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Coatings, Volume 10, Issue 12 (December 2020) – 129 articles

Cover Story (view full-size image): Natural wood with warm colors, varied patterns, mellow gloss, and fine texture is appreciated in people’s lives. However, natural resources are in short supply, especially precious timber in the wood industry. The application of natural wood textures in furniture and wood products, aiming to achieve a pleasing sensory experience by mimicking the surface characteristics of natural wood, has long been the subject of surface decoration. In the increasing trend to manufacture imitation wood material, inkjet printing is a relatively new technique that allows additive contact-free manufacturing based on digital image data. However, the main strategies such as image processing, texture designing, and printing workflows are central issues for replicating real wood surface texture to fabricate the vivid 3D wood texture. View this paper
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Open AccessArticle
Reactive High-Power Impulse Magnetron Sputtering of Chromium-Carbon Films
Coatings 2020, 10(12), 1269; https://doi.org/10.3390/coatings10121269 - 21 Dec 2020
Viewed by 268
Abstract
Chromium-carbon films were deposited by utilizing reactive high-power impulse magnetron sputtering at different mixture ratios of ethyne and argon atmosphere, and different substrate bias voltages and deposition temperature, with the same pulse frequency, duty cycle, and average power. The microstructure and mechanical properties [...] Read more.
Chromium-carbon films were deposited by utilizing reactive high-power impulse magnetron sputtering at different mixture ratios of ethyne and argon atmosphere, and different substrate bias voltages and deposition temperature, with the same pulse frequency, duty cycle, and average power. The microstructure and mechanical properties of the obtained films were compared. The films consist of amorphous or nanocrystalline chromium carbide, hydrogenated amorphous carbon, and minor α-chromium phase. Decreasing the fraction of ethyne increases the content of the α-chromium phase but decreases hydrogenated amorphous carbon phase. The film’s hardness increases by enhancing the negative substrate bias and raising the deposition temperature, which could be attributed to the increase of film density and the Hall–Petch strengthening effect induced by the nanoscale crystallization of the amorphous carbide phase. Full article
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Open AccessArticle
Microstructure and Wear Behavior of Plasma-Sprayed TiO2–SiAlON Ceramic Coating
Coatings 2020, 10(12), 1268; https://doi.org/10.3390/coatings10121268 - 21 Dec 2020
Viewed by 304
Abstract
In this study, atmospheric plasma spray was employed to deposit TiO2–SiAlON ceramic coating on 316 stainless steel. The phases and microstructure of the ceramic coating were investigated. Additionally, comparative studies on the tribological performances of the substrate and the ceramic coating, [...] Read more.
In this study, atmospheric plasma spray was employed to deposit TiO2–SiAlON ceramic coating on 316 stainless steel. The phases and microstructure of the ceramic coating were investigated. Additionally, comparative studies on the tribological performances of the substrate and the ceramic coating, under both dry and starved lubrication conditions, were carried out. The SiAlON phase was preserved, while partial TiO2 anatase was transformed to rutile phase. The wear rate of the coating was roughly 1/3 of that of the substrate under both conditions. The wear mechanisms of the ceramic coating were surface fracture and abrasive wear in both cases, and the coating under starved lubrication underwent less abrasion. The pores in the coating served as micro-reservoirs, forming an oil layer on the mating surface, and improving tribological properties during sliding. Full article
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Open AccessArticle
Junction-Producing Algorithm Connecting Carbon Nanotube to Carbon Nanocone to Obtain Funnel-Like Nanostructure: Nanochimney Generator
Coatings 2020, 10(12), 1267; https://doi.org/10.3390/coatings10121267 - 21 Dec 2020
Viewed by 288
Abstract
This study aims to provide a computational algorithm which contributes to the understanding and implementation of carbon nanochimneys. The structure resembles a tube ending with an inverted funnel, with a connection region that uses non-hexagonal rings as defects in order to match the [...] Read more.
This study aims to provide a computational algorithm which contributes to the understanding and implementation of carbon nanochimneys. The structure resembles a tube ending with an inverted funnel, with a connection region that uses non-hexagonal rings as defects in order to match the boundaries of the two linked nanostructures. They are important for applications such as thermal transport, gas storage, or separation. The algorithm is written in Python 3.7 and provides a .pdb file with the coordinates of all the atoms included in the system. The parameters that can be specified are the carbon nanotube dimensions, for either armchair or zigzag conformations, five levels of disclination for the carbon nanocone along with the base diameter of the latter. Full article
(This article belongs to the Special Issue Advances in Polymer/Graphene Composite for Bio-Applications)
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Open AccessArticle
Curing Reaction Kinetics of the EHTPB-Based PBX Binder System and Its Mechanical Properties
Coatings 2020, 10(12), 1266; https://doi.org/10.3390/coatings10121266 - 21 Dec 2020
Viewed by 264
Abstract
In this research, differential scanning calorimetry (DSC) was employed to compare the curing reaction kinetics of the epoxidized hydroxyl terminated polybutadiene-isophorone diisocyanate (EHTPB-IPDI) and hydroxyl terminated polybutadiene-isophorone diisocyanate (HTPB-IPDI) binder systems. Glass transition temperature (Tg) and mechanical properties of the [...] Read more.
In this research, differential scanning calorimetry (DSC) was employed to compare the curing reaction kinetics of the epoxidized hydroxyl terminated polybutadiene-isophorone diisocyanate (EHTPB-IPDI) and hydroxyl terminated polybutadiene-isophorone diisocyanate (HTPB-IPDI) binder systems. Glass transition temperature (Tg) and mechanical properties of the EHTPB-IPDI and HTPB-IPDI binder systems were determined using the DSC method and a universal testing machine, respectively. For the EHTPB-IPDI binder system, the change of viscosity during the curing process in the presence of dibutyltin silicate (DBTDL) and tin 2-ethylhexanoate (TECH) catalysts was studied, and the activation energy was estimated. The results show that the activation energies (Ea) of the curing reaction of the EHTPB-IPDI and HTPB-IPDI binder systems are 53.8 and 59.1 kJ·mol−1, respectively. While their average initial curing temperatures of the two systems are 178.2 and 189.5 °C, respectively. The EHTPB-IPDI binder system exhibits a higher reactivity. Compared with the HTPB-IPDI binder system, the Tg of the EHTPB-IPDI binder system is increased by 5 °C. Its tensile strength and tear strength are increased by 12% and 17%, respectively, while its elongation at break is reduced by 10%. Epoxy groups and isocyanates react to form oxazolidinones, thereby improving the mechanical properties and thermal stability of polyurethane materials. These differences indicate that the EHTPB-IPDI binder system has better thermal stability and mechanical properties. During the EHTPB-IPDI binder system’s curing process, the DBTDL catalyst may ensure a higher viscosity growth rate, indicating a better catalytic effect, consistent with the prediction results obtained using the non-isothermal kinetic analysis method. Full article
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Open AccessArticle
Effect of Hot-Dip Galvanizing Process on Selective Oxidation and Galvanizability of Medium Manganese Steel for Automotive Application
Coatings 2020, 10(12), 1265; https://doi.org/10.3390/coatings10121265 - 21 Dec 2020
Viewed by 301
Abstract
A medium manganese steel with 7.5 wt.% Mn for automobile application was galvanized in a continuous Hot Dip Galvanizing (HDG) simulator under different galvanizing conditions. It was shown that the effects of dew point, annealing temperature and annealing atmosphere on the surface oxidation [...] Read more.
