SiO2 Protective Layer Research Articles

Enhanced atomic-oxygen resistance of surface-siliconized polyimide film via an in-situ precursor network at the interface

In order to allow polyimide (PI) to resist the erosion of atomic oxygen (AO) in Low Earth Orbit to extend the life of the aircraft, an in-situ precursor network approach was proposed to manufacture the inorganic gradient microstructure across the organic/inorganic transition interface and simplify the process, which create a three-tier microstructure film and lead the dense SiO2 protective layer firmly grasps the PI film. Benefiting from the integrated structure, SiO2-coated PI film shows remarkable surface and interface state after 3000 times mechanical bending, which able to delay the initial AO corrosion caused by the defect of the protective layer, resistance to AO reported as AO erosion yield of 2.39 × 10−26 cm3 O atom−1 under 7 × 1021O atoms cm−2 AO fluence. This work proposes a novel approach for the fabrication of high-performance and AO resistant PI to enable the aircraft to complete more efficient and highly integrated flight missions and shows great potential in the general preparation of organic-inorganic interface.

Study of KCl-induced hot corrosion behavior of high velocity oxy-fuel sprayed NiCrAlY and NiCrBSi coatings deposited on 12CrMoV boiler steel at 700 ℃

The hot corrosion behavior of two kind of HVOF-sprayed NiCr-based coatings with different oxide-forming elements (such as Al and Si) was investigated and compared in the presence of KCl salt at 700 ℃. The results showed that the hot corrosion resistance of NiCrBSi coating was superior to that of NiCrAlY coating. NiCrAlY coating was seriously corroded and severe internal oxidation was produced along the splat boundaries, while the corrosion of NiCrBSi coating was relatively mild and the inner coating remained intact, which was ascribed to the denser structure and the generation of a SiO2 protective layer.

Improving oxidation resistance of TZM alloy by deposited Si–MoSi2 composite coating with high silicon concentration

The oxidation behavior of Si–MoSi2 composite coating deposited on titanium-zirconium-molybdenum alloy (TZM) at 1200 °C in air was discussed. The oxidation tests show that the mass loss of coated samples is only 0.021 mg/cm2 after oxidation at 1200 °C for 9 h, whereas the bare TZM suffers serious volatilization and decomposition, and the mass loss is only 2.488 mg/cm2 after oxidation for 20 min. The coated samples presents good oxidation resistance compared to the bare TZM alloy at medium temperature, which is due to the formation of self-healing SiO2 protective layer and the dense structure of coating. Moreover, the high surface silicon concentration also plays a positive role in the rapid formation of SiO2 protective layer.

In Situ Generated Yb2Si2O7 Environmental Barrier Coatings for Protection of Ceramic Components in the Next Generation of Gas Turbines

AbstractIn face of an accelerating climate change, the reduction and substitution of fossil fuels is crucial to decarbonize energy production. Gas turbines can operate with versatile fuel sources like natural gas and future fuels such as hydrogen and ammonia. Furthermore, thermal efficiencies above 60% can be achieved using non‐oxide silicon‐based ceramic components. However, water vapor is one of the main combustion products leading to rapid corrosion because of volatilization of the protective SiO2 layer at 1200 °C. An in situ generated Yb2Si2O7 double layered environmental barrier coating system composed of silazanes and the active fillers Yb2O3 and Si processed at 1415 °C for 5 h in air protects a Si3N4 substrate very effectively from corrosion. It exhibits a dense microstructure with a total thickness of 68 µm, overcomes 15 thermal cycling tests between 1200 and 20 °C and shows almost no mass loss after very harsh hot gas corrosion at 1200 °C for 200 h (pH2O = 0.15 atm, v = 100 m s−1). The excellent adhesion strength (36.9 ± 6.2 MPa), hardness (6.9 ± 1.6 GPa) and scratch resistance (28 N) demonstrate that the coating system is very promising for application in the next generation of gas turbines.

Superstrong, Lightweight, and Exceptional Environmentally Stable SiO2@GO/Bamboo Composites.

