Coatings, Volume 5, Issue 3 (September 2015) – 19 articles , Pages 232-575

Tung oil is uniquely reactive among plant-based natural oils due to the series ofconjugated carbon-carbon double bonds in its fatty acid chains. These conjugatedcarbon-carbon double bonds impart a high reactivity towards cationic polymerization in thepresence of other reactive co-monomers, such as divinylbenzene and styrene. An impressivedecrease in the cure time of tung oil-based thermosets has been achieved when the resinsinvestigated were microwaved in the presence of carbon nanotubes (CNTs). However, thefast cure compromised the overall thermo-mechanical properties of the materialsinvestigated. Microwave power, exposure time, and CNT loading effects have been assessedby means of dielectric analysis (DEA), thermogravimetric analysis (TGA), differentialscanning calorimetry (DSC), dynamic mechanical analysis (DMA), and proton nuclearmagnetic resonance (1H NMR) spectroscopy of extracts obtained by Soxhlet extraction.Possible reasons were proposed to explain the overall inferior properties observed wheneverfaster cure rates were achieved. Full article

The photocatalyst composite coatings on alumina (Al₂O₃) balls had been prepared by mechanical coating technique (MCT) with titanium (Ti) powder, adding a certain content of chromium (Cr) powder and a subsequent oxidation process. The effect of oxidation conditions and adding Cr on the composite coatings of chromium-titanium dioxide (Cr-TiO₂) was investigated. The results show Cr-TiO₂ coatings are with mixed-phase of anatase and rutile under different oxidation conditions, and the mass fraction of the rutile phase (X_R) has been obviously increased when under 973 K. The SEM images indicate that adding Cr could significantly accelerate the growth of surface structures, especially at 1073 K. The photocatalytic activity of Cr-TiO₂ coatings firstly increases, then decreases, with the addition of Cr. Compared with that of two other oxidation conditions, the enhancement on photocatalytic activity by adding Cr under visible light is relatively higher, especially at 973 K for 10 h. Full article

This work reports on a very effective route to produce bio-based polyurethanes (PUs) and composites with high content of renewable carbon sources. The PUs are prepared with polyols synthesized from macauba oil (Acrocomia aculeata) and methylene diphenyl diisocyanate, at different [NCO]/[OH] molar ratios. Later, biocomposites are prepared with the as-obtained PUs reinforced with coconut husk fibers. The successful synthesis of natural oil-based polyols is ascribed to the hydroxylation and consumption of carbon-carbon double bonds in the fatty acid chains of the original starting oil as attested by FTIR spectroscopy. According to different thermal analysis techniques (TG, DTG, and DTA), the increase in the [NCO]/[OH] molar ratio improves the thermal stability of PUs, likely due to an increase of crosslinks. Dynamic mechanical analysis evidences the reinforcement effect of coconut husk fibers in bio-based PUs. The present PUs and composites are of low-cost and environmentally friendly materials for structural applications. Full article

The effect of synthesis conditions and niobium incorporation levels on the photocatalytic properties of Nb/MCM-41 molecular sieves was assessed. Niobium pentoxide supported on MCM-41 mesoporous silica was obtained using two methods: sol-gel and incipient impregnation, in each case also varying the percentage of niobium incorporation. The synthesized Nb-MCM-41 ceramic powders were characterized using the spectroscopic techniques of infrared spectroscopy (IR), Raman spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The photodegradation capacity of the powders was studied using the organic molecule, methylene blue. The effect of both the method of synthesis and the percentage of niobium present in the sample on the photodegradation action of the solids was determined. The mesoporous Nb-MCM-41 that produced the greatest photodegradation response was obtained using the sol-gel method and 20% niobium incorporation. Full article

This paper is an attempt to elucidate the effects of the important spray characteristics on the surface morphology and light absorbance of spray-on P3HT:PCBM thin-films, used as an active layer in polymer solar cells (PSCs). Spray coating or deposition is a viable scalable technique for the large-scale, fast, and low-cost fabrication of solution-processed solar cells, and has been widely used for device fabrication, although the fundamental understanding of the underlying and controlling parameters, such as spray characteristics, droplet dynamics, and surface wettability, is still limited, making the results on device fabrication not reproducible and unreliable. In this paper, following the conventional PSC architecture, a PEDOT:PSS layer is first spin-coated on glass substrates, followed by the deposition of P3HT:PCBM using an automatic ultrasonic spray coating system, with a movable nozzle tip, to mimic an industrial manufacturing process. To gain insight, the effects of the spray carrier air pressure, the number of spray passes, the precursor flow rate, and precursor concentration are studied on the surface topography and light absorbance spectra of the spray-on films. Among the results, it is found that despite the high roughness of spray-on films, the light absorbance of the film is satisfactory. It is also found that the absorbance of spray-on films is a linear function of the number of spray passes or deposition layers, based on which an effective film thickness is defined for rough spray-on films. The effective thickness of a rough spray-on P3HT:PCBM film was found to be one-quarter of that of a flat film predicted by a simple mass balance. Full article

