Coatings

1150 KiB

Open AccessArticle

Antimicrobial Films Based on Chitosan and Methylcellulose Containing Natamycin for Active Packaging Applications

by Serena Santonicola, Verónica García Ibarra, Raquel Sendón, Raffaelina Mercogliano and Ana Rodríguez-Bernaldo de Quirós

Coatings 2017, 7(10), 177; https://doi.org/10.3390/coatings7100177 - 24 Oct 2017

Cited by 31 | Viewed by 5842

Abstract

Biodegradable polymers are gaining interest as antimicrobial carriers in active packaging. In the present study, two active films based on chitosan (1.5% w/v) and methylcellulose (3% w/v) enriched with natamycin were prepared by casting. The antimicrobial’s release [...] Read more.

Biodegradable polymers are gaining interest as antimicrobial carriers in active packaging. In the present study, two active films based on chitosan (1.5% w/v) and methylcellulose (3% w/v) enriched with natamycin were prepared by casting. The antimicrobial’s release behavior was evaluated by immersion of the films in 95% ethanol (v/v) at different temperatures. The natamycin content in the food simulant was determined by reversed-high performance liquid chromatography with diode-array detection (HPLC-DAD). The apparent diffusion (D_P) and partition (K_P/S) coefficients were calculated using a mathematical model based on Fick’s Second Law. Results showed that the release of natamycin from chitosan based film (D_P = 3.61 × 10⁻¹³ cm²/s) was slower, when compared with methylcellulose film (D_P = 3.20 × 10⁻⁸ cm²/s) at the same temperature (p < 0.05). To evaluate the antimicrobial efficiency of active films, cheese samples were completely covered with the films, stored at 20 °C for 7 days, and then analyzed for moulds and yeasts. Microbiological analyses showed a significant reduction in yeasts and moulds (7.91 log CFU/g) in samples treated with chitosan active films (p < 0.05). The good compatibility of natamycin with chitosan, the low D_p, and antimicrobial properties suggested that the film could be favorably used in antimicrobial packagings. Full article

(This article belongs to the Special Issue Advances in Antimicrobial Coatings)

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470 KiB

Open AccessCommunication

Evaluation of Selected Properties of Alder Wood as Functions of Sanding and Coating

by Emilia-Adela Salca, Tomasz Krystofiak and Barbara Lis

Coatings 2017, 7(10), 176; https://doi.org/10.3390/coatings7100176 - 21 Oct 2017

Cited by 26 | Viewed by 5506

Abstract

The objective of this study was to optimize the sanding and coating processes of black alder wood to promote and support its use in furniture manufacturing. Two criteria have been applied for process optimization, namely, the minimum surface roughness of the samples and [...] Read more.

The objective of this study was to optimize the sanding and coating processes of black alder wood to promote and support its use in furniture manufacturing. Two criteria have been applied for process optimization, namely, the minimum surface roughness of the samples and power consumption during sanding as a function of various sanding systems. The surface roughness of the sanded specimens and the power consumption during sanding strongly depends on the grit size used. Two eco-varnishes were applied to the samples by spraying. Moreover, the effect of the surface preparation and varnish type on the coating properties expressed by the varnish layer adherence to the substrate and surface glossiness was evaluated. For better glossiness values, the UV-cured varnish was preferred. The sanding with a grit sequence of 60, 120, and 150 grit size abrasives was found to be optimal when applied to black alder wood, and it is recommended to obtain performant UV-coated wood surfaces for furniture products. Full article

(This article belongs to the Special Issue Wood Coatings)

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8884 KiB

Open AccessArticle

Effect of Coating Palm Oil Clinker Aggregate on the Engineering Properties of Normal Grade Concrete

by Fuad Abutaha, Hashim Abdul Razak and Hussein Adebayo Ibrahim

Coatings 2017, 7(10), 175; https://doi.org/10.3390/coatings7100175 - 21 Oct 2017

Cited by 21 | Viewed by 7647

Abstract

Palm oil clinker (POC) is a waste material generated in large quantities from the palm oil industry. POC, when crushed, possesses the potential to serve as an aggregate for concrete production. Experimental investigation on the engineering properties of concrete incorporating POC as aggregate [...] Read more.

Palm oil clinker (POC) is a waste material generated in large quantities from the palm oil industry. POC, when crushed, possesses the potential to serve as an aggregate for concrete production. Experimental investigation on the engineering properties of concrete incorporating POC as aggregate and filler material was carried out in this study. POC was partially and fully used to replace natural coarse aggregate. The volumetric replacements used were 0%, 20%, 40%, 60%, 80%, and 100%. POC, being highly porous, negatively affected the fresh and hardened concrete properties. Therefore, the particle-packing (PP) method was adopted to measure the surface and inner voids of POC coarse aggregate in the mixtures at different substitution levels. In order to enhance the engineering properties of the POC concrete, palm oil clinker powder (POCP) was used as a filler material to fill up and coat the surface voids of POC coarse, while the rest of the mix constituents were left as the same. Fresh and hardened properties of the POC concrete with and without coating were determined, and the results were compared with the control concrete. The results revealed that coating the surface voids of POC coarse with POCP significantly improved the engineering properties as well as the durability performance of the POC concrete. Furthermore, using POC as an aggregate and filler material may reduce the continuous exploitation of aggregates from primary sources. Also, this approach offers an environmental friendly solution to the ongoing waste problems associated with palm oil waste material. Full article

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

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4998 KiB

Open AccessArticle

Effects of the Amount and Type of Diol Ring Openers on the Properties of Oligolactide Acrylates for UV-Curable Printing Inks

by Santi Kulsiriswad, Kawee Srikulkit and Onusa Saravari

Coatings 2017, 7(10), 174; https://doi.org/10.3390/coatings7100174 - 20 Oct 2017

Cited by 6 | Viewed by 5052

Abstract

This study aimed to synthesize low viscosity oligolactide acrylates for UV-curable inks from oligolactide diols. Firstly, low molecular weight oligolactide diols were prepared by ring opening reaction of L-lactide with diols. Oligolactide acrylates were then synthesized by functionalizing the oligolactide diols with acrylic [...] Read more.

