Oxygen Barrier Layer Research Articles

High-performance and robust operation of anode-supported solid oxide fuel cells in mixed-gas atmosphere

We demonstrate the high-performance and robust operation of anode-supported solid oxide fuel cells under a mixed-gas atmosphere applying a novel cell structure and characterization method, useful for minimizing the conventional problems of mixed-gas operation with anode-supported solid oxide fuel cells. To achieve the exothermic methane (CH4) partial oxidation and sufficient difference in oxygen partial pressure even in mixed-gas mode, a composite of metallic rhodium and cerium dioxide (CeO2) was chosen as the optimized reforming and oxygen barrier layer after the comprehensive catalytic experiment. We also obtained increased cell operation reliability through the combination of anode pre-reduction, an optimized material system, and a customized characterization jig (including cathode-ahead layout and impinging jet flow). According to the cell test at 600°C under a feeding gas of CH4 and O2, an open-circuit voltage and maximum power density of 0.916 V and 0.422 W/cm2, respectively, were successfully achieved. Copyright © 2015 John Wiley & Sons, Ltd.

Oxidation and erosion resistant property of SiC/Si–Mo–Cr/MoSi2 multi-layer coated C/C composites

To improve the oxidation and erosion resistance of C/C composites, a multi-layer SiC/Si–Mo–Cr/MoSi2 coating was prepared on them by a combination technique of pack cementation and a super supersonic plasma spraying technique. X-ray diffraction and scanning electron microscopy were used to analyze the phase and microstructure of the coatings. After a static oxidation test at 1773K in air for 200h, compared with the SiC/Si–Mo–Cr coated samples, the mass loss of the SiC/Si–Mo–Cr/MoSi2 coated samples decreased by 56.1%. After adding a MoSi2 layer on the SiC/Si–Mo–Cr coating by the super supersonic plasma spraying, the corrosion protection time in a wind tunnel at 1873K could be prolonged from 93h to 124h. The deposited outer MoSi2 layer could act as oxygen barrier layer and seal the initial penetrating cracks in the SiC/Si–Mo–Cr coating, resulting in the improvement of the oxidation and erosion resistance of the coated samples.

Properties of co-extruded nanoclay-filled aliphatic nylon (PA6)/linear low-density polyethylene and aromatic nylon (MXD6)/ linear low-density polyethylene multilayer films

In this study, coextruded multilayer films with aliphatic (polyamide 6) and aromatic (poly (m-xylene adipamide)) nylons as well as their in-situ polymerized nanocomposites with 4 wt% nanoclay, as an oxygen barrier layer (core), and a linear low-density polyethylene, as a moisture barrier layer (skin), were produced and characterized. Five-layer films were prepared by cast coextrusion and rapidly cooled using an air knife. Dynamic rheological measurements showed that the selected materials can be coextruded with a minimum interfacial instability between the melt flows in the feed block. Type of crystals, crystallinity and thermal transitions of layers were investigated using differential scanning calorimetry and modulated differential scanning calorimetry. The mechanical, optical, oxygen and water vapor barrier properties of the coextruded multilayer films were measured and discussed. Although the crystallinity of the poly (m-xylene adipamide) layer in the multilayer films was lower compared to the polyamide 6 layer, the impermeability to oxygen and water vapor was much better for the former multilayer films. In addition, substituting the neat polyamide 6 and poly (m-xylene adipamide) by their nanocomposites improved the oxygen barrier of the multilayer films by more than 50%. The series resistance model was not able to predict the barrier properties of the multilayer films due to the difference in polymer behavior for the single layer and multilayer, and boundary adjacent layer effects. The coextruded polyamide linear low-density polyethylene multilayer films showed higher toughness, tear and flex crack resistance compared to the poly (m-xylene adipamide)/linear low-density polyethylene samples. The pristine poly (m-xylene adipamide)-based multilayer film showed a lower haze compared to the polyamide 6 films due to very little crystallinity in the former.

Complementary Resistive Switching in Niobium Oxide-Based Resistive Memory Devices

For the applications of resistive random access memory (RRAM), we study the complementary resistive switch (CRS) behavior of a bilayer Nb2O5-∞/NbOy RRAM. The CRS effect is explained by the redistribution of oxygen vacancies inside the two niobium oxide layers. Improved CRS effects were observed using W top electrode (TE) instead of Pt, which can be attributed to the oxygen barrier layer derived from a self-formed WO∞ layer between the W TE and the Nb2O5-∞ oxide film. The niobium oxide-based CRS devices within a single memory cell can be directly integrated into a crossbar memory array without the need of extra diodes; this can significantly reduce the fabrication complexity.

