Formation Of SiO2 Layer Research Articles

Low-oxygen silicon preparation using vacuum treatment by oxidation control and moisture removal kinetics investigation

Diamond wire saw silicon powder (DWSSP) is a waste produced during silicon wafer processing for photovoltaic (PV) modules, and it shows significant reutilization potential. However, the presence of moisture leads to silicon oxidation and the formation of a surface SiO2 layer that hinders the recovery of high-purity silicon. In this study, vacuum treatment (VT) was used to prepare low-oxygen silicon by controlling the oxidation and removing moisture from DWSSP waste, thus preventing SiO2 layer formation. The oxygen content in DWSSP decreased by 15.01 %, from 7.26 % to 6.17 %, and the SiO2 layer thickness also decreased by 10.29 %, from 2.04 nm to 1.83 nm after the VT process. Additionally, the VT process lowered the moisture boiling point, facilitating surface evaporation and internal diffusion of moisture. This increased the moisture effective diffusion coefficient from 5.16 × 10−10–6.16 × 10−9 m2 s−1 to 1.21 × 10−9–6.88 × 10−9 m2 s−1 and reduced the apparent activation energy from 32.17 kJ mol−1 to 16.05 kJ mol−1. The efficient moisture removal of VT inhibited the growth of the SiO2 layer to enable the preparation of low-oxygen silicon during silicon recovery.

Alloying on the high-temperature oxidation behavior of Nb-Ti-Si-based alloy additively manufactured by laser directed energy deposition

Nb-Si-based alloys have important application prospects in the new generation of high-thrust-to-weight ratio aero-engines hot-end components. Understanding how alloying affects the microstructure and oxidation resistance of Nb-Si-based alloys is crucial for their applications. In this work, the effects of Zr, Cr and Mo on the microstructure and high-temperature oxidation resistance of Nb-23Ti-14Si-based alloys prepared by laser directed energy deposition (LDED) were investigated. Results showed that the oxidation resistance at 1250 °C of as-deposited Nb-23Ti-14Si-based alloys enhanced by Zr, Cr and Mo alloying, of these, Cr is the most significant, followed by Zr and Mo. The oxide film of Nb-23Ti-14Si-based alloys have three distinct oxide layer: the inner, middle, and outer oxide layer. The formation of SiO2 layer in the Nb-23Ti-14Si-based alloys' outer oxide layer when Zr and Cr alloying, respectively. Furthermore, following oxidation at 1250 °C for 20 h, and the weight gain per unit area is around 32.52 mg/cm2, and the creation of CrNbO4 layer when Cr content is up to 10 at.%.

High temperature oxidation of additively manufactured silicon carbide/carbon fiber nanocomposites

An additive manufacturing process and subsequent pyrolysis cycle were used to fabricate SiC matrix/carbon fiber hybrid composites. The matrix was fabricated using a mixture of preceramic polymer and acrylate monomers, while polyacrylonitrile (PAN) precursor was used to fabricate fibers via electrospinning. The precursor matrix and reinforcing fibers at 0, 2, 5, or 10 wt% were printed using digital light processing, and both were simultaneously pyrolyzed to yield the final ceramic matrix composite structure. After pyrolysis, XRD and SEAD analysis proved the existence of SiC nanocrystals and turbostratic carbon structure in the matrix, while the reinforcement phase was shown to have a turbostratic carbon structure similar to commercial carbon fibers. Thermogravimetric analysis (TGA) in air up to 1400 °C was used to evaluate the oxidation resistance of this material. TGA results showed some weight loss due to oxidation of SiC and/or carbon up to about 900 °C, followed by weight gain to about 1200 °C due to the formation of a protective SiO2 layer. Although increasing carbon fiber content negatively impacted the total mass loss for the first heating cycle, exposure of the composite to second-run air revealed negligible weight loss. This is explained by SiO2 layer formation which acts as a protective film that prevents oxygen diffusion. Oxidation of SiC and the formation of a glassy layer has been proven to protect the sample from further oxidation, as well as provide healing of surface cracks and defects as revealed by SEM analysis.

