SiO2 Coatings Research Articles

Mechanistic Insights on Permeation of Water over Iron Cations in Nanoporous Silicon Oxide Films for Selective H2 and O2 Evolution

Electrocatalysts encapsulated by an ultrathin and semipermeable oxide layer offer a promising avenue for efficient, selective, and cost-effective production of hydrogen through photoelectrochemical water splitting. This architecture is especially attractive for Z-scheme water splitting, for which a nanoporous oxide film can be leveraged to mitigate undesired, yet kinetically facile, reactions involving redox shuttles, such as aqueous iron cations, by limiting transport of these species to catalytically active sites. In this work, molecular dynamics simulations were combined with electrochemical measurements to provide a mechanistic understanding of permeation of water and Fe(III)/Fe(II) redox shuttles through nanoporous SiO2 films. It is shown that even for SiO2 pores with a width as small as 0.8 nm, water does not experience any energy barrier for permeating into the pores due to a favorable interaction with hydrophilic silanol groups on the oxide surface. In contrast, permeation of Fe(III) and Fe(II) into microporous SiO2 pores is limited due to high energy barriers, which stem from a combination of distortion and dehydration of the second and third ion solvation shells. Our simulations and experimental results show that SiO2 coatings can effectively mitigate undesired Fe(III)/Fe(II) redox reactions at underlying electrodes by attenuating permeation of iron cations, while allowing water to permeate and thus participate in water splitting reactions. In a broader context, our study demonstrates that selectivity of solvated cations can be manipulated by controlling the pore size and surface chemistry of oxide films.

Deposition of Thick SiO2 Coatings to Carbonyl Iron Microparticles for Thermal Stability and Microwave Performance.

Thick dielectric SiO2 shells on the surface of iron particles enhance the thermal and electrodynamic parameters of the iron. A technique to deposit thick, 500-nm, SiO2 shell to the surface of carbonyl iron (CI) particles was developed. The method consists of repeated deposition of SiO2 particles with air drying between iterations. This method allows to obtain thick dielectric shells up to 475 nm on individual CI particles. The paper shows that a thick SiO2 protective layer reduces the permittivity of the 'Fe-SiO2-paraffin' composite in accordance with the Maxwell Garnett medium theory. The protective shell increases the thermal stability of iron, when heated in air, by shifting the transition temperature to the higher oxide. The particle size, the thickness of the SiO2 shells, and the elemental analysis of the samples were studied using a scanning electron microscope. A coaxial waveguide and the Nicholson-Ross technique were used to measure microwave permeability and permittivity of the samples. A vibrating-sample magnetometer (VSM) was used to measure the magnetostatic data. A synchronous thermal analysis was applied to measure the thermal stability of the coated iron particles. The developed samples can be applied for electromagnetic compatibility problems, as well as the active material for various types of sensors.

Nanoporous Mg-doped SiO2 nanoparticles with tunable infrared emissivity toward effective radiative cooling coatings

SiO2 is the hotspot radiative cooling material due to its selective radiation or the Mie resonance effect generated by micro/nanospheres of a specific size. Herein, we demonstrate the modulation of the infrared emissivity of the intrinsic SiO2 at the atmospheric window by doping Mg2+ in nanoporous SiO2 nanoparticles via a modified stöber method. The effects of the Mg-doping on the crystallinity, morphology, infrared emissivity of the nanoparticles and the radiative cooling properties of the corresponding coatings are investigated. Results show that the Mg-doping at a level of 0.226–2.26 % can induce cristobalite nanocrystals after sintering at 1000 ℃, transform the morphology from spheres to irregular nanoporous particles, and improve the infrared emissivity up to 0.96. XPS proves the formation of Mg-O bonds and the change of the binding energy of Si 2p and O 1s, supporting the successful doping of Mg2+ in the lattice of SiO2. All-inorganic Mg-doped SiO2 coatings on FTO substrates are prepared via tape casting, which exhibit rough and porous microstructure and high solar reflectivity up to ∼86 %, with the thickness of ∼90 µm. The Mg-doping improves the radiative cooling capacity of the coatings obviously, and the best temperature reduction of 17.8 ℃ compared with the empty space is achieved, 3–5 ℃ lower than the pure SiO2 coating and 4.5 ℃ lower than the commercial SiO2 coating. Our work offers an effective way to modulate the infrared emission of emitter, enriching the technical measures to improve the overall performance of the sub-ambient radiative cooling devices.

