Petr Sajdl

Cytocompatibility of plasma and thermally treated biopolymers

This paper is focused on the surface characterization of plasma and consequently thermally treated biocompatible polymers. PLLA (poly(L-lactide acid) and PMP (poly-4-methyl-1-pentene) are studied. The influence of Ar plasma treatment on the surface polarity of substrate measured immediately after treatment and during the polymer surface aging is studied. Surface roughness, morphology, wettability, and surface chemistry were determined. Plasma treatment leads to significant changes in PLLA surface morphology and chemistry, with the PMP being slightly affected. The higher resistance to plasma fluence results in smaller ablation of PMP than that of PLLA. The plasma treatment improves cell adhesion and proliferation on the PMP. Plasma treatment of PLLA influences mostly the homogeneity of adhered and proliferated VSMC.

Periodic nanostructure induced on PEN surface by KrF laser irradiation

There are several kinds of periodic surface structures, ranging from dots to ripples. The most common pattern is a ripple-like structure, where the direction of the ripples is parallel with the main polarisation of the laser beam. The distance between individual ripples (their period) depends on several factors, namely: the chemical structure of the polymer, wavelength of the laser irradiation and the angle of laser beam incidence. Oriented polyethylene naphthalate (PEN) foils with a thickness of 50 μm were used. The samples were irradiated with a KrF laser under laser beam incidence 0-45° to the laser beam. Selected polymer samples were also exposed by irradiation through a contact mask. Surface roughness and the dimensions of the ripple-like structures were measured by atomic force microscopy in tapping mode. The concentration of the elements on the surface was obtained from Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS) spectra measured by X-ray Photoelectron Spectroscopy (XPS) spectrometer. The surface morphology and dimensions of prepared structures were evaluated and compared with those prepared on pristine samples without mask. The transition between the irradiated surface under the slits and the shielded surface in between the slits was evaluated. The optimal input parameters for nanopattern with high periodicity were determined. The shape and the surface roughness of the ripple pattern depend strongly on the angle of incidence of the laser beam. The surface roughness and ripple width increase with the angle of laser beam incidence. Irradiation with laser leads to changes in chemical composition of the PEN surface layer. Even at initial phase of pattern formation a significant increase of carbonyl and carboxyl groups was detected.

Nanocrystalline diamond protects Zr cladding surface against oxygen and hydrogen uptake: Nuclear fuel durability enhancement

In this work, we demonstrate and describe an effective method of protecting zirconium fuel cladding against oxygen and hydrogen uptake at both accident and working temperatures in water-cooled nuclear reactor environments. Zr alloy samples were coated with nanocrystalline diamond (NCD) layers of different thicknesses, grown in a microwave plasma chemical vapor deposition apparatus. In addition to showing that such an NCD layer prevents the Zr alloy from directly interacting with water, we show that carbon released from the NCD film enters the underlying Zr material and changes its properties, such that uptake of oxygen and hydrogen is significantly decreased. After 100–170 days of exposure to hot water at 360 °C, the oxidation of the NCD-coated Zr plates was typically decreased by 40%. Protective NCD layers may prolong the lifetime of nuclear cladding and consequently enhance nuclear fuel burnup. NCD may also serve as a passive element for nuclear safety. NCD-coated ZIRLO claddings have been selected as a candidate for Accident Tolerant Fuel in commercially operated reactors in 2020.

Surface analysis of the Heusler Ni49.7Mn29.1Ga21.2 Alloy: The composition, phase transition, and twinned microstructure of martensite

Surface analysis was used to study the dynamics of the martensitic transformation on macro- and mesoscopic scales. The chemical state, morphology, and magnetic and surface structure were monitored at particular stages of the phase transition. At room temperature, the martensitic phase of the Ni49.7Mn29.1Ga21.2 (100) single crystal exhibited macroscopic a/c twinning and a corresponding magnetic domain structure characterized by magnetization vector in and out of the surface plane. Induced by radiation heating, the transformation from martensite to austenite takes place separately at the surface and in the bulk. Its dynamics depend on the history of the sample treatment which affects the crystallographic orientation of twins and minor changes of the surface stoichiometry. The interfaces (twin planes) between twin variants in the martensitic phase were noticeable also in the austenitic phase, thanks to the shape memory effect of this material.

Characterization of Surface Nanostructures on“Thin” Polyolephine Foils

Surface properties of nanostructures on 7 polyolephine foils were characterized using different analytical methods to discuss an effect of halogen presence in polymer chain to surface properties. Both sides of these foils were examined and compared. Surface roughness and morphology were determined by atomic force microscopy, contact angle by goniometry, surface polarity by electrokinetic analysis. X-ray photoelectron and ultraviolet visible spectroscopies were used for determination of surface chemistry. Combination of different analyses gives complex information about surface properties of the foils, which may be of importance for any future experiments, as well as for their application e.g. in tissue engineering and electronics.

Electrochemical Study of Pre ‐ and Post‐Transition Corrosion of Zr Alloys in PWR Coolant

Corrosion properties of Zr-Sn and Zr-Nb zirconium alloys were studied under simulated PWR conditions (or, more exactly, VVER conditions — boric acid, potassium hydroxide, lithium hydroxide) at temperatures up to 340°C and 15MPa using in-situ electrochemical impedance spectroscopy (EIS) and polarization measurements. EIS spectra were obtained in a wide range of frequencies (typically 100kHz — 100μHz). It enabled to gain information of both dielectric properties of oxide layers developing on the Zr-alloys surface and of the kinetics of the corrosion process and the associated charge and mass transfer phenomena. Experiments were run for more than 380 days; thus, the study of all the corrosion stages (pre-transition, transition, post-transition) was possible.