Development of lightweight structural materials from fast-growing bamboos is of great significance to building a sustainable society. However, previously developed structural bamboos by delignification combined with densification would easily fail under large external loading after exposure to water due to structure collapse, severely limiting their practical applications. Here, we demonstrate an ultrastrong and exceptional environmentally stable bamboo composite consisting of a graphene oxide (GO)/bamboo core and hierarchical SiO2 protection layer. The GO/bamboo composite exhibits ultrahigh tensile strength (641.6 MPa), superb flexural strength (428.4 MPa), and excellent toughness (17.5 MJ/m3), which are increased by about 480, 250, and 360% compared with natural bamboo, respectively. As a result, the specific tensile strength of the GO/bamboo composite is up to 513.3 MPa·cm3/g due to its low density (1.25 g/cm3), outperforming engineering structural materials such as aluminum alloys, steels, and titanium alloys. These large improvements benefit from the well-preserved bamboo scaffold and the strong hydrogen bonds between bamboo fibers and GO nanosheets. On the other hand, the SiO2@GO/bamboo composite shows superhydrophobicity due to the construction of hierarchical SiO2 layers, which endows it with outstanding water resistance. Moreover, the bamboo composite shows an ultralow coefficient of thermal expansion (≈2.3 × 10-6 K-1), indicating its excellent dimensional stability. Considering the ultrahigh mechanical performance and outstanding environmental stability, the developed lightweight SiO2@GO/bamboo composite is hopeful to be a green and sustainable structural material for practical engineering applications.

Characterization of microstructure and oxidation resistance of Y modified silicide composite coating on Mo–Cr–W–Al–Ti substrate

Y modified silicide composite coating (Si–Y coating) was prepared on Mo–Cr–W–Al–Ti substrate by Si and Y2O3 co-deposition at 1200 °C for 20 h. The oxidation resistance of the coating was studied by analyzing the phase constituents and microstructure. A double layer coating has been observed: a thick outer layer consisting of (Mo, X)Si2, (Cr, X)Si2 and Al2O3, and a thin inner layer of (Mo, X)5Si3, (Cr, X)5Si3, Al2O3. The Si–Y coating possessed better oxidation resistance under high temperature conditions than the unmodified one, the mass gain of 5.97 mg/cm2 after 18 cycles of oxidation at 1300 °C in air for 150 h for the former and the beginning of weight loss after 18 h under the same condition for the latter. The dispersed Y2Ti2O7 contained in the compact SiO2 protective layer acts as a “skeleton” to improve the oxidation resistance of the Si–Y coating.

Microstructure dependent ablation behaviour of precursor derived SiOC ceramic foam for high temperature applications

Ablation behaviour of poly(hydridomethylsiloxane) derived open and closed porous structured SiOC ceramic foams was evaluated using oxy-acetylene flame at 1500 °C for various time durations. X-ray diffraction and scanning electron microscopy analyses of ablated SiOC ceramic foams revealed the formation of a thin protective SiO2 layer inhibiting further oxidation. The closed porous structured SiOC ceramic foams exhibited very low mass ablation rate in contrast to open porous structured SiOC ceramic foams owing to the differences in thermal energy dissipation mechanism. The feasibility of the plausible foam reduction reactions pertaining to the ablation mechanism was further investigated by computing the Gibbs energy and HR-TEM analysis. The study corroborated the significance of tailoring the microporous structured SiOC ceramic foams as potential thermal protection material for high temperature applications.

Protecting Perovskite Solar Cells against Moisture-Induced Degradation with Sputtered Inorganic Barrier Layers

We describe a general approach for protecting metal halide perovskite solar cells against degradation in high-humidity environments using a sputtered barrier coating. A SiO2 protective layer, applied to two different types of perovskite solar cells, was deposited without strongly impacting the initial device performance. The degradation of the cells was imaged in real time using laser beam-induced current (LBIC) measurements in an accelerated test. We show that SiO2 barrier films can improve the tolerance of the devices to extreme humidity conditions and extend lifetimes by a factor of ∼60 when a 45 nm SiO2 barrier layer is applied to CH3NH3PbI3 and by a factor of ∼600 when a 300 nm barrier is applied to a triple-cation perovskite material. The LBIC data revealed that the approach promises protection against degradation initiation at the edges of scribed lines, which will be necessary for the fabrication of monolithically integrated modules.

Structure optimization of epoxy-functionalized polysiloxanes and tribological properties of the polysiloxane/molybdenum disulfide lubricating coating for low-earth orbit environment

This paper investigates applicability of polysiloxane/MoS2 lubricating coatings in low-earth orbit (LEO). Results show that wear resistance of the polysiloxane lubricating coatings is related to R/Si value and epoxy group of the epoxy-functionalized polysiloxanes resin. The prepared polysiloxane lubricating coatings exhibited better wear resistance than existing organic coating due to the synergistic effect of low surface energy polysiloxane and MoS2. Furthermore, the polysiloxane coating achieved excellent AO resistance ascribe to the generation of SiO2 protective layer. The thickness of SiO2 layer was only 60 nm, which has no effect on vacuum tribological properties of the polysiloxanes lubricating coating. After AO irradiation, the polysiloxane lubricating coating maintained a low friction coefficient and excellent wear resistance under the vacuum condition.

