Coatings

12 pages, 3766 KiB

Open AccessArticle

Anti-Icing Performance of Hydrophobic Silicone–Acrylate Resin Coatings on Wind Blades

by Ke Xu, Jianlin Hu, Xingliang Jiang, Wei Meng, Binhuan Lan and Lichun Shu

Coatings 2018, 8(4), 151; https://doi.org/10.3390/coatings8040151 - 23 Apr 2018

Cited by 18 | Viewed by 6033

The icing of wind blades poses a serious threat to the operation of wind turbines. The application of superhydrophobic coatings on wind blades can serve as a potential anti-icing method. This study presents the findings of simulations of the icing environment of wind [...] Read more.

The icing of wind blades poses a serious threat to the operation of wind turbines. The application of superhydrophobic coatings on wind blades can serve as a potential anti-icing method. This study presents the findings of simulations of the icing environment of wind blades coated with hydrophobic silicone–acrylate resin in an artificial climate chamber. Artificial icing tests were performed on NACA7715 wind blades with four different silicone–acrylate resin coatings and on uncoated wind blades, with test performed at five different wind speeds and three different angles of attack. Results show that wind blade surfaces with higher hydrophobicity yield better anti-icing performance, and that the ice mass of the wind blades decreases with increasing wind speeds and angles of attack. In addition, variations in ice mass, shape, and distribution on different wind blades indicate that increased hydrophobicity can help limit the areas that are subject to freezing. Hydrophobicity can affect the air cavities of the ice deposited on the wind blades, and surfaces with increased hydrophobicity can lead to lower ice mass and less ice adhesion. In brief, surfaces with higher hydrophobicity demonstrate better anti-icing performance and benefit from active de-icing. Full article

(This article belongs to the Special Issue Superhydrophobic Coatings)

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10 pages, 3579 KiB

Open AccessArticle

Effects of Annealing on Residual Stress in Ta₂O₅ Films Deposited by Dual Ion Beam Sputtering

by Qipeng Lv, Mingliang Huang, Shaoqian Zhang, Songwen Deng, Faquan Gong, Feng Wang, Yanwei Pan, Gang Li and Yuqi Jin

Coatings 2018, 8(4), 150; https://doi.org/10.3390/coatings8040150 - 20 Apr 2018

Cited by 20 | Viewed by 8406

Abstract

Optical coatings deposited by the dual ion beam sputtering (DIBS) method usually show high compressive stress, which results in severe wavefront deformation of optical elements. Annealing post-treatment has been widely used to control the residual stress of optical coatings. However, the effect of [...] Read more.

Optical coatings deposited by the dual ion beam sputtering (DIBS) method usually show high compressive stress, which results in severe wavefront deformation of optical elements. Annealing post-treatment has been widely used to control the residual stress of optical coatings. However, the effect of annealing on the stress of Ta₂O₅ films deposited by the IBS method has not been reported in detail. In this study, different thicknesses of Ta₂O₅ films were deposited by IBS and annealed at different temperatures from 473 to 973 K in air, and the effect of annealing on the stress of Ta₂O₅ films was investigated. The as-deposited Ta₂O₅ films deposited by IBS show high compressive stress, which are about 160 MPa. The compressive stress decreases linearly with the increasing temperature, and the wavefront deformation of Ta₂O₅ films increases linearly with film thickness (within 20 μm) at the same annealing temperature. When the temperature rises to 591 K, Ta₂O₅ films with zero-stress can be obtained. Ta₂O₅ films show tensile stress instead of compressive stress with further increasing annealing temperature, and the tensile stress increases with increasing temperature. Meanwhile, with the increasing annealing temperature, the refractive index of Ta₂O₅ film decreases, indicating the decreasing packing density. The atomic force microscope (AFM) test results show that surface roughness of Ta₂O₅ films slowly increases with the increasing of annealing temperature. Moreover, X-ray photoelectron spectroscopy (XPS) analysis shows that the Ta in Ta₂O₅ films can be further oxidized with increasing annealing temperature, namely, the absorption of Ta₂O₅ film can be reduced. X-ray diffraction (XRD) analysis shows that the annealing temperature should be below 923 K to maintain the amorphous structure of the Ta₂O₅ film. Full article

(This article belongs to the Special Issue Applications of Optical Thin Film Coatings)

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12 pages, 9312 KiB

Open AccessArticle

Effects of Graphene-Oxide-Modified Coating on the Properties of Carbon-Fiber-Reinforced Polypropylene Composites

by Sean Bowman, Xiaoyu Hu, Qiuran Jiang, Yiping Qiu, Wanshuang Liu and Yi Wei

Coatings 2018, 8(4), 149; https://doi.org/10.3390/coatings8040149 - 19 Apr 2018

Cited by 8 | Viewed by 5486

Abstract

Graphene oxide (GO) modified with ferrites (GO@Fe₃O₄) were studied to determine their effect on the interfacial properties of continuous carbon-fiber-reinforced thermoplastic composites. The GO@Fe₃O₄ were introduced by mixing them directly in an acrylic-styrene (AS) sizing emulsion [...] Read more.

Graphene oxide (GO) modified with ferrites (GO@Fe₃O₄) were studied to determine their effect on the interfacial properties of continuous carbon-fiber-reinforced thermoplastic composites. The GO@Fe₃O₄ were introduced by mixing them directly in an acrylic-styrene (AS) sizing emulsion suitable for the making of continuous carbon-fiber-reinforced thermoplastics and towpregs. A magnetic field was then generated during the online sizing using coils in order to change the morphology of the coating on the fiber. The effect on the obtained sizing quality and final properties of continuous carbon-fiber-reinforced thermoplastic composites was then studied. The results showed that the topography of the sized fibers was modified, showing a kind of “drag” effect and more than a 32% increase was obtained for interlaminar shear strength. Full article

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16 pages, 4325 KiB

Open AccessArticle

One-Step Fabrication and Localized Electrochemical Characterization of Continuous Al-Alloyed Intermetallic Surface Layer on Magnesium Alloy

by Zhenxuan Fu, Xu Chen, Bin Liu, Jie Liu, Xiaopeng Han, Yida Deng, Wenbin Hu and Cheng Zhong

Coatings 2018, 8(4), 148; https://doi.org/10.3390/coatings8040148 - 18 Apr 2018

Cited by 11 | Viewed by 5732

Abstract

A continuous intermetallic compound coating was fabricated on AZ91D magnesium alloy via heat treatment at 400 °C in AlCl₃-NaCl molten salts for 10 h. The microstructure and composition of the coating were characterized by scanning electron microscope and energy dispersive X-ray [...] Read more.

