Environmentally friendly flame‐retardant materials produced by atmospheric pressure plasma modifications

The objective of this work was to investigate plasma modification of viscose for environmentally friendly flame‐retardant cellulosic materials. Sodium silicate layers were predeposited onto viscose and cotton flannel substrates and grafted/crosslinked using atmospheric pressure plasma. The modified cellulosic fabrics tested with the automated 45° angle test chamber showed significant improvement in their flame‐retardant properties. Analysis conducted by TGA and DSC exhibited enhanced thermal stability of the treated fabrics. Furthermore, the surface analysis (XPS and SEM) confirmed the presence of the SiO₂ network attached to the substrate even after intense ultrasound washes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Fabrication of superhydrophilic self-cleaning SiO2–TiO2 coating and its photocatalytic performance

Generally, superhydrophilic self-cleaning coatings are prepared from semiconductors with photocatalytic properties. Organic pollutants attached to the coating surface can be degraded by its photocatalytic performance realizing a self-cleaning goal. Herein, SiO₂–TiO₂ composite particles were fabricated by the hydrolysis and precipitation of TiOSO₄, and SiO₂ microspheres were chosen as carriers, which are inexpensive and environmentally friendly. Then, superhydrophilic self-cleaning SiO₂–TiO₂ coatings were fabricated by spraying the composites on the surfaces of substrates. The morphology, structure and self-cleaning performance of the SiO₂–TiO₂ coating were characterized and tested. The results revealed that nano-TiO₂ was loaded on the surfaces of SiO₂ microspheres uniformly forming a hierarchical micro/nanostructure. The SiO₂–TiO₂ composite particles exhibited excellent photocatalytic degradation performance, and the degradation rate of methyl orange (10 ppm) was more than 98% under UV irradiation for 40 min. Furthermore, the coating prepared with the SiO₂–TiO₂ composite particles exhibited superhydrophilicity. A water droplet spreads completely on the coating surface in 0.35 s, and the contact angle reaches 0°. In addition, rhodamine B (RhB) and methylene blue (MB) on the coating surface can be degraded efficiently under sunlight irradiation. The SiO₂–TiO₂ composite particles can be sprayed directly on the surfaces of concrete, brick, wood, and glass slides. Therefore, the particles showed good adaptability to different substrates. The superhydrophilic property was due to the hydrophilicity of SiO₂ and TiO₂, the hierarchical micro/nanostructure of the SiO₂–TiO₂ composites, and the photoinduced superhydrophilicity of TiO₂. The above experimental results show that the as-prepared superhydrophilic self-cleaning SiO₂–TiO₂ coating has a large application potential.     

Flocculation of reed pulp suspensions by quaternary chitosan‐nanoparticle SiO2 retention aid systems

The microparticle retention aid system has been a focus on the studies of paper‐making chemicals. N‐(2‐Hydroxy‐3‐trimethylammonio)‐propyl chitosan chlorider [quaternary chitosan (QCS)]—nanoparticle SiO₂ dual component system was investigated in this work. The adsorpton kinetic experiments indicated that there was a very fast (<1 min) polymer adsorption under good mixing conditions. Adsorption of QCS onto the fiber surface was followed by a rearrangement to reach an equilibrium conformation. At the same time, QCS chains, existing on the surface of fiber, could permeate into the porous of the fiber, resulting in the reducing of zeta potential of the cellulosic fiber. In addition, the flocculation would be increased with the increasing of SiO₂ when the fiber substrates surfaces was net positively charged by an adsorbed QCS layer. It was also found that ionic strength decreased significantly the flocculation efficiency in pure QCS system, whereas the turbidity of the reed pulp suspension increased slightly with the increasing of NaCl concentration in QCS‐SiO₂ systems. The effect of shear force on the flocculation was tested. It was shown shear led to floc breakage and decreased the flocculation. These phenomena were very obvious for one‐component system (QCS or C‐St), but the microparticle system (QCS‐SiO₂ or C‐St‐SiO₂) was shear resistance. Dynamic drainage experiment indicated that the turbidity of white water was decreased with the increasing of dosage of SiO₂ in experimental level. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Plasma resistance of quartz with a glass coating layer by aerosol deposition

ABSTRACT

To improve the plasma resistance behaviour, glass frits of SiO₂–Al₂O₃–Y₂O₃ with various powder sizes were coated onto quartz substrates by the aerosol deposition (AD) method. The thickness and microstructure of the coating layers were observed using a surface profiler and scanning electron microscopy. Plasma resistance was measured via the quartz substrate, after exposure to an inductively coupled plasma etcher. The coating layers were densely formed on the quartz substrates without additional heat treatment, and the layer thickness changed for the glass frit size distribution and AD process conditions. The SiO₂–Al₂O₃–Y₂O₃ glass coating layer showed a higher plasma resistance than quartz. Furthermore, the AD coating layer was evenly etched after plasma exposure. This study improves the lifetime of plasma chamber components in the semiconductor industry.     