Confocal microscopy is introduced as a new and generally applicable method for the characterization of the vertically-aligned carbon nanotubes (VACNT) forest height. With this technique process control is significantly intensified. The topography of the substrate and VACNT can be mapped with a height resolution down to 15 nm. The advantages of confocal microscopy, compared to scanning electron microscopy (SEM), are demonstrated by investigating the growth kinetics of VACNT using Al₂O₃ buffer layers with varying thicknesses. A process optimization using confocal microscopy for fast VACNT forest height evaluation is presented. Full article

Photocatalytic activity of Portland cement pastes blended with nanoparticles of titanium oxynitride (TiO_2−xN_y) was studied. Samples with different percentages of TiO_2−xN_y (0.0%, 0.5%, 1%, 3%) and TiO₂ (1%, 3%) were evaluated in order to study their self-cleaning properties. The presence of nitrogen in the tetragonal structure of TiO₂ was evidenced by X-ray diffraction (XRD) as a shift of the peaks in the 2θ axis. The samples were prepared with a water/cement ratio of 0.5 and a concentration of Rhodamine B of 0.5 g/L. After 65 h of curing time, the samples were irradiated with UV lamps to evaluate the reduction of the pigment. The color analysis was carried out using a Spectrometer UV/Vis measuring the coordinates CIE (Commission Internationale de l’Eclairage) L*, a*, b*, and with special attention to the reddish tones (Rhodamine B color) which correspond to a* values greater than zero. Additionally, samples with 0.5%, 1%, 3% of TiO_2−xN_y and 1%, 3% of TiO₂ were evaluated under visible light with the purpose of determining the Rhodamine B abatement to wavelengths greater than 400 nm. The results have shown a similar behavior for both additions under UV light irradiation, with 3% being the addition with the highest photocatalytic efficiency obtained. However, TiO_2−xN_y showed activity under irradiation with visible light, unlike TiO₂, which can only be activated under UV light. Full article

This review presents the latest results of studies directed at photocatalyst coatings of titanium dioxide (TiO₂) prepared by mechanical coating technique (MCT) and its application. Compared with traditional coating techniques, MCT is a simple, low cost and useful coating formation process, which is proposed and developed based on mechanical frictional wear and impacts between substrate materials and metal powder particles in the bowl of planetary ball mill. The formation process of the metal coatings in MCT includes four stages: The nucleation by adhesion, the formation and coalescence of discrete islands, formation and thickening of continuous coatings, exfoliation of continuous coatings. Further, two-step MCT was developed based on the MCT concept for preparing composite coatings on alumina (Al₂O₃) balls. This review also discusses the influence on the fabrication of photocatalyst coatings after MCT and improvement of its photocatalytic activity: oxidation conditions, coating materials, melt salt treatment. In this review, the oxidation conditions had been studied on the oxidation temperature of 573 K, 673 K, 773 K, 873 K, 973 K, 1173 K and 1273 K, the oxidation time of 0.5 h, 1 h, 3 h, 10 h, 15 h, 20 h, 30 h, 40 h, and 50 h. The photocatalyst coatings showed the highest photocatalytic activity with the oxidation condition of 1073 K for 15 h. The metal powder of Ti, Ni and Cr had been used as the coating materials. The composite metal powder could affect the surface structure and photocatalytic activity. On the other hand, the melt salt treatment with KNO₃ is an effective method to form the nano-size structure and enhance photocatalytic activity, especially under visible light. Full article

In this review, we discuss the basic concepts related to (co-)evaporation and (co)sputtering based fabrication methods and the electrical properties of polymer-metal nanocomposite films. Within the organic-inorganic hybrid nanocomposites research framework, the field related to metal-polymer nanocomposites is attracting much interest. In fact, it is opening pathways for engineering flexible composites that exhibit advantageous electrical, optical, or mechanical properties. The metal-polymer nanocomposites research field is, now, a wide, complex, and important part of the nanotechnology revolution. So, with this review we aim, starting from the discussion of specific cases, to focus our attention on the basic microscopic mechanisms and processes and the general concepts suitable for the interpretation of material properties and structure–property correlations. The review aims, in addition, to provide a comprehensive schematization of the main technological applications currently in development worldwide. Full article

