Rafał Wróblewski

Microstructure-property relationships of urethane magnetorheological elastomers

Studies on the structure of urethane magnetorheological elastomers (MREs), with respect to their magnetic and mechanical properties, are reported. MREs were obtained from a mixture of polyurethane gel and carbonyl-iron particles cured in a magnetic field of 100 and 300 mT. Samples with different numbers of particles (1.5, 11.5 and 33 vol%) were produced. The microstructure and magnetic properties of the obtained MREs were studied. Also, the displacement of the samples in an external magnetic field was examined using a specially designed experimental set-up. The influences of the number of ferromagnetic particles and their arrangement in relation to the external magnetic field were investigated. It was found that the microstructure of the MREs depends on the number of ferrous particles and the fabrication conditions. The orientation of the iron particles into aligned chains is possible for a lower volume content of the ferromagnetic fillers. The high carbonyl-iron volume content in the matrix leads to the formation of more complex microstructures, similar to three-dimensional lattices. The magnetic measurements also confirmed the existence of the microstructure anisotropy for the MREs with 1.5 and 11.5 vol% of iron particles. The structural and magnetic anisotropy has not been found in the MREs with 33 vol% of Fe. To evaluate the effect of the external magnetic field on the magnetorheological properties, the displacement under magnetic field, the compressive strength, and the rheological properties were measured. The experiments showed that both the particle content and the field strength used during curing have a significant effect on the microstructure of the MREs and, in consequence, on their properties.

Steric effects in alkylalane dioldiates [tBuAl(OC(CH3)2CH2C(CH3)2O)]2 a new (monoalkyl)alane O, O'-chelate complex

Abstract The dependence of the structure of alkylalane dioldiates on the steric bulk of the substituents on the aluminium, as well as steric hindrances of diol moiety is reported. Reactions of R3Al [where R=iBu, tBu] with 2,4-dimethylpentane-2,4-diol, butane-1,4-diol and propane-1,3-diol lead to the formation of alkylalane dioldiates, [tBuAl(OC(CH3)2CH2C(CH3)2O)]2 (1), iBu5Al3[(OC(CH3)2CH2C(CH3)2O)]2 (2) [tBu2Al(O(CH2)4OH)]2 (3), iBu5Al3(O(CH2)4O)2 (4) and tBu5Al3(O(CH2)3O)2 (5). The molecular structures of 1 and 3 have been determined by single crystal X-ray diffraction. In the reactions of iBu3Al with diols the trinuclear complexes of the general formula [R5Al3(diol(2H))2] (2 and 4) are formed irrespective of the diol moiety steric hindrances. tBu3Al reacts with diols to yield the products depending on the length of diol backbone and steric hindrances of the diol moiety. The interaction of the sterically crowded 2,4-dimethylpentane-2,4-diol with tBu3Al gives the new (monoalkyl)alane O,O′-chelate complex 1. In the case of unhindered aliphatic diols like butane-1,4-diol and propane-1,3-diol, the compound 3 with the strong intra-molecular hydrogen bonding interaction and the trimetallic compound 5 were obtained, respectively.

Effect of the processing conditions on the microstructure of urethane magnetorheological elastomers

The aim of the study was to develop an innovative processing method of magnetorheological elastomers (MRE). This method comprises optimization of the MRE structure in the context of their performance in the magnetic field. The influence of the amount of ferromagnetic particles and their arrangement in relation to the external magnetic field was investigated. As matrixes various elastomers, with different stiffness, were used. Their properties were compared with commercially available silicone rubbers. It was found that the structure of the MRE produced depends on the viscosity of the matrix before curing and the magnetic field strength applied. Two different magnetic field strengths were used: 100 and 300 mT. The amount of the carbonyl iron particles was equal to 1.5, 11.5 and 33.0 vol. %. Scanning electron and light microscopy techniques were used for the MRE microstructure observations. The influence of curing conditions on the thermal properties of the MRE was investigated. To evaluate the external magnetic field effect on the magnetorheological properties a deflection under magnetic field was measured. The experiment showed that application of the magnetic field increases stiffness of the material.

Magnetic and Martensitic Transformations in Ni46Mn41.5-xFexSn12.5 Melt Spun Ribbons

Four alloys with nominal compositions Ni46Mn41.5-xFexSn12.5 (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 (TC) and martensitic (Ms) transformations were determined by a vibrating sample magnetometer (VSM). Both the Ms and TC 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 Ms. 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.

Modification of the properties of Ni-Mn-Ga magnetic shape memory alloys by minor addition of terbium

Effect of terbium addition on the structure, phase constitution and hardness of the Ni49Mn29Ga22 alloy was studied. The Tb content varied in the range of 0-2 at.%. It was found that the Tb addition substantially refines the grain size, which dropped from 200-400 μm, for the Tb-free alloy, down to 30-50 μm for the 2 at.% Tb material. The terbium exhibited negligible solubility in the matrix phase and formed grain boundary layer. The mean composition of the boundary layer was: Tb - 16, Ni - 55, Mn - 7 and Ga - 22 at.%. The phase analysis revealed the presence of the following major phases in the alloys: Ni2MnGa, Ni3Ga. All the alloys studied exhibited martensitic structure at room temperature. The Tb addition did not affect the Curie temperature, which is consistent with the finding that Tb does not dissolve in the Ni2MnGa phase. However, it was found that Tb addition changed the phase transformations temperatures. The As temperature (martensite-to-austenite transformation starting temperature) and Ms temperature (martensite-to-austenite starting temperature) grow slightly for low Tb concentrations and subsequently decrease for higher the Tb contents. The Tb containing alloys exhibited increased hardness, by about 40%, which was apparently caused by the grain refinement. No significant effect of the Tb addition on the magnetic shape memory effect was observed.

Microstructure and Magnetic Properties of Two Phase β+γ Ferromagnetic Co-Ni-Al Alloys

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.

Effect of Annealing Conditions on the Structure of Ni50Mn29Ga21 Shape Memory Alloy

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.