Effect of heat‐treatment on the performance of gas barrier layers applied by atomic layer deposition onto polymer‐coated paperboard

The effect of heat treatment on the gas barrier of the polymer‐coated board further coated with an Al₂O₃ layer by atomic layer deposition (ALD) was studied. Heat treatment below the melting point of the polymer followed by quenching at room temperature was used for the polylactide‐coated board [B(PLA)], while over‐the‐melting‐point treatment was utilized for the low‐density polyethylene‐coated board [B(PE)] followed by quenching at room temperature or in liquid nitrogen. Heat treatment of B(PLA) and B(PE) followed by quenching at room temperature improved the water vapor barrier. However, because of the changes in the polymer morphology, quenching of B(PE) with liquid nitrogen impaired the same barrier. No improvement in oxygen barrier was observed explained by, e.g., the spherulitic structure of PLA and the discontinuities and possible short‐chain amorphous material around the spherulites forming passages for oxygen molecules. This work emphasizes the importance of a homogeneous surface prior to the ALD growth Al₂O₃ barrier layer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Nano‐engineered nickel catalysts supported on 4‐channel α‐Al2O3 hollow fibers for dry reforming of methane

A nickel (Ni) nanoparticle catalyst, supported on 4‐channel α‐Al₂O₃ hollow fibers, was synthesized by atomic layer deposition (ALD). Highly dispersed Ni nanoparticles were successfully deposited on the outside surfaces and the inside porous structures of hollow fibers. The catalyst was employed to catalyze the dry reforming of methane (DRM) reaction and showed a methane reforming rate of 2040 Lh^?1gNi^?1 at 800°C. NiAl₂O₄ spinel was formed when Ni nanoparticles were deposited on alpha‐alumina substrates by ALD, which enhanced the Ni‐support interaction. Different cycles (two, five, and ten) of Al₂O₃ ALD films were applied on the Ni/hollow fiber catalysts to further improve the interaction between the Ni nanoparticles and the hollow fiber support. Both the catalyst activity and stability were improved with the deposition of Al₂O₃ ALD films. Among the Al₂O₃ ALD coated catalysts, the catalyst with five cycles of Al₂O₃ ALD showed the best performance. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2625–2631, 2018     

Preparation of phosphor coated with a polymer by emulsion polymerization and its application in low‐density polyethylene

The long‐afterglow phosphor SrAl₂O₄ : Eu²⁺, Dy³⁺ is liable to hydrolyze in water with deterioration of its luminescent properties. In this study, in situ emulsion polymerization was first used to prepare phosphor coated with poly(methyl methacrylate‐co‐butyl acrylate) [P(MMA‐co‐BA)] to improve water resistance. Fourier transform infrared spectra suggested that the polymer attached to the phosphor by chemical bonding. Observation by scanning electron microscopy (SEM) showed that a polymer layer formed on the surface of the phosphor. The resistance to water of the phosphor coated with the polymer layer was much better than that of the uncoated phosphor because the transparent polymer layer could suppress its hydrolysis process. Low‐density polyethylene (LDPE) plastics, doped with long‐afterglow phosphors, were manufactured with an extrusion technique. Through coating with P(MMA‐co‐BA), the compatibility of phosphor with the LDPE matrix was improved, as determined by SEM. The luminous LDPE plastics blended with the phosphor coated with polymer showed long and strong phosphorescence with little loss of persistence phosphorescence compared to the uncoated phosphor. The LDPE plastics still retained their mechanical properties through doping with 3% (mass fraction) of the phosphors. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Influence of argon plasma on the deposition of Al2O3 film onto the PET surfaces by atomic layer deposition

In this paper, polyethyleneterephthalate (PET) films with and without plasma pretreatment were modified by atomic layer deposition (ALD) and plasma-assisted atomic layer deposition (PA-ALD). It demonstrates that the Al₂O₃ films are successfully deposited onto the surface of PET films. The cracks formed on the deposited Al₂O₃ films in the ALD, plasma pretreated ALD, and PA-ALD were attributed to the energetic ion bombardment in plasmas. The surface wettability in terms of water contact angle shows that the deposited Al₂O₃ layer can enhance the wetting property of modified PET surface. Further characterizations of the Al₂O₃ films suggest that the elevated density of hydroxyl -OH group improve the initial growth of ALD deposition. Chemical composition of the Al₂O₃-coated PET film was characterized by X-ray photoelectron spectroscopy, which shows that the content of C 1s reduces with the growing of O 1s in the Al₂O₃-coated PET films, and the introduction of plasma in the ALD process helps the normal growth of Al₂O₃ on PET in PA-ALD.     

