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Corrosion resistance of aluminum alloys
Kouba, Jan ; Pacal,, Bohumil (referee) ; Zmrzlý, Martin (advisor)
This diploma thesis deals with cerium-based conversion coatings for aluminium alloys. At first the mechanism of protection of metals by inhibitory substances is described in the theoretical section. The next chapter is devoted to application of lanthanide salts as cathodic corrosion inhibitors. Then the characterization of alloy AA 2024 follows. The main part is dedicated to the growth mechanism of the cerium-based mixed conversion coating on the alloy AA 2024. Finally, the factors affecting the character and the quality of obtained coatings are commented. In the experimental part an influence of the thermal activation together with the activation by a hydrogen peroxide was observed. The created film was characterized using SEM and EDS. The level of corrosion protection was evaluated by the polarization resistance measurement. erized using SEM and EDS. The level of corrosion protection was evaluated by the polarization resistance measurement.
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Magnetic properties of Ce compounds studied by specific heat
Čermák, Petr ; Javorský, Pavel (advisor)
Materials containing the 4f (rare earth) or 5f (actinides) exhibit a large variety of interesting physical properties. The Ce-based compounds have a special place among the rare-earth compounds. The Ce atom contains only a single f-electron that is responsible for the magnetic behavior. The 4f states in compounds with the heavy rare earths have a well localized character, whereas many Ce-based compounds are on the borderline between the localized and itinerant behavior. These compounds show large variety of the magnetic ground states what is a result of the competition between the long-range order of the RKKY type and the screening of the localized moments by conduction electrons. We observe nonmagnetic states with a mixed valence (between Ce3+ and Ce4+), metallic systems with a long-range order of the Ce moments (ferromagnetic, antiferromagnetic or more complex structures). To analyze the electronic properties, the heat capacity data, and namely their low-temperature part, play an indispensable role. This diploma work comprise the sample preparation of selected cerium compounds, their phase characteristics and the heat capacity measurements at low temperatures (0.4 - 300 K). The main part is focused on the data analysis and comparison with theoretical models.
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Physical phenomena in ytterbium- and cerium-based compounds
Fikáček, Jan ; Sechovský, Vladimír (advisor) ; Arnold, Zdeněk (referee) ; Andreev, Alexander (referee)
This work contains a study of CeRuSn, which undergoes two structural transitions at 290 K and 256 K both connected with large temperature hysteresis. During the transitions the lattice shrinks along the c axis. At low temperatures the compound orders antiferromagnetically below 2.8(1) K. A strong magnetocrystalline anisotropy is caused by very shortened Ce-Ru separations pointing approximately along the c axis. Due to a strong hybridization, two thirds of Cerium atoms are in a non integer valence state. For the first time synthesized single-crystals of YbPt2Si2 a Yb2Pt3Si5 show no magnetic ordering. A maximum, which is visible in the temperature dependences of magnetic susceptibility originate in thermal population of the magnetic Yb3+ state. Powered by TCPDF (www.tcpdf.org)
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Magnetic properties of Ce compounds studied by specific heat
Čermák, Petr ; Javorský, Pavel (advisor)
Materials containing the 4f (rare earth) or 5f (actinides) exhibit a large variety of interesting physical properties. The Ce-based compounds have a special place among the rare-earth compounds. The Ce atom contains only a single f-electron that is responsible for the magnetic behavior. The 4f states in compounds with the heavy rare earths have a well localized character, whereas many Ce-based compounds are on the borderline between the localized and itinerant behavior. These compounds show large variety of the magnetic ground states what is a result of the competition between the long-range order of the RKKY type and the screening of the localized moments by conduction electrons. We observe nonmagnetic states with a mixed valence (between Ce3+ and Ce4+), metallic systems with a long-range order of the Ce moments (ferromagnetic, antiferromagnetic or more complex structures). To analyze the electronic properties, the heat capacity data, and namely their low-temperature part, play an indispensable role. This diploma work comprise the sample preparation of selected cerium compounds, their phase characteristics and the heat capacity measurements at low temperatures (0.4 - 300 K). The main part is focused on the data analysis and comparison with theoretical models.
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Photoelectron spectroscopy study of adsorption on sputtered ceria films prepared in-situ
Duchoň, Tomáš ; Veltruská, Kateřina (advisor) ; Václavů, Michal (referee)
During this work CeOx films were prepared by magnetron sputtering on a graphite foil and a monocrystalline silicon wafer. Samples were characterised by the method of x-ray photoelectron spectroscopy in situ and then exposed to effects of the atmosphere. Influences of substrate, target substrate distance and duration of sputtering on stoichiometry of prepared films were observed. It was found out, that exposition to atmosphere reduces prepared films. Reduction was higher on films prepared on graphite foil and sputtered from greater distance.
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Corrosion resistance of aluminum alloys
Kouba, Jan ; Pacal,, Bohumil (referee) ; Zmrzlý, Martin (advisor)
This diploma thesis deals with cerium-based conversion coatings for aluminium alloys. At first the mechanism of protection of metals by inhibitory substances is described in the theoretical section. The next chapter is devoted to application of lanthanide salts as cathodic corrosion inhibitors. Then the characterization of alloy AA 2024 follows. The main part is dedicated to the growth mechanism of the cerium-based mixed conversion coating on the alloy AA 2024. Finally, the factors affecting the character and the quality of obtained coatings are commented. In the experimental part an influence of the thermal activation together with the activation by a hydrogen peroxide was observed. The created film was characterized using SEM and EDS. The level of corrosion protection was evaluated by the polarization resistance measurement. erized using SEM and EDS. The level of corrosion protection was evaluated by the polarization resistance measurement.
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