A continuous intermetallic compound coating was fabricated on AZ91D magnesium alloy via heat treatment at 400 °C in AlCl₃-NaCl molten salts for 10 h. The microstructure and composition of the coating were characterized by scanning electron microscope and energy dispersive X-ray spectrometry. The results showed that the coating has a two-layer structure (the outer Mg₂Al₃ phase layer and the inner Mg₁₇Al₁₂ phase layer) up to 37 μm thick with compact and planar interfaces between the layers and the substrate. The corrosion property of the coating was investigated using electrochemical impedance spectroscopy (EIS) and two localized electrochemical techniques, i.e., localized electrochemical impedance spectroscopy (LEIS) and scanning vibrating electrode technique (SVET). The charge transfer resistance (R_ct) of the Al-alloyed coating was 2119 Ω cm². The localized impedance and current density maps obtained through LEIS and SVET indicate not only significantly improved corrosion resistance (the impedance modulus increased by one order of magnitude and the current density decreased to approximately 3.8%, compared with the substrate) but also defect-free surface condition. Full article

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13 pages, 1017 KiB

Open AccessArticle

Hydrocolloid-Based Coatings are Effective at Reducing Acrylamide and Oil Content of French Fries

by Asmaa Al-Asmar, Daniele Naviglio, Concetta Valeria L. Giosafatto and Loredana Mariniello

Coatings 2018, 8(4), 147; https://doi.org/10.3390/coatings8040147 - 18 Apr 2018

Cited by 43 | Viewed by 8220

Abstract

French fries are popular products worldwide. However, this product is a sufferable source of high acrylamide due to high temperature and low moisture. The main objective of this study was to evaluate the effect of grass pea flour (GPF), transglutaminase (TGase)-treated (GPF + [...] Read more.

French fries are popular products worldwide. However, this product is a sufferable source of high acrylamide due to high temperature and low moisture. The main objective of this study was to evaluate the effect of grass pea flour (GPF), transglutaminase (TGase)-treated (GPF + TGase), chitosan (CH), and pectin (PEC) hydrocolloid coating solutions on the formation of acrylamide, water retention as well as on oil content. In addition, the Daily Intake (DI) and Margin of Exposure (MOE) were calculated to estimate variations in risk assessment by applying coating solutions before frying. Our results showed that the highest acrylamide content was detected in the control sample, reaching a value of 2089 µg kg⁻¹. Hydrocolloid coating solutions were demonstrated to be an effective way to reduce acrylamide formation, with the percentage of acrylamide reduction equal to 48% for PEC, >38% for CH, ≥37% for GPF + TGase, and >31% for GPF, respectively. We hypothesized that the coatings were able to increase the water retention and, thus reduce the Maillard reaction, which is responsible for acrylamide formation. In fact, the MOE value for coated French fries was increase, resulting in being closer to the safety level to avoid carcinogenic risk. Moreover, our coatings were effective in reducing oil uptake. Full article

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11 pages, 10599 KiB

Open AccessArticle

Target Voltage Hysteresis Behavior and Control Point in the Preparation of Aluminum Oxide Thin Films by Medium Frequency Reactive Magnetron Sputtering

by Qingfu Wang, Liping Fang, Qinghe Liu, Lin Chen, Qinguo Wang, Xiandong Meng and Hong Xiao

Coatings 2018, 8(4), 146; https://doi.org/10.3390/coatings8040146 - 18 Apr 2018

Cited by 8 | Viewed by 10113

Abstract

Aluminum oxide thin films were prepared by medium frequency reactive magnetron sputtering. The target voltage hysteresis behavior under different argon partial pressure and target power conditions were studied. The results indicate that the target voltage hysteresis loop of aluminum oxide thin film preparation [...] Read more.

Aluminum oxide thin films were prepared by medium frequency reactive magnetron sputtering. The target voltage hysteresis behavior under different argon partial pressure and target power conditions were studied. The results indicate that the target voltage hysteresis loop of aluminum oxide thin film preparation has typical behavior of that for reactive sputtering deposition of compound films. The target voltage feedback control approach was applied to circumvent the hysteresis problem. The microstructure and chemical composition of the aluminum oxide thin films prepared at different target voltage control points were investigated by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and Auger electron spectroscopy. The results indicated that the prepared aluminum oxide thin films, which are compact and mostly amorphous, can be obtained with target voltage control point in the range of 25~35%. Full article

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13 pages, 61489 KiB

Open AccessEditor’s ChoiceArticle

Effects of Laser Microtexturing on the Wetting Behavior of Ti6Al4V Alloy

by Juan Manuel Vazquez-Martinez, Jorge Salguero Gomez, Pedro Francisco Mayuet Ares, Severo Raul Fernandez-Vidal and Moises Batista Ponce

Coatings 2018, 8(4), 145; https://doi.org/10.3390/coatings8040145 - 17 Apr 2018

Cited by 20 | Viewed by 4910

Abstract

Surface modification procedures by laser techniques allow the generation of specific topographies and microstructures that enable the adaptation of the external layers of materials for specific applications. In laser texturing processes, it is possible to maintain control over the microgeometry and dimensions of [...] Read more.

Surface modification procedures by laser techniques allow the generation of specific topographies and microstructures that enable the adaptation of the external layers of materials for specific applications. In laser texturing processes, it is possible to maintain control over the microgeometry and dimensions of the surface pattern through varying the processing parameters. One of the main areas of interest in the field of surface modification treatments is the ability to generate topographies that are associated with specific surface finishes, in terms of roughness, that can improve the manufactured part’s functional capabilities. In this aspect, several types of phenomena have been detected, such as the friction and sliding wear behavior or wetting capacity, which maintain a high dependence on surface roughness. In this research, surface texturing treatments have been developed by laser techniques through using the scanning speed of the beam (V_s) as a control parameter in order to generate samples that have topographies with different natures. Through assessments of surface finish using specialized techniques, the dimensional and geometrical features of the texturized tracks have been characterized, analyzing their influence on the wetting behavior of the irradiated layer. In this way, more defined texturing grooves has been developed by increasing the V_s, which also improves the hydrophobic characteristics of the treated surface. However, due to the lack of uniformity in the solidification process of the irradiated area, some deviations from the expected trends and singular points can be observed. Using the contact angle method to evaluate the wetting behavior of the applied treatments found increases in the contact angle values for high texturing speeds, finding a maximum value of 65.59° for V_s = 200 mm/s. Full article

(This article belongs to the Special Issue Laser Surface Treatment)

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14 pages, 6755 KiB

Open AccessArticle

Fabrication of Self-healing Superhydrophobic Surfaces from Water-Soluble Polymer Suspensions Free of Inorganic Particles through Polymer Thermal Reconstruction

by Yalun Shen, Yitian Wu, Zhehong Shen and Hao Chen

Coatings 2018, 8(4), 144; https://doi.org/10.3390/coatings8040144 - 16 Apr 2018

Cited by 18 | Viewed by 6429

Abstract

Self-healing superhydrophobic surfaces have been fabricated by casting and drying water-soluble amphiphilic polymer suspensions at room temperature through thermal reconstruction. When compared with previous methods, this approach exploits modified natural hierarchical microstructures from wood instead of artificially constructing them for superhydrophobic morphology, which [...] Read more.