Effect of Coating Thickness on the Atomic Oxygen Resistance of Siloxane Coatings Synthesized by Plasma Polymerization Deposition Technique

Atomic oxygen in the low Earth orbit (LEO) environment is highly oxidizing. Due to the high flight speed of spacecraft, the relative kinetic energy of high-flux atomic oxygen bombarding the spacecraft surface can reach up to about 5 eV. Therefore, atomic oxygen is one of the most dangerous space environment factors in LEO, which seriously affects the safe operation and service life of spacecraft in orbit. In order to meet the requirements for the high reliability and long lifetime of spacecraft, effective protection measures must be taken on their sensitive surfaces. Siloxane is a coating with an organic–inorganic hybrid structure. Compared with SiO2 and other inorganic atomic oxygen protective coatings, it has better flexibility and is better at anti-atomic oxygen performance. In this paper, the plasma polymerization deposition technique was used to prepare large-area siloxane coatings on different substrates with different thicknesses for improving atomic oxygen resistance by optimizing the process parameters. The thickness of the coating was measured by different methods, and the results showed that the thickness distribution was consistent. By observing the surface morphology of the coating, it was uniform and compact without obvious defects, so the uniformity of large-area coating was also ideal. The adhesion and heat/humidity resistance of siloxane coatings were examined by pull-off testing and damp-heat testing, respectively. The results showed that the siloxane coatings with a thickness of about 400 nm exhibited better physical properties. At the same time, the ground simulation testing of atomic oxygen confirmed that siloxane coatings with a thickness of 418 nm presented the best performance of atomic oxygen resistance. The atomic oxygen erosion yield of siloxane coatings with a thickness of 418 nm was as low as 5.39 × 10−27 cm3/atoms, which was three orders of magnitude lower than that of the uncoated Kapton substrate and presented a good anti-atomic oxygen performance. Meanwhile, it has also successfully passed the damp-heat test. The coating thickness is only several hundred nanometers and does not increase the weight of the spacecraft, which makes it a relatively ideal LEO atomic oxygen protection material. Furthermore, a possible mechanism was proposed to explicate the physicochemical process of atomic oxygen attacking the coating materials.

ZnO–SiO2 composite coating with anti-reflection and photoluminescence properties for improving the solar cell efficiency

Photoluminescence and anti-reflection both have the potential to improve solar cells efficiency. In order to obtain a coating with photoluminescence and anti-reflection both properties, in this paper, ZnO nanoparticles as photoluminescent materials were added into SiO2 sol to prepare anti-reflection coatings by the dip-coating procedure. Different contents of polyethylene glycol were added to the ZnO–SiO2 composite sol to adjust the refractive index of the ZnO–SiO2 coatings. The peak transmittance of the best coating is up to 98.37% at 615 nm and the average transmittance in the 400–1100 nm band is 95.64%. Our results prove that photoluminescence can further improve the utilization of light in the 300–400 nm band. In general, the ZnO–SiO2 coating can increase the photovoltaic conversion efficiency by 6.25%. Therefore, the results show that the ZnO–SiO2 coatings with anti-reflection and photoluminescence have potential applications in Si solar cells and other photovoltaic systems.