This study aimed to synthesize low viscosity oligolactide acrylates for UV-curable inks from oligolactide diols. Firstly, low molecular weight oligolactide diols were prepared by ring opening reaction of L-lactide with diols. Oligolactide acrylates were then synthesized by functionalizing the oligolactide diols with acrylic acid. In this study, three diol ring openers having short and long alkyl chain length were used to investigate the effects of the amount and type of diols on the properties of the oligolactide acrylates. The obtained oligomers were characterized, and the viscosities of oligolactide acrylates were measured. Results showed that oligolactide acrylates were successfully synthesized in all cases of ring openers, as confirmed by ¹H-NMR (proton nuclear magnetic resonance spectroscopy) and FTIR (Fourier transform infrared spectroscopy). An increase in the alkyl chain length of the ring openers resulted in oligomers with lower viscosity and a decrease in T_g. Following that, the obtained oligolactide acrylates were employed for the formulation of UV-curable screen printing inks and their properties were investigated. Results showed that the inks formulated from oligomers with lower molecular weight exhibited better ink flow. Additionally, all ink films cured by UV radiation were very flexible with excellent adhesion, high impact resistance, and excellent water resistance. Full article

(This article belongs to the Special Issue Coating—A Sustainable Future)

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5419 KiB

Open AccessArticle

Thermal Conductivity and Wear Behavior of HVOF-Sprayed Fe-Based Amorphous Coatings

by Haihua Yao, Zheng Zhou, Liang Wang, Zhen Tan, Dingyong He and Lidong Zhao

Coatings 2017, 7(10), 173; https://doi.org/10.3390/coatings7100173 - 19 Oct 2017

Cited by 25 | Viewed by 6004

Abstract

To protect aluminum parts in vehicle engines, metal-based thermal barrier coatings in the form of Fe₅₉Cr₁₂Nb₅B₂₀Si₄ amorphous coatings were prepared by high velocity oxygen fuel (HVOF) spraying under two different conditions. The microstructure, thermal [...] Read more.

To protect aluminum parts in vehicle engines, metal-based thermal barrier coatings in the form of Fe₅₉Cr₁₂Nb₅B₂₀Si₄ amorphous coatings were prepared by high velocity oxygen fuel (HVOF) spraying under two different conditions. The microstructure, thermal transport behavior, and wear behavior of the coatings were characterized simultaneously. As a result, this alloy shows high process robustness during spraying. Both Fe-based coatings present dense, layered structure with porosities below 0.9%. Due to higher amorphous phase content, the coating H-1 exhibits a relatively low thermal conductivity, reaching 2.66 W/(m·K), two times lower than the reference stainless steel coating (5.85 W/(m·K)), indicating a good thermal barrier property. Meanwhile, the thermal diffusivity of amorphous coatings display a limited increase with temperature up to 500 °C, which guarantees a steady and wide usage on aluminum alloy. Furthermore, the amorphous coating shows better wear resistance compared to high carbon martensitic GCr15 steel at different temperatures. The increased temperature accelerating the tribological reaction, leads to the friction coefficient and wear rate of coating increasing at 200 °C and decreasing at 400 °C. Full article

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3300 KiB

Open AccessArticle

Efficacy of Hydrophobic Coatings in Protecting Oak Wood Surfaces during Accelerated Weathering

by Miloš Pánek, Eliška Oberhofnerová, Aleš Zeidler and Přemysl Šedivka

Coatings 2017, 7(10), 172; https://doi.org/10.3390/coatings7100172 - 18 Oct 2017

Cited by 35 | Viewed by 6464

Abstract

The durability of transparent coatings applied to an oak wood exterior is relatively low due to its anatomic structure and chemical composition. Enhancement of the protection of oak wood against weathering using transparent hydrophobic coatings is presented in this study. Oak wood surfaces [...] Read more.

The durability of transparent coatings applied to an oak wood exterior is relatively low due to its anatomic structure and chemical composition. Enhancement of the protection of oak wood against weathering using transparent hydrophobic coatings is presented in this study. Oak wood surfaces were modified using UV-stabilizers, hindered amine light stabilizer (HALS), and ZnO and TiO₂ nanoparticles before the application of a commercial hydrophobic topcoat. A transparent oil-based coating was used as a control coating system. The artificial weathering test lasted 6 weeks and colour, gloss, and contact angle changes were regularly evaluated during this period. The changes in the microscopic structure were studied with confocal laser scanning microscopy. The results proved limited durability against weathering of both tested hydrophobic coatings. The formation of micro-cracks causing the leaching of degraded wood compounds and discolouration of oak wood were observed after 1 or 3 weeks of the weathering test. Until then, an oil-based coating film had protected the wood sufficiently, but after 6 weeks the wood was fully defoliated to its non-homogenous thickness, which was caused by the presence of large oak vessels, and by the effects of specific oak tannins. Using transparent hydrophobic coatings can prolong the service life of the exteriors of wood products by decreasing their moisture content. Without proper construction protection against rainwater, the hydrophobic coating itself cannot guarantee the preservation of the natural appearance of wood exteriors. Full article

(This article belongs to the Special Issue Wood Coatings)

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2851 KiB

Open AccessArticle

Atmospheric Pressure Plasma Coating of Wood and MDF with Polyester Powder

by Robert Köhler, Philipp Sauerbier, Holger Militz and Wolfgang Viöl

Coatings 2017, 7(10), 171; https://doi.org/10.3390/coatings7100171 - 17 Oct 2017

Cited by 25 | Viewed by 6858

Abstract

In this study, polyester powder based on iso- and teraphthalic acid was deposited with an atmospheric plasma jet. The powder was fed into the effluent plasma zone and deposited on European beech wood (Fagus sylvatica L.), Grand fir (Abies grandis Lindl.) [...] Read more.