Preparation and properties of fluorinated silicon two‐component polyurethane hydrophobic coatings

A polyurethane (PU) hydrophobic coating was prepared by the two‐component method, polycarbonate diol and isophorone diisocyanate becoming a two‐phase composition. The PU films with hydrophobic surface were prepared by establishing a rough structure on the surface of silica (SiO₂) modified with silane coupling agents (γ‐(2,3‐epoxypropoxy)propytrimethoxysilane (KH560) and (heptadecafluoro‐1,1,2,2‐tetradecyl)trimethoxysilane (FAS)). First, the surface of SiO₂ was covered by a layer of hydrophobic methyl and fluorocarbon (C–F) groups. Then, the SiO₂ and modified SiO₂ were obtained by the introduction of KH560 and FAS with the silanol reaction by ultrasonic stirring. The effect of SiO₂ and modified SiO₂ on the structure and hydrophobic properties of PU was investigated by a series of test instruments. The results showed that the introduction of SiO₂ and modified SiO₂ was beneficial for increasing the roughness of the PU coating surface; the roughness of FAS/SiO₂‐PU could reach up to 14.790 nm, four times better than pure PU. A hydrophobic modified PU coating with water contact angle 123° was fabricated by using the hydrophobic C–F group FAS as a low surface energy material and establishing a micro rough structure on the surface of PU. Moreover, PU modified with KH560 and FAS can reduce the glass transition temperature (T_g) of soft segments, resulting in improvement of micro‐phase separation. © 2020 Society of Chemical Industry     

Influence of fumed silica on the flame‐retardant properties of ethylene vinyl acetate/aluminum hydroxide composites

The flammability and synergistic flame‐retardant effects of fumed silica (SiO₂) in ethylene vinyl acetate (EVA)/aluminum hydroxide (ATH) blends were studied with limiting oxygen index measurements, UL 94 testing, cone calorimeter testing (CONE), and thermogravimetric analysis (TGA). The results show that the addition of a given amount of fumed SiO₂ can apparently improve UL 94 rating. The CONE data indicated that the addition of fumed SiO₂ greatly reduced the heat release rate. The TGA data showed that this synergistic flame‐retardant mechanism of fumed SiO₂ in the EVA/ATH materials was mainly due to the physical process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Reduced graphene oxide/silica nanocomposite-reinforced anticorrosive fluorocarbon coating

Reduced graphene oxide-silica (rGO/SiO₂) nanocomposite filler was prepared with a ball milling process and then modified using a coupling agent of NH₂C₃H₆Si(OC₂H₅)₃ (KH-550) to improve its dispersion in the fluoroethylene vinyl ether (FEVE) coating. The surface properties and morphologies of the modified rGO/SiO₂ (M-rGO/SiO₂) nanocomposite filler and M-rGO/SiO₂-reinforced FEVE coating were characterized by using Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). Electrochemical impedance spectroscopy (EIS) and Tafel polarization curves were applied to illustrate the corrosion resistance of the coating. The results showed that the M-rGO/SiO₂ composite can disperse well in the coating and efficiently extend the corrosion path, enhancing the anti-corrosion property of the FEVE coating. Therefore, the |Z|_{0.01 Hz} of M-rGO/SiO₂ reinforced FEVE coating maintained at around 10¹⁰ Ω·cm² in the 30 days test cycle and a protection efficiency of up to 95.18% was achieved.     

Adhesion of SiO2 thin films to plasma-treated SUS304 stainless steel substrates

The adhesion strength of the coated SiO₂ thin film to SUS304 stainless steel substrates with various surface treatment conditions is studied in this research. The surface of the SUS304 stainless steel substrate is first treated with 1000-W plasma and then a SiO₂ thin film is deposited onto the surface via radio-frequency magnetron sputtering. Scanning electron microscopy is employed to observe the surface and cross section of the coating and X-ray diffraction is used to analyze the crystallographic structure. Moreover, a nanoscratch test instrument was employed to examine the indentation, scratches, coating hardness, modulus of elasticity, coefficient of friction, and critical adhesion of the SiO₂ film and to obtain surface profiles. A comparison of the coating adhesion of the substrate surfaces with and without plasma treatment indicates that critical adhesion increases significantly after Ar/N₂/O₂ plasma treatment.     

