Coatings

14 pages, 5923 KiB

Open AccessArticle

Electrodeposition of Co-B/SiC Composite Coatings: Characterization and Evaluation of Wear Volume and Hardness

by A. Villa-Mondragón, A. Martínez-Hernández, F. Manríquez, Y. Meas, J. J. Pérez-Bueno, Francisco J. Rodríguez-Valadez, J.C. Ballesteros, J. Morales-Hernández, Alia Méndez-Albores and G. Trejo

Coatings 2019, 9(4), 279; https://doi.org/10.3390/coatings9040279 - 25 Apr 2019

Cited by 3 | Viewed by 3191

Abstract

In this research work, Co-B/SiC composite coatings were synthesized by electrochemical deposition from colloidal suspensions with different content of SiC. The Co-B/SiC films obtained were heat treatment at 350 °C. The composition, morphology, and structure of the Co-B/SiC composite coatings were analyzed using [...] Read more.

In this research work, Co-B/SiC composite coatings were synthesized by electrochemical deposition from colloidal suspensions with different content of SiC. The Co-B/SiC films obtained were heat treatment at 350 °C. The composition, morphology, and structure of the Co-B/SiC composite coatings were analyzed using glow discharge spectrometry (GDS), scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Hardness and tribological properties were also studied. The results showed that an increase in the SiC concentration in the colloidal suspensions resulted in both an increase in the SiC content and a decrease in the B content in the obtained Co-B/SiC coatings. The Co-B/SiC coatings were adherent, glossy, and soft, and exhibited a homogeneous composition in all thicknesses. Besides, an increase in the SiC particle content of the Co-B/SiC composite coating from 0 to 2.56 at.% SiC reduced the hardness of the film from 680 to 360 HV and decreased the wear volume values from 1180 to 23 μm³ N⁻¹ m⁻¹, respectively (that is, the wear resistance increased). Moreover, when the Co-B/SiC coatings with SiC content ranging from 0 to 2.56 at.% SiC were subjected to a heat treatment process, the obtained coating hardness values were in the range of 1200 to 1500 HV, and the wear volume values were in the range of 382 to 19 μm³ N⁻¹ m⁻¹. Full article

(This article belongs to the Special Issue Manufacturing and Surface Engineering II)

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8 pages, 7263 KiB

Open AccessArticle

A Zinc-Rich Coating Fabricated on a Magnesium Alloy by Oxide Reduction

by Dongzhu Lu, Yanliang Huang, Jizhou Duan and Baorong Hou

Coatings 2019, 9(4), 278; https://doi.org/10.3390/coatings9040278 - 25 Apr 2019

Cited by 6 | Viewed by 3807

Abstract

The corrosion resistance of magnesium alloys could be enhanced by covering metallic coatings on the surface. The zinc-rich coating is one of these metallic coatings. To fabricate a zinc-rich coating on magnesium alloys, the substrate should be pretreated carefully, and a protective atmosphere [...] Read more.

The corrosion resistance of magnesium alloys could be enhanced by covering metallic coatings on the surface. The zinc-rich coating is one of these metallic coatings. To fabricate a zinc-rich coating on magnesium alloys, the substrate should be pretreated carefully, and a protective atmosphere is usually required. In this research, a zinc-rich coating was successfully fabricated on the AZ91D magnesium alloy in air by a diffusion alloying method, with zinc oxide as the zinc source. At the same time, the pretreatment of the magnesium alloy matrix was greatly simplified. The as-diffusion-alloyed zinc-rich intermetallic layer was investigated, utilizing SEM, EDS, and XRD, respectively. It is inferred that zinc oxide was reduced into Zn atoms by the active Mg atoms, and the Mg atoms were coming from the magnesium alloy matrix. Then the Zn atoms passed through the oxide film and formed an intermetallic layer on the magnesium alloy surface. Thus, taking advantage of the activity of Mg atoms, magnesium alloys could be surface alloyed with oxides. Full article

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14 pages, 2865 KiB

Open AccessArticle

Solution-Processed Mg-Substituted ZnO Thin Films for Metal-Semiconductor-Metal Visible-Blind Photodetectors

by Chien-Yie Tsay, Shih-Ting Chen and Man-Ting Fan

Coatings 2019, 9(4), 277; https://doi.org/10.3390/coatings9040277 - 25 Apr 2019

Cited by 39 | Viewed by 4228

Abstract

The effects of Mg on the microstructural, optical, and electrical properties of sol-gel derived ZnO transparent semiconductor thin films and the photoelectrical properties of photodetectors based on Mg_xZn_1−xO (where x = 0 to 0.3) thin films with the [...] Read more.

The effects of Mg on the microstructural, optical, and electrical properties of sol-gel derived ZnO transparent semiconductor thin films and the photoelectrical properties of photodetectors based on Mg_xZn_1−xO (where x = 0 to 0.3) thin films with the metal-semiconductor-metal (MSM) configuration were investigated in this study. All the as-synthesized ZnO-based thin films had a single-phase wurtzite structure and showed high average transmittance of 91% in the visible wavelength region. The optical bandgap of Mg_xZn_1−xO thin films increased from 3.25 to 3.56 eV and the electrical resistivity of the films rose from 6.1 × 10² to 1.4 × 10⁴ Ω·cm with an increase in Mg content from x = 0 to x = 0.3. Compared with those of the pure ZnO thin film, the PL emission peaks of the MgZnO thin films showed an apparent blue-shift feature in the UV and visible regions. The photo-detection capability was investigated under visible, UVA, and UVC light illumination. Linear I-V characteristics were obtained in these ZnO-based photodetectors under dark and light illumination conditions, indicating an ohmic contact between the Au electrodes and ZnO-based thin films. It was found that the pure ZnO photodetector exhibited the best photoconductivity gain, percentage of sensitivity, and responsivity under UVA illumination. Under UVC illumination, the photoconductivity gain and percentage of sensitivity of the MgZnO photodetectors were better than those of the pure ZnO photodetector. Full article

(This article belongs to the Special Issue Thin Films and Coatings by Sol-Gel Chemistry: Synthesis, Characterization and Applications)

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10 pages, 6036 KiB

Open AccessArticle

Enhanced Wear Resistance of 316 L Stainless Steel with a Nanostructured Surface Layer Prepared by Ultrasonic Surface Rolling

by Cong Wang, Jing Han, Jiyun Zhao, Yuanming Song, Jiaxiang Man, Hua Zhu, Jiapeng Sun and Liang Fang

Coatings 2019, 9(4), 276; https://doi.org/10.3390/coatings9040276 - 25 Apr 2019

Cited by 16 | Viewed by 2908

Abstract

The low hardness and poor wear resistance of AISI 316 L austenitic stainless-steel sabotage its outer appearance and shorten its service life when it is subjected to sliding. In this paper, the single-pass ultrasonic surface rolling (USR) process was used to modify the [...] Read more.