A medium manganese steel with 7.5 wt.% Mn for automobile application was galvanized in a continuous Hot Dip Galvanizing (HDG) simulator under different galvanizing conditions. It was shown that the effects of dew point, annealing temperature and annealing atmosphere on the surface oxidation of steel could be comprehensively evaluated by the consideration of oxygen partial pressure P(O2). Although Mn2SiO4 was a thermodynamic stable phase when P(O2) varied from 10−28 to 10−21 atm, it was difficult to form Mn–Si–O composite oxide because there was no enrichment of silicon on the steel surface. So, this oxide was generally formed in the Fe substrate and had little effect on the galvanizability. With the increase in P(O2) above 10−25 atm, MnO particles in the form of the thermodynamic stable phase became coarser and tended to aggregate, which hindered the formation of a continuous inhibition layer, resulting in the defects of bare spots on the galvanized surface of the steel. When the oxygen partial pressure greater than 10−22 atm, film-like MnO layer was formed on the surface of steel sample, which obviously deteriorated the galvanizability. The galvanizability of the steel can be improved by the regulation of oxygen partial pressure; based on this, the reasonable zinc plating process parameters can be developed. Full article
(This article belongs to the Special Issue Coatings and Interfaces)
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Open AccessArticle
Laser Shock Induced Deformation of Copper Foil on Diverse Molds and the Cross-Sectional Microstructure Changes
Coatings 2020, 10(12), 1264; https://doi.org/10.3390/coatings10121264 - 21 Dec 2020
Viewed by 278
Abstract
The microscale structures prepared on copper foil by laser shock deformation was introduced in the paper. The various sizes of hexagonal structures were successfully fabricated on copper foil with different molds. The influence of laser energy on the deformation depth of a hexagonal [...] Read more.
The microscale structures prepared on copper foil by laser shock deformation was introduced in the paper. The various sizes of hexagonal structures were successfully fabricated on copper foil with different molds. The influence of laser energy on the deformation depth of a hexagonal structure was studied using experiments. The morphology of the hexagonal structures on copper foil was observed by a three-dimensional profilometer, and mechanical property were characterized by a nanoindenter. A finite element model was established in order to describe the copper foil forming mechanism on mold and calculate the residual stress distribution. The microstructures and cross-section deformation of copper foil on different molds were also observed. The results indicated that the depth of hexagonal structures on 50# mold was higher than that of the structures on 100# mold and 230# mold, and the depth of hexagonal structures increased with the increasing of pulse laser energy. The copper foil above the mold hexagon side was bent and thinned after laser shock, and the grains of copper foil were also refining. The mechanical properties of copper foil were improved after laser shock was performed on the mold. Full article
(This article belongs to the Section Surface Characterization, Deposition and Modification)
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Open AccessArticle
The Effect of Hydroxyl on the Superhydrophobicity of Dodecyl Methacrylate (LMA) Coated Fabrics through Simple Dipping-Plasma Crosslinked Method
Coatings 2020, 10(12), 1263; https://doi.org/10.3390/coatings10121263 - 21 Dec 2020
Viewed by 306
Abstract
In order to obtain stable superhydrophobicity, suitable hydrophobic treatment agents should be selected according to different material properties. In this paper, cotton and poly(ethylene terephthalate) (PET) fabrics were respectively coated with dodecyl methacrylate (LMA) via argon combined capacitively coupled plasma (CCP), and the [...] Read more.
In order to obtain stable superhydrophobicity, suitable hydrophobic treatment agents should be selected according to different material properties. In this paper, cotton and poly(ethylene terephthalate) (PET) fabrics were respectively coated with dodecyl methacrylate (LMA) via argon combined capacitively coupled plasma (CCP), and the surface hydrophobicity and durability of the treated cotton and polyester fabrics are also discussed. An interesting phenomenon happened, whereby the LMA-coated cotton fabric (Cotton-g-LMA) had better water repelling and mechanical durability properties than LMA-coated PET fabric (PET-g-LMA), and LMA-coated hydroxyl-grafted PET fabrics (PET fabrics were successively coated with polyethylene glycol (PEG) and LMA, PET-g-PEG & LMA) had a similar performance to cotton fabrics. The water contact angles of Cotton-g-LMA, PET-g-LMA and PET-g-PEG & LMA were 156°, 153° and 155°, respectively, and after 45 washing cycles or 1000 rubbing cycles, the corresponding water contact angles decreased to 145°, 88°, 134° and 146°, 127° and 143°, respectively. Additionally, thermoplastic polyurethane (TPU) and polyamides-6 (PA6) fabrics all exhibited the same properties as the PET fabric. Therefore, the grafting of hydroxyl can improve the hydrophobic effect of LMA coating and the binding property between LMA and fabrics effectively, without changing the wearing comfort. Full article
(This article belongs to the Special Issue Science and Technology of Fabric Coatings)
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Open AccessArticle
Effect of Bagasse and Coconut Peat Fillers on Asphalt Mixture Workability
Coatings 2020, 10(12), 1262; https://doi.org/10.3390/coatings10121262 - 21 Dec 2020
Viewed by 324
Abstract
Workability is of importance during asphalt construction, which plays a role in increasing stability and other performances. Using different mineral fillers can result in different asphalt workability in the same mix design. While fillers can increase stability, viscosity with regards to asphalt mastic [...] Read more.
