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  • 89 Reads
The Influence of CrAlN Coating Chemical Composition on Soldering Resistance in Contact with Al-Si-Cu Alloy

During the high pressure die casting (HPDC) process the die material is exposed to thermal fatigue, erosion, and corrosion. Corrosion leads to the soldering of cast alloy to tool surfaces which consequently bonds the casting with die material. Besides wear, such a process reduces the casting quality, production efficiency, and endanger the tool integrity. Application of thin ceramic coatings on die surfaces reduces the soldering effects and improves the die performance. However, the development of ceramic coatings for these purposes still requires detailed information on the phenomena involved in these processes. In this study, the soldering performance of a complex nanolayer CrAlN coatings, with three chemical compositions (high-Cr, balanced Cr:Al and high-Al content) were evaluated. The cast alloy soldering was evaluated by the detachment test in three configurations. In this test, a simple casting is formed in contact with flat coated surfaces. Upon casting solidification, the formed joint is dismantled and a force required for this process was recorded. To characterize and quantify the exhibited wear after detachment test surfaces of coated samples were analyzed by different microscopy techniques. Two forms of wear were detected on investigated samples. Cast alloy soldering processes induced formation of thin layers of cast alloy on the surfaces of all investigated coatings. Additionally, substrate corrosion through the coating growth defects caused coating layer delamination during the detachment test. The evaluated coatings displayed different behaviors regarding the extent of wear and values of detachment force. The coating with balanced CrAlN composition exhibited the best soldering and corrosion resistance and displayed the lowest ejection force. In terms of soldering and corrosion resistance, the high-Al coating outperformed the high-Cr content coating. However, high-Al and high-Cr coating exhibited significantly higher and quite comparable values of detachment force. Based on the quantitative results it was postulated that, besides soldering and substrate corrosion, the casting-coating bonding strength depends also on “pure” sticking effects of cast alloy to coated surfaces.

  • Open access
  • 151 Reads
Characterization of Electrochemical Sensors Based on Carbon Nanotubes and MIPs for Determination of Ferulic Acid

In order to mitigate the impacts caused by the rampant consumption of fossil fuels, many countries are investing in the development and optimization of alternatives that minimize dependence on fossil energy. The production of first generation ethanol (1G) appears as an attractive option, but it competes with the food chain, generating the need to find other sources of energy. The second generation of ethanol (2G), characterized by its relevant production potential, is considered a good alternative, which can be produced from sugarcane bagasse. Therefore, it is extremely important to evaluate the efficiency of 2G ethanol production processes, mainly in the compositional analysis of hydrolysates from the pre-treatment of lignocellulosic biomass, to promote greater production. Thus, the development of electrochemical sensors composed of graphite/paraffin composite electrodes coated with multi-walled carbon nanotubes (MWCNTs) modified with molecularly printed polymers (MIPs) are an excellent option for carrying out rapid analyzes. Due to the highly sensitive electrical properties of the MWCNTs and the molecular impression of the polymers that allow a high affinity with the model molecule, the sensor has high selectivity, good sensitivity and reproducibility for the determination of ferulic acid. For this reason, the present work presents a morphological study using the Scanning Electron Microscopy (SEM) technique and electrochemistry using the Cyclic Voltammetry (CV) technique.

  • Open access
  • 168 Reads
Chemical Solution Deposition of BiFeO3 Films with Layer-by-Layer Control of the Coverage and Composition

Chemical solution deposition of BiFeO3 thin films is one of the most commercially available techniques to produce large-scale low-cost coatings for further application in memory devices. In this contribution, we implemented piezoresponse force and conductive atomic force microscopies to study the layer-by-layer sol-gel deposition of BiFeO3 thin films focusing on the local phase distribution, morphology, piezoelectric response, and leakage current. The final properties of resulting thin films are found to be determined not only by the composition of the gel and crystallization step but by the gelation step as well. The drying temperature and treatment duration of the solution is shown to drastically influence the film coverage, which finally determines the morphology of the films and behavior of the crystallization process.