Interaction of slip‐ and flame‐spray coated carbon‐bonded alumina filters with steel melts

Ceramic foam filters play an essential role in the quest for cleanliness of cast steel parts as they facilitate turbulence reduction during mold filling as well as removal of nonmetallic inclusions. A coating on these filters is able to increase their strength and filtration efficiency by improving the adhesion of inclusions to the filter strands. In this study, Al₂O₃‐C filters were coated with an alumina slip via slip and flame spraying. The phase composition and the microstructure of the coatings were investigated before and after immersion into molten steel contained in a metal casting simulator. After contact with molten steel, Al₂O₃‐C reference filter shows intense decarburization which often influence the quality of cast steel parts due to formation of gas bubbles. Slip‐sprayed alumina coatings on such a filter promote the deposition of inclusions due to formation of a vitreous alumina layer but will also cause gas bubble formation as they exhibit a high porosity. Flame‐spray coatings have low porosity and hence, prevent formation of gas bubbles. Furthermore, they showed the highest reactivity toward the steel melt and hence, are recommended for filtration of cast products with a high demand on cleanliness.     

Al2O3/CrAlSiN multilayer coating deposited using hybrid magnetron sputtering and atomic layer deposition

In this study, Al₂O₃/CrAlSiN multilayer coatings with various periods were prepared using a hybrid process involving overlapping magnetron sputtering of CrAlSiN and atomic layer deposition (ALD) of Al₂O₃. The influence of the number of Al₂O₃ layers on the mechanical properties, corrosion behavior and oxidation characteristics of the coatings was studied using nano/micro indentation, electrochemical corrosion, and high temperature static oxidation tests. The results show that the multilayer structure can effectively prevent crack propagation during the coating and subsequently increase the coating toughness. A substantial improvement in the resistance to electrochemical and oxidation corrosion was observed in the Al₂O₃/CrAlSiN multilayer coatings and increasing the number of Al₂O₃ layers dramatically increases the corrosion durability. The Al₂O₃ ALD layers are expected to inhibit the diffusion of corrosive substances such as ions and oxygen and the increase of the Al₂O₃ layer number decreases the diffusion fluxes of the coating elements to the surface and limit the oxide growth, resulting in the evolution of the oxidation produces from irregular particles to nano-walls/fibers. It is supposed that the PVD/ALD hybrid process may open a new hard coating design concept by providing a superior toughness and corrosion/oxidation resistance.     

Atomic layer deposition onto carbon fiber fabrics

Carbon fiber fabrics, consisting of interwoven bundles of 3000 single fibers, were coated with Al₂O₃ using the atomic layer deposition (ALD) process, exposing the fabrics to alternating pulses of trimethyl aluminium and water vapors. The thickness and uniformity of the coatings were investigated using scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The obtained coatings were conformal, 84 ALD cycles gave rise to approximately 20‐nm‐thick coatings and 168 ALD cycles to approximately 40‐nm‐thick coatings. It was found, that a uniform coating can be obtained at a purge time of 40 seconds. Reducing purge times below 20 seconds gives rise to increased particle growth and thus the coating becomes inhomogeneous. Initially, the samples that were coated had a size of 2×10 cm (thickness 0.3 mm). The size of the fabric was subsequently increased up to 8×20 cm and a uniform coating of the same quality was obtained. By oxidizing the coated fabrics, fabrics composed of interwoven alumina microtubes were obtained. Infiltration of the microtubes with solutions of two distinguishable fluorescent dyes showed that interchange of the dyes between warp and weft microtubes occurs, but is absent at approximately 20% of the crossovers. Taking all our findings into account, we conclude that the majority of the fibers were separated from each other by the coating prior to the oxidation. This work demonstrates that ALD is a suitable method to produce thin, conformal coatings on the surface of carbon fiber fabrics.     

Electrochemically induced alumina coatings on stainless steel: composition and behaviour at high temperature

Alumina coatings were formed by electrolytic treatment on an Fe-17% Cr stainless steel functionalized by surface conversion treatment to induce a particular surface morphology, suited to anchoring the ceramic layer. As deposited, the coatings appeared amorphous. They were composed of two layers: the superficial layer was constituted only of aluminium compounds while the deep layer had a composition gradient. Heating the coated steel caused interface reactions between the electrochemically-induced deposit and the initial conversion coating compounds. These reactions act to strengthen coat adhesion to the substrate with formation of crystallized mixed oxide such as Fe(Cr,AI)₂O₄. Moreover, Al₂O₃ phases appeared and acted as a barrier which prevented the thermal oxidation of the stainless steel.     