Workability is of importance during asphalt construction, which plays a role in increasing stability and other performances. Using different mineral fillers can result in different asphalt workability in the same mix design. While fillers can increase stability, viscosity with regards to asphalt mastic needs to be considered for working in the field. Nowadays, waste natural materials can allow agriculturists to get more income by recycling in many industries. In this study, the objective is to determine the effect of using bagasse and coconut peat as filler on mastic viscosity and the resistance to failure performances. Findings show that the viscosities of asphalt mastic with coconut peat and bagasse fillers are relatively similar to those with limestone filler for all temperatures at 20 percent filler content. Additionally, the stabilities and flows of asphalt mixtures mixed with waste natural fillers were close to those mixed with mineral fillers at equivalent temperatures. In conclusion, the mastic viscosity is vital for determining the workability of asphalt mixture. The waste natural fillers including bagasse and coconut peat give similar mastic viscosity to limestone filler and higher than granite filler, which shows less difference to performance results. Full article
(This article belongs to the Special Issue Pavement Surface Coatings)
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Open AccessArticle
Characteristics of MgIn2O4 Thin Film Transistors Enhanced by Introducing an MgO Buffer Layer
Coatings 2020, 10(12), 1261; https://doi.org/10.3390/coatings10121261 - 20 Dec 2020
Viewed by 332
Abstract
In this work, an MgIn2O4 (MIO) thin film transistor (TFT) with a bottom gate structure was fabricated. The MIO channel layer was deposited by RF sputtering using a single MgIn2O4 target. The performance of MIO TFT was [...] Read more.
In this work, an MgIn2O4 (MIO) thin film transistor (TFT) with a bottom gate structure was fabricated. The MIO channel layer was deposited by RF sputtering using a single MgIn2O4 target. The performance of MIO TFT was highly related to oxygen vacancies. As-deposited MIO TFT showed a low field-effect mobility due to doping of Mg. An MgO buffer layer was introduced to enhance the mobility of MIO TFT due to improvement of the interface with the channel layer. In addition, oxygen vacancies in the MIO channel were suppressed because of oxygen diffusion from the buffer layer. MIO TFT with a 5 nm MgO buffer layer showed an on/off current ratio of 9.68 × 103, a field-effect mobility of 4.81 cm2/V∙s, which was increased more than an order of magnitude compared with the device without a buffer layer, a threshold voltage of 2.01 V, and a subthreshold swing of 0.76 V/decade, which was improved more than 20% compared with the as-deposited one. Full article
(This article belongs to the Special Issue Advances in Thin Film Transistors: Properties and Applications)
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Open AccessArticle
Insights in to the Electrochemical Activity of Fe-Based Perovskite Cathodes toward Oxygen Reduction Reaction for Solid Oxide Fuel Cells
Coatings 2020, 10(12), 1260; https://doi.org/10.3390/coatings10121260 - 19 Dec 2020
Viewed by 433
Abstract
The development of novel oxygen reduction electrodes with superior electrocatalytic activity and CO2 durability is a major challenge for solid oxide fuel cells (SOFCs). Here, novel cobalt-free perovskite oxides, BaFe1−xYxO3−δ (x = 0.05, 0.10, [...] Read more.
The development of novel oxygen reduction electrodes with superior electrocatalytic activity and CO2 durability is a major challenge for solid oxide fuel cells (SOFCs). Here, novel cobalt-free perovskite oxides, BaFe1−xYxO3−δ (x = 0.05, 0.10, and 0.15) denoted as BFY05, BFY10, and BFY15, are intensively evaluated as oxygen reduction electrode candidate for solid oxide fuel cells. These materials have been synthesized and the electrocatalytic activity for oxygen reduction reaction (ORR) has been investigated systematically. The BFY10 cathode exhibits the best electrocatalytic performance with a lowest polarization resistance of 0.057 Ω cm2 at 700 °C. Meanwhile, the single cells with the BFY05, BFY10 and BFY15 cathodes deliver the peak power densities of 0.73, 1.1, and 0.89 W cm−2 at 700 °C, respectively. Furthermore, electrochemical impedance spectra (EIS) are analyzed by means of distribution of relaxation time (DRT). The results indicate that the oxygen adsorption-dissociation process is determined to be the rate-limiting step at the electrode interface. In addition, the single cell with the BFY10 cathode exhibits a good long-term stability at 700 °C under an output voltage of 0.5 V for 120 h. Full article
(This article belongs to the Special Issue Surface Engineering of C/N/O Functionalized Materials)
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Open AccessArticle
Analysis of Surface Roughness and Flank Wear Using the Taguchi Method in Milling of NiTi Shape Memory Alloy with Uncoated Tools
Coatings 2020, 10(12), 1259; https://doi.org/10.3390/coatings10121259 - 19 Dec 2020
Viewed by 368
Abstract
The aim of this study was to optimize machining parameters to obtain the smallest average surface roughness (Ra) and flank wear (Vb) values as a result of the surface milling of a nickel-titanium (NiTi) shape memory alloy (SMA) with uncoated cutting tools with [...] Read more.
The aim of this study was to optimize machining parameters to obtain the smallest average surface roughness (Ra) and flank wear (Vb) values as a result of the surface milling of a nickel-titanium (NiTi) shape memory alloy (SMA) with uncoated cutting tools with different nose radius (rε) under dry cutting conditions. Tungsten carbide cutting tools with different rε (0.4 mm and 0.8 mm) were used in milling operations. The milling process was performed as lateral/surface cutting at three different cutting speeds (Vc) (20, 35 and 50 m/min), feed rates (fz) (0.03, 0.07 and 0.14 mm/tooth) and a constant axial cutting depth (0.7 mm). The effects of machining parameters in milling experiments were investigated based on the Taguchi L18 (21 × 32) orthogonal sequence, and the data obtained were analyzed using the Minitab 17 software. To determine the effects of processing parameters on Ra and Vb, analysis of variance (ANOVA) was used. The analysis results reveal that the dominant factor affecting the Ra is the cutting tool rε, while the main factor affecting Vb is the fz. Since the predicted values and measured values are very close to each other, it can be said that optimization is correct according to the validation test results. Full article
(This article belongs to the Special Issue Advanced Coating Materials for Machining Processes)
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Open AccessArticle
Pulsed Magnetron Sputtering of Strongly Thermochromic VO2-Based Coatings with a Transition Temperature of 22 °C onto Ultrathin Flexible Glass
Coatings 2020, 10(12), 1258; https://doi.org/10.3390/coatings10121258 - 19 Dec 2020
Viewed by 329
Abstract
The reversible semiconductor-to-metal transition of vanadium dioxide (VO2) makes VO2-based coatings a promising candidate for thermochromic smart windows, reducing the energy consumption of buildings. This paper deals with maximizing the application potential of these coatings in terms of their [...] Read more.
