Anna Przybył

The approach advanced by Harrison puts in the spotlight the fundamental role of bistability in hysteresis modeling. The description is based on physical premises concerning irreversible thermodynamics. In the original model, the upscaling of irreversible phenomena acting on the micromagnetic level is carried out by the introduction of a phenomenological parameter β. In the present paper, an alternative approach is proposed. The outputs of individual outputs of elementary hysteresis units (hysterons) are considered like in the stop model. A verification of the proposed model is carried out using measurement data for a praseodymium–dysprosium ribbon sample and a cylinder core made of cobalt-based amorphous material.

In the present paper, the phase structure, magnetic properties, and magnetization reversal processes in the (Nd10Fe67B23)93Nb7 alloy ribbon were investigated. The X-ray diffraction analysis revealed a coexistence of the following phases: hard magnetic Nd2Fe14B, metastable soft magnetic Nd2Fe23B3, and paramagnetic Nd1+εFe4B4. Moreover, the changes in phase composition were noticed after heat treatment. In order to check magnetic measurements, the hysteresis loops were collected. The magnetization reversal curves were studied by constructing the reversible part of magnetization dependence on the irreversible part of magnetization.

In the present paper, the influence of partial substitution of Mn by Pd on structure, thermomagnetic properties, and phase transitions in the MnCoGe alloys was investigated. The studies of phase constitution revealed an occurrence of the orthorhombic TiNiSi-type and hexagonal Ni₂Ti- type phases. Deep analysis of the XRD pattern supported by the Rietveld analysis allowed us to notice the changes in lattice parameters and quantity of recognized phases depending on the Pd content. An increase of palladium in alloy composition at the expense of manganese induced a rise in the Curie temperature. The values of ΔS_M measured for the variation of external magnetic field ~5 T equaled 8.88, 23.99, 15.63, and 11.09 for Mn_0.97Pd_0.03CoGe, Mn_0.95Pd_0.05CoGe, Mn_0.93Pd_0.07CoGe, and Mn_0.9Pd_0.1CoGe alloy, respectively. The highest magnetic entropy change ΔS_M was observed for samples with Pd content x = 0.05 induced by magnetostructural transformation. The analysis of the n vs. T curves allowed confirmation of the XRD and DSC results of an occurrence of the first-order magnetostructural transition in Mn_0.95Pd_0.05CoGe and Mn_0.93Pd_0.07CoGe alloys samples.

Magnetic properties of hard magnets are currently attracting a great deal of attention. In the paper, the modified Harrison model was used to describe the saturating hysteresis loops of three praseodymium–dysprosium ribbons that differed in their chemical composition and processing conditions. Microstructural studies (TEM and diffraction patterns) were performed for the ribbons under consideration. The Harrison model incorporates a number of physically tangible concepts such as the anhysteretic curve, bifurcations, and bi-stability. The modification of the original approach consisted of adding an additional degree of freedom in the modeling by freeing the restraints present in the original version, in which both coercivity and remanence are functions of temperature only.

The aim of this work was to investigate the effect of partial substitution of Mn by Nb on structure and thermomagnetic properties in the (Mn, Nb)-Co-Ge alloy. The master alloys were prepared by arc-melting in an arc furnace with high purity of constituent elements under a low pressure of Ar. The prepared specimens were studied in as-cast state. The X-ray was performed by BRUKER D8 Advance diffractrometer with Cu Kα radiation. The analysis of the XRD pattern revealed coexistence of two orthorhombic phases with different lattice constants. The analysis of the temperature dependence of magnetizaton confirmed the XRD results and showed that produced material manifested two magnetic phase transitions corresponding to detected phases. The values of the Curie temperature were 275 and 325 K. The values of magnetic entropy change ∆SM equaled 3.30 and 2.13 J/(kg K), respectively for recognized phases. Biphase structure of produced material allowed to reach relatively high refigeration capacity 307 J/(kg). Moreover, the analysis of field dependences of magnetic entropy change (∆SM = CBn) allowed to construct temperature dependence of exponent n. The analysis of elaborated n vs. T curve confirmed biphasic structure of produced material.

