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  • Open access
  • 85 Reads
Microstructural Refinement and Improvement of Microhardness of a Hypoeutectic Al-Fe Alloy Treated by Laser Surface Remelting

In the laser surface remelting (LSR) treatment, only a small region is heat affected, surpassing the melting temperature, and followed by a rapid cooling at 105 – 108 K/s, producing an extremely refined microstructure. The laser treated region shows a more homogeneous microstructure and better mechanical properties than the substrate. The LSR is a great technique to improve the Al alloys properties, increasing the hardness and wear resistance without modifying the composition of the material. Iron is commonly found as an impurity in Al-based alloys, but in the 2618 commercial alloy, around 1wt.% of Fe is intentionally added to improve the high temperature strength and the corrosion resistance. In addition, Al-Fe based alloys are used in packaging, architectural sheets and high voltage cables. In this work, LSR experiments were performed, with a CO2 laser operating in a continuous-wave mode, to investigate the influence of process parameters on the treated surface of an as-cast Al-1wt.%Fe alloy. These parameters cover work distance (z = 6 and 8 mm), laser beam speed (v = 500, 750 and 1000 mm/s) and laser average power (P = 400, 600 and 800 W), setting a total of 18 combinations. The configuration of z = 6 mm, v = 500 mm/s and P = 800 W resulted in a remelted pool with 710 µm width and 242 µm length without major porosities, therefore being the largest stable pool amongst all parameters combinations. The resulting cellular microstructure had an interphase spacing of 0.93±0.17 µm, a decrease of about 14 times in relation to that of the substrate. The effects of LSR on the microhardness were remarkable, with the remelted pool presenting Vickers microhardness of 49±2 HV which corresponds to an increase of about 40% when compared to the original substrate.

  • Open access
  • 70 Reads
Novel catalysts for selective catalytic reduction of NOx by NH3 prepared by atomic layer deposition of V and Ti oxides on SiO2 powder
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Based on the air quality in Europe - 2019 report of European Environment Agency, nitrogen oxides (NOx) are included to the most harmful air pollutants in terms of damage to ecosystems. Moreover, NO2 is one of the most Europe’s dangerous pollutants to human health. Anthropogenic emissions of NOx are mainly generated by combustion of fossil fuels. Nitrogen oxides being emitted into the atmosphere cause such environmental problems as acid rains, acidification of soil, lakes and rivers, eutrophication and photochemical smog.

The most effective and widely used technology achieved for today to purify flue gases from NOx is selective catalytic reduction using ammonia (NH3-SCR de-NOx). Nowadays, one of the most significant directions in the field of NH3-SCR de-NOx is applying of new nonconventional methods and preparation of new catalysts possessing high specific surface area, uniformity, dispersion of active sites, high activity and selectivity. Atomic layer deposition (ALD) is an attractive technique for deposition of uniformly distributed active catalytic layers or nanoparticles on highly porous substrates being characterized by a complex structure and highly developed surface, where the application of conventional methods (e.g. impregnation or deposition precipitation) can be problematic. The significant advantage of ALD application for preparation of supported catalysts is that the preparation process can be controlled on the atomic scale providing the required thickness of an active layer synthesized with accuracy of up to one atom. Moreover, ALD ensures the formation of catalysts in a gas phase instead of a liquid phase, which enhance the possibility of active species to be deposited inside pores which are very small in size.

In this study ALD was applied for preparation of VxOy-based NH3-SCR de-NOx catalysts. Highly porous silica gel powder (63-100μm) with a specific surface area of up to 450 m2·g-1 was used as a substrate for active layer deposition. VxOy/SiO2 with different metal loadings (wt.%) and (VxOy+TiO2)/SiO2 catalysts were prepared by applying the following metal precursors: vanadium (V) tri-i-propoxy oxide (VTIP) and titanium tetrachloride (TiCl4), while deionised water was used as the co-reactant. ICP-OES results revealed that vanadium loadings in VxOy/SiO2 catalysts were 0.3, 0.7, 1.1 and 1.6 wt.%, while the metals loading in the TiO2-promoted VxOy/SiO2 catalyst was 1.04 wt.% and 0.15 wt.% for V and Ti, respectively. According to XPS spectra V2O3 and V2O5 species were identified in the prepared VxOy/SiO2 catalyst with the predominance of vanadium (V) compounds (V2O5/V2O3 ratio was 1.6 and 6.3 for as-synthesized and calcined samples, respectively). V2O5 is found as an active vanadium form for NH3-SCR de-NOx. Additionally, TEM, XRD and BET analyses were conducted to provide a comprehensive characterization of the catalysts prepared.