The reversible semiconductor-to-metal transition of vanadium dioxide (VO2) makes VO2-based coatings a promising candidate for thermochromic smart windows, reducing the energy consumption of buildings. This paper deals with maximizing the application potential of these coatings in terms of their performance, an industry-friendly preparation technique, and an industrially relevant substrate. We present a scalable sputter deposition technique for the preparation of strongly thermochromic ZrO2/V0.984W0.016O2/ZrO2 coatings on ultrathin flexible glass and standard glass at a relatively low substrate surface temperature (330 °C) and without any substrate bias voltage. The V0.984W0.016O2 layers were deposited by a controlled high-power impulse magnetron sputtering of a V target, combined with a simultaneous pulsed dc magnetron sputtering of a W target. We explain the fundamental principles of this technique using the discharge characteristics measured for both discharges. We characterize the coating structure (X-ray diffraction) and a wide range of optical properties (spectrophotometry and spectroscopic ellipsometry). We find that the coatings combine a transition temperature of 22 °C, a luminous transmittance approaching 50%, a modulation of the solar energy transmittance over 10% and a temperature-independent color. The results in general, and the successful transfer from a standard glass to the ultrathin flexible glass in particular, are crucial for future applications of the coatings on smart windows. Full article
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Open AccessArticle
Durable Flame-Resistant and Ultra-Hydrophobic Aramid Fabrics via Plasma-Induced Graft Polymerization
Coatings 2020, 10(12), 1257; https://doi.org/10.3390/coatings10121257 - 18 Dec 2020
Viewed by 305
Abstract
A durable flame-resistant and ultra-hydrophobic phosphorus–fluoride coating on aramid fabrics was achieved by plasma-induced graft polymerization. The aramid fabrics were activated and roughed through the low-pressure plasma firstly, which involves the sequential coating of a mixture of phosphorus–fluoride emulsion copolymer. When potentially exposed [...] Read more.
A durable flame-resistant and ultra-hydrophobic phosphorus–fluoride coating on aramid fabrics was achieved by plasma-induced graft polymerization. The aramid fabrics were activated and roughed through the low-pressure plasma firstly, which involves the sequential coating of a mixture of phosphorus–fluoride emulsion copolymer. When potentially exposed to flame or water, such a surface produces a dual effect in which it is intumescent and waterproof, successfully giving the coated fabrics flame-resistant ultra-hydrophobic bifunctional properties. Thus, adhesive coatings provide a convenient way to resolve the issue of washing durability of the coatings. The as-prepared fabrics last for 10 repeatable washing cycles without losing their flame resistance and superhydrophobicity, suggesting future applications as advanced multifunctional textiles. Compared to an untreated coating, its char length was less than 1 cm with no measurable after-flame or after-glow times, and its static water contact angle remained stable above 170°. Meanwhile, the control sample was unable to extinguish the fire with a damage length of 10.6 cm and a water contact angle of 100°. All the results indicate that plasma-reactive polar groups interact between phosphorus and fluorine elements, leading to an increased relative atom ratio P and F through Energy-Dispersive Spectrometer (EDS) spectra and XPS analysis, which inhibits the flammability and wettability. Full article
(This article belongs to the Special Issue Science and Technology of Fabric Coatings)
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Open AccessArticle
Modified Epoxy with Chitosan Triazine Dihydrazide Derivatives for Mechanical and Corrosion Protection of Steel
Coatings 2020, 10(12), 1256; https://doi.org/10.3390/coatings10121256 - 18 Dec 2020
Viewed by 337
Abstract
Modification of the curing exothermic reaction of epoxy resin with polyamine (PA) hardeners by new chemically bonded fillers to improve the mechanical properties and anticorrosion performances of the epoxy coatings is the main goal for wide applications of epoxy coatings. In this work, [...] Read more.
Modification of the curing exothermic reaction of epoxy resin with polyamine (PA) hardeners by new chemically bonded fillers to improve the mechanical properties and anticorrosion performances of the epoxy coatings is the main goal for wide applications of epoxy coatings. In this work, the chemical structure of chitosan was modified with triazine hydrazide moiety that contains primary, secondary, and tertiary amine groups to act as activator and dangling chain linkers during the curing of epoxy/PA system. Different molecular masses of chitosan were modified with triazine dihydrazide moiety (Ch-TH2), and their chemical structures and surface morphologies were identified. Their thermal stabilities were investigated, and the grafting percentages with triazine hydrazide were determined from thermal analysis. Different weight percentages of Ch-TH2 ranged from 1 to 10 Wt. % were added to the epoxy/PA system, and their curing characteristics, such as heat enthalpy and glass transition temperature, were determined from non-isothermal dynamic scanning calorimetric thermograms. The effects of molecular masses, triazine dihydrazide %, and Ch-TH2 Wt. % on the mechanical, adhesion and anticorrosive properties of the cured epoxy/PA coatings for steel were investigated. The optimum Ch-TH2 Wt. % was selected from 3 to 6 Wt. % to improve the mechanical, adhesion, and anticorrosive properties of the cured epoxy/PA coatings. Full article
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Open AccessArticle
Fluorescent Silica Hybrid Film-Forming Materials Based on Salicylaldazine
Coatings 2020, 10(12), 1255; https://doi.org/10.3390/coatings10121255 - 18 Dec 2020
Viewed by 357
Abstract
Fluorescent film-forming materials were obtained by embedding salicylaldazine (SAA) in silica hybrids generated by sol–gel processes from different silane precursors in acid catalysis. Tuned local environments for the fluorophore were generated in the hosting network by modifying silica sols with organic groups through [...] Read more.
Fluorescent film-forming materials were obtained by embedding salicylaldazine (SAA) in silica hybrids generated by sol–gel processes from different silane precursors in acid catalysis. Tuned local environments for the fluorophore were generated in the hosting network by modifying silica sols with organic groups through the co-condensation of tetraethylortosilicate (TEOS) and different alkoxysilanes hydrolysis products. The photophysical properties of the luminescent hybrid films were studied in direct relationship with structural, textural, and surface properties and based on interactions between SAA species and the silica hosting network. Film-forming materials were studied in order to determine differences in absorption and fluorescence emission due to the environments around the fluorophore. The variations recorded in the fluorescence emission spectra of the hybrid films were related to interactions established between the fluorophore species and their sterically hindered surroundings of the host hybrid silica, where free molecular motions are restricted. The influence of the type and amount of network modifier and of the fluorophore loading on the transparency of the films and fluorescence intensity was also investigated. The study carried out led to the elucidation of the necessary conditions for obtaining luminescent film-forming materials with high luminescence intensity and transparency useful for the design of new light concentrators. Full article
(This article belongs to the Special Issue Multifunctional Antireflective Coatings and Nanocomposites)
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Open AccessArticle
Particle Velocimetry, CFD, and the Role of Particle Sphericity in Cold Spray
Coatings 2020, 10(12), 1254; https://doi.org/10.3390/coatings10121254 - 18 Dec 2020
Viewed by 322
Abstract
Implementation of the cold spray (CS) technology in manufacturing and repair creates a demand for reliable quality control and process monitoring measures. In this regard, particle size and impact velocity are undoubtedly the most important control parameters in CS. Several in-flight measurement systems [...] Read more.