Processing and Validation of Whey-Protein-Coated Films and Laminates at Semi-Industrial Scale as Novel Recyclable Food Packaging Materials with Excellent Barrier Properties

A biopolymer coating for plastic films was formulated based on whey protein, and its potential to replace current synthetic oxygen barrier layers used in food packaging such as ethylene vinyl alcohol copolymers (EVOH) was tested. The whey-coating application was performed at semi-industrial scale. High barrier to oxygen with transmission rate down to ranges of 1 cm3(STP) m−2d−1bar−1at and 50% relative humidity (r.h.) but interesting humidity barrier down to ranges of 3 g m−2d−1(both normalized to 100 μm thickness) were reached, outperforming most existing biopolymers. Coated films were validated for storing various food products showing that the shelf life and sensory attributes were maintained similar to reference packaging films while complying with food safety regulations. The developed whey coating could be enzymatically removed within 2 hours and is therefore compatible with plastic recycling operations to allow multilayer films to become recyclable by separating the other combined layers. A life cycle assessment was performed showing a significant reduction in the environmental impact of the packaging thanks in particular to the possibility of recycling materials as opposed to incinerating those containing EVOH or polyamide (PA), but due to the use of biosourced raw materials.

Characterization studies of aluminum oxide barrier coatings on polymeric substrates

Aluminum coatings are widely used as oxygen and water barrier layers on food packaging materials to protect the product from contamination and to extend its shelf life. Thin layers of aluminum, of the order of a few tens of nanometers, are thermally evaporated onto polymeric web in high speed roll-to-roll vacuum metallizers. More recently, transparent barrier layers, based on silica or aluminum oxide, have been introduced to allow product visibility and provide retortable, sterilizable, or microwaveable packaging. In all cases, though, the barrier characteristics are critically dependent on both the structure and properties of the coating and the nature and surface properties of the polymer film substrate. This paper, therefore, reports on characterization trials of aluminum oxide (AlOx) coatings deposited onto polyethylene terephthalate (PET) and biaxially oriented polypropylene (BOPP) film substrates. Coating structures and properties have been investigated by scanning electron microscopy and atomic force microscopy; the influence of process parameters on barrier levels has been determined; surface energies have been determined through contact angle measurements; and coating-to-substrate adhesion has been assessed using “pull-off” tests. The main findings of this study are that the barrier performance of AlOx coated PET and BOPP films strongly depends on the surface properties of the plain film and the aluminum oxide film growth. While AlOx coated PET films deliver consistent barrier results, BOPP reveals considerable variations, depending on the individual substrate.

Increased Performance of Thermoplastic Packaging Materials by Using a Mild Oxidizing Biobased Additive

Green additives such as prodegradants based on natural fatty acids and iron can improve the environmental profile of thermoplastic packaging materials. We present two studies in which this is demonstrated. In the first study, the addition of a green prodegradant to a 5-layer gas barrier laminate during processing provided a laminate with significantly reduced oxygen transmission due to the resulting oxygen-consuming degradation process. The result shows that material reduction and cost efficiency of packaging laminates can be combined, since 5-layer laminates with reduced oxygen barrier layer thickness and retained gas barrier properties are feasible. The products are interesting from an ecological and economic aspect. In the second study, the addition of a green prodegradant to several qualities of polypropylene that are used in packaging applications leads to materials that are readily degraded in accelerated weathering. The molecular weight of the modified polypropylenes after 830 hours of accelerated weathering is reduced from typically 80.000 g/mole to 1.500–2.500 g/mole. At such molecular weight levels, digestion by microorganisms is feasible. The mild prodegradant used in the study does not lead to degradation during processing. Thermoplastics containing such additives are therefore fully recyclable provided that they have not been exposed to a long period of weathering.

Clay Nanopaper with Tough Cellulose Nanofiber Matrix for Fire Retardancy and Gas Barrier Functions

Nacre-mimicking hybrids of high inorganic content (>50 wt %) tend to show low strain-to-failure. Therefore, we prepared clay nanopaper hybrid composite montmorillonite platelets in a continuous matrix of nanofibrillated cellulose (NFC) with the aim of harnessing the intrinsic toughness of fibrillar networks. Hydrocolloid mixtures were used in a filtration approach akin to paper processing. The resulting multilayered structure of the nanopaper was studied by FE-SEM, FTIR, and XRD. Uniaxial stress-strain curves measured in tension and thermal analysis were carried out by DMTA and TGA. In addition, fire retardance and oxygen permeability characteristics were measured. The continuous NFC matrix is a new concept and provides unusual ductility to the nanocomposite, allowing inorganic contents as high as 90% by weight. Clay nanopaper extends the property range of cellulose nanopaper and is of interest in self-extinguishing composites and in oxygen barrier layers.

