Pavla Roupcová

Non-aqueous template-assisted synthesis of mesoporous nanocrystalline silicon orthophosphate

The first synthesis of mesoporous nanocrystalline silicon orthophosphate Si5P6O25 is presented. The synthetic procedure is based on the non-hydrolytic sol–gel reaction in the presence of Pluronic P123 template and subsequent calcination in air. The condensation of silicon acetate, Si(OAc)4, and tris(trimethylsilyl)phosphate, OP(OSiMe3)3 (TTP), in non-aqueous solvents driven by elimination of trimethylsilyl acetate provides a homogeneous network with a high content of Si–O–P bonds and SiO6 moieties. After burning out the template, mesoporous silicon orthophosphate was obtained with surface areas up to 128 m2 g−1 and pore sizes around 20 nm. The nanocrystalline Si5P6O25 phase forms relatively easily (500 °C, 4 h) in comparison with other synthetic routes. All samples were characterized by SEM, TEM, elemental analysis, TGA, nitrogen adsorption, SAXS, 1H, 13C, 29Si, and 31P solid-state NMR spectroscopy, and powder XRD. These xerogels showed superior catalytic activity and selectivity in methylstyrene dimerization.

Experimental Study of the Sb-Sn-Zn Alloy System

The Sb-Sn-Zn alloy was prepared and researched by experimental methods, which allow obtaining information on the thermodynamic stability of the coexisting phases. Thermal analysis was used to determine the phase transition temperatures of experimental alloys. Equilibrium composition of coexisting phases after long-term temperature equilibration was determined by electron microscopy. The existence of one ternary stoichiometric phase Sb2SnZn was experimentally confirmed by diffraction technique. The CALPHAD method for prediction of the phase diagram of the Sb-Sn-Zn system from binary subsystems was used in this work.

Towards near-permanent CoCrMo prosthesis surface by combining micro-texturing and low temperature plasma carburising

An advanced surface engineering process combining micro-texture with a plasma carburising process was produced on CoCrMo femoral head, and their tribological properties were evaluated by the cutting-edge pendulum hip joint simulator coupled with thin film colorimetric interferometry. FESEM and GDOES showed that precipitation-free C S-phase with a uniform case depth of 10μm was formed across the micro-textures after duplex treatment. Hip simulator tests showed that the friction coefficient was reduced by 20% for micro-metre sized texture, and the long-term tribological property of microtexture was enhanced by the C-supersaturated crystalline microstructure formed on the surface of duplex treated CoCrMo, thereby enhancing biotribological durability significantly. In-situ colorimetric interferometry confirmed that the maximum film thickness around texture area was 530nm, indicating that the additional lubricant during sliding motion might provide exceptional bearing life.

A Novel Composite Material Designed from FeSi Powder and Mn0.8Zn0.2Fe2O4 Ferrite

A design of the novel microcomposite material composed of spherical FeSi particles and Mn0.8Zn0.2Fe2O4 ferrite is reported together with a characterization of basic mechanical and electrical properties. The sol-gel autocombustion method was used for a preparation of Mn0.8Zn0.2Fe2O4 ferrite, which has a spinel-type crystal structure as verified by XRD and TEM analysis. The final microcomposite samples were prepared by a combination of the traditional PM compaction technique supplemented with unconventional microwave sintering process of the prepared green compacts. The composition and distribution of the secondary phase formed by the spinel ferrite were examined by SEM. It is demonstrated that the prepared composite material has a tight arrangement without any significant porosity, which manifests itself through superior mechanical properties (high mechanical hardness, Young modulus, and transverse rupture strength) and specific electric resistivity compared to the related composite materials including resin as the organic binder.

Magnetic properties of 42CrMo4 steel

Low alloyed high-grade chrome-molybdenum ferritic steel was investigated from the point of views of magnetic properties in dependence on heat and mechanical treatment. This steel can be used as components of magnetic circuits or some parts in electrical equipment. The basic information on structure and phase composition was obtained by optical and scanning electron microscopy, X-ray Powder Diffraction and Mossbauer Spectroscopy. The temperature stability of the material was proved by measurements of temperature dependences of magnetic moment. The magnetic parameters were obtained by measuring of magnetic hysteresis loops in dependence on saturation field and their frequencies. The results are discussed from the point of view of possible applications as a magnetic material in the very extremely environment, where high mechanical stresses and elevated temperatures can occur.

