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    Electroless Deposition of Ni-P/SiO2 Composite Coating
    (Mendel University in Brno, 2016-10-30) Buchtík, Martin; Kosár, Petr; Wasserbauer, Jaromír; Zmrzlý, Martin
    Electroless deposit Ni–P/SiO2 composite coating was performed on the steel substrate, DIN EN 10130. The preparation of nickel coating included two main steps. In the first step, the fraction of SiO2 particles sized the tens of nanometres was obtained by sedimentation. In the second step, the composite coating was plated on the steel substrate. The actual deposition process contains the deposition of plain Ni-P interlayer which served as the nucleation center for the deposition of Ni-P/SiO2 composite coating with co-deposited SiO2 particles. The morphology of deposited composite coating was studied by scanning electron microscope (SEM). Amount of individual elements in deposited coatings was determinated by EDS analysis. The microhardness of deposited composite coating was subsequently compared with microhardness value of the plain Ni–P coating.
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    Characterization of Electroless Ni–P Coating Prepared on a Wrought ZE10 Magnesium Alloy
    (MDPI, 2018-03-07) Buchtík, Martin; Kosár, Petr; Wasserbauer, Jaromír; Tkacz, Jakub; Doležal, Pavel
    Electroless low-phosphorus Ni–P coating was deposited on a wrought ZE10 magnesium alloy including an advanced pre-treatment of the material surface before deposition. Uniform Ni–P coating with an average thickness of 10 µm was formed by 95.6 wt % Ni and 4.4 wt % P. The content of Ni and P was homogeneous in the entire cross-section of the coating. Applying the Ni–P coating to the magnesium substrate, the surface microhardness increased from 60 ± 4 HV 0.025 to 690 ± 30 HV 0.025. Using the scratch test, it was determined that deposited Ni–P coating exhibits a high degree of adhesion to the magnesium substrate. Electrochemical corrosion properties of Ni–P coating were analyzed using the polarization tests in 0.1 M NaCl, while the deposited Ni–P coating showed an improvement of the corrosion resistance when compared to the ZE10 magnesium alloy. Using the scanning electron microscopy analysis, it was determined that the fine morphology of the deposited Ni–P coating did not contain visible microcavities. The absence of macrodefects due to the adequate pre-treatment before coating was reflected on the mechanism of the coated ZE10 degradation in a 0.1 M NaCl solution.
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    Comparison of Electrochemical Methods for the Evaluation of Cast AZ91 Magnesium Alloy
    (MDPI AG, 2016-11-15) Tkacz, Jakub; Minda, Jozef; Fintová, Stanislava; Wasserbauer, Jaromír
    Linear polarization is a potentiodynamic method used for electrochemical characterization of materials. Obtained values of corrosion potential and corrosion current density offer information about material behavior in corrosion environments from the thermodynamic and kinetic points of view, respectively. The present study offers a comparison of applications of the linear polarization method (from 100 mV to +200 mV vs. EOCP), the cathodic polarization of the specimen (100 mV vs. EOCP), and the anodic polarization of the specimen (+100 mV vs. EOCP), and a discussion of the differences in the obtained values of the electrochemical characteristics of cast AZ91 magnesium alloy. The corrosion current density obtained by cathodic polarization was similar to the corrosion current density obtained by linear polarization, while a lower value was obtained by anodic polarization. Signs of corrosion attack were observed only in the case of linear polarization including cathodic and anodic polarization of the specimen.
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    Improvement of AZ91 Alloy Corrosion Properties by Duplex NI-P Coating Deposition
    (MDPI, 2020-03-17) Wasserbauer, Jaromír; Buchtík, Martin; Tkacz, Jakub; Fintová, Stanislava; Minda, Jozef; Doskočil, Leoš
    The corrosion behavior of duplex Ni-P coatings deposited on AZ91 magnesium alloy was studied. The electroless deposition process of duplex Ni-P coating consisted in the preparation of low-phosphorus Ni-P coating (5.7 wt.% of P), which served as a bond coating and high-phosphorus Ni-P coating (11.5 wt.% of P) deposited on it. The duplex Ni-P coatings with the thickness of 25, 50, 75 and 100 µm were deposited on AZ91 magnesium alloy. The electrochemical corrosion behavior of coated AZ91 magnesium alloy was investigated by electrochemical impedance spectroscopy and potentiodynamic polarization method in 0.1 M NaCl. Obtained results showed a significant improvement in the corrosion resistance of coated specimens when compared to uncoated AZ91 magnesium alloy. From the results of the immersion tests in 3.5 wt.% NaCl, 10% solution of HCl and NaOH and 5% neutral salt spray, a noticeable increase in the corrosion resistance with the increasing thickness of the Ni-P coating was observed.
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    Silver Nanoparticles Stabilised by Cationic Gemini Surfactants with Variable Spacer Length
    (MDPI, 2017-10-23) Pisárčik, Martin; Jampílek, Josef; Lukáč, Miloš; Horáková, Renáta; Devínsky, Ferdinand; Bukovský, Marián; Kalina, Michal; Tkacz, Jakub; Opravil, Tomáš
    The present study is focused on the synthesis and investigation of the physicochemical and biological properties of silver nanoparticles stabilized with a series of cationic gemini surfactants having a polymethylene spacer of variable length. UV-VIS spectroscopy, dynamic light scattering, scanning electron microscopy and zeta potential measurements were applied to provide physicochemical characterization of the silver nanoparticles. The mean size values of the nanoparticles were found to be in the 50 to 115 nm range. From the nanoparticle size distributions and scanning electron microscopy images it results that a population of small nanoparticles with the size of several nanometers was confirmed if the nanoparticles were stabilized with gemini molecules with either a short methylene spacer (two or four CH2 groups) or a long spacer (12 CH2 groups). The average zeta potential value for silver nanoparticles stabilized with gemini molecules is roughly independent of gemini surfactant spacer length and is approx. +58 mV. An interaction model between silver nanoparticles and gemini molecules which reflects the gained experimental data, is suggested. Microbicidal activity determinations revealed that the silver nanoparticles stabilized with gemini surfactants are more efficient against Gram-negative bacteria and yeasts, which has a direct relation to the interaction mechanism of nanoparticles with the bacterial cell membrane and its structural composition.