Oxidation Of Si Research Articles

Formation mechanism of AlN-SiC solid solution with multiple morphologies in Al-Si-SiC composites under flowing nitrogen at 1300 °C

The non-oxide-reinforced phase AlN-SiC solid solution with high performance was successfully synthesized in the resin-bonded Al-Si-SiC composites under flowing nitrogen at 1300 °C. The AlN-SiC solid solution was synthesized by three paths of liquid-solid, gas-solid and gas-gas reactions through modulation of Al/Si ratio, and controllable microstructure of AlN-SiC solid solution was attained. The phase composition and microstructure of the sintered samples were characterized by XRD and SEM, combined with thermodynamics, the formation mechanism of AlN-SiC solid solution was investigated and the reaction model was established. Al was not detected while Si was detested by XRD. Granular, short columnar and whisker-like AlN-SiC solid solution were generated and their positions varied. As the temperature increases, the partial pressure of oxygen decreases due to the oxidation of Al, Si and SiC on the surface of the sample, inside the sample, the active oxidation takes place, generating Al2O(g), SiO(g) and CO(g). Due to the low oxygen partial pressure, Al is preferentially nitrided to form a thin AlN layer on its surface. The AlN layer is broken as the temperature increases, then liquid Al with carbon from resin begins to flow, leaving the residual shell of AlN in situ. When it flows to the surface of Si, Al-Sialloy is formed locally inside the Si particles under the wetting effect of C, then hexagonal AlN-SiC solid solution is formed inside the Si shell. Part of SiO(g) + CO(g) diffuses into the interior of the AlN residual shell and reacts by aggregation to form a granular AlN-SiC solid solution in the shell wall; others diffuses into the pores of the sample for vapor deposition, and finally forms stacked hexagonal flaky whiskers. The in-situ generated of AlN-SiC solid solution with multiple morphologies in the composite plays a joint toughening effect, which can significantly enhance the comprehensive performance of the composite. In this experiment, the synthesis of AlN-SiC solid solution without sintering aids under normal pressure at a low temperature. It is expected to be applied to the blast furnace and to realize the longevity of blast furnace.

5,291‐ppi OLED display enabled by monolithic integration of C‐axis‐aligned crystalline IGZO FET and Si CMOS

AbstractFor the first time in the world, we have fabricated an organic light‐emitting diode (OLED) display that monolithically integrates Si CMOS and oxide semiconductor FETs (OSFETs). OSFETs can be monolithically stacked on Si CMOS. With this OS/Si monolithic stack technology, we have fabricated driver circuits with Si CMOS and pixel circuits with OSFETs. This enables displays to have thin bezels. In addition, fabricating pixel circuits with OSFETs, which have higher breakdown voltage than Si CMOS, allows the use of tandem OLED devices that require high driving voltage. This enables an OLED display with a pixel density over 5,000 ppi.

Study on Surface Modification of Fe–Si–Cr Alloy by Selective Oxidation Heat Treatment and its Corrosion Properties

Corrosion properties of the insulating oxide layer formed on the Fe–Si–Cr alloy through the selective oxidation heat treatment are evaluated to find out that the oxide layer can play a role as a barrier layer against corrosion. Preferential oxidation of Si and Cr during the selective oxidation heat treatment results in a two‐layered oxide layer. From the X‐ray photoelectron spectroscopy and transmission electron microscope results, it is revealed that the inner layer is SiO2 and the outer layer is Cr2O3, and they keep growing with the heat treatment time. The oxide layer formed by the selective oxidation heat treatment causes the ennoblement of the corrosion potential, but additional ennoblement does not occur with the growth of the oxide layer. However, the thickness of the oxide layer influences anti‐corrosion performance in terms of corrosion resistance and deterioration. The thicker the oxide layer is, the higher the corrosion resistance and the slower the deterioration become so that the protection property withstands for 3 h in the 3.5 wt% NaCl solution when the oxide layer has 44.3 nm thickness.

Structural Characterization of Titanium-Silica Oxide Using Synchrotron Radiation X-ray Absorption Spectroscopy.