The low hardness and poor wear resistance of AISI 316 L austenitic stainless-steel sabotage its outer appearance and shorten its service life when it is subjected to sliding. In this paper, the single-pass ultrasonic surface rolling (USR) process was used to modify the surface of 316 L austenitic stainless steel. A nanostructured surface layer with a depth span of 15 μm was fabricated. Dry wear tests of USR samples were performed on a ring-on-block tester at room temperature, and the results were compared with those for the as-received sample. The USR sample showed a significant reduction in wear mass loss and an improved hardness, as well as a decreased surface roughness. The detailed wear mechanism was also investigated by SEM observations of the worn surfaces. It was indicated that oxidation and abrasive wear, accompanied by mild adhesion, dominated the wear of USR 316 L stainless steel at both low and high speeds. The superior wear performance of USR 316 L was attributed to its nanostructured surface layer, which was characterized by a high hardness and thereby suppressed the severe abrasive wear. The results provided an alternative approach to modifying the surface of 316 L stainless steel, without changing its surface chemical components. Full article

(This article belongs to the Special Issue Mechanical Properties of Nanostructured Coatings)

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10 pages, 4858 KiB

Open AccessArticle

Inkjet Printing in Liquid Media: Intra-Volumetric Drop Coalescence in Polymers

by Anastasiia Klestova, Ekaterina Sergeeva and Alexandr V. Vinogradov

Coatings 2019, 9(4), 275; https://doi.org/10.3390/coatings9040275 - 23 Apr 2019

Cited by 8 | Viewed by 3206

Abstract

The tendency to develop flexible and transparent materials has been growing in the last decade. As inkjet printing technology has become a widespread method for the fabrication of functional materials, the investigation of the inkjet printing process seems to be essential with regard [...] Read more.

The tendency to develop flexible and transparent materials has been growing in the last decade. As inkjet printing technology has become a widespread method for the fabrication of functional materials, the investigation of the inkjet printing process seems to be essential with regard to polymers, which are a viscous and flexible media. In this study, we evaluated the dependence of ink drop coalescence on process parameters such as polymer viscosity (controlled by polymerization time), drop spacing and drop speed. The results showed that drop coalescence was mostly influenced by drop speed, while drop spacing and substrate polymer viscosity did not significantly affect the printing results. The presented data are crucial for understanding the processes involved in the fabrication of flexible materials by inkjet printing. Full article

(This article belongs to the Special Issue Thin Coatings and Patterns by Inkjet Printing Technology)

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19 pages, 6785 KiB

Open AccessEditor’s ChoiceArticle

Development of Belt-Type Microstructure Array Flexible Mold and Asymmetric Hot Roller Embossing Process Technology

by Yung-Jin Weng

Coatings 2019, 9(4), 274; https://doi.org/10.3390/coatings9040274 - 22 Apr 2019

Cited by 5 | Viewed by 3607

Abstract

This study proposed the belt-type microstructure array flexible mold designed hot roller embossing process technology. An extrusion molding system was integrated with belt-type hot roller embossing process technology and, deriving the asymmetric principle as the basis of prediction, designed a belt-type microstructure array [...] Read more.

This study proposed the belt-type microstructure array flexible mold designed hot roller embossing process technology. An extrusion molding system was integrated with belt-type hot roller embossing process technology and, deriving the asymmetric principle as the basis of prediction, designed a belt-type microstructure array hot roller embossing process system. This study first focused on the design and manufacturing of a belt-type hot roller embossing process system (roll to belt-type). It then carried out system integration and testing, along with the film extrusion system, to fabrication microstructure array production. Hot embossing was used to replicate the array of the plastic micro lens as the microstructure mold. The original master mold was fabricated with micro electromechanical technology and the PC micro lens array as the microstructure (inner layer) film using the gas-assisted hot embossing technology. A microstructure composite belt and magnetic belt were produced on the hot roller embossing by an innovated coated casting technique. The forming accuracy of the belt-type microstructure array flexible mold hot roller embossing process and the prediction precision of numerically simulated forming were discussed. The proposed process technology is expected to effectively reduce the process cycle time with the advantages of being a fast and continuous process. Full article

(This article belongs to the Special Issue Design, Manufacturing and Measurement of Optical Film Coatings)

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16 pages, 25386 KiB

Open AccessArticle

Coating Effects of ε-Polylysine and Rosmarinic Acid Combined with Chitosan on the Storage Quality of Fresh Half-Smooth Tongue Sole (Cynoglossus semilaevis Günther) Fillets

by Na Li, Wenru Liu, Yong Shen, Jun Mei and Jing Xie

Coatings 2019, 9(4), 273; https://doi.org/10.3390/coatings9040273 - 22 Apr 2019

Cited by 26 | Viewed by 3313

Abstract

The study was to evaluate the effects of chitosan-based coating combined with rosmarinic acid (RA) with different concentrations of ε-polylysine (ε-PL) on flavor retention and sensorial properties of half-smooth tongue sole fillets during storage at 4 °C. Results showed that chitosan-based coatings combined [...] Read more.

The study was to evaluate the effects of chitosan-based coating combined with rosmarinic acid (RA) with different concentrations of ε-polylysine (ε-PL) on flavor retention and sensorial properties of half-smooth tongue sole fillets during storage at 4 °C. Results showed that chitosan-based coatings combined with ε-PL and RA contributed to the reduction of off-flavor compounds, such as total volatile base nitrogen (TVB-N), trimethylamine (TMA), and ATP-related compounds, and accumulation of free amino acids (FAAs). Nineteen volatile organic compounds were analyzed by gas chromatography-mass spectrometer (GC/MS) during storage, including seven alcohols, six aldehydes, and six ketones. The coating treated fresh half-smooth tongue sole (HTS) fillets significantly reduced the relative content of off-odor volatiles, such as 1-octen-3-ol, propanal, hexanal, and octanal. According to sensory evaluation results, chitosan-based coating combined with ε-PL and RA was an effective way to maintain quality of HTS fillets during refrigerated storage. Full article

(This article belongs to the Special Issue Coatings and Interfacial Films for Food Applications—Themed Issue to Celebrate Prof. Raffaele Porta’s Career)

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8 pages, 1666 KiB

Open AccessArticle

Ripple Formation during Oblique Angle Etching

by Mehmet F. Cansizoglu, Mesut Yurukcu and Tansel Karabacak

Coatings 2019, 9(4), 272; https://doi.org/10.3390/coatings9040272 - 22 Apr 2019

Viewed by 3277

Abstract

Chemical removal of materials from the surface is a fundamental step in micro- and nano-fabrication processes. In conventional plasma etching, etchant molecules are non-directional and perform a uniform etching over the surface. However, using a highly directional obliquely incident beam of etching agent, [...] Read more.

