On the basis of dielectric measurements performed in a wide temperature range (173–373 K), a comprehensive analysis of the dielectric and electrical properties of magnetite nanoparticles electrical conduction mechanism of compressed spherical shaped Fe3O4 nanoparticles was proposed. The electrical conductivity of Fe3O4 nanoparticles was related to two different mechanisms (correlated barrier hopping and non-overlapping small polaron tunneling mechanisms); the transition between them was smooth. Additionally, role of grains and grain boundaries with charge carrier mobility and with observed hopping mechanism was described in detail. It has been confirmed that conductivity dispersion (as a function of frequencies) is closely related to both the long-range mobility (conduction mechanism associated with grain boundaries) and to the short-range mobility (conduction mechanism associated with grains). Calculated electron mobility increases with temperature, which is related to the decreasing value of hopping energy for the tunneling of small polarons. The opposite scenario was observed for the value of electron hopping energy.

The HR3C is a new steel for pressure components used in the construction of boilers with supercritical working parameters. In the HR3C steel, due to adding Nb and N, the compounds such as MX, CrNbN and M23C6 precipitate during service at elevated temperature, resulting in changes in mechanical properties. This paper presents the results of microstructure investigations after ageing at 650, 700 and 750 °C for 5,000 h. The microstructure investigations were carried out using scanning and transmission electron microscopy. The qualitative and quantitative identification of the existing precipitates was carried out using X-ray analysis of phase composition. The effect elevated temperature on microstructure and mechanical properties of the examined steel was described.

This paper presents the evaluation of durability for the material of repair welded joints made from (13HMF) 14MoV6-3 steel after long-term service, and from material in the as-received condition and after long-term service. Microstructure examinations using a scanning electron microscope, hardness measurements and creep tests of the basic material and welded joints of these steels were carried out. These tests enabled the time of further safe service of the examined repair welded joints to be determined in relation to the residual life of the materials. The evaluation of residual life and disposable life, and thus the estimation and determination of the time of safe service, is of great importance for the operation of components beyond the design service life. The obtained test results are part of the materials' characteristics developed by the Institute for Ferrous Metallurgy for steels and welded joints made from these steels to work under creep conditions.

The work presents the research results of modern composite materials. The matrix material was EN AC AlSi12 alloy while the reinforcement ceramic preforms, obtained through sintering process of Al2O3 Alcoa CL 2500 powder with addition of carbon fibers as pore forming agent burned out during sintering. The composites were produced with use of porous material pressure infiltration method. The main limitation of base technology is a difficulty in obtaining composite materials with volumetric participation of ceramic phase in amount not less than 20%. Obtained on the base of ceramic preforms composite materials were tested with scanning electron microscopy. Additionally, hardness and tensile test was performed for acquired materials. Achieved results indicate the possibility of producing, with use of pressure infiltration method, porous preforms composed of Al2O3 particles, new composite material with desired microstructure and properties, being a cheaper alternative for materials with base of ceramic fibers.

The purpose of this work was to elaborate the method of manufacturing of composite materials based on porous mullite preforms infiltrated by AlSi12 aluminium alloy. The process of manufacturing the metal matrix composites by pressure infiltration is the subject of many scientific studies because it is characterized by high efficiency and allows for accurate mapping of elements of shape and surface of elements, while the structure and properties of the composites are determined by ceramic skeletons. The eutectic aluminium alloy AlSi12 was used as a matrix while as a reinforcement were used ceramic preforms fabricated by sintering of halloysite nanotubes (HNT) powder with an addition of carbon fibres as pore forming agents. The observations of the structure were made on the light microscope and in the scanning electron microscope. The developed technology of manufacturing of composite materials with the pore ceramic mullite infiltration ensures the expected structure and can be used in practice. The composite materials made by the developed method can find application as an alternative material for elements fabricated from light metal matrix composite material reinforced with ceramic fibrous preforms.