Papers by Author: Marcin Leonowicz

Abstract: A hydrogen-based treatment, including Hydrogen Decrepitation (HD) and Hydrogen Disproportionation-Desorption-Recombination (HDDR), was used as part of a recycling procedure for scrap neodymium-iron-boron magnets. Chemical methods of removing nickel coating out of magnets were tested, however ineffectively. Powders were obtained from magnets after the HD and were further processed by the HDDR. Finally, material with maximum energy product (BH)_max of 74 kJ/m³ was produced. Chemical composition of magnets (MS, EDS), magnetic properties (VSM) and microstructure observations (SEM) were carried out.

Abstract: Four alloys with nominal compositions Ni₄₆Mn_41.5-xFe_xSn_12.5 (x=0, 2, 4, 6 at.%) were cast in an induction vacuum furnace and homogenized. Then they were melted in quartz tubes and ejected onto a rotating copper wheel to produce ribbons. The X-Ray phase analyses of as melt spun ribbons have shown that in both, the ternary as well as in the quaternary alloys a single phase of the Heusler L2₁ type ordered structure was found. The characteristic temperatures of magnetic (T_C) and martensitic (M_s) transformations were determined by a vibrating sample magnetometer (VSM). Both the M_s and T_C increase with the increase of Fe content in all alloys, which is in accordance with the theory of valence electron concentration (e/a) influence on M_s. The phase structures, chemical compositions, grains sizes and type of microsegregation were characterized by transmission electron microscope (TEM). The equi-axed grains of size from 0.95 to 1.7 μm were observed in all ribbons. The grains posses the L2₁ structure at room temperature, however in the alloys with higher Fe content the different type of martensite was observed at the grain boundaries of L2₁ phase. Appearance of this martensite was explained in relation to microsegregation of particular elements during melt spinning process and simultaneous change in the e/a ratio.

Abstract: Two types of non-Newtonian fluids, magneto rheological (MRF) and shear thickening (STF) fluids, respectively were chosen as candidates for energy dissipation study in smart body armour. A series of magneto rheological fluids was synthesized on a basis of synthetic oil and carbonyl iron. The shear modules for the MRF containing 75 wt% of carbonyl iron, obtained in a magnetic field of 230 kA/m were as follows: complex shear modulus G* - 1.2 MPa, storage modulus G-1.2 MPa and loss modulus G 0.35 MPa. The studies revealed also that the silica fumed, dispersed in polypropylene glycol or polyethylene oxide, demonstrates shear thickening properties. The best combination of the properties (high viscosity, obtained at high shear rate) represents the material composed of the silica fumed (SF) and PEO300. Change of the volume fraction of the SF and variation of the molecular weight of the oligomer enables tailoring of the STF properties. Ballistic tests revealed that the structures containing PE bags with MRF (in magnetic field) or STF can enhance the protective performance of body armours providing their flexibility.

Abstract: Ferromagnetic or superparamagnetic nanocrystallites, stabilized in carbon matrix, were prepared by the procedure comprising formation of the appropriate metal acrylamide complex, followed by frontal polymerization and pyrolysis of the polymer. The pyrolysis products were in a form of beads, which contained in their volume randomly distributed nanocrystallites. The nanocrystallites had various composition, magnetic properties and sizes ranging from few to tens of nanometers, depending on the element type. Application of this procedure stabilizes the nanostructure and enables processing of nanoparticles within a narrow window of sizes. The magnetic parameters depend on the crystallite size, determined by their chemical composition. The nanocrystallites pyrolysed at 773 K exhibited ferromagnetic properties for Co and Fe, and superparamagnetic behaviour for the Ni. The nanocrystallites can potentially be applied as sensors for tagging the biological substances or for targeted drug delivery.

Abstract: Effect of annealing conditions on the structure and phase transition temperatures for polycrystalline Ni50Mn29Ga21 alloy was studied. The final structure strongly depends on the annealing temperature and cooling rate. Ordering of the austenitic phase, performed by annealing at elevated temperatures, plays an important role in formation of the proper martensitic structure. For the Ni50Mn29Ga21 alloy annealing below the ordering temperature (1033 K) forms 5M modulated martensitic structure, irrespective of the cooling rate. The 7M modulated martensitic structure can be produced after annealing above the ordering temperature, followed by slow cooling.

Abstract: The microstructure, texture and magnetic properties of two ferromagnetic alloys of composition Co35Ni37Al28 and Co37Ni35Al28 (in at. %) were investigated with optical microscopy (OM), analytical transmission electron microscopy (TEM), scanning electron microscopy (SEM) techniques as well as a vibrating sample magnetometer (VSM). The alloys were plastically deformed and heat treated in order to promote the martensitic transformation. Differential scanning calorimetry (DSC) revealed a drop of Ms temperature due to the increase of Co content in the alloys. The elongated twinned grains of size about 200 m and small precipitates of  phase were identified with the OM techniques. The TEM observations showed the twinned L10 non modulated martensite within the elongated grains and a small amount of ordered ’ phase after the heat treatment. The chemical composition of different martensite grains was established using point analyses of a HAADF-EDS technique. The magnetic phase transition temperatures were determined on the deformed samples using VSM method.

Abstract: In this study the hydroxyapatite powder was sintered together with magnetite nanopowder, which due to its low reactivity is commonly used in medicine, eg. in magnetic resonance. Two types of sintered materials, containing equal content 6 mol% of biogenic hydroxyapatite (BGHAp), reinforced with 50 wt% of different glass phases, were tested. The same technological conditions comprising two-stage sintering with T1 (1100°C) and T2 (780°C) were used for both types of materials. For selected specimens 2 wt% of 9 nm powder of Fe3O4 was added. The microhardness of the specimens varies within quite wide range from 150 to 508 HV0.025. Compressive splitting strength of the specimens (measured along the sample diameter) is within a range of 3.61 – 4.99 MPa. Young’s modulus, modulus of rigidity and Poisson’s ratio are in the ranges of: 20.81 – 24.86 GPa, 7.89 – 9.71 GPa and 0.252 – 0.307, respectively. Indentation fracture toughness KIC is within a range of 0.6-1.0 MPa m1/2. The hysteresis loops were determined in order to asses the possibility of application of this material as affecting the drug delivery carriers. The specimens exhibit magnetization of the order of 1.5 emu/g.

Abstract: The formation of novel carbon nanostructures containing Fe-Nd-B nanocrystallites is reported. Tests were performed in a DC arc plasma reactor under He atmosphere using (Fe-Nd-B)- filled anodes. The influence of the operational parameters pressure and anode composition on the product morphology was studied. The products were analyzed by HR TEM, MFM and magnetic measurements. Emission spectroscopy was performed to determine the temperature and C2 radical distribution in the arc.