In the past decades, Mg alloys have been studied intensively as potential orthopedic applications. The present research work, the FEA of the obtained contact stresses in the case of the load applied on Mg-0.5Ca-xMn alloys has been investigated. It has been used the NCB Curved Femur Shaft Plate type as a model in order to establish the necessary modeling parameters. The objective of the present work was to highlight the strain values at the contact point on the surface of the Mg-0.5Ca-xMn alloys. The results showed that the highest stresses observed near the gaps of the plate and in the screws. It means that all mechanical loads are sustained by the plate and screws, and the patient’s femur can be recovered.

This study aims to obtain the relationship between density and compressive strength of foamed concrete. Foamed concrete is a preferred building material due to the low density of its concrete. In foamed concrete, the compressive strength reduces with decreasing density. Generally, a denser foamed concrete produces higher compressive strength and lower volume of voids. In the present study, the tests were carried out in stages in order to investigate the effect of sand–cement ratio, water to cement ratio, foam dosage, and dilution ratio on workability, density, and compressive strength of the control foamed concrete specimen. Next, the test obtained the optimum content of processed spent bleaching earth (PSBE) as partial cement replacement in the foamed concrete. Based on the experimental results, the use of 1:1.5 cement to sand ratio for the mortar mix specified the best performance for density, workability, and 28-day compressive strength. Increasing the sand to cement ratio increased the density and compressive strength of the mortar specimen. In addition, in the production of control foamed concrete, increasing the foam dosage reduced the density and compressive strength of the control specimen. Similarly with the dilution ratio, the compressive strength of the control foamed concrete decreased with an increasing dilution ratio. The employment of PSBE significantly influenced the density and compressive strength of the foamed concrete. An increase in the percentage of PSBE reduced the density of the foamed concrete. The compressive strength of the foamed concrete that incorporated PSBE increased with increasing PSBE content up to 30% PSBE. In conclusion, the compressive strength of foamed concrete depends on its density. It was revealed that the use of 30% PSBE as a replacement for cement meets the desired density of 1600 kg/m³, with stability and consistency in workability, and it increases the compressive strength dramatically from 10 to 23 MPa as compared to the control specimen. Thus, it demonstrated that the positive effect of incorporation of PSBE in foamed concrete is linked to the pozzolanic effect whereby more calcium silicate hydrate (CSH) produces denser foamed concrete, which leads to higher strength, and it is less pore connected. In addition, the regression analysis shows strong correlation between density and compressive strength of the foamed concrete due to the R² being closer to one. Thus, production of foamed concrete incorporating 30% PSBE might have potential for sustainable building materials.

The preparation of polystyrene/thermoplastic starch (PS/TPS) blends was divided into three stages. The first stage involved the preparation of TPS from sago starch. Then, for the second stage, PS was blended with TPS to produce a TPS/PS blend. The ratios of the TPS/PS blend were 20:80, 40:60, 60:40, and 80:20. The final stage was a modification of the composition of TPS/PS blends with succinic anhydride and ascorbic acid treatment. Both untreated and treated blends were characterized by their physical, thermal, and surface morphology properties. The obtained results indicate that modified blends have better tensile strength as the adhesion between TPS and PS was improved. This can be observed from SEM micrographs, as modified blends with succinic anhydride and ascorbic acid had smaller TPS dispersion in PS/TPS blends. The micrograph showed that there was no agglomeration and void formation in the TPS/PS blending process. Furthermore, modified blends show better thermal stability, as proved by thermogravimetric analysis. Water uptake into the TPS/PS blends also decreased after the modifications, and the structural analysis showed the formation of a new peak after the modification process.

This paper clarified the microstructural element distribution and electrical conductivity changes of kaolin, fly ash, and slag geopolymer at 900 °C. The surface microstructure analysis showed the development in surface densification within the geopolymer when in contact with sintering temperature. It was found that the electrical conductivity was majorly influenced by the existence of the crystalline phase within the geopolymer sample. The highest electrical conductivity (8.3 × 10⁻⁴ Ωm⁻¹) was delivered by slag geopolymer due to the crystalline mineral of gehlenite (3Ca₂Al₂SiO₇). Using synchrotron radiation X-ray fluorescence, the high concentration Ca boundaries revealed the appearance of gehlenite crystallisation, which was believed to contribute to development of denser microstructure and electrical conductivity.