Acknowledgement: The research was funded by Russian Science Foundation, grant number 19-72-10076. The equipment of the Ural Center for Shared Use “Modern nanotechnology” UrFU was used.

  • Open access
  • 99 Reads
NiOOH/FeOOH Supported on Reduced Graphene Oxide Composite Electrodes for Ethanol Electrooxidation

Composite materials are defined as materials made from two or more constituent materials with different physical or chemical properties, in order to obtain a new property in the developed material. In view of this objective, in this work nickel (Ni) and Ni-Fe alloy microparticles were electrosynthesized at reduction potentials in the range from -0.70 V to -1.20 V (50 mV s-1) by cyclic voltammetry (CV) onto graphite/paraffin electrode surface modified with nanosheets of reduced graphene oxide (rGO). Previously, the rGO was electrodeposited by CV from a suspension of 1 mg mL-1 of graphene oxide in PBS solution with pH 9.18, in the potential range from -1.50 V to 0.50 V (10 mV s-1). After electrodeposition of metals, the oxyhydroxides were formed by CV in an alkaline medium of 0.10 mol L-1 of NaOH in a potential range of -0.20 V to 1.0 V (100 mV s-1) with successive scans until stabilization of currents. In order to characterize the developed composite electrodes, the surfaces were investigated by high resolution scanning electron microscopy (FEG-SEM) and energy-dispersive X-ray spectroscopy (EDX). It was observed that NiOOH microparticles had sphere morphologies, while NiOOH/FeOOH had undefined shapes. EDX spectroscopy showed the presence of C, Ni, Fe and O in spectra confirming the formation of oxyhydroxides on the surface of composite electrodes. In order to test the electrochemical performance of the developed composite electrodes, ethanol electrooxidation was carried out in an alkaline medium of 0.10 mol L-1 of NaOH in the potential range from -0.20 V to 1.0 V (100 mV s-1) by CV. The electrodes were able to induce the electrooxidation of ethanol at a potential of 0.55 V for the electrode made of NiOOH/FeOOH and around of 0.60 V for the electrode modified with NiOOH.

  • Open access
  • 338 Reads
An Economical and Environmental Alternative to Traditional Can Manufacturing Using a New Pre-laminated Steel

Metal containers are the most commonly used packaging worldwide in both the food and beverage industry. Some manufacturing processes in the canning industry include multi-step transformations that take large aluminum or steel coils and make them into two or three-piece cans. During this process, the containers are sprayed to obtain a better surface for the contents; however, this spray produces volatile organic compounds (VOC). This paper presents a new and environmentally friendly can manufacturing method, which uses a novel pre-laminated two-layer polymer steel. As experimentally proven, this innovative polymer-coated steel successfully withstands every manufacturing requirement. The specimens were tested in an ironing simulator, measuring roughness and friction coefficients. The development of an upper bound ironing model, along with a supporting neural network, allows an insight into the design of new materials for can manufacturing.

  • Open access
  • 244 Reads
2D and 3D Electrospun Silk Fibroin Gelatin Coatings to Improve Scaffold Performances in Cardiovascular Applications

3D scaffolds and 2D matrices fabricated by electrospinnig show morphology similar to that of native ECM, however their mechanical and biological properties are often inadequate, particularly in applications in contact with blood, e.g. in blood vessel substitutes. Biocoatings can improve the performance of these substrates, in particular cross-linked gelatin is among the most used substances.

In this work, a gelatin coating was applied to electrospun silk fibroin (ESF) mats and tubes intended for the regeneration of cardiovascular tissues. The crosslinking reaction used is based on a Michael-type addition in water that promotes the formation of covalent bonds between gelatin amino groups and β-carbons of N-N’-methylene bis-acrylamide (MBA)[1].

Interestingly, when the reacting mixture is applied to a substrate containing primary or even secondary amino groups, these groups can participate in the reaction, being incorporated into the gelatin coating, thus increasing the coating stability on the surface.

