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1.
Electrochemical impedance studies of corrosion protected surfaces covered by epoxy polyamide coating systems
Saša Skale, Valter Doleček, Mojca Slemnik, 2008, original scientific article

Abstract: Electrochemical impedance spectroscopy (EIS) was used to study the corrosion behavior of different types of commercial quality epoxy polyamide dry coatingson mild steel, with thickness between 150 and 250 ▫$/mu$▫m, which were previously weather accelerated in a wet chamber. The following data were established on the basis of impedance curves and corresponding equivalent circuits: the coating capacity that relates to the coating dimension, the pore resistance that represents conductive paths through the pores, and Warburg coefficients, which are the measure of ion diffusion through the coating. EIS data were compared with a criterion in the European standard, and samples were classified on the basis of their quality, also receiving a final ranking by summing-up all the individual rankings. Suggestions have been made, namely that the use of anticorrosive active pigments is obsolete, when the thickness of the coatings exceeds 200 ▫$/mu$▫m.
Keywords: electrochemical impedance spectroscopy, metal-coatings, epoxy polyamide coatings, weathering, ISO 12944
Published: 31.05.2012; Views: 1599; Downloads: 72
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2.
Substitution of the constant phase element by Warburg impedance for protective coatings
Saša Skale, Valter Doleček, Mojca Slemnik, 2007, original scientific article

Abstract: This paper proposes an alternative model for fitting electrochemical impedance spectra of protective coatings. It describes broadening of the semicircle in the complex plane, in the absence of corrosion reactions. In addition the infinite Warburg impedance circuit element is represented, which bridges existing parallel elements of the plate capacitor and resistor of a classical equivalent electrical circuit. The Warburg impedance element is the result of the Fick's second law on partial differential equation solution. The proposed model and, for comparison the model with the CPE element, are used on our epoxy protective system to describe EIS measurements. The proposed model shows a better quality of fitting for our EIS data in comparison to the model with CPE.
Keywords: metal-coatings, electrochemical impedance spectroscopy, Nyquist charts, constant phase element, Warburg impedance
Published: 01.06.2012; Views: 1411; Downloads: 79
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3.
Surface modification of silicone with polysaccharides for the development of antimicrobial urethral catheters
Matej Bračič, 2016, doctoral dissertation

Abstract: In this work, alternative polysaccharide-based coatings were used to improve the antimicrobial and antifouling properties of silicone surfaces used for urethral catheters. The introduction of a catheter in the urethra is commonly connected with a high risk of microbial infections which often result in long-term health damage. Polysaccharide-based coatings like chitosan, carboxymethyl chitosan, and a synergistic formulation between hyaluronic acid and a natural lysine-based surfactant, were used to treat silicone surfaces to overcome the infection problems as an alternative to conventional approaches, which include the administration of antibiotics or coatings with metal ions. The polysaccharide-based macromolecular solutions and dispersions were firstly characterised by means of pH-titrations, dynamic light scattering and scanning electron microscopy in order to determine the size of particles in dispersions and their pH dependant charging behaviour. The knowledge gained from this was used to thoroughly study the interactions of the polysaccharide-based solutions and dispersions with the model silicone surfaces. The model surfaces were ultra-thin films prepared by dissolution of silicone in toluene and subsequent spin-coating on quartz crystals. The influence of pH, salt concentration, and various surface activation processes on the adsorption behaviour was evaluated by means of a very precise quartz crystal microbalance with dissipation. This knowledge was transferred to the application of the coatings on real systems i.e. casted silicone sheets and silicone tubes. The surface morphology, surface chemistry, as well as the mechanical and chemical stability of the coatings were further characterised on both model and real systems. For this purpose different microscopy and spectroscopy methods, pH-potentiometric titrations and methods for evaluation of mechanical properties were used. Finally the antimicrobial and antifouling properties were evaluated. The antimicrobial properties were tested against gram-positive and gram-negative bacteria as well as fungi, which are commonly found in infected urine, while the antifouling properties were tested by measuring the adhesion of bovine serum albumin, fibrinogen, and lysozyme biomolecules onto functionalised model films using the quartz crystal microbalance. The results showed that homogeneous and stable coatings can be achieved by adsorption from dispersions of the polysaccharide-based nanoparticles of 200-300 nm in size, which are formed by precipitation; i.e. careful pH adjustments of chitosan to pH = 6.5, carboxymethyl chitosan to pH = 7, and by mixing the hyaluronic acid and natural lysine-based surfactant solutions at concentrations of 2.5 x 10-4 mol/L and 1.25 x 10- 3 mol/L for the hyaluronic acid and 5.0 x 10-4 mol/L and 1.2 x 10-3 mol/L for the surfactant, respectively . The mass of the coatings on model silicone films can be increased by a 3-step adsorption, which directly influences the antimicrobial properties of the coatings that are improved with increasing coating mass, reaching values of up to 90 % in reduction of microorganism growth. It was also shown that the hyaluronic acid-natural surfactant formulation is superior to the chitosan coatings. The same conclusions were drawn from the antifouling evaluation where the zwitterionic nature of the formulation between natural based lysine surfactant and HA successfully suppressed the adhesion of biomolecules on silicone surfaces, while the chitosan coatings only moderately prevented the adhesion of proteins. One can conclude that the polysaccharide-based coatings can be successfully introduced to silicone surfaces from dispersion and as such successfully prevent biomolecule adhesion and reduce the growth of pathogen microorganisms which can be found in the urine during urethral infections.
Keywords: Urethral catheters, Antimicrobial coatings, Silicone, Polysaccharides, Natural surfactants
Published: 24.10.2016; Views: 966; Downloads: 168
.pdf Full text (5,86 MB)