In this study, polyester powder based on iso- and teraphthalic acid was deposited with an atmospheric plasma jet. The powder was fed into the effluent plasma zone and deposited on European beech wood (Fagus sylvatica L.), Grand fir (Abies grandis Lindl.) and medium density fiberboard (MDF). The substrates were annealed subsequent to the coating process. To exclude decomposition of the polyester layers by the plasma treatment, the surface chemistry of the layers has been examined by X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) and compared with the polyester powder reference. Furthermore, topographical investigations were carried out using laser scanning microscopy (LSM). Adhesive strength of the layers was evaluated by dolly test and gloss measurements with a goniophotometer. The deposited layers showed no chemical changes compared to the reference. The adhesive strength of the layer met practical requirements of >1 MPa. It was demonstrated that the deposition of a macroscopic layer is possible without a pretreatment or the usage of additives. Therefore this coating process by atmospheric pressure plasma for wood and wood based materials could represent an environmental-friendly alternative to conventional coating methods. Full article

(This article belongs to the Special Issue Wood Coatings)

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2467 KiB

Open AccessArticle

Marching-on-in-Degree Time-Domain Integral Equation Solver for Transient Electromagnetic Analysis of Graphene

by Quanquan Wang, Huazhong Liu, Yan Wang and Zhaoneng Jiang

Coatings 2017, 7(10), 170; https://doi.org/10.3390/coatings7100170 - 17 Oct 2017

Cited by 2 | Viewed by 4065

Abstract

The marching-on-in-degree (MOD) time-domain integral equation (TDIE) solver for the transient electromagnetic scattering of the graphene is presented in this paper. Graphene’s dispersive surface impedance is approximated using rational function expressions of complex conjugate pole-residue pairs with the vector fitting (VF) method. Enforcing [...] Read more.

The marching-on-in-degree (MOD) time-domain integral equation (TDIE) solver for the transient electromagnetic scattering of the graphene is presented in this paper. Graphene’s dispersive surface impedance is approximated using rational function expressions of complex conjugate pole-residue pairs with the vector fitting (VF) method. Enforcing the surface impedance boundary condition, TDIE is established and solved in the MOD scheme, where the temporal surface impedance is carefully convoluted with the current. Unconditionally stable transient solution in time domain can be ensured. Wide frequency band information is obtained after the Fourier transform of the time domain solution. Numerical results validate the proposed method. Full article

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

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4068 KiB

Open AccessArticle

Deposition of Photocatalytic TiO₂ Coating by Modifying the Solidification Pathway in Plasma Spraying

by Kui Wen, Min Liu, Xuezhang Liu, Chunming Deng and Kesong Zhou

Coatings 2017, 7(10), 169; https://doi.org/10.3390/coatings7100169 - 13 Oct 2017

Cited by 18 | Viewed by 4635

Abstract

The deposition of photocatalytic TiO₂ coatings with plasma spraying is attractive for large-scale applications due to its low cost and simplicity, but it is still a challenge to obtain a TiO₂ coating with high anatase content. The solidification pathway of inflight [...] Read more.

The deposition of photocatalytic TiO₂ coatings with plasma spraying is attractive for large-scale applications due to its low cost and simplicity, but it is still a challenge to obtain a TiO₂ coating with high anatase content. The solidification pathway of inflight melted particles was investigated in the present paper, and TiO₂ coatings with enhanced photocatalytic activity were obtained without a significant loss of the microhardness. The coating microstructure, phase composition, and crystallite size were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Photocatalytic performance was evaluated by decomposing an aqueous solution of methylene blue. Results showed that the anatase content in TiO₂ coating was augmented to 19.9% from 4%, and the time constant of the activity was increased to 0.0046 h⁻¹ from 0.0017 h⁻¹. Full article

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

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6069 KiB

Open AccessArticle

Chitosan Coating on Silica-Modified Polymethyl Methacrylate for Dental Applications

by Mieszko Więckiewicz, Eric Wolf, Katarzyna Walczak, Heike Meissner and Klaus Boening

Coatings 2017, 7(10), 168; https://doi.org/10.3390/coatings7100168 - 13 Oct 2017

Cited by 8 | Viewed by 5944

Abstract

Chitosan is a cationic natural polymer that is widely used as a topical dressing in wound management. Temporary coatings of removable denture bases with chitosan might be useful as supportive treatment in oral medicine. The aim of this study was to analyze the [...] Read more.

Chitosan is a cationic natural polymer that is widely used as a topical dressing in wound management. Temporary coatings of removable denture bases with chitosan might be useful as supportive treatment in oral medicine. The aim of this study was to analyze the thickness, uniformity, and adhesive strength of chitosan coatings on simulated denture bases made from polymethyl methacrylate (PMMA). According to a standardized protocol, 20 PMMA cylinders (13 mm diameter, 5 mm in height) as well as 20 cubes (a = 25 mm) with intaglio U-shaped profiles were manufactured to simulate average sized alveolar ridges. Cylinders as well as cubes were divided into four test series with n = 5 each. After sandblasting with silica-modified alumina, one frontal surface of the PMMA cylinders and the intaglio surfaces of the U-shaped profiles was coated with chitosan acetate solution according to the following protocols: one layer of 2% chitosan acetate solution (test series I), one layer of 4% chitosan acetate solution (test series II), two layers of 2% chitosan acetate solution (test series III), and two layers of 4% chitosan acetate solution (test series IV). After drying and neutralization with NaOH, each cube was cut transversely and the coating thickness across the U-shaped profile assessed with a light microscope. Adhesive strength was evaluated by simulated tooth brushing and the loss of chitosan coating was evaluated qualitatively. Statistical analysis used Friedman ANOVA test for dependent samples and Kruskal-Wallis test for independent samples, post-hoc Dunn’s test (p < 0.05), and binomial test (p = 0.05). The mean chitosan coating thicknesses in the depth of the U-profiles were 71 µm (test series I), 77 µm (test series II), 121 µm (test series III), and 517 µm (test series VI). The thickness continuously decreased with rising angulation of the U-profile side walls. In test series I, the chitosan coating thickness significantly dropped above a 30° angulation of the U-profile side walls. In test series II to IV, the chitosan thickness drop was not statistically significant at angulations of 30° and 60°, but was at 90° angulation of the U-profile side walls. Adhesion strength was rated fair to good and did not differ significantly among the four test series. The coating technique described revealed chitosan layers with overall good adhesion strength but differing thicknesses. Coatings with one or two layers of 4% chitosan acetate solution allowed a relatively uniform chitosan thickness and thus might be usable in oral medicine. Full article