ESF mats and tubes, obtained as described in [2] were coated with gelatin MBA-crosslinked in situ by loading or dipping the ESF samples with the crosslinking solution, by use of static or dynamic home-made systems. SEM analysis on coated samples showed a homogeneous coating with gelatin penetrating the whole thickness of the SF matrix {»120 µm for mats and » 212 µm for tubes), with an increase of thickness of about 40% in wet conditions. Water uptake tests indicated for coated samples a faster and higher swelling (1600% after 14 days) than not coated ones (500%), due to the presence of gelatin.

Tensile mechanical tests showed higher values of ultimate stress and elastic modulus for silk fibroin samples (sb=2.4, E=1.82 MPa) compared to gelatin-coated ones (sb=1.2, E=0.58 MPa), with not significant differences in the ultimate deformation (»150%).

Indirect cytocompatibility tests, performed by culturing L929 cells in the presence of eluates obtained by immersing coated and uncoated samples up to 7 days in culture medium, demonstrated a cell viability higher than the control. In direct contact tests using L929 cells, a good cytocompatibility was demonstrated by both coated and uncoated ESF samples, with a cell viability increasing with the culture time (up to 7 days) and a flattened and stretched morphology at SEM.

Primary human umbilical vein endothelial cell (HUVEC), obtained by enzymatic digestion (Cittadella Hospital, PD,I) were seeded onto ESF and ESF-coated samples and cultured under standard tissue culture conditions. Cell adhesion on the matrices was analysed by OM after fixing with formalin and staining with toluidine blue. After 7 days from seeding, cell proliferation was evaluated by a protein assay (BCA Protein Assay kit) and the results indicated a significantly higher (p<0.05) cell growth on gelatin-coated ESF samples.

Overall, these results point out that the described gelatin coating allows producing a structure with adequate mechanical properties for cardio-vascular applications and biological characteristics even better than those of silk fibroin.


[1]Contessi Negrini, N., Tarsini, P., Tanzi, M.C., Farè, S., Chemically crosslinked gelatin hydrogels as scaffolding materials for adipose tissue engineering (2019) J. Appl. Polym. Sci. 136 (8), 47104

[2] Marelli B, Alessandrino A, Fare S, Freddi G, Mantovani D, Tanzi MC. Compliant electrospun silk fibroin tubes for small vessel bypass grafting. Acta Biomater. (2010) 6:4019–26.

  • Open access
  • 69 Reads
New Advances on Fibroblast Growth Factor-Based Coatings for Hip Replacement Implants

It is already well known that the tissue-implant interface is one of the most critical factors for the success of the implant integration. The use of bioactive and biomimetic surfaces is of great interest in biomedical applications especially in tissue engineering. Therefore, in our study we aimed to obtain successful coatings based on hydroxyapatite, antibiotics and growth factors in order to increase the biocompatibility of commercial implant materials by promoting cell attachment and growth without toxic effects as well as inhibition of microbial biofilm formation. In this way, homogenous mixtures of hydroxyapatite, kanamycin and fibroblast growth factor (HAP/KAN, HAP/FGF and HAP/KAN/FGF) were coated on titanium-based metal plates for hip replacement implants. The coatings were able to impair the initial adherence of bacterial cells and to reduce the biofilm formation throughout the release of antibiotic. The cytocompatibility of these samples was investigated on murine normal osteoblasts (MC3T3-E1 cell line) with fibroblast-like morphology by evaluating their influence on cellular viability and potential to generate an inflammatory response. In addition, the adhesion and proliferation, as well as the actin cytoskeleton organization, were observed after 24 h of cell culture on these coatings. The results confirmed the biocompatibility of all coatings, the cell number counted for HAP/KAN/FGF sample being equal to control. Since it is well known that NO is a marker of inflammation with an essential role in regulating apoptotic death and cell viability, our study showed that cell growth on these surfaces did not induce nitric oxide (NO) release, NO level being maintained close to control values for all tested samples. Also, an excellent cell adherence and spreading on these coatings deposited on hip implants was evidenced by fluorescence microscopy, supporting their usage as substrates in tissue engineering applications. 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
  • 59 Reads
Hybrid Oxidation of Titanium Substrates for Biomedical Applications