Thermally Induced Structural Transformations of Fe40Ni40P14B6 Amorphous Alloy

Thermal stability and thermally induced structural transformations of Fe40Ni40P14B6 amorphous alloy were examined under non-isothermal and isothermal conditions. Formation of metastable α-(Fe,Ni), and stable γ-(Fe,Ni) and (Fe,Ni)3(P,B) crystalline phases as the main crystallization products was observed, while the presence of small amounts of other crystalline phases like Fe23B6 and Fe2NiB was indicated by electron diffraction in HRTEM. Thermomagnetic curve indicated that Fe content in different crystalline phases is very different, resulting in markedly different Curie temperatures after crystallization. Transmission electron microscopy and atomic force microscopy study suggested multiple-layered platelet-shaped morphology, both on the surface and in the bulk of the crystallized alloy sample. The thermal treatment heating rate and maximum temperature affected surface roughness and grain size inhomogeneity.

Influence of long-term ageing upon the capacity of hydrogen storage in two novel Mg-Ni-In-C alloys

We have shown previously that the addition of In and C enhances the hydrogen desorption capacity and considerably improves the kinetics of hydrogen desorption from Mg-Ni based alloys, important from the perspective of hydrogen storage. In this paper, we present the results of tests of the long-term stability of the sorption behaviour of these materials. We studied how the capacity and sorption kinetics changed 5 years from the preparation of two chosen Mg-Ni-In-C alloys differing in indium concentration. Kinetic curves and PCT isotherms were measured at temperatures of 250–350◦C. It was found that long-term storage of the hydrogencharged samples led to no significant downgrade in hydrogen sorption kinetics. However, the absorption capacity somewhat decreased from about 5 wt.% H2 to about 3 wt.% H2 due to partial phase decomposition. Relatively intensive tentative oxidation during preparation, which had a slightly beneficial effect on the desorption rate of freshly-prepared samples, caused almost total blocking of hydrogen sorption in the aged samples. K e y w o r d s: hydrogen, hydrogen storage, magnesium alloys, indium

Spinodal decomposition of Ag-Cu nanoparticles

Ag-Cu nanoparticles (NPs) of near-eutectic composition were prepared by solvothermal synthesis at 230C from metallo-organic precursors in organic solvent. The nanoparticle size was measured by both dynamic light scattering (DLS) and small angle X-ray scattering (SAXS) method. The size and shape were evaluated by electron microscopy (SEM, TEM and HRTEM), the thermal properties were investigated by differential scanning calorimetry (DSC) and temperature controlled Xray diffraction method (XRD). HRTEM results show that AgCu nanoparticles with face centered cube (fcc) crystal lattice exist as a substitutional solid solution in contrast to bulk AgCu system, which reveals spinodal decomposition under eutectic temperature. The phase diagram respecting size of the AgCu NPs was calculated by the CALPHAD method using surface tension of the bulk Ag-Cu alloy in liquid and solid (fcc) states. The predicted eutectic melting point depression was not experimentally observed when the nanoparticles were melted by DSC. The samples melt at eutectic temperature exactly as bulk AgCu alloy. The microparticles consisting of the eutectic copper and silver rich phases were observed by SEM after melting. A spontaneous separation of copper and silver atoms was observed by temperature controlled X-ray diffraction method (XRD). The temperature treatment of the AgCu NPs showed that a spinodal decomposition and crystallinity changes (size evaluation using Scherrer equation) occur at a narrow range of temperature. The reason for the phenomenon observed can be the metastable state of the nanoparticles but there are also other unknown effects at the nano-scale level that hinder the Cu- and Ag-rich phase separation at low temperatures. The open question is also if the general equilibrium thermodynamics can be used to describe the AgCu NPs system under view.