Self-healing superhydrophobic surfaces have been fabricated by casting and drying water-soluble amphiphilic polymer suspensions at room temperature through thermal reconstruction. When compared with previous methods, this approach exploits modified natural hierarchical microstructures from wood instead of artificially constructing them for superhydrophobic morphology, which involves neither organic solvent nor inorganic particles nor complex procedures. The obtained superhydrophobic surface has acceptable resistance to abrasion. The surface can recover superhydrophobicity spontaneously at room temperature upon damage, which can be accelerated at a higher temperature. After depleting healing agents, the polymer suspension can be sprayed or cast onto wood surfaces to replenish healing agents and to restore self-healing ability. The superhydrophobic surface greatly increases the mold inhibition and water resistance of wood, which would prolong the service life of wood based materials. Full article

(This article belongs to the Special Issue Superhydrophobic Coatings)

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10 pages, 8321 KiB

Open AccessArticle

Evaluation of Thermal Degradation of DLC Film Using a Novel Raman Spectroscopy Technique

by Muyang He and Changdong Yeo

Coatings 2018, 8(4), 143; https://doi.org/10.3390/coatings8040143 - 16 Apr 2018

Cited by 16 | Viewed by 6776

Abstract

Diamond-like carbon (DLC) films are extensively used in various industries due to their superior protective and lubrication properties. However, DLC films including sp² and sp³ carbon bonding are metastable materials, which can be thermally degraded (or graphitized) at elevated temperature. In [...] Read more.

Diamond-like carbon (DLC) films are extensively used in various industries due to their superior protective and lubrication properties. However, DLC films including sp² and sp³ carbon bonding are metastable materials, which can be thermally degraded (or graphitized) at elevated temperature. In this study, a novel Raman spectroscopy technique was developed to evaluate the in-situ thermal stability of DLC films. When a laser beam is applied onto a DLC film, the surface temperature can increase depending on the laser power, laser duration time, and surface reflectivity. Based on this laser heating concept, the Raman spectrum data of DLC films (i.e., G peak position and width) were obtained at the controlled Raman laser power, which enabled to determine the critical temperature to initiate the thermal degradation of DLC films. Two different designs of DLC film (i.e., types A and B with different initial sp²-to-sp³ ratio) were prepared and their thermal stability was evaluated using the proposed Raman spectroscopy technique. From the systematic data analysis and comparison, it could be observed that the type-A DLC film showed the significant change of Raman parameters (i.e., G peak position and width) at lower laser power value (=lower temperature) than the type-B DLC film, which indicated that the type-B DLC film had better thermal stability. Full article

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19 pages, 19683 KiB

Open AccessArticle

Efficiently Extracted Cellulose Nanocrystals and Starch Nanoparticles and Techno-Functional Properties of Films Made Thereof

by Christoph Metzger, Solange Sanahuja, Lisa Behrends, Sven Sängerlaub, Martina Lindner and Heiko Briesen

Coatings 2018, 8(4), 142; https://doi.org/10.3390/coatings8040142 - 14 Apr 2018

Cited by 13 | Viewed by 8273

Abstract

Cellulose nanocrystals (CNC) and starch nanoparticles (SNP) have remarkable physical and mechanical characteristics. These properties particularly facilitate their application as high-performance components of bio-based packaging films as alternatives to fossil-based counterparts. This study demonstrates a time-efficient and resource-saving extraction process of CNC and [...] Read more.

Cellulose nanocrystals (CNC) and starch nanoparticles (SNP) have remarkable physical and mechanical characteristics. These properties particularly facilitate their application as high-performance components of bio-based packaging films as alternatives to fossil-based counterparts. This study demonstrates a time-efficient and resource-saving extraction process of CNC and SNP by sulfuric acid hydrolysis and neutralization. The yields of the hydrolyzed products were 41.4% (CNC) and 32.2% (SNP) after hydrolysis times of 3 h and 120 h, respectively. The nanoparticle dispersions were wet-coated onto poly(lactic acid) (PLA) and paper substrates and were incorporated into starch films. No purification or functionalization of the nanoparticles was performed prior to their application. Techno-functional properties such as the permeability of oxygen and water vapor were determined. The oxygen permeability of 5–9 cm³ (STP) 100 µm m⁻² d⁻¹ bar⁻¹ at 50% relative humidity and 23 °C on PLA makes the coatings suitable as oxygen barriers. The method used for the extraction of CNC and SNP contributes to the economic production of these nanomaterials. Further improvements, e.g., lower ion concentration and narrower particle size distribution, to achieve reproducible techno-functional properties are tangible. Full article

(This article belongs to the Special Issue Functional Coatings for Food Packaging Applications)

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13 pages, 98064 KiB

Open AccessArticle

Self-Assembled Composite Langmuir Films via Fluorine-Containing Bola-Type Derivative with Metal Ions

by Nianrui Qu, Shuxin Sun, Qianran Zhao, Tifeng Jiao, Jingxin Zhou, Ruirui Xing, Faming Gao, Lexin Zhang and Qiuming Peng

Coatings 2018, 8(4), 141; https://doi.org/10.3390/coatings8040141 - 14 Apr 2018

Cited by 1 | Viewed by 4831

Abstract

The design and preparation of functional bolaamphiphile-based composite films are of key importance for application in a wide variety of fields. This study demonstrates a new approach to constructing composite films by the Langmuir-Blodgett (LB) method using a fluorine-containing bola-type diacid derivative with [...] Read more.

The design and preparation of functional bolaamphiphile-based composite films are of key importance for application in a wide variety of fields. This study demonstrates a new approach to constructing composite films by the Langmuir-Blodgett (LB) method using a fluorine-containing bola-type diacid derivative with different metal ions. The bola-type molecule we used could be spread on water surfaces and metal ion subphases to fabricate various nanostructured ultrathin films. The obtained data demonstrated that the employed metal ions, including Ag(I), Cu(II), and Eu(III) ions in subphase solutions, can regulate the organized molecular stacking and form interfacial nanostructures deposited in LB films. It was found that the interfacial coordinating interactions can easily occur between carboxyl groups in a molecular skeleton with metal ions in the formed composite films. The formation of composite films was confirmed by changes in the surface pressure-area isotherms, morphologies, and spectra of the transferred LB films. While various research works have achieved the regulation of functions and nanostructures of sophisticated bola-type compounds, we here demonstrate a simple routine to modulate the nanostructures and organized packing of bola-type compounds composite films by changing the metal ions in subphase solutions. Full article

(This article belongs to the Special Issue Nanostructured Thin Films)

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10 pages, 5517 KiB

Open AccessArticle

Microstructure Evolution of a Magnesium Phosphate Protective Layer on Concrete Structures in a Sulfate Environment

by Jun Li, Yongsheng Ji, Guodong Huang and Linglei Zhang

Coatings 2018, 8(4), 140; https://doi.org/10.3390/coatings8040140 - 14 Apr 2018

Cited by 10 | Viewed by 5021

Abstract

This study investigates the resistance of an uncoated magnesium phosphate cement (MPC) protective layer to sulfate attacks through changes in its compressive strength and appearance. X-ray Diffraction (XRD) and scanning electron microscopy (SEM) microanalyses are conducted on the MPC layer concrete both before [...] Read more.

