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[en] The aim of present research was to measure and analyze the dynamic changes of internal pressure in shrinking vs. non-shrinking materials during convective drying for the use as a possible process control method. Drying experiments were carried out on wet and fired clay at 50°C and 60°C. In addition, the shrinkage curve was investigated. Experimental measurements show the existence of 4 stages of the process. The comparison of the results for wet and fired clay shows differences in pressure trends. During drying the internal pressure changes from underpressure to overpressure at the level of 3÷5kPa, what correlates well with transition from the first to the second drying period. (Author)
[en] Gypsum is a popular building material. Drying and rewetting of gypsum is a process of practical importance. This work presents the experimental results of kinetic of drying, heating and internal pressure development in rewetted gypsum cylinders. Analysis of the observed changes is presented. Additionally sorption isotherms, permeability and dependence of Young’s modulus on moisture content were measured. These data will be used in the model of the process under development. (Author)
[en] UTGe compounds form α-hydrides with a small H concentration and β-hydrides accommodating up to 2 H atoms/f.u. Hydrogen absorption has a significant impact on the 5f magnetism. The Curie temperature-TC of suspected ferromagnetic superconductor UCoGe increases to 50 K. Magnetic susceptibility of spin fluctuator UFeGe increases, but long-range magnetic order is not achieved. For ferromagnetic URhGe only α-hydride could be obtained, which moderate increase of TC and spontaneous moment. The α-hydride of UCoGe is surprisingly paramagnetic and non-superconducting despite of a small volume expansion (0.25 %).
[en] Hydrogen pressure of 0.5-140 bar has been applied to synthesize hydrides of UCoGe. Besides an α hydride crystallizing in the structure type of the parent compound, which loses the weak ferromagnetism found in pure UCoGe, two distinctly different β hydrides were identified. The almost pure β hydride (UCoGeH1.7) is a ferromagnet below TC = 50 K. The highest H2 pressures (>130 bar) produce admixture of another hydride called β′ hydride, with less H/f.u. and TC = 8 K, obtained presumably as a decay product of a full hydride UCoGeH2.0 unstable at ambient conditions. The value of the Sommerfeld coefficient of electronic specific heat γ increases over 100 mJ mol-1 K-2 for the magnetic hydrides. (paper)
[en] UTGe compounds absorb hydrogen up to 2 H atoms/f.u., which has a dramatic impact on the 5f magnetism. The TC value of UCoGe increases to 50 K. Magnetic susceptibility of spin fluctuator UFeGe markedly increases. For ferromagnetic URhGe only α-hydride could be obtained, which moderate increase of TC and spontaneous moment. The α-hydride of UCoGe is surprisingly paramagnetic despite of a small volume expansion (0.25 %).
[en] Polycrystalline and epitaxial U–Zr thin films have been grown on glass and single-crystal sapphire substrates using ultra-high vacuum magnetron sputtering at high temperatures (T = 800 °C). Mixed α- and γ-U phases were detected for polycrystalline U–Zr alloy thin films with the prevailing crystal structure controlled by composition. Epitaxial U–Zr thin film samples were determined to form bi-layered structures of single-crystal γ-U and α-U phases or γ-U, δ UZr2 and α-U phases depending on the concentration of the alloying element. (paper)
[en] High-pressure techniques were used to determine the structural behaviour of the superconducting ferromagnet UCoGe up to 30 GPa enabling us to determine the link between the effect of pressure on the material magnetic properties and crystal structure. The TiNiSi type structure of UCoGe was preserved up to the highest pressure. The a direction, equivalent to the shortest U-U links, was identified as the critical soft direction. The data are compared with the structural variations in UCoGe α-hydride, which becomes non-magnetic and non-superconducting despite a volume expansion. We show that at least in this case, but probably more generally, the structure impact of hydrogenation is definitely not equivalent to negative pressure.
[en] We have characterized UFe2+x films prepared by sputter deposition onto fused silica (SiO2) and Si(111) substrates with the film thickness ranging from 75 nm to 900 nm. The X-ray diffraction results showed an amorphous character of the deposited material. Some of the films showed in addition a pattern of highly textured cubic Laves phase. Rutherford Backscattering Spectroscopy with 2 MeV He+ ions has been used to determine the composition, thickness and concentration depth profile of the films. A large ageing affect was observed within 1 month after that the films were exposed to air. Magnetic measurements revealed TC increasing with relative Fe concentration and reaching approx. 450 K in UFe3.0.
[en] UFe2 is one of rare examples of combination of 3d and 5f magnetism in a compound with relatively high TC = 162 K. U-excess is known to reduce the TC value markedly. To prepare the Laves phase with an Fe excess is much more difficult. It can be achieved by sputter deposition, but the structure becomes amorphous. TC can increase at least to 240 K (for UFe4), but the segregation of α-Fe cannot be avoided for very high Fe concentrations.