(This article belongs to the Special Issue Dental Implant Surface: Science and Technology)

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2678 KiB

Open AccessCommunication

Enhanced Efficiency of Dye-Sensitized Solar Counter Electrodes Consisting of Two-Dimensional Nanostructural Molybdenum Disulfide Nanosheets Supported Pt Nanoparticles

by Chao-Kuang Cheng, Jeng-Yu Lin, Kai-Chen Huang, Tsung-Kuang Yeh and Chien-Kuo Hsieh

Coatings 2017, 7(10), 167; https://doi.org/10.3390/coatings7100167 - 13 Oct 2017

Cited by 16 | Viewed by 5444

Abstract

This paper reports architecturally designed nanocomposites synthesized by hybridizing the two-dimensional (2D) nanostructure of molybdenum disulfide (MoS₂) nanosheet (NS)-supported Pt nanoparticles (PtNPs) as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). MoS₂ NSs were prepared using the hydrothermal method; PtNPs [...] Read more.

This paper reports architecturally designed nanocomposites synthesized by hybridizing the two-dimensional (2D) nanostructure of molybdenum disulfide (MoS₂) nanosheet (NS)-supported Pt nanoparticles (PtNPs) as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). MoS₂ NSs were prepared using the hydrothermal method; PtNPs were subsequently reduced on the MoS₂ NSs via the water–ethylene method to form PtNPs/MoS₂ NSs hybrids. The nanostructures and chemical states of the PtNPs/MoS₂ NSs hybrids were characterized by high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Detailed electrochemical characterizations by electrochemical impedance spectroscopy, cyclic voltammetry, and Tafel-polarization measurement demonstrated that the PtNPs/MoS₂ NSs exhibited excellent electrocatalytic activities, afforded a higher charge transfer rate, a decreased charge transfer resistance, and an improved exchange current density. The PtNPs/MoS₂ NSs hybrids not only provided the exposed layers of 2D MoS₂ NSs with a great deal of catalytically active sites, but also offered PtNPs anchored on the MoS₂ NSs enhanced I₃⁻ reduction. Accordingly, the DSSCs that incorporated PtNPs/MoS₂ NSs CE exhibited an outstanding photovoltaic conversion efficiency (PCE) of 7.52%, which was 8.7% higher than that of a device with conventional thermally-deposited platinum CE (PCE = 6.92%). 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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4689 KiB

Open AccessArticle

A Novel Image Segmentation Approach for Microstructure Modelling

by Michael Watson and Matthew Marshall

Coatings 2017, 7(10), 166; https://doi.org/10.3390/coatings7100166 - 4 Oct 2017

Cited by 3 | Viewed by 3964

Abstract

Microstructure models are used to investigate bulk properties of a material given images of its microstructure. Through their use the effect of microstructural features can be investigated independently. Processes can then be optimised to give the desired selection of microstructural features. Currently automatic [...] Read more.

Microstructure models are used to investigate bulk properties of a material given images of its microstructure. Through their use the effect of microstructural features can be investigated independently. Processes can then be optimised to give the desired selection of microstructural features. Currently automatic methods of segmenting SEM images either miss cracks leading to large overestimates of properties or use unjustifiable methods to select a threshold point which class cracks as porosity leading to over estimates of porosity. In this work, a novel automatic image segmentation method is presented which produces maps for each phase in the microstructure and an additional phase of cracks. The selection of threshold points is based on the assumption that the brightness values for each phase should be normally distributed. The image segmentation method has been compared to other available methods and shown to be as or more repeatable with changes of brightness and contrast of the input image than relevant alternatives. The resulting modelling route is able to predict density and specific heat to within experimental error, while the expected under predictions for thermal conductivity are observed. Full article

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3949 KiB

Open AccessArticle

Multilayer CVD Diamond Coatings in the Machining of an Al6061-15 Vol % Al₂O₃ Composite

by Mohammadmehdi Shabani, Joaquim Sacramento, Filipe J. Oliveira and Rui F. Silva

Coatings 2017, 7(10), 165; https://doi.org/10.3390/coatings7100165 - 3 Oct 2017

Cited by 16 | Viewed by 5942

Abstract

Ceramic cutting inserts coated with ten-fold alternating micro- and nanocrystalline diamond (MCD/NCD) layers grown by hot filament chemical vapor deposition (CVD) were tested in the machining of an Al based metallic matrix composite (MMC) containing 15 vol % Al₂O₃ particles. [...] Read more.

Ceramic cutting inserts coated with ten-fold alternating micro- and nanocrystalline diamond (MCD/NCD) layers grown by hot filament chemical vapor deposition (CVD) were tested in the machining of an Al based metallic matrix composite (MMC) containing 15 vol % Al₂O₃ particles. Inserts with total coating thicknesses of approximately 12 µm and 24 µm were produced and used in turning: cutting speed (v) of 250 to 1000 m·min⁻¹; depth of cut (DOC) from 0.5 to 3 mm and feed (f) between 0.1 and 0.4 mm·rev⁻¹. The main cutting force increases linearly with DOC (ca. 294 N per mm) and with feed (ca. 640 N per mm·rev⁻¹). The thicker coatings work within the following limits: DOC up to 1.5 mm and maximum speeds of 750 m·min⁻¹ for feeds up to 0.4 mm·rev⁻¹. Flank wear is predominant but crater wear is also observed due to the negative tool normal rake. Layer-by-layer wear of the tool rake, and not total delamination from the substrate, evidenced one of the advantages of using a multilayer design. The MCD/NCD multilayer diamond coated indexable inserts have longer tool life than most CVD diamond systems and behave as well as most polycrystalline diamond (PCD) tools. Full article

(This article belongs to the Special Issue Diamond and Diamond-Like Coatings: Deposition, Characterization, and Applications)

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4497 KiB

Open AccessArticle

Chemical Vapor Deposition of Bi-Te-Ni-Fe on Magnesium Oxide Substrate and Its Seebeck Effect

by Yong X. Gan, Anan S. Hamdan, Jeremy B. Gan and Mingheng Li

Coatings 2017, 7(10), 164; https://doi.org/10.3390/coatings7100164 - 1 Oct 2017

Cited by 7 | Viewed by 6505

Abstract

In this work, a Bi-Te-Ni-Fe complex coating material was obtained on magnesium oxide substrate by a single step ambient pressure chemical vapor deposition (CVD). Nickel acetate, bismuth acetate, iron (III) nitrate, and tellurium (IV) chloride dissolved in N,N-dimethylformamide (DMF) served [...] Read more.