This study investigates the resistance of an uncoated magnesium phosphate cement (MPC) protective layer to sulfate attacks through changes in its compressive strength and appearance. X-ray Diffraction (XRD) and scanning electron microscopy (SEM) microanalyses are conducted on the MPC layer concrete both before and after etching, where changes in the microstructure of the magnesium phosphate protective layer are analyzed during the corrosion process. In addition, this study also explores the intrinsic mechanisms of the MPC protective layer in terms of the resistance of concrete to sulfate. The results showed that the erosion resistance of the concrete to sulfate can be dramatically improved by the MPC protective layer. The structure and composition of the MPC protective layer are different in the sulfate erosion environment compared with those exposed to other environments: the protective layer is more closely bonded to the concrete and has a more compact structure. Therefore, the MPC protective layer is verified to have a significant protective effect on concrete against sulfate corrosion. Full article

(This article belongs to the Special Issue Advanced Coatings for Corrosion Protection in Extreme Environments)

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14 pages, 45427 KiB

Open AccessArticle

Effect of Reaction Conditions on the Surface Modification of Cellulose Nanofibrils with Aminopropyl Triethoxysilane

by Eduardo Robles, Levente Csóka and Jalel Labidi

Coatings 2018, 8(4), 139; https://doi.org/10.3390/coatings8040139 - 13 Apr 2018

Cited by 57 | Viewed by 13146

Abstract

Nine different surface modifications of cellulose nanofibrils (CNF) with 3-aminopropyl triethoxysilane (ATS) by using three different solvent systems (water, ethanol, and a mixture of both) were investigated. The effect of reaction conditions, such as silane to cellulose ratio and solvent type were evaluated [...] Read more.

Nine different surface modifications of cellulose nanofibrils (CNF) with 3-aminopropyl triethoxysilane (ATS) by using three different solvent systems (water, ethanol, and a mixture of both) were investigated. The effect of reaction conditions, such as silane to cellulose ratio and solvent type were evaluated to determine their contribution to the extent of the silane modification. Nanofibril properties were evaluated by infrared spectroscopy, powder X-ray diffraction, surface free energy, thermogravimetry, ¹³C and ²⁹Si nuclear magnetic resonance, and electronic microscopy. The influence of the solvent in the solvolysis of the silane was reflected in the presence or absence of ethoxy groups in the silane. On the other hand, whereas the surface modification was increased directly proportionally to silane ratio on the reaction, the aggregation of nanofibrils was also increased, which can play a negative role in certain applications. The increment of silane modification also had substantial repercussions on the crystallinity of the nanofibrils by the addition of amorphous components to the crystalline unit; moreover, silane surface modifications enhanced the hydrophobic character of the nanofibrils. Full article

(This article belongs to the Special Issue Surface Modification of Cellulose Fibres)

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15 pages, 30457 KiB

Open AccessFeature PaperArticle

Lanthanum-Silica Sol-Gel Coatings for Protecting Metallic Materials in Museums: Approaches to Copper, Bronze, Lead and Steel

by Javier Peña-Poza, Fernando Agua, Cristina Gil, María-Ángeles Villegas and Manuel García-Heras

Coatings 2018, 8(4), 138; https://doi.org/10.3390/coatings8040138 - 12 Apr 2018

Cited by 1 | Viewed by 5290

Abstract

Museum objects made from metals face the challenge of delaying corrosion in exhibition rooms, showcases and holdings. This study examined some innovative solutions used to protect such items based on sol-gel coatings doped with lanthanum. These coatings were prepared from sols based on [...] Read more.

Museum objects made from metals face the challenge of delaying corrosion in exhibition rooms, showcases and holdings. This study examined some innovative solutions used to protect such items based on sol-gel coatings doped with lanthanum. These coatings were prepared from sols based on TEOS as a precursor. Lanthanum acetate/nitrate was added as a doping agent and corrosion inhibitor. The coatings were deposited upon slabs of copper, bronze, lead and steel, since they are among the most common metals present in museums items. The coatings application was accomplished by immersion-extraction, and the remaining sols were gelled and characterized by Fourier transformed infrared spectroscopy and differential thermal analysis and thermogravimetry. To evaluate the behaviour and resistance of the coatings, tests of accelerated aging were carried out in climatic and Kesternich chambers, as well as under an atmosphere saturated with organic acids and under UV irradiation. The simulated conditions tested were undertaken to approach real conditions inside a conventional museum showcase. The microstructure of the coatings before and after accelerated aging tests was observed through optical and field emission scanning electron microscopies. The results indicated that these coatings can be a useful preventive, conservation avenue to protect copper, bronze and lead items exhibited in museums. Full article

(This article belongs to the Special Issue Communications from TechnoHeritage 2017)

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14 pages, 3206 KiB

Open AccessEditor’s ChoiceReview

2D Materials-Coated Plasmonic Structures for SERS Applications

by Ming Xia

Coatings 2018, 8(4), 137; https://doi.org/10.3390/coatings8040137 - 12 Apr 2018

Cited by 30 | Viewed by 8515

Abstract

Two-dimensional (2D) materials, such as graphene and hexagonal boron nitride, are new kinds of materials that can serve as substrates for surface enhanced Raman spectroscopy (SERS). When combined with traditional metallic plasmonic structures, the hybrid 2D materials/metal SERS platform brings extra benefits, including [...] Read more.

Two-dimensional (2D) materials, such as graphene and hexagonal boron nitride, are new kinds of materials that can serve as substrates for surface enhanced Raman spectroscopy (SERS). When combined with traditional metallic plasmonic structures, the hybrid 2D materials/metal SERS platform brings extra benefits, including higher SERS enhancement factors, oxidation protection of the metal surface, and protection of molecules from photo-induced damages. This review paper gives an overview of recent progress in the 2D materials-coated plasmonic structure in SERS application, focusing on the fabrication of the hybrid 2D materials/metal SERS platform and its applications for Raman enhancement. Full article

(This article belongs to the Special Issue Graphene and Other 2D Layered Nanomaterial-Based Films: Synthesis, Properties and Applications)

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16 pages, 19468 KiB

Open AccessFeature PaperArticle

Sharply Reduced Biofilm Formation from Cobetia marina and in Black Sea Water on Modified Siloxane Coatings

by Danail Akuzov, Lia Franca, Ingo Grunwald and Todorka Vladkova

Coatings 2018, 8(4), 136; https://doi.org/10.3390/coatings8040136 - 11 Apr 2018

Cited by 12 | Viewed by 5766

Abstract

Siloxane fouling release coatings are currently the only viable non-toxic commercial alternative to toxic biocide antifouling paints. However, they only partially inhibit biofouling since biofilms remain a major issue. With the aim to improve the bacterial resistance of siloxane coatings modified with non-ionic [...] Read more.