Sol-Gel Synthesis of MgO–Al2O3–ZrO2–SiO2 Coatings on Quartz Ceramics

Sol-Gel Synthesis of MgO–Al2O3–ZrO2–SiO2 Coatings on Quartz Ceramics

Acrylonitrile Butadiene Polystyrene–SiO2 Composite Nanostructures for Self-Regulated Superhydrophobic Liquid Dosage Systems

Superhydrophobic coatings are widely studied for fluid regulation due to their water-repellent surface characteristics. However, there are not many reports on fluid behavior when it flows from a region of higher wettability to that of lower wettability. A fundamental understanding of such behavior would be very useful for regulating the fluid flow through a superhydrophobic channel. Therefore, this work focused on the fabrication of superhydrophobic nanostructured coatings inside fine cylindrical channels and the investigation of the fluid flow behavior through them. The superhydrophobic SiO2 coatings were obtained through an ultrasound-assisted one-step immersion technique. A self-stratified mechanically durable conformal superhydrophobic coating was obtained inside millimeter-sized fine 3D structures. A binder-free precursor solution has low viscosity and thereby enhances the penetration of the solvent into the polymer surface through ultrasonication. The self-stratification-based surface formation mechanism was explained using scanning electron microscopy images. The fluid behavior inside the superhydrophobic channels was experimentally investigated by analyzing the flow through the hollow cylindrical superhydrophobic channels. Experiments were conducted for different channel lengths (l) and radii (r), and mathematical formulations were developed to determine the maximum pressure (Pmax) that the superhydrophobic cylinders could hold when the fluid inside the channel was under static equilibrium. Finally, a self-regulated fluid delivery system was postulated based on the experimental and theoretical findings.

Effects of sol contents and sintering temperatures on SiO2 coated needled carbon fibre felt composites

ABSTRACT Carbon fibre has excellent mechanical properties at high temperatures but weak oxidation resistance. The paper prepared the anti-oxidative silica coating on the surface of needled carbon fibre felt by the sol–gel method and discussed the effects of sol content and sintering temperature on the coatings’ performance. The phase composition, density, thermal conductivity and thermal stability of derived composites were characterised, and the structure and morphology of SiO2 coatings were also analysed by scanning electron microscopy. The results indicated that a uniform and complete coating could be formed on the fibre surface when the sol content exceeds 20%. Ceramic particles sintered below 1200°C were amorphous silica, while those sintered at 1350°C were cristobalite. Compared with other processes, 20% silica sol content or sintering at 1350°C could provide better antioxidant protection. The new coating process is significant for retarding fibre oxidation in a high-temperature environment.

High-repetition rate picosecond laser-induced damage properties of Ta2O5:SiO2 coatings

High-repetition rate laser-induced damage of Ta2O5:SiO2 coatings was investigated at 355 nm wavelength and a repetition rate of 30 kHz. Laser-induced damage thresholds of coatings with different mixture ratios were measured. The relationships between laser-induced damage threshold and the material band gap and defect absorption were analyzed. Laser-induced damage threshold decreased with increase in number of laser pulses owing to enhancement of the absorption. Enhancement of absorption is attributed to the increase in density of mid-state defects induced by the picosecond laser pulses. The relationship between mid-state defects and the material mixture ratio was also analyzed.

Ultralow Index SiO2 Antireflection Coatings Produced via Magnetron Sputtering.

Antireflection (AR) coatings with graded refractive index profiles approaching air offer unparalleled AR performance but lack a scalable fabrication process that would enable them to be used more widely in applications such as architecture and solar energy conversion. This work introduces a sputtering-based sacrificial porogen process to fabricate multilayer nanoporous SiO2 coatings with tunable refractive index down to neff = 1.11. Using this approach, we demonstrate a step-graded bilayer AR coating with outstanding wide-angle AR performance (single side average reflectivity in the visible spectrum ranges from 0.2% at normal incidence to 0.7% at 40°), good adhesion, and promising environmental durability. These results open up a path to produce ultrahigh performance AR coatings over large area by using industrial-scale magnetron sputtering systems.