Oxidation behavior and interface evolution of tri-layer Si/Yb2SiO5/LaMgAl11O19 thermal and environmental barrier coatings under isothermal heat treatment at 1300 °C

A tri-layer Si/Yb2SiO5/LaMgAl11O19 thermal and environmental barrier coatings (TEBCs) was prepared for protecting SiCf/SiC substrate by using atmospheric plasma spraying technology (APS). While the introduction of the thermal barrier coatings (TBCs) improves the temperature capability of the environmental barrier coatings (EBCs), it generates vertical crack in the as-deposited TEBCs due to the mismatch of coefficient of thermal expansion (CTE) between Yb2SiO5 EBCs and LaMgAl11O19 TBCs. Isothermal oxidation tests of coated samples were performed at 1300 °C in air for 50, 100, 200, and 300 h. The oxidation behavior and interface evolution of TEBCs were investigated. After 50 h of isothermal oxidation, the crack healing was observed in the coating due to the crystalline of amorphous phase and grain growth. However, the width of vertical crack increased with the oxidation times due to the increasing of residual stresses, which provide rapid diffusion channel for oxygen into surface of Si, resulting in the formation of SiO2 layer. Eventually, the mechanical spallation of coating was observed in the surface of bond coat due to the thermal mismatch and the growth of SiO2 layer. After isothermal oxidation, the Yb3Al5O12 reaction layer was formed in the interface between Yb2SiO5 and LaMgAl11O19 layers due to the inter-diffusion of atoms. Furthermore, the growth of thermally grown oxide (TGO) and Yb2Si2O7 layer at the interface between Si and Yb2SiO5 layers followed approximately the parabolic law.

Interfacial Reactions between Si and SiO2 with Ceramic Additives

In this study, 10 wt.% ceramics—Al2O3, La2O3, Y2O3, MgO, and TiO2—were employed as additives for amorphous SiO2 after pressing and annealing at 1300 °C. The amorphous SiO2 changed to cristobalite SiO2. Through X-ray diffraction, scanning electron microscopy, and transmission electron microscopy with energy-dispersive spectrometry, the reaction phases of La2Si2O7, Y2Si2O7, and MgSiO3 (Mg2SiO4) were found in the SiO2 with 10 wt.% La2O3, Y2O3, and MgO additives. Cracks formed in the Si and SiO2–ceramic additive sites because of the difference in the coefficients of thermal expansion among the Si, SiO2, ceramic additives, and reaction phases. After Si came into contact with the SiO2–ceramics, two types of microstructures were found: those with and those without an amorphous SiO2 reaction layer at the interface. Amorphous SiO2 layer formation is due to the replacement of the Si position in SiO2 by Al3+ and Ti4+ impurities, which can break the bonds between Si atoms. The O content in the Si decreased from 6–9 × 1017 atoms/cm3 for SiO2 to less than ~1016 for SiO2–Al2O3 and SiO2–MgO. The average resistivity of the Si was 3 Ω·cm for SiO2 and decreased to 0.12–0.36 Ω·cm for the SiO2 with ceramic additives.

Modification of plasma-generated SiC nanoparticles by heat treatment under air atmosphere

Plasma-generated SiC nanoparticles are easily functionalized due to their ability to be easily oxidized. In this study, SiC nanoparticles were synthesized in non-thermal arc plasmas via hexamethyldisilane decomposition, and the products were modified by heat treatment under air atmosphere. Results indicated that the plasma-generated SiC nanoparticles were C-coated SiC nanoparticles with an average size of 8 nm, while the heat treatment transformed the initial carbon coating layers into SiO2 layers to form SiO2-coated SiC nanoparticles by surface oxidation. The formation of SiO2 layers enhanced the photoluminescence performance in the blue-green emission region, and also resulted in a blue-shift in the photoluminescence peak mainly due to the surface/defect states. The C-coated SiC nanoparticles exhibited excellent microwave absorption ability, and the optimal reflection loss approached −38.4 dB at 11.7 GHz under an absorber thickness of 2.0 mm; however the formation of SiO2 layers after modification decreased the conduction loss of SiC nanoparticles, thus weakening their microwave absorption. These results afford a new strategy for designing and synthesizing C/SiO2-coated SiC nanoparticles.

