Number Of Coatings Research Articles

Improvement of a reduction-resistant Ce 0.8Sm 0.2O 1.9 electrolyte by optimizing a thin BaCe 1−xSm xO 3− α layer for intermediate-temperature SOFCs

Sm 3+-doped ceria (SDC) electrolytes growing various BaCe 1−xSm xO 3− α (BCS) layers over the electrolyte surface were investigated in order to develop high-performance solid oxide fuel cells in the temperature range of 600–900 °C. The BCS layers were grown by a solid-state reaction of the electrolyte substrate and a BaO film spin-coated previously over the substrate surface under different preparation conditions. The thickness of the layer was controlled with a precision of micrometer by the number of coats. The composition of the layer was optimized by the sintering temperature. As a result, a dense and microcrack-free BCS layer was formed over the electrolyte surface, and the junction between the electrolyte and layer was almost homogeneous. A hydrogen-air fuel cell with the improved electrolyte showed open-circuit voltages (OCVs) ranging from 857 (900 °C) to 1002 mV (600 °C). Furthermore, the peak power densities of this fuel cell were higher than those of a fuel cell with an uncoated SDC electrolyte.

Sol?Gel SiO2-ZrO2 Coatings for Optical Applications

SiO2-ZrO2 based nanostructured multilayers films have been prepared by sol–gel processing from metallorganic precursors by low temperature inorganic polymerization reactions. Simultaneous gelation of both precursors was realized. Homogeneous and transparent films were obtained at room temperature by dip- and spin-coating on glass and silicon wafer substrates. Samples with successively deposited layers (1–3 layers) and successive thermal treatments have been also studied. Each deposited layer was thermally treated for 1 h at 300°C. The coatings were characterized by XRD, spectroellipsometry (SE), UV-VIS spectroscopy and AFM methods. The influence of substrates, number of coatings and number of thermal treatments on the optical and structural properties of the films was established. The thickness of three deposited SiO2-ZrO2 layers is about 496 nm on glass substrates and 413 nm on the silicon wafer substrate. The films deposited on glass are more porous than those deposited on silicon. The properties of optical waveguide prepared from SiO2-ZrO2 layers on silicon substrates will be discussed.

Torsion of an isotropic shaft of arbitrary cross-section embedded with multicoated or graded circular cylinders of cylindrically orthotropic materials

Finding a geometric configuration that is amenable to an exact determination or characterization of the torsional rigidity is a relatively new territory that has only recently begun to be explored. For example, a circular cross-section with an assemblage of composite cylinders was only recently known to be an exactly solvable microgeometry. A host shaft with arbitrary cross-section, equivalent to higher orders of boundary data, necessitates that the coated cylinder be sufficiently multiply coated. The present analysis is to provide a theoretical framework showing how to design a neutral cylinder with any number of coatings or with graded shear moduli in a cross-section under torsion. Specifically we consider that the constituents are cylindrically orthotropic with the shear moduli μ r and μ θ . The host shaft is isotropic with the shear modulus μ 0 . A simple and unified mathematical framework is first proposed for the analysis of a multicoated cylinder. It is proven that only a two by two matrix, resulting from a serial multiplication of matrices of the same order, will enter into the resulting expression. Next, the multicoated cylinder, which consists of piecewise constant shear moduli, is generalized into a graded cylinder, with a continuous variation of the shear modulus along the radial direction. We find that the warping field of a neutral graded cylinder, with varying radial and tangential shear moduli, is governed by a second-order, homogeneous, ordinary differential equation. The method of Frobenius is adopted to obtain series solutions for the warping functions. An interesting result for the neutrality of the embedded cylinders (multicoated or graded) is that when the geometric mean of the shear moduli μ G = √μ r μ θ is identical to the shear modulus μ 0 of the host shaft, the neutrality condition is satisfied for any cross-section of the host shaft. Finally, a condition is given for the torsional rigidity of the host shaft to remain the same with the inclusion of the embedded cylinders.