Siloxane fouling release coatings are currently the only viable non-toxic commercial alternative to toxic biocide antifouling paints. However, they only partially inhibit biofouling since biofilms remain a major issue. With the aim to improve the bacterial resistance of siloxane coatings modified with non-ionic surfactant (NIS), antioxidant (AO) or both NIS/AO, the ability of PEG-silane co-cross-linker was investigated to reduce Cobetia marina adhesion and multispecies biofilm formation from natural seawater. Surface physical-chemical and physical-mechanical parameters relevant to bio-adhesion were estimated before the testing of the biofilm formation. Slightly reduced biofilm from C. marina and sharply reduced multispecies biofilm, formed in natural sea water, were found on the PEG-silane co-cross-linked coatings without modifying additives. However, both C. marina growth and biofilm formation from natural sea water were sharply reduced on the PEG-silane co-cross-linked coatings containing NIS or AO, even more, no C. marina adhesion was seen on the coating containing NIS and AO simultaneously. Possible explanations of the observed effects are presented in this article. It was concluded that the PEG-silane co-cross-linker, toghether with NIS and AO, can be used as an efficient tool to additionally reduce the bioadhesion of Gram-negative marine bacteria and multispecies biofilm formation on siloxane antifouling coatings. Full article

(This article belongs to the Special Issue Novel Marine Antifouling Coatings)

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14 pages, 18387 KiB

Open AccessArticle

Physicochemical and Biological Activity Analysis of Low-Density Polyethylene Substrate Modified by Multi-Layer Coatings Based on DLC Structures, Obtained Using RF CVD Method

by Karol Kyzioł, Julia Oczkowska, Daniel Kottfer, Marek Klich, Łukasz Kaczmarek, Agnieszka Kyzioł and Zbigniew Grzesik

Coatings 2018, 8(4), 135; https://doi.org/10.3390/coatings8040135 - 10 Apr 2018

Cited by 12 | Viewed by 5607

Abstract

In this paper, the surface properties and selected mechanical and biological properties of various multi-layer systems based on diamond-like carbon structure deposited on low-density polyethylene (LDPE) substrate were studied. Plasma etching and layers deposition (incl. DLC, N-DLC, Si-DLC) were carried out using the [...] Read more.

In this paper, the surface properties and selected mechanical and biological properties of various multi-layer systems based on diamond-like carbon structure deposited on low-density polyethylene (LDPE) substrate were studied. Plasma etching and layers deposition (incl. DLC, N-DLC, Si-DLC) were carried out using the RF CVD (radio frequency chemical vapor deposition) method. In particular, polyethylene with deposited N-DLC and DLC layers in one process was characterized by a surface hardness ca. seven times (up to ca. 2.3 GPa) higher than the unmodified substrate. Additionally, its surface roughness was determined to be almost two times higher than the respective plasma-untreated polymer. It is noteworthy that plasma-modified LDPE showed no significant cytotoxicity in vitro. Thus, based on the current research results, it is concluded that a multilayer system (based on DLC coatings) obtained using plasma treatment of the LDPE surface can be proposed as a prospective solution for improving mechanical properties while maintaining biocompatibility. Full article

(This article belongs to the Special Issue Functional Ceramic Coatings)

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16 pages, 39636 KiB

Open AccessArticle

Tribological Properties of New Cu-Al/MoS₂ Solid Lubricant Coatings Using Magnetron Sputter Deposition

by Ming Cao, Lan Zhao, Libin Wu and Wenquan Wang

Coatings 2018, 8(4), 134; https://doi.org/10.3390/coatings8040134 - 6 Apr 2018

Cited by 21 | Viewed by 6274

Abstract

The increasing demands of environmental protection have led to solid lubricant coatings becoming more and more important. A new type of MoS₂-based coating co-doped with Cu and Al prepared by magnetron sputtering, including Cu/MoS₂ and Cu-Al/MoS₂ coatings, for lubrication [...] Read more.

The increasing demands of environmental protection have led to solid lubricant coatings becoming more and more important. A new type of MoS₂-based coating co-doped with Cu and Al prepared by magnetron sputtering, including Cu/MoS₂ and Cu-Al/MoS₂ coatings, for lubrication applications is reported. To this end, the coatings were annealed in an argon atmosphere furnace. The microstructure and the tribological properties of the coatings prior to and following annealing were analyzed using scanning electron microscopy, energy dispersive spectrometry, X-ray diffractometry (XRD) and with a multi-functional tester for material surface properties. The results demonstrated that the friction coefficient of the Cu/MoS₂ coating was able to reach as low as 0.07, due to the synergistic lubrication effect of the soft metal Cu with MoS₂. However, the wear resistance of the coating was not satisfied. Although the lowest friction coefficient of the Cu-Al/MoS₂ coatings was 0.083, the wear resistance was enhanced, which was attributed to the improved the toughness of the coatings due to the introduction of aluminum. The XRD results revealed that the γ₂-Cu₉Al₄ phase was formed in the specimen of Cu-Al/MoS₂ coatings. The comprehensive performance of the Cu-Al/MoS₂ coatings after annealing was improved in comparison to substrate heating, since the heat-treatment was beneficial for the strengthening of the solid solution of the coatings. Full article

(This article belongs to the Special Issue Coatings Tribology)

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12 pages, 7359 KiB

Open AccessArticle

Chitosan Based Regenerated Cellulose Fibers Functionalized with Plasma and Ultrasound

by Urška Vrabič Brodnjak, Adolf Jesih and Diana Gregor-Svetec

Coatings 2018, 8(4), 133; https://doi.org/10.3390/coatings8040133 - 5 Apr 2018

Cited by 19 | Viewed by 5758

Abstract

The great potential of regenerated cellulose fibers, which offer excellent possibilities as a matrix for the design of bioactive materials, was the lead for our research. We focused on the surface modification of fibers to improve the sorption properties of regenerated cellulose and [...] Read more.

The great potential of regenerated cellulose fibers, which offer excellent possibilities as a matrix for the design of bioactive materials, was the lead for our research. We focused on the surface modification of fibers to improve the sorption properties of regenerated cellulose and biocomposite regenerated cellulose/chitosan fibers, which are on the market. The purpose of our investigation was also the modification of regenerated cellulose fibers with the functionalization by chitosan as a means of obtaining similar properties to biocomposite regenerated cellulose/chitosan fibers on the market. Argon gas plasma was used for fiber surface activation and chitosan adsorption. Ultrasound was also used as a treatment procedure for the surface activation of regenerated cellulose fibers and treatment with chitosan. Analyses have shown that ultrasonic energy or plasma change the accessibility of free functional groups, structure and reactivity, especially in regenerated cellulose fibers. Changes that occurred in the morphology and in the structure of fibers were also reflected in their physical and chemical properties. Consequently, moisture content, sorption properties and water retention improved. Full article

(This article belongs to the Special Issue Surface Modification of Cellulose Fibres)

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20 pages, 25338 KiB

Open AccessArticle

Enhancement of the Corrosion Resistance of 304 Stainless Steel by Cr–N and Cr(N,O) Coatings

by Mihaela Dinu, Emile S. Massima Mouele, Anca C. Parau, Alina Vladescu, Leslie F. Petrik and Mariana Braic

Coatings 2018, 8(4), 132; https://doi.org/10.3390/coatings8040132 - 5 Apr 2018

Cited by 36 | Viewed by 10307

Abstract

Chromium nitride and oxynitride coatings were deposited as monolayers ((Cr–N), Cr(N,O)) and bilayers (Cr–N/Cr(N,O), Cr(N,O)/Cr–N) on 304 steel substrates by reactive cathodic arc method. The coatings were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), surface profilometry, [...] Read more.