In this work, a Bi-Te-Ni-Fe complex coating material was obtained on magnesium oxide substrate by a single step ambient pressure chemical vapor deposition (CVD). Nickel acetate, bismuth acetate, iron (III) nitrate, and tellurium (IV) chloride dissolved in N,N-dimethylformamide (DMF) served as the metal sources for Ni, Bi, Fe, and Te, respectively. Hydrogen was used as the carrier gas. The substrate was kept at 500 °C in a quartz tube reaction chamber. The chemical vapor deposition time was two hours. Scanning electron microscopic observation revealed porous morphology of the deposited material with a needle-like submicron fine structure. These needle-like entities form networks with fairly uniform distribution on the substrate. Thermoelectric property test showed that the coating is p-type with a Seebeck coefficient of 179 µV/K. Time-dependent potential data were obtained to show the sensitivity of the Seebeck effect to temperature changes. Full article

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1888 KiB

Open AccessArticle

Influence of Coating Formulation on Its Mechanical Properties and Cracking Resistance

by Laurence Podgorski, Mari De Meijer and Jean-Denis Lanvin

Coatings 2017, 7(10), 163; https://doi.org/10.3390/coatings7100163 - 30 Sep 2017

Cited by 9 | Viewed by 4744

Abstract

The mechanical properties of coatings strongly influence wood coatings’ performance, as coatings may be stressed by dimensional variations of wood when exposed outdoors. Within the European project SERVOWOOD (2014–2016), the influence of coating formulation on mechanical properties and cracking resistance has been studied. [...] Read more.

The mechanical properties of coatings strongly influence wood coatings’ performance, as coatings may be stressed by dimensional variations of wood when exposed outdoors. Within the European project SERVOWOOD (2014–2016), the influence of coating formulation on mechanical properties and cracking resistance has been studied. Several acrylic and alkyd formulations with different pigment volume concentrations (PVCs), with and without UV protection have been applied on pine samples and exposed to artificial weathering (EN 927-6) for 12 weeks. Persoz hardness of coatings applied on wood was assessed before and after weathering. Tensile tests on free films have been carried out at −10 °C, 20 °C, and 45 °C. For each formulation, elastic modulus, tensile strength, and strain at break have been determined for the three test temperatures. For each test temperature, there was no correlation between the elastic modulus and strain at break, nor between tensile strength and strain at break. The results showed a relation between Persoz hardness and elastic modulus. The best performing formulation had a mean elastic modulus at room temperature lower than 400 MPa and a mean strain at break higher than 30%. Full article

(This article belongs to the Special Issue Wood Coatings)

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4248 KiB

Open AccessArticle

Electrochemical Behavior of Bilayer Thermal-Spray Coatings in Low-Temperature Corrosion Protection

by Esmaeil Sadeghimeresht and Nicolaie Markocsan

Coatings 2017, 7(10), 162; https://doi.org/10.3390/coatings7100162 - 30 Sep 2017

Cited by 14 | Viewed by 6514

Abstract

Cr₃C₂-NiCr coatings are greatly used to protect critical components in corrosive environments and to extend their lifetime and/or improve functional performance. However, the pores formed during spraying restrict the coating’s applicability area for many corrosion protection applications. To overcome [...] Read more.

Cr₃C₂-NiCr coatings are greatly used to protect critical components in corrosive environments and to extend their lifetime and/or improve functional performance. However, the pores formed during spraying restrict the coating’s applicability area for many corrosion protection applications. To overcome this technical challenge, bilayer coatings have been developed, in which an additional layer (the so-called “intermediate layer”) is deposited on the substrate before spraying the Cr₃C₂-NiCr coating (the so-called “top layer”). The corrosion behavior of the bilayer coating depends on the composition and microstructure of each layer. In the present work, different single-layer coatings (i.e., Cr₃C₂-NiCr, Fe- and Ni-based coatings) were initially sprayed by a high-velocity air fuel (HVAF) process. Microstructure analysis, as well as electrochemical tests, for example, open-circuit potential (OCP) and polarization tests, were performed. The potential difference (ΔE) had a great influence on galvanic corrosion between the top and intermediate layers, and thus, the coatings were ranked based on the OCP values (from high to low) as follows: NiCoCrAlY > NiCr > Cr₃C₂-NiCr > NiAl > Fe-based coatings (alloyed with Cr) > pure Ni. The Ni-based coatings were chosen to be further used as intermediate layers with the Cr₃C₂-NiCr top layer due to their capabilities to show high OCP. The corrosion resistance (R_p) of the bilayer coatings was ranked (from high to low) as follows: NiCoCrAlY/Cr₃C₂-NiCr > NiCr/Cr₃C₂-NiCr > NiAl/Cr₃C₂-NiCr > Ni/Cr₃C₂-NiCr. It was shown that splat boundaries and interconnected pores are detrimental for corrosion resistance, however, a sufficient reservoir of protective scale-forming elements (such as Cr or/and Al) in the intermediate layer can significantly improve the corrosion resistance. Full article

(This article belongs to the Special Issue Coatings for Corrosion Mitigation)

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3191 KiB

Open AccessArticle

Novel Electrodeposited Ni-B/Y₂O₃ Composite Coatings with Improved Properties

by Rana Abdul Shakoor, Umesh Somaji Waware, Kamran Ali, Ramazan Kahraman, Anton Popelka, Moinuddin Mohammed Yusuf and Anwarul Hasan

Coatings 2017, 7(10), 161; https://doi.org/10.3390/coatings7100161 - 29 Sep 2017

Cited by 29 | Viewed by 5609

Abstract

Ni-B/Y₂O₃ composite coatings were developed through an electrodeposition process to study the effect of addition of Y₂O₃ particles on structure, surface, thermal, mechanical, and anticorrosion properties of Ni-B coatings. It is revealed that parent crystal structure of [...] Read more.

