Miroslav Cieslar

Polypyrrole–silver composites prepared by the reduction of silver ions with polypyrrole nanotubes

Polypyrrole nanotubes were prepared by the oxidation of pyrrole with iron(III) chloride in the presence of methyl orange. They were subsequently used for the reduction of silver ions to silver nanoparticles. The nanotubular form of polypyrrole is compared with the classical globular morphology in its ability to reduce silver ions. Both polypyrrole salts and bases were used in the experiments. The content of metallic silver in the resulting composite, determined by thermogravimetric analysis, was 21–31 wt%. Elemental composition is also discussed on the basis of energy-dispersive X-ray spectroscopy. Contrary to the expectation, the conductivity of polypyrrole nanotubes in salt form, 35.7 S cm−1, was reduced to 20.9 S cm−1 after the incorporation of silver. The presence of silver had generally little effect on the conductivity. The temperature dependence of conductivity reveals that the composites maintain the semiconducting character of polypyrrole and their conductivity increased with increasing temperature. The conductivity of the composites surprisingly increased when the samples were placed in vacuo.

Assessment of the Al Corner of the Ternary Al–Fe–Si System

The present work provides a review of the information available on the Al-rich corner of the Al–Fe–Si system as well as a CALPHAD type assessment making use of the COST 507 database as a starting point. The description of the intermetallic compounds has been modified to account for substitution of Al and Si in the ternary Al-Fe-Si system and to take new experimental information into account.

The influence of alloy composition on phase transformations and recrystallization in twin-roll cast Al-Mn-Fe alloys

Twin-roll casting (TRC) is an advantageous substitution for Direct-Chill (DC) casting in the manufacturing of rolled aluminium products. The results of a study of the phase transformations and their interaction with recrystallization occurring during the annealing of TRC Al-Mn based alloys are reported. Four alloys with different contents of Mn, Si and Fe were investigated. Precipitation was studied by resistometric measurements in the course of a heating at linear rate. The microstructural processes responsible for the observed changes in resistivity were identified by TEM examinations of quenched specimens. The changes in the microstructure and solute content during homogenisations at 450°C and 610°C were monitored by conductivity and hardness measurements and polarised light microscopy. It was elucidated that the temperature and kinetics of phase transformations are influenced not only by the content of Mn, but also by Si content. In alloys with low Si content, the decomposition of solid solution and the transformation of primary phases occur in much larger temperature range than in the alloys with high Si content. The precipitation of Mn and Si, concurrent to recrystallization, was observed to retard the latter, especially in alloys with high Mn and Si content.

The influence of Cr and Ce additions on the mechanical properties of Fe3Al based alloys

Abstract The influence of Cr and Ce solutes on the hardness evolution of an Fe–28 at.% Al alloy during isothermal and isochronal annealing in the temperature range 300–1000°C was studied. In the Cr-containing alloys, Cr–Fe–(C) precipitates were found after hot working and cooling. These precipitates were dissolved during annealing at 1000°C for 2 h. Subsequent isothermal and isochronal annealing caused their reprecipitation starting above 300°C. Preferentially they nucleate on dislocations, nearest-neighbor antiphase boundaries and subgrain and grain boundaries. It appears that the precipitate formation decreases the hardness of the alloy. The Ce addition and the Ce-containing particles influence neither the formation of Cr–Fe–(C) precipitates nor the evolution of hardness of the alloy.

Multi-wall carbon nanotubes with nitrogen-containing carbon coating

Polyaniline coating was deposited on the surface of multi-wall carbon nanotubes of Russian and Taiwanese origin in situ during the polymerization of aniline. The deposited polyaniline film was subsequently carbonized under an inert atmosphere at various temperatures to produce coaxial coating of the carbon nanotubes with nitrogen-containing carbon. The new materials were investigated by infrared and Raman spectroscopies, which demonstrated the conversion of the polyaniline coating to a carbonized structure. X-ray photoelectron spectroscopy proved that the carbonized overlayer contains nitrogen atoms in various covalent bonding states. Transmission electron microscopy confirmed the coaxial structure of the composites. The Brunauer-Emmett-Teller method was used to estimate the specific surface area, the highest being 272 m2 g−1. The conductivity of 0.9–16 S cm−1 was measured by the four-point method, and it was only a little affected by the carbonization of the polyaniline coating.