Fabrication of superhydrophobic transparent cyclic olefin copolymer (COC)-SiO2 nanocomposite surfaces

A superhydrophobic cyclic olefin copolymer (COC) nanocomposite coating was produced with a very simple and easy method. Self-cleaning superhydrophobic COC surfaces were obtained by only adding surface hydrophobized SiO₂ nanoparticles by dip coating method. The influence of concentration of SiO₂ and the coating temperatures on the wettability of the surfaces were investigated. The surface wettability of the coatings was examined with the contact angle measurements and the surface roughness and morphology were analyzed by using atomic force microscope and scanning electron microscopy analysis. Surfaces with certain amounts of COC and SiO₂ showed superhydrophobic character with high water contact angle of 169⁰. Also, the obtained superhydrophobic surfaces show superior water repellent, high transparency, and self-cleaning characteristics.     

Use of cryogenic machining to improve the adhesion of sphene bioceramic coatings on titanium substrates for dental and orthopaedic applications

Rods of commercially pure titanium were machined using standard oil-based emulsion and cryogenic cooling, and were then coated with sphene (CaTiSiO₅) bioceramic by spray coating using an automatic airbrush. The sphene bioceramic was synthesized in-situ starting from a suspension of polysiloxane that used as SiO₂ precursor, CaCO₃ and TiO₂ nanoparticles. The suspension was deposited on the machined substrates, which were heat treated up to 950?°C in order to promote the formation of sphene ceramic. The produced coated prototypes were characterized to evaluate the effect of the machining conditions on surface roughness and microstructure of the substrate, and thereby their effect on coating adhesion. Nanoindentation tests were employed to determine the hardness and elastic modulus of the coating through its thickness. Results showed that the reduced amount of defects on the surface of the cryo-machined substrates, contributed to increase the hardness, elastic modulus and adhesion strength of the coating-substrate interfaces compared to standard machined samples, therefore improving adhesion of the coating to the underlying substrate.     

Facile fabrication of water repellent coatings from vinyl functionalized SiO2 spheres

Water repellent SiO₂ particulate coatings were prepared by a one-step introduction of vinyl groups on the coating surface. Rough surface structure and low surface energy could be directly obtained. Vinyl functionalized SiO₂ (vinyl-SiO₂) spheres with average diameter of 500 nm were first synthesized by a sol–gel method in aqueous solution using vinyltriethoxysilane as the precursor. The multilayer SiO₂ coating fabricated by dip-coating method was highly hydrophobic with a water contact angle of 145.7° ± 2.3°. The superhydrophobic SiO₂ coating with a water contact angle up to 158° ± 1.7° was prepared by spraying an alcohol mixture suspension of the vinyl-SiO₂ spheres on the glass substrate. In addition, the superhydrophobic SiO₂ coating demonstrated good stability under the acidic condition. However, it lost its hydrophobicity above 200°C because of the oxidation and degradation of vinyl groups.     

Study on silica coated chrome oxide green pigment and its performance

In this study, sodium silicate (Na₂SiO₃) was used as the precursor of SiO₂ to prepare Cr₂O₃/SiO₂ composite pigments. First, using cetyltrimethylammonium bromide to surface modification of the chromium oxide green pigment to make the surface of the particles positively charged. The negatively charged SiO₂ sol coats the surface of the pigment particles through electrostatic attraction. Then use HCl solution acid to precipitate SiO₂, and finally get Cr₂O₃/SiO₂ composite pigment. The structure of the modified pigment was analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), particle size distribution analysis, and X-ray diffraction (XRD) characterization. The influence of silica coating on the tinting strength, dispersibility of pigment in water, and hiding power of the chromium oxide green pigment were further investigated. The results demonstrate that SEM, TEM, and particle size analysis shows that this experimental method can obtain a good silica coating. When the coating quantity is 30%, the full coating of chromium oxide green by silica is achieved. According to the XRD analysis before and after the chromium oxide green coating, as the reaction temperature increases, the intensity of the SiO₂ diffraction peak becomes larger and the crystallization effect becomes better. In the test of pigment performance, it can be concluded that the coloring power, hiding power, and dispersibility of Cr₂O₃/SiO₂ composite pigments are better than those of uncoated chromium oxide green pigments.     

