Thermal spraying has been present for over a century, being greatly refined and optimized during this time. It has become nowadays a reliable and cost-efficient method to deposit thick coatings with ...a wide variety of feedstock materials and substrates. Thermal-sprayed coatings have been successfully applied in fields such as aerospace or electricity production, becoming an essential component of today’s industry. To overpass the traditional capabilities of those coatings, new functionalities and coherent responses are being integrated, opening the field of functional and smart coatings. The aim of this paper is to present a comprehensive review of the current state of functional and smart coatings produced using thermal spraying deposition. It will first describe the different thermal spraying technologies, with a focus on how different techniques achieve the thermal and kinetic energy required to form a coating. It will as well focus on the environment to which feedstock particles are exposed in terms of temperature and velocity. It will first deal with the state-of-the-art functional and smart coatings applied using thermal spraying techniques; a discussion will follow on the fundamentals on which the coatings are designed and the efficiency of its performance; finally, the successful applications both current and potential will be described. The inherent designing flexibility of thermal-sprayed functional and smart coatings has been exploited to explore exciting new possibilities on many different fields. Some applications include, but not limited to, prevention of bacteria contamination and infection on hygienic environments. Here, thermal spray has been used to efficiently deposit antimicrobial compounds on medical furniture and appliances and to develop biocidal and biocompatible coatings for prosthetic implants. The attachment of hard and soft foulers such as algae or molluscs, which represents a considerable issue for any marine or freshwater installation, can be prevented on components where the use of traditional anti-fouling strategies such as paints is not optimal for certain materials (i.e., polymers). Another interesting approach pursued is the development of superhydrophobic surfaces, with contact angles as high as 160° and slide angles below 5°, leading to high droplet mobility. This adds capabilities as self-cleaning or corrosion resistance in addition to the characteristic robustness of thermal-sprayed coatings. The electric and magnetic properties of the feedstock materials have also led to the application of thermal spraying techniques in the creation of patterned structures with desired electromagnetic properties for their use on microelectronics. The possibility to intercalate layers of thermal-sprayed materials doped with optical-reactive elements has led to the development of online and offline temperature sensors which can be readily integrated in current thermal barrier coatings. To finalize the examples of the many applications of thermal-sprayed functional and smart coatings, autonomous self-healing or self-lubricant coatings have been developed. Advantage has been taken of a beneficial phase transformation triggered by the corresponding event (such as a crack or the tribological interactions, respectively) to promote self-healing. Another approach has been the release of an encapsulated component which effectively heals the coating or provides lubrication when required. All these exciting developments pave the way for the numerous applications that are to come in the next decade, making the field of thermal-sprayed coatings a unique opportunity for research and development.
This paper presents the out-of-phase thermo-mechanical stress analysis of thermal barrier coating (TBC) system in real working conditions used as thermal barrier in diesel engine cylinder heads. The ...coating system in this research comprises 350μm zirconium oxide top coat (TC) and 150μm metallic bond coat (BC). These layers were deposited on the substrate, aluminum A356 alloy, by the aid of air plasma spray (APS) method. Afterwards, the specimen was subjected to thermo-mechanical fatigue (TMF) loadings. Based on the experimental conditions, FE simulations were performed by both time-independent and time-dependent substrate material properties in ABAQUS software. Simulation results related to heat transfer analysis demonstrate only about 10.5% comparative error compared to experimental results. Moreover, defining time-dependent properties, which were obtained from two-layer visco-plastic model, yields results with 15% less comparative error in comparison to the results based on time-independent material properties. In addition, the effects of roughness and porosity in coating layers and substrate were studied on three different models by the aid of a scanning electron microscopy image. Obtained results based on real geometry illustrate that consideration of porosity in TC layer has an effective role in the stress distribution of this layer. However, BC layer stress distribution is much more dependent on interface morphology.