In this study, titania–silica oxides (TixSiy oxides) were successfully prepared via the sol–gel technique. The Ti and Si precursors were titanium (IV), isopropoxide (TTIP), and tetraethylorthosilicate (TEOS), respectively. In this work, the effects of pH and the Ti/Si atomic ratio of titanium–silicon binary oxide (TixSiy) on the structural characteristics of TixSiy oxide are reported. 29Si solid-state NMR and FTIR were used to validate the chemical structure of TixSiy oxide. The structural characteristics of TixSiy oxide were investigated using X-ray diffraction, XRF, Fe-SEM, diffraction particle size analysis, and nitrogen adsorption measurements. By applying X-ray absorption spectroscopy (XAS) obtained from synchrotron light sources, the qualitative characterization of the Ti–O–Si and Ti–O–Ti bonds in Ti–Si oxides was proposed. Some Si atoms in the SiO2 network were replaced by Ti atoms, suggesting that Si–O–Ti bonds were formed as a result of the synthesis accomplished using the sol–gel technique described in this article. Upon increasing the pH to alkaline conditions (pH 9.0 and 10.0), the nanoparticles acquired a more spherical shape, and their size distribution became more uniform, resulting in an acceptable nanostructure. TixSiy oxide nanoparticles were largely spherical in shape, and agglomeration was minimized. However, the Ti50Si50 oxide particles at pH 10.0 become nano-sized and agglomerated. The presence of a significant pre-edge feature in the spectra of Ti50Si50 oxide samples implied that a higher fraction of Ti atoms occupied tetrahedral symmetry locations, as predicted in samples where Ti directly substituted Si. The proportion of Ti atoms in a tetrahedral environment agreed with the value of 1.83 given for the Ti–O bond distance in TixSiy oxides produced at pH 9.0 using extended X-ray absorption fine structure (EXAFS) analysis. Photocatalysis was improved by adding 3% wt TiO2, SiO2, and TixSiy oxide to the PLA film matrix. TiO2 was more effective than Ti50Si50 pH 9.0, Ti50Si50 pH 10.0, Ti50Si50 pH 8.0, and SiO2 in degrading methylene blue (MB). The most effective method to degrade MB was TiO2 > Ti70Si30 > Ti50Si50 > Ti40Si60 > SiO2. Under these conditions, PLA/Ti70Si30 improved the effectiveness of the photocatalytic activity of PLA.

Unveiling the mechanism of yttrium significantly improving high-temperature oxidation resistance of super-austenitic stainless steel S32654

Aiming at serious catastrophic oxidation problem of super-austenitic stainless steel S32654, the influence of different rare earth elements on its oxidation behavior was comparatively investigated at 1200 °C. The mechanism of Y significantly improving high-temperature oxidation resistance of S32654 was unveiled. The results demonstrated that Y played much better beneficial roles than Ce and La in the initial formation of oxide layer: (1) Y promoted Cr segregation to steel surface to combine with O; (2) its preferential oxidation provided nucleation cores for Cr2O3. Both roles jointly promoted the selective oxidation of Cr and then the formation of protective Cr-rich oxide layer. This provided good prerequisites for inhibiting the formation and volatilization of MoO3. Additionally, Y cation segregation to oxide grain boundaries further promoted the selective oxidation of Cr and Si to form more protective oxide layer. These beneficial roles of Y essentially eliminated the synergistic effects of MoO3 volatilization and lamellar Cr2N precipitation on catastrophic oxidation. Accordingly, the oxidation resistance of Y-bearing S32654 was improved by 22%–45%.