Waterproof Breathable Polymeric Coatings Based on Polyurethanes

The performance of environmentally friendly water-based polyurethane dispersions (PUD) for waterproof breathable coating was studied. The effect of the nature of PUD, number of coatings, incorporation of additives, and processing conditions on the breathable properties of cotton fabric was evaluated. The relative proportions of hydrophilic and hydrophobic components had a direct influence on the breathable properties of the coated cotton samples. The increase in hydrophilic component resulted in an increased water vapor penetration and lower water resistance to water penetration in the coated samples. For all the compositions, the durability of the coatings was found to improve with the incorporation of polymeric binder in the coating formulation. The air permeability values of the coated samples were found to be orders of magnitude lower than the control (uncoated) fabric sample.

Laser cladding of wear resistant metal matrix composite coatings

A number of coatings with wear-resistant properties as well as with a low friction coefficient are produced by laser cladding. The structure of these coatings is determined by required performance and realized as metal matrix composite (MMC), where solid lubricant serves as a ductile matrix (e.g. CuSn), reinforced by appropriate ceramic phase (e.g. WC/Co). One of the engineered coating with functionally graded material (FGM) structure has a dry friction coefficient 0.12. Coatings were produced by coaxial injection of powder blend into the zone of laser beam action. Metallographic and tribological examinations were carried out confirming the advanced performance of engineered coatings.

Positively charged composite nanofiltration membrane prepared by poly(N,N‐dimethylaminoethyl methacrylate)/polysulfone

AbstractPoly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) can be crosslinked by quaternization to develop a positively charged dense network structure. According to this mechanism, PDMAEMA/polysulfone (PSF) positively charged nanofiltration membrane was developed by interfacial crosslinking polymerization using PSF plate microfiltration membrane as support layer, PDMAEMA aqueous solution as coating solution, and p‐xylylene dichloride/n‐heptane as crosslinking agent. Technique and condition of developing membrane such as concentration of coating solution, coating time, pH value of coating solution, content of low molecular weight additive in coating solution, concentration of crosslinking agent, crosslinking time, and number of coatings were studied. FTIR, SEM, and X‐ray photoelectron spectroscopy were used to characterize the structure of membranes. This membrane had rejection to inorganic salts in water solution, the rejection rate to MgSO4 (1 g/L water solution at 0.8 MPa and 30°C) was about 90%, and permeation flux was about 10–20 L m−2 h−1. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2721–2728, 2004

Rapid Amperometric Immunoassay for Escherichia coli Based on Graphite Coated Nylon Membranes

AbstractAn amperometric immunosensor for rapid detection of bacteria has been developed. A graphite‐coated nylon membrane serves as a support for antibody immobilization and as a working electrode. The different parameters affecting sensor preparation such as, selection of the conductive material, pore size of the nylon membrane, number of coatings and the ratios of the graphite to the binder were optimized. A “sandwich” immunoassay scheme was used and amperometric detection of captured bacteria was conducted by the electro‐reduction of iodine formed as the product of a peroxidase catalyzed reaction. This approach has been used for detection of total Escherichia coli with a low detection limit of 40 cells/mL. The developed system can be easily adapted for rapid analysis of different pathogenic microorganisms.

TiO 2(Fe 3+) nanostructured thin films with antibacterial properties

TiO 2-based nanostructured Fe 3+-doped coatings have been prepared by the sol–gel method on glass substrates. The coatings were characterized by X-ray diffraction and spectroellipsometry methods. The influence of Fe 3+ dopant concentration, number of coatings, and calcination temperature on the films structure was established. The antibacterial activity against E. coli, has been studied applying the so-called antibacterial-drop test. The bactericidal activity for the above bacteria cells was estimated by relative number of bacteria survived calculated from the number of viable cells which form colonies on the nutrient agar plates. The coatings exhibited a high antibacterial activity, which was enhanced with the increase of the temperature of thermal treatment and formation of anatase crystalline structure. The long thermal treatment results in rutile crystalline structure formation followed by the decrease in the antibacterial activity of the coating.

The preparation and properties of CeO2–TiO2 film by sol–gel spin-coating process

Ultraviolet absorbing CeO2–TiO2 coatings were prepared by the sol–gel spin-coating process heat treated at 500 8C. The films obtained were brilliant yellow, adherent and had some pattern on the soda-lime glass substrate. The optical transmittance, thickness and hardness of the films as a function of the number of coatings, aging time (0, 24, 48, 96 h) or aging temperature (28, 35, 40, 50 ˚C) were determined, and surface microstructure of the films was observed by SEM. We found some pattern on the surface of films. This pattern was similar to that of the stage for fixing the substrate. The pattern on the surface of films would be caused by the difference of thermal conductivity to slide glass in the part of metal of the stage and hollow part of the stage.