Implementation of the cold spray (CS) technology in manufacturing and repair creates a demand for reliable quality control and process monitoring measures. In this regard, particle size and impact velocity are undoubtedly the most important control parameters in CS. Several in-flight measurement systems for particle velocimetry are now available commercially for CS. These systems provide great potential to be used as a diagnostic tool for validating CS system performance in industrial applications. However, post processing the velocimetry data is required in many instances for achieving a complete understanding of the particle flow field. In this study, particle velocimetry is used in conjunction with computational fluid dynamics (CFD) simulations to: (i) identify the physical factors that dictate the particle velocity and its variability; (ii) develop high fidelity CFD models to accurately predict particle flight parameters that cannot be measured by available experimental tools; and (iii) present the capabilities of state-of-the-art velocimeters as a reliable diagnostic tool for measuring the consistency and repeatability of CS systems in manufacturing settings. In-flight particle size, location, and velocity are measured using a commercially available velocimeter for aluminum and copper particles sprayed with supersonic nozzles using helium, nitrogen, and air by two high pressure CS systems. As a result of this work, particle sphericity was clearly identified to have strong effects on particle velocity and to be one of the main factors of the variability of particle velocity. Furthermore, methods for building a high-fidelity 3D-CFD model was presented. CFD models were validated using particle velocimetry and schlieren imaging. Finally, particle velocimetry is shown to be a valid diagnostics tool for CS with systems capable of measuring in-flight particle velocities along with particle sizes. This article also outlines steps necessary for conducting cold spray process diagnostics repeatably and reliably. Full article
(This article belongs to the Special Issue Recent Developments of Cold Spray Coating)
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Open AccessArticle
The Effects of Transition Metal Oxides (Me = Ti, Zr, Nb, and Ta) on the Mechanical Properties and Interfaces of B4C Ceramics Fabricated via Pressureless Sintering
Coatings 2020, 10(12), 1253; https://doi.org/10.3390/coatings10121253 - 18 Dec 2020
Viewed by 343
Abstract
There is little available research on how different transition metal oxides influence the behavior of B4C-based ceramics, especially for Ta2O5 and Nb2O5. B4C-MeB2 (Me = Ti, Zr, Nb, and Ta) multiphase [...] Read more.
There is little available research on how different transition metal oxides influence the behavior of B4C-based ceramics, especially for Ta2O5 and Nb2O5. B4C-MeB2 (Me = Ti, Zr, Nb, and Ta) multiphase ceramic samples were prepared via in situ pressureless sintering at 2250 °C, involving the mixing of B4C and MeOx powders, namely TiO2, ZrO2, Nb2O5, and Ta2O5. The phase constituents, microstructures, and mechanical properties of the samples were tested. The results indicated that different transition metal elements had different effects on the ceramic matrix, as verified through a comparative analysis. Additionally, the doped WC impurity during the ball milling process led to the production of (Me, W)B2 and W2B5, which brought about changes in morphology and performance. In this study, the Ta2O5-added sample exhibited the best performance, with elastic modulus, flexural strength, Vickers hardness, and fracture toughness values of 312.0 GPa, 16.3 GPa, 313.0 MPa, and 6.08 MPa·m1/2, respectively. The comprehensive mechanical properties were better than the reported values when the mass fraction of the second phase was around five percent. Full article
(This article belongs to the Special Issue Surface Engineering of C/N/O Functionalized Materials)
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Open AccessArticle
Effects of the Nitrogen Flow Ratio and Substrate Bias on the Mechanical Properties of W–N and W–Si–N Films
Coatings 2020, 10(12), 1252; https://doi.org/10.3390/coatings10121252 - 18 Dec 2020
Viewed by 345
Abstract
The reactive gas flow ratio and substrate bias voltage are crucial sputtering parameters for fabricating transition metal nitride films. In this study, W–N films were prepared using sputtering with nitrogen flow ratios (f) of 0.1–0.5. W–N and W–Si–N films were then [...] Read more.
The reactive gas flow ratio and substrate bias voltage are crucial sputtering parameters for fabricating transition metal nitride films. In this study, W–N films were prepared using sputtering with nitrogen flow ratios (f) of 0.1–0.5. W–N and W–Si–N films were then prepared using an f level of 0.4 and substrate bias varying from 0 to −150 V by using sputtering and co-sputtering, respectively. The variations in phase structures, bonding characteristics, mechanical properties, and wear resistance of the W–N and W–Si–N films were investigated. The W–N films prepared with nitrogen flow ratios of 0.1–0.2, 0.3, and 0.4–0.5 displayed crystalline W, amorphous W–N, and crystalline W2N, respectively. The W–N films prepared using a nitrogen flow ratio of 0.4 and substrate bias voltages of −50 and −100 V exhibited favorable mechanical properties and high wear resistance. The mechanical properties of the amorphous W–Si–N films were not related to the magnitude of the substrate bias. Full article
(This article belongs to the Special Issue New Hard and Superhard Coatings)
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Open AccessFeature PaperArticle
4-(Trifluoromethoxy)phenyl-Containing Polymers as Promising Anodic Materials for Electrochromic Devices
Coatings 2020, 10(12), 1251; https://doi.org/10.3390/coatings10121251 - 18 Dec 2020
Viewed by 307
Abstract
Three 4-(trifluoromethoxy)phenyl-based polydithienylpyrroles (PTTPP, P(TTPP-co-DTC), and P(TTPP-co-DTP)) were synthesized electrochemically and their electrochromic behaviors were characterized. The introduction of electron withdrawing trifluoromethoxy unit in the side chain of polydithienylpyrroles (PSNS) decreases the HOMO and LUMO energy levels of PSNS. [...] Read more.