Issues related to the improvement in bioactivity of titanium materials used in implantology for the regeneration and replacement of bone tissue are of great application importance due to the elimination of undesirable interactions between tissues with physiological fluids during the operation of implants. Therefore titanium oxidation for biomedical applications is still a challenge in obtaining both good mechanical and physicochemical properties of thin oxide layers as well as the required good adhesion to titanium substrates and of course bioactivity. Interesting techniques for TiO2 layers formation are electrochemical methods (anodizing), electric discharge treatments, plasma methods (PVD) and diffusive methods (Fluidized Bed FB). Each method aims to create a thin homogenous oxide layer characterized by thermal stability and re-passivation in the presence of body fluid environment. However, an important aspect here is also phase composition of thin oxide layers, essential in the processes of osseointegration. Accordingly research carried out by the Author aims to produce such a titanium substrate, where surface zone is Tiα(O) solid solution formed with Fluidized Bed diffusion process (883K, 913K for 6h / 8h) and the outer layer is TiO2 oxide produced by PVD magnetron sputtering. Effects of such hybrid oxidation on titanium physiochemical properties were investigated with TEM / EFTEM, SIMS, RS and Nanoindentation tests. Results showed that hybrid oxidation made it possible to generate favourable synergetic effect between Fluidized Bed and PVD oxide layers and to reduce the stresses at their interface. In turn, variable share of TiO2 oxide phases (rutile + anatase mixture) obtained at the titanium surface allowed for the significant enhancement of hydroxyapatite growth which was confirmed by 7 / 14 days Kokubo tests. Hybrid processes also influenced the decrease in the surface roughness parameters, important for implant materials. Intensive formation of hydroxyapatite compounds shows the potential of applying hybrid oxidation for the improvement of titanium surface bioactivity and confirms the method is novel outlook in TiO2 oxide layers properties modification for biomedical applications.

  • Open access
  • 215 Reads
Resistance to Cavitation Erosion and Sliding Wear of MCrAlY and NiCrMo Metallic Coatings

Bulk cobalt- and nickel-based metallic materials exhibit superior resistance to cavitation erosion and sliding wear. Thus, thermally deposited High Velocity Oxygen Fuel (HVOF) coatings seem promising for increasing the wear resistance of the bulk metal substrate. However, the effect of chemical composition on the cavitation erosion and sliding wear resistance of M(Co,Ni)CrAlY and NiCrMo coatings has not yet been exhaustively studied. In this study, High Velocity Oxygen Fuel (HVOF) coatings such as CoNiCrAlY, NiCoCrAlY, and NiCrMoFeCo were deposited on AISI 310 (X15CrNi25-20) steel coupons. The microstructure, hardness, phase composition (X-ray diffraction, XRD) and surface morphology of the as-sprayed coatings were examined. Cavitation erosion tests were conducted using the vibratory method in accordance with the ASTM G32 standard. Sliding wear was examined with the use of a ball-on-disc tribometer, and friction coefficients were measured. The mechanism of wear was identified with the scanning electron microscope equipped with an energy dispersive spectroscopy (SEM-EDS) method. In comparison to the NiCrMoFeCo coating, the CoNiCrAlY and NiCoCrAlY coatings have a lower wear resistance.

  • Open access
  • 115 Reads
Preliminary Studies on HVOF Sprayed Coatings on the Magnesium Alloys
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In the field of modern techniques development, which improve and/or regenerate the component’s surface properties, high velocity oxy-fule spraying (HVOF) of carbides or metals and its alloys is a good alternative method to other conventional surface engineering ones, including magnesium foundry alloys. Coatings manufactured by thermal spraying are used to improve the durability and life time of machine parts, both, the new and regenerated ones, by changing the surface layer properties.

In this work the results of the HVOF sprayed coatings deposited onto AZ31 magnesium alloy substrate. The feeding material was composite powder Cr3C2 - NiCr. The coatings were investigated in terms of their microstructure and selected mechanical properties. For structure examinations the microscopy studies (light and scanning ones) were used as well as phase composition analysis. In case of mechanical properties, the wear resistance was determined also microharndess has been measured.