Martensitic transformation, magnetic entropy, and adiabatic temperature changes in bulk and ribbon Ni48Mn39.5Sn12.5−xInx (x = 2, 4, 6) metamagnetic shape memory alloys

Martensitic transformation, magnetic entropy, and direct adiabatic temperature changes in Ni48Mn39.5Sn12.5− xInx (x = 2, 4, 6) metamagnetic Heusler bulk and grain-constrained ribbon alloys were studied. All alloys showed a typical L21 structure in austenite and the 4O structure in martensite. Their relative volume contributions changed depending on In content. With increasing In concentration, the martensitic transformation temperature increased, whereas the Curie temperature of austenite decreased. The magnetic entropy change under magnetic field of 5 T attained maximum of 20 J/kgK in the bulk and 14.4 J/kgK in the ribbon alloys with the Ni48Mn39.5Sn8.5In4 nominal composition. The corresponding adiabatic temperature change under 1.7 T yielded 1.3 K for the Ni48Mn39.5Sn8.5In4 bulk alloy. Despite grain confinement, melt spinning was found to stabilize martensite phase. Changes observed were discussed with relation to strengthened covalency imposed by In substitution

Structure and magnetic properties of thermodynamically predicted rapidly quenched Fe85-xCuxB15 alloys

In this work, based on the thermodynamic prediction, the comprehensive studies of the influence of Cu for Fe substitution on the crystal structure and magnetic properties of the rapidly quenched Fe85B15 alloy in the ribbon form are performed. Using thermodynamic calculations, the parabolic shape dependence of the DGamoprh with a minimum value at 0.6% of Cu was predicted. The DGamoprh from the Cu content dependence shape is also asymmetric, and, for Cu = 0% and Cu = 1.5%, the same DGamoprh value is observed. The heat treatment optimization process of all alloys showed that the least lossy (with a minimum value of core power losses) is the nanocomposite state of nanocrystals immersed in an amorphous matrix obtained by annealing in the temperature range of 300–330 C for 20 min. The minimum value of core power losses P10/50 (core power losses at 1T@50Hz) of optimally annealed Fe85-xCuxB15 x = 0,0.6,1.2% alloys come from completely different crystallization states of nanocomposite materials, but it strongly correlates with Cu content and, thus, a number of nucleation sites. The TEM observations showed that, for the Cu-free alloy, the least lossy crystal structure is related to 2–3 nm short-ordered clusters; for the Cu = 0.6% alloy, only the limited value of several -Fe nanograins are found, while for the Cu-rich alloy with Cu = 1.2%, the average diameter of nanograins is about 26 nm, and they are randomly distributed in the amorphous matrix. The only high number of nucleation sites in the Cu = 1.2% alloy allows for a sufficient level of grains’ coarsening of the -Fe phase that strongly enhances the ferromagnetic exchange between the -Fe nanocrystals, which is clearly seen with the increasing value of saturation induction up to 1.7T. The air-annealing process tested on studied alloys for optimal annealing conditions proves the possibility of its use for this type of material

Probing the interactions of phenol with oxygenated functional groups on curved fullerene-like sheets in activated carbon

The mechanism(s) of interactions of phenol with oxygenated functional groups (OH, COO and COOH) in nanopores of activated carbon (AC) is a contentious issue among researchers. This mechanism is of particular interest because a better understanding of the role of such groups in nanopores would essentially translate to advances in AC production and use, especially in regard to the treatment of organic-based wastewaters. We therefore attempt to shed more light on the subject by employing density functional theory (DFT) calculations in which fullerene-like models integrating convex or concave structure, which simulate the eclectic porous structures on AC surface, are adopted. TEM analysis, EDS mapping and Boehm titration are also conducted on actual phenol-adsorbed AC. Our results suggest the widely-reported phenomenon of decreased phenol uptake on AC due to increased concentration of oxygenated functional groups is possibly attributed to the increased presence of the latter on the convex side of the curved carbon sheets. Such a system effectively inhibits phenol from getting direct contact with the carbon sheet, thus constraining any available π–π interaction, while the effect of groups acting on the concave part of the curved sheet does not impart the same detriment

Effect of Cryogrinding on Chemical Stability of the Sparingly Water-Soluble Drug Furosemide

Purpose To investigate the effect of cryogrinding on chemical stability of the diuretic agent furosemide and its mixtures with selected excipients. Methods Furosemide was ground at liquid nitrogen temperature for 30, 60, 120 and 180 min. Mixtures of furosemide-PVP and furosemide-inulin (1:1) were milled under cryogenic conditions. Materials were analyzed by XRD, UPLC, MS and NMR. Results Upon increasing the milling time, a significant build-up of an unidentified impurity 1, probably the main degradation product, was noticed. Cogrinding of furosemide with PVP and inulin worsened chemical stabilization of the pharmaceutical. The main degradation product formed upon cryomilling was subsequently identified as 4-chloro-5-sulfamoylanthranilic acid (CSA). Based on some theoretical considerations involving specific milling conditions, the milling intensity and an expected specific milling dose have been calculated. Results indicate that cryogenic grinding is capable to initiate mechanically induced decomposition of furosemide.Conclusions Cryogenic grinding can activate and accelerate not only structural changes (solid state amorphization) but also chemical decomposition of pharmaceuticals. A cryogenic milling device should be considered as a chemical reactor, where under favourable conditions chemical reactions could be mechanically initiated

The Structure and Magnetic Properties of Rapidly Quenched Fe72Ni8Nb4Si2B14 Alloy

The complex structural and magnetic studies of the annealed rapidly quenched Cu-free Fe72Ni8Nb4Si2B14 alloy (metallic ribbons form) are reported here. Based on the calorimetric results, the conventional heat treatment process (with heating rate 10 °C/min and subsequent isothermal annealing for 20 min) for wound toroidal cores has been optimized to obtain the least lossy magnetic properties (for the minimum value of coercivity and magnetic core losses at 50 Hz). For optimal conditions, the complex permeability in the 104–108 Hz frequency range together with core power losses obtained from magnetic induction dependence up to the frequency of 400 kHz was successfully measured. The average and local crystal structure was investigated by the use of the X-ray diffraction method and the transmission electron microscopy observations and proved its fully glassy state. Additionally, for the three temperature values, i.e., 310, 340 and 370 °C, the glass relaxation process study in the function of annealing time was carried out to obtain a deeper insight into the soft magnetic properties: magnetic permeability and cut-off frequency. For this type of Cu-free soft magnetic materials, the control of glass relaxation process (time and temperature) is extremely important to obtain proper magnetic properties

Simulation study of topological point defects in graphitic layer - curvature effect and pair correlation function analysis

The effect of three types of topological defects, single vacancy, double vacancy and the Stone-Thrower-Wales defect on the atomic arrangement in a single graphitic layer is studied using computer simulations. The topological defects were positioned on the perfect hexagonal graphitic layer 20 Å in diameter with different distance from the layer edge and then the geometry of the system was independently optimized using the reactive bond order potential, the semi-empirical quantum-chemical PM7 and the density functional theory method. Curvature and the distortion of the graphitic layer caused by the defects are analyzed and their influence on the pair correlation function is discussed