Chemical removal of materials from the surface is a fundamental step in micro- and nano-fabrication processes. In conventional plasma etching, etchant molecules are non-directional and perform a uniform etching over the surface. However, using a highly directional obliquely incident beam of etching agent, it can be possible to engineer surfaces in the micro- or nano- scales. Surfaces can be patterned with periodic morphologies like ripples and mounds by controlling parameters including the incidence angle with the surface and sticking coefficient of etching particles. In this study, the dynamic evolution of a rippled morphology has been investigated during oblique angle etching (OAE) using Monte Carlo simulations. Fourier space and roughness analysis were performed on the resulting simulated surfaces. The ripple formation was observed to originate from re-emission and shadowing effects during OAE. Our results show that the ripple wavelength and root-mean-square roughness evolved at a more stable rate with accompanying quasi-periodic ripple formation at higher etching angles (θ > 60°) and at sticking coefficient values (S_c) 0.5 ≤ S_c ≤ 1. On the other hand, smaller etching angle (θ < 60°) and lower sticking coefficient values lead to a rapid formation of wider and deeper ripples. This result of this study can be helpful to develop new surface patterning techniques by etching. Full article

(This article belongs to the Special Issue Modelling and Simulation of Coating 2019)

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12 pages, 1833 KiB

Open AccessArticle

Numerical Model for Calculating the Unstable State Temperature in Asphalt Pavement Structure

by Naiji Zhang, Guoxiong Wu, Bin Chen and Cong Cao

Coatings 2019, 9(4), 271; https://doi.org/10.3390/coatings9040271 - 22 Apr 2019

Cited by 5 | Viewed by 3412

Abstract

In this study, we determined the factors that influence of the temperature on an asphalt pavement by developing a two-dimensional unsteady temperature numerical calculation model using the finite difference method and Matlab. Based on the temperatures obtained by a buried sensor in a [...] Read more.

In this study, we determined the factors that influence of the temperature on an asphalt pavement by developing a two-dimensional unsteady temperature numerical calculation model using the finite difference method and Matlab. Based on the temperatures obtained by a buried sensor in a construction project, we collected the temperatures at different depths in the pavement structure in real time, and we then compared and analyzed the calculated and measured data. The results showed that the temperature in the asphalt pavement structure was significantly correlated with meteorological factors, such as the air temperature, but it also exhibited obvious hysteresis. Compared with the measured data, the maximum deviation in the numerical model based on the variations in the atmospheric temperature and solar radiation was 3 °C. Thus, it is necessary to effectively optimize the selection of asphalt pavement materials by simulating the temperature conditions in the asphalt pavement structure. Full article

(This article belongs to the Collection Pavement Surface Coatings)

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9 pages, 2272 KiB

Open AccessArticle

Oscillating Magnetic Drop: How to Grade Water-Repellent Surfaces

by Angelica Goncalves Dos Santos, Francisco Javier Montes-Ruiz Cabello, Fernando Vereda, Miguel A. Cabrerizo-Vilchez and Miguel A. Rodriguez-Valverde

Coatings 2019, 9(4), 270; https://doi.org/10.3390/coatings9040270 - 21 Apr 2019

Cited by 5 | Viewed by 3141

Abstract

Evaluation of superhydrophobic (SH) surfaces based on contact angle measurements is challenging due to the high mobility of drops and the resolution limits of optical goniometry. For this reason, some alternatives to drop-shape methods have been proposed such as the damped-oscillatory motion of [...] Read more.

Evaluation of superhydrophobic (SH) surfaces based on contact angle measurements is challenging due to the high mobility of drops and the resolution limits of optical goniometry. For this reason, some alternatives to drop-shape methods have been proposed such as the damped-oscillatory motion of ferrofluid sessile drops produced by an external magnetic field. This approach provides information on surface friction (lateral/shear adhesion) from the kinetic energy dissipation of the drop. In this work, we used this method to compare the low adhesion of four commercial SH coatings (Neverwet, WX2100, Ultraever dry, Hydrobead) formed on glass substrates. As ferrofluid, we used a maghemite aqueous suspension (2% v/v) synthesized ad hoc. The rolling magnetic drop is used as a probe to explore shear solid–liquid adhesion. Additionally, drop energy dissipates due to velocity-dependent viscous stresses developed close to the solid–liquid interface. By fitting the damped harmonic oscillations, we estimated the decay time on each coating. The SH coatings were statistically different by using the mean damping time. The differences found between SH coatings could be ascribed to surface–drop adhesion (contact angle hysteresis and apparent contact area). By using this methodology, we were able to grade meaningfully the liquid-repelling properties of superhydrophobic surfaces. Full article

(This article belongs to the Special Issue Superhydrophobic Coatings for Corrosion and Tribology)

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11 pages, 7395 KiB

Open AccessArticle

Formation of Pentagonal Dimples in Icosahedral Diamond Crystals Grown by Hot Filament Chemical Vapor Deposition: Approach by Non-Classical Crystallization

by Chang Weon Song, Rongguang Jin, Jung-Woo Yang, Nong-Moon Hwang and Kwang Ho Kim

Coatings 2019, 9(4), 269; https://doi.org/10.3390/coatings9040269 - 20 Apr 2019

Cited by 1 | Viewed by 3129

Abstract

In this study, acetone was used as a carbon source to deposit diamond films using tantalum filaments by hot filament chemical vapor deposition (HFCVD). For acetone fluxes of 80, 90, 130 and 170 standard cubic centimeters per min (sccm) and the respective hydrogen [...] Read more.

In this study, acetone was used as a carbon source to deposit diamond films using tantalum filaments by hot filament chemical vapor deposition (HFCVD). For acetone fluxes of 80, 90, 130 and 170 standard cubic centimeters per min (sccm) and the respective hydrogen fluxes of 420, 410, 370, and 330 sccm, film thickness appeared to increase with increasing acetone, and high quality diamonds were deposited with well-defined facets of (111) and (100). For acetone fluxes of 210 and 250 sccm and the respective hydrogen fluxes of 290 and 250 sccm, however, the diamond quality was degraded with cauliflower-shaped structures evolving and the film thickness decreased with increasing acetone. The degradation of diamond quality was confirmed by Raman spectra and X-ray diffraction (XRD). Many diamond crystals grown at acetone fluxes of 80, 90, 130 and 170 sccm consisted of five (111) facets, indicating an icosahedral structure. At the corner where the five (111) facets met, there were pentagonal dimples, which implied that diamond crystals must have been etched. The decrease in film thickness at high acetone fluxes of 210 and 250 sccm also implied that the deposited film must have been etched. These results indicate that the two irreversible processes of deposition and etching occur simultaneously, which would violate the second law of thermodynamics from the classical concept of crystal growth by an individual atom. These puzzling results could be successfully explained by non-classical crystallization, where the building blocks for diamond films are nanoparticles formed in the gas phase. Full article

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19 pages, 3233 KiB

Open AccessFeature PaperReview

Electrochemical Strategies for Titanium Implant Polymeric Coatings: The Why and How

by Stefania Cometa, Maria Addolorata Bonifacio, Monica Mattioli-Belmonte, Luigia Sabbatini and Elvira De Giglio

Coatings 2019, 9(4), 268; https://doi.org/10.3390/coatings9040268 - 20 Apr 2019

Cited by 22 | Viewed by 5517

Abstract

Among the several strategies aimed at polymeric coatings deposition on titanium (Ti) and its alloys, metals commonly used in orthopaedic and orthodontic prosthesis, electrochemical approaches have gained growing interest, thanks to their high versatility. In this review, we will present two main electrochemical [...] Read more.