Using ab initio alloy theory, we investigate the equilibrium bulk properties and elastic mechanics of the single bcc solid-solution Al_xHf_1−xNbTaTiZr (x = 0–0.7, 1.0) high entropy alloys. Ab initio predicted equilibrium volume is consistent with the available experiment. We make a detailed investigation of the alloying effect of Al and Hf on the equilibrium volume, elastic constants and polycrystalline elastic moduli. Results imply that the partial replacement Hf with Al increases the stability of the bcc phase and decreases the ductility of the Al_xHf_1−xNbTaTiZr HEAs. The inner ductility of Al_0.4Hf_0.6NbTaTiZr is predicted by the calculations of ideal tensile strength. Full article

Brick constitutes a significant part of the construction materials used in historic buildings around the world. This material was used in Architectural Heritage for structural scope, and even for building envelopes. Thus, components made of clay brick were subjected to weathering for a long time, and this causes their deterioration. One of the most important causes for deterioration is biodeterioration caused by algae and cyanobacteria. It compromises the aesthetical properties, and, at a later stage, the integrity of the elements. In fact, traditional products used for the remediation/prevention of biofouling do not ensure long-term protection, and they need re-application over time. The use of nanotechnology, especially the use of photocatalytic products for the prevention of organic contamination of building façades is increasing. In this study, TiO₂-based photocatalytic nano-coatings were applied to ancient brick, and its efficiency towards biofouling was studied. A composed suspension of algae and cyanobacteria was sprinkled on the bricks’ surface for a duration of twelve weeks. Digital Image Analysis and colorimetric measurements were carried out to evaluate algal growth on specimens’ surfaces. Results show that photocatalytic nano-coating was able to inhibit biofouling on bricks’ surfaces. In addition, substrata (their porosity and roughness) clearly influences the adhesion of algal cells. Full article

Suspension plasma spraying has become an emerging technology for the production of thermal barrier coatings for the gas turbine industry. Presently, though commercial systems for coating production are available, coatings remain in the development stage. Suitable suspension parameters for coating production remain an outstanding question and the influence of suspension properties on the final coatings is not well known. For this study, a number of suspensions were produced with varied solid loadings, powder size distributions and solvents. Suspensions were sprayed onto superalloy substrates coated with high velocity air fuel (HVAF) -sprayed bond coats. Plasma spray parameters were selected to generate columnar structures based on previous experiments and were maintained at constant to discover the influence of the suspension behavior on coating microstructures. Testing of the produced thermal barrier coating (TBC) systems has included thermal cyclic fatigue testing and thermal conductivity analysis. Pore size distribution has been characterized by mercury infiltration porosimetry. Results show a strong influence of suspension viscosity and surface tension on the microstructure of the produced coatings. Full article

Diamond-like carbon (DLC) coatings were deposited with a new direct ion deposition system using a novel 360 degree ion source operating at acceleration voltage between 4 and 8 kV. Cross-sectional TEM images show that the coatings have a three layered structure which originates from changes in the deposition parameters taking into account ion source condition, ion current density, deposition angles, ion sputtering and ion source movement. Varying structural growth conditions can be achieved by tailoring the deposition parameters. The coatings show good promise for industrial use due to their high hardness, low friction and excellent adhesion to the surface of the samples. Full article

(Al_0.34Cr_0.22Nb_0.11Si_0.11Ti_0.22)₅₀N₅₀ high-entropy nitride coatings prepared by reactive magnetron sputtering have been proved to have high hardness and superior oxidation resistance. Their thermal stability, adhesion strength, and cutting performance were investigated in this study. Hardness of the coating is 36 GPa, which only decreases slightly to 33 GPa after 900 °C annealing either in air or in vacuum for 2 h. No significant change in phase and microstructure were detected after annealing at 1000 °C. Rockwell C indentation and scratch tests shows that Ti interlayer provides a good adhesion between the nitride film and WC/Co substrates. In various milling tests, inserts coated with (Al_0.34Cr_0.22Nb_0.11Si_0.11Ti_0.22)₅₀N₅₀ have evidently smaller flank wear depth than commercial inserts coated with TiN and TiAlN, even with their smaller thickness. Therefore, the (Al_0.34Cr_0.22Nb_0.11Si_0.11Ti_0.22)₅₀N₅₀ coating has great potential in hard coating applications. Full article