  • Open access
  • 66 Reads
Synthesis and Characterizations of 2D Platinum Diselenide

Platinum diselenide (PtSe2), which belongs to the transition metals dichalcogenide (TMDCs) class of 2D materials, is characterized with a transition from semimetal to semiconductor with a thickness variation from bulk to monolayer and found versatile applications especially in sensors and mid-infrared detectors. In this study we report the large-scale synthesis of PtSe2 layers by thermally assisted selenization of pre-deposited platinum films in horizontal quartz-tube Chemical Vapour Deposition (CVD) reactor. Raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) are used for characterization of the obtained 2D PtSe2. It is observed that the Raman spectra of PtSe2 show strong dependence on the thickness (Pt deposition time). XPS analysis was applied to examine the chemical compositions in order to assess the quality of the synthesized PtSe2 films. All the studied properties reveal great potential to obtain continuous layers with controlled thickness and composition and further potential for integration in functional heterostructures for future nanoelectronic and optoelectronic devices.

  • Open access
  • 83 Reads
Novel Coatings Based on Nanostructured Cefepime-Functionalized Magnetite for Implantable Devices

The aim of this study was to obtain biocompatible coatings based on polylactic acid, hydroxyapatite and nanostructured Cefepime-functionalized magnetite for enhancing the activity of next-generation implants against antibiotic-resistant pathogens. Mixtures of various ratios of polylactic acid, hydroxyapatite and nanostructured Cefepime-functionalized magnetite (Fe3O4@CEF, HAP/Fe3O4@CEF and PLA/Fe3O4@CEF) were obtained and deposited on glass slides by Matrix Assisted Pulsed Laser Evaporation (MAPLE). The in vitro biological effects of these coated surfaces on murine normal osteoblasts (MC3T3-E1 Subclone 4 (ATCC cat. no. CRL-2593)) were investigated by observing their morphological features and measuring the cell viability and nitric oxide (NO) release as an indicator of inflammation and cell death. A good biocompatibility was noticed for all samples investigated within this study, according to formazan-based assay. Also, no increase in NO level was induced after 24 h of cell growth on these coated glass slides. Moreover, the visible microscopy images showed the good cell attachment on these modified surfaces and proved that the proliferative capacity of osteoblasts was not disturbed in the presence of tested samples. The coatings succeeded to reduce the microbial attachment as well as the subsequent Escherichia coli colonization and biofilm development on these surfaces. In conclusion, these novel coatings can become suitable surfaces for implantable devices with an enhanced biocompatibility and reduced bacterial colonization. In conclusion, these novel coatings can become suitable surfaces for implantable devices with an enhanced biocompatibility and reduced bacterial colonization. Acknowledgements. This work has been funded by the Operational Programme Human Capital of the Ministry of European Funds through the Financial Agreement 51668/09.07.2019, SMIS code 124705, and through the project no. 77PD/2018 NANO-BIO-INT (PN-III-P1-1.1-PD-2016-1562).

  • Open access
  • 147 Reads
Development of biodegradable electrospun dressing based on PVA/CA with antimicrobial potential for chronic wounds
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Published: 09 May 2020 by MDPI in 2nd Coatings and Interfaces Web Conference session Posters

