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Coatings, Volume 8, Issue 3 (March 2018)

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Cover Story (view full-size image) Photocatalytic paint-like coatings may be a way to protect building materials from microbial [...] Read more.
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Open AccessArticle Tube Inner Coating of Non-Conductive Films by Pulsed Reactive Coaxial Magnetron Plasma with Outer Anode
Coatings 2018, 8(3), 115; https://doi.org/10.3390/coatings8030115
Received: 20 February 2018 / Revised: 7 March 2018 / Accepted: 19 March 2018 / Published: 20 March 2018
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Abstract
The double-ended coaxial magnetron pulsed plasma (DCMPP) method with auxiliary outer anode was introduced in order to achieve the uniform coating of non-conductive thin films on the inner walls of insulator tubes. In this study, titanium (Ti) was employed as a cathode (sputtering
[...] Read more.
The double-ended coaxial magnetron pulsed plasma (DCMPP) method with auxiliary outer anode was introduced in order to achieve the uniform coating of non-conductive thin films on the inner walls of insulator tubes. In this study, titanium (Ti) was employed as a cathode (sputtering target), and a glass tube was used as a substrate. In an argon (Ar) and oxygen (O2) gas mixture, magnetron plasma was generated. Oxygen gas was introduced to deposit a titanium oxide (TiO2) film. A comparison between films coated with and without an auxiliary outer anode was made. As a result, it was clearly shown that the DCMPP method using an auxiliary outer anode enhanced the uniformity of the deposited non-conductive film compared to the conventional DCMPP method. Moreover, the optimum conditions under which the thin TiO2 film was deposited on the inner wall of the glass tube were revealed. From the results, it was supposed that the auxiliary outer anode contributed to the uniformity of the distributions of deposited negative charge on the non-conductive film and consequently the electric field and the plasma density uniform. Full article
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Open AccessArticle The Properties of Binary and Ternary Ti Based Coatings Produced by Thermionic Vacuum Arc (TVA) Technology
Coatings 2018, 8(3), 114; https://doi.org/10.3390/coatings8030114
Received: 7 February 2018 / Revised: 5 March 2018 / Accepted: 16 March 2018 / Published: 20 March 2018
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Abstract
A series of the multicomponent thin films (binary: Ti-C; Ti-Ag and ternary: Ti-C-Ag; Ti-C-Al) were fabricated by Thermionic Vacuum Arc (TVA) technology in order to study the wear resistance and the anticorrosion properties. The effects of Ti amount on the microstructure, tribological and
[...] Read more.
A series of the multicomponent thin films (binary: Ti-C; Ti-Ag and ternary: Ti-C-Ag; Ti-C-Al) were fabricated by Thermionic Vacuum Arc (TVA) technology in order to study the wear resistance and the anticorrosion properties. The effects of Ti amount on the microstructure, tribological and morphological properties were subsequently investigated. TVA is an original deposition method using a combination of anodic arc and electron gun systems for the growth of films. The samples were characterized using scanning electron microscope (SEM) and a transmission electron microscope (TEM) accompanied by selected area electron diffraction (SAED). Tribological properties were studied by a ball-on-disc tribometer in the dry regime and the wettability was assessed by measuring the contact angle with the See System apparatus. Wear Rate results indicate an improved sliding wear behavior for Ti-C-Ag: 1.31 × 10−7 mm3/N m (F = 2 N) compared to Ti-C-Al coating wear rate: 4.24 × 10−7 mm3/N m. On the other hand, by increasing the normal load to 3 N an increase to the wear rate was observed for Ti-C-Ag: 2.58 × 10−5 mm3 compared to 2.33 × 10−6 mm3 for Ti-C-Al coating. Full article
(This article belongs to the Special Issue Advances in Coatings Vacuum Deposition Systems)
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Open AccessFeature PaperArticle The Influence of Aluminizing Process on the Surface Condition and Oxidation Resistance of Ti–45Al–8Nb–0.5(B, C) Alloy
Coatings 2018, 8(3), 113; https://doi.org/10.3390/coatings8030113
Received: 3 March 2018 / Revised: 17 March 2018 / Accepted: 19 March 2018 / Published: 20 March 2018
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Abstract
One of the major barriers limiting the suitability of TiAl intermetallic alloys for use in the demanding aircraft and automotive industries is their susceptibility to degradation as a result of oxidation at temperatures exceeding 760 °C. Paper presents the characteristics of resistance to
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One of the major barriers limiting the suitability of TiAl intermetallic alloys for use in the demanding aircraft and automotive industries is their susceptibility to degradation as a result of oxidation at temperatures exceeding 760 °C. Paper presents the characteristics of resistance to cyclic oxidation at 950 °C for Ti–45Al–8Nb–0.5(B, C) alloy with and without protective coating obtained as a result of aluminizing using out of pack method. The characteristics of surface condition were determined by scanning electron microscope with EDS system, transmission electron microscope, and X-ray diffractometer. The favorable behavior of the Ti–45Al–8Nb–0.5(B, C) alloy with a protective coating under cyclic oxidation conditions is a result of a higher content of Al2O3 in the microstructure of the scale and the presence of Al and Nb-rich phases at the substrate interface, which probably constitue a barrier for oxidation process. The high temperature oxidation test revealed that aluminide coating was responsible for a remarkable improvement in the oxidation resistance. Full article
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Open AccessArticle Microstructure, Microhardness, and Wear Resistance of AlCoCrFeNiTi/Ni60 Coating by Plasma Spraying
Coatings 2018, 8(3), 112; https://doi.org/10.3390/coatings8030112
Received: 7 February 2018 / Revised: 8 March 2018 / Accepted: 15 March 2018 / Published: 19 March 2018
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Abstract
In this comparative study, Ni60 was used as a reinforcement and added into an AlCoCrFeNiTi high-entropy alloy (HEA) matrix coating in order to enhance its hardness and wear resistance. An AlCoCrFeNiTi/Ni60 coating was prepared by plasma spraying with mechanically-blended AlCoCrFeNiTi/Ni60 powder. The coating
[...] Read more.