Porosity tailoring of electrophoretically derived zirconia coatings using acidic and alkaline-based sol-gel post-treatment to enhance anti-corrosion performance

In this work, the post-treatment sol-gel methods based on acidic and alkaline catalyzed tetraethylorthosilicate (TEOS) solutions were applied to refine the porosity network of electrophoretically deposited ZrO2 coating on anodically oxidized 316 L substrate to improve the corrosion resistance. The ZrO2 coating dipped in alkaline TEOS solution manifested the best barrier performance, arising from the formation of a dense continuous SiO2 interlayer at the coating/substrate interface as well as narrowing the interconnected pores in the coating's body. This was related to the easily inward diffusion of the alkaline hydrolyzed TEOS molecules with an inert surface charge into the negatively charged ZrO2 coating through the open pores toward the interface. However, the acidic-catalyzed TEOS molecules mostly preferred to form a relatively thin SiO2 layer on the surface of ZrO2 coating, which provided a poor barrier performance. This corresponded to the established electrostatic repulsion forces between the positively charged ZrO2 particles and acidic-hydrolyzed TEOS molecules with positive surface charge, which restricted the unlimited diffusion of TEOS molecules. Based on the microscopic observations and electrochemical impedance results, a possible mechanism for refinement of the porous network of ZrO2 coating and formation of SiO2 layers in the acidic and alkaline TEOS solutions was suggested.

Experimental and theoretical study on air reaction wetting and brazing of Si3N4 ceramic by Ag-CuO filler metal: Performance and interfacial behavior

Reactive air brazing of Si3N4 ceramic was successfully achieved by using Ag-CuO filler metal. The effects of CuO content on the wettability of Ag-CuO/Si3N4 system and the shear strength of Si3N4/Si3N4 joint were investigated, and meanwhile the interfacial behavior was analyzed and discussed. Moreover, the work of adhesion, interfacial energy, and electronic properties of Ag/Si3N4, Ag/CuO and Ag/SiO2 interfaces were evaluated by first-principles calculations. The Ag-CuO/Si3N4 system transforms from no-wetting into wetting due to the oxidation of Si3N4 substrate and the formation of SiO2 layer on the substrate surface. The maximum average joint shear strength of over 50 MPa is obtained as the CuO content is 8 at.%. Compared with the Ag(111)/Si3N4(0001) interface, the Ag(110)/CuO(001) and Ag(110)/SiO2(001) interfaces show stronger interfacial bonding due to the formation of Ag-O ionic bond, indicating that the addition of CuO and the formation of SiO2 contribute to the enhancement of interfacial bonding.

Fabrication of 60 wt% SiO2 filled hybrid nanocomposite and its application in erosion-corrosion and radiation resistance

Organic-inorganic hybrid nanocomposites are promising coating materials applied in hazardous space environment. The more the inorganic content is, the higher chemical passivity it has. However, the inorganic component highly filled hybrid nanocomposite increases the tendency of phase separation dramatically. To overcome this problem, we adopted easy control sol-gel method and improved mol ratio of reagents and synthesis process. The as-received epoxy-modified polysiloxane/60 wt% SiO2 hybrid coating was uniform, continuous and exhibited good adhesion and transparency. It reduced the mean erosion yield of Kapton about 2 orders of magnitude to 3.62 × 10−26 cm3 atom−1 and 4.16 × 10−26 cm3 atom−1 after AO and AO + VUV exposure, respectively. The surface characteristics and the erosion kinetic curve revealed that the performance of the as-received hybrid coating was comparable with the best existed coating systems and the hybrid coating with higher inorganic content performed better than which with lower inorganic content. According to the results and references, we concluded that the reason why the hybrid coating with attractive AO/VUV resistance was that the introduction of 60 wt% SiO2 could accelerate the formation of SiO2 layer on top of the hybrid coating, what's more, mitigate the tensile stress in the SiO2 layer.

High temperature oxidation behavior of type 444 stainless steel in synthetic automotive exhaust gas

The oxidation behaviors of type 444 ferritic stainless steel (FSS) were studied in air and synthetic exhaust gas at 1000, 1050 and 1100 °C, respectively, by means of mass gain, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The oxidation rate of 444 FSS enlarges in both environments with the increase of temperature, but is faster in synthetic exhaust gas than in air under isothermal conditions. The oxidation rate becomes very fast since the occurrence of breakaway transition. Both the higher temperature and the synthetic exhaust gas facilitate the breakaway oxidation. The breakaway oxidation results mainly from the growth of oxide nodules and the spallation of oxide scale. The synthetic exhaust gas isn't conducive to the formation of SiO2 layer in comparison with the air. The oxidation mechanisms are discussed on the basis of the oxide scale characteristics.