Chromium nitride and oxynitride coatings were deposited as monolayers ((Cr–N), Cr(N,O)) and bilayers (Cr–N/Cr(N,O), Cr(N,O)/Cr–N) on 304 steel substrates by reactive cathodic arc method. The coatings were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), surface profilometry, and scratch tester. The anticorrosive properties of the coatings were assessed by electrochemical tests in 0.10 M NaCl + 1.96 M H₂O₂, carried out at 24 °C. Cr₂N, CrN, and Cr(N,O) phases were identified in the coatings by grazing incidence X-ray diffraction (GI-XRD) measurements. The measured adhesion values ranged from 19 N to 35 N, the highest value being obtained for the bilayer with Cr(N,O) on top. Electrochemical tests showed that Cr(N,O) presence in both mono- and bilayered coatings determined the lowest damage in corrosive solution, as compared to the Cr–N coatings. This improvement was ascribed to the more compact structure, lower coatings porosity, and smoother surface. Full article

(This article belongs to the Special Issue Coatings for Harsh Environments)

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9 pages, 6003 KiB

Open AccessArticle

Recent Advances in Low-Temperature Deposition Methods of Transparent, Photocatalytic TiO₂ Coatings on Polymers

by Jonathan Watté, Matthias Van Zele, Klaartje De Buysser and Isabel Van Driessche

Coatings 2018, 8(4), 131; https://doi.org/10.3390/coatings8040131 - 4 Apr 2018

Cited by 14 | Viewed by 5297

Abstract

In this paper, we present an overview as well as current advances in the low-temperature deposition of highly crystalline suspensions of titania nanoparticles on polymers for photocatalytic applications. The presence of preformed titania nanoparticles yields the possibility of producing photocatalytically active coatings at [...] Read more.

In this paper, we present an overview as well as current advances in the low-temperature deposition of highly crystalline suspensions of titania nanoparticles on polymers for photocatalytic applications. The presence of preformed titania nanoparticles yields the possibility of producing photocatalytically active coatings at reduced temperatures. Transparent and photocatalytically active TiO₂ coatings that degrade organic matter, have been widely applied to bestow self-cleaning properties onto surfaces. This low-temperature deposition method and its transition to polymers would open an entire array of possible self-cleaning applications. During this research, incorporation of a silica buffer layer was applied to improve the compatibility of the inorganic coating on a substrate, such as polymethylmethacrylate (PMMA) and polyphenylsulphone (PPSU). The photocatalytic activity of the obtained coating was analyzed for its photocatalytic abilities by evaluating the color removal of a dye solution (methylene blue, MB) under UV irradiation and compared with commercial Pilkington Activ^® self-cleaning glass. Our results indicate that the titania-coated silica-polymer systems yield a higher photocatalytic activity towards the degradation of organic pollutants. This method proves that the deposition of highly crystalline anatase suspensions on silica buffer layers is a viable method to produce photocatalytic coatings on heat-sensitive substrates. Full article

(This article belongs to the Special Issue Nanostructured Thin Films)

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10 pages, 9182 KiB

Open AccessArticle

Realization of Graphene on the Surface of Electroless Ni–P Coating for Short-Term Corrosion Prevention

by Qin-Ying Wang, Jing Yu, Jiao Xu, Hao-Ming Fang, Shuang Liu, Yi-Rong Tang, Yu-Chen Xi and Shu-Lin Bai

Coatings 2018, 8(4), 130; https://doi.org/10.3390/coatings8040130 - 4 Apr 2018

Cited by 8 | Viewed by 5183

Abstract

Graphene was first fabricated on the surface of an electroless Ni–P coating/carbon steel (Ni–P–G) to improve its corrosion resistance. Meanwhile, an electroless Ni–P coating (Ni–P) was heated (Ni–P–H) under the same condition as Ni–P–G for comparison. The morphological results showed that a wavy [...] Read more.

Graphene was first fabricated on the surface of an electroless Ni–P coating/carbon steel (Ni–P–G) to improve its corrosion resistance. Meanwhile, an electroless Ni–P coating (Ni–P) was heated (Ni–P–H) under the same condition as Ni–P–G for comparison. The morphological results showed that a wavy multilayer graphene was formed on the surface of Ni–P–G. The layer number of the graphene film was 5–10 according to the analysis of Raman spectra and observation by a high-resolution transmission electron microscope. The I_D/I_G ratio calculated from the Raman spectrum revealed that the graphene growing at the grain of Ni–P–H had larger grain size than that growing at the grain boundary. The electrochemical results showed a higher R_p, a lower CPE_dl, and a lower corrosion rate of Ni–P–G than Q235 steel, Ni–P, and Ni–P–H, indicating a higher corrosion resistance. In addition, the surface potential map achieved by a scanning Kelvin probe presented a more positive surface potential of Ni–P–G than Ni–P with the difference being around 375–750 mV, demonstrating a lower corrosion tendency of Ni–P–G. Full article

(This article belongs to the Special Issue Advanced Coatings for Corrosion Protection in Extreme Environments)

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17 pages, 28603 KiB

Open AccessArticle

Investigation of Element Effect on High-Temperature Oxidation of HVOF NiCoCrAlX Coatings

by Pimin Zhang, Ru Lin Peng, Xin-Hai Li and Sten Johansson

Coatings 2018, 8(4), 129; https://doi.org/10.3390/coatings8040129 - 3 Apr 2018

Cited by 9 | Viewed by 5970

Abstract

MCrAlX (M: Ni or Co or both, X: minor elements) coatings have been used widely to protect hot components in gas turbines against oxidation and heat corrosion at high temperatures. Understanding the influence of the X-elements on oxidation behavior is important in the [...] Read more.

MCrAlX (M: Ni or Co or both, X: minor elements) coatings have been used widely to protect hot components in gas turbines against oxidation and heat corrosion at high temperatures. Understanding the influence of the X-elements on oxidation behavior is important in the design of durable MCrAlX coatings. In this study, NiCoCrAlX coatings doped with Y + Ru and Ce, respectively, were deposited on an Inconel-792 substrate using high velocity oxygen fuel (HVOF). The samples were subjected to isothermal oxidation tests in laboratory air at 900, 1000, and 1100 °C and a cyclic oxidation test between 100 and 1100 °C with a 1-h dwell time at 1100 °C. It was observed that the coating with Ce showed a much higher oxidation rate than the coating with Y + Ru under both isothermal and cyclic oxidation tests. In addition, the Y + Ru-doped coating showed significantly lower β phase depletion due to interdiffusion between the coating and the substrate, resulting from the addition of Ru. Simulation results using a moving phase boundary model and an established oxidation-diffusion model showed that Ru stabilized β grains, which reduced β-depletion of the coating due to substrate interdiffusion. This paper, combining experiment and simulation results, presents a comprehensive study of the influence of Ce and Ru on oxidation behavior, including an investigation of the microstructure evolution in the coating surface and the coating-substrate interface influenced by oxidation time. Full article

(This article belongs to the Special Issue Thermal Barrier Coatings)

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12 pages, 5070 KiB

Open AccessArticle

Thickness-Dependent Bioelectrochemical and Energy Applications of Thickness-Controlled Meso-Macroporous Antimony-Doped Tin Oxide

by Daniel Mieritz, Runli Liang, Haojie Zhang, Anne-Marie Carey, Shaojiang Chen, Alex Volosin, Su Lin, Neal Woodbury and Dong-Kyun Seo

Coatings 2018, 8(4), 128; https://doi.org/10.3390/coatings8040128 - 2 Apr 2018

Cited by 1 | Viewed by 4196

Abstract

Coatings of hierarchically meso-macroporous antimony-doped tin oxide (ATO) enable interfacing adsorbed species, such as biomacromolecules, with an electronic circuit. The coating thickness is a limiting factor for the surface coverage of adsorbates, that are electrochemically addressable. To overcome this challenge, a carbon black-based [...] Read more.

