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Coatings, Volume 4, Issue 1 (March 2014) – 10 articles , Pages 1-202

Cover Story (view full-size image): In this study, the microstructural details and tribological performances of Fe-based coatings (Fe–Cr–Ni–B–C and Fe–Cr–Ni–B–Mo–C) manufactured by HVOF thermal spray process are evaluated. Ni–Cr–Fe–Si–B–C and WC–CoCr coatings were chosen as references. Microstructural investigation reveals a high density and low oxide content for HVOF Fe-based coatings. Particle melting and rapid solidification resulted in a metastable austenitic phase with precipitates of mixed carbides and borides of chromium and iron which lead to remarkably high nanohardness. Tribological performances were evaluated by means of the ball on-disk dry sliding wear test, the rubber-wheel dry particle abrasion test, and the cavitation erosion wear test. A higher wear resistance validates Fe-based coatings as a future alternative to the more expensive and less environmentally friendly Ni-based alloys. View this paper.
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919 KiB  
Review
Applications of Oxide Coatings in Photovoltaic Devices
by Sonya Calnan
Coatings 2014, 4(1), 162-202; https://doi.org/10.3390/coatings4010162 - 24 Mar 2014
Cited by 43 | Viewed by 14033
Abstract
Metalloid and metal based oxides are an almost unavoidable component in the majority of solar cell technologies used at the time of writing this review. Numerous studies have shown increases of ≥1% absolute in solar cell efficiency by simply substituting a given layer [...] Read more.
Metalloid and metal based oxides are an almost unavoidable component in the majority of solar cell technologies used at the time of writing this review. Numerous studies have shown increases of ≥1% absolute in solar cell efficiency by simply substituting a given layer in the material stack with an oxide. Depending on the stoichiometry and whether other elements are present, oxides can be used for the purpose of light management, passivation of electrical defects, photo-carrier generation, charge separation, and charge transport in a solar cell. In this review, the most commonly used oxides whose benefits for solar cells have been proven both in a laboratory and industrial environment are discussed. Additionally, developing trends in the use of oxides, as well as newer oxide materials, and deposition technologies for solar cells are reported. Full article
(This article belongs to the Special Issue Novel Thin Film Materials for Photovoltaic Applications)
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12 KiB  
Editorial
Acknowledgement to Reviewers of Coatings in 2013
by Coatings Editorial Office
Coatings 2014, 4(1), 160-161; https://doi.org/10.3390/coatings4010160 - 24 Feb 2014
Viewed by 3473
Abstract
The editors of Coatings would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2013. [...] Full article
270 KiB  
Review
Biomedical Nanoparticles: Overview of Their Surface Immune-Compatibility
by Olimpia Gamucci, Alice Bertero, Mariacristina Gagliardi and Giuseppe Bardi
Coatings 2014, 4(1), 139-159; https://doi.org/10.3390/coatings4010139 - 12 Feb 2014
Cited by 96 | Viewed by 9213
Abstract
Diagnostic- and therapeutic release-aimed nanoparticles require the highest degree of biocompatibility. Some physical and chemical characteristics of such nanomaterials are often at odds with this requirement. For instance, metals with specific features used as contrast agents in magnetic resonance imaging need particular coatings [...] Read more.
Diagnostic- and therapeutic release-aimed nanoparticles require the highest degree of biocompatibility. Some physical and chemical characteristics of such nanomaterials are often at odds with this requirement. For instance, metals with specific features used as contrast agents in magnetic resonance imaging need particular coatings to improve their blood solubility and increase their biocompatibility. Other examples come from the development of nanocarriers exploiting the different characteristics of two or more materials, i.e., the ability to encapsulate a certain drug by one core-material and the targeting capability of a different coating surface. Furthermore, all these “human-non-self” modifications necessitate proofs of compatibility with the immune system to avoid inflammatory reactions and resultant adverse effects for the patient. In the present review we discuss the molecular interactions and responses of the immune system to the principal nanoparticle surface modifications used in nanomedicine. Full article
(This article belongs to the Special Issue Advances in Medical Device Coatings)
1217 KiB  
Article
Tribology and Micromechanics of Chromium Nitride Based Multilayer Coatings on Soft and Hard Substrates
by Juergen M. Lackner, Wolfgang Waldhauser, Lukasz Major and Marcin Kot
Coatings 2014, 4(1), 121-138; https://doi.org/10.3390/coatings4010121 - 12 Feb 2014
Cited by 39 | Viewed by 10512
Abstract
The tribological protection of carbon fiber reinforced epoxy composites (CFC) is essential for broadening their use from structural to functional applications, e.g., to linear bearings in mechanical engineering. However, their wear resistance in sliding and rolling contacts is low. This work focusses on [...] Read more.