Development and characterization of PET/Fish Gelatin–nanoclay composite/LDPE laminate

AbstractA three‐layer laminate film was developed with the following structure: polyethylene terephthalate (PET)/fish gelatin (FG)–nanoclay composite/low‐density polyethylene (LDPE). The FG–nanoclay composite material functioned as the oxygen barrier layer and demonstrated comparable oxygen barrier properties when compared with a similar laminate utilizing ethylene vinyl alcohol as the barrier layer at a relative humidity (RH) of up to 50%. The introduction of nanometer‐sized filler clay into the FG matrix lowered the oxygen permeability (OP) because of the tortuosity effect of the clay particles. In addition, the FG–nanoclay composite film exhibited bond strengths similar to both LDPE and PET. The hydrophilic nature of FG significantly increases OP under high (>50%) RH conditions. However, this new FG laminate film could be a possible alternative for packaging designers desiring a more sustainable packaging material for low‐RH (<50%) applications. Copyright © 2009 John Wiley & Sons, Ltd.

Co-extrusion of multilayer poly(m-xylylene adipimide) nanocomposite films for high oxygen barrier packaging applications

Multilayer packaging films incorporating a montmorillonite layered silicate (MLS)/poly(m-xylylene adipimide) (MXD6) nanocomposite as the oxygen barrier layer and low-density polyethylene (LDPE) as the moisture resistant layer were produced through the co-extrusion process at the laboratory and pilot scale level. Extrusion screw speeds were varied from 30 to 130 rpm in order to produce samples with varying layer thicknesses. The multilayer film structure was scaled up from the laboratory scale to the pilot-level scale based on oxygen transmission data obtained from the laboratory-scale process parameters. Laboratory-scale film results indicated that the film which demonstrated an optimal oxygen transmission rate (OTR) of 0.3 cm 3/(m 2 day) at 60%RH and water vapor transmission rate (WvTR) of 1.4 g/(m 2 day) at 90%RH had a structure that contained a core barrier film layer of nanocomposite MXD6 that makes up roughly 34% of the total film thickness, with the remainder of the film material consisting of maleic anhydride grafted polyolefin tie layers and LDPE skin layers. The OTR of the films changed as the relative humidity of the test environment was varied from 0 to 90%. However, for the pilot-scale trial it was necessary to reduce the target thickness of the core nylon barrier layer to 22% due to layer-to-layer melt flow instabilities that occurred during processing. The barrier properties of the multi-layer co-extruded films were highly dependant on overall film thickness. The highest performing oxygen barrier pilot-scale film had an OTR of 0.3 cm 3/(m 2 day) (60%RH) and a WvTR of 2.4 g/(m 2 day) (90%RH) with a core nylon layer of 1.5 mil and a total thickness of 7.7 mil. Correlation of the layer thicknesses to the barrier and mechanical properties of the pilot-scale multilayer films indicated that an increased nanocomposite core layer thickness improved the oxygen barrier performance and decreased film elongation while improving the tear resistance of the films.

Scaling the MOSFET gate dielectric: From high- k to higher- k? (Invited Paper)

We discuss options for metal–oxide-semiconductor field-effect transistor (MOSFET) gate stack scaling with thin titanium nitride metal gate electrodes and high-permittivity (‘high- k’) gate dielectrics, aimed at gate-first integration schemes. Both options are based on further increasing permittivity of the dielectric stack. First, we show that hafnium-based stacks such as TiN/HfO 2 can be scaled to capacitance equivalent thickness in inversion ( T inv) of 10 Å and equivalent oxide thickness (EOT) of 6 Å by using silicon nitride instead of silicon oxide as a high- k/channel interfacial layer. This is based on the higher dielectric constant of Si 3N 4 and on its resistance to oxidation. Although the nitrogen introduces positive fixed charges, carrier mobility is not degraded. Secondly, we investigate whether Ti-based ‘higher- k’ dielectrics have the potential to ultimately replace Hf. We discuss oxygen loss from TiO 2 as a main challenge, and identify two migration pathways for such oxygen atoms: In addition to well-known down-diffusion and channel Si oxidation, we have newly observed oxygen up-diffusion through the TiN metal gate, forming SiO 2 at the poly-Si contact. We further address the performance of Si 3N 4 and HfO 2 as oxygen barrier layers.