Coatings of hierarchically meso-macroporous antimony-doped tin oxide (ATO) enable interfacing adsorbed species, such as biomacromolecules, with an electronic circuit. The coating thickness is a limiting factor for the surface coverage of adsorbates, that are electrochemically addressable. To overcome this challenge, a carbon black-based templating method was developed by studying the composition of the template system, and finding the right conditions for self-standing templates, preventing the reaction mixture from flowing out of the mask. The thicknesses of as-fabricated coatings were measured using stylus profilometry to establish a relationship between the mask thickness and the coating thickness. Cyclic voltammetry was performed on coatings with adsorbed cytochrome c to check whether the entire coating thickness was electrochemically addressable. Further, bacterial photosynthetic reaction centers were incorporated into the coatings, and photocurrent with respect to coating thickness was studied. The template mixture required enough of both carbon black and polymer, roughly 7% carbon black and 6% poly(ethylene glycol). Coatings were fabricated with thicknesses approaching 30 µm, and thickness was shown to be controllable up to at least 15 µm. Under the experimental conditions, photocurrent was found to increase linearly with the coating thickness, up to around 12 µm, above which were diminished gains. Full article

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14 pages, 84272 KiB

Open AccessArticle

Effects of Long-Term Static Bending Deformation on a Barrier Thin Film for Flexible Organic Optoelectronic Devices

by Hung-I Lu, Dinh-Phuc Tran, Chih-Kuang Lin and Bao-Dong To

Coatings 2018, 8(4), 127; https://doi.org/10.3390/coatings8040127 - 30 Mar 2018

Cited by 4 | Viewed by 5776

Abstract

The objective of this study is to investigate the effect of long-term static bending on the encapsulation properties of a commercial barrier thin film for flexible optoelectronic devices. Encapsulation properties of the barrier film are evaluated under long-term static bending at various radii [...] Read more.

The objective of this study is to investigate the effect of long-term static bending on the encapsulation properties of a commercial barrier thin film for flexible optoelectronic devices. Encapsulation properties of the barrier film are evaluated under long-term static bending at various radii of curvature. Experimental results reveal that no significantly detrimental effect on the water vapor transmission rate (WVTR) at 40 °C and 90% RH is found for compressive bending up to 1000 h and for tensile bending up to 100 h with a radius of curvature of 5 mm or larger. However, WVTR of the barrier thin film is significantly increased and cracks are found in the barrier film when subjected to tensile bending of a radius of 10 mm or 5 mm for 1000 h. The expected WVTR of the given barrier thin film is numerically computed using a three-dimensional (3D) finite element model. Numerical results indicate that, with the presence of cracks in the barrier thin film, the WVTR increases for an apparent increase in moisture entrances. The WVTR calculated by the 3D cracking model concurs with the experimental results. Full article

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10 pages, 2160 KiB

Open AccessEditor’s ChoiceArticle

Application of Industrial XRF Coating Thickness Analyzer for Phosphate Coating Thickness on Steel

by Aleksandr Sokolov, Jelena Hasikova, Aleksej Pecerskis, Vladimir Gostilo, Ki Yong Lee, Hoobok Jung and Jung Hyun Lim

Coatings 2018, 8(4), 126; https://doi.org/10.3390/coatings8040126 - 30 Mar 2018

Cited by 3 | Viewed by 8080

Abstract

The results of industrial application of an online X-ray fluorescence coating thickness analyzer for measuring the thickness of phosphate coatings on moving steel strips are considered in the article. The target range of coating thickness to be measured is from tens to hundreds [...] Read more.

The results of industrial application of an online X-ray fluorescence coating thickness analyzer for measuring the thickness of phosphate coatings on moving steel strips are considered in the article. The target range of coating thickness to be measured is from tens to hundreds of mg/m² in a measurement time of 10 s. The measurement accuracy observed during long-duration factory acceptance test was 10–15%. The coating thickness analyzer consists of two XRF gauges, mounted above and below the steel strip and capable of moving across the moving strip system for their suspension and relocation and electronic control unit. Fully automated software was developed to automatically and continuously (24/7) control both gauges, scanning both sides of the steel strip, and develop and test methods for measuring new coatings. It allows performing offline storage and retrieval of the measurement results, remotely controlling the analyzer components and measurement modes from a control room. The developed XRF coating thickness analyzer can also be used for real-time measurement of other types of coatings, both metallic and non-metallic. Full article

(This article belongs to the Special Issue Advanced Nondestructive Evaluation and Characterization of Surface)

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10 pages, 8549 KiB

Open AccessArticle

The High-Temperature Resistance Properties of Polysiloxane/Al Coatings with Low Infrared Emissivity

by Jun Zhao, Wei Luo, Lun Qi, Le Yuan, Gang Huang, Yan Huang and Xiaolong Weng

Coatings 2018, 8(4), 125; https://doi.org/10.3390/coatings8040125 - 28 Mar 2018

Cited by 28 | Viewed by 9345

Abstract

High-temperature-resistant coatings with low infrared emissivity were prepared using polysiloxane resin and flake aluminum as the adhesive and pigment, respectively. The heat resistance mechanisms of the polysiloxane/Al coating were systematically investigated. The composition, surface morphology, infrared reflectance spectra, and thermal expansion dimension (Δ [...] Read more.

High-temperature-resistant coatings with low infrared emissivity were prepared using polysiloxane resin and flake aluminum as the adhesive and pigment, respectively. The heat resistance mechanisms of the polysiloxane/Al coating were systematically investigated. The composition, surface morphology, infrared reflectance spectra, and thermal expansion dimension (ΔL) of the coatings were characterized by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy, and thermal mechanical analysis (TMA), respectively. The results show that thermal decomposition of the resin and mismatch of ΔL between the coating and the substrate facilitate the high temperature failure of the coating. A suitable amount of flake aluminum pigments could restrain the thermal decomposition of the resin and could increase the match degree of ΔL between the coating and substrate, leading to an enhanced thermal resistance of the coating. Our results find that a coating with a pigment to binder ratio (P/B ratio) of 1.0 could maintain integrity until 600 °C, and the infrared emissivity was as low as 0.27. Hence, a coating with high-temperature resistance and low emissivity was obtained. Such coatings can be used for infrared stealth technology or energy savings in high-temperature equipment. Full article

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20 pages, 8791 KiB

Open AccessArticle

Laser-Assisted Removal of Graffiti from Granite: Advantages of the Simultaneous Use of Two Wavelengths

by José Santiago Pozo-Antonio, Athanasia Papanikolaou, Kristalia Melessanaki, Teresa Rivas and Paraskevi Pouli

Coatings 2018, 8(4), 124; https://doi.org/10.3390/coatings8040124 - 28 Mar 2018

Cited by 24 | Viewed by 7805

Abstract

Currently, removal of graffiti from stone monuments is a particularly challenging task. Lasers, being highly controllable and precise tools with minimal chemical waste, offer a key solution in this respect and a significant amount of research has been dedicated to this subject. Studies [...] Read more.