Humidity sensing behaviors of nanocrystalline Al-doped ZnO thin films prepared by sol–gel process

Nanocrystalline Al-doped ZnO(AZO) thin films prepared by sol–gel method were used for studying the variation of resistance with humidity. The particle size of the films exhibits nanometer order with zincite structure and the thickness of the films increases linearly with the number of coatings. The AZO film coated five times and annealed at 500 °C exhibits the highest sensitivity for the humidity, which shows three order change in the resistance during the relative humidity variation from 20 to 90%. It is considered that the high humidity sensitivity is due to proton hopping between water molecules adsorbed on the film surfaces with capillary nanopores.

Synthesis and applications of cyclic carbonate functional polymers in thermosetting coatings

Thermosetting coatings based on the cyclic carbonate–amine reaction are attractive since polyurethane coatings can be made without the use of isocyanates. Cyclic carbonate functional polymers were prepared via the free radical solution copolymerization of vinyl ethylene carbonate with vinyl ester monomers. The level of vinyl ethylene carbonate was varied from 10 to 50%. In order to develop an understanding of the kinetics of the reaction of cyclic carbonates with amines, kinetics of a number of amines were determined with a model cyclic carbonate, propylene carbonate. The kinetic information was used to help select appropriate amine crosslinkers and develop thermosetting coatings using cyclic carbonate functional polymers and oligomers. For screening of coating properties, clear coating formulations were applied to pretreated metal panels and cured at 80°C for 45 min. A number of coatings were prepared to study the effect of amine, stoichiometry, solvent, and copolymer composition on the coatings properties. Coatings prepared had excellent solvent resistance, good gloss, and high pendulum hardness.

A Core−Shell Structured Hydrogel Thin Layer on Surfaces by Lamination of a Poly(ethylene glycol)-b-poly(d,l-lactide) Micelle and Polyallylamine

A thin hydrogel possessing layer-by-layer structure was prepared on substrates from a stabilized reactive micelle from a poly(ethylene glycol)−poly(d,l-lactide) (PEG−PLA) bearing an acetal group at the PEG end and a methacryloyl group at the PLA end. The hydrogel layer was formed by coating the aminated surfaces with the micelle and polyallylamine (PAlAm) alternately in the presence of a reducing reagent. Each step of the alternate coating of the micelle and PAlAm was characterized with scanning probe microscopy and the ζ-potential measurement over a pH range of 2−11. When the micelle was the topmost layer, the ζ-potential exhibited a small absolute value, suggesting full masking of the electrostatic charge from the inner layer. The ζ-potential of the surface with a PAlAm top layer showed a large positive value of ∼50 mV up to pH 8 and declined to zero, attributed exclusively to the protonation and deprotonation of PAlAm. The alternation of ζ-potential with the coatings indicates the unmixing of the micelle and PAlAm. Scanning probe microscopy revealed that the surface coated with a monolayer of micelles consisted of granules on the order of the micelle size. With an increase in the number of coatings, the surface undulation was promoted and the nodular size increased. The thickness of the layer, estimated by tapping-mode scanning of the area scratched by the strong force contact mode, was found to increase with the number of coatings, and the increase corresponded approximately to the size of the micelle for each step of the coating. Of interest, the diminution of the well scratched by the probe was observed after a short period indicative of the reorganization of the elastic network to recover entropic reduction. Because of its unique structure, the thin hydrogel layer can be applied as a controlled release matrix of hydrophobic drugs.

Interfacial stress analysis for multi-coating systems using an advanced boundary element method

This paper focuses on the interfacial stress analysis for multi-coating systems using an advanced boundary element method (BEM) developed earlier in [Luo JF, Liu YJ, Berger EJ (1998) Analysis of two-dimensional thin structures (from micro- to nano-scales) using the boundary element method. Comput. Mech. 22(5):404–412]. The advanced BEM with thin-body capabilities for two-dimensional linear elasticity is extended to general multi-domain problems and validated by the analytical solution of a special multi-coating problem. Detailed interfacial stress analysis for a two-layer coating system under uniform load distribution is investigated, through which the influence of coating thickness and material of the multi-coating system can be studied. The developed multi-coating analysis capability using the BEM provides not only a robust numerical tool for interfacial stress analysis of multi-coating systems with arbitrary coating thickness and number of coatings, but also the basis for future work concerning interface cracks, thermal effects and contact mechanics.