Analytical characterization of silane films modified with cerium activated nanoparticles and its relation with the corrosion protection of galvanised steel substrates

Galvanised steel substrates were pre-treated in bis-1,2-[triethoxysilyilpropyl]tetrasulphide silane solutions containing SiO₂ or CeO₂ nanoparticles activated with cerium ions. The surface composition was investigated by infrared spectroscopy. The film thickness was determined by scanning electron microscopy. The results showed that the barrier properties of silane films modified with nanoparticles depend upon the concentration of nanoparticles. The results also showed that the silane film thickness increases when the nanoparticles are activated with cerium ions. The anti-corrosion behaviour of the cerium activated nanoparticles was also investigated at the microscale level, in artificial induced defects, using the scanning vibrating electrode technique (SVET). The substrates treated with the silane coating modified with CeO₂ nanoparticles revealed improved corrosion behaviour comparatively to the coatings modified with SiO₂ nanoparticles. X-ray photoelectron spectroscopy and Auger electron spectroscopy experiments carried out on the defects after immersion in NaCl solutions revealed the presence of a surface film containing zinc corrosion products and cerium/ceria compounds.     

Investigation of novel intumescent flame retardant low-density polyethylene based on SiO2@MAPP and double pentaerythritol

To improve the flame-retardant property of low-density polyethylene (LDPE) composites, a novel intumescent flame retardant (IFR) consisting of ammonium polyphosphate (APP) covered by silicon dioxide and 3-(Methylacryloxyl) propyltrimethoxy silane (KH-570) (SiO₂@MAPP) and double pentaerythritol (DPER) was synthesized. Various methods were applied to structural characterization and property investigations of different samples. The results indicated that the solubility of APP decreased after coating with silicon dioxide (SiO₂) and KH-570. The flame retardancy of LDPE composites was improved with addition of IFR containing SiO₂@MAPP/DPER. With 30 wt% addition of IFR containing SiO₂@MAPP /DPER, the limiting oxygen index reached 26.8% and the tensile strength was 3.30 MPa. The tensile strength was 7.14% higher than that of 30 wt% IFR without SiO₂@MAPP. The smoke density test showed that the flue gas emission was obviously improved. The addition of SiO₂@MAPP effectively increased the residual carbon content of composites and thermal stability of the composites.     

Influence of interface structure on microstructure and dielectric properties of bismuth magnesium niobate thin films

Bismuth magnesium niobate (Bi_3/2MgNb_3/2O₇, BMN) thin films were prepared on bare SiO₂/HR-Si and Pt/TiO₂/SiO₂/HR-Si substrates by using sol-gel spin coating technique followed by rapid thermal annealing process. The influence of the interface on crystalline structure and tunable dielectric properties of the two types of BMN films were investigated. It was found that the BMN films prepared on SiO₂/Si substrate with a BMN/SiO₂ interface structure had higher orientation and better crystallinity. The deposited BMN thin films with a BMN/SiO₂ interface structure exhibited superior tunability of 52.5%, while it showed a relative small tunability value of the film with BMN/Pt interface structure. It suggests that the interface state between the films and substrates, electric field distribution, and orientation degree are responsible for the impacts on the microstructure and tunable dielectric properties of the BMN thin films.     

Synthesis and field emission properties of carbon nanotubes/nanofibers grown on pyrolyzed polyaniline–SiO2 substrates

Pyrolyzed polyaniline–SiO₂ substrates with the rough surface containing some holes were prepared by the pyrolysis of polyaniline–SiO₂ composites at temperature of 900 °C. Carbon nanotubes/nanofibers (CNTs/CNFs) were grown on the rough surface and inside the holes using a CVD method with a xylene–ferrocene mixture as a carbon and catalyst precursor source. The structural and morphological properties of CNTs were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated that the SiO₂ content of the substrates was responsible to the diameter and electron field emission properties of CNTs.     