Among the several strategies aimed at polymeric coatings deposition on titanium (Ti) and its alloys, metals commonly used in orthopaedic and orthodontic prosthesis, electrochemical approaches have gained growing interest, thanks to their high versatility. In this review, we will present two main electrochemical procedures to obtain stable, low cost and reliable polymeric coatings: electrochemical polymerization and electrophoretic deposition. Distinction should be made between bioinert films—having mainly the purpose of hindering corrosive processes of the underlying metal—and bioactive films—capable of improving biological compatibility, avoiding inflammation or implant-associated infection processes, and so forth. However, very often, these two objectives have been pursued and achieved contemporaneously. Indeed, the ideal coating is a system in which anti-corrosion, anti-infection and osseointegration can be obtained simultaneously. The ultimate goal of all these coatings is the better control of properties and processes occurring at the titanium interface, with a special emphasis on the cell-coating interactions. Finally, advantages and drawbacks of these electrochemical strategies have been highlighted in the concluding remarks. Full article

(This article belongs to the Special Issue Surfaces Modification and Analysis for Innovative Biomaterials)

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9 pages, 9995 KiB

Open AccessArticle

Recovery Behavior of Microstructured Thiol-Ene Shape-Memory Film

by Algirdas Lazauskas, Viktoras Grigaliūnas and Dalius Jucius

Coatings 2019, 9(4), 267; https://doi.org/10.3390/coatings9040267 - 20 Apr 2019

Cited by 5 | Viewed by 3445

Abstract

In this work, surface microstructurization was coupled with shape-memory polymer to generate reversibly tunable surface properties. A photopolymerizable thiol-ene composition comprising a mixture of pentaerythritol tetrakis(3-mercaptopropionate) (PETMP), 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TTT) and 2,2-dimethoxy-2-phenylacetophenone (DMPA) was used to prepare microstructured thiol-ene shape-memory film via casting and [...] Read more.

In this work, surface microstructurization was coupled with shape-memory polymer to generate reversibly tunable surface properties. A photopolymerizable thiol-ene composition comprising a mixture of pentaerythritol tetrakis(3-mercaptopropionate) (PETMP), 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TTT) and 2,2-dimethoxy-2-phenylacetophenone (DMPA) was used to prepare microstructured thiol-ene shape-memory film via casting and UV polymerization on the electron beam lithography fabricated arrays of 1 µm and 2 µm square pits. The mechanical deformation via compression and recovery of the surface microstructure were investigated. Results show that, after heat treatment of the deformed thiol-ene film, the recovery yields for microstructures were not worse than 90% ± 2% and 93% ± 2% for structures imprinted with 1 µm and 2 µm square pit micro imprint stamps. Additionally, heat treatment of deformed thiol-ene film resulted in the recovery of intense diffraction colors and laser diffraction patterns. This study opens up an avenue of incorporating microstructured shape-memory films for new products, e.g., optical security devices, superhydrophobic coatings, medical diagnostics and biosensors. Full article

(This article belongs to the Special Issue Advances in Flexible Films and Coatings)

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15 pages, 20128 KiB

Open AccessArticle

Feasibility and Surface Evaluation of the Pigment from Scytalidium cuboideum for Inkjet Printing on Textiles

by Sarath M. Vega Gutierrez, Yujuan He, Yu Cao, Derek Stone, Zielle Walsh, Rajiv Malhotra, Hsiou-Lien Chen, Chih-Hung Chang and Seri C. Robinson

Coatings 2019, 9(4), 266; https://doi.org/10.3390/coatings9040266 - 19 Apr 2019

Cited by 13 | Viewed by 4372

Abstract

Textile inkjet printing is an increasingly popular process in the textile industry, as it allows for the incorporation of complex and detailed patterns onto fabrics, as well as the production of small and medium volumes of printed text. Unfortunately, most of the dyes [...] Read more.

Textile inkjet printing is an increasingly popular process in the textile industry, as it allows for the incorporation of complex and detailed patterns onto fabrics, as well as the production of small and medium volumes of printed text. Unfortunately, most of the dyes used by the textile industry come from synthetic and/or non-renewable sources. There has been some research to date in using fungal pigments from wood rotting fungi (‘spalting’ fungi) as textile dyes, however these have never been tested in inkjet printing. Of particular interest is the red crystallizing pigment from Scytalidium cuboideum, which has previously shown exceptional stability on textiles. To test this pigment in an inkjet setting, cotton and polyester fabrics were printed with three different ink formulations involving the red pigment: hexadecyltrimethylammonium bromide (CTAB), ethanol, and acetone. The CTAB and ethanol-based ink formulations formed a ‘mesh-like’ structure on the surface of the cotton and polyester fibers, and turned the fabric purple. Acetone formulas formed crystal structures on the surface and turned the fabric red. These results show promise for turning the red pigment of S. cuboideum into an environmentally friendly, inkjet colorant, however further research is required to evaluate the crocking and explain the crystallization differences between inks. Full article

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11 pages, 17943 KiB

Open AccessArticle

Effect of B Content on Microstructure and Wear Resistance of Fe-3Ti-4C Hardfacing Alloys Produced by Plasma-Transferred Arc Welding

by Lin Zong, Ning Guo, Rongguang Li and Hongbing Yu

Coatings 2019, 9(4), 265; https://doi.org/10.3390/coatings9040265 - 19 Apr 2019

Cited by 16 | Viewed by 3054

Abstract

The Fe-3Ti-xB-4C (x = 1.71, 3.42, 5.10, 6.85 wt. %) hardfacing alloys are deposited on the surface of a low-carbon steel by plasma transferred arc (PTA) weld-surfacing process. Microstructure, hardness and wear resistance have been investigated using scanning electron microscopy [...] Read more.