Three 4-(trifluoromethoxy)phenyl-based polydithienylpyrroles (PTTPP, P(TTPP-co-DTC), and P(TTPP-co-DTP)) were synthesized electrochemically and their electrochromic behaviors were characterized. The introduction of electron withdrawing trifluoromethoxy unit in the side chain of polydithienylpyrroles (PSNS) decreases the HOMO and LUMO energy levels of PSNS. PTTPP film displays three various colors (grayish-yellow at 0 V, grayish-blue at 1.0 V, and bluish-violet at 1.4 V) from reduced to oxidized states. The optical contrast of PTTPP, P(TTPP-co-DTC), and P(TTPP-co-DTP) electrodes are 24.5% at 1050 nm, 49.0% at 916 nm, and 53.8% at 1302 nm, respectively. The highest η of the PTTPP electrode is 379.64 cm2 C−1 at 1050 nm. Three ECDs based on PTTPP, P(TTPP-co-DTC), or P(TTPP-co-DTP) as anodic film and PProDOT-Et2 as cathodic film were fabricated. PTTPP/PProDOT-Et2 ECD showed high transmittance change (35.7% at 588 nm) and high η (890.96 cm2·C−1 at 588 nm). P(TTPP-co-DTC)/PProDOT-Et2 and P(TTPP-co-DTP)/PProDOT-Et2 ECDs showed high transmittance change, rapid response time, adequate open circuit memory, and good electrochemical redox stability. Based on these findings, this work provides novel insights for appropriate design of high transmittance change and high efficient multi-colored electrochromic polymers. Full article
(This article belongs to the Special Issue Organic Synthesis and Characteristics of Thin Films)
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Open AccessFeature PaperArticle
Depth-Resolved Phase Analysis of Expanded Austenite Formed in Austenitic Stainless Steel
Coatings 2020, 10(12), 1250; https://doi.org/10.3390/coatings10121250 - 18 Dec 2020
Viewed by 265
Abstract
Expanded austenite γN formed after nitrogen insertion into austenitic stainless steel and CoCr alloys is known as a hard and very wear resistant phase. Nevertheless, no single composition and lattice expansion can describe this phase with nitrogen in solid solution. Using in [...] Read more.
Expanded austenite γN formed after nitrogen insertion into austenitic stainless steel and CoCr alloys is known as a hard and very wear resistant phase. Nevertheless, no single composition and lattice expansion can describe this phase with nitrogen in solid solution. Using in situ X-ray diffraction (XRD) during ion beam sputtering of expanded austenite allows a detailed depth-dependent phase analysis, correlated with the nitrogen depth profiles obtained by time-of-flight secondary ion mass spectrometry (ToF-SIMS) or glow discharge optical emission spectroscopy (GDOES). Additionally, in-plane XRD measurements at selected depths were performed for strain analysis. Surprisingly, an anomalous peak splitting for the (200) expanded peak was observed for some samples during nitriding and sputter etching, indicating a layered structure only for {200} oriented grains. The strain analysis as a function of depth and orientation of scattering vector (parallel/perpendicular to the surface) is inconclusive. Full article
(This article belongs to the Special Issue Design, Characterization and Applications of Functional Coatings)
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Open AccessReview
Current Challenges and Innovative Developments in Hydroxyapatite-Based Coatings on Metallic Materials for Bone Implantation: A Review
Coatings 2020, 10(12), 1249; https://doi.org/10.3390/coatings10121249 - 18 Dec 2020
Viewed by 319
Abstract
Biomaterials are in use for the replacement and reconstruction of several tissues and organs as treatment and enhancement. Metallic, organic, and composites are some of the common materials currently in practice. Metallic materials contribute a big share of their mechanical strength and resistance [...] Read more.
Biomaterials are in use for the replacement and reconstruction of several tissues and organs as treatment and enhancement. Metallic, organic, and composites are some of the common materials currently in practice. Metallic materials contribute a big share of their mechanical strength and resistance to corrosion properties, while organic polymeric materials stand high due to their biocompatibility, biodegradability, and natural availability. To enhance the biocompatibility of these metals and alloys, coatings are frequently applied. Organic polymeric materials and ceramics are extensively utilized for this purpose due to their outstanding characteristics of biocompatibility and biodegradability. Hydroxyapatite (HAp) is the material from the ceramic class which is an ultimate candidate for coating on these metals for biomedical applications. HAp possesses similar chemical and structural characteristics to normal human bone. Due to the bioactivity and biocompatibility of HAp, it is used for bone implants for regenerating bone tissues. This review covers an extensive study of the development of HAp coatings specifically for the orthopaedic applications that include different coating techniques and the process parameters of these coating techniques. Additionally, the future direction and challenges have been also discussed briefly in this review, including the coating of HAp in combination with other calcium magnesium phosphates that occur naturally in human bone. Full article
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Open AccessArticle
Vapor-Stripping and Encapsulating to Construct Particles with Time-Controlled Asymmetry and Anisotropy
Coatings 2020, 10(12), 1248; https://doi.org/10.3390/coatings10121248 - 18 Dec 2020
Viewed by 288
Abstract
An innovative chemical vapor sublimation and deposition (CVSD) process was shown to produce nanoscale anisotropic hybrid materials. Taking advantage of controlled thermodynamic properties and the mass transfer of molecules, this process allowed for water vapor sublimation from an iced template/substrate and stagewise vapor [...] Read more.
An innovative chemical vapor sublimation and deposition (CVSD) process was shown to produce nanoscale anisotropic hybrid materials. Taking advantage of controlled thermodynamic properties and the mass transfer of molecules, this process allowed for water vapor sublimation from an iced template/substrate and stagewise vapor deposition of poly-p-xylylene onto the sublimating ice substrate. In this study, the use of sensitive soybean agglutinin (SBA) protein tubes was demonstrated as an example to prepare the anisotropic hybrid material based on the CVSD process. The rationale of a timing parameter, Δt, was controlled to program the sublimation of the SBA-ice templates and the deposition of poly-p-xylylene during the CVSD process. As a result of this control, a stripping stage occurred, during which SBA tubes were exposed on the particle surface, and a subsequent encapsulation stage enabled the transformation of the ice templates into a nanometer-sized anisotropic hybrid material of poly-p-xylylene as the matrix with encapsulated SBA tubes. The timing parameter Δt and the controlled stripping and encapsulating stages during CVSD represent a straightforward and intriguing mechanism stemming from physical chemistry fundamentals for the fabrication of hybrid materials from sensitive molecules and with predetermined sizes and asymmetrical shapes. A simulation analysis showed consistency with the experimental results and controllability of the timing mechanism with predictable particle sizes. Full article
(This article belongs to the Special Issue Biointerface Coatings for Biomaterials and Biomedical Applications)
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Open AccessArticle
Wavelength-Selective Coatings on Glass with High Hardness and Damage Resistance
Coatings 2020, 10(12), 1247; https://doi.org/10.3390/coatings10121247 - 17 Dec 2020
Viewed by 280
Abstract
Wavelength-selective coatings are broadly applied across diverse industries such as solar energy management, infrared sensing, telecommunications, laser optics, and eye-protective lenses. These coatings have historically not been optimized for hardness or mechanical durability and typically suffer from higher susceptibility to scratch and damage [...] Read more.