Corrosion protection of zirconium surface based on Heusler alloy

Abstract Fe and Si films were tested as corrosion protection layers for Zr in nuclear industry applications. Surface chemistry of Zr in dependence on the preparation conditions and layout of the films was complexly investigated by various spectroscopic and microscopic techniques. Corrosion experiments were carried out in autoclave conditions with in-situ Electrochemical Impedance Spectroscopy. A clean Zr surface is characteristic with disposition to disorder and rough morphology demonstrated in facets, steps or terraces. Upon deposition of Fe and Si atoms in amounts in the order of single monolayers and subsequent annealing at 400°C, the original (1×1) Zr surface structure rearranges into (2√3×2√3)R30°. Corrosion experiments show that a thicker Si overlayer successfully suppresses oxygen uptake of the underlying Zr material by forming a diffusion barrier. The barrier effect of the films was also confirmed for hydrogen.

Koroze slitin Zr–Nb a Zr–Sn za simulovaných podmínek reaktoru VVER

Abstract Oxidační kinetiku lze v případě koroze zirkoniových slitin rozdělit do dvou stádií, která jsou od sebe oddělená transientním stavem. Výskyt transientního stavu je z korozního hlediska klíčový, neboť při něm dochází ke zvýšení rychlosti oxidace. V této práci byly pomocí in-situ elektrochemické impedanční spektroskopie studovány slitiny zirkonia Zr–Nb a Zr–Sn při teplotě 340 °C a tlaku 15 MPa v prostředí, které simulovalo chladivo reaktoru VVER. Cílem dlouhodobých experimentů (až 9000 h) bylo charakterizovat oxidační kinetiku v závislosti na expoziční době a typu zirkoniové slitiny. Výsledky ukázaly, že za uvedených experimentálních podmínek dochází u slitiny zirkonia Zr–Sn k dřívějšímu dosažení přechodu, tzv. transientnímu stavu.

Testování mechanických vlastností Inconelu 713 a 738 pro pokročilé reaktory

Abstract Mezi kovové konstrukční materiály pro komponenty pokročilých plynem chlazených reaktorů patří niklové superslitiny Inconel 713 a 738. V rámci projektu aplikovaného výzkumu řešeného na VŠCHT Praha a CV Řež byly testovány mechanické vlastnosti těchto slitin ve výchozím stavu a po expozici vzorků v heliu obsahujícím stopové nečistoty (CO, H2, CH4, H2O) při teplotě 900 °C po dobu 1000 hod. Vzorky testovaných slitin byly vyrobeny: a) z původního litého materiálu (virgin), b) přepracovaného materiálu z výroby (revert 100R) a c) materiálu získaného slitím těchto materiálů v poměru 50V/50R. K určení mechanických vlastností materiálů po expozicích byly provedeny tahové zkoušky a strukturní analýza pomocí SEM. Porovnány byly změny vlastností po expozici jednotlivých testovaných slitin i stejné slitiny vyrobené různými postupy. Zatímco mez kluzu a mez pevnosti poklesly u Inconelu 713 jen zlehka, u Inconelu 738 poklesly výrazně. Stav 50V/50R vykazoval lepší mechanické vlastnosti než stav revert 100R.

Koroze slitin zirkonia v prostøedí vyšších koncentrací lithia/ Corrosion of zirconium alloys in the environments with elevated concentration of lithium

Série dlouhodobých in-situ experimentů byla zaměřena na studium negativního vlivu lithných iontů na dva typy slitiny zirkonia s niobem Zr1Nb. Chování slitin bylo sledováno pomocí in-situ aplikovaných elektrochemických metod v experimentální vysokotlaké - vysokoteplotní smyčce (280 °C, 8 MPa), umožňující cirkulaci média. Experimenty byly prováděny jak v prostředí, které simuluje běžné složení chladiva reaktoru typu VVER, tak v prostředí o vyšších koncentracích lithia (70 a 200 mg l-1 Li+ ve formě LiOH). V obou typech expozičního prostředí bylo cílem sledovat přenosové parametry oxidické vrstvy, změny v korozní rychlosti, difúzních parametrech a polovodivém charakteru oxidu. Z výsledků vyplynulo, že v prostředí vyšších koncentrací lithia dochází v době expozice 200 hodin ke zvyšování korozní rychlosti. Lithné ionty taktéž významně ovlivňují hustotu dopantů tedy polovodivé chování oxidické vrstvy zirkonia. Abstract A series of long-term in-situ experiments studied the negative impact of lithium ions on two types of zirconium-niobium alloys Zr1Nb. Behaviour of the alloys was monitored by in-situ applied electrochemical methods in an experimental high-pressure and high-temperature circuit (280 °C, 8 MPa) enabling media circulation. The experiments were executed in the environment that simulates standard composition of a coolant in both a water reactor and environments with elevated concentrations of lithium (70 and 200 mg l-1 Li+ in a form of LiOH). In both exposure environments, the goal of the experiments was to monitor transport parameters of the oxidic layer, changes in the corrosion rate, diffusion parameters and the oxide semi-conductive character. The results implied that the corrosion rate increases after 200 hours of exposure to environments with elevated concentration of lithium. Lithium ions substantially affect the density of dopants, i.e. the semi-conductive behaviour of the zirconium oxidic layer.