Surface Grafting SiO2 on Lithium-Rich Layered Oxide Cathode Material for Improving Structural Stability

Surface grafting of SiO2 layer was carried out to alleviate the intrinsic issues of lithium-rich layered oxide Li1.2Mn0.54Ni0.13Co0.13O2 (LRLC). After analyzing the pristine and SiO2 coated samples by XRD, XPS, SEM and TEM characterizations, it is found that the surface of LRLC cathode material is successfully decorated with SiO2 layer while maintaining the pristine structure and morphology. The introduction of SiO2 coating prevents the erosion of cathode material from the electrolyte and inhibits the formation of spinel structure. More importantly, the capacity retention of the optimized 0.25 wt.% SiO2-coated LRLC sample after 200 cycles at 1 C delivers as high as 89.7%, much higher than that of the pristine sample (74.2%). There are obvious cracks on the surface of pristine sample after 200 cycles, while the surface of SiO2-coated LRLC samples remains intact, which convincingly proves that SiO2 layer can substantially promote the structural stability of cathode material. As last, the modification mechanism of SiO2 layer in the layered cathode material is elucidated. All in all, the shielding and scavenging effects of SiO2 protective layer towards HF hinder the electrolyte from corroding the cathode material, and improve the electrochemical performances, especially structure stability of the cathode material.

Porous TiO2 thin film-based photocatalytic windows for an enhanced operation of optofluidic microreactors in CO2 conversion

SummaryUsing a photocatalytic window can simplify the design of an optofluidic microreactor, providing also a more straightforward operation. Therefore, the development of TiO2 coatings on glass substrates seems appealing, although a priori they would imply a reduced accessible area compared with supported nanoparticle systems. Considering this potential drawback, we have developed an endurable photocatalytic window consisting on an inner protective SiO2 layer and an outer mesoporous anatase layer with enhanced surface area and nanoscopic crystallite size (9–16 nm) supported on a glass substrate. The designed photocatalytic windows are active in the CO2-to-methanol photocatalytic transformation, with maximum methanol yield (0.52 μmol·h−1·cm−2) for greatest porosity values and minimum crystallite size. Compared with benchmark supported nanoparticle systems, the nanoscopic thickness of the coatings allowed to save photoactive material using only 11–22 μg·cm−2, while its robustness prevented the leaching of active material, thus avoiding the decay of performance at long working periods.

High temperature oxidation of higher manganese silicides

The oxidation kinetics and mechanisms of higher manganese silicides (HMS) MnSi1.75, MnSi (1.75-x)Gex, MnSi(1.75-x)Alx (with x = 0.005 and 0.01)were studied and the effects of densification methods and dopant concentration discussed. Oxidation experiments were conducted using thermogravimetry (TGA), while post characterization with X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscope (SEM) showed that spark plasma sintering (SPS) is a better densification method than hot pressing (HP). Except for undoped HMS, HMS doped with 0.5at% Ge had the lowest oxidation rate. Stable formation of a SiO2 protective layer was the main reason for improved oxidation resistance in air in the temperature range 200 °C–500 °C.

Processing optimization of SiO2-capped aluminum-doped ZnO thin films for transparent heater and near-infrared reflecting applications

In this study, a series of optimization steps were performed in the production of Al-doped ZnO (AZO) thin films to tailor their properties as efficient transparent heaters and for near-infrared (NIR) reflectance. The films were produced on 50 × 75 mm2 glass substrates via magnetron sputtering and capped with a protective SiO2 layer. Processing parameters such as deposition temperature, film thickness, and annealing conditions were all optimized in terms of structure, morphology, optical/electrical properties, and heating/deicing behavior. Electro-thermal characteristics of the films were investigated using a thermal imaging infrared camera under various input voltages. The optimized AZO/SiO2 coatings displayed impressive room-temperature electrical conductivity (σ) of nearly 3774 S/cm with a sheet resistance (Rs) of 3.53 Ω/□, carrier concentration (η) of 1.14 × 1021, and Hall mobility (µ) of 20.48 cm2/Vs. These films exhibited very high optical transmittance (above 96%) in the visible range and reflectance (73% at 2500 nm) in the NIR region. The highest figure of merit (FOM) was achieved as 237 (× 10–3 Ω−1). Deicing tests were performed with samples cooled to − 40 °C and resulted with complete removal of ice/water only within 3 min. In addition, the heater exhibited a high surface temperature of 161 °C (12 V), a good thermal resistance value (219 °C cm2/Watts) with stable and reversible heating behavior. More importantly, these results reveal the potential of optimized AZO/SiO2 coatings as alternatives to transparent tin-doped indium oxide heaters and NIR reflecting mirrors for vehicular applications.