The incidence of chronic wounds (CW) is growing at an accelerated rate around the world. CW are characterized for failing to progress through the orderly phases of the healing process, stalling at the inflammatory stage. This disorder is often triggered by infections. To address this problem, wound dressings with a nano-architecture and functionalized with active biomolecules are being engineered. The introduction of antimicrobial peptides (AMPs), as pexiganan (or MSI-78), which display broad spectrum of antibacterial activity and reduce bacterial resistance, has been considered a viable solution. Here, nanofibrous mats were electrospun with an architecture resembling the extracellular-matrix. To this effect, poly(vinyl alcohol) (PVA) and cellulose acetate (CA)-based meshes were prepared at different ratios from 100/0 to 70/30% (v/v) and characterized. The process was kept as green as possible by resorting to acetic acid/distilled water as solvents and low temperatures. Optimal conditions for PVA/CA processing were established at 29 kV, feeding rate of 0.8 mL/h and distance between needle and collector of 17 cm. To increase PVA stability in aqueous medium, a crosslinking process was carried out with glutaraldehyde (GA) vapor, a less toxic approach than GA immersion or GA addition to the polymer solution. Highly stable films were obtained. Their degradation profile was mapped after 28 days of incubation in distilled water, revealed that only less than 20% of their overall mass was lost after that period. Pexiganan was examined for its antibacterial action against Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa and Escherichia coli demonstrating minimum inhibitory concentrations (MIC) ranging from 7.8 to 62.5 µg/mL. Surface anchoring at MIC value (62.5 µg/mL) was performed using a poly(ethylene glycol)-spacer, the succinimidyl-ester (NHS)-PEG2-Maleimide, as a binding agent which allowed for covalent and electrostatic bonding to take place by means of the N-terminal cysteine-modified pexignan. Preliminary antimicrobial results are very promising.

  • Open access
  • 128 Reads
Surface Topography and Grain Morphology of Nanolayer TiAlN/TiSIN Coating Governed by Substrate Material and Rotation during Deposition

Nanolayer TiAlN/TiSiN coating is one of the most advanced contemporary protective coatings. It has been applied for protection of machining tools, forming tools, and die casting tools. However, due to its versatile properties, there is a high potential for broadening its application, for example for protection of biomedical implants. Each application requires specific base materials, for example cold working steels are used for forming, while stainless steels are applied for biomedical purposes. Different materials and their pre-treatment might result in different coating properties even if coating was conducted in a single batch. Real tools and components have complex geometries, and as such require a multiple-axis rotation during the deposition. Among other properties, grain morphology and surface topography are of great importance in a real application. Since systematic studies on the effect of substrate materials and rotation during deposition on these properties are very scarce, in this article we studied TiAlN/TiSiN coating magnetron sputtered on five different substrates, prepared with 1‑fold, 2-fold, and 3-fold rotations. Cold-work tool steel (X153CrMoV12), hot-work tool steel (X37CrMoV5-1), plasma nitrided hot-work tool steel, surgical stainless steel (X2CrNiMo18-15-3), and cemented carbide (WC/Co) were used as substrate materials. 3D stylus profilometry and atomic force microscopy were used for evaluation of micro and nano topography. The coated surgical steel has the highest roughness (Sa) which corresponds to the highest number of coating growth defects. However, the size of the individual growth defects was considerably smaller for this substrate than for other substrate materials. The observed difference is linked to differences in the concentration of specific carbides contained in a specific steel. Since different carbides have different polishing and ion-etching rates, coatings on different steels may have different concertation of defects. Columnar grain analysis revealed that coating on surgical steel exhibited the smallest column diameter (125 nm) and their highest uniformity. Column diameter on other substrates is around 215 nm, while hot-working tool steel exhibited the largest columns (235 nm). Such finding suggests that the same coating may exhibit different mechanical properties on different substrates. Coatings produced with the higher degree of rotation (2-fold, 3-fold) have less defects and smoother surface. There was no clear trend between columnar grain size and number of rotational degrees.

  • Open access
  • 337 Reads
Measuring the Thickness of Metal Films: A Selection Guide to the Most Suitable Technique

The determination of the thickness has a fundamental importance in all the fields in which the implementation of films and coatings are required and takes a crucial role in electroplating sector. The thickness influences many aspects of the coatings such as electrical, mechanical, corrosion protection and even aesthetical properties. In the multitude of applications of thin layer coatings, the variability of thicknesses and materials is very high as well as the possible techniques that can be used to determine the characteristics of the layers of interest. The first distinction that can be made between these techniques is that which divides destructive techniques from non-destructive ones, in which however the semi or micro-destructive techniques are immediately difficult to place. Other important parameters to consider are the cost, both for the purchase of the instrumentation and for each single analysis, the difficulties in preparing and measuring the sample and data processing and obviously the detectable thickness ranges, the possible measurable materials, precision and accuracy. The purpose of this work is to compare the characteristics of the various investigation methods, with a particular focus on metal films applications, so that it will be easier to choose the most suitable technique for each purpose. Among the many techniques examined, the main ones are electron and optical microscopy, profilometry, ellipsometry and X-ray techniques.