Ablative properties of laminated ZrB2-SiC ceramic modified by SiC whisker in oxyacetylene environment

To improve the long-term service of existing laminated ceramics at ultra-high temperature, laminated ZrB2-SiC/SiCw (ZSS) ceramic was prepared by hot-pressing with SiCw (SiC-whisker) as interface layer. After ablated in oxyacetylene at 3000 °C for 100 s, the structure of ZSS remained intact and the linear and mass ablation rates were 0.12 ± 0.03 μm s−1 and 0.43 ± 0.09 mg s−1, respectively. Such excellent ablation resistance of ZSS was attributed to the reduction of the surface temperature and the formation of SiO2 layer by SiC whisker, which resulted in prominent oxidation protection and strong bonding strength at interface.

Synthesis and emission characteristics of lead-free novel Cs4SnBr6/SiO2 nanocomposite

Lead-free Cs4SnBr6 nanostructures were synthesized using the high-temperature wet chemical method with as prepared cesium oleate and oleylammonium bromide. A new type of the SiO2 layer formation method was followed using TEOS and m-cresol. Phase stability of the Cs4SnBr6 and Cs4SnBr6/SiO2 aged samples was analyzed by the X-ray diffraction method. Transmission electron microscopy micrographs show that the hexagonally shaped particles covered with a thin SiO2 layer for Cs4SnBr6/SiO2 and were verified with TEM-EDS spectra. Synthesized particles showed a bright orange colour fluorescence emission under UV light and were confirmed with fluorescence emission spectroscopy.

Mechanism study of SiO2 layer formation and separation at the Si die sidewall during nanosecond laser dicing of ultrathin Si wafers with Cu backside layer

Laser dicing of ultrathin dies is promising and is gaining importance because of its cost and quality advantages over mechanical and plasma dicing. However, the effects of laser dicing on the mechanical strength and microstructure of ultrathin Si dies need to be further understood, especially when dicing through Si wafers with backside Cu layer. A critical phenomenon effecting the Si die sidewall strength after nanosecond laser dicing of Si wafers with backside Cu is the formation and separation of a SiO2 layer at the sidewall. The mechanisms behind the SiO2 layer formation and separation were studied in this work. Si wafer samples without and with backside Cu layer were prepared by dicing with nanosecond laser using standard production parameters. The microstructure and phases formed were investigated by energy dispersive spectroscopy and nanobeam diffraction in a transmission electron microscope. In die samples without backside Cu, the sidewall consists of a thin surface layer of amorphous Si, followed by a polycrystalline Si layer, and finally an epitaxial Si layer. In die samples with backside Cu, the sidewall microstructure was observed to be vastly different. At the upper region of the sidewall, a surface layer of polycrystalline Cu was found, followed by a polycrystalline Cu3Si layer, a SiO2 layer mixed with Cu3Si, and finally a thick SiO2 layer. The Cu3Si catalyzes the growth of the SiO2 through an oxidation step of the Cu3Si on the sidewall surface as well as at the SiO2/Si interface. In the lower region of the sidewall, the microstructure is similar to the upper region, but there is a separation of the SiO2 layer from the crystalline Si. The SiO2 undergoes a decomposition reaction at the SiO2/Si interface, releasing volatile SiO which causes microvoids to form and grow laterally at the interface. The growth and coalescence of the microvoids eventually lead to the separation of the SiO2 layer from the crystalline Si, leaving behind a clean and rough crystalline Si surface with a peak-to-peak roughness of 100–200 nm. In the areas where the SiO2 layer has separated from the Si die sidewall, the fracture strength of the sidewall is dependent on the material property and surface roughness of the crystalline Si, and not on the SiO2 layer. In the sidewall region near the die frontside, the SiO2 thickness is more than regions near the die backside, and no microvoiding and separation at the SiO2/Si interface were detected. This is hypothesized to be due to a higher O2 pressure at the upper region of the narrow dicing trench which is open to the atmosphere compared to the lower regions where there could be O2 deprivation and lower O2 pressure.