4.
Morphology and corrosion properties PVD Cr-N coatings deposited on aluminium alloys
Darja Kek-Merl, Ingrid Milošev, Peter Panjan, Franc Zupanič, 2011, original scientific article

Abstract: The attempt to find an alternative coating for corrosion protection of Al- alloys was made. PVD coatings are one of the possible alternatives for replacement of ecological unfriendly chromate coatings. Chromium-nitride (Cr-N) and Ni/Cr-N coatings were sputtered on aluminium substrates (AA7075 and cladded AA2024). Surface and sub-surface characterizations were performed by AFM and SEM. Special attention was given to defects incorporated into coatings, since they play important role in the corrosion protection of the coating/substrate systems. The cross-sections through the typical defects were performed by ion beam milling incorporated into the SEM. The Vickers hardness of the Cr-N with and without layer of Ni on both substrates was determined. After the coatings deposition, the values of Vickers hardness (10 mN load) increase for 10 to 100-fold compared to the substrates. The corrosion behaviour of Cr-N and Ni/Cr-N thin films was investigated in near neutral 0.1 M solution of NaCl using potentiodynamics electrochemical measurement. Cr-N and Ni/Cr-N coatings shift the corrosion potentials to more positive values. The best corrosion resistance among the tested coating/substrate systems were found for Ni/Cr-N on AA7075 substrate.
Keywords: Al-alloys, corrosion properties, CrN films, FIB, PVD coatings
Published: 17.03.2017; Views: 430; Downloads: 43
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5.
The influence of surface coatings on the tooth tip deflection of polymer gears
Boštjan Trobentar, Srečko Glodež, Jože Flašker, Boštjan Zafošnik, 2016, original scientific article

Abstract: When designing gear drives made of polymer, the tooth tip deflection is a crucial parameter in respect to the proper gear drive operation. Excessive tooth tip deflection can lead to serious disturbances of gear meshing and consequently to increased noise and wear of the teeth flanks. In such cases the tooth tip deflection can be reduced through the use of stiff surface coatings on the tooth flanks. In this paper the influence of different coating materials and thicknesses on the tooth tip deflection of polymer gears is analysed using comprehensive finite element computational analysis. The numerical results obtained are then used to define an approximate equation for the calculation of gear tooth tip deflection for the coating material used and the thickness of the surface coating layer. The results show that the tooth tip deflection decreases with large values of the coating material Young’s modulus and with the coating layer thickness.
Keywords: polymer gears, surface coatings, tooth deflection, numerical analysis
Published: 27.03.2017; Views: 475; Downloads: 231
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6.
Novel chitosan/diclofenac coatings on medical grade stainless steel for hip replacement applications
Matjaž Finšgar, Amra Perva-Uzunalić, Janja Stergar, Lidija Gradišnik, Uroš Maver, 2016, original scientific article

Abstract: Corrosion resistance, biocompatibility, improved osteointegration, as well the prevention of inflammation and pain are the most desired characteristics of hip replacement implants. In this study we introduce a novel multi-layered coating on AISI 316LVM stainless steel that shows promise with regard to all mentioned characteristics. The coating is prepared from alternating layers of the biocompatible polysaccharide chitosan and the non-steroid anti-inflammatory drug (NSAID), diclofenac. Electrochemical methods were employed to characterize the corrosion behavior of coated and uncoated samples in physiological solution. It is shown that these coatings improve corrosion resistance. It was also found that these coatings release the incorporated drug in controlled, multi-mechanism manner. Adding additional layers on top of the as-prepared samples, has potential for further tailoring of the release profile and increasing the drug dose. Biocompatibility was proven on human-derived osteoblasts in several experiments. Only viable cells were found on the sample surface after incubation of the samples with the same cell line. This novel coating could prove important for prolongation of the application potential of steel-based hip replacements, which are these days often replaced by more expensive ceramic or other metal alloys.
Keywords: corrosion, corrosion resistance, chitosan, biocompatibility, biomaterials, biomedical materials, coatings, stainless steel
Published: 23.06.2017; Views: 689; Downloads: 218
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