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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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    The field of solid solutions in ternary system of synthetic apatite-type alkaline earth element-yttrium-silicate oxybritholite phases of the composition: AEE(delta)Y(10-delta)[SiO4](6)O3-0.5 delta, where AEE=Ca, Sr and Ba
    (Elsevier Ltd, 2016-01-08) Ptáček, Petr; Opravil, Tomáš; Šoukal, František; Tkacz, Jakub; Másilko, Jiří; Bartoníčková, Eva
    This contribution deals with the synthesis, properties and investigation of the field of solid solutions formed between the three end-members of apatite-type alkaline earth element-yttrium-silicate oxybritholites with the hexagonal structure (P6(3)/m). The stoichiometric composition of these compounds corresponds to the formula AEE(delta)Y(10-delta)(SiO4)(6)O3-0.5 delta, where AEE=Ca, Sr and Ba and parameter delta -> 2. These compounds and their solid solutions crystallize from non-equilibrium high temperature flux as the main product of sinter-crystallization process. Increasing ionic radius of AEE cations has significant effect to the lattice parameters, properties and miscibility of apatite phases. While there is non-limited miscibility of solid solutions formed between Ca2Y8[SiO4](6)O-2 and Sr2Y8[SiO4](6)O-2, the highest content of barium in the binary solution with these species is limited to 28% and 38%, respectively. The connecting line of these points marks out the borderline for the field of solid solutions in the ternary system. All attempts for the preparation of pure Ba2Y8[SiO4](6)O-2 end-member via the ceramic method were not successful.
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    Determination of Critical Parameters of Drug Substance Influencing Dissolution: A Case Study
    (Hindawi Publishing Corporation, 2014-09-15) Bojňanská, Erika; Kalina, Michal; Pařízek, Ladislav; Bartoníčková, Eva; Opravil, Tomáš; Veselý, Michal; Pekař, Miloslav; Jampílek, Josef
    The purpose of this study was to specify critical parameters (physicochemical characteristics) of drug substance that can affect dissolution profile/dissolution rate of the final drug product manufactured by validated procedure from various batches of the same drug substance received from different suppliers.The target was to design a sufficiently robust drug substance specification allowing to obtain a satisfactory drug product. For this reason, five batches of the drug substance and five samples of the final peroral drug products were analysed with the use of solid state analysis methods on the bulk level. Besides polymorphism, particle size distribution, surface area, zeta potential, and water content were identified as important parameters, and the zeta potential and the particle size distribution of the drug substance seem to be critical quality attributes affecting the dissolution rate of the drug substance released from the final peroral drug formulation.
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    The formation of feldspar strontian (SrAl2Si2O8) via ceramic route: Reaction mechanism, kinetics and thermodynamics of the process
    (Elsevier, 2016-05-15) Ptáček, Petr; Šoukal, František; Opravil, Tomáš; Bartoníčková, Eva; Wasserbauer, Jaromír
    The reaction mechanism, the equilibrium composition, the temperature range of stability of formed intermediates as well as the kinetics and thermodynamics of activated state during the formation of monoclinic strontium-aluminum-silicate feldspar stroncian (SrAl2Si2O8) via the ceramic route from the mixture of SrCO3, Al2O3 and SiO2 is described in this work. Strontian does not appear up to the temperature of 1150 degrees C and is the only stable phase at the temperature >= 1600 degrees C. Three independent reactions lead to two parallel reaction pathways, i.e. the formation of strontian from single or binary oxides (1) and with Sr-gehlenite as the intermediate (2). Since the reaction rate constants ratio is higher than one (k(1)/k(2) > 1), the first reaction route is favored according to the Wegscheider principle. The kinetics of chemical reaction of 1.5 order corresponding to the kinetic function F-2/3 ((1 - alpha)(-1/2) - 1) was determined as the rate determining the mechanism of formation of strontian. The integral and differential methods show that the process requires average apparent activation energy of 229.3 kJ mol(-1). The determined average value of frequency factor is 2.1 x 10(5) S-1
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    The effect of heat-treatment on properties of Ni-P coatings deposited on AZ91 magnesium alloy
    (MDPI, 2019-07-23) Buchtík, Martin; Hasoňová, Michaela; Másilko, Jiří; Wasserbauer, Jaromír
    The present study reports the effect of phosphorus content in deposited electroless nickel (Ni–P) coatings, the heat treatment on the microhardness and its microstructural characteristics, and the influence of the temperature on the microstructure of the Mg alloy substrate during the heat treatment. The deposition of Ni–P coatings was carried out in the electroless nickel bath, and the resulting P content ranged from 5.2 to 10.8 wt.%. Prepared samples were heat-treated in the muffle furnace at 400 °C for 1 h after the coating deposition. The cooling of the samples to room temperature was proceeded in the air. For as-deposited and heat-treated samples, it was determined that with the increasing P content, the microhardness was decreasing. This may be caused by the changes in the structure of the Ni–P coating. The X-ray diffraction patterns of the as-deposited Ni–P coatings showed that the microstructure changed their nature from crystalline to amorphous with the increasing P content. The heat treatment of prepared samples led to the significant increase of microhardness of Ni–P coatings. All the heat-treated samples showed the crystalline character, regardless of the P content and the presence of hard Ni3P phase, which can have a positive effect on the increase of microhardness. The metallographic analysis showed changes of substrate microstructure after the heat treatment. The prepared coatings were uniform and with no visible defects