  • Open access
  • 119 Reads
Electrodeposited White Bronzes: A Comparison between Zn-Bearing and Zn-Free Coatings
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Published: 13 May 2020 by MDPI in 2nd Coatings and Interfaces Web Conference session Posters

White bronzes are ternary alloys composed by Cu, Zn and Sn, named after their bright whitish colour. This class of alloys share excellent hardness, corrosion and tarnishing resistance, and is commonly adopted in galvanic industrial processes as technological grade coating, to obtain layers with particular aestethical and/or anticorrosive properties. Despite the widespread employment of white bronzes in fashion and electronics industry, recent literature lacks a characterization of these electrodeposited alloys in respect to more common binary (Cu-Sn) white bronzes.

In this presentation, a thorough characterization of a commercial ternary Cu-Zn-Sn white bronze, produced by electrodeposition, is reported. Structural, Chemical and Physical characteristics of the deposited coating were investigated by various techniques (e.g. FIB/SEM, XRF, XRD, EDX, microhardness, colour and corrosion tests). Results were compared with a similar set of measures obtained from a binary electrodeposited Cu-Sn white bronze (with a high tin content), in order to shed some light on the influence of Zn in the coating properties.

  • Open access
  • 72 Reads
Tannins Encapsulation for Personalised Products Application
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Published: 13 May 2020 by MDPI in 2nd Coatings and Interfaces Web Conference session Posters

Tannins are secondary metabolites of plants, polymers consisting mainly of glycosides, found in nature as hydrolysable tannins or condensed tannins, as well as a combination of them.

In the European H2020 funded Stance4Health project, one of the objective is to develop special tannin extracts (from chestnut wood, quebracho wood, oak wood, tara pods, chinese gallnuts) with differential effects on the gut microbiota and human health, aiming for a personalised modulation of gut microbiota activity at the individual level.

The tannins will be extracted by means of water, ethanol or water-ethanol mixtures at different ratios. Novel dietary supplements enriched with different tannin extracts in order to exert novel biological activities, will be produced in an individualised manner, being the entry step in the European Food Sector for personalised nutrition. Due to their astringency and bitter flavor, will be define how the bitterness can be modify by coating the bitter‐tasting tannins extracted using alginate or gum-like or combination of maltodextrin-gum Arabic (ratio of 40:60 (w/w)) formulas to form double-phase emulsion micro-encapsulation or using the spray-dry method to obtain HPMC particles with tannins. The final product targeted is a powder form that can be easily re-dispersed in water for personalization at individual level.

Besides, it is well-known their antioxidant, antimicrobial (increase the shelf-life of foods) and antibacterial (inhibitor to foodborne bacteria) effects, and therefore their application as food enhancements and food preservatives it is of high importance due to their protective nature.

Acknowledgement. The research leading to these results has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 816303 (STANCE4HEALTH).

  • Open access
  • 158 Reads
Chitosan-Based Blended Films for Wound Dressing Applications
Published: 13 May 2020 by MDPI in 2nd Coatings and Interfaces Web Conference session Posters

Chronic wounds (CW) have numerous entry ways for pathogen invasion and prosperity, which further damages host tissue and hinders tissue remodeling. Essential oils (EOs) exert quick and efficient antimicrobial (AM) action, unlikely to induce bacterial resistance. Cinnamon leaf oil (CLO) is a well-studied EO with strong AM properties. In this work, CLO was added to chitosan (Ch) and polyvinyl alcohol (PVA) solutions. Ch is a natural cationic polysaccharide with antibacterial, anti-inflammatory and regenerative properties. PVA adds flexibility and hydrophilicity to the blend. Ch (100-300 KDa and 9.7±0.6% of DA) and PVA (72 KDa, 88% hydrolysed) films were prepared by solvent casting and phase inversion method (as previously done by the lab). CLO-enriched films included CLO added to Ch shortly before blending, and were based on its minimum inhibitory concentration (MIC; 19.7 µg/mL for S. aureus and 26.2 µg/mL for E. coli). Films chemical composition, thermogravimetric analysis, differential scanning calorimetry, and water absorption capability were tested. Films were successfully built. AM activity, via halo and shake flask tests, was particularly increased with CLO. This study is a first proof of concept that CLO can be dispersed into Ch and PVA films and show bactericidal effects, opening new perspectives for CW therapeutics.

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