Rheological Characteristics of Fe-C-Cr(Ni) Alloys.

The principal objective of this project was to investigate the rheological properties of Fe-C-Cr and Fe-C-Ni-based low-alloy steels using an Anton Paar high-temperature rotational viscometer up to 1550 °C. The emphasis was placed on determining the liquidus temperatures and evaluating the flow and viscosity curves and the temperature dependence of dynamic viscosity. All were studied depending on the change in the content of chromium (0.010-4.863 wt%), nickel (0.001-4.495 wt%), and carbon (0.043-1.563 wt%). It was shown that the dynamic viscosity decreases with increasing nickel content and increases with increasing carbon and chromium content. The experimental data of the flow curves were fitted using the Herschel-Bulkley model with a good agreement between the measured and calculated values. Characterization of the internal structure was performed by SEM and EDX analyses, confirming non-significant changes in the microstructure of the original and remelted samples. The phase composition of the selected samples was also determined using JMatPro 12.0 simulation software (Sente Software Ltd., Guildford, UK).

The Effect of Trace Oxygen Addition on the Interface Behavior of Low-Alloy Steel.

This work aims to assess the effect of an oxygen content graded in minimal quantities, on the order of hundreds of ppms, on the determination of surface tension of low-alloy FeCOCr and FeCONi steels in contact with a corundum substrate. Oxygen, as a surface-active element, was segregated at the surface where it interacted with the major components of the alloys, leading to a reduction in surface tension. The sessile drop method was used for wetting tests in the temperature range from steel liquidus temperatures to 1600 °C under nonoxidizing conditions. The effect of oxygen on surface tension and wetting angles was verified by statistical analysis using the Kruskal-Wallis test, which supported the results stating that the values of these quantities decreased with increasing oxygen content. Furthermore, liquidus temperatures, which are of practical importance, were determined by the optical and DTA methods and then compared with theoretically calculated temperature values. It turned out that the increased chromium content causes difficulties in determining surface tension up to 1550 °C due to the formation of a thin Cr2O3 layer. In addition, SEM and XRD analyses accompanied by calculations in the FactSage oxide database were performed to better understand the wetting mechanism.

Synthesis of vacant graphitic carbon nitride in argon atmosphere and its utilization for photocatalytic hydrogen generation.

Graphitic carbon nitride (C3N4) was synthesised from melamine at 550 °C for 4 h in the argon atmosphere and then was reheated for 1-3 h at 500 °C in argon. Two band gaps of 2.04 eV and 2.47 eV were observed in all the synthetized materials. Based on the results of elemental and photoluminescence analyses, the lower band gap was found to be caused by the formation of vacancies. Specific surface areas of the synthetized materials were 15-18 m2g-1 indicating that no thermal exfoliation occurred. The photocatalytic activity of these materials was tested for hydrogen generation. The best photocatalyst showed 3 times higher performance (1547 µmol/g) than bulk C3N4 synthetized in the air (547 µmol/g). This higher activity was explained by the presence of carbon (VC) and nitrogen (VN) vacancies grouped in their big complexes 2VC + 2VN (observed by positron annihilation spectroscopy). The effect of an inert gas on the synthesis of C3N4 was demonstrated using Graham´s law of ammonia diffusion. This study showed that the synthesis of C3N4 from nitrogen-rich precursors in the argon atmosphere led to the formation of vacancy complexes beneficial for hydrogen generation, which was not referred so far.

Adsorption of nerve agent simulants onto vermiculite structure: Experiments and modelling.

Chemical warfare agents are still a threat to humanity despite the existence of a ban on their production and use. There are many new materials that have been experimentally verified to be effective in degrading and eliminating various chemical warfare agents; however, clay minerals still remain very effective, environmentally friendly and not expensive. Vermiculites modified with hexadecylpyridinium, hexadecyltrimethylammonium and tetramethylammonium cations were used for static sorption of vapours of two simulants of nerve agents: dimethyl methyl phosphonate and diethyl ethyl phosphonate. The materials before and after sorption were characterized using infrared spectroscopy, X-ray diffraction and carbon phase analysis. The breakthrough time and capture of simulants were measured using dynamic sorption test. Molecular modelling was used to confirm the experimental results and provide a deeper insight into the structure of the materials and sorption processes.

Polyaniline as a Precursor of Multi-Layer Graphene: Microscopic and Microspectroscopic Study.

Aluminosilicate-based nanocomposites containing multi-layer graphene were prepared from polyaniline/montmorillonite intercalate in two different forms: tablets and thin layers. Starting materials, polyaniline/montmorillonite powder and polyaniline/montmorillonite layers deposited on quartz glass, were prepared by in situ polymerization of aniline in presence of montmorillonite particles. Powder was compacted into tablets using pressure 400 MPa. Samples were calcined at 1300 °C in argon atmosphere and multi-layer graphene was formed from polyaniline in both cases as confirmed by Raman microspectroscopy. Changes in morphology and surface conductivity of uncalcined and calcined samples were observed using atomic force microscopy and conductive atomic force microscopy. Also the differences between surface and internal volume of tablets were studied. Conductive atomic force microscopy revealed that the most conductive areas can be found solely on the edges of aluminosilicate particles formed from montmorillonite during calcination process. Detailed observation of multi-layer graphene in these areas was performed using transmission electron microscopy.