Ni-B/Y₂O₃ composite coatings were developed through an electrodeposition process to study the effect of addition of Y₂O₃ particles on structure, surface, thermal, mechanical, and anticorrosion properties of Ni-B coatings. It is revealed that parent crystal structure of Ni-B matrix is preserved by addition of Y₂O₃, however, a noticeable improvement in crystallinity is observed. The analysis of the surface exhibits formation of dense and nodular deposits in the two types of coatings, but incorporation of Y₂O₃ particles in Ni-B matrix has resulted in a noteworthy change in grain size and surface roughness. Thermal analysis of the surfaces indicates that Ni-B-Y₂O₃ composite coatings demonstrate superior thermal stability compared to Ni-B coatings. The nanoindentation analysis shows a significant enhancement in the mechanical characteristics of the Ni-B matrix by addition of Y₂O₃ particles. This may be contemplated as the result of grain refinement and dispersion hardening of the Ni-B matrix by the presence of hard Y₂O₃ particles. A decent improvement in the corrosion protection efficiency (73.6%) is also observed by addition of Y₂O₃ particles into Ni-B matrix. Simultaneous improvement of mechanical and anticorrosion properties suggests potential applications of Ni-B-Y₂O₃ coatings in oil and gas, automobile, and many other industries. Full article

(This article belongs to the Special Issue Innovative Coatings for Automotive Industry)

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3754 KiB

Open AccessArticle

Prediction of the Corrosion Current Density in Reinforced Concrete Using a Self-Organizing Feature Map

by Mehdi Nikoo, Łukasz Sadowski and Mohammad Nikoo

Coatings 2017, 7(10), 160; https://doi.org/10.3390/coatings7100160 - 29 Sep 2017

Cited by 19 | Viewed by 6513

Abstract

A disadvantage of using linear polarization resistance (LPR) in the measurement of corrosion current density is the need to partially destroy a concrete cover. In this article, a new technique of predicting the corrosion current density in reinforced concrete using a self-organizing feature [...] Read more.

A disadvantage of using linear polarization resistance (LPR) in the measurement of corrosion current density is the need to partially destroy a concrete cover. In this article, a new technique of predicting the corrosion current density in reinforced concrete using a self-organizing feature map (SOFM) is presented. For this purpose, air temperature, and also the parameters determined by the resistivity four-probe method and galvanostatic resistivity measurements, were employed as input variables. The corrosion current density, predicted by the destructive LPR method, was employed as the output variable. The weights of the SOFM were optimized using the genetic algorithm (GA). To evaluate the accuracy of the SOFM, a comparison with the radial basis function (RBF) and linear regression (LR) was performed. The results indicate that the SOFM–GA model has a higher ability, flexibility, and accuracy than the RBF and LR. Full article

(This article belongs to the Special Issue Surface Treatments and Coatings for Structural Steel and Reinforced Concrete)

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2065 KiB

Open AccessArticle

Thermoplastic Polyurethanes Stemming from Castor Oil: Green Synthesis and Their Application in Wood Bonding

by Shaolong Li, Changlian Xu, Wenfeng Yang and Qingru Tang

Coatings 2017, 7(10), 159; https://doi.org/10.3390/coatings7100159 - 29 Sep 2017

Cited by 13 | Viewed by 7457

Abstract

We report an efficient and green approach to synthesize a linear castor oil-based polyurethane (CPU) without using any solvent or catalyst. Diol monomers were first synthesized by the aminolysis reaction between castor oil and diamines; this was accomplished within 6 h at 130 [...] Read more.

We report an efficient and green approach to synthesize a linear castor oil-based polyurethane (CPU) without using any solvent or catalyst. Diol monomers were first synthesized by the aminolysis reaction between castor oil and diamines; this was accomplished within 6 h at 130 °C. Polymerization of the diols and isocyanate was further confirmed by Fourier transform infrared (FTIR), ¹H-nuclear magnetic resonance (¹H-NMR), and gel permeation chromatography analyses. The resultant CPUs showed a good thermal stability with an initial degradation temperature higher than 300 °C, and their mechanical and wood bonding property can be modulated by the structures of diamine. In addition, the CPUs possessed a satisfying water resistance property with the water absorption amount lower than 2%. The green conversion of castor oil to thermoplastic polyurethane affords new opportunities in bio-based industries. Full article

(This article belongs to the Special Issue Binders, Pigments, Dyes and Additives)

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3791 KiB

Open AccessArticle

Effect of Graphene Coating on the Heat Transfer Performance of a Composite Anti-/Deicing Component

by Long Chen, Yidu Zhang and Qiong Wu

Coatings 2017, 7(10), 158; https://doi.org/10.3390/coatings7100158 - 28 Sep 2017

Cited by 40 | Viewed by 10428

Abstract

The thermal conductivity of a graphene coating for anti-/deicing is rarely studied. This paper presents an improved anti-/deicing efficiency method for composite material anti-/deicing by using the heat-transfer characteristic of a graphene coating. An anti-/deicing experiment was conducted using the centrifugal force generated [...] Read more.

The thermal conductivity of a graphene coating for anti-/deicing is rarely studied. This paper presents an improved anti-/deicing efficiency method for composite material anti-/deicing by using the heat-transfer characteristic of a graphene coating. An anti-/deicing experiment was conducted using the centrifugal force generated by a helicopter rotor. Results showed that the graphene coating can accelerate the internal heat transfer of the composite material, thereby improving the anti-icing and deicing efficiency of the helicopter rotor. The spraying process parameters, such as coating thickness and spraying pressure, were also studied. Results showed that reducing coating thickness and increasing spraying pressure are beneficial in preparing a graphene coating with high thermal conductivity. This study provides an experimental reference for the application of a graphene coating in anti-/deicing. Full article

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13812 KiB

Open AccessArticle

The Phase Evolution and Property of FeCoCrNiAlTi_x High-Entropy Alloying Coatings on Q253 via Laser Cladding

by Bin He, Nannan Zhang, Danyang Lin, Yue Zhang, Fuyu Dong and Deyuan Li

Coatings 2017, 7(10), 157; https://doi.org/10.3390/coatings7100157 - 28 Sep 2017

Cited by 34 | Viewed by 5409

Abstract

High-entropy alloys (HEAs) are emerging as a hot research frontier in the metallic materials field. The study on the effect of alloying elements on the structure and properties of HEAs may contribute to the progress of the research and accelerate the application in [...] Read more.