In this comparative study, Ni60 was used as a reinforcement and added into an AlCoCrFeNiTi high-entropy alloy (HEA) matrix coating in order to enhance its hardness and wear resistance. An AlCoCrFeNiTi/Ni60 coating was prepared by plasma spraying with mechanically-blended AlCoCrFeNiTi/Ni60 powder. The coating microstructure was observed and analyzed. Bonding strength, microhardness, and wear resistance of the coating were investigated. The results showed that a compact AlCoCrFeNiTi/Ni60 coating with Ni60 splats uniformly distributed in the AlCoCrFeNiTi matrix was deposited. After spraying, matrix body-centered cubic (BCC), face-centered cubic, and ordered BCC phases were detected in the coating. The added large Ni60 particles played an important role in strengthening the coating. Tensile test results showed that bonding strength of this coating was above 60.1 MPa, which is far higher than that of the AlCoCrFeNiTi HEA coating in the previous study. An average microhardness of 676 HV was obtained for the main body of the coating, which is much higher than that of the AlCoCrFeNiTi HEA coating. Solution hardening in γ-Ni and dispersion strengthening of the hard interstitial compounds, such as Cr7C3, CrB, Cr2B, and Cr23C6 increased the hardness of Ni60, and then the AlCoCrFeNiTi/Ni60 coating. During wear testing at 25 °C, adhesive wear and abrasive wear occurred, while, at 500 °C, abrasive wear took place. Volume wear rates of the coating at 25 °C and 500 °C were 0.55 ± 0.06 × 10−4 mm3·N−1·m−1 and 0.66 ± 0.02 × 10−4 mm3·N−1·m−1, respectively. Wear resistance of this coating was better than that of the AlCoCrFeNiTi HEA coating, which can be attributed to addition of the hard Ni60. Therefore, Ni60 is an appropriate reinforcement to further enhance the wear resistance of HEA coating. Full article
(This article belongs to the Special Issue Coatings Tribology)
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Open AccessArticle The Effect of Deposition Parameters on the Structure and Mechanical Properties of Chromium Oxide Coatings Deposited by Reactive Magnetron Sputtering
Coatings 2018, 8(3), 111; https://doi.org/10.3390/coatings8030111
Received: 7 February 2018 / Revised: 3 March 2018 / Accepted: 13 March 2018 / Published: 19 March 2018
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Abstract
Appropriate conditions for depositing hard Cr2O3 coatings by reactive sputtering techniques have yet to be defined. To fill this gap, the effect of principal deposition parameters, including deposition pressure, temperature, Cr-target voltage, and Ar/O2 ratio, on both the structure
[...] Read more.
Appropriate conditions for depositing hard Cr2O3 coatings by reactive sputtering techniques have yet to be defined. To fill this gap, the effect of principal deposition parameters, including deposition pressure, temperature, Cr-target voltage, and Ar/O2 ratio, on both the structure and mechanical properties of chromium oxide coatings was investigated. A relationship between processing, structure, and the mechanical properties of chromium oxide coatings was established. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray Photoelectron Spectroscopy (XPS) were used to characterize the morphology, structure, and chemical compositions of the coatings that were prepared. An optical profilometer was employed to measure both the roughness and thickness of the coatings. The hardness and Young’s modulus of the coatings both as-deposited and after annealing conditions were measured by nanoindentation. The results showed that depositing hard Cr2O3 coatings is a highly critical task, requiring special deposition conditions. Cr2O3 coatings with a high hardness of approximately 25 GPa could be achieved at room temperature, at a low pressure of 1.6 × 10−1 Pa, where Cr-target voltage and oxygen content were 260 V and between 15–25 vol % of total gas, respectively. A dense stoichiometric Cr2O3 structure was found to be responsible for the high chromium oxide coating hardness observed. Full article
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Open AccessFeature PaperArticle Effect of Untampered Plasma Coating and Surface Texturing on Friction and Running-in Behavior of Piston Rings
Coatings 2018, 8(3), 110; https://doi.org/10.3390/coatings8030110
Received: 17 February 2018 / Revised: 13 March 2018 / Accepted: 16 March 2018 / Published: 19 March 2018
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Abstract
The running-in behavior and the associated transient friction characteristics of a piston ring with different surface treatments are experimentally evaluated using a custom-made engine testing apparatus. Results are reported for a series of running-in and steady-state experiments on piston rings with different combinations
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The running-in behavior and the associated transient friction characteristics of a piston ring with different surface treatments are experimentally evaluated using a custom-made engine testing apparatus. Results are reported for a series of running-in and steady-state experiments on piston rings with different combinations of coated and textured surfaces. Comparisons are provided between five different types of piston rings: (1) with no textures; (2) with textures only; (3) with coating only; (4) first textured and then coated; and (5) first coated and then textured. A combination of the texturing and coating showed 12.5% improvement in the frictional behavior and up to 50% improvement in break-in time compared to cases when only one surface treatment was applied. Full article
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Open AccessArticle Thermoelectric Properties and Morphology of Si/SiC Thin-Film Multilayers Grown by Ion Beam Sputtering
Coatings 2018, 8(3), 109; https://doi.org/10.3390/coatings8030109
Received: 6 February 2018 / Revised: 2 March 2018 / Accepted: 6 March 2018 / Published: 19 March 2018
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Abstract
Multilayers (MLs) of 31 bi-layers and a 10-nm layer thickness each of Si/SiC were deposited on silicon, quartz and mullite substrates using a high-speed, ion-beam sputter deposition process. The samples deposited on the silicon substrates were used for imaging purposes and structural verification
[...] Read more.