Preparation and enhanced oxidation behavior of microalloyed Mo5SiB2 alloy at 1300 °C

Microalloyed Mo5SiB2 alloys were fabricated by spark plasma sintering (SPS). The effects of different sintering temperatures and yttrium additions on the microstructure and high-temperature oxidation behavior of the alloys were systematically investigated. For the optimum Mo-13Si-25B-0.2Y alloy sintered at 1750 °C, adding small amounts of rare-earth yttrium refined the grains to an average size of ~400 nm without reducing the Mo5SiB2 content. During oxidation at 1300 °C, the “fishlike” Y2Si2O7 and Y2O3 phases were formed and anchored on the surface of the oxide layers, promoting the oxidation of silicon and accelerating the formation and coverage of the oxide protective film. Moreover, yttrium promoted the in situ deformation of a self-generated protective borosilicate glass film under high-temperature oxidation by accelerating Si oxidation. With prolonged oxidation time, viscous flow occurred to repair the internal cracks and tiny defects caused by the volatilization of MoO3 and prevented the inward diffusion of oxygen, as evidenced by a low oxidation rate constant of 0.95 mg2 cm−4 h−1 at 1300 °C for 50 h in the Mo-13Si-25B-0.2Y alloy.

Microwave-ignited DC-plasma ejection from basalt: Powder-generation and lightning-like effects

A phenomenon of dusty plasma ejected from basalt is presented, in the form of a stable, long-lived fire-pillar, solely sustained by a direct-current (DC) supply. The plasma is emitted to the air atmosphere from a molten hotspot, initially created in the basalt rock by localized microwave-heating (LMH). After an LMH-to-DC transition, the plasma column is solely sustained as a fire-pillar of ∼2 cm diameter, ∼4-cm height using a DC supply of ∼0.2 kV, ∼5 A, steadily lasting for periods longer than 3 min. The dusty-plasma products, accumulated in a powder form, consist of micro- and nanoparticles of basalt's components, including oxides of Si, Na, Fe, P, K, Mg, and Ti. The experimental conditions for the DC sustainability of basalt's dusty-plasma column are analyzed by various theoretical estimates. A possible relevance of these laboratory observations is attributed to atmospheric fire-pillar-like effects, associated, for instance, with volcanic-, ball-lighting, and lunar dusty-plasma phenomena. A potential application, utilizing this effect of DC-sustained dusty-plasma columns, is proposed for the direct extraction of mineral powders from rocks.

Segregation-induced formation of Ge nanocrystals in silicon oxide

The investigation of initial stage of Si1 – xGex alloy deposition and clarification of Ge nanocrystal formation mechanism has been carried out. It was found that at the initial stages of growing layers of Si1 – xGex alloys, the density of island nuclei Si1 – xGex increases by a factor of 2.5–3.4 compared to the density of polycrystalline silicon islands (from 1.07 ⋅ 1011 to 1.90 ⋅ 1011 cm–2 and from 3.1 ⋅ 1010 to 4.3 ⋅ 1010 cm–2 respectively). A decrease in the thickness of the layer corresponding to the end of the induction period and the formation of a continuous Si1 – xGex layer to 8–10 nm (for polycrystalline silicon, the thickness of a similar layer is approximately 22 nm) has been established. It is shown that the Ge nanocrystal formation is occurred by segregationist pushback of Ge atoms by the SiO2 /Si1 – xGex oxidation front and oxidation through grain boundaries during oxidation of Si1 – xGex thin layers, produced by chemical vapor deposition. The MOS structure with array of Ge nanocrystal, which has the hysteresis capacitance characteristics of 1.7–1.8 V and leakage current density from 1.5 ⋅ 10–16 to 2.2 ⋅ 10–16 A/µm2 was obtained.

High-entropy (Hf0.25Zr0.25Ti0.25Cr0.25)B2 ceramic incorporated SiC-Si composite coating to protect C/C composites against ablation above 2400 K