Hybrid Coatings of SiO2–Recycled PET Unsaturated Polyester Resin by Sol-Gel Process

Hybrid coatings of SiO2 and recycled unsaturated polyester resin (R-UPR) from recycled polyethylene-terephthalate (PET) were prepared by the sol-gel process on glass substrates. First, SiO2 was synthesized by the sol-gel process using a tetraethyl orthosilicate (TEOS) solution. Next, bis(2-hydroxypropyl-terephthalate) (BHPT) was synthesized from mechanical and chemical recycling (glycolysis) of post-consumer PET bottles in propylene glycol (PG) using ZnA as catalyst, in a Vessel-type reactor (20–200 °C); maleic anhydride (MA) was added and, following the same procedure, the unsaturated polyester (UP) was synthetized, which was cooled to room temperature. Next, styrene (St) and benzoyl-peroxide (PBO)-initiator were added to obtain R–UPR. TEOS (T) and three hybrid solutions were synthesized, with molar ratios of 0:1:0 (T), 1:2:0.25 (H1), 1:1:0.25 (H2), and 1:0:0.25 (H3) for R–UPR:TEOS:3-trimethoxy-(silyl)-propyl-methacrylate (TMSPM), respectively, with which TC, HC1, HC2, and HC3 coatings were elaborated using the immersion technique and polymerized (120 °C for 24 h). The solutions were characterized by FT–IR and TGA, and the coatings by SEM, nanoindentation, AFM, adhesion, and contact angle. The results showed that SiO2 enhanced mechanical (hardness and Young’s modulus) and thermal properties of the R-UPR. The coatings adhered perfectly to the substrate, with thicknesses of micrometer units and a flat surface; in addition, hydrophilicity decreased as SiO2 decreased.

Design and optimization of single, double and multilayer anti-reflection coatings on planar and textured surface of silicon solar cells

The present silicon solar cell industry's main concern is to increase efficiency by minimizing the surface reflection. As a result, lately, much attention has been paid to the composition and number of the layers used for anti-reflection coatings in order to reduce surface reflection. In the present work, single, double, triple, and quadruple anti-reflection coatings on silicon solar cells have been designed and optimized using FDTD and PC1D simulation methods. The different combinations of SiO2, SiON, Si3N4, and SiNx coatings on both planar and textured surfaces were simulated and their optical and electrical parameters were investigated. Compared to planar surfaces, the designed coatings on textured surfaces showed better optical and electrical results for almost all investigated parameters. On textured surfaces, SiO2/Si3N4/SiNx acquired the lowest weighted average reflection (0.121%), SiO2/SiNx, SiON/SiNx, SiO2/Si3N4/SiNx, and SiO2/SiON/Si3N4/SiNx the highest Jsc(38.5 mA/cm2) and finally SiO2/Si3N4/SiNx and SiO2/SiON/Si3N4/SiNx both the highest Voc(705.7 mV) and η(23%).

Argon and Other Defects in Amorphous SiO2 Coatings for Gravitational-Wave Detectors

Amorphous SiO2 thin films are one of the two components of the highly reflective mirror coatings of gravitational-wave detectors. For this study, layers of amorphous SiO2 on crystalline Si substrates were produced by ion-beam sputtering (IBS), using accelerated neutralized argon ions as sputtering particles, as is the case for the actual mirror coatings of gravitational-wave detectors. The aim of this study is to investigate the possible presence of various defects in the materials in order to improve the coating quality. We provide evidence that, due to the synthesis method, about 0.2 wt.% of Ar is present in the coatings, and it can be released by means of thermal treatments, starting around 400 °C. The time and temperature to obtain the total release of Ar increases with the coating thickness; for a thickness of 100 nm, all argon is released below 600 °C, while an isotherm of one hour at 900 °C is necessary for a coating 5 μm thick. Besides the Ar atoms left from the synthesis, other defects, such as Si clusters and silicon dangling bonds, are present in the coatings. The concentration of both of them is strongly reduced by thermal treatments either in vacuum or in air. The overall thickness of the coating is slightly increased after thermal treatments, as witnessed by the change of the period of interference fringes.