The tribological protection of carbon fiber reinforced epoxy composites (CFC) is essential for broadening their use from structural to functional applications, e.g., to linear bearings in mechanical engineering. However, their wear resistance in sliding and rolling contacts is low. This work focusses on the possibility of improving their tribological properties by the application of thin hard multi-layered coatings. Chromium nitride (CrN) single layer and chromium-CrN multilayer coatings of ~4 µm thickness, partly finished with a 1 µm diamond-like carbon (DLC) top layer, were deposited by magnetron sputtering at low temperatures on soft CFC and for comparison of the mechanical behavior on comparatively hard austenitic steel substrates. Structural investigations showed especially that the multilayer coatings possess a very fine grained, columnar microstructure and a very low density of intercolumnar micro-cracks, while the single layer coatings possess a coarse structure. The indentation testing and the analysis of the deformed and fractured cross-sections revealed a tougher behavior with improved plastic deformability of the multilayers in comparison to CrN single layers. However, in wear testing only coatings with DLC top layers significantly improved the tribological material properties of CFC. This is due to the reduced shear forces in sliding on low-friction DLC coatings on the soft epoxy-based CFC, decreasing the total dynamic stresses during sliding under high loads. Full article
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1447 KiB  
Article
Microstructural Characteristics and Tribological Behavior of HVOF-Sprayed Novel Fe-Based Alloy Coatings
by Andrea Milanti, Heli Koivuluoto, Petri Vuoristo, Giovanni Bolelli, Francesco Bozza and Luca Lusvarghi
Coatings 2014, 4(1), 98-120; https://doi.org/10.3390/coatings4010098 - 29 Jan 2014
Cited by 58 | Viewed by 11148
Abstract
Thermally-sprayed Fe-based coatings have shown their potential for use in wear applications due to their good tribological properties. In addition, these kinds of coatings have other advantages, e.g., cost efficiency and positive environmental aspects. In this study, the microstructural details and tribological performances [...] Read more.
Thermally-sprayed Fe-based coatings have shown their potential for use in wear applications due to their good tribological properties. In addition, these kinds of coatings have other advantages, e.g., cost efficiency and positive environmental aspects. In this study, the microstructural details and tribological performances of Fe-based coatings (Fe-Cr-Ni-B-C and Fe-Cr-Ni-B-Mo-C) manufactured by High Velocity Oxygen Fuel (HVOF) thermal spray process are evaluated. Traditional Ni-based (Ni-Cr-Fe-Si-B-C) and hard-metal (WC-CoCr) coatings were chosen as references. Microstructural investigation (field-emission scanning electron microscope FESEM and X-Ray diffractometry XRD) reveals a high density and low oxide content for HVOF Fe-based coatings. Particle melting and rapid solidification resulted in a metastable austenitic phase with precipitates of mixed carbides and borides of chromium and iron which lead to remarkably high nanohardness. Tribological performances were evaluated by means of the ball on-disk dry sliding wear test, the rubber-wheel dry particle abrasion test, and the cavitation erosion wear test. A higher wear resistance validates Fe-based coatings as a future alternative to the more expensive and less environmentally friendly Ni-based alloys. Full article
(This article belongs to the Special Issue Advanced Thermal Spray Coatings for Emerging Applications)
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820 KiB  
Article
Spray-on PEDOT:PSS and P3HT:PCBM Thin Films for Polymer Solar Cells
by Morteza Eslamian and Joshua E. Newton
Coatings 2014, 4(1), 85-97; https://doi.org/10.3390/coatings4010085 - 21 Jan 2014
Cited by 19 | Viewed by 12301
Abstract
PEDOT:PSS electron-blocking layer, and PEDOT:PSS + P3HT:PCBM stacked layers are fabricated by ultrasonic atomization and characterized by scanning electron microscopy (SEM) and optical profilometry. The measured thicknesses based on SEM and optical profilometry are quite different, indicating the incapability of measurement techniques for [...] Read more.