The ablation behavior and protection mechanism of high-entropy (Hf0.25Zr0.25Ti0.25Cr0.25)B2 ceramic incorporated SiC–Si (HETMB2-SiC-Si) composite coating on C/C composite were investigated under ultra-high temperature (up to 2404 K) dynamic ablation test using oxyacetylene torch (OAT). Thermodynamic computations, multicomponent oxide phase diagrams, schematic diagram of the oxidation protection effect of multi-component ceramics, as well as microstructure and composition evolution analyses were built and carried out. Compared with the monolithic or conventional solid-solution diborides incorporated SiC-based composite coatings, the HETMB2-SiC-Si composite coatings presented the minor mass and thickness changes after ablation for 60 s. The oxidation-dominated ablation procedure with good resistance to mechanical scouring mainly contains the selective oxidation of each elements in the coating materials, the phase separation of the Zr, Hf and Ti (group IVB) oxides, the selective melting of Si (group IVA) and Cr (group VIB) oxides, as well as the oxygen diffusion. This resulted in differentiated oxidation scale with enhanced high-temperature thermally-stable and defect-sealing ability under different ablation environments (regions). This work provides precious and insightful information for introducing high‐entropy materials to improve the heat resistance of high-temperature thermal protection systems applied in increasingly severe environments.

High temperature oxidation resistance of physical vapor deposited Hf-Si-B2±z thin films

Within physical vapor deposited Hf-Si-B2±z thin films, selective diffusion-driven oxidation of Si is identified to cause outstanding oxidation resistance at temperatures up to 1500 °C. After 60 h at 1200 °C, the initially 2.47 µm thin Hf0.20Si0.23B0.57 thin film exhibits a dense oxide scale of only 1.56 µm. The thermally induced decomposition of metastable Hf-Si-B2±z leads not only to the formation of Si precipitates within the remaining thin film (related to a non-homogenous Si distribution after the deposition) but also to pure Si layers on top and bottom of the Hf-Si-B2±z coatings next to the excellent adherend SiO2 based scales.

Controllable Si oxidation mediated by annealing temperature and atmosphere

The morphology evolution by thermal annealing induced dewetting of gold (Au) thin films on silicon (Si) substrates with a native oxide layer and its dependences on annealing temperature and atmosphere are investigated. Both dewetting degree of thin film and Au/Si interdiffusion extent are enhanced with the annealing temperature. Au/Si interdiffusion can be observed beyond 800 °C and Au–Si droplets form in both argon and oxygen (Ar + O2) and argon and hydrogen (Ar + H2) environments. In Ar + O2 case, the passive oxidation (Si + O2 → SiO2) of diffused Si happens and thick silicon oxide (SiOx) covering layers are formed. A high temperature of 1050 °C can even activate the outward growth of free-standing SiOx nanowires from droplets. Similarly, annealing at 800 °C under Ar + H2 situation also enables the slight Si passive oxidation, resulting in the formation of stripe-like SiOx areas. However, higher temperatures of 950–1050 °C in Ar + H2 environment initiate both the SiOx decomposition and the Si active oxidation (2Si + O2 → 2SiO(g)), and the formation of solid SiOx is absent, leading to the only formation of isolated Au–Si droplets at elevated temperatures and droplets evolve to particles presenting two contrasts due to the Au/Si phase separation upon cooling.

Compact Integration of Hydrogen–Resistant a–InGaZnO and Poly–Si Thin–Film Transistors

The low–temperature poly–Si oxide (LTPO) backplane is realized by monolithically integrating low–temperature poly–Si (LTPS) and amorphous oxide semiconductor (AOS) thin–film transistors (TFTs) in the same display backplane. The LTPO–enabled dynamic refreshing rate can significantly reduce the display’s power consumption. However, the essential hydrogenation of LTPS would seriously deteriorate AOS TFTs by increasing the population of channel defects and carriers. Hydrogen (H) diffusion barriers were comparatively investigated to reduce the H content in amorphous indium–gallium–zinc oxide (a–IGZO). Moreover, the intrinsic H–resistance of a–IGZO was impressively enhanced by plasma treatments, such as fluorine and nitrous oxide. Enabled by the suppressed H conflict, a novel AOS/LTPS integration structure was tested by directly stacking the H–resistant a–IGZO on poly–Si TFT, dubbed metal–oxide–on–Si (MOOS). The noticeably shrunken layout footprint could support much higher resolution and pixel density for next–generation displays, especially AR and VR displays. Compared to the conventional LTPO circuits, the more compact MOOS circuits exhibited similar characteristics.