Preparations, characterizations, thermal and flame retardant properties of cotton fabrics finished by boron-silica sol-gel coatings

This work aims to improve the thermal stability and flame retardancy of cotton fabrics by using sol-gel processes. A hybrid sol was prepared by using silica sol, coupling agent of γ-Methacryloxypropyltrimethoxysilane (KH570) and flame retardant of sodium octaborate tetrahydrate (DOT) and then finished on the surface of cotton fabric. Fourier infrared spectroscopy (FTIR), X-ray electron spectroscopy (XPS), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA), limiting oxygen index (LOI) and vertical burning test (VBT) were used to characterize the functional groups, surface element compositions, microscopic morphologies, thermal stability and flame retardancy of cotton fabrics, respectively. The results show that sols are successfully converted into gel coatings onto cotton fabrics. SiO2-KH570-DOT@Cotton shows the highest char residue rate (41.7%) and ΔLOI/Δm (6.0%/g) values. SiO2, KH570 and DOT coatings have shown some competitive but more synergistic effects in flame retardancy. The three-dimensional structure of SiO2 gel can provide structural support, effectively block heat transfer and transports of oxygen. KH570 has a significant coupling effect of increasing interfacial compatibility between sols and cotton fabrics. DOT is thermally decomposed to generate boric acid to accelerate the carbonization degrees of cotton fibers and thus improve the thermal stabilities of char layers.

Effect of gamma irradiation on the critical heat flux of sintered nano-coated surfaces

The electrophoretic deposition (EPD) technique was used to manufacture uniform SiO2, Al2O3, ZrO2, and TiO2 thin film coatings on thin steel plates (1.5 mm by 90 mm) to study heat transport properties when in contact with water at boiling temperature. To find the thickness and uniformity of the coatings, scanning electron microscope (SEM) images were made. The captured images showed that the coating thickness is uniformly increased by the EPD method. To investigate the effect of sintering, the coated plates were placed in a furnace at various temperatures. To investigate the effect of gamma irradiation on the critical heat flux (CHF) of the coated surfaces, the test specimens were irradiated in a gamma cell with different dose rates, and then BET, SEM, and EDS analyses were performed. Significant enhancement in CHF, for the hydrophilic surfaces, can be achieved by the EPD method. The results showed that the CHF for the sintered nano-coated surfaces, SiO2, Al2O3, ZrO2, and TiO2, increase by 24%, 23%, 19%, and 10%, compared to those of unsintered nanocoated surfaces, respectively. It was observed that irradiation significantly decreases the maximum pore diameter while it increases the porosity, pore surface area, and pore volume. The CHF of the nano-coated surfaces irradiated at 300 kGy increased by 12%, 8%, 5%, and 12% for SiO2, Al2O3, ZrO2, and TiO2, respectively. Nevertheless, the effect of gamma irradiation on the sintered surfaces was insignificant.

Tannic acid reinforced sol-gel silica coatings for corrosion protection of zinc substrates

Silica (SiO2) coatings are a widely discussed inorganic coating alternative, offering a feasible and simple method of passive corrosion protection, with the option of enhancement by incorporating different inhibitors into the matrix. The novelty of the present study lies in the reinforcement of the sol-gel SiO2 coating system, by the addition of different tannic acid (TA) amounts in the sol phase and producing nano scale coatings by dip-coating technique, on Zn. Tannic acid is a non-toxic substance, which acts as anodic corrosion inhibitor. Long term corrosion measurements were carried out to check the durability and corrosion resistance of the thin coatings. They were characterized by Electrochemical Impedance Spectroscopy and Potentiodynamic polarization curves, as well as by physical methods (SEM, contact angle and adhesion measurements). The pseudo-porosity of the coatings was also evaluated. It has been concluded that SiO2 coatings containing TA in an optimal concentration show lower corrosion current densities than simple SiO2 coatings, good adhesion to the zinc substrate, and lower porosity. The interactions occurring between the SiO2 and TA put in evidence by FT-IR, Raman spectroscopy offer an explanation of the better corrosion behavior of the SiO2+TA coating compared to the pure SiO2.