Electrochemical and time-of-flight secondary ion mass spectrometry analysis of ultra-thin metal oxide (Al2O3 and Ta2O5) coatings deposited by atomic layer deposition on stainless steel

Ultra-thin (5–50 nm) layers of aluminium and tantalum oxides deposited by atomic layer deposition (ALD) on a stainless steel substrate (316L) for corrosion protection have been investigated by electrochemical methods (linear scan voltammetry, LSV, and electrochemical impedance spectroscopy, EIS) and time-of-flight secondary ion mass spectrometry, ToF-SIMS. The effects of the deposition temperature (250 °C and 160 °C) and coating thickness were addressed. ToF-SIMS elemental depth profiling shows a marked effect of the organic and water precursors used for deposition and of the substrate surface contamination on the level of C and OH trace contamination in the coating, and a beneficial effect of increasing the deposition temperature. The polarization data show a decrease of the current density by up to four orders of magnitude with increasing coating thickness from 5 to 50 nm. The 50 nm films block the pitting corrosion in 0.8 M NaCl. The uncoated surface fraction (quantified from the current density and allowing a ranking of the efficiency of the coating, also confirmed by the capacitance and resistance values extracted from the EIS data) was 0.03% with a 50 nm thick Al₂O₃ film deposited at 250 °C. The correlation between the porosity values of the coatings and the level of C and OH traces observed by ToF-SIMS points to a marked effect of the coating contaminants on the sealing performance of the coatings and on the corrosion resistance of the coated systems.     

Nickel–alumina graded coatings obtained by dipping and EPD on nickel substrates

Nickel substrates have been coated by Ni/Al₂O₃ composite films by a dipping process using aqueous suspensions that contain a temporary binder. Two-layer and three-layer graded coatings have been produced, consisting of pure Ni powder and Ni/Al₂O₃ composites with Al₂O₃ contents of 15 and 30 vol.% as intermediate layers to release sintering and thermal stresses. The laminates were further coated with a ceramic layer of Al₂O₃/ZrO₂ that was deposited by electrophoretic deposition using a non-aqueous suspension. A continuous, thin Al₂O₃ layer surrounding Ni grains developed at the intermediate composite layer of Ni/Al₂O₃ allows the ceramic coating to maintain strongly adhered to the nickel substrate by means of a porous substrate/coating interface.     

Effects of SnO2 layer coated on carbon nanofiber for the methanol oxidation reaction

Carbon nanofibers (CNFs) are used as active materials for electrodes in various energy devices, such as lithium ion secondary batteries, supercapacitors, and fuel cells. Recent studies have shown that nanoscale coatings on carbon nanotubes increase the output and lifespan of these devices owing to the improvement of their mechanical and chemical properties. Among various coating methods, atomic layer deposition (ALD) can adjust the thickness of the coating layer conformally without any directional growth. Therefore, ALD can coat particles with high aspect ratios, such as CNFs, even at nanometer levels of thickness.In this work, we grew two different morphologies of a SnO₂ layer on CNF. We used two types of ALD equipment: flow-type ALD (static ALD), and fluidized bed reactor-type ALD (dynamic ALD). Static ALD could form a discontinuous SnO₂, while a uniform SnO₂ layer was formed by pre-inserting a layer of Al₂O₃. On the other hand, dynamic ALD formed a uniform SnO₂ layer without pre-insertion of an Al₂O₃ layer. X-ray photoelectron spectroscopy analysis revealed that both Sn⁴⁺ and Sn²⁺ were present in SnO₂ on the CNF deposited by static ALD, probably due to the formation of an interfacial layer between the SnO₂ and CNF. When the dynamic ALD method was used, only Sn⁴⁺ was present in the SnO₂ on CNF. Cyclic voltammetry analysis was performed to characterize the electrochemical properties of the SnO₂-coated CNF as an electrode on a direct methanol fuel cell. It was revealed that the discontinuous SnO₂ on CNF deposited by static ALD showed the highest current efficiency as well as enhanced electrocatalytic stability.     