Copper chalcopyrite is a promising candidate for a photocathode material for photoelectrochemical (PEC) water splitting because of its high half-cell solar-to-hydrogen conversion efficiency (HC-STH), relatively simple and low-cost preparation process, and chemical stability. This paper reviews recent advances in copper chalcopyrite photocathodes. The PEC properties of copper chalcopyrite photocathodes have improved fairly rapidly: HC-STH values of 0.25% and 8.5% in 2012 and 2015, respectively. On the other hand, the onset potential remains insufficient, owing to the shallow valence band maximum mainly consisting of Cu 3d orbitals. In order to improve the onset potential, we explored substituting Cu for Ag and investigate the PEC properties of silver gallium selenide (AGSe) thin film photocathodes for varying compositions, film growth atmospheres, and surfaces. The modified AGSe photocathodes showed a higher onset potential than copper chalcopyrite photocathodes. It was demonstrated that element substitution of copper chalcopyrite can help to achieve more efficient PEC water splitting. Full article

This paper reports on an experimental and analytical investigation conducted into efficacy of the scraping shear-test method in estimating the shearing adhesive strength of a thermally sprayed coating. It was found that the critical average shear stress, the apparent failure strength of WC-Co thermal spray coating, depends on both the dimensions of the test piece and the loading position around the interface between the coating and the substrate. More specifically, the apparent critical shear stress decreased as the height and width of the test piece increased. In addition, the apparent critical shear stress increased with increasing coating thickness and with decreasing loading point distance measured from the interface. Consequently, the real adhesive strength of thermally sprayed coating could not be ascertained from these experimental results. Furthermore, most of the failure initiation points were inside the coating, as opposed to at the interface. This fact means that the results of the tests do not indicate the interfacial adhesive strength, but rather the shear strength of the coating. Three-dimensional finite element method (FEM) analysis showed that the distributions of the shearing stress at the loading points were virtually the same at failure, regardless of the dimensions of the test piece. These results suggest that the scraping test method needs a corresponding numerical analysis of the failure mode in order to produce reliable results and is not necessarily able to estimate the interfacial adhesive strength of thermally sprayed coating. Full article

A series of polyester films doped with a hole transport molecule, p-diethylaminobenzaldehyde-1,1'-diphenylhydrazone (DEH), have been systematically exposed to ultraviolet radiation with a peak wavelength of about 375 nm. The electronic performance of the films, evaluated using time-of-flight and space-charge current injection methods, is observed to continuously degrade with increasing ultraviolet exposure. The degradation is attributed to photo cyclic oxidation of DEH that results in the creation of indazole (IND) molecules which function as bulk hole traps. A proposed model for the generation dynamics of the IND traps is capable of describing both the reduction in current injection and the associated time-of-flight hole mobility provided around 1% of the DEH population produce highly reactive photo-excited states which are completely converted to indazole during the UV exposure period. The rapid reaction of these states is incompatible with bulk oxygen diffusion-reaction kinetics within the films and is attributed to the creation of excited states within the reaction radius of soluble oxygen. It is suggested that encapsulation strategies to preserve the electronic integrity of the films should accordingly focus upon limiting the critical supply of oxygen for photo cyclic reaction. Full article

A model for spinodal decomposition must account for interface effects that include gradient and strain energy terms. The measurement of diffusion in the Cu-Ni(Fe) alloy for the special case of nanolaminate structured coatings is considered wherein the composition fluctuation is one-dimensional along <111>. An analytic approach is taken to model the kinetics of the transformation process that provides quantification of the strain energy dependence on the composition wavelength, as well as the intrinsic diffusivities and higher-order gradient-energy coefficients. The variation of the wave amplification factor R with wavenumber is modeled first to incorporate the boundary condition for growth at infinite wavelength. These results are used next to determine the gradient energy coefficients K_μ by modeling the interdiffusion coefficient Ď_B variation with wavenumber, where a unique determination of the diffusion coefficient Ď is made. The value of the strain energy component that originates from interface strains associated with the epitaxial growth between layers is then determined by assessing the variation of wavelength-dependent amplification factors. A peak value of 9.4 × 10⁷ J·m⁻³ for the strain energy is computed for Cu-Ni(Fe) nanolaminate coatings with 2–4 nm composition wavelengths. Full article

The present study concerns the ecodesign of the application of an aqueous nano-TiO₂ suspension on a porous limestone used in historical monuments with a spraying system through the LCA methodology, in order to define the most critical aspects of the process and to try to minimize the environmental burden during the implementation of the application process. Because of the limited knowledge currently available regarding the effects that nano-TiO₂ may have on the environment or human health, a precautionary approach has been adopted in all life cycle steps, to assess the risk of having nanoparticle emissions from a nanocoating surface and for workers, who can come into contact with or inhale the nanoparticles released. The energy-intensive operations in the application stage greatly contribute to the total environmental damage, while the impact generated by nanoparticle emissions during the use phase contributes 2.9%. In addition, the self-cleaning and de-polluting transparent titania coating produces a benefit of −0.13%. Full article