Juraj Ďurišin

Characterization of mechanochemically synthesized lead selenide

Mechanochemical synthesis of lead selenide PbSe nanocrystals was performed by high-energy milling of lead and selenium powders in a planetary ball mill. The structure properties of synthesized lead selenide were characterized by XRD analysis that confirmed crystalline nature of PbSe nanocrystals. Calculated average size of PbSe crystallites was 37 nm. The methods of particle size distribution analysis, specific surface area measurement, SEM and TEM were used for the characterization of surface and morphology of PbSe nanocrystals. SEM analysis revealed agglomerates of PbSe particles. However, HRTEM analysis confirmed perfect stoichiometric PbSe cubes with NaCl structure as well. UV-VIS-NIR spectrophotometry was used to confirm the blue shift of the small particles occurring in the powder product obtained by the mechanochemical synthesis.

VPS and reliability of solder joint

This paper deals with presentation of some new aspects of solder ternary alloy 96.5Sn3Ag0.5Cu (wt.%) - SAC305, in order to determine variations in mechanical properties and microstructure caused by treatment in vapour phase soldering (VPS) as well as by accelerated isothermal aging. These specimens have been melted and solidified on HASL (hot air solder levelling) and Ni/Au (ENIG) PCB (printed circuit board) substrate in order to prevent compositional changes due to interfacial reactions. Emphasis was placed on studying the effect of anomalous behaviours of intermetallic compounds Cu6Sn5 during ageing processes.

Mechanochemical synthesis of nanocrystalline lead selenide: industrial approach

Abstract Mechanochemical synthesis of lead selenide PbSe nanoparticles was performed by high-energy milling of lead and selenium powder in a laboratory planetary ball mill and in an industrial eccentric vibratory mill. Structural properties of the synthesized lead selenide were characterized using X-ray diffraction that confirmed crystalline nature of PbSe nanoparticles. The average size of PbSe crystallites of 37 nm was calculated from X-ray diffraction data using the Williamson – Hall method. The methods of particle size distribution analysis, specific surface area measurement, scanning electron microscopy and transmission electron microscopy were used for characterization of surface, mean particle size, and morphology of PbSe. An application of industrial mill verified a possibility of the synthesis of a narrow bandgap semiconductor PbSe at ambient temperature and in a relatively short reaction time.

Local structure of explosively welded titanium–stainless steel bimetal

Abstract Bimetals targeted for industrial applications are usually designed to combine the properties of two dissimilar metals, e.g. high strength, high hardness and low cost of steels with chemically resistive titanium. In this work the structure of one particular, but for industries very interesting, bimetallic system – Cr/Ni stainless steel clad with titanium has been studied. The material was prepared by explosion welding, a method capable of joining a wide variety of similar or dissimilar materials. Our analysis is based on X-ray micro-diffraction experimentation utilizing hard monochromatic X-rays focused down to micrometer size. In this way the bimetal in bulk form was analyzed and microstructural differences between the joined materials and their interface were determined.

Structural Analysis of Dispersion Strengthened Materials and Processes

Dispersion strengthened materials are characterized by high strength properties and good temperature stability of structure until to temperatures of 0.9 melting temperature of aluminium. Dispersion strengthened Al A14C3 materials are prepared by powder metallurgy way and the raw powder mixtures are generally consolidated by hot extrusion obtaining a fully dense material. This work is focused on a study of the microstructure in AI A14C3 materials containing 4 and 12 vol. % A14C3. The microstructure was analyzed by transmission electron microscopy and X-ray diffraction methods. The several microstructural features: morphology, size and distribution of particles of dispersoid, grain size and crystallite size of aluminium matrix, micro strain and dislocations density in materials were determined. The aim is an analysis of the effect of A14C3 amount on the microstructure formation during hot extrusion and analysis of the microstructure evolution at temperature loading and after cooling to ambient temperature. After hot extrusion the Al 12 vol. % A14C3 alloy is characterized by finer grains, higher micro strain and dislocations density and by a very low intensity of aluminium matrix deformation texture in comparison to Al 4 vol. % A14C3 material. In the hot extruded system with 4 vol. % A14C3 a strong deformation texture was observed. Therefore the amount of dispersoid strongly affects the formation of microstructures. The higher volume of A14C3 particles provides effective hindrance of the dislocations motion in Al matrix by the attractive interaction between dislocations and particles during extrusion. Both amounta of A14C3 dispersoid insure the thermal stability of microstructure of analyzed materials to 773 K.