The Fe-3Ti-xB-4C (x = 1.71, 3.42, 5.10, 6.85 wt. %) hardfacing alloys are deposited on the surface of a low-carbon steel by plasma transferred arc (PTA) weld-surfacing process. Microstructure, hardness and wear resistance have been investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), Rockwell hardness tester and abrasive wear testing machine, respectively. The results show that the microstructure in all alloys is composed of austenite, martensite, Fe₂₃(C,B)₆, Ti(C,B) and Fe₂B. The volume fraction of eutectic borides and Ti(C,B) carbides increases with increasing B content. Many brittle bulk Fe₂B phase arises when the boron content increases to 6.85%, which causes the formation of microcracks in the hardfacing layer. The microhardness of the hardfacing alloys is significantly improved with the B addition, however, the wear resistance of hardfacing alloys increases firstly and then decreases with increasing of B content. The hardfacing alloy with the 5.10% B content has the best wear resistance, which is attributed to high volume fraction of eutectic borides and fine Ti(C,B) particles distributed in the austenite and lath martensite matrix with high hardness and toughness. The formation of brittle bulk Fe₂B particles in the hardfacing alloy with the 6.85% B leads to the fracture and spalling of hard phases during wear, thus, reducing the wear resistance. Full article

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12 pages, 3735 KiB

Open AccessArticle

Understanding the Unique Role of Phospholipids in the Lubrication of Natural Joints: An Interfacial Tension Study

by Aneta D. Petelska, Katarzyna Kazimierska-Drobny, Katarzyna Janicka, Tomasz Majewski and Wiesław Urbaniak

Coatings 2019, 9(4), 264; https://doi.org/10.3390/coatings9040264 - 19 Apr 2019

Cited by 15 | Viewed by 4379

Abstract

Some solid lubricants are characterized by a layered structure with weak (van der Waals) inter-interlayer forces which allow for easy, low-strength shearing. Solid lubricants in natural lubrication are characterized by phospholipid bilayers in the articular joints and phospholipid lamellar phases in synovial fluid. [...] Read more.

Some solid lubricants are characterized by a layered structure with weak (van der Waals) inter-interlayer forces which allow for easy, low-strength shearing. Solid lubricants in natural lubrication are characterized by phospholipid bilayers in the articular joints and phospholipid lamellar phases in synovial fluid. The influence of the acid–base properties of the phospholipid bilayer on the wettability and properties of the surface have been explained by studying the interfacial tension of spherical lipid bilayers based on a model membrane. In this paper, we show that the phospholipid multi-bilayer can act as an effective solid lubricant in every aspect, ranging from a ‘corrosion inhibitor’ in the stomach to a load-bearing lubricant in bovine joints. We present evidence of the outstanding performance of phospholipids and argue that this is due to their chemical inertness and hydrophilic–hydrophobic structure, which makes them amphoteric and provides them with the ability to form lamellar structures that can facilitate functional sliding. Moreover, the friction coefficient can significantly change for a given phospholipid bilayer so it leads to a lamellar-repulsive mechanism under highly charged conditions. After this, it is quickly transformed to result in stable low-friction conditions. Full article

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24 pages, 10011 KiB

Open AccessArticle

Long-Term Hydrolytic Degradation of the Sizing-Rich Composite Interphase

by Andrey E. Krauklis, Abedin I. Gagani and Andreas T. Echtermeyer

Coatings 2019, 9(4), 263; https://doi.org/10.3390/coatings9040263 - 19 Apr 2019

Cited by 24 | Viewed by 4271

Abstract

Glass fiber-reinforced composites are exposed to hydrolytic degradation in subsea and offshore applications. Fiber-matrix interphase degradation was observed after the matrix was fully saturated with water and typical water absorption tests according to ASTM D5229 were stopped. Due to water-induced dissolution, fiber-matrix interphase [...] Read more.

Glass fiber-reinforced composites are exposed to hydrolytic degradation in subsea and offshore applications. Fiber-matrix interphase degradation was observed after the matrix was fully saturated with water and typical water absorption tests according to ASTM D5229 were stopped. Due to water-induced dissolution, fiber-matrix interphase flaws were formed, which then lead to increased water uptake. Cutting sample plates from a larger laminate, where the fibers were running parallel to the 1.5 mm long short edge, allowed the hydrolytic degradation process to be studied. The analysis is based on a full mechanistic mass balance approach considering all the composite’s constituents: water uptake and leaching of the matrix, dissolution of the glass fibers, and dissolution of the composite interphase. These processes were modeled using a combination of Fickian diffusion and zero-order kinetics. For the composite laminate studied here with a saturated epoxy matrix, the fiber matrix interphase is predicted to be fully degraded after 22 to 30 years. Full article

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13 pages, 1802 KiB

Open AccessArticle

Effect of Tea Polyphenols on Curdlan/Chitosan Blending Film Properties and Its Application to Chilled Meat Preservation

by Ying Zhou, Tonglin Xu, Yu Zhang, Chong Zhang, Zhaoxin Lu, Fengxia Lu and Haizhen Zhao

Coatings 2019, 9(4), 262; https://doi.org/10.3390/coatings9040262 - 19 Apr 2019

Cited by 34 | Viewed by 4014

Abstract

Incorporating phenolic acids into polysaccharide films improves their physical properties, in turn improving their potential commercial applicability as a preservation material for different foods. This study aimed to develop films from curdlan and tea polyphenols, and determine the effect of their contents on [...] Read more.

Incorporating phenolic acids into polysaccharide films improves their physical properties, in turn improving their potential commercial applicability as a preservation material for different foods. This study aimed to develop films from curdlan and tea polyphenols, and determine the effect of their contents on the water vapor permeability (WVP) and mechanical properties (tensile strength and elongation at break) of the films. Different ratios of tea polyphenols were incorporated into the curdlan-based films to improve their properties. The results obtained showed that the tensile strength and elongation at break of films were likely to be significantly decreased by adding tea polyphenols, especially at a content of 0.6%, which resulted in a 50% decrease. Meanwhile, the WVP and moisture content of the films was also decreased. However, a low WVP can prevent moisture loss from food. Other film properties, such as antioxidant efficiency, were also investigated. The results showed that the antioxidant potential of the film can be improved by tea polyphenols. The composite films were also applied to the preservation of chilled meat, which resulted in the shelf life being extended by about 3–5 days. Some properties, such as water resistance and DPPH (1,1-diphenyl-2-picrylhydrazyl) free radical scavenging capacity of the composite film, were improved. Full article

(This article belongs to the Special Issue Biodegradable Films and Composite Coatings: Current and Future Trends)

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11 pages, 7566 KiB

Open AccessArticle

Effect of Different ZrN Addition on Microstructure and Wear Properties of Titanium Based Coatings by Laser Cladding Technique

by Xiaodong Li, Shasha Liu, Jiawei Wang, Mengxiao Yu and Haibo Tang

Coatings 2019, 9(4), 261; https://doi.org/10.3390/coatings9040261 - 18 Apr 2019

Cited by 7 | Viewed by 3237

Abstract

In order to improve the wear resistance of TC11 titanium alloy, a mixture of ZrN (10 wt.%, 20 wt.%, 30 wt.%, and 40 wt.%) and TC11 alloy powders are laser cladded on a forged TC11 substrate. The microstructure and wear property of coatings [...] Read more.