Microbending Loss and Stresses Induced by both Temperature Variation and Axial Strain in Multi-coated Optical Fibers

The microbending loss and the stresses induced by both the temperature variation and the axial strain in multi-coated optical fibers are studied. Optical fibers with two up to six coatings are considered. A recurrence relation is obtained for the lateral pressure on the glass fiber, from which the microbending loss and the stresses are calculated. It is found that the microbending loss can be minimized by increasing the number of coatings.

Bead Compacts. I. Effect of Compression on Maintenance of Polymer Coat Integrity in Multilayered Bead Formulations

Little information is available on the comparability of beads for oral sustained-release dosage forms. It is known that polymer-coated beads may fuse together to produce a non-disintegrating controlled-release matrix tablet when compressed. This study evaluates the effect of compression on beads with multiple layers of polymer and drug coat, and the effect of cushioning excipients and compaction pressure on drug release from compressed bead formulations. The multilayered beads consist of several alternating layers of acetaminophen (APAP) and polymer coats (Aquacoat®) with an outer layer of mannitol as a cushioning excipient. Percent drug release versus time profiles showed that the release of drug decreases from noncompacted beads as the amount and number of coatings increases, with only 43% of drug released in 24 hr for coated beads with 10 layers. It was shown that the compacted multilayered beads will disintegrate in gastrointestinal fluids, providing a useful drug release pattern. It was shown that beads of drug prepared by any method can be spray-layered with excipients such as Avicel and mannitol. Spray-layering of the cushioning excipient onto beads can provide an effective way to circumvent segregation issues associated with mixing of the polymer-coated beads and powdered or spherical/nonspherical cushioning excipients. Spray layering of the cushioning excipient can also provide excellent flow properties of the final formulation as visually observed in our experiments. Triple-layered caplets (TLC) were also prepared with outer layers of Avicel PH-101 or polyethylene oxide (PEO), and a center layer of polymer-coated beads. For TLC, the polymer coating on the beads fractured, and nondisintegrating matrix formulations were obtained with both caplet formulations.

Optically transparent and non-linear LiNbO3 : polyimide composite : preparation and characterization

Ferroelectric materials, both in single crystal and ceramic form, are being used and studied for their applications in various devices. Ferroelectric ceramic thin films have received increasing interest during recent years due to the possibility of their use in thin film capacitors [1], piezoelectric transducers [2], SAW devices [3], IR detectors [4], electro-optic wave guides and other optically non linear devices [5, 6]. Various preparation techniques such as evaporation [7], sputtering [8], CVD, sol-gel [9, 10] etc., have been developed to deposit thin films. The main advantage of the sol-gel technique is that it gives optical quality films without expensive infrastructure, at a fairly low processing temperature. In the sol-gel technique, films are prepared using metal alkoxide precursors by either spin coating the sol on a substrate or dip coating the substrate. The films are sintered at 500 to 600 8C. The film thickness can be increased by increasing the number of coatings. However, it has been observed that as the film thickness increases beyond a few micrometres, film adhesion becomes poor and cracks also start to develop. Moreover, the substrate on which the film is being deposited also plays an important role in its characteristics. For non-linear optical devices, thicker films are required to increase the optical interaction length, and, as such, sol-gel derived films are not very suitable, especially for transversal exposure. To increase the thickness of the films without compromising the mechanical properties, we have prepared ceramic:polymer composite films. The polymer used for this purpose is polyimide, which can withstand the desired sintering temperatures [11]. This paper deals with the preparation of LiNbO3:Polyimide composite films. Structural, optical and electrical characterization of these films is also reported. Polyimide (PI) films were prepared by dissolving equimolecular proportions of 4-4 diamino diphenyl methane and tetracarboxylic acid in DMF to obtained polyamic acid. The viscosity of polyamic acid was adjusted to give films of about 40–50 im thickness. Films of polyamic acid were cast on glass substrates and were dried in a vacuum oven at 60 8C. Imidisation was done by sintering these films at 350 8C for two hours. To prepare polyimide:LiNbO3 composite films, ammonium salt of polyamic acid was prepared by adding ammonium hydroxide to polyamic acid. This ammonium salt of polyamic acid was dissolved in alcohol and was used for composite film preparation. A sol of LiNbO3 was prepared by dissolving lithium hydroxide in absolute ethanol and adding an equimolecular amount of niobium ethoxide to it. This sol was added dropwise to the prepared alcoholic solution of polyamic acid with continuous stirring to avoid gelation or lump formation. Composite films were then cast from this solution. Drying of the composite film and imidisation were carried out as mentioned earlier for the polyimide films. The thickness of the films thus obtained was about 35 im. A weighed portion of the film was burnt at 700 8C in a crucible. The residue, which was LiNbO3, was weighed and the weight percentage of LiNbO3 in the composite was determined to be about 15%. The X-ray diffractogram of the film was taken on a Rigaku diffractometer, while the optical transmission was recorded on a Hitachi spectrophotometer. A scanning electron micrograph was taken on a Philips scanning electron microscope. Aluminium electrodes of 1 cm diameter were vacuum deposited on the film for electrical measurements. Dielectric measurements were carried out on a Hewlett Packard impedance analyzer. Optical phase conjugation was carried out using a 35 mW He-Ne laser. The X-ray diffractogram of the film is shown in Fig. 1. The presence of LiNbO3 crystallites in the composite is clearly indicated by the presence of broad and clear peaks. The planes responsible for these peaks are marked on the diffractogram. The broadness of the peaks suggests that the crystallisation of LiNbO3 has just begun.