Multilayers (MLs) of 31 bi-layers and a 10-nm layer thickness each of Si/SiC were deposited on silicon, quartz and mullite substrates using a high-speed, ion-beam sputter deposition process. The samples deposited on the silicon substrates were used for imaging purposes and structural verification as they did not allow for accurate electrical measurement of the material. The Seebeck coefficient and the electrical resistivity on the mullite and the quartz substrates were reported as a function of temperature and used to compare the film performance. The thermal conductivity measurement was performed for ML samples grown on Si, and an average value of the thermal conductivity was used to find the figure of merit, zT, for all samples tested. X-ray diffraction (XRD) spectra showed an amorphous nature of the thin films. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to study the film morphology and verify the nature of the crystallinity. The mobility of the multilayer films was measured to be only 0.039 to 1.0 cm2/Vs at room temperature. The samples were tested three times in the temperature range of 300 K to 900 K to document the changes in the films with temperature cycling. The highest Seebeck coefficient is measured for a Si/SiC multilayer system on quartz and mullite substrates and were observed at 870 K to be roughly −2600 μV/K due to a strain-induced redistribution of the states’ effect. The highest figure of merit, zT, calculated for the multilayers in this study was 0.08 at 870 K. Full article
(This article belongs to the Special Issue Novel Thin Film Materials for Thermoelectric Applications)
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Open AccessArticle Electronic Structure Characterization of Hydrogen Terminated n-type Silicon Passivated by Benzoquinone-Methanol Solutions
Coatings 2018, 8(3), 108; https://doi.org/10.3390/coatings8030108
Received: 10 January 2018 / Revised: 14 March 2018 / Accepted: 16 March 2018 / Published: 17 March 2018
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Abstract
The electrical passivation mechanism of benzoquinone-methanol solutions on silicon has been examined through the study of the silicon surface electronic structure. Surface photovoltage (SPV) measurements using both X-ray photoelectron spectroscopy (XPS) and scanning Kelvin probe microscopy (SKPM) indicate a downward band bending of
[...] Read more.
The electrical passivation mechanism of benzoquinone-methanol solutions on silicon has been examined through the study of the silicon surface electronic structure. Surface photovoltage (SPV) measurements using both X-ray photoelectron spectroscopy (XPS) and scanning Kelvin probe microscopy (SKPM) indicate a downward band bending of H-Si and benzoquinone (BQ) and methanol (ME) treated samples. This suggests the creation of an accumulation layer of majority carriers near the surface, with a significant field-effect contribution to the observed surface passivation. The highest SPV values recorded for the ME-Si and BQ-Si samples of about −220 mV are approaching the Fermi level—conduction band crossover. Density functional theory (DFT) calculations show that a dipole is formed upon bonding of BQ radicals on the surface, decreasing the surface electron affinity and work function. Considering the 0.07 eV shift due to the dipole and the 0.17 eV downward band bending, the work function of BQ-Si is found to be 4.08 eV. Both the dipole and downward band bending contribute to the formation of surface electron accumulation, and decrease the minority carrier density of n-Si passivated by BQ. Full article
(This article belongs to the Special Issue Advanced Surface Passivation Processes for Solar Cells)
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Open AccessArticle Effects of V and Cr on Laser Cladded Fe-Based Coatings
Coatings 2018, 8(3), 107; https://doi.org/10.3390/coatings8030107
Received: 7 February 2018 / Revised: 4 March 2018 / Accepted: 13 March 2018 / Published: 15 March 2018
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Abstract
Fe-based coatings with high V and Cr content were obtained by laser cladding using Fe-based powder with different Cr3C2 and FeV50 content. The results showed that Fe-based coatings were uniform and dense. The constituent phases were mainly composed of
[...] Read more.
Fe-based coatings with high V and Cr content were obtained by laser cladding using Fe-based powder with different Cr3C2 and FeV50 content. The results showed that Fe-based coatings were uniform and dense. The constituent phases were mainly composed of α-Fe solid solution with the increase of Cr3C2 and FeV50, γ-Fe and V8C7 phases were achieved. The microstructure of the coatings exhibited a typical dendrite structure. The concentration of C, V and Cr were saturated in dendritic areas, and the other alloying elements were mainly dissolved in the interdendritic areas. The hardness and wear resistance of Fe-based coatings were enhanced with the Cr3C2 and FeV50 addition. The specimen with 15% Cr3C2 and 16% FeV50 had the highest hardness of 66.1 ± 0.6 HRC, which was 1.05 times higher than the sample with 4.5% Cr3C2 and 5% FeV50, and the wear resistance of the former was three times greater than the latter. Full article
(This article belongs to the Special Issue Laser Surface Treatment)
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Open AccessArticle The Influence of Process Parameters on the Structure, Phase Composition, and Texture of Micro-Plasma Sprayed Hydroxyapatite Coatings
Coatings 2018, 8(3), 106; https://doi.org/10.3390/coatings8030106
Received: 8 February 2018 / Revised: 6 March 2018 / Accepted: 12 March 2018 / Published: 15 March 2018
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Abstract
In this study, hydroxyapatite (HA) coatings were deposited on Ti-6Al-4V by micro-plasma spraying (MPS). The influence of the process parameters on the microstructure of HA coatings was investigated. The splat morphology and spreading behavior were examined to understand the influence of process parameters
[...] Read more.
In this study, hydroxyapatite (HA) coatings were deposited on Ti-6Al-4V by micro-plasma spraying (MPS). The influence of the process parameters on the microstructure of HA coatings was investigated. The splat morphology and spreading behavior were examined to understand the influence of process parameters on the coating. The texture strength of HA coatings was characterized by X-ray diffraction (XRD). The texture coefficients were all applied to characterize the variation in texture. The morphology of splats and coatings were characterized by scanning electron microscopy (SEM). XRD pattern shows that the texture intensity of the c-axis of HA was greatly influenced by spraying distance and spraying current. SEM reveals the different texture strength of HA coatings with different ratios of columnar grains. The strongest c-axis texture was found in the coating by 60 mm spraying distance with a spraying current of 40 A. In the cross-section SEM images of the coating with the strongest c-axis texture, uniform distribution columnar grains were observed in the upper part (~100 μm). The investigation of splats indicates that columnar grain growth occurs after fully melted particles impact the heated substrate. By controlling the melting state prior to in-flight particle impacts, columnar grain growth can be achieved during slow solidification of the disk shape splat during MPS. Full article
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Open AccessArticle Evolution of the Three-Dimensional Structure and Growth Model of Plasma Electrolytic Oxidation Coatings on 1060 Aluminum Alloy
Coatings 2018, 8(3), 105; https://doi.org/10.3390/coatings8030105
Received: 28 January 2018 / Revised: 7 March 2018 / Accepted: 13 March 2018 / Published: 15 March 2018
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Abstract
A deeper understanding of plasma electrolytic oxidation (PEO) can in turn shed light on the evolution of coating structures during such oxidation processes. Here, a three-dimensional (3D) structure of PEO coating was investigated based on the morphologies at different locations in a PEO
[...] Read more.