PEDOT:PSS electron-blocking layer, and PEDOT:PSS + P3HT:PCBM stacked layers are fabricated by ultrasonic atomization and characterized by scanning electron microscopy (SEM) and optical profilometry. The measured thicknesses based on SEM and optical profilometry are quite different, indicating the incapability of measurement techniques for non-uniform thin films. The thickness measurements are compared against theoretical estimations and a qualitative agreement is observed. Results indicate that using a multiple pass fabrication strategy results in a more uniform thin film. It was also found that the film characteristics are a strong function of solution concentration and spraying passes, and a weak function of substrate speed. Film thickness increases with solution concentration but despite the prediction of theory, the increase is not linear, indicating a change in the film porosity and density, which can affect physical and opto-electrical properties. Overall, while spray coating is a viable fabrication process for a wide range of solar cells, film characteristics can be easily altered by a change in process parameters. Full article
(This article belongs to the Special Issue Novel Thin Film Materials for Photovoltaic Applications)
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656 KiB  
Review
Spray-on Thin Film PV Solar Cells: Advances, Potentials and Challenges
by Morteza Eslamian
Coatings 2014, 4(1), 60-84; https://doi.org/10.3390/coatings4010060 - 21 Jan 2014
Cited by 131 | Viewed by 19263
Abstract
The capability to fabricate photovoltaic (PV) solar cells on a large scale and at a competitive price is a milestone waiting to be achieved. Currently, such a fabrication method is lacking because the effective methods are either difficult to scale up or expensive [...] Read more.
The capability to fabricate photovoltaic (PV) solar cells on a large scale and at a competitive price is a milestone waiting to be achieved. Currently, such a fabrication method is lacking because the effective methods are either difficult to scale up or expensive due to the necessity for fabrication in a vacuum environment. Nevertheless, for a class of thin film solar cells, in which the solar cell materials can be processed in a solution, up scalable and vacuum-free fabrication techniques can be envisioned. In this context, all or some layers of polymer, dye-sensitized, quantum dot, and copper indium gallium selenide thin film solar cells illustrate some examples that may be processed in solution. The solution-processed materials may be transferred to the substrate by atomizing the solution and carrying the spray droplets to the substrate, a process that will form a thin film after evaporation of the solvent. Spray coating is performed at atmospheric pressure using low cost equipment with a roll-to-roll process capability, making it an attractive fabrication technique, provided that fairly uniform layers with high charge carrier separation and transport capability can be made. In this paper, the feasibility, the recent advances and challenges of fabricating spray-on thin film solar cells, the dynamics of spray and droplet impaction on the substrate, the photo-induced electron transfer in spray-on solar cells, the challenges on characterization and simulation, and the commercialization status of spray-on solar cells are discussed. Full article
(This article belongs to the Special Issue Novel Thin Film Materials for Photovoltaic Applications)
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949 KiB  
Review
Nano and Microscale Topographies for the Prevention of Bacterial Surface Fouling
by Mary V. Graham and Nathaniel C. Cady
Coatings 2014, 4(1), 37-59; https://doi.org/10.3390/coatings4010037 - 17 Jan 2014
Cited by 121 | Viewed by 14075
Abstract
Bacterial surface fouling is problematic for a wide range of applications and industries, including, but not limited to medical devices (implants, replacement joints, stents, pacemakers), municipal infrastructure (pipes, wastewater treatment), food production (food processing surfaces, processing equipment), and transportation (ship hulls, aircraft fuel [...] Read more.