Development of Passive and Active Barrier Coatings on the Basis of Inorganic–Organic Polymers

With a new kind of barrier coating material, namely inorganic–organic polymers, it is possible to obtain excellent barrier properties against oxygen, water vapor, and flavor permeation. These hybrid polymers can be synthesized by the sol–gel technique. If extremely low permeation values are needed, the combination of hybrid polymer coatings with thin inorganic oxidic layers (SiO x , AlO x ) is very effective and leads to permeation values for oxygen and water vapor below 10−3 cm3/m2 · d · bar or g/m2 · d. These passive barrier layers can be further improved by the combination with active oxygen barrier layers which have been developed for the food packaging industry. This approach makes these multilayer laminates promising candidates for special applications in the food packaging industry as well as for sophisticated applications in technical areas: the encapsulation of sensitive organic devices like solar cells, organic light emitting diodes, or polymer electronic systems.

Effects of oxide thickness, Al 2O 3 interlayer and interface asperity on residual stresses in thermal barrier coatings

During high temperature operation, the thermally grown oxide (TGO) usually forms along the bondcoat/topcoat interface in thermal barrier coating (TBC) and was characterized as a driving force for the failure of the coating system. The effects of TGO thickness and Al 2O 3 interlayer applied as an oxygen barrier layer between the bondcoat and topcoat on the magnitude of residual stresses in TBC during cooling process were interpreted using concentric-circle model. The results were coupled with finite element method. The influences of interface asperity and interface topography on the distribution of residual stresses normal to interfaces in TBC were also discussed.

Thermal Conductivity, Phase Stability, and Oxidation Resistance of Y3Al5O12(YAG)/Y2O3–ZrO2(YSZ) Thermal-Barrier Coatings

This paper describes a new multilayer TBC that incorporates a 10 μm-thick oxygen barrier layer of yttrium–aluminum garnet (YAG) into a typical YSZ TBC system. The thermal conductivity of as-sprayed YAG/YSZ coatings was reduced due to excessive porosity and amorphous areas in the YAG layer. After long-term heat treatments, the conductivity of the multilayer was unaffected by the presence of YAG. Sintering and recrystallization of the amorphous YAG regions occurred during high-temperature heat treatments. While YAG itself possesses excellent phase stability, its presence also improved the phase stability of zirconia near the YAG/YSZ interface, inhibiting the outward diffusion of yttrium from high-yttria t-ZrO2 The YAG layer reduced the NiCoCrAlY bond-coat oxidation rate by a factor of three during isothermalfurnace tests conducted at 1200° C.

Synthesis and characterization of poly[(methyl methacrylate)‐co‐(methacrylic acid)] for a UV‐sensitive aqueous base developable lithographic plate

AbstractSyntheses of the copolymers of methyl methacrylate and methacrylic acid were carried out by free radical chain polymerization in the presence of benzoyl peroxide (BPO) as an initiator. The effects of the monomer ratio and polymerization time on the averaged molecular weights, polydispersity index, and glass transition temperature were investigated. FTIR and NMR were used for functional group characterization, GPC for average molecular weights and the distribution, elemental analysis for CHO content, and DSC for the glass transition temperature. The copolymers were mixed with tripropylene glycol diacrylate (TPGDA) and trimethylol propane ethoxylated triacrylate (TMPEOTA), 2‐hydroxy‐2‐methyl‐1‐phenyl‐propan‐1‐one (Darocur® 1173) and benzophenone (Darocur® BP) with anthraquinone for visibility of images. The photosensitive coating was spin‐coated onto the anodized aluminum plate on which a thin film was formed. The wet film was then coated with PVA solution as an oxygen barrier layer. The plate assembled with a control wedge and a black color separation film was exposed to UV radiation at different exposure times. The plate was developed in a dilute alkaline developer. The resulting plate was evaluated for its reproduction properties in terms of surface properties (hydrophilic/hydrophobicity) by contact angle measurement of image/nonimage areas, resolution by microline, tone reproduction, and adhesion tests. The article describes the results of the syntheses, characterizations, and uses of the copolymer as a binder of a negative, lithographic printing plate. The present lithographic printing plate is good for a medium viscosity printing ink to produce medium printing quality on uncoated paper. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1829–1837, 2002

Integration of high dielectric Ba 0.5Sr 0.5TiO 3 films into amorphous TaSiN barrier layer structures