Wavelength-selective coatings are broadly applied across diverse industries such as solar energy management, infrared sensing, telecommunications, laser optics, and eye-protective lenses. These coatings have historically not been optimized for hardness or mechanical durability and typically suffer from higher susceptibility to scratch and damage events than uncoated glass. In this work, we describe a family of wavelength-selective coatings with hardness and scratch resistance that are significantly higher than the chemically strengthened glass substrates on which the coatings are fabricated. The coatings are made using industrially scalable reactive sputtering methods. Wavelength-selective coatings are fabricated with nanoindentation hardness as high as 16–20 GPa over indentation depths ranging from 200 to 800 nm, as well as excellent durability in aggressive scratch testing. Tunable visible to near-infrared wavelength selectivity ratios (reflectance of stopband: reflectance of passband) as high as 7:1 are achieved. The feasibility of narrowband hard coating design is also demonstrated, with visible narrowband transmission having a peak FWHM of ~8 nm (~1.6%). A unique “buried layers” hard coating design strategy is shown to deliver particularly excellent hardness profiles. These designs can be tailored for a variety of different wavelengths and selectivity ratios, enabling new uses of wavelength-selective optics in mechanically demanding applications. Full article
(This article belongs to the Special Issue Thin Films and Surface Optics)
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Open AccessReview
Preparation and Characterization of NbxOy Thin Films: A Review
Coatings 2020, 10(12), 1246; https://doi.org/10.3390/coatings10121246 - 17 Dec 2020
Viewed by 430
Abstract
Niobium oxides (NbO, NbO2, Nb2O5), being a versatile material has achieved tremendous popularity to be used in a number of applications because of its outstanding electrical, mechanical, chemical, and magnetic properties. NbxOy films possess [...] Read more.
Niobium oxides (NbO, NbO2, Nb2O5), being a versatile material has achieved tremendous popularity to be used in a number of applications because of its outstanding electrical, mechanical, chemical, and magnetic properties. NbxOy films possess a direct band gap within the ranges of 3.2–4.0 eV, with these films having utility in different applications which include; optical systems, stainless steel, ceramics, solar cells, electrochromic devices, capacitor dielectrics, catalysts, sensors, and architectural requirements. With the purpose of fulfilling the requirements of a vast variety of the named applications, thin films having comprehensive properties span described by film composition, morphology, structural properties, and thickness are needed. The theory, alongside the research status of the different fabrication techniques of NbxOy thin films are reported in this work. The impact of fabrication procedures on the thin film characteristics which include; film thickness, surface quality, optical properties, interface properties, film growth, and crystal phase is explored with emphases on the distinct deposition process applied, are also described and discussed. Full article
(This article belongs to the Special Issue Metal Oxide Films and Their Applications)
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Open AccessArticle
Effect of Substrate Strain, Aluminum Thickness and Corona Pretreatment on the Electrical Resistance of Physical Vapor Deposited Aluminum Coatings
Coatings 2020, 10(12), 1245; https://doi.org/10.3390/coatings10121245 - 17 Dec 2020
Viewed by 306
Abstract
Aluminum coatings applied to polymer films by physical vapor deposition should be defect-free for applications such as packaging and electronic devices. However, cracks can appear in the aluminum coating as the polymer film stretches, becoming manifest as an increase in resistance. We evaluated [...] Read more.
Aluminum coatings applied to polymer films by physical vapor deposition should be defect-free for applications such as packaging and electronic devices. However, cracks can appear in the aluminum coating as the polymer film stretches, becoming manifest as an increase in resistance. We evaluated the effect of different aluminum thicknesses (10–85 nm), polymer films (polyethylene terephthalate or polypropylene), and corona doses (0–280 W∙min/m2) on the relative increase in resistance during stretching (strain = 0–100%). We found that the thickness of the aluminum coating was inversely related to the increase in resistance. Corona pretreatment led to an increase in surface energy (≤40 mN/m for polypropylene; ≤50 mN/m for polyethylene terephthalate) although high corona doses resulted in overtreatment, which limited the adhesion of aluminum to the substrate and led to a greater increase in resistance. Varying the coating thickness had a much greater effect than the corona pretreatment, suggesting that thicker aluminum coatings are more effective than corona pretreatment as a strategy to increase coating stability. The effect of aluminum thickness and strain on resistance was described using a fit function containing three fit factors. Full article
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Open AccessArticle
Reinforced Superhydrophobic Anti-Corrosion Epoxy Resin Coating by Fluorine–Silicon–Carbide Composites
Coatings 2020, 10(12), 1244; https://doi.org/10.3390/coatings10121244 - 17 Dec 2020
Viewed by 313
Abstract
SiC was modified by fluorine-containing organic substance 1H,1H,2H,2H-trifluoro-noctyltriethoxysilane (FAS) to change its hydrophilicity from hydrophilic to superhydrophobic nanoparticles, and the optimum conditions for hydrophobicity were effectively explored. Then, different content of fluorine-modified SiC (F–SiC) nanoparticles were added to the epoxy resin (EP) matrix [...] Read more.
SiC was modified by fluorine-containing organic substance 1H,1H,2H,2H-trifluoro-noctyltriethoxysilane (FAS) to change its hydrophilicity from hydrophilic to superhydrophobic nanoparticles, and the optimum conditions for hydrophobicity were effectively explored. Then, different content of fluorine-modified SiC (F–SiC) nanoparticles were added to the epoxy resin (EP) matrix to prepare composite coating samples. The results showed that the surface of SiC was modified by FAS to show superhydrophobicity, and the dispersion in EP was significantly improved. After adding F–SiC, the hydrophobicity, wear resistance and corrosion resistance of the coating were significantly improved. In addition, the corrosion resistance of the composite coating containing different contents of F–SiC was analyzed through electrochemical and salt spray tests. The results showed that the corrosion resistance of the coating was the best when the addition amount was 3 wt %. In general, the composite coating with 3 wt % F–SiC had the best overall performance. Compared with the EP coating, the water contact angle of 3 wt % F–SiC/EP composite coating was increased by 62.9%, the friction coefficient was reduced by 73.5%, and the corrosion current was reduced by three orders of magnitude. This study provides a new idea for the development of ultra-wear-resistant and anti-fouling heavy-duty coatings. Full article
(This article belongs to the Special Issue Coatings for Corrosion Mitigation II)
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Open AccessArticle
The Potential of High-Fluence Ion Irradiation for Processing and Recovery of Diamond Tools
Coatings 2020, 10(12), 1243; https://doi.org/10.3390/coatings10121243 - 17 Dec 2020
Viewed by 337
Abstract
The graphitization and surface growth of synthetic diamonds by high-fluence irradiation with 30 keV argon and carbon ions have been experimentally studied. scanning electron microscope (SEM) and atomic force microscope (AFM) show removal of traces of mechanical polishing. The ion-induced roughness does not [...] Read more.