A deeper understanding of plasma electrolytic oxidation (PEO) can in turn shed light on the evolution of coating structures during such oxidation processes. Here, a three-dimensional (3D) structure of PEO coating was investigated based on the morphologies at different locations in a PEO coating and on the elemental distribution along certain sections. The coating surface was dominated by a crater- or pancake-like structure of alumina surrounded by Si-rich nodules. A barrier layer with a thickness of ~1 μm consisting of clustered cells was present at the aluminum/coating interface. As the coating thickened, the PEO coating gradually evolved into a distinct three-layer structure, which included a barrier layer, an internal structure with numerous closed holes, and an outer layer with a rough surface. During the PEO process, molten zones formed along with the plasma discharges. The volume and lifetime of the molten zones changed with oxidation time. The diversities of cooling rates around the molten zones resulted in structural differences along a certain section of the coating. A growth and discharge model of PEO coatings was established based on the 3D structure of the particular coating studied herein. Full article
(This article belongs to the Special Issue New Generation Coatings for Metals)
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Open AccessArticle Durable Superomniphobic Surface on Cotton Fabrics via Coating of Silicone Rubber and Fluoropolymers
Coatings 2018, 8(3), 104; https://doi.org/10.3390/coatings8030104
Received: 11 February 2018 / Revised: 4 March 2018 / Accepted: 14 March 2018 / Published: 15 March 2018
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Abstract
Performance textiles that protect human from different threats and dangers from environment are in high demand, and the advancement in functionalization technology together with employing advanced materials have made this an area of research focus. In this work, silicone rubber and environmentally friendly
[...] Read more.
Performance textiles that protect human from different threats and dangers from environment are in high demand, and the advancement in functionalization technology together with employing advanced materials have made this an area of research focus. In this work, silicone rubber and environmentally friendly fluoropolymers have been employed to explore superomniphobic surface on cotton fabrics without compromising comfort much. It has been found that a cross-linked network between the rubber membrane and the fluoropolymers has been formed. The surface appearance, morphology, handle, thickness and chemical components of the surface of cotton fabrics have been changed. The coated fabrics showed resistance to water, aqueous liquid, oil, chemicals and soil. The comfort of the coated fabrics is different to uncoated cotton fabrics due to the existence of coated layers on the surface of cotton fabrics. This work would benefit the development and design of the next generation of performance textiles with balanced performance and comfort. Full article
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Open AccessArticle Study of Calcium Ethoxide as a New Product for Conservation of Historical Limestone
Coatings 2018, 8(3), 103; https://doi.org/10.3390/coatings8030103
Received: 20 February 2018 / Revised: 7 March 2018 / Accepted: 12 March 2018 / Published: 13 March 2018
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Abstract
The combination of multiple physical, chemical and biological factors causes the weathering of limestone used in the field of cultural heritage. To overcome the limitations of traditional consolidating products and to meet the requirements of the historical building substrates, during the European collaborative
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The combination of multiple physical, chemical and biological factors causes the weathering of limestone used in the field of cultural heritage. To overcome the limitations of traditional consolidating products and to meet the requirements of the historical building substrates, during the European collaborative project NANOMATCH, alkaline earth alkoxides were developed and studied as consolidating agents for limestone. Among these new products, calcium ethoxide, with the formula Ca(OEt)2, was chosen for this study and investigated in depth as an alternative consolidating treatment. It was first characterized through a study of the carbonation process: its kinetics, reaction pathway and the evaluation of formed mineralogical phases. Subsequently, it was applied on limestones with different total open porosity to test its performance as a consolidating agent. The compatibility and the efficiency of the treatment were investigated with a multi-technique approach and compared with results obtained with a reference product, based on nanolime. This study indicates that calcium ethoxide shows better results with respect to the reference product, both in terms of compatibility and consolidation effect. Full article
(This article belongs to the Special Issue Communications from TechnoHeritage 2017)
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Open AccessArticle Applications of Poly(indole-6-carboxylic acid-co-2,2′-bithiophene) Films in High-Contrast Electrochromic Devices
Coatings 2018, 8(3), 102; https://doi.org/10.3390/coatings8030102
Received: 14 February 2018 / Revised: 2 March 2018 / Accepted: 9 March 2018 / Published: 13 March 2018
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Abstract
Two homopolymers (poly(indole-6-carboxylic acid) (PInc) and poly(2,2′-bithiophene) (PbT)) and a copolymer (poly(indole-6-carboxylic acid-co-2,2′-bithiophene) (P(Inc-co-bT))) are electrodeposited on ITO electrode surfaces via electrochemical method. Electrochemical and electrochromic properties of PInc, PbT, and P(Inc-co-bT) films were characterized using cyclic
[...] Read more.
Two homopolymers (poly(indole-6-carboxylic acid) (PInc) and poly(2,2′-bithiophene) (PbT)) and a copolymer (poly(indole-6-carboxylic acid-co-2,2′-bithiophene) (P(Inc-co-bT))) are electrodeposited on ITO electrode surfaces via electrochemical method. Electrochemical and electrochromic properties of PInc, PbT, and P(Inc-co-bT) films were characterized using cyclic voltammetry and in situ UV-Vis spectroscopy. The anodic P(Inc-co-bT) film prepared using Inc./bT = 1/1 feed molar ratio shows high optical contrast (30% at 890 nm) and coloring efficiency (112 cm2 C−1 at 890 nm). P(Inc-co-bT) film revealed light yellow, yellowish green, and bluish grey in the neutral, intermediate, and oxidation states, respectively. Electrochromic devices (ECDs) were constructed using PInc, PbT, or P(Inc-co-bT) film as anodic layer and PEDOT-PSS as cathodic layer. P(Inc-co-bT)/PMMA-PC-ACN-LiClO4/PEDOT-PSS ECD showed high ∆T (31%) at 650 nm, and PInc/PMMA-PC-ACN-LiClO4/PEDOT-PSS ECD displayed high coloration efficiency (416.7 cm2 C−1) at 650 nm. The optical memory investigations of PInc/PMMA-PC-ACN-LiClO4/PEDOT-PSS, PbT/PMMA-PC-ACN-LiClO4/PEDOT-PSS, and P(Inc-co-bT)/PMMA-PC-ACN-LiClO4/PEDOT-PSS ECDs exhibited that ECDs had adequate optical memory in bleaching and coloring states. Full article
(This article belongs to the Special Issue Polymer Thin Films)
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Open AccessArticle Evaluation of the Ultraviolet-Curing Kinetics of Ultraviolet-Polymerized Oligomers Cured Using Poly (Ethylene Glycol) Dimethacrylate
Received: 27 January 2018 / Revised: 4 March 2018 / Accepted: 6 March 2018 / Published: 9 March 2018
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Abstract
Ultraviolet (UV)-curable oligomers are increasingly being used in various industries because they can be applied rapidly and have excellent physical properties. Ultraviolet polymerization is used for manufacturing such oligomers. Reactive diluents, which are employed during the secondary curing of UV-curable oligomers, can help
[...] Read more.