In order to improve the wear resistance of TC11 titanium alloy, a mixture of ZrN (10 wt.%, 20 wt.%, 30 wt.%, and 40 wt.%) and TC11 alloy powders are laser cladded on a forged TC11 substrate. The microstructure and wear property of coatings are systematically analyzed. The results show that the microstructure of sample with 10 wt.% ZrN addition has a very fine α + β two-phase microstructure, powders of ZrN are fully melted with no new phase appearance. By increasing the amount of ZrN to 20 wt.%, new phases of TiN_0.3 precipitate with the dendritic morphology in the coating. A further increase in ZrN to 30 wt.% and 40 wt.% do not significantly change the microstructure of the cladded layer but increase the microhardness significantly, phases of TiN form with further enhancement of coating hardness. At the bottom of the cladded layer, the morphology of TiN_0.3 and TiN precipitations changes into a spherical shape with small size. However, the wear performance of the coatings gradually reduces due to the increase of brittleness, and the superior wear properties of the coating are achieved when sample consisted of 20 wt.% ZrN. Full article

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9 pages, 1649 KiB

Open AccessArticle

Thermal, Optical, and Microstructural Properties of Magnetron Sputter-Deposited CuSi Films for Application in Write-Once Blu-Ray Discs

by Feng-Min Lai, Yao-Tsung Yang and Sin-Liang Ou

Coatings 2019, 9(4), 260; https://doi.org/10.3390/coatings9040260 - 18 Apr 2019

Cited by 1 | Viewed by 3520

Abstract

In this study, 16-nm-thick CuSi films were deposited at room temperature by DC magnetron sputtering. The thermal, optical, and microstructural properties of CuSi films were investigated in detail. Moreover, the CuSi film was further used as a recording layer for write-once blu-ray disc [...] Read more.

In this study, 16-nm-thick CuSi films were deposited at room temperature by DC magnetron sputtering. The thermal, optical, and microstructural properties of CuSi films were investigated in detail. Moreover, the CuSi film was further used as a recording layer for write-once blu-ray disc (BD-R) applications. Based on the result of the reflectivity–temperature measurement, the CuSi layer had a decrease in the reflectivity between 180 and 290 °C. The as-deposited CuSi film possessed the Cu₃Si phase. After annealing at 300 °C, the Si atoms existed in the CuSi film segregated and crystallized to the cubic Si phase. The activation energy of Si crystallization in the CuSi film was determined to be 1.2 eV. The dynamic tests presented that the BD-R containing the CuSi recording layer had minimum jitter values of 7.0% at 6 mW and 7.2% at 9 mW, respectively, for 1× and 4× recording speeds. This reveals that the CuSi film has great potential in BD-R applications. Full article

(This article belongs to the Special Issue Advanced Thin Films Deposited by Magnetron Sputtering)

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18 pages, 4511 KiB

Open AccessArticle

Effect of Surface Pre-Treatments on the Formation and Degradation Behaviour of a Calcium Phosphate Coating on Pure Magnesium

by Jiaping Han, Carsten Blawert, Shawei Tang, Junjie Yang, Jin Hu and Mikhail L. Zheludkevich

Coatings 2019, 9(4), 259; https://doi.org/10.3390/coatings9040259 - 18 Apr 2019

Cited by 8 | Viewed by 3162

Abstract

Calcium phosphate (CaPh) coatings are considered promising surface treatments for Mg-based implants. Normally, the phase conversion process of CaPh compounds occurs during immersion in simulated body fluid (SBF) and allows the easy penetration of a corrosive medium. To solve the issue, pre-treatment is [...] Read more.

Calcium phosphate (CaPh) coatings are considered promising surface treatments for Mg-based implants. Normally, the phase conversion process of CaPh compounds occurs during immersion in simulated body fluid (SBF) and allows the easy penetration of a corrosive medium. To solve the issue, pre-treatment is often performed, creating an effective barrier that further improves the corrosion resistance of the underlying Mg. In the present work three pre-treatments including hydrothermal treatment, anodization, and plasma electrolytic oxidation (PEO) were performed on pure Mg prior to CaPh deposition. Results indicated that the composition, morphology, and thickness of the CaPh coatings were strongly influenced by the pre-treatments. Dicalcium phosphate dihydrate (DCPD) was formed on PEO surface, whilst DCPD and hydroxyapatite (HA) were deposited on hydrothermally prepared and anodized surfaces. HA could be deposited on the studied samples during immersion in SBF. The electrochemical impedance spectrum indicated that CaPh coating combined with PEO pre-treatment had the highest corrosion resistance at 120 h due to the superior barrier properties conferred by the PEO layer. Full article

(This article belongs to the Special Issue Bioactive Surfaces and Coatings for Bone Regeneration)

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12 pages, 1863 KiB

Open AccessArticle

The Effects of an Interlayer Debond on the Flexural Behavior of Three-Layer Beams

by Ilaria Monetto

Coatings 2019, 9(4), 258; https://doi.org/10.3390/coatings9040258 - 17 Apr 2019

Cited by 10 | Viewed by 2424

Abstract

Debonds at the interfaces between layers of multilayered systems make the degree of the composite action reduce. As a consequence, the global stiffness of such composites decreases. In order to investigate this reduction, even simplified analytical models are preferable to numerical analyses. This [...] Read more.

Debonds at the interfaces between layers of multilayered systems make the degree of the composite action reduce. As a consequence, the global stiffness of such composites decreases. In order to investigate this reduction, even simplified analytical models are preferable to numerical analyses. This paper analyzes the flexural response of a three-point bending three-layer beam having a debonded portion at the upper interface to investigate the effects of the interlayer debond on the flexural stiffness of the three-layer beam and to examine the feasibility of detecting the presence of possible manufacturing or in-service flaws. A more general model proposed and validated previously by the author was specialized to solve the equilibrium problem considered. A parametric analysis was then performed on varying the model parameters and evaluating the maximum deflection to compare with that for perfectly bonded layers as a measure of the reduction of the flexural stiffness due to the presence of the debond. The numerical results obtained show that the flexural behavior of the sandwich beam under consideration is affected strongly by the length of the debond but only moderately by its position along the interface unless the outer faces are quite stiffer than the core. Full article

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9 pages, 3025 KiB

Open AccessArticle

Kinetically Deposited Copper Antimicrobial Surfaces

by Victor Champagne, Kristin Sundberg and Dennis Helfritch

Coatings 2019, 9(4), 257; https://doi.org/10.3390/coatings9040257 - 17 Apr 2019

Cited by 36 | Viewed by 5526

Abstract

Bacterial and viral contamination of contact surfaces increases the risk of infection. A great deal of work has been done on the capabilities of copper and its alloys to protect against a variety of microorganisms endangering public health, particularly in healthcare and food [...] Read more.