Nanostructured Pt-Ru Catalyst Supported on Si-Containing Ordered Mesoporous Carbon Hollow Spheres for the Ethanol Oxidation Reaction

Pt-Ru nanoparticles were dispersed on N-doped Ordered Mesoporous Carbon Hollow Spheres containing Si (N-OMCHS-Si), to obtain the Pt-Ru/N-OMCHS-Si nanocatalyst. Its catalytic activity for the Ethanol Oxidation Reaction (EOR) was evaluated in acid media. Pt-Ru/N-OMCHS-Si showed a higher mass catalytic activity at more negative onset potential (Eonset) for the EOR than Pt-Ru/N-OMCHS (i.e., support without Si), Pt/C and Pt-Ru/C (where C is Vulcan XC-72). Pt-Ru/N-OMCHS-Si also demonstrated a high tolerance to CO, oxidizing the molecule at potentials of comparable negative values as Pt-Ru/C. Moreover, Pt-Ru/N-OMCHS-Si showed enhanced electrochemical stability after Accelerated Degradation Test (ADT) compared to Pt-Ru/C. The high performance of Pt-Ru/N-OMCHS-Si was ascribed to the formation of Pt-Ru alloyed phases and the presence of Si oxides at the hollow spheres.

High Temperature Oxidation Behavior of New Martensitic Heat-Resistant Steel

The research focuses on the high temperature oxidation resistance of martensitic heat-resistant steel. A new type of martensitic heat-resistant steel was developed with the addition of Al and Cu, and the oxidation behavior of the new martensitic heat-resistant steel at 650 °C and 700 °C was analyzed. The high temperature oxidation kinetics curves of new martensitic heat-resistant steel at 650 °C and 700 °C were determined and plotted by cyclic oxidation experiment and discontinuous weighing method. XRD technique was applied to qualitatively analyze the surface oxide of the material after oxidation. The surface and cross-section morphology of the material were observed by field emission scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), and the oxidation mechanism at high temperature was analyzed. The results show that the oxide film can be divided into two layers after oxidation at 650 ºC for 200 h. The outer oxide film is mainly composed of Fe and Cu oxides, and the inner oxide film is mainly composed of Al2O3, SiO2 and Cr2O3. After oxidation at 700 ºC for 200 h, the outer layer is mainly composed of Fe, Cu, Mn oxides, and the inner layer is mainly composed of Cr, Al and Si oxides. The addition of a small amount of Cu promotes the diffusion of Al and Si elements, facilitates the formation of Al2O3 and SiO2, and improves the high-temperature oxidation resistance of martensitic heat-resistant steel.

Time-dependent power laws in the oxidation and corrosion of metals and alloys

Using the equations which describe the oxide thickness as a function of the oxidation time and temperature in the thermal oxidation of Si, various experimental results on the oxidation and corrosion of metals and alloys available in the literature are analyzed. By the analyses, it is found that the weight loss of copper by atmospheric corrosion and the weight gains of austenitic stainless steel and Ni–Cr alloy by high temperature oxidation follow a time-dependent power law in which both diffusion and reaction are involved. It is also found that the pitting corrosion of aluminum alloys by the immersion with seawater and the high-temperature oxidation of Al(431) follow a time-dependent power law of a reaction-limited kind. In addition, an estimation is given of the activation energy for the pitting corrosion of mild steel by the immersion with seawater.

Influence of Al and Si Oxides in Geopolymer Nano-Silica Composite

Influence of Al and Si Oxides in Geopolymer Nano-Silica Composite

Effect of Silicon on Dynamic/Static Corrosion Resistance of T91 in Lead-Bismuth Eutectic at 550 °C.