Ultraviolet (UV)-curable oligomers are increasingly being used in various industries because they can be applied rapidly and have excellent physical properties. Ultraviolet polymerization is used for manufacturing such oligomers. Reactive diluents, which are employed during the secondary curing of UV-curable oligomers, can help elucidate the curing behaviors of these oligomers. In this study, poly (ethylene glycol) dimethacrylate (PEGDMA) was used as the reactive diluent for UV-curable oligomers. Photodifferential scanning calorimetry (photo-DSC) and shrinkage measurements revealed that the curing behavior of the polymers was dependent on the size and number of molecules of PEGDMA. The effect of the small-size PEGDMA on curing behavior was greater than that of the larger molecules. Further, in most cases, the use of a larger amount of PEGDMA resulted in lower reactivity. Full article
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Open AccessFeature PaperArticle Superhydrophobic, Superoleophobic and Antimicrobial Coatings for the Protection of Silk Textiles
Coatings 2018, 8(3), 101; https://doi.org/10.3390/coatings8030101
Received: 7 February 2018 / Revised: 28 February 2018 / Accepted: 7 March 2018 / Published: 9 March 2018
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Abstract
A method to produce multifunctional coatings for the protection of silk is developed. Aqueous dispersion, free of any organic solvent, containing alkoxy silanes, organic fluoropolymer, silane quaternary ammonium salt, and silica nanoparticles (7 nm in mean diameter) is sprayed onto silk which obtains
[...] Read more.
A method to produce multifunctional coatings for the protection of silk is developed. Aqueous dispersion, free of any organic solvent, containing alkoxy silanes, organic fluoropolymer, silane quaternary ammonium salt, and silica nanoparticles (7 nm in mean diameter) is sprayed onto silk which obtains (i) superhydrophobic and superoleophobic properties, as evidenced by the high contact angles (>150°) of water and oil drops and (ii) antimicrobial properties. Potato dextrose agar is used as culture medium for the growth of microorganisms. The protective coating hinders the microbial growth on coated silk which remains almost free of contamination after extensive exposure to the microorganisms. Furthermore, the multifunctional coating induces a moderate reduction in vapor permeability of the treated silk, it shows very good durability against abrasion and has a minor visual effect on the aesthetic appearance of silk. The distinctive roles of the silica nanoparticles and the antimicrobial agent on the aforementioned properties of the coating are investigated. Silica nanoparticles induce surface structures at the micro/nano-meter scale and are therefore responsible for the achieved extreme wetting properties that promote the antimicrobial activity. The latter is further enhanced by adding the silane quaternary ammonium salt in the composition of the protective coating. Full article
(This article belongs to the Special Issue Superhydrophobic Coatings)
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Open AccessArticle The Synthesis and Morphology of a Perfluoroalkyl Oligosiloxane@SiO2 Resin and Its Performance in Anti-Fingerprint Coating
Coatings 2018, 8(3), 100; https://doi.org/10.3390/coatings8030100
Received: 27 December 2017 / Revised: 20 February 2018 / Accepted: 8 March 2018 / Published: 9 March 2018
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Abstract
In order to improve the hydro- and oleo-phobic properties of anti-fingerprint coating, novel oligosiloxane intermediate bearing perfluorodecyl/octyl and triethoxy silylethylene groups were synthesized; then, a series of nano-hybrid perfluoroalkyl oligosiloxane resins (FSi@SiO2) were synthesized using the hydrolysis and condensation of FVPS
[...] Read more.
In order to improve the hydro- and oleo-phobic properties of anti-fingerprint coating, novel oligosiloxane intermediate bearing perfluorodecyl/octyl and triethoxy silylethylene groups were synthesized; then, a series of nano-hybrid perfluoroalkyl oligosiloxane resins (FSi@SiO2) were synthesized using the hydrolysis and condensation of FVPS with tetraethylorthosilicate. The chemical structure, morphology, and performance of FSi@SiO2 were investigated. The results indicate that the FSi@SiO2 is a nano hybrid fluorinated polysiloxane resin with mean particle sizes of 200–400 nm. And under nanoparticles and perfluoroalkyl groups bonded in the resin, FSi@SiO2 not only showed a micro rough morphology in atomic force microscopy observation but also could provide the treated substrates with excellent hydro- and oleo-phobicity. As a result, the water and oil contact angles reached 120.3° and 87.5° on the treated glass, respectively; meanwhile, fingerprints were easily cleaned without any stains. Full article
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Open AccessArticle Experimental Evaluation of Polyester and Epoxy–Polyester Powder Coatings in Aggressive Media
Received: 13 February 2018 / Revised: 6 March 2018 / Accepted: 7 March 2018 / Published: 8 March 2018
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Abstract
Protective coatings are the most widely used corrosion protection method for construction materials in different environmental conditions. They isolate metals from aggressive media, making the structure more durable. Today, alongside good anti-corrosive properties, coatings need to be safe for the environment and harmless
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Protective coatings are the most widely used corrosion protection method for construction materials in different environmental conditions. They isolate metals from aggressive media, making the structure more durable. Today, alongside good anti-corrosive properties, coatings need to be safe for the environment and harmless to those who apply them. The high volatile organic compound (VOC) content in conventional solvent-borne coatings presents a huge ecological problem. A solution for indispensable solvent emission reduction is the application of powder coatings. This study evaluates the corrosion performance and surface morphology of polyester and epoxy–polyester powder coatings. Electrochemical impedance spectroscopy (EIS), open circuit potential (OCP) measurement, salt spray chamber and humidity chamber testing followed by adhesion testing were used to investigate the protective properties of powder coatings. Scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDX) was used to analyse the surface morphology and chemical composition, whereas the microstructure and coating uniformity were determined by optical microscope examination. The research revealed a negative influence of coating surface texture on coating thickness and consequently a lack of barrier and adhesion properties. The epoxy–polyester powder coating showed a better performance than the polyester coating. All tested coatings showed uniform structure. Full article
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Open AccessArticle Comparative Study of Furnace and Flash Lamp Annealed Silicon Thin Films Grown by Plasma Enhanced Chemical Vapor Deposition
Received: 29 November 2017 / Revised: 6 March 2018 / Accepted: 6 March 2018 / Published: 8 March 2018
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Abstract
Low-temperature growth of microcrystalline silicon (mc-Si) is attractive for many optoelectronic device applications. This paper reports a detailed comparison of optical properties, microstructure, and morphology of amorphous silicon (a-Si) thin films crystallized by furnace annealing and flash lamp annealing (FLA) at temperatures below