Lacquered tinplate: Corrosion resistance in the function of lacquering conditions

It is well known that the pack tests normally used to evaluate the corrosion resistance of tinplate in the can industry are inadequate for routine work. In this paper, electrochemical impedance is presented as an alternative. Using this technique, it was possible to characterize the better lacquer between two “first line” products. Variables involved in the lacquering, such as number of coats and curing temperature, were taken into account. Variables involved in the packing process, such as sterilization and mechanical deformation, were also studied. The general results pointed out that impedance is a powerful tool, giving meaningful and non-subjective information about the quality of the lacquered tinplates in a short time.

Numerical description of texture evolution in a growing film, starting from random orientations

In physically vapour deposited TiN coatings a continuous evolution of the texture can be observed during deposition. The texture evolves from random near the substrate to a definite texture ((111) orientation) near the outer surface. This evolution seems to be typical for a number of coatings. This texture evolution was modelled, using the tendency for the smallest possible surface energy as the driving force. The experimental trends observed in a number of experiments could be reproduced or explained, e.g. the evolution towards larger column diameters for thicker films, the sharpening of the angular distribution of the columns, and the dependence of the texture on deposition parameters.

Separation of CO 2 by modified γ-Al 2O 3 membranes at high temperature

The composite membranes of γ-Al 2O 3 were fabricated by sol-gel coating with boehmite (AlOOH) sol. The thickness of the membranes were in the range of 2–5 μm depending on the number of coatings and the concentration of the sol. The permeabilities of He, N 2, and CO 2 were measured at temperatures of 298–673 K and pressures of 101.3–405.2 KPa. The permeability through γ-Al 2O 3 membrane was constant with the pressure difference and decreased with the square root of temperature. The main mechanism of gas transport through γ-Al 2O 3 membrane was thus proved as Knudsen diffusion. CaO was impregnated on the γ-Al 2O 3 membrane to improve separation factor by introducing interactions between CO 2 gas molecules and the pore wall, but high separation factor was not obtained. Silica modified γ-Al 2O 3 membrane was also prepared to increase the separation factor. The separation factor of CO 2 to N 2 was increased to 1.4 at 298 K though it decreased with increasing temperature. The separation experiment of a CO 2/N 2 mixture was also performed. The separation factor was 1.72 at 298 K and 1.5 at 673 K, which were much higher than that of the Knudsen diffusion mechanism, 0.8.

Protection of materials by advanced high temperature coatings

Coatings are mandatory to protect hot components in turboengines and energy producing systems. The materials or alloys of these components are, indeed, subjected to a number of attacks which include oxidation, sulphidation, carburisation, chlorination, fluorination, hot corrosion by molten salt deposits and erosion-corrosion. Since 40 years a considerable number of coatings have been perfected to answer this problem. In this paper the wealth of available coatings and coating deposition processes are reviewed and a classification is proposed to shed some light in this maze of coatings