Bacterial and viral contamination of contact surfaces increases the risk of infection. A great deal of work has been done on the capabilities of copper and its alloys to protect against a variety of microorganisms endangering public health, particularly in healthcare and food processing applications. This work has conclusively shown the effectiveness of copper for touch surface disinfection; however, the optimum microstructural characteristics of the copper surface have not been established. The sterilization effectiveness of three kinetically sprayed copper surfaces and two copper feedstocks were examined. The surfaces were inoculated with methicillin-resistant Staphylococcus aureus (MRSA) and influenza A virus. After a two-hour exposure to the surfaces, the surviving microorganisms were assayed, and the results contrasted. These tests showed substantial antimicrobial differences between the coatings generated by the spray techniques and those obtained by different feedstock powders. The significance of the copper spray application was demonstrated, and the application-dependent mechanism for antimicrobial effectiveness was explained. Full article

(This article belongs to the Special Issue Cold Spraying: Recent Trends and Future Views)

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10 pages, 5024 KiB

Open AccessArticle

Analysis of High-Efficiency Mo-Based Solar Selective Absorber by Admittance Locus Method

by Hung-Pin Chen, Chao-Te Lee, Wei-Bo Liao, Ya-Chen Chang, Yu-Sheng Chen, Meng-Chi Li, Cheng-Chung Lee and Chien-Cheng Kuo

Coatings 2019, 9(4), 256; https://doi.org/10.3390/coatings9040256 - 17 Apr 2019

Cited by 7 | Viewed by 3294

Abstract

High absorptivity and low emissivity are characteristics needed in an ideal solar selective absorber. In high-temperature applications, such as a solar concentration power system in which the solar surface works under a long-term high temperature (about 400 to 800 °C), the absorber material [...] Read more.

High absorptivity and low emissivity are characteristics needed in an ideal solar selective absorber. In high-temperature applications, such as a solar concentration power system in which the solar surface works under a long-term high temperature (about 400 to 800 °C), the absorber material has to maintain high absorption in the visible region, high reflectance in the infrared region, and excellent thermal stability at high temperature. In this research, the design of a molybdenum-based (Mo-based) solar selective absorber was analyzed by the admittance locus method, and the films were deposited by magnetron sputtering. The ratio of the extinction coefficient to the refractive index of the Mo layer was close to 1, so that the Mo-based solar selective absorber had a broad absorption band, high absorption, and good solar selectivity. Its average reflectance in the visible region was less than 0.4%. The experimental absorption was 97.1% (simulated absorption was 98%) and the emissivity was from 13% to 20% (simulated emissivity was 8% to 26%) as the temperature increased from 400 to 800 °C. Full article

(This article belongs to the Special Issue Design, Manufacturing and Measurement of Optical Film Coatings)

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7 pages, 1360 KiB

Open AccessArticle

Hydrogen-Assisted Sputtering Growth of TiN on Ceramic Substrates

by Jaewon Choi, Wonjin Jeon, Dongjin Kang, Doowon Kang and Jungyol Jo

Coatings 2019, 9(4), 255; https://doi.org/10.3390/coatings9040255 - 17 Apr 2019

Cited by 6 | Viewed by 3949

Abstract

Titanium nitride (TiN) has mechanical and electrical characteristics applicable for very large scale integration (VLSI) and discrete electronic devices. This study assessed the effect of hydrogen on sputtering growth of TiN on ceramic substrates. Although ceramic substrate is used in discrete device applications [...] Read more.

Titanium nitride (TiN) has mechanical and electrical characteristics applicable for very large scale integration (VLSI) and discrete electronic devices. This study assessed the effect of hydrogen on sputtering growth of TiN on ceramic substrates. Although ceramic substrate is used in discrete device applications due to its insulating property, ceramic is also porous and contains oxygen and water vapor gases, which can be incorporated into TiN films during growth. In addition, discrete devices are usually packaged in glass sealing at 700 °C, and reaction with the trapped gases can significantly degrade the quality of the TiN film. In order to evaluate ways to minimize the effects of these gases on TiN, hydrogen gas was introduced during sputtering growth. The main hypothesis was that the hydrogen gas would react with oxygen to lower the oxygen density in the vacuum chamber, which would suppress the effects of the trapped gases in the ceramic and ultimately improve the quality of the TiN film. Improvements in TiN quality were confirmed by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and resistance measurements. During the glass-sealing process, N₂-purging at 400 °C was effective at keeping the TiN in a low resistance state. These results show that introducing hydrogen gas during sputtering growth could solve the problems caused by ceramic substrates. Full article

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14 pages, 3007 KiB

Open AccessArticle

Electrochemical Impedance Spectroscopy Study of Waterborne Epoxy Coating Film Formation

by Natalija Končan Volmajer, Miha Steinbücher, Peter Berce, Peter Venturini and Miran Gaberšček

Coatings 2019, 9(4), 254; https://doi.org/10.3390/coatings9040254 - 16 Apr 2019

Cited by 15 | Viewed by 4278

Abstract

The film formation process in waterborne (WB) epoxy coatings is studied using electrochemical impedance spectroscopy (EIS) measurements and dynamic mechanical analysis (DMA). Ten epoxy coatings with different pigment volume concentration were prepared on standard steel substrates and carefully monitored over four weeks (30 [...] Read more.

The film formation process in waterborne (WB) epoxy coatings is studied using electrochemical impedance spectroscopy (EIS) measurements and dynamic mechanical analysis (DMA). Ten epoxy coatings with different pigment volume concentration were prepared on standard steel substrates and carefully monitored over four weeks (30 days). It is shown that impedance spectroscopy can serve as a very sensitive tool for accurate experimental detection of the critical pigment volume concentration. We also show that the optimal film formation process and corrosion stability of coatings are greatly affected by the coating pigment volume concentration (PVC) value. As a whole, the study confirms that the optimization of coating protection ability needs to take into account both maximization of the barrier effect as well as maximization of the degree of epoxy-amino cross-linking. Full article

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10 pages, 5859 KiB

Open AccessArticle

The Effects of Annealing Temperature on the Structural Properties of ZrB₂ Films Deposited via Pulsed DC Magnetron Sputtering

by Wei-Chun Chen, Chao-Te Lee, James Su and Hung-Pin Chen

Coatings 2019, 9(4), 253; https://doi.org/10.3390/coatings9040253 - 16 Apr 2019

Cited by 5 | Viewed by 3438

Abstract

Zirconium diboride (ZrB₂) thin films were deposited on a Si(100) substrate using pulsed direct current (dc) magnetron sputtering and then annealed in high vacuum. In addition, we discussed the effects of the vacuum annealing temperature in the range of 750 to [...] Read more.