The graphitization and surface growth of synthetic diamonds by high-fluence irradiation with 30 keV argon and carbon ions have been experimentally studied. scanning electron microscope (SEM) and atomic force microscope (AFM) show removal of traces of mechanical polishing. The ion-induced roughness does not exceed 20 nm. Raman spectroscopy and the measurement of electrical conductivity confirm the graphitization of the surface layer when irradiated with argon ions at the temperature of 230 °C and the diamond structure of the synthesized layer when irradiated with carbon ions at the temperature of 650 °C. Full article
(This article belongs to the Special Issue Technologies of Coatings and Surface Hardening for Tool Industry)
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Open AccessArticle
Antimycobacterial, Antioxidant and Cytotoxicity Activities of Mesoporous Nickel Oxide Nanoparticles for Healthcare
Coatings 2020, 10(12), 1242; https://doi.org/10.3390/coatings10121242 - 17 Dec 2020
Viewed by 350
Abstract
Nanobiotechnology has offered great attention in drug delivery and the development of various medicines used to treat microorganism infections. The present investigation deals with antimycobacterial activity, in-vitro hemolysis assay, and antioxidant activity of nickel oxide nanoparticles (NiO NPs). NiO NPs, with controlled size [...] Read more.
Nanobiotechnology has offered great attention in drug delivery and the development of various medicines used to treat microorganism infections. The present investigation deals with antimycobacterial activity, in-vitro hemolysis assay, and antioxidant activity of nickel oxide nanoparticles (NiO NPs). NiO NPs, with controlled size and shape, prepared by a simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method was scanned using field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) digital images for surface morphology confirmation. Spherical irregular island-type NPs of about 24 nm diameter are obtained. The X-ray diffraction pattern demonstrates the synthesis of polycrystalline and cubic in phase NiO NPs. The Raman spectrum has revealed the presence of two vibration bands cantered at 550 and 1095 cm−1 for one photon longitudinal optical, and two longitudinal optical modes, respectively. The as-prepared NiO NPs endow 10 µg/mL against Mycobacterium tuberculosis (M. tuberculosis, MTCC-300) and 10 µg/mL against Mycobacterium phlei (M. phlei, MTCC-1723) inhibitory concentrations. The hemolytic activity of NiO NPs has also been explored. The antioxidant result demonstrates 63.44% for NiO NPs over 88.23% for standard, i.e., di(phenyl)-(2, 4, 6-trinitrophenyl) viminoazaniun antioxidant. Taken together, NiO NPs act as a potential candidate against mycobacteria. Full article
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Open AccessArticle
Evaluation of the Performance of a Warm Mix Asphalt (WMA) Considering Aged and Unaged Specimens
Coatings 2020, 10(12), 1241; https://doi.org/10.3390/coatings10121241 - 17 Dec 2020
Viewed by 262
Abstract
In the last decades, all technology production sectors reached a high level of development, without neglecting the attention to environmental aspects and safeguarding energy resources. Moreover, in the sector of pavement industry, some alternatives of bituminous mixtures were proposed to reduce the greenhouse [...] Read more.
In the last decades, all technology production sectors reached a high level of development, without neglecting the attention to environmental aspects and safeguarding energy resources. Moreover, in the sector of pavement industry, some alternatives of bituminous mixtures were proposed to reduce the greenhouse gas emissions. One of these is the warm mix asphalt (WMA), a mixture produced and compacted at lower temperatures compared to traditional hot mix asphalt (HMA) (about 40 °C less), to allow a reduction of emissions into the atmosphere and the costs. Other operative benefits concern the health of workers during the whole road construction process, the reduction of distances to which the mixture can be transported, and therefore also the positioning of the plants. However, it is not all benefits, since reduced production temperatures can bring short- and long-term water sensitivity issues, which could threaten the pavement performance. This paper evaluated the performance (water sensitivity, stiffness, fatigue, and permanent deformation) of a WMA produced using a warm mix fabrication bitumen and compared it with an HMA tested in parallel. In general, except for the resistance to permanent deformation, the WMA presented performances comparable to HMA. Regarding the fatigue behavior of asphalt mixtures, the WMA was less affected by ageing conditions, despite it showing lower performance than HMA. Full article
(This article belongs to the Special Issue Pavement Surface Coatings)
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Open AccessArticle
Distribution of Characteristic Times: A High-Resolution Spectrum Approach for Visualizing Chemical Relaxation and Resolving Kinetic Parameters of Ionic-Electronic Conducting Ceramic Oxides
Coatings 2020, 10(12), 1240; https://doi.org/10.3390/coatings10121240 - 17 Dec 2020
Viewed by 349
Abstract
Surface exchange coefficient (k) and bulk diffusion coefficient (D) are important properties to evaluate the performance of mixed ionic-electronic conducting (MIEC) ceramic oxides for use in energy conversion devices, such as solid oxide fuel cells. The values of k [...] Read more.
Surface exchange coefficient (k) and bulk diffusion coefficient (D) are important properties to evaluate the performance of mixed ionic-electronic conducting (MIEC) ceramic oxides for use in energy conversion devices, such as solid oxide fuel cells. The values of k and D are usually estimated by a non-linear curve fitting procedure based on electrical conductivity relaxation (ECR) measurement. However, the rate-limiting mechanism (or the availability of k and D) and the experimental imperfections (such as flush delay for gaseous composition change, τf) are not reflected explicitly in the time–domain ECR data, and the accuracy of k and D demands a careful sensitivity analysis of the fitting error. Here, the distribution of characteristic times (DCT) converted from time–domain ECR data is proposed to overcome the above challenges. It is demonstrated that, from the DCT spectrum, the rate-limiting mechanism and the effect of τf are easily recognized, and the values of k, D and τf can be determined conjunctly. A strong robustness of determination of k and D is verified using noise-containing ECR data. The DCT spectrum opens up a way towards visible and credible determination of kinetic parameters of MIEC ceramic oxides. Full article
(This article belongs to the Special Issue Surface Engineering of C/N/O Functionalized Materials)
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