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Low-temperature growth of microcrystalline silicon (mc-Si) is attractive for many optoelectronic device applications. This paper reports a detailed comparison of optical properties, microstructure, and morphology of amorphous silicon (a-Si) thin films crystallized by furnace annealing and flash lamp annealing (FLA) at temperatures below the softening point of glass substrate. The initial a-Si films were grown by plasma enhanced chemical vapor deposition (PECVD). Reflectance measurement indicated characteristic peak in the UV region ~280 nm for the furnace annealed (>550 °C) and flash lamp annealed films, which provided evidence of crystallization. The film surface roughness increased with increasing the annealing temperature as well as after the flash lamp annealing. X-ray diffraction (XRD) measurement indicated that the as-deposited samples were purely amorphous and after furnace crystallization, the crystallites tended to align in one single direction (202) with uniform size that increased with the annealing temperature. On the other hand, the flash lamp crystalized films had randomly oriented crystallites with different sizes. Raman spectroscopy showed the crystalline volume fraction of 23.5%, 47.3%, and 61.3% for the samples annealed at 550 °C, 650 °C, and with flash lamp, respectively. The flash lamp annealed film was better crystallized with rougher surface compared to furnace annealed ones. Full article
(This article belongs to the Special Issue Plasma Etching and Deposition)
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Open AccessArticle Characterization of Electroless Ni–P Coating Prepared on a Wrought ZE10 Magnesium Alloy
Received: 19 February 2018 / Revised: 1 March 2018 / Accepted: 6 March 2018 / Published: 7 March 2018
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Abstract
Electroless low-phosphorus Ni–P coating was deposited on a wrought ZE10 magnesium alloy including an advanced pre-treatment of the material surface before deposition. Uniform Ni–P coating with an average thickness of 10 µm was formed by 95.6 wt % Ni and 4.4 wt %
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Electroless low-phosphorus Ni–P coating was deposited on a wrought ZE10 magnesium alloy including an advanced pre-treatment of the material surface before deposition. Uniform Ni–P coating with an average thickness of 10 µm was formed by 95.6 wt % Ni and 4.4 wt % P. The content of Ni and P was homogeneous in the entire cross-section of the coating. Applying the Ni–P coating to the magnesium substrate, the surface microhardness increased from 60 ± 4 HV 0.025 to 690 ± 30 HV 0.025. Using the scratch test, it was determined that deposited Ni–P coating exhibits a high degree of adhesion to the magnesium substrate. Electrochemical corrosion properties of Ni–P coating were analyzed using the polarization tests in 0.1 M NaCl, while the deposited Ni–P coating showed an improvement of the corrosion resistance when compared to the ZE10 magnesium alloy. Using the scanning electron microscopy analysis, it was determined that the fine morphology of the deposited Ni–P coating did not contain visible microcavities. The absence of macrodefects due to the adequate pre-treatment before coating was reflected on the mechanism of the coated ZE10 degradation in a 0.1 M NaCl solution. Full article
(This article belongs to the Special Issue New Generation Coatings for Metals)
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Open AccessArticle Influence of Cu Content on the Structure, Mechanical, Friction and Wear Properties of VCN–Cu Films
Received: 21 January 2018 / Revised: 25 February 2018 / Accepted: 3 March 2018 / Published: 7 March 2018
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Abstract
VCN–Cu films with different Cu contents were deposited by reactive magnetron sputtering technique. The films were evaluated in terms of their microstructure, elemental composition, mechanical, and tribological properties by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), high resolution transmission electron microscopy (HR-TEM), Raman
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VCN–Cu films with different Cu contents were deposited by reactive magnetron sputtering technique. The films were evaluated in terms of their microstructure, elemental composition, mechanical, and tribological properties by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), high resolution transmission electron microscopy (HR-TEM), Raman spectrometry, nano-indentation, field emission scanning electron microscope (FE-SEM), Bruker three-dimensional (3D) profiler, and high-temperature ball on disc tribo-meter. The results showed that face-centered cubic (fcc) VCN, hexagonal close-packed (hcp) V2CN, fcc-Cu, amorphous graphite and CNx phases co-existed in VCN–Cu films. After doping with 0.6 at.% Cu, the hardness reached a maximum value of ~32 GPa. At room temperature (RT), the friction coefficient and wear rate increased with increasing Cu content. In the temperature range of 100–500 °C, the friction coefficient decreased, but the wear rate increased with the increase of Cu content. Full article
(This article belongs to the Special Issue Coatings Tribology)
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Open AccessArticle Study of Topography and Distribution State of the Nanoscale Passivation Film on a Rough Tinplate Surface
Received: 10 January 2018 / Revised: 20 February 2018 / Accepted: 1 March 2018 / Published: 6 March 2018
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Abstract
Topography observation of the nanoscale passivation film on tinplate using a scanning electron microscope and an electro-optical surface profilometer showed that it was difficult to observe the true topography because of the high surface roughness of the tinplate. Topography observation using a profilometer
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Topography observation of the nanoscale passivation film on tinplate using a scanning electron microscope and an electro-optical surface profilometer showed that it was difficult to observe the true topography because of the high surface roughness of the tinplate. Topography observation using a profilometer on bright tin plating with low surface roughness and work function measurement on tinplate surface using a Scanning Kelvin Probe Microscope (SKPM) were then carried out to solve the problem. The results indicated that there was a thin chemical passivation film distributed uniformly in different areas of microscopic bulges and valleys on the tinplate surface, and the film became more uniform with longer passivation time. In comparison, the electrolytic passivation film was thick, and the distribution uniformity was poorer. Specifically, the film was thicker on microscopic bulges and thinner in microscopic valleys, and this was worse with longer passivation time. Thus, the difference in performances of the corrosion and paint adhesion of the tinplate treated with different passivation processes can be explained in terms of the topography and distribution state of the passivation film. Full article
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Open AccessArticle Bacterial Biofilm Characterization and Microscopic Evaluation of the Antibacterial Properties of a Photocatalytic Coating Protecting Building Material
Received: 2 February 2018 / Revised: 28 February 2018 / Accepted: 4 March 2018 / Published: 5 March 2018
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Abstract
Use of photocatalytic paint-like coatings may be a way to protect building materials from microbial colonization. Numerous studies have shown the antimicrobial efficiency of TiO2 photocatalysis on various microorganisms. However, few have focused on easy-to-apply solutions and on photocatalysis under low irradiance.