Investigation into the adsorption of methylene blue on the surface of a "core–shell" type catalyst for the Fenton system

The catalytic oxidation of organic substances, in particular by the Fenton method, is one of the effective methods of wastewater treatment. The oxidation efficiency is affected by the adsorption properties of the catalyst when using heterogeneous catalysts in the Fenton process. In this work, the adsorption kinetics of methylene blue dye from aqueous solutions of different concentrations on the surface of the synthesized nanostructured magnetosensitive catalyst CoFe2O4/SiO2/CoMnO2 was studied by spectrophotometric analysis and the kinetic parameters of the process were determined. The CoMnO2-based "core–shell" catalyst has a magnetically sensitive cobalt ferrite core coated with a protective layer of porous SiO2, on the surface of which clusters of cobalt and manganese oxides are placed as catalytic centers. The process of adsorption of methylene blue from an aqueous solution can be considered as a quasi-chemical reaction of displacement of solvent molecules from the adsorption layer by dye molecules. The equilibrium state is described by the Langmuir equation, in which the effective adsorption constant is the ratio of the equilibrium constants of the Langmuir interactions of the dye and the solvent, respectively, with the active center of the adsorbent. The limiting adsorption of methylene blue and the adsorption constant characterizing the affinity of the dye to the catalyst surface were determined. The specific area of the catalyst was calculated under the condition of a known landing plane of the dye molecule. The influence of the adsorption properties of the catalyst on the efficiency of the Fenton process was established.

Synthesis of hollow TiO2@SiO2 spheres via a recycling template method for solar heat protection coating

The development of a simple and environmentally friendly method to synthesize hollow TiO2 structures is urgent for realizing high NIR reflectance and low thermal conductivity. Hollow TiO2@SiO2 structures have been successfully synthesized by a recycling template method. The synthesis process involves four steps as follows: 1) preparation of SiO2 spheres, 2) synthesis of SiO2@TiO2 core-shell structure by coating mesoporous TiO2 shell on SiO2 and crystallization by calcination, 3) etching the SiO2@TiO2 to form the hollow TiO2 spheres, and 4) coating the hollow TiO2 spheres with a SiO2 protection layer to produce hollow TiO2@SiO2 structures. The SiO2 serves as a template to support and synthesize hollow TiO2 shell, and then after being etched, to form a Na2SiO3 solution as a coating agent to protect TiO2 shell from photocatalytic activity. The as-synthesized hollow TiO2@SiO2 structures not only have high NIR reflectance, but also have a high thermal barrier performance due to the hollow structure. Moreover, the NIR reflectance of the coating made from hollow TiO2@SiO2 reached 94.9%, and the temperature of the inner surface of the coating board is reduced about 16 °C, compared with the surface without coating. The weather resistance studies reveal that the hollow TiO2@SiO2 sample is very stable under the UV irradiation. In particular, the hollow TiO2@SiO2 structures synthesized by using this method shows multifunctional responses towards solar heat.

Atomic Force Microscopy Based Top-Illumination Electrochemical Tip-Enhanced Raman Spectroscopy.

Electrochemical tip-enhanced Raman spectroscopy (EC-TERS) is a powerful technique for the in situ study of the physiochemical properties of the electrochemical solid/liquid interface at the nanoscale and molecular level. To further broaden the potential window of EC-TERS while extending its application to opaque samples, here, we develop a top-illumination atomic force microscopy (AFM) based EC-TERStechnique by using a water-immersion objective of a high numerical aperture to introduce the excitation laser and collect the signal. This technique not only extends the application of EC-TERS but also has a high detection sensitivity and experimental efficiency. We coat a SiO2 protection layer over the AFM-TERS tip to improve both the mechanical and chemical stability of the tip in a liquid TERS experiment. We investigate the influence of liquid on the tip-sample distance to obtain the highest TERS enhancement. We further evaluate the reliability of the as-developed EC-AFM-TERS technique by studying the electrochemical redox reaction of polyaniline. The top-illumination EC-AFM-TERS is promising for broadening the application of EC-TERS to more practical systems, including energy storage and (photo)electrocatalysis.