Preparation and characterization of magnetic star‐shaped amphiphilic copolymer nanoparticles of S‐Fe3O4‐PLA‐b‐MPEG

Magnetic star‐shaped amphiphilic copolymers (S‐Fe₃O₄‐PLA‐b‐MPEG) consisting of Fe₃O₄ as the core, poly(L ,D ‐lactide) (PLA) as the inner layer, and monomethyl polyethylene glycol (MPEG) as the out shell were synthesized. The syntheses included ring‐opening polymerization of L ,D ‐lactide initiated by hydroxyl modified Fe₃O₄ (Fe₃O₄‐(OH) _n), followed by the esterification of the PLA with MPEG. The structure of the star block copolymers were characterized by Fourier Transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction, transmission electron microscopy, nanoparticle size analyzer, and vibrating sample magnetometer. The nanoparticles in aqueous solution were made from the amphiphilic star copolymer. The average size of the nanoparticles was adjustable and increased with the increase of the PLA segments in the copolymer. The cytotoxicity grade of the nanoparticles was zero determined by the analysis of cytotoxicity. The nanoparticles could potentially be used as the drug vehicles for magnetic‐response controlled release. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Mechanical recycling of nanocellulose containing multilayer packaging films

The aim of this study was to demonstrate mechanical recycling of low density polyethylene (LDPE) films coated with a thin layer of cellulose nanofibrils (CNFs). CNF acts as an effective barrier against oxygen and mineral oil residues. Two different CNF grades were tested, and both were applied onto plasma activated LDPE film using a pilot coating line. The coated films were shredded with the help of liquid nitrogen, compacted and compounded with virgin LDPE and compatibilizer, and processed into cast films and injection molded test specimens. The CNF coatings were completely blent as microscale agglomerates in the LDPE matrix. The effect of these agglomerates on the barrier and heat sealing properties was statistically insignificant compared to recycled uncoated LDPE. The mechanical properties were only moderately changed. CNF‐coated LDPE films can therefore be recycled back into films without sacrificing the characteristic properties of the base polymer. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46237.     

Uniform color coating of multilayered TiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> films by atomic layer deposition

Thin film optics, based on light interference characteristics, are attracting increasing interest because of their ability to enable a functional color coating for various applications in optical, electronic, and solar industries. Here, we report on the dependence of coloring characteristics on single-layer TiO₂ thicknesses and alternating TiO₂/Al₂O₃ multilayer structures prepared by atomic layer deposition (ALD) at a low growth temperature. The ALD TiO₂ and Al₂O₃ thin films were studied at a low growth temperature of 80°C. Then, the coloring features in the single-layer TiO₂ and alternating TiO₂/Al₂O₃ multilayers using both the ALD processes were experimentally examined on a TiN/cut stainless steel sheet. The Essential Macleod software was used to estimate and compare the color coating results. The simulation results revealed that five different colors of the single TiO₂ layers were shown experimentally, depending on the film thickness. For the purpose of highly uniform pink color coating, the film structures of TiO₂/Al₂O₃ multilayers were designed in advance. It was experimentally demonstrated that the evaluated colors corresponded well with the simulated color spectrum results, exhibiting a uniform pink color with wide incident angles ranging from 0° to 75°. This article advances practical applications requiring highly uniform color coatings of surfaces in a variety of optical coating areas with complex topographical structures.     

Oxygen barrier coating deposited by novel plasma‐enhanced chemical vapor deposition

We report the use of a novel plasma‐enhanced chemical vapor deposition chamber with coaxial electrode geometry for the SiO_x deposition. This novel plasma setup exploits the diffusion of electrons through the inner most electrode to the interior samples space as the major energy source. This configuration enables a gentle treatment of sensitive materials like low‐density polyethylene foils and biodegradable materials. SiO_x coatings deposited in the novel setup were compared with other state of the art plasma coatings and were found to possess equally good or better barrier properties. The barrier effect of single‐layer coatings deposited under different reaction conditions was studied. The coating thickness and the carbon content in the coatings were found to be the critical parameters for the barrier property. The novel barrier coating was applied on different polymeric materials, and it increased the barrier property of the modified low‐density polyethylene, polyethylene terephthalate, and polylactide by 96.48%, 99.69%, and 99.25%, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Atomic layer deposition TiO2/Al2O3 nanolayer of dyed polyamide/aramid blend fabric for high intensity UV light protection

Ultraviolet (UV) irradiation can cause a severe damage to textiles, such as color fading, polymer degradation, and mechanical strength decrease. The aim of this study was to deposit inorganic UV blocking agents onto polyamide/aramid dyed fabric using atomic layer deposition (ALD) technique to produce functional fabrics that are resistant to high intensity UV light. Scanning electron microscopy (coupled to energy‐dispersive spectroscopy), X‐ray photoelectron spectroscopy, and thermogravimetry studies demonstrated that TiO₂, Al₂O₃, and TiO₂/Al₂O₃ nanolayer could be successfully deposited onto the fiber surface. The dyed fabrics with different ALD coatings showed excellent high intensity UV resistance and were also more resistant to high intensity UV‐induced mechanical strength damage. These results suggested that the ALD technology could be effective technique to improve the properties of dyed fabrics. POLYM. ENG. SCI., 55:1296–1302, 2015. © 2015 Society of Plastics Engineers     