Luminescence of SiO2 layers on silicon at various types of excitation

We present a comparative analysis of Cathodoluminescence (CL), Photoluminescence (PL) and Electroluminescence (EL) spectra measured on Si-SiO2 structures with various thicknesses of SiO2 layer. The spectral distributions of the luminescence depend on the technology of the SiO2 layer formation, on its thickness and the type of excitation. The analysis indicates that CL and EL spectra of the Si-SiO2 structures, grown by thermal oxidation of silicon in a "dry" oxygen, are almost identical in spectral composition. The PL of the Si-SiO2 structures provides additional information about the optically active centers in the SiO2 layer. The PL spectra allow tracking changes in the SiO2 layer while increasing its thickness in more detail than the EL and CL. We suggest that there is a substantial difference in the excitation mechanisms of luminescence by electrons (CL and EL) and photons (PL). Therefore, in general case, the luminescence centers identified in PL cannot be directly used for the interpretation of CL and EL spectra. However, analysis of the PL and EL spectra before and after the field degradation of the Si-SiO2 structure as well as analysis of PL spectra of the oxide layers formed by various technologies shows that the model of luminescence centers proposed for red photoluminescence is acceptable for the red luminescence excited by electrons in Si-SiO2 structure.

Effect of oxidation and residual stress on mechanical properties of SiC seal coated C/SiC composite

The effect of oxidation and thermal residual stress on mechanical properties of SiC seal coated C/SiC composite at ambient temperature and high temperature were studied. The oxidation of SiC seal coated C/SiC composite at 1300 and 1500°C resulted in carbon fibres burn area near through thickness micro cracks in the SiC seal coating. With the increase in exposure time, the formation of SiO2 layer in SiC matrix near carbon fibres burns area was found. Residual mechanical properties of SiC seal coated C/SiC composite after exposure in air show significant degradation. First time, a continuous measurement of Young's modulus with temperature of C/SiC composite was carried out using an impulse excitation technique. The effect of relaxation of thermal residual stress on mechanical properties was observed with the help of continuous measurement of Young's modulus as a function of temperature in an inert atmosphere.

Ultrafast activation efficiency of three peroxides by Fe78Si9B13 metallic glass under photo-enhanced catalytic oxidation: A comparative study

Metallic glasses with long-range disordered atomic structure have recently been attracted a great deal of research attention in catalytic field. Compared to crystalline materials, the metallic glasses present many advanced catalytic properties, yet the catalytic mechanism is not sufficiently understood. In this work, an Fe78Si9B13 glassy ribbon manufactured by melt-spinning method was applied for the first time to compare its activation behavior on three peroxides, including hydrogen peroxide (H2O2), persulfate (PS) and peroxymonosulfate (PMS). It was shown that Fe78Si9B13 metallic glass had exceptionally high capability for activating these three common peroxides to produce reactive radicals (OH and/or SO4•−). The dominant species of H2O2 in this work was demonstrated as hydroxyl radical (OH) while the PS and PMS activation mainly generated sulfate radical (SO4•−). The order of predominant radical generation rate by Fe78Si9B13 activation under UV−vis irradiation was PS > H2O2> PMS. The relative contribution of sulfate radical (SO4•−) in PS activation was 78% compared to 61% in PMS. All the peroxides activated by Fe78Si9B13 metallic glass presented a radical generation rate at least ∼2 times higher than other iron-containing materials. Crystal violet (CV) dye was used to investigate the catalytic performance of Fe78Si9B13 metallic glass for peroxides, which showed an ultrafast dye degradation rate with completely color removal within 15min. The radical evolution mechanisms for H2O2, PS and PMS activation were also investigated. The change in surface morphology of ribbon after 5th run reused indicated that the inclusions of Si leading to formation of SiO2 layer played an important role in the surface stability of ribbons.