•Study of out-of-phase thermo-mechanical stress analysis in TBC based on the experiment•Consideration of the real geometry (roughness and porosity) on stress distribution•Effect of using time-dependent material properties for substrate on stress results•Accumulation of axial stresses in all layers and its effect on total axial force•Comparison of both heat transfer and stress results (simulation and experiment)
In this research, a finite element model was developed in order to simulate the two-step residual stress distribution of a thermal barrier coating system, considered to be used in diesel engine ...cylinder head, with a real roughness and real porosity. Two steps including the bond coat and the top coat deposition processes were taken into account. The real geometry of coating layers, including the roughness and the porosity, was also considered based on a scanning electron microscopy image. Then, effects of the convective heat transfer coefficient and initial substrate and substrate/bond coat preheating temperatures on the residual stress were studied. Obtained results illustrate that the residual stress, regarding the two steps of coating processes, are different, particularly in the substrate. Numerical results indicate that while the convective heat transfer coefficient in BC deposition had no striking effect, it was an influential factor in the residual stress distribution when TC was deposited. Moreover, preheating temperature for depositions of the bond coat layer and the top coat layer has a pivotal role in stress distribution of all layers. In addition, consideration of the porosity in the top coat layer causes remarkable decrease in axial stress distribution in substrate and much more local stress concentrations in TC layer compared to those of BC layer due to larger and more irregular pores.
This article presents the cyclic behavior of the A356.0 aluminum alloy under low-cycle fatigue (or isothermal) and thermo-mechanical fatigue loadings. Since the thermo-mechanical fatigue (TMF) test ...is time consuming and has high costs in comparison to low-cycle fatigue (LCF) tests, the purpose of this research is to use LCF test results to predict the TMF behavior of the material. A time-independent model, considering the combined nonlinear isotropic/kinematic hardening law, was used to predict the TMF behavior of the material. Material constants of this model were calibrated based on room-temperature and high-temperature low-cycle fatigue tests. The nonlinear isotropic/kinematic hardening law could accurately estimate the stress–strain hysteresis loop for the LCF condition; however, for the out-of-phase TMF, the condition could not predict properly the stress value due to the strain rate effect. Therefore, a two-layer visco-plastic model and also the Johnson–Cook law were applied to improve the estimation of the stress–strain hysteresis loop. Related finite element results based on the two-layer visco-plastic model demonstrated a good agreement with experimental TMF data of the A356.0 alloy.
Cancer is one of the most complex diseases that has resulted in multiple genetic disorders and cellular abnormalities. Globally, cancer is the most common health concern disease that is affecting ...human beings. Great efforts have been made over the past decades in biology with the aim of searching novel and more efficient tools in therapy. Thus, small interfering RNAs (siRNAs) have been considered one of the most noteworthy developments which are able to regulate gene expression following a process known as RNA interference (RNAi). RNAi is a post-transcriptional mechanism that involves the inhibition of gene expression through promoting cleavage on a specific area of a target messenger RNA (mRNA). This technology has shown promising therapeutic results for a good number of diseases, especially in cancer. However, siRNA therapeutics have to face important drawbacks in therapy including stability and successful siRNA delivery in vivo. In this regard, the development of effective siRNA delivery systems has helped addressing these issues by opening novel therapeutic windows which have allowed to build up important advances in Nanomedicine. In this review, we discuss the progress of siRNA therapy as well as its medical application via nanoparticle-mediated delivery for cancer treatment.
In cold climates, precautions must be taken to prevent water from freezing and bursting pipes in aboveground water distribution systems. Conventionally, electric heat tracing cables are installed ...around pipes to replace the heat lost and prevent liquid from freezing. A multi-layered thermal sprayed coating that includes an electrically insulating alumina layer and a nickel-chromium conductive layer has been applied to carbon steel pipes to provide more efficient and uniform heating. Prospective environmental life cycle assessment (LCA) was used to compare the environmental performance of the two systems with the coating-based heating system modeled based on laboratory-scale production, a laboratory heating test, and conservative assumptions. Under initial assumptions, including a shorter expected life, the coating-based heating system generated more environmental damage during fabrication but used less energy during operation. From a life cycle perspective, the coating-based heating system was found to be environmentally preferable when used in areas with longer, colder winters and where electricity was generated from non-renewable energy sources. Break-even analysis was used to determine the energy efficiency required for the coating-based heating system to be environmentally preferable in different climate regions using different electricity mixes. However, if the coating-based heating system proves to have an expected life similar to the heat tracing cables, it would likely prove to be environmentally preferable in most climate regions. The environmental impact of the coating-based heating system would be further improved by reducing the environmental impact of coating materials production, deposition, recovery, and recycling.