MoSi2-based cylindrical susceptor for rapid high-temperature induction heating in air

Conductive susceptors are necessary for heating non-conductive materials in induction heating systems. Susceptor materials should have sufficient electrical conductivity and thermal/chemical stability under a range of environmental conditions. However, many susceptor materials oxidize in high-temperature environments, resulting in degradation and poor durability. Here, we used intermetallic MoSi2 ceramics as a susceptor material and designed a cylindrical susceptor to apply to rapid high-temperature induction heating in an oxidizing environment. MoSi2 was prepared by self-propagating high-temperature synthesis (SHS), and then used to fabricate cylindrical susceptors by slip casting. The optimal thickness of the susceptor was controlled by modelling. A MoSi2-based cylindrical susceptor with SiO2 protective layer showed higher heating rate (4.2–26.8 °C/s at 0.5–2.5 kW) than a commercial rod-type susceptor (7.7–13.6 °C/s at 1.0–2.5 kW) of the same material. In addition, our susceptor endured high temperatures below 1700 °C and severe thermal cycle (700–1600 °C, heating for 2min and cooling for 1min) during 36 cycles. In general, these results demonstrate that the MoSi2-based susceptor can be applied to a rapid induction heating furnace that can be used in air at a high temperature of 1600 °C (equal to the available temperature of a commercial graphite susceptor in H2).

Absorption enhancement and efficiency improvement of an organic solar cell embedded with core–shell Au@ITO nanoparticles

In this paper, we propose a new design of plasmonic organic solar cells (OSCs). It consists of a protective layer of SiO2, an anti-reflective glass of ITO, a compact buffer of PEDOT:PSS, an absorbing organic material of P3HT:PCBM, and a reflective layer of Al. A square periodic array of core–shell nanoparticles (Au@ITO NPs) is embedded in the active layer of P3HT:PCBM in order to enhance the absorption of OSC. Although ITO coating slightly reduces efficiency, it prevents the oxidation of gold NPs and increases the OSC lifetime. We study the effect of numerous parameters such as the core radius, shell thickness, and core material on the optical absorption by solving Maxwell’s equations using the three-dimensional finite-difference time-domain method. The drift–diffusion and Poisson’s equations are solved with an in-house software tool by discretizing the solar cell using the finite element method. To the best of our knowledge, this paper is the first to apply the real model of trap-assisted recombination and Auger recombination of used materials to the simulations to match them with the experimental results. The numerical results show the proposed OSC embedded with Au@ITO NPs has the built-in potential of 2.9 V, short-circuit current of 16.63 mA/cm2, the open-circuit voltage of 1.14 V, maximum power of 17.25 mW/cm2, fill-factor of 0.91, the conduction band of 2.8 eV, electron quasi-Fermi level of 2.35 eV, hole quasi-Fermi level of 0.6 eV and an efficiency of 17.25%. Furthermore, the performance of the proposed OSC has an improvement of 25% compared to conventional OSCs.

A Strategy for Polysulfides/Polyselenides Protection Based on Co9S8@SiO2/C Host in Na‐SeS2 Batteries

AbstractTo obtain unbroken sulfides with delicate morphology from metal–organic frameworks (MOFs), a method for in situ growth of SiO2 protective layers on the surface of MOFs is proposed. This strategy can be successfully expanded to a variety of MOFs (ZIF‐67, Cu‐MOF, ZIF‐8, and PBA). Importantly, room‐temperature Na‐SeS2 batteries with Co9S8@SiO2/C prepared from ZIF‐67 as cathode host are assembled. Due to the hollow structure that can relieve the volume expansion and the co‐adsorption of sodium polysulfides/sodium polyselenides by Co9S8@SiO2/C, the SeS2/Co9S8@SiO2/C cathode shows excellent rate performance and Coulombic efficiency. In addition, ex situ X‐ray diffraction and in situ Raman results show that S8 and Se8 are generated after the discharge of SeS2, and Se8 is preferentially oxidized during charging.

Magnetism and Afterglow United: Synthesis of Novel Double Core-Shell Eu2+ -Doped Bifunctional Nanoparticles.

Afterglow–magnetic nanoparticles (NPs) offer enormous potential for bioimaging applications, as they can be manipulated by a magnetic field, as well as emitting light after irradiation with an excitation source, thus distinguishing themselves from fluorescent living cells. In this work, a novel double core–shell strategy is presented, uniting co‐precipitation with combustion synthesis routes to combine an Fe3O4 magnetic core (≈15 nm) with an afterglow SrAl2O4:Eu2+,Dy3+ outer coat (≈10 nm), and applying a SiO2 protective middle layer (≈16 nm) to reduce the luminescence quenching caused by the Fe core ions. The resulting Fe3O4@SiO2@SrAl2O4:Eu2+,Dy3+ NPs emit green light attributed to the 4f65d1→4f7(8S7/2) transition of Eu2+ under UV radiation and for a few seconds afterwards. This bifunctional nanocomposite can potentially be applied for the detection and separation of cells or diagnostically relevant molecules.