High-entropy alloys (HEAs) are emerging as a hot research frontier in the metallic materials field. The study on the effect of alloying elements on the structure and properties of HEAs may contribute to the progress of the research and accelerate the application in actual production. FeCoCrNiAlTi_x (x = 0, 0.25, 0.5, 0.75, and 1 in at.%, respectively) HEA coatings with different Ti concentrations were produced on Q235 steel via laser cladding. The constituent phases, microstructure, hardness, and wear resistance of the coatings were investigated by XRD, SEM, microhardness tester and friction-wear tester, respectively. The results show that the structure of the coating is a eutectic microstructure of FCC and BCC₁ at x = 0. The structure of coatings consists of both proeutectic FCC phase and the eutectic structure of BCC₁ and BCC₂. With the continuous addition of Ti, the amount of eutectic structure decreases. The average hardness of the FeCoCrNiAlTi_x HEA coatings at x = 0, 0.25, 0.5, 0.75, and 1 are 432.73 HV, 548.81 HV, 651.03 HV, 769.20 HV, and 966.29 HV, respectively. The hardness of coatings increases with the addition of Ti, where the maximum hardness is achieved for the HEA at x = 1. The wear resistance of the HEA coatings is enhanced with the addition of Ti, and the main worn mechanism is abrasive wear. Full article

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

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3005 KiB

Open AccessArticle

Microstructure, Mechanical and Corrosion Behaviors of CoCrFeNiAl_0.3 High Entropy Alloy (HEA) Films

by Libo Gao, Weibing Liao, Hongti Zhang, James Utama Surjadi, Dong Sun and Yang Lu

Coatings 2017, 7(10), 156; https://doi.org/10.3390/coatings7100156 - 26 Sep 2017

Cited by 51 | Viewed by 7205

Abstract

The HEA-CoCrFeNiAl_0.3 thin film in this study has been successfully developed by radio frequency (RF) magnetron sputtering to meet the increasing demand in engineering applications. Its microstructure and surface profile were investigated accordingly. The as-synthesized HEA film was found to have a [...] Read more.

The HEA-CoCrFeNiAl_0.3 thin film in this study has been successfully developed by radio frequency (RF) magnetron sputtering to meet the increasing demand in engineering applications. Its microstructure and surface profile were investigated accordingly. The as-synthesized HEA film was found to have a homogeneous element distribution and ultra-smooth surface, exhibiting a typical face-centered cubic (FCC) solid solution. The film showed better mechanical properties than its bulk counterpart, with a Young’s modulus and hardness of ~201.4 GPa and ~11.5 GPa, respectively. Furthermore, corrosion tests demonstrated decreased sensitivity to localized corrosion in comparison to the commercial 304 stainless steel in NaCl solution. Full article

(This article belongs to the Special Issue High Entropy Alloy Coatings)

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11434 KiB

Open AccessArticle

Biodegradable Mg/HA/TiO₂ Nanocomposites Coated with MgO and Si/MgO for Orthopedic Applications: A Study on the Corrosion, Surface Characterization, and Biocompatability

by Shahrouz Zamani Khalajabadi, Aminudin Bin Haji Abu, Norhayati Ahmad, Mohammed Rafiq Abdul Kadir, Ahmad Fauzi Ismail, Rozita Nasiri, Waseem Haider and Norizah Bt Hj Redzuan

Coatings 2017, 7(10), 154; https://doi.org/10.3390/coatings7100154 - 26 Sep 2017

Cited by 20 | Viewed by 7034

Abstract

In the field of orthopedics, magnesium (Mg) and magnesium-based composites as biodegradable materials have attracted fundamental research. However, the medical applications of magnesium implants have been restricted owing to their poor corrosion resistance, especially in the physiological environment. To improve the corrosion resistance [...] Read more.

In the field of orthopedics, magnesium (Mg) and magnesium-based composites as biodegradable materials have attracted fundamental research. However, the medical applications of magnesium implants have been restricted owing to their poor corrosion resistance, especially in the physiological environment. To improve the corrosion resistance of Mg/HA/TiO₂ nanocomposites, monolayer MgO and double-layer Si/MgO coatings were fabricated layer-by-layer on the surface of a nanocomposite using a powder metallurgy route. Then, coating thickness, surface morphology, and chemical composition were determined, and the corrosion behavior of the uncoated and coated samples was evaluated. Field-emission scanning electron microscopy (FE-SEM) micrographs show that an inner MgO layer with a porous microstructure and thickness of around 34 μm is generated on the Mg/HA/TiO₂ nanocomposite substrate, and that the outer Si layer thickness is obtained at around 23 μm for the double-layered coated sample. Electrochemical corrosion tests and immersion corrosion tests were carried out on the uncoated and coated samples and the Si/MgO-coated nanocomposite showed significantly improved corrosion resistance compared with uncoated Mg/HA/TiO₂ in simulated body fluid (SBF). Corrosion products comprising Mg(OH)₂, HA, Ca₃(PO₄)₂, and amorphous CaP components were precipitated on the immersed samples. Improved cytocompatibility was observed with coating as the cell viability ranged from 73% in uncoated to 88% for Si/MgO-coated Mg/HA/TiO₂ nanocomposite after nine days of incubation. Full article

(This article belongs to the Special Issue Coatings for Corrosion Mitigation)

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8186 KiB

Open AccessArticle

Trajectory Optimization of Electrostatic Spray Painting Robots on Curved Surface

by Wei Chen, Hao Liu, Yang Tang and Junjie Liu

Coatings 2017, 7(10), 155; https://doi.org/10.3390/coatings7100155 - 25 Sep 2017

Cited by 22 | Viewed by 9432

Abstract

In this paper, a new practical electrostatic rotating bell (ESRB) cumulative rate model of painting is derived, and an experimental study on painting is carried out. First, the experimental method is used to obtain the radial thickness profile function of the spatial paint [...] Read more.

