Dariusz Kata

Rotary jet-spinning of hematite fibers

This work presents fabrication of purely ceramic submicron fibers by rotary jet-spinning – a recently developed method. An inertial force is used to form fibrous jets made of viscous dispersions, which then solidify during solvent evaporation. Precursor suspensions were prepared with the use of water as the only solvent, non-toxic Fe2O3 ceramic powder and poly(ethylene oxide) – a fiber-forming agent. The obtained fibers were in the range of 0.2–1.4 µm in diameter. This work presents a concept that utilizes ceramic fibers that could potentially be used for arsenic removal based on adsorption-enhanced filtration. We prove that ceramic fibers can be formed by simply adding non-agglomerated particles to a polymer solution. The nonwoven fiber-based approach will allow higher flow rates of the filtrate during purification and enable heat treatment for cleaning the filters. However, by changing the type of particles and/or preparing a mixture of them, the application range of the final product can be significantly broadened.

Thermal properties of AlN polycrystals obtained by pulse plasma sintering method

Aluminum nitride (AlN) polycrystals were prepared by pulse plasma sintering (PPS) technique. The starting AlN powder mixtures were composed with 3.0 wt%, 5.0 wt% and 10 wt% of yttrium oxide (Y2O3), respectively. Relative density of each polycrystal was measured by hydrostatic method and evaluated higher than 97%. X-ray diffraction (XRD) method was used for phase examination of the samples after heat treatment. Microstructure examination supported by computer-aided analysis was performed by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results were correlated with thermal conductivity of the samples carried out by laser pulse method (LFA). The influence of the rapid sintering technique and yttrium oxide additive content on the thermal conductivity and microstructure appearance of AlN polycrystals was clearly shown.

Methodology for determining material constants of anisotropic materials belonging to the transversely isotropic system by ultrasound method

The paper presents the methodology and results of the ultrasound determination of material constants of anisotropic materials belonging to the transversely isotropic system. Ultrasound through-transmission method was used for determining material constants. Based on the measurements of velocities of longitudinal and transverse ultrasounds waves propagation, respectively polarized in required directions all the elastic and the material constant of the test materials were determined. Measurements of all the velocities necessary to determine the elastic constants were performed on a specially prepared individual samples. The tests were carried out on porous polycrystalline anisotropic graphites of anisotropy in Youngs modulus of up to 26% and Al2O3 composites with up to 30% of hBN causing anisotropy of Youngs modulus of up to 50%. It was found that for all tested samples the value of Youngs modules and modules stiffness decreasing with increasing porosity in the graphites and increasing content of hBN in Al2O3.

Grain-Boundary Interaction between Inconel 625 and WC during Laser Metal Deposition

In this study, the laser metal deposition (LMD) of the Inconel 625–tungsten carbide (WC) metal matrix composite was investigated. The composite coating was deposited on Inconel 625 substrate by powder method. A powder mixture containing 10 wt% of WC (5 µm) was prepared by wet mixing with dextrin binder. Coating samples obtained by low-power LMD were pore- and crack-free. Ceramic reinforcement was distributed homogenously in the whole volume of the material. Topologically close-packed (TCP) phases were formed at grain boundaries between WC and Inconel 625 matrix as a result of partial dissolution of WC in a nickel-based alloy. Line analysis of the elements revealed very small interference of the coating in the substrate material when compared to conventional coating methods. The average Vickers hardness of the coating was about 25% higher than the hardness of pure Inconel 625 reference samples.

The adsorption of polystyrene nanoparticles on selected commercially available fibers: a streaming potential study:

The article describes the analysis of the adsorption properties of commercially available fibers. Negatively charged polystyrene particles were used for the adsorption on the selected fibers at different pH ranges of the used electrolyte. The streaming potential method proved useful in the assessment of the electrokinetic properties of the fibers. As expected, good adsorption was observed for most fibers that were positively charged in the conditions of the experiments due to electrostatic attraction. Interestingly, for some fibres an increase in zeta potential was observed in the conditions in which both the adsorbent and the adsorbate were negatively charged. An explanation was proposed for this phenomenon, but could not be proved. The adsorption in the conditions of the isoelectric points of the fibers resulted in little to no changes in their zeta potential in most cases. Moreover, in some cases, the adsorption study produced scattered and irreproducible results. This behavior may have its origin in the nature of the selected fibers, which were mostly technical fibers for applications in fields other than adsorption.

In search of the elusive IrB{sub 2}: Can mechanochemistry help?

We produced hexagonal ReB2-type IrB2 diboride and orthorhombic IrB monoboride phases, that were previously unknown and saw them produced by mechanochemical syntheses. High energy ball milling of elemental Ir and B powder for 30 h, followed by annealing of the powder at 1050 °C for 48 h, resulted in the formation of the desired phases. Both traditional laboratory and high resolution synchrotron X-ray diffraction (XRD) analyses were used for phase identification of the synthesized powder. Additionally, scanning electron microscopy and transmission electron microscopy were employed, along with XRD, to further characterize the microstructure of the phases produced.

Synthesis of ceramic-based porous gradient structures for applications in energy conversion and related fields

Porous, graded ceramic structures are of high relevance in the field of energy conversion as well as in catalysis, and additionally in filtration technology and in biomedical applications. Among different technologies for the tailored design for such structures we demonstrate here a new environmental friendly UV curing-based concept to prepare laminated structures with pore sizes ranging from a few microns up to 50 microns in diameter and with porosities ranging from 10% up to 75 vol.% porosity.

Composites Produced by SHS Method – Current Development and Future Trends

Basic stages of progress in composite materials, prepared by SHS method, from a scientific approach to a promising and rapidly developing applications are discussed in this paper. The systematic review of different forms of composites prepared directly by SHS or by SHS-origin precursors is presented. Powders are usually the starting material for manufacturing of ceramic and a lot of attention has been paid to find new routes for synthesis powders in form of nano or micro particles. The present work is aimed at efficient and convenient powder processing by SHS as an important target for future composites technology. The use of SHS may bring a considerable development in ceramic technology, by enabling a manufacturing of sinterable, high-purity nano or micro powders. It can be demonstrated in different ceramic systems explored by the authors and coworkers using SHS e.g. (a) Si-C-N, (b) Al-O-N as well as (c) Ti-Si-C-N. Rapid combustion conditions were successfully used to manufacturing composite powders and nanopowders suitable for preparing multiphase composite materials having controlled properties.