Pokročilé keramické materiály
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- ItemCorrelation of Dielectric Properties and Vibrational Spectra of Composite PVDF/Salt Fibers(MDPI, 2024-08-26) Dallaev, Rashid; Sarkar, Ranjini; Selimov, Daud; Papež, Nikola; Kočková, Pavla; Schubert, Richard; Částková, Klára; Orudzhev, Farid; Ramazanov, Shihgasan; Holcman, VladimírNitride salts were added to polyvinylidene fluoride fibers and then the fiber mats were prepared by electrospinning. An experimental investigation of the structure was provided by Raman, FTIR, SEM, and XRD. The phase ratio of the polymer was studied both theoretically and experimentally in connection with the addition of the hydrates Mg(NO3)2, Ca(NO3)2, and Zn(NO3)2 salts. The com-parison of simulated and experimental data for vibrational spectroscopies is discussed. We provide a comparison of triboelectric, dielectric, and compositional characterization of PVDF fibers doped with three types of nitride hydrates. Doping of PVDF fibers with magnesium nitrate hexahydrate leads to significant improvement of the triboelectric performance.
- ItemOxidation Behavior and Outward Diffusion of Al Along Oxide Grain Boundaries of FeCrAl Alloys Overdoped with Zr and Hf(SPRINGER, 2024-02-01) Daradkeh, Samer Issa Abdel Razzaq; Recalde, Oscar; Mousa, Marwan Suleiman; Sobola, Dinara; Boll, TorbenThe formation of the alpha-Al2O3 scale on reactive element (RE)-doped FeCrAl alloys is commonly believed to be primarily caused by inward oxygen transport along grain boundaries. However, this study suggests that metal ion outward diffusion also plays a role in the development of the oxide scales and their microstructural characteristics. The study examines the oxidation behavior and grain boundary outward diffusion of iron-chromium alloys containing similar to 10 at% aluminum and similar to 22 at% chromium, doped with an over-critical concentration of REs, i.e., Zr and Hf. All samples were investigated after thermal exposure at 1100 degrees C by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atom probe tomography (APT). As a result of the overdoping, a considerable increase in oxide growth, an increase in the depth of internal oxidation, and RE-oxide formation near and at oxide grain boundaries (GBs) were observed as a consequence of increased inward and outward diffusion. The effect of overdoping manifests itself differently depending on the RE type and amount due to different solubility, ionic size, and electronic structure of alumina. The sample with Zr retained the adhesion of alumina to the alloy after the first and second thermal exposure, while Hf overdoping resulted in severe spallation after the second thermal exposure.
- ItemElectrical Characterization of Epoxy Nanocomposite under High DC Voltage(MDPI, 2024-04-01) Alsoud, Ammar Awadallah Ahmad; Daradkeh, Samer Issa Abdel Razzaq; Al-Bashaish, Saleh R.; Shaheen, Adel A; Ahmad, M D (Assa’d) Jaber; Abuamr, Adel M.; Mousa, Marwan Suleiman; Holcman, VladimírThis work studies the direct current breakdown characteristics of unfilled epoxy and epoxy nonconductive nanocomposites (SiO2,MgO and Al2O3). It also examines the variation of electrical properties in epoxy nanocomposites. The novel aspect of this study is that the samples of Epoxy nanocomposite were exposed to high voltages of up to six kilo volts for three hours using field electron microscopy under high vacuum conditions (10-5 mbar). The current emitted from these samples was measured at three different intervals of time. In addition, the influence of high voltage on the permittivity, loss factor (tan(delta)), and conductivity of the epoxy nanocomposite was studied. This evaluation was conducted before and after applying the voltage at room temperature, The frequency range extends from 10-2-10-7 Hz using the Novo Control Alpha-A analyzer. Current-voltage characterization was performed through field electron microscopy. The samples were characterized by scanning electron microscopy-energy dispersive X-ray spectroscopy and Fourier Transform Infrared Spectroscopy. The unfilled epoxy exhibited structural degradation, resulting in the formation of holes when exposed to high voltages of up to six kilo volts, leading to a reduction in electrical properties. Nevertheless, the addition of nanoparticles shows a significant increase in the operational lifetime of the epoxy nanocomposite. The degree of increase in the lifetime of epoxy composite varied depending on several factors such as the type of NPs introduced and their respective sizes. The epoxy/Al2O3 nanocomposite comparing with epoxy/MgO and epoxy/SiO2 nanocomposite showed elevated resistance to direct current breakdown strength and maintaining its dielectric.
- ItemStructural and electrical characterization of cadmium phosphate glasses doped with different concentration of sodium chloride(IOP Publishing, 2024-12-01) Assayed, Ghada A.I.; Shaheen, Adel A; Alsoud, Ammar Awadallah Ahmad; Al-Bashaish, Saleh R.; Mousa, Marwan Suleiman; Knápek, Alexandr; Sobola, DinaraThe electrical characteristics of cadmium phosphate glasses doped with varying concentrations of sodium chloride [ Cd-3( PO4)(2)](1-x) [ NaCl](x) , where x = 0, 2, 4 ,6 mol.% NaCl, were investigated with respect to both dopant levels and temperature. Electrical impedance spectroscopy was employed, and impedance measurements were taken across the frequency spectrum from 10(2) Hz to 10(6) Hz. Samples were characterized by scanning electron microscopy-energy dispersive x-ray spectroscopy, x-ray diffraction analysis and Fourier Transform Infrared Spectroscopy. The fi ndings revealed a decrease in bulk resistance with increasing temperature and dopant concentration, indicating a rise in DC- conductivity and suggesting a semiconducting behavior in the material. Moreover, the activation energy values were noted to decrease as dopant concentration increased. Analysis of the AC-conductivity variation with frequency delineated two distinct regions: a low-frequency region where AC-conductivity increased with frequency, indicative of a "pumping force" effect aiding charge carrier movement through various conduction states, and a high-frequency region or frequency-independent zone signifying a transition towards a more ohmic behavior in the material. The study highlighted a decrease in both the dielectric constant and dielectric loss with rising temperature and frequency across all dopant concentrations. Furthermore, the Reaction Coefficient "s" was found to be less than one, suggesting that the conduction mechanism can be elucidated in terms of the Correlated Barrier Hopping ( CBH ) model.
- ItemOptical Properties of Yttrium Ferrite Films Prepared by Pulse Laser Deposition(MDPI, 2024-11-18) Sobola, Dinara; Fawaeer, Saleh Hekmat Saleh; Kočková, Pavla; Schubert, Richard; Dallaev, Rashid; Trčka, TomášThis study investigates the optical properties of yttrium ferrite thin films fabricated via pulse laser deposition. Yttrium orthoferrite, a ferrimagnetic material known for its potential applications in spintronics and photonics, was deposited on single-crystal substrates under controlled conditions to analyze its optical characteristics. The influence of deposition time on the film quality and optical properties was examined. Atomic force microscopy in contact mode revealed surface roughness variations up to 35 nm, indicating the films' ability to cover substrate defects. Reflectance measurements determined the optical band gap, which decreased from 3.17 eV for thinner films (44 nm) to 2.91 eV for thicker films (93 nm). Forbidden electronic transitions were also observed, attributed to heteroepitaxial growth and phonon interactions. These results demonstrate the effect of film thickness on morphology and optical properties, making YFeO3 films promising for a range of optoelectronic applications.