In this paper, a new practical electrostatic rotating bell (ESRB) cumulative rate model of painting is derived, and an experimental study on painting is carried out. First, the experimental method is used to obtain the radial thickness profile function of the spatial paint distribution of static spray. Then, a spatial trajectory-planning scheme for a spray-painting robot based on a rectangular model is presented. This method designs the spatial path of the spray-painting robot by using the cuboid model method after the optimal value is taken as the width d of the overlapping area of the two spray-painting strokes in the plane. The experimental results illustrate that the paint thickness basically meets the requirements, and the experimental results verify the effectiveness of the trajectory optimization method. Full article

(This article belongs to the Special Issue Innovative Coatings for Automotive Industry)

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7814 KiB

Open AccessReview

A Guide to and Review of the Use of Multiwavelength Raman Spectroscopy for Characterizing Defective Aromatic Carbon Solids: from Graphene to Amorphous Carbons

by Alexandre Merlen, Josephus Gerardus Buijnsters and Cedric Pardanaud

Coatings 2017, 7(10), 153; https://doi.org/10.3390/coatings7100153 - 25 Sep 2017

Cited by 297 | Viewed by 21378

Abstract

sp² hybridized carbons constitute a broad class of solid phases composed primarily of elemental carbon and can be either synthetic or naturally occurring. Some examples are graphite, chars, soot, graphene, carbon nanotubes, pyrolytic carbon, and diamond-like carbon. They vary from highly ordered [...] Read more.

sp² hybridized carbons constitute a broad class of solid phases composed primarily of elemental carbon and can be either synthetic or naturally occurring. Some examples are graphite, chars, soot, graphene, carbon nanotubes, pyrolytic carbon, and diamond-like carbon. They vary from highly ordered to completely disordered solids and detailed knowledge of their internal structure and composition is of utmost importance for the scientific and engineering communities working with these materials. Multiwavelength Raman spectroscopy has proven to be a very powerful and non-destructive tool for the characterization of carbons containing both aromatic domains and defects and has been widely used since the 1980s. Depending on the material studied, some specific spectroscopic parameters (e.g., band position, full width at half maximum, relative intensity ratio between two bands) are used to characterize defects. This paper is addressed first to (but not limited to) the newcomer in the field, who needs to be guided due to the vast literature on the subject, in order to understand the physics at play when dealing with Raman spectroscopy of graphene-based solids. We also give historical aspects on the development of the Raman spectroscopy technique and on its application to sp² hybridized carbons, which are generally not presented in the literature. We review the way Raman spectroscopy is used for sp² based carbon samples containing defects. As graphene is the building block for all these materials, we try to bridge these two worlds by also reviewing the use of Raman spectroscopy in the characterization of graphene and nanographenes (e.g., nanotubes, nanoribbons, nanocones, bombarded graphene). Counterintuitively, because of the Dirac cones in the electronic structure of graphene, Raman spectra are driven by electronic properties: Phonons and electrons being coupled by the double resonance mechanism. This justifies the use of multiwavelength Raman spectroscopy to better characterize these materials. We conclude with the possible influence of both phonon confinement and curvature of aromatic planes on the shape of Raman spectra, and discuss samples to be studied in the future with some complementary technique (e.g., high resolution transmission electron microscopy) in order to disentangle the influence of structure and defects. Full article

(This article belongs to the Special Issue Diamond and Diamond-Like Coatings: Deposition, Characterization, and Applications)

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1183 KiB

Open AccessArticle

Wood-Rotting Fungal Pigments as Colorant Coatings on Oil-Based Textile Dyes

by Mardonio E. Palomino Agurto, Sarath M. Vega Gutierrez, Hsiou-Lien Chen and Seri C. Robinson

Coatings 2017, 7(10), 152; https://doi.org/10.3390/coatings7100152 - 23 Sep 2017

Cited by 25 | Viewed by 6060

Abstract

Opportunities for alternatives to synthetic textile dyes are of increasing importance as the world looks to minimize its ecological footprint. Fungal pigments within a unique class of wood-rotting (“spalting”) fungi have been under investigation for several years as a possible solution, and have [...] Read more.

Opportunities for alternatives to synthetic textile dyes are of increasing importance as the world looks to minimize its ecological footprint. Fungal pigments within a unique class of wood-rotting (“spalting”) fungi have been under investigation for several years as a possible solution, and have been shown to be ideally suited as textile dye coatings. Unfortunately, the solvent currently in use for these colorants is dichloromethane (DCM), which is an environmental problem as well as a potential human carcinogen. Recently, researchers found that the pigments from Chlorociboria species, Scytalidium cuboideum, and Scytalidium ganodermophthorum could be carried in some natural oils, which opened up a potential method of delivering pigments onto a host of substrates without utilizing DCM. Although the pigments can be carried in oil, no testing has thus far been conducted as to how oil affects the binding properties of the pigments onto textiles, or how the oil might affect the pigments directly. In this paper, the pigments produced by three well-known wood-rotting fungi were carried in raw linseed oil and applied to cotton, polyester, and nylon. Only the red pigment produced visible color change on the textiles. Cotton and polyester showed the greatest color change when the pigments were dripped onto the fabric, while polyester showed the most color when the textile was submerged into the pigment solution. Unfortunately, the colors faded significantly for all the tests except the saturation test. This indicates that while natural oils may be excellent, nontoxic alternative carriers for DCM, the pigments are not stable within them except at very high concentrations, and therefore natural oils—including raw linseed oil—are not ideal for use in conjunction with these pigments. Full article

(This article belongs to the Special Issue Binders, Pigments, Dyes and Additives)

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Coatings, Volume 7, Issue 10 (October 2017) – 26 articles

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