Multipass lock-in thermography for the study of optical coating absorption.

The development of high-power lasers requires optics with very low absorption to avoid detrimental thermal effects. In this work, we discuss our recent developments on the use of lock-in thermography to measure absorption. We apply this technique in a multipass configuration to increase the effective power on the tested samples. We present a system based on a kW-class ytterbium fiber laser operating at 1.07 µm wavelength, which enables exposing samples to 5 kW effective power and measuring absorption in the ppm range. The implementation, calibration procedure, and obtained performance are discussed with some applications to single-layer coatings of HfO2,Ta2O5,TiO2,Nb2O5, and SiO2 deposited by plasma-assisted electron beam deposition.

Numerical Modeling of the Mechanical Reliability of Multicoated Nanoencapsulated Phase‐Change Materials with Improved Thermal Performance

Nanoencapsulated phase‐change materials (nePCMs) are investigated for enhancing thermal energy storage. However, the shell of these nanocapsules may fail due to stress developed during thermal processes, leading to melting enthalpy loss. To overcome this problem, SiO2 and Al2O3 coatings on Sn nanoparticles are synthesized by atomic layer deposition (ALD). To study the influence of shell thickness and composition on the probability of failure (POF) of nePCM shells in single‐ and multicoated nePCMs, a probabilistic numerical tool combining Monte Carlo techniques and a thermomechanical finite‐element model with phase change are used. The uncertainties of the material and geometrical properties of nePCMs are included in the analysis. Both deterministic and probabilistic failure criteria are taken into account to consider the effect of dispersion on tensile strength. The results indicate that multicoated nePCMs enhance thermomechanical performance in relation to their single‐coated counterparts. Both the numerical simulations and experiments confirm that the POF of nePCM shells and melting enthalpy loss in multicoated nePCMs lower with shell thickness. The results after 50 ALD cycles indicate that Al2O3 coatings exhibit better performance because a POF of 1.66% is obtained with 1.1% enthalpy loss, while the POF for SiO2 is 72.38% with 3.5% enthalpy loss.

High-Activity and Excellent-Reusability Γ-Fe2o3/Sio2 Coating on Tc4 Titanium Alloy by Plasma Electrolytic Oxidation for Enhanced Photo-Fenton Degradation

High-Activity and Excellent-Reusability Γ-Fe2o3/Sio2 Coating on Tc4 Titanium Alloy by Plasma Electrolytic Oxidation for Enhanced Photo-Fenton Degradation

Transparent superhydrophobic film with anti-fouling and anti-scaling ability by facile method of dip-coating SiO2 Sol

In the past decades, the studies of materials with transparency and durable superhydrophobicity have captured much attention because of the versatile uses in outdoor glass wall, automobile windshield and solar panel. In this paper, a superhydrophobic and transparent SiO2 film with transmittance over 44% was obtained on glass substrate with a facile method of dip-coating without further modification. The contact angle and sliding angle of water droplet on the superhydrophobic film is 163.1° and 4°, respectively. The results reveal the performance of superhydrophobicity originates from the synergistic effects of rough SiO2 structures and hydrophobic alkyl with low surface energy. The SiO2 coating exhibits self-cleaning ability, anti-fouling property and anti-scaling performances. Furthermore, the SiO2 coatings have good thermal stability and resistance ability to acid and base. The techniques adopted here have the advantage of simple process, low cost and fluorine-free treatment, which may provide an useful reference for the preparation of transparent and superhydrophobic film in practice.