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Use of photocatalytic paint-like coatings may be a way to protect building materials from microbial colonization. Numerous studies have shown the antimicrobial efficiency of TiO 2 photocatalysis on various microorganisms. However, few have focused on easy-to-apply solutions and on photocatalysis under low irradiance. This paper focuses on (a) the antibacterial properties of a semi-transparent coating formulated using TiO 2 particles and (b) the microscopic investigations of bacterial biofilm development on TiO 2 -coated building materials under accelerated growth conditions. Results showed significant antibacterial activity after few hours of testing. The efficiency seemed limited by the confinement of the TiO 2 particles inside the coating binder. However, a pre-irradiation with UV light can improve efficiency. In addition, a significant effect against the formation of a bacterial biofilm was also observed. The epifluorescence approach, in which fluorescence is produced by reflect rather than transmitted light, could be applied in further studies of microbial growth on coatings and building materials. Full article
(This article belongs to the Special Issue Biological Coatings for Buildings)
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Open AccessArticle Effect of Precipitate Embryo Induced by Strain on Natural Aging and Corrosion Behavior of 2024 Al Alloy
Received: 11 January 2018 / Revised: 13 February 2018 / Accepted: 27 February 2018 / Published: 4 March 2018
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Abstract
Pre-aging precipitates in 2024 Al alloy re-dissolved during rolling, and Mg and Cu atoms were enriched in the dislocation structure to form “precipitate embryo”, which is beneficial for the formation of second phase during the subsequent natural aging process. Due to the solubility
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Pre-aging precipitates in 2024 Al alloy re-dissolved during rolling, and Mg and Cu atoms were enriched in the dislocation structure to form “precipitate embryo”, which is beneficial for the formation of second phase during the subsequent natural aging process. Due to the solubility of the large precipitate particles during deformation, the precipitates in the natural aging 2024 Al alloy were consist of two parts: The undissolved pre-precipitates and the natural aging precipitates derived from the embryos. The electrochemical corrosion behavior and passive film of the samples with different pre-aging time and strain were investigated by electrochemical tests and SEM. The results showed that the corrosion resistance and the passive film performance were deteriorated with the increase of pre-aging time due to the simultaneous increase of the quantity of the two-parts precipitates. The corrosion resistance can be improved by the increase of strain, because there will be smaller grain size and the existence of large undissolved precipitates in smaller strain samples. Full article
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Open AccessArticle Enhanced Tribological Properties of Polymer Composite Coating Containing Graphene at Room and Elevated Temperatures
Received: 12 January 2018 / Revised: 12 February 2018 / Accepted: 26 February 2018 / Published: 2 March 2018
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Abstract
To improve the tribology properties of the polymer coating under elevated temperature, the epoxy coating was reinforced with nano graphene. The micro-hardness, heat conductivity, and thermo-gravimetric properties of the coating were enhanced as filled graphene. The friction and wear properties of the polymer
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To improve the tribology properties of the polymer coating under elevated temperature, the epoxy coating was reinforced with nano graphene. The micro-hardness, heat conductivity, and thermo-gravimetric properties of the coating were enhanced as filled graphene. The friction and wear properties of the polymer coating were studied using a pin-on-disc tribo-meter under room and elevated temperatures. The results showed that under room temperature, the friction coefficient and the wear rate of the coating adding 4.0 wt % graphene was 80% and 76% lower than that of the neat epoxy coating, respectively. As the test temperature increased, the friction coefficient of the graphene/polymer coatings decreased at first and then slightly increased. The friction coefficient was at its lowest value under 150 °C and then increased as the temperature rose to 200 °C. By adding 4.0 wt % graphene, the friction coefficient and wear rate of the polymer coating were further reduced, especially at elevated temperatures. Full article
(This article belongs to the Special Issue Coatings Tribology)
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Open AccessArticle Detection of AFB1 via TiO2 Nanotubes/Au Nanoparticles/Enzyme Photoelectrochemical Biosensor
Received: 5 January 2018 / Revised: 17 February 2018 / Accepted: 27 February 2018 / Published: 2 March 2018
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Abstract
TiO2 nanotubes/Au nanoparticles/enzyme photoelectrochemical biosensor is developed by the chemical bonding of acetylcholinesterase with Au nanoparticles-modified TiO2 photoactive electrode, based on the inhibitory effect of aflatoxin B1 on acetylcholinesterase activity. In this method, AuNPs were deposited on the surface of
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TiO2 nanotubes/Au nanoparticles/enzyme photoelectrochemical biosensor is developed by the chemical bonding of acetylcholinesterase with Au nanoparticles-modified TiO2 photoactive electrode, based on the inhibitory effect of aflatoxin B1 on acetylcholinesterase activity. In this method, AuNPs were deposited on the surface of the electrode by potentiostatic deposition and the acetylcholinesterase was chemically crosslinked to the surface for determination of aflatoxin B1. Enzymatic hydrolysate is generated to capture the photogenerated holes of UV-sensitized TiO2 nanotube arrays, causing magnification of the photoelectrochemical signal. The photoelectrochemical biosensor morphological and structural details were evaluated, applying different techniques, such as X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Aflatoxin B1 competitively inhibits acetylcholinesterase, leading to a decrease in photocurrent that should have been increased. The detection performance of biosensors for different concentrations of AFB1 is discussed. The linear response range of the biosensor is from 1–6 nM with detection limitation of 0.33 nM, the linear equation is I (μA) = −0.13C (nM) + 9.98 (μA), with a correlation coefficient of 0.988. This new biosensor could be used to detect Aflatoxin B1 in foods. Full article
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Open AccessArticle Nano Diesel Soot Particles Reduce Wear and Friction Performance Using an Oil Additive on a Laser Textured Surface
Received: 24 November 2017 / Revised: 4 February 2018 / Accepted: 6 February 2018 / Published: 27 February 2018
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Abstract
Tribological properties of nano diesel soot (DS) as an additive were investigated. Textures in linear radiating arrays were prepared on the surface of a spring-steel plate by laser radiation. The texture densities were 19.6%, 22.1%, and 44.2%, and the depth was 30 μm.