The 9–12% Cr ferritic–martensitic heat-resistant steel is the main candidate structural material for the Lead-cooled Faster Reactor. The lower Gibbs free energy change of Si oxide can promote the formation of a stable oxide layer, which can improve the corrosion resistance of the material. Therefore, it is of great significance to study the effect of silicon (Si) on the corrosion resistance of T91 steel in lead–bismuth eutectic (LBE). The corrosion resistance of T91 steel with Si contents of 0.5 wt.%, 1.3 wt.%, and 2.0 wt.%, both in dynamic and static LBE at 550 °C, was investigated. The microstructure was analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM), while the oxide films were characterized by electron probe microanalysis (EPMA). Results show that the addition of Si is conducive to improving the corrosion resistance of T91 steel in LBE. T91 steel with high Si content has a thinner and more stable oxide film. The change of Si content can change the contact angle between the steel and LBE, and the contact angle is the largest when the Si content is 1.3 wt.%. The Si-rich oxide layer is usually located in the inner oxide layer, which promotes the formation of a Cr oxide layer located in the internal oxidation zone (IOZ). Si will not enter the precipitated phase, but only change the ferrite content. The oxidation model of T91 steel containing Si in LBE was also proposed.

A comprehensive characterization of virgin and recycled 316L powders during laser powder bed fusion

The primary constraints hindering the widespread adoption of laser powder bed fusion (LPBF) are expensive raw materials, internal defects, difficulty in controlling the quality and stability, and lack of consistency in the powder feedstock. The spatters induced by the violent interaction between the laser and powder can be deposited on the unmelted powder bed, and if not effectively separated by sieving, they would pose a significant detriment to the characteristics and consistency of the recycled powders. In this work, a systematic investigation of the evolution mechanism of 316L powders after 10 and 30 successive recycling in the LPBF process was presented. Firstly, the variation mechanism of particle size distribution and morphology of 316L powder and the generation mechanism of heterogeneous particles were studied. Then, changes in microstructure and hardness trends were characterized. Finally, we emphasized the changes of chemical composition, phase composition, magnetic properties, and the formation mechanism of oxide spots. The results show that the circulation had significant effects on the physical properties, phase transformation, mechanical properties, and magnetic properties of the 316L powders, but had minor effects on the chemical composition, surface and cross-sectional microstructure. In addition, a large number of oddly shaped, large-diameter spatters were identified in the recycled powders, which could not be separated effectively by sieving, and the formation mechanism of the spatters were elaborated. Based on the comprehensive high-temperature oxidation thermodynamics and experimental results, it was concluded that the circular oxide spots on the spatter surface were a composite of multiple oxides of Mn and Si. Further, it was also shown that the ferrite content, XRD peak characteristics, and magnetic properties in the recycled powders were governed by the droplet solidification modes, which in turn is determined by the chemical composition and cooling rates.

Hydrophilic direct bonding of GaN and Si substrates by wet treatments using H2SO4/H2O2 mixture and NH3/H2O2 mixture

GaN substrates were directly bonded with Si substrates by wet treatments using H2SO4/H2O2 and NH3/H2O2 mixtures. Under the optimized condition, the tensile strength reached 7.36 MPa, and a part of the Si substrate was fractured within the bulk instead of the bonding interface. There is an amorphous intermediate layer with a thickness of 1.7 nm, which mainly consists of Si oxides, at the bonding interface. It is remarkable that wafer-scale GaN/Si integration was successfully achieved by using common cleaning methods. It is believed that the proposed direct bonding technique would contribute to future heterogeneous integration because the GaN and Si substrates can be bonded through the atomically thin intermediate layer without vacuum processes.

Dependence of magnetic properties in superparamagnetic Co-granular thin films on deposition rate and effectiveness of a new pulsed DC reactive sputtering method for film fabrication with high deposition rate.

The superparamagnetic thin films with a granular structure show a characteristic magnetization curve. In this study, Co-Al2O3 granular thin films were fabricated by the sputtering method with normal DC source for Co deposition, RF source for Al2O3 deposition, and pulsed DC reactive sputtering were used for fabrication of non-magnetic matrix of oxide or nitride of Al or Si. As a result, Co-Al2O3 superparamagnetic thin films with high magnetization could be obtained with high deposition rate. Very high deposition rate was obtained for fabrication of oxide or nitride films of Al or Si using the pulsed DC reactive sputtering method. This deposition rate was 5 times larger than RF sputtering method. It is expected that a sputtering method with DC source for Co deposition and pulsed DC source for matrix deposition will be effective to realize very high magnetization in the superparamagnetic granular thin films.