Positron-Lifetime Investigation of Thermal Stability of Ultra-Fine Grained Nickel

Thermal stability of ultra-fine grained (UFG) nickel (mean grain size 114 nm) prepared by high pressure torsion was studied by means of positron-lifetime spectroscopy (PLS) combined with TEM. The experimental results obtained by PLS are interpreted using the diffusion trapping model, which allows for determination of important physical parameters characterizing the specimens. The microstructure of the material studied is strongly inhomogeneous. The grain interiors with low dislocation density are separated by distorted regions with high numbers of dislocations. We have found that positrons are trapped at dislocations inside the distorted regions and in the microvoids situated inside the grains. Structure evolution with increasing temperature was studied in details using isochronal annealing of the specimen. We have found that recovery of the UFG structure involves the abnormal grain growth followed by further recrystallization in the whole volume of samples. It was shown that PLS is sensitive to structure changes, caused by the magnetostriction phenomenon.

The influence of processing route on the plastic deformation of Al-Zn-Mg-Cu alloys

Abstract A fine-grained microstructure of Al–Zn–Mg–Cu alloys was produced by several processing routes — by thermomechanical treatment of conventionally cast ingots, by modern powder metallurgy, and by severe plastic deformation in equal channel angular pressing. The plastic deformation of these materials was investigated in a temperature range between 523 and 773 K and the deformation characteristics were correlated with the results of microstructure investigation. The grain size and its stability at elevated temperatures were found to play the decisive role in the deformation behaviour of the alloys studied.

Precipitation in the Fe–28Al–4Cr intermetallic alloy with Ce addition ☆

Abstract Annealing experiments were carried out in order to determine the temperature range for the existence of Cr–Fe–(C) and Ce-containing particles found in the structure of a hot-extruded Fe–28Al–4Cr–0.1Ce (at.%) alloy. The carbon content in the Cr–Fe–C particles ranges from 15 to 30 at.%., the Cr:Fe ratio in the matrix and grain boundary variant of the particles is 7:3, and 6:4, respectively. Cr–Fe particles without carbon were also found. The matrix Cr–Fe–(C) precipitates form as rods or rhomboidal platelets, the grain boundary particles are thin platelets of irregular shape. All Cr–Fe rich particles are completely dissolved after annealing for 2 h at 950°C, and they reappear when the quenched alloy is heated in the temperature range from 300 to 800°C. At 700°C the precipitate is already formed after 5 min of annealing. The Ce-containing particles, mostly 1–10 μm in diameter, present a broad range of compositions. Nevertheless, more than half of the analyzed particles were identified as the Fe 17 Ce 2 compound. The Ce-containing particles do not dissolve even after annealing for 6 h at 1175°C.

Investigation of spatial distribution of defects in ultra-fine grained copper

Ultra-fine grained copper prepared by high pressure torsion has been studied by means of slow positron implantation spectroscopy with Doppler broadening measurement. In addition, conventional positron lifetime and Doppler broadening spectroscopy have been utilised. Defects present in the specimens were identified, their spatial distribution and depth profile have been determined. The results are discussed in correlation with those obtained by XRD and TEM.

The influence of dispersoids on the recrystallization of aluminium alloys

Abstract The influence of dispersoids on the softening processes in twin-roll cast and cold-rolled Al – Fe – Mn – Si aluminium alloy was studied. Before rolling, the specimens were thermo-mechanically pre-treated in order to create a different second-phase dispersion. The influence of the initial microstructure was studied by means of electrical resistivity, light and electron microscopy. The evolution of softening was monitored by microhardness measurements. The depletion of the Al matrix from solutes connected with formation of a dense dispersion of precipitates results in the enhancement of (sub)grain-boundary mobility. As a consequence, full recrystallization occurs at lower temperatures in pre-annealed specimens with low solute concentrations. The presence of coarser precipitates formed during the pre-treatment results in the formation of a fine-grained microstructure.