Preparation and barrier property of poly(vinyl alcohol)/SiO<Subscript>2</Subscript> hybrid coating films

Using sol-gel method, poly(vinyl alcohol)/SiO₂ hybrid coating materials with an improved gas barrier property could be produced. Phase compatibility between organic PVA segments and inorganic silicate network in the hybrid was evaluated by analyzing FT-IR spectra and investigating the crystallization behavior in terms of X-ray diffraction patterns for the hybrid gels. For the preparation of coating film with barrier property, the biaxially oriented polypropylene (BOPP) substrate was coated with the hybrid sols by a spin coating method. Morphological analysis for the fractured surface of the hybrid gel and the surface of the coated film was performed not only to examine the microstructure of the hybrid, but also to propose evidence for the oxygen permeation behavior through the coated film. It was revealed that an optimum amount of inorganic silicate precursor, TEOS, should be used to obtain high barrier PVA/SiO₂ hybrid coating materials with enhanced micro-phase morphology and optical transparency. This homogeneous morphology densified with nano-structured silicate, obtained at optimal conditions, was found to result in a significant increase in the oxygen barrier property of film coated with PVA/SiO₂ hybrid by about 50 times relative to the pure BOPP substrate. In addition, the effect of pretreatments of the BOPP substrate surface on the barrier property was also examined.     

Thermal shock resistance of tri‐layer Yb2SiO5/Yb2Si2O7/Si coating for SiC and SiC‐matrix composites

A new tri‐layer Yb₂SiO₅/Yb₂Si₂O₇/Si coating was fabricated on SiC, C/SiC, and SiC/SiC substrates, respectively, using atmospheric plasma spray (APS) technique. All coated samples were subjected to thermal shock test at 1350°C. The evolution of phase composition and microstructure and thermo‐mechanical properties of those samples before and after thermal shock test were characterized. Results showed that adhesion between all the 3 layers and substrates appeared good. After thermal shock tests, through microcracks which penetrated the Yb₂SiO₅ top layer were mostly halted at the Yb₂SiO₅‐Yb₂Si₂O₇ interface and no thermal growth oxide (TGO) was formed after 40‐50 quenching cycles, implying the excellent crack propagation resistance of the environmental barrier coating (EBC) system. Transmission electron microscopy analysis confirmed that twinnings and dislocations were the main mechanisms of plastic deformation of the Yb₂Si₂O₇ coating, which might have positive effects on crack propagation resistance. The thermal shock behaviors were clarified based on thermal stresses combined with thermal expansion behaviors and elastic modulus analysis. This study provides a strategy for designing EBC systems with excellent crack propagation resistance.     

Simulation of SiO2/S coating deposition in a pilot plant set-up for coking inhibition

The anti-coking SiO₂/S coating was prepared on the inner surface of HK40 alloy tube in a pilot plant set-up by atmospheric pressure chemical vapour deposition (APCVD). The coating deposition was simulated using the computational fluid dynamics code, Fluent. The reaction parameters of the surface reaction for SiO₂ formation were determined based on the comparison between the experimental and the calculated values. Further, the influences of the inlet flow rate and mass concentration of source materials on the coating deposition rate were investigated. The simulated results showed that an increase of inlet flow rate led to the decrease of mass conversion of gas intermediates. The coating deposition rate along the reactor tube increased by 1–5 times as the inlet flow rate increased from 10 to 80 g min⁻¹. The mass conversion rate of the gas intermediate, Si(OH)₄, changed little at different inlet mass concentrations of source materials when the inlet flow rate was 30 g min⁻¹, and it had an increase for sulphide intermediates. The coating deposition rate along the reactor tube increased by about 10 times with increasing the inlet mass concentration from 0.2% to 2%. In the conditions we studied, SiO₂/S coating deposition was surface reaction rate limited. When the inlet flow rate was 30–40 g min⁻¹ with the resource material concentration of 1–1.6%, the SiO₂/S coating was about 15 μm at the tube outlet with the silicon-containing intermediate conversion rate of above 30% and a good uniformity of S along the reactor. This work provides a theoretical basis for optimisation of operational parameters of the anti-coking SiO₂/S coating preparation in the pilot plant set-up.     

Catalytic Fabrication of SiC/SiO2 coated graphite and its behaviour in Al2O3–C castable systems

SiC/SiO₂ coated graphite was prepared via a combined sol-gel coating and catalytic conversion route, using graphite flake and tetraethyl orthosilicate as the starting materials, and Fe(NO₃)₃·9H₂O as the catalyst precursor. X-ray diffraction analysis and microstructural examination revealed that a homogeneous coating comprising SiC and cristobalite (SiO₂) and covering the whole surface of graphite was formed. As prepared SiC/SiO₂ coated graphite exhibited better oxidation resistance and water wettability than its uncoated counterpart. Also, oxidation resistance and slag corrosion resistance of a model Al₂O₃–C castable using coated graphite as a carbon source were better than in the case of its counterpart using uncoated graphite.