Techno-economic assessment of thermal-sprayed coatings for temperature control and protection of water distribution steel pipes against freezing and subsequent bursting was conducted. A ...data-intensive model was developed to compare the technical and economic implications associated with fabrication, shipping, installation, operation, and maintenance of multilayered coatings, as heating systems, with those of conventional heat tracing cables. The bi-layered coating deposited onto the pipe was composed of an alumina layer, as the electrical insulator, and a nickel-chromium layer, as the heating element. These layers were deposited onto the pipe using the powder flame spraying process. Furthermore, copper coating was deposited onto the nickel-chromium layer using the low-pressure cold spray method where proper electrical contact was needed. Costs were estimated on a per unit length basis for a 60-mm (2.38-inch) diameter pipe and can be scaled by engineers in the field for longer and larger pipes. The material cost for both heating systems was approximately $25 USD per meter of 60-mm diameter steel pipe. However, the total cost of fabricating the coating system was noticeably higher due mainly to the labor cost. After conducting the heating tests based on low-temperature working conditions in a cold room, it was found that the efficiency of the coating-based heating system was higher than that of conventional heating cables, which was mainly due to the intimate contact between the coating-based heating element and pipe substrate. Based on the obtained results, the improved performance of the coating systems should be viewed in light of the increased fabrication and maintenance costs by end users for large-scale protection of steel pipes against bursting during freeze events.
•Synthesis of a metal complex of 1,4,8,11-tetraaza14annulene derivative.•Spectroscopic and electrochemical behavior of the metal complex.•Catalytic activity of the metal complex.
A new Co (II) ...complex of 6,13-disubstituted 1,4,8,11-tetraaza14annulene derivative has been synthesized by template condensation reaction of 2-(1-quinolinium-1-yl) trimethinium salt (B) with 1,2-diaminopyridine in the presence of Co (II) acetate in DMF. The electrochemical behavior of the metal complex showed a CoII/CoI redox couple at about −0.99V vs. Ag/Ag+ in DMF solvent. Axial ligation of N-donor ligands such as pyridine and imidazole was found to shift the reduction potential of CoII/CoI to more negative potential. The binding of N-donor axial ligands to the metal complex was monitored by measuring changes at about 458nm (maximun absorption of the metal complex) and shifts in the CoII/CoI redox couple potential upon addition of various concentrations of the N-donor axial ligand. Results showed that the number of axial ligand molecules bound to the metal complex is ≈1 and the oxidized state of cobalt (CoII) is more stabilized than the reduced state (CoI) in the presence of the axial ligand. The metal complex also showed catalytic activity toward hydrogen peroxide decomposition in the presence of the N-donor axial ligand.
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► The chelate complex formed under the above mentioned conditions and measured spectrophotometrically can offer a sensitive, simple cheap and rapid procedure for the determination of ...the three cephalosporins in bulk, tablets and vials dosage forms. ► Also the complex formed was found to be soluble in presence of a surfactant, without the need for organic solvent to extract the reaction products. ► From the calculation of stability constant of the complex, the latter was found to be stable. ► The method had been validated for the determination of these antibacterials. ► The statistical analysis of the results confirmed that the developed method was accurate and precise and could be recommended for use in quality control labs.
The complexation reaction of cephalosporins namely cefotaxime (CTX), cefuroxime (CRX), and cefazolin (CEFAZ) with palladium (II) ions have been studied in water and DMF in 25°C by the spectrophotometric methods. The method is based on the formation of yellow to yellowish brown complex between palladium (II) chloride and the investigated cephalosporins in the presence of sodium lauryl sulfate (SLS) as surfactant. The complexation process was optimized in terms of pH, temperature and contact time. The stoichiometry of all the complexes was found to be 2:1 (metal ion/ligand) for CTX, CRX, and 1:2 for CEFAZ. The stoichiometry of palladium (II)–cephalosporins was estimated by mole ratio and continuous variation methods and emphasized by the KINFIT program. These drugs could be determined by measuring the absorbance of each complex at its specific λmax. The results obtained are in good agreement with those obtained using the official methods. The proposed method was successfully applied for the determination of these compounds in their dosage forms.
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