Zirconium diboride (ZrB₂) thin films were deposited on a Si(100) substrate using pulsed direct current (dc) magnetron sputtering and then annealed in high vacuum. In addition, we discussed the effects of the vacuum annealing temperature in the range of 750 to 870 °C with flowing N₂ on the physical properties of ZrB₂ films. The structural properties of ZrB₂ films were investigated with X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The XRD patterns indicated that the ZrB₂ films annealed at various temperatures exhibited a highly preferred orientation along the [0001] direction and that the residual stress could be relaxed by increasing the annealing temperature at 870 °C in a vacuum. The surface morphology was smooth, and the surface roughness slightly decreased with increasing annealing temperature. Cross-sectional TEM images of the ZrB₂/Si(100) film annealed at 870 °C reveals the films were highly oriented in the direction of the c-axis of the Si substrate and the film structure was nearly stoichiometric in composition. The XPS results show the film surfaces slightly contain oxygen, which corresponds to the binding energy of Zr–O. Therefore, the obtained ZrB₂ film seems to be quite suitable as a buffer layer for III-nitride growth. Full article

(This article belongs to the Special Issue Physical Vapor Deposition)

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10 pages, 3736 KiB

Open AccessArticle

The Role of Ammonium Chloride in the Powder Thermal Diffusion Alloying Process on a Magnesium Alloy

by Dongzhu Lu, Quantong Jiang, Meng Zheng, Jie Zhang, Yanliang Huang and Baorong Hou

Coatings 2019, 9(4), 252; https://doi.org/10.3390/coatings9040252 - 15 Apr 2019

Cited by 11 | Viewed by 3598

Abstract

The powder thermal diffusion alloying method could be utilized to fabricate Al-rich intermetallic coatings on magnesium alloys in the air. While the role of ammonium chloride powder in the diffusion alloying source is still to be investigated. This research took the AZ91D magnesium [...] Read more.

The powder thermal diffusion alloying method could be utilized to fabricate Al-rich intermetallic coatings on magnesium alloys in the air. While the role of ammonium chloride powder in the diffusion alloying source is still to be investigated. This research took the AZ91D magnesium alloy as the substrate. Diffusion sources with various powders were utilized as the diffusion source. Microstructure observation and phase identification were enrolled to investigate the role of the ammonium chloride powder in the diffusion alloying process. Results indicate that HCl gas could turn some solid Al powder into gaseous AlCl₃ to enhance the transport of active Al atoms, moreover, it reacts with the dense MgO film and converts it to a loose one, which enables the AlCl₃ gas to penetrate MgO and arrive the matrix to form a protective coating. Furthermore, the ammonium chloride content should be confined to 10 wt. % of the diffusion alloying source. Too much ammonium chloride powder would result in a worse intermetallic coating. Full article

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7 pages, 2681 KiB

Open AccessArticle

TiO₂ Nano Flowers Based EGFET Sensor for pH Sensing

by Chih-Chiang Yang, Kuan-Yu Chen and Yan-Kuin Su

Coatings 2019, 9(4), 251; https://doi.org/10.3390/coatings9040251 - 15 Apr 2019

Cited by 31 | Viewed by 5316

Abstract

In this study, pH sensors were successfully fabricated on a fluorine-doped tin oxide substrate and grown via hydrothermal methods for 8 h for pH sensing characteristics. The morphology was obtained by high-resolution scanning electron microscopy and showed randomly oriented flower-like nanostructures. The TiO [...] Read more.

In this study, pH sensors were successfully fabricated on a fluorine-doped tin oxide substrate and grown via hydrothermal methods for 8 h for pH sensing characteristics. The morphology was obtained by high-resolution scanning electron microscopy and showed randomly oriented flower-like nanostructures. The TiO₂ nanoflower pH sensors were measured over a pH range of 2–12. Results showed a high sensitivity of the TiO₂ nano-flowers pH sensor, 2.7 (μA)^1/2/pH, and a linear relationship between I_DS and pH (regression of 0.9991). The relationship between voltage reference and pH displayed a sensitivity of a 46 mV/pH and a linear regression of 0.9989. The experimental result indicated that a flower-like TiO₂ nanostructure extended gate field effect transistor (EGFET) pH sensor effectively detected the pH value. Full article

(This article belongs to the Special Issue Advances in Thin Film Transistors: Properties and Applications)

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12 pages, 1975 KiB

Open AccessArticle

Photovoltaic Characteristics of Multiwalled Carbon Nanotube Counter-Electrode Materials for Dye-Sensitized Solar Cells Produced by Chemical Treatment and Addition of Dispersant

by Sedong Kim, Otgonbayar Dovjuu, Soon-Ho Choi, Hyomin Jeong and Ji-Tae Park

Coatings 2019, 9(4), 250; https://doi.org/10.3390/coatings9040250 - 15 Apr 2019

Cited by 10 | Viewed by 4003

Abstract

Multiwalled carbon nanotubes (MWCNTs) have excellent electrical conductivity and good chemical stability, and are used as counter electrodes in dye-sensitized solar cells (DSSCs). The counter electrodes collect electrons from the external circuit and catalyze the redox reaction in the electrolyte. Electrocatalysis is an [...] Read more.

Multiwalled carbon nanotubes (MWCNTs) have excellent electrical conductivity and good chemical stability, and are used as counter electrodes in dye-sensitized solar cells (DSSCs). The counter electrodes collect electrons from the external circuit and catalyze the redox reaction in the electrolyte. Electrocatalysis is an important step for generating energy from triiodide reduction in DSSCs. In this study, chemically treated MWCNTs were investigated for improving the photovoltaic performance of DSSCs. The MWCNTs were modified through chemical oxidation with sulfuric acid/nitric acid (H₂SO₄/HNO₃) or potassium persulfate/sodium hydroxide (K₂S₂O₈/NaOH). Nanocellulose (CNC) was used as a dispersant to improve the photovoltaic performance and dispersibility as an alternative material for counter electrodes in DSSCs. The counter electrodes were prepared on fluorine-doped tin oxide (FTO) glass substrates by spin coating nanofluids. Morphological and structural investigations were performed using scanning transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) spectroscopy, and Raman spectroscopy. The electrical conductivity and UV light absorption of the DSSCs were analyzed to evaluate their photovoltaic performance. The results of these analyses showed that chemical functionalization and addition of CNC were effective for increasing the electrical conductivity and UV light absorption. Finally, all result trends were the same. Increasing the dispersibility of the counter electrode was found to improve the reduction of I₃⁻ at the interface between the MWCNTs and the electrolyte, thereby, improving the energy conversion efficiency. Full article

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