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Tribological properties of nano diesel soot (DS) as an additive were investigated. Textures in linear radiating arrays were prepared on the surface of a spring-steel plate by laser radiation. The texture densities were 19.6%, 22.1%, and 44.2%, and the depth was 30 μm. The results indicated that the textured surface was interacted with additive favorably to improve its tribological performance. Friction coefficients and wear rates of textured surfaces with additive in oil were generally much lower compared to the original surface without additive. The higher area density of the textured surface with the additive in oil had the lowest friction coefficient, as low as 0.12, and also the minimum wear rate, as low as 1 × 103 μm/N·m in 100 °C, to be achievable. Such results can be attributed to the formation of the tribo-film and the storage function of the micro-dimple. Full article
(This article belongs to the Special Issue Binders, Pigments, Dyes and Additives)
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Open AccessArticle Synthesis of Eugenol-Based Silicon-Containing Benzoxazines and Their Applications as Bio-Based Organic Coatings
Received: 9 January 2018 / Revised: 14 February 2018 / Accepted: 21 February 2018 / Published: 27 February 2018
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Abstract
In this work, several bio-based main-chain type benzoxazine oligomers (MCBO) were synthesized from eugenol derivatives via polycondensation reaction with paraformaldehyde and different diamine. Afterwards, their chemical structures were confirmed by Fourier Transform Infrared Spectroscopy (FT-IR) and Nuclear Magnetic Resonance Spectroscopy (1H-NMR).
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In this work, several bio-based main-chain type benzoxazine oligomers (MCBO) were synthesized from eugenol derivatives via polycondensation reaction with paraformaldehyde and different diamine. Afterwards, their chemical structures were confirmed by Fourier Transform Infrared Spectroscopy (FT-IR) and Nuclear Magnetic Resonance Spectroscopy (1H-NMR). The curing reaction was monitored by Differential Scanning Calorimetry (DSC) and FT-IR. The polybenzoxazine films were prepared via thermal ring-opening reaction of benzoxazine groups without solvent, and their thermodynamic properties, thermal stability, and coating properties were investigated in detail. Results indicated that the cured films exhibited good thermal stability and mechanical properties, showing 10% thermal weight loss (Td10%) temperature as high as 408 °C and modulus at a room temperature of 2100 MPa as well as the glass transition temperature of 123 °C. In addition, the related coatings exhibited high hardness, excellent adhesion, good flexibility, low moisture absorption, and outstanding solvent resistance. Full article
(This article belongs to the Special Issue Coatings from Renewable Resources)
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Open AccessArticle Theoretical Study on the Influence of Hard Coating on Vibration Characteristics of Fiber-Reinforced Composite Thin Shell
Received: 14 January 2018 / Revised: 13 February 2018 / Accepted: 23 February 2018 / Published: 27 February 2018
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Abstract
The influence of hard coating on vibration characteristics of fiber-reinforced composite thin shell (FCTS) is investigated theoretically. The theoretical model of the hard coating FCTS is firstly established by using the classical laminated shell theory, Love’s first approximation theory, Rayleigh-Ritz method, and strain
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The influence of hard coating on vibration characteristics of fiber-reinforced composite thin shell (FCTS) is investigated theoretically. The theoretical model of the hard coating FCTS is firstly established by using the classical laminated shell theory, Love’s first approximation theory, Rayleigh-Ritz method, and strain energy method. The values of the natural frequency, modal shape, resonant response, and modal loss factor of the hard-coating shell are obtained, and the corresponding analysis procedure is also summarized. The verification of such a theoretical method is performed by a case study, and the analysis results show a good agreement between the presented method and finite element method. The main findings from this study include: (I) The natural frequencies of FCTS with hard coating firstly decrease and then increase with the increase of elastic modulus and loss factor of hard coating, and they also show an increasing tendency when the thickness of hard coating rises; (II) Increasing the values of elastic modulus, loss factor, and thickness of hard coating can help to reduce the vibration response of FCTS. However, with the increase of modal order of the composite shell, the reduction rates of resonant responses and the increased levels of modal loss factor will decrease. Full article
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Open AccessArticle New Method to Identify Field Joint Coating Failures Based on MFL In-Line Inspection Signals
Received: 6 January 2018 / Revised: 8 February 2018 / Accepted: 24 February 2018 / Published: 27 February 2018
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Abstract
Above ground indirect detections and random excavations that have applied the past years for buried long distance oil and gas pipelines can only identify some damaged coating locations. Hence, large number of field joint coating (FJC) failures happen unconsciously until they lead to
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Above ground indirect detections and random excavations that have applied the past years for buried long distance oil and gas pipelines can only identify some damaged coating locations. Hence, large number of field joint coating (FJC) failures happen unconsciously until they lead to failures of the pipelines. Based on the analysis of magnetic flux leakage (MFL) in-line inspection (ILI) signals, combined with the statistical results of 414 excavations from two different pipeline sections, a new method to identify the failed FJC is established. Though it can only identify FJC failures when there are signs of corrosion on pipe body, it is much more efficient and cost-saving. The concluded identification rule still needs more validations and improvements to be more applicable and accuracy. Full article
(This article belongs to the Special Issue Advanced Nondestructive Evaluation and Characterization of Surface)
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