The high- k dielectric material (Ba,Sr)TiO 3 has been intensively investigated for possible applications in dynamic random access memory circuits. During the BST deposition process in O 2 ambient, typically at 650°C, the diffusion of oxygen through the bottom electrode into the poly Si plug must be prevented. Amorphous TaSiN films are excellent candidates as oxygen barrier layers. Ba 0.5Sr 0.5TiO 3 (BST) films with thickness of 100 nm were deposited on the electrode structure SiO 2/TaSiN/Pt. The sol–gel method was used to grow the BST films. The barrier effect for oxygen diffusion is studied in TaSiN layers with thickness of 50 nm, which were deposited by a reactive sputter process. X-ray photoemission spectroscopy results confirm that this amorphous material is a suitable barrier against oxygen diffusion at 650°C. The BST films, deposited at 650°C and post-annealed at 650°C show a dielectric constant of 100 at 100 kHz and a dissipation factor of less than 5%.

Modeling of the effect of Al 2O 3 interlayer on residual stress due to oxide scale in thermal barrier coatings

The thermally grown oxide (TGO) formed at the bondcoat/topcoat interface has been characterized as the driving force for coating spallation when a thermal barrier coating system is exposed to high temperature environment. To improve the oxidation resistance of the system, a plasma-sprayed Al 2O 3 interlayer was applied between the bondcoat and topcoat, as an oxygen barrier layer. This article discusses the effects of the additional Al 2O 3 layer on the residual stress induced by a TGO. Analytical modeling, coupled with finite element analysis, shows that the incorporation of a thin Al 2O 3 interlayer reduces residual stress at the interface. Hence, considering the oxygen–penetration–inhibiting role of the interlayer, this multilayered system was proposed as one potential alternative in improving TBC reliability.

Investigation of oxygen diffusion barrier properties of reactively sputtered iro2 thin films

High quality IrO2 films are of great interest as electrodes and oxygen barrier layers for PZT and SBT based integrated non-volatile ferroelectric memories. The investigated IrO2 films were reactively DC-sputtered in an Ar/O2 atmosphere. Generic curves were used for the optimization of the film preparation. The microstructure of the sputtered films was characterized by XRD and it was found that the texture can be adjusted from (110) to (200) by slightly varying the oxygen partial pressure at higher substrate temperatures. This change in microstructure is accompanied by a compositional change from oxygen substoichiometric to oxygen overstoichiometric films. Moreover, the influence of the microstructure on thermal stability and oxygen barrier effectiveness was investigated by SIMS depth profiling using an 18O2 tracer diffusion method. Oxygen diffusion for process-relevant temperatures (550°-765°C) was systematically investigated and for the first time oxygen diffusion coefficients in IrO2 were determined by fitting a mathematical model to the measured profiles.

Application of sol-gel derived films for ZnO/ n-Si junction solar cells

ZnO/ n-Si heterojunction solar cells were fabricated on n-Si substrates by spin coating of the ZnO precursor solution produced by the sol-gel process. In order for the ZnO films to have proper electrical conductivity, the films were doped with an n-type dopant such as aluminum, and were subsequently annealed at a temperature of 450°C under reducing environments. The ohmic contacts were formed between n-Si and Al for a bottom electrode by doping the rear surface of the Si substrate with phosphorous atoms. The front surface of the Si substrate was also doped with phosphorous atoms for improving the efficiency of the solar cells. The substrate doping was carried out with PSG (phosphosilicate glass) films produced by the sol-gel process. As a result, the conversion efficiencies of the fabricated solar cells ranging up to about 5.3% were obtained. These efficiencies were found to decrease rather quickly with time because of silicon oxide film grown at the ZnO/Si interface as a result of oxygen penetration through the porous structure of the ZnO films. Oxygen barrier layers should be needed in order to prevent the decrease of conversion efficiencies.

Photodegradation of Organic Photochromes in Polymers - Naphthopyrans and Naphthoxazines Series -

The natural solar and artificial induced photodegradation of naphthopyran and naphthoxazine series was investigated in PMMA and in a polyurethane network. The degradation profiles through the depth of the coatings were monitored by Raman spectroscopy in function of the cumulated UV-A doses. The analyses of the formed photoproducts in each series were carried out by different off-line hyphenated chromatographic techniques. The detected products are clearly oxidized species and are similar to those found in apolar solvents. Moreover, the mechanisms of degradation seem to be of the same order between natural solar exposure and artificial solar simulation (suntests) that allows to use Xenon arc sources for accelerated degradation tests. The use of an oxygen barrier layer above the photochromic coating allows to demonstrate the formation of the naphtho[1,2]furan, which is the precursor of the 2-hydroxy-1-naphthaldehyde formation, in the naphthopyran series.