lower fiber content (mass ablation rate: 16.53 mg/s; linear ablation rate: 0.072 mm/s) because the presence of PDCs‐SiBCN partially compensates for the detrimental effect of carbon fibers on ablation performance. Csf/SiC‐BN composites with and without PBSZ show similar phase composition mainly containing quartz, amorphous SiO2, and matrix crystallization products and morphology after ablation because of similar phase composition before ablation. The ablation mechanism is oxidative corrosion and mechanical scouring and stripping.

Optical properties of nanocomposites based on polypropylene modified by nanoparticles of oxide compounds

The optical properties in UV, visible and near IR spectral regions for nanocomposites based on polypropylene modified by nanoparticles of oxide compounds ZrO2, Al2O3, SiO2, MgO, TiO2, ZnO were studied. A shift of the main optical absorption edge to the short-wave region upon modification by dielectric nanoparticles (MgO, ZrO2, and Al2O3) was established. The absorption edge shifts to the long-wave region upon the introduction of semiconductor nanoparticles (ZnO, TiO2) and amorphous SiO2 particles. In all spectra, the absorption bands at 1200, 1400, and 1720 nm characterized by overtone vibrations of CH, CH2, and CH3 molecular groups were recorded. OH groups make a certain contribution to the bands at 1400 and 1720 nm. The dependence of the intensity of these absorption bands on the type and concentration of nanoparticles used in the modification of polypropylene was analyzed. X-ray diffraction analysis of the studied nanocomposites was carried out, the formation of β-PP was registered upon modification by Al2O3 nanoparticles. Photoluminescence spectra of nanocomposites were studied. It was found that the introduction of nanoparticles (except SiO2) does not lead to the formation of new luminescence bands in PP.

Speciation of toxic metals in metal finishing filter cake by X-ray absorption spectroscopy

The speciation of Cr, Zn, Cu and Pb in two metal finishing filter cakes (TX and ST) was investigated by X-ray absorption spectroscopy (XAS) complemented by X-ray fluorescence (XRF) and X-ray diffraction (XRD). XRF showed that concentrations of Cr, Zn, Cu and Pb were 1.4%, 0.19%, 0.20% and 0.01%, respectively, in TX, and 12.6%, 3.3%, 1.3% and 0.21% in ST. No crystalline phases were detected in TX by XRD whereas ST was dominated by calcite. Cr and Fe K edge XAS showed Cr to be trivalent and octahedrally coordinated, co-precipitated with Fe as CrxFe1-x-(oxy)hydroxides in both filter cakes. Zn, P and Ca K edge XAS showed that 2ZnCO3∙3Zn(OH)2 and Zn3(PO4)2 were the dominant zinc-containing phases, with combined tetrahedral and octahedral coordination; Zn phases were slightly more crystalline in TX than ST. Pb L3 edge X-ray absorption near edge spectroscopy (XANES) found that Pb was likely adsorbed on amorphous SiO2. Cu, Si and S K edge XAS showed that all Cu was divalent, and the dominant copper phases were found to be Cu2Cl(OH)3, Cu(OH)2 and CuSO4·5H2O for ST, whereas Cu appeared to adsorb to amorphous SiO2 for TX, which contained much less Pb. Cr is thus immobilized in the filter cakes in a phase with low solubility at environmentally feasible pH values, whereas Zn, Cu and Pb could be released when the pH decreases below 8 or above 11. These findings are significant for the development of waste management regulations and/or metal recovery methods (e.g., hydro/pyrometallurgy).

Improved Thermal Stability and Oxygen‐Barrier Performance of SiO2 Thin Films by Modifying Amorphous Network Structure

Due to low‐refractive‐index and grain‐boundary‐free features, amorphous SiO2 thin films possess inherent advantages in serving as antireflective and protective layers against atmosphere. However, under high‐temperature and/or oxidation harsh environment, the thermodynamic instability of SiO bonds and “depolymerization” process among tetrahedral units [SiO4] would result in their insufficient thermal stability and oxygen‐barrier failure. By taking amorphous network former, small element electronegativity, and high oxide dissociation energy into considerations, low‐level Zr dopant is introduced to induce short‐ and medium‐range structural modification in amorphous SiO2 thin films, aiming to shorten SiO bond length and enhance network connectivity, respectively. As expected, the fabricated SiZrO thin films exhibit superior thermal stability and oxygen‐barrier performance without sacrificing their low‐index attribute. The Zr doping significantly elevates the oxygen‐inward‐diffusion activation energy from 0.94 to 1.95 eV in SiO2 network. Further, utilizing as protective layer for W‐SiO2 cermet, the SiZrO can effectively prevent the oxidation of W nanoparticles caused by oxygen inward diffusion. Undoubtedly, the exploration of amorphous SiZrO thin films offers exciting prospects for the application of functional coatings and devices under extreme conditions.