Rational synthesis of silylated Beta zeolites and selective ring opening of 1-methylnaphthalene over the NiW-supported catalysts

Heavy oil has been by-produced from refinery and petrochemical processes, and its use as low-value fuels has been restricted by stricter environmental regulations due to heavy molecules, multi-ring aromatics, and high sulfur content. In a bi-functional catalyst system of metal and zeolitic acid, balancing metallic (from metal element) and acidic function (from zeolite elements) is essential for harnessing the selective ring opening (SRO) reaction with the aim of upgrading the heavy oil. Here, we report a synthetic strategy to control the acid site distribution of Beta zeolite through the silylation reaction with tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), and tetrabutyl orthosilicate (TBOS) as silylation agents. As the size of alkyl chain group in the silylation agents gets larger, the silylation agents were suppressed to spread into the channels and thus the formation of SiO2 layer was intentionally occurred on the external surface of the zeolite. Resulting from the selectively deposited SiO2 layer, NiW metals supported on each silylated Beta zeolite altered the metal distribution and further the balance of metallic and acidic function. NiW catalyst supported on TBOS-silylated Beta zeolite exhibited the best catalytic performance toward the SRO reaction of 1-methylnaphthalene in a fix-bed reaction system, proving the optimal balance of metallic and acidic functions. We expect that this study will benefit the control over the selective silylation reaction in order to optimize the balance of metallic and acidic functions in the bi-functional catalysts, and, hence, to promote properly aromatic saturation (hydrogenation) and ring opening (hydrocracking) for selective ring opening products.

Evaluation of physicochemical properties of SiO2-coated stainless steel after sterilization

The study of most of the literature devoted to the use of coronary stents indicates that their efficiency is determined by the physicochemical properties of the implant surface. Therefore, the authors of this study suggested conditions for the formation of SiO2 layers obtained with the use of sol–gel methodology showing physicochemical properties adequate to the specific conditions of the cardio-vascular system. Previous experience of authors helped them much to optimize the coating of 316LVM steel surface with SiO2. The values of parameters that determine the usefulness of the coating in medical applications have been determined. In order to identify the phenomena taking place at the boundary of phases and to evaluate the usefulness of the proposed surface modification, taking into consideration the medical sterilization (steam or ethylene oxide (EO)), the potentiodynamic, impedance, adhesion, surface morphology and biological assessment characterizations were performed. Regardless of the usage of the sterilizing agent (steam, EO) the study showed the reduction of critical force causing layer's delamination. The research results of corrosion resistance study also confirmed a slight decrease of SiO2 barrier properties of the samples after sterilization in contact with the artificial plasma. SiO2 layers after the sterilization process did not show significant features of cytotoxicity and had no negative influence on blood cell counts, which confirmed the results of quantitative and qualitative studies.

Formation of an Anti-Contamination Layer with Polystyrene Nanobeads over Cover Glass for Solar Cells

In this study, a colloidal solution was mixed with hydrophobic polymer nanobeads and TEOS (tetra-ethylorthersilicate) for the preparation of an anti-contamination compound, the anti-contaminative properties of which were investigated for its application as an anti-fouling agent for cover glasses used for solar cells. Polystyrene spherical beads of approximately 250 nm were used as the hydrophobic polymer, and were synthesized by the suspension synthesis method. TEOS was used in order to enhance the stability of polymer nanobeads coated over the surface of a cover glass, due to the formation of SiO2 layer. The ratio of TEOS/PS was controlled to 0/50, 1.2/50, 2.4/50 and 5/50, and the water contact angle on the coated surface of the cover glasses was measured after thermal treatment at 400, 500 and 600°C (Ed note: you mention other temperatures, including 650°C, within the text). The contact angle of glass treated with a TEOS/PS ratio of 1.2/50 at 600°C was approximately 100°, which was about 2.5 times that of the non-coated cover glass, and its transmittance was analyzed and determined to be the same as that of the non-coated cover glass, using a UV-Vis spectrophotometer.

Synthesis and Characteristic of AA6061/SiC Sand Cast Composite

The present work focuses on the fabrication of aluminum (6061-T6) matrix composites (AMCs) reinforced with various weight percentages of SiC particulates using sand casting method. The addition of Mg in the melt during the process has improved the wettability between Al and SiC there by reduced the formation of SiO2 layer on the surface. The fabricated AMCs were characterized using optical microscopy (OM), scanning electron microscopy (SEM), hardness tester and universal tensile testing machine. The OM and SEM images revealed the presence of homogeneous dispersion of SiC particle in the matrix. Using X-ray diffraction (XRD) test, the dispersion of reinforcement has been identified. With the increases in weight percentage of SiC particles in the aluminum matrix improved the mechanical properties of composites.