Sol–gel derived CeO2/α‐Al2O3 bilayer thin film as an anti‐coking barrier and its catalytic coke oxidation performance

A CeO₂/α‐Al₂O₃ bilayer was coated on a high temperature alloy (Incoloy 800H) by sol–gel dip‐coating and was evaluated for its potential as an anticoking barrier and coke oxidation catalyst. The bilayer effectively functioned as a barrier to metal surface catalyzed coking. The film prevented filamentous catalytic coking via blocking surface active metallic sites on the Incoloy substrate. Furthermore, the bilayer reduced the oxidation temperature of pyrolytic coke deposited on the film surface as compared to a bare oxidized Incoloy substrate, mostly owing to the oxidation catalytic activity of the CeO₂ layer. Finally, it is demonstrated that the presence of the α‐Al₂O₃ buffer layer is critically important to the overall performance. Without the α‐Al₂O₃ layer, a CeO₂ layer nearly completely lost both its barrier and oxidation catalytic functions. It is presumed that metallic species migrating from the substrate during high temperature treatments are responsible for the CeO₂ deactivation, likely by blocking catalytic sites on the CeO₂ surface. © 2018 American Institute of Chemical Engineers AIChE J, 64: 4019–4026, 2018     

Chemical and electrochemical characterization of TiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> atomic layer depositions on AZ-31 magnesium alloy

In this study, innovative TiO₂/Al₂O₃ mono/multilayers were applied by atomic layer depositions (ALD) on ASTM-AZ-31 magnesium/aluminum alloy to enhance its well-known scarce corrosion resistance. Four different configurations of ALD layers were tested: single TiO₂ layer, single Al₂O₃ layer, Al₂O₃/TiO₂ bilayer and Al₂O₃/TiO₂/Al₂O₃/TiO₂ multilayer deposited using Al[(CH₃)]₃ (trimethylaluminum, TMA), and TiCl₄ and H₂O precursors. All depositions were performed at 120°C to obtain an amorphous-like structure of both oxide layers. The four coatings were then investigated using different techniques, such as scanning electron microscope (SEM), stylus profilometer, glow discharge optical emission spectrometry (GDOES) and polarization curves in 0.05-M NaCl solution. The thickness of all the coatings was around 100 nm. The layers compositions were successfully investigated by the GDOES technique, although obtained data seem to be affected by substrate roughness and differences in sputtering rates between ceramic oxides and metallic magnesium alloy. Corrosion resistance showed to be strongly enhanced by the nanometric coatings, giving lower corrosion current densities in 0.05-M NaCl media with respect to the uncoated substrate (from 10⁻⁴ to 10⁻⁶ A/cm² for the single layers and from 10⁻⁴ to 10⁻⁸ A/cm² for the bi- and multilayers). All polarization curves on coated samples also showed a passive region, wider for the bi-layer (from −0.58 to −0.43 V with respect to Ag/AgCl) and multilayer (from −0.53 to −0.38 V with respect to Ag/AgCl) structures.     

Preparation and application of an ultraviolet curable coating containing nanoscale α‐aluminum oxide

This study focuses on the preparation of an organic–inorganic ultraviolet (UV) curable coating containing the nanoscale α‐aluminum oxide (α‐Al₂O₃) powder and UV curable resin. This developed coating can form a protection film on the poly(vinyl chloride) (PVC) plastic tile surface. Thus, the abrasion resistance of the PVC plastic tile surface is improved. Besides, the adhesion between this UV cured film and the PVC plastic tile surface is well. After treatment with the UV curable coating that contains 6 wt % α‐Al₂O₃, the abrasion resistance of the PVC plastic tile surface can be improved up to 57%. From the result of a scanning electron microscopy (SEM) mapping photograph, it shows that the nanoscale α‐Al₂O₃ powder is well dispersed in the cured coating film. Under the wavelength of the visible light in the range of 400–800 nm, the degree of transparency for the coated film on poly(ethylene terephthalate) (PET) sheet is about 82–90%. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5747–5752, 2006     

Basic Study of Adhesion of Several Alumina‐based Washcoats Deposited on Stainless Steel Microchannels

The adhesion of several washcoats deposited on stainless steel microchannels was investigated by performing a mechanical test (drop test) after application‐oriented tests, temperature cycling, and water exposure. For this study alumina washcoats (γ‐Al₂O₃) and washcoats of commercially available alumina‐based catalyst powders (Pt/Al₂O₃, Rh/Al₂O₃) were used. The deposited washcoats showed very good adhesion not only for fresh samples but also after the application‐oriented tests.