Preparation of TiO2 composite photocatalyst using amorphous SiO2 microspheres loaded with spent SCR catalysts

The products of S-SCR grinding and alkali treatment (S-SCR-T, primarily consisting of anatase TiO2 with a size less than 20 nm) were utilized as photocatalysts, while SiO2 microspheres (MS-SiO2) were used as carriers. A TiO2 composite photocatalyst (M-Si/SR-Ti) was prepared by wet mechanical grinding. The results demonstrate that in M-Si/SR-Ti, S-SCR-T was uniformly loaded on the MS-SiO2 surface in a well-dispersed state and firmly bonded at the interface with Si–O–Ti bonds. M-Si/SR-Ti prepared under optimized conditions exhibited excellent photocatalytic degradation and recycling properties for methyl orange. The degradation rate of methyl orange solution at 10 ppm for 60 min under UV irradiation was 97%, which was comparable to that of S-SCR-T, and remained unchanged after four cycles of recycling. Compared with S-SCR-T, M-Si/SR-Ti exhibited significantly improved settlement recovery performance in water. The loading of S-SCR-T on the MS-SiO2 surface, which increased the exposure of the nano-TiO2 active site and decreased the energy gap, was the mechanism responsible for improving the photocatalytic performance of M-Si/SR-Ti. This study positively impacted the effort to efficiently utilize and increase the value of S-SCR and reduce the cost of the photocatalyst.

The effect of degree of sintering on the structural and mechanical properties of Si3N4–SiO2 glass ceramics

Silica-based glass ceramics have been extensively used in biomedical applications due to their superior biocompatibility and controllable properties. However, their low mechanical strength limits their application. This could be addressed by optimizing the crystalline phase which determines their final properties. Silicon nitride has attracted attention due to its combination of good mechanical and biological properties. Therefore, to combine the advantage of silica-based glass and silicon nitride ceramic, this study developed a silicon nitride-silicon dioxide (Si3N4–SiO2) glass ceramics. The effects of spark plasma sintering parameters on the structural and mechanical properties of Si3N4–SiO2 glass ceramics were investigated. Full densification was reached at a sintering temperature of 1300 °C, a holding time of 10 min and an applied pressure of 80 MPa (relative density = 99.19 %). No silicon oxynitride (Si2N2O) crystalline phase was formed in the sintered glass ceramics, as confirmed by XRD. The interface between the β-Si3N4 crystalline and amorphous SiO2 was investigated by HRTEM, and the results indicated that an amorphous interfacial oxide was formed at the interface. The mechanical properties increased with increasing sintering temperature, as a result of the increased density. The Si3N4–SiO2 glass ceramics sintered at 1500 °C exhibited the highest value of toughness and flexural strength, at 4.6 ± 0.28 MPa m1/2 and 360 ± 27 MPa. The indentation cracks observed by SEM showed that the large β-Si3N4 grains promoted crack deflection, while the equiaxed Si3N4 grains with a lower aspect ratio led to transgranular fracture. The mechanical properties of these Si3N4–SiO2 glass ceramics are comparable to commercial glass ceramics, indicating their promising aspects in biomedical applications.

High-temperature oxidation mechanism and microstructure evolution of Cr-Mn-Si alloyed steel oxidized by Fe2O3 contained in mold flux

The high-temperature oxidation behavior of Cr-Mn-Si alloyed steel by Fe2O3 contained mold flux in high temperatures, and its effect on microstructure evolution were investigated in detail by TEM, EBSD, CLSM, SEM, and XPS. A novel oxidation mechanism was firstly revealed that the Fe2O3 in mold flux melts during high temperatures plays a role of oxidizing alloyed steels by the released free oxygen ions (O2−) from the transformation of Fe2O3 (Fe3+) to FeO (Fe2+). The formed oxidized dots within the oxide layer changed from SiO2 and MnSiO3 to MnCr2O4 spinel phases by increasing the content of Fe2O3 in the mold flux. Notably, the amorphous SiO2 was discovered in the core region of MnSiO3 phase due to its selective oxidative behavior in high temperatures. This research provides conclusive evidence that the small size MnSiO3 oxides can be acted as a nucleation core for the refinement of austenite grains through in-situ observation.