Currently, removal of graffiti from stone monuments is a particularly challenging task. Lasers, being highly controllable and precise tools with minimal chemical waste, offer a key solution in this respect and a significant amount of research has been dedicated to this subject. Studies related to the laser cleaning of carbonate stones (such as limestone and marble) reported the extraction of the graffiti layer, although minimal damage to the substrate can be also detected. Recently, research efforts have been focused on the cleaning of granite, which is a complex stone due to its grained and polymineralic texture. Tests involving different wavelengths indicated that the effectiveness of the cleaning procedure is highly dependent on two components: The composition of the binding medium of the graffiti and the fissure system of the granite. In that direction, the aim of this paper is to investigate and to compare the cleaning effectiveness of two wavelengths emitted from a nanosecond (ns) Q-Switched Nd:YAG laser system (IR at 1064 nm and UV at 355 nm), as well as their simultaneous application at different energy density ratios F_IR/F_UV. The effectiveness of this combined methodology has been shown in several other cases; i.e., for the removal of pollution crusts from carbonate stones (marble). For this study, three different in composition graffiti paints (blue, black, and silver) were applied on a fine-grained granite originating from the NW Iberian Peninsula. Prior to the irradiation tests, the damage thresholds of the granite, as well as the extraction thresholds of the graffiti, were determined. Then, several tests involving a variety of parameters (fluence value, number of pulses, etc.) were performed and the most satisfactory irradiation conditions from each individual wavelength as well as their combination were compared, based on graffiti extraction level and any damage induced on the granite forming minerals. The analytical techniques used for the evaluation were stereomicroscopy, color measurements in CIELAB and CIELCH color spaces, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) and confocal microscopy. The experiments indicated the superiority of the combined laser cleaning regarding blue and black graffiti extraction. Full article

(This article belongs to the Special Issue Communications from TechnoHeritage 2017)

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10 pages, 9187 KiB

Open AccessArticle

Production of Antagonistic Compounds by Bacillus sp. with Antifungal Activity against Heritage Contaminating Fungi

by Mara Silva, Tânia Rosado, Marina Gonzalez-Pérez, Débora Gobbo, Dora Teixeira, António Candeias and Ana Teresa Caldeira

Coatings 2018, 8(4), 123; https://doi.org/10.3390/coatings8040123 - 28 Mar 2018

Cited by 7 | Viewed by 5175

Abstract

In recent years, the population has become acutely aware of the need to conserve the world’s resources. The study of new compounds produced by natural means is important in the search for alternative green solutions that act against biodeteriogenic fungi, which promote biodeterioration [...] Read more.

In recent years, the population has become acutely aware of the need to conserve the world’s resources. The study of new compounds produced by natural means is important in the search for alternative green solutions that act against biodeteriogenic fungi, which promote biodeterioration of built cultural heritage sites. The present paper reports new solutions, derived from Bacillus sp. CCLBH 1053 cultures, to produce lipopeptides (LPP) that can act as green biocides to promote the safeguarding of stone artwork. In the stationary phases of bacteria growth, peptone supplementation and sub-lethal heat activation improve the second cycle of sporulation, greatly enhancing LPP production. The bioactive compounds produced by Bacillus cultures suppress biodeteriogenic fungi growth on stone materials, and, hence, provide an important contribution to the development of new biocides for cultural heritage rehabilitation. Full article

(This article belongs to the Special Issue Communications from TechnoHeritage 2017)

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13 pages, 22076 KiB

Open AccessArticle

Cold-Sprayed AZ91D Coating and SiC/AZ91D Composite Coatings

by Yingying Wang, Bernard Normand, Xinkun Suo, Marie-Pierre Planche, Hanlin Liao and Junlei Tang

Coatings 2018, 8(4), 122; https://doi.org/10.3390/coatings8040122 - 26 Mar 2018

Cited by 10 | Viewed by 5338

Abstract

As an emerging coating building technique, cold spraying has many advantages to elaborate Mg alloy workpieces. In this study, AZ91D coatings and AZ91D-based composite coatings were deposited using cold spraying. Coatings were prepared using different gas temperatures to obtain the available main gas [...] Read more.

As an emerging coating building technique, cold spraying has many advantages to elaborate Mg alloy workpieces. In this study, AZ91D coatings and AZ91D-based composite coatings were deposited using cold spraying. Coatings were prepared using different gas temperatures to obtain the available main gas temperature. Compressed air was used as the accelerating gas, and although magnesium alloy is oxidation-sensitive, AZ91D coatings with good performance were obtained. The results show that dense coatings can be fabricated until the gas temperature is higher than 500 °C. The deposition efficiency increases greatly with the gas temperature, but it is lower than 10% for all coating specimens. To analyze the effects of compressed air on AZ91D powder particles and the effects of gas temperature on coatings, the phase composition, porosity, cross-sectional microstructure, and microhardness of coatings were characterized. X-ray diffraction and oxygen content analysis clarified that no phase transformation or oxidation occurred on AZ91D powder particles during cold spraying processes with compressed air. The porosity of AZ91D coatings remained between 3.6% and 3.9%. Impact melting was found on deformed AZ91D particles when the gas temperature increased to 550 °C. As-sprayed coatings exhibit much higher microhardness than as-casted bulk magnesium, demonstrating the dense structure of cold-sprayed coatings. To study the effects of ceramic particles on cold-sprayed AZ91D coatings, 15 vol % SiC powder particles were added into the feedstock powder. Lower SiC content in the coating than in the feedstock powder means that the deposition efficiency of the SiC powder particles is lower than the deposition efficiency of AZ91D particles. The addition of SiC particles reduces the porosity and increases the microhardness of cold-sprayed AZ91D coatings. The corrosion behavior of AZ91D coating and SiC reinforced AZ91D composite coating were examined. The SiC-reinforced AZ91D composite coating reveals higher corrosion potential than magnesium substrate; therefore, it serves as a cathode for the magnesium substrate, the same as the AZ91D coating on magnesium substrate. As the SiC powder is semi-conductive, the embedded SiC particles reduce the electrochemical reaction of the AZ91D coating. The addition of SiC particles increases the corrosion potential of the coating, meanwhile increasing the galvanic potential and decreasing the negative galvanic current of the coating-substrate couple. Full article

(This article belongs to the Special Issue New Generation Coatings for Metals)

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