Bacterial surface fouling is problematic for a wide range of applications and industries, including, but not limited to medical devices (implants, replacement joints, stents, pacemakers), municipal infrastructure (pipes, wastewater treatment), food production (food processing surfaces, processing equipment), and transportation (ship hulls, aircraft fuel tanks). One method to combat bacterial biofouling is to modify the topographical structure of the surface in question, thereby limiting the ability of individual cells to attach to the surface, colonize, and form biofilms. Multiple research groups have demonstrated that micro and nanoscale topographies significantly reduce bacterial biofouling, for both individual cells and bacterial biofilms. Antifouling strategies that utilize engineered topographical surface features with well-defined dimensions and shapes have demonstrated a greater degree of controllable inhibition over initial cell attachment, in comparison to undefined, texturized, or porous surfaces. This review article will explore the various approaches and techniques used by researches, including work from our own group, and the underlying physical properties of these highly structured, engineered micro/nanoscale topographies that significantly impact bacterial surface attachment. Full article
(This article belongs to the Special Issue Advances in Medical Device Coatings)
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1933 KiB  
Article
Abrasion, Erosion and Cavitation Erosion Wear Properties of Thermally Sprayed Alumina Based Coatings
by Ville Matikainen, Kari Niemi, Heli Koivuluoto and Petri Vuoristo
Coatings 2014, 4(1), 18-36; https://doi.org/10.3390/coatings4010018 - 02 Jan 2014
Cited by 65 | Viewed by 11881
Abstract
Thermally-sprayed alumina based materials, e.g., alumina-titania (Al2O3-TiO2), are commonly applied as wear resistant coatings in industrial applications. Properties of the coatings depend on the spray process, powder morphology, and chemical composition of the powder. In this study, [...] Read more.
Thermally-sprayed alumina based materials, e.g., alumina-titania (Al2O3-TiO2), are commonly applied as wear resistant coatings in industrial applications. Properties of the coatings depend on the spray process, powder morphology, and chemical composition of the powder. In this study, wear resistant coatings from Al2O3 and Al2O3-13TiO2 powders were sprayed with plasma and high-velocity oxygen-fuel (HVOF) spray processes. Both, fused and crushed, and agglomerated and sintered Al2O3-13TiO2 powders were studied and compared to pure Al2O3. The coatings were tested for abrasion, erosion, and cavitation resistances in order to study the effect of the coating structure on the wear behavior. Improved coating properties were achieved when agglomerated and sintered nanostructured Al2O3-13TiO2 powder was used in plasma spraying. Coatings with the highest wear resistance in all tests were produced by HVOF spraying from fused and crushed powders. Full article
(This article belongs to the Special Issue Advanced Thermal Spray Coatings for Emerging Applications)
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717 KiB  
Article
Ink-Jet Printing of Gluconobacter oxydans: Micropatterned Coatings As High Surface-to-Volume Ratio Bio-Reactive Coatings
by Marcello Fidaleo, Nadia Bortone, Mark Schulte and Michael C. Flickinger
Coatings 2014, 4(1), 1-17; https://doi.org/10.3390/coatings4010001 - 19 Dec 2013
Cited by 10 | Viewed by 7063
Abstract
We formulated a latex ink for ink-jet deposition of viable Gram-negative bacterium Gluconobacter oxydans as a model adhesive, thin, highly bio-reactive microstructured microbial coating. Control of G. oxydans latex-based ink viscosity by dilution with water allowed ink-jet piezoelectric droplet deposition of 30 × [...] Read more.
We formulated a latex ink for ink-jet deposition of viable Gram-negative bacterium Gluconobacter oxydans as a model adhesive, thin, highly bio-reactive microstructured microbial coating. Control of G. oxydans latex-based ink viscosity by dilution with water allowed ink-jet piezoelectric droplet deposition of 30 × 30 arrays of two or three droplets/dot microstructures on a polyester substrate. Profilometry analysis was used to study the resulting dry microstructures. Arrays of individual dots with base diameters of ~233–241 µm were obtained. Ring-shaped dots with dot edges higher than the center, 2.2 and 0.9 µm respectively, were obtained when a one-to-four diluted ink was used. With a less diluted ink (one-to-two diluted), the microstructure became more uniform with an average height of 3.0 µm, but the ink-jet printability was more difficult. Reactivity of the ink-jet deposited microstructures following drying and rehydration was studied in a non-growth medium by oxidation of 50 g/L D-sorbitol to L-sorbose, and a high dot volumetric reaction rate was measured (~435 g·L−1·h−1). These results indicate that latex ink microstructures generated by ink-jet printing may hold considerable potential for 3D fabrication of high surface-to-volume ratio biocoatings for use as microbial biosensors with the aim of coating microbes as reactive biosensors on electronic devices and circuit chips. Full article
(This article belongs to the Special Issue Advancing Coatings with Biotechnology)
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