Thermal Stability and Phase Transformations of Multicomponent Iron-Based Amorphous Alloys

Due to their excellent functional properties enabling their applicability in different fields of modern technology, amorphous alloys (metallic glasses) based on iron have been attracting attention of many scientists. In this chapter, the results of multidisciplinary research of five multicomponent iron-based amorphous alloys with different chemical composition, Fe81Si4B13C2, Fe79.8Ni1.5Si5.2B13C0.5, Fe75Ni2Si8B13C2, Fe73.5Cu1Nb3Si15.5B7, and Fe40Ni40P14B6, are summarized in order to study the influence of chemical composition on their physicochemical properties and functionality. The research involved thermal stability, mechanism, thermodynamics, and kinetics of microstructural transformations induced by thermal treatment and their influence on functional properties. Determination of crystallization kinetic triplets of individual phases formed in the alloys is also included. The results obtained for different alloys are compared, correlated, and discussed in terms of the alloy composition and microstructure

Thermal stability and mechanism of thermally induced crystallization of Fe73.5Cu1Nb3Si15.5B7 amorphous alloy

Investigation of thermal stability of the alloy revealed stepwise crystallization process, manifested by two distinct complex exothermic peaks in differential scanning calorimetry curves. Kinetic parameters of individual crystallization steps were found using the Kissinger and Vyazovkin methods. Structural characterization of thermally treated samples showed formation of different iron-based phases including α-Fe(Si), Fe2B, Fe16Nb6Si7 and Fe2Si and some metastable intermediary species. Morphology characterization of the surface and cross-section of the thermally treated samples showed granulated structure composed of several different phases and indicated occurrence of impingement effects during crystal growth. Value of estimated lifetime suggested very high stability against crystallization at room temperature and abrupt decrease of lifetime with temperature increase

Influence of synthesis parameters and thermal treatment on functional properties of Fe3O4-BaTiO3 multiferroics obtained by mechanical activation

Mechanical activation of a mixture of polycrystalline powders Fe3O4 (50% wt.) and BaTiO3 (50% wt.) was performed in a planetary ball-mill, with different milling times (3 h, 6 h and 12 h). Average crystallite size determined by XRD analysis ranges from 12 to 30 nm, depending on the milling time. The activated powders were pressed into disc-shaped samples, 8 mm in diameter and 1.5 mm thick, applying the pressure of 500 MPa,. Thermoelectric measurements conducted in the temperature range from room temperature to 350 °C revealed that the electrical resistivity of the sample depends on temperature and activation time. At room temperature, the maximum value of specific electrical resistivity (ρ0 = 1 MΩm) was observed for the sample obtained by pressing the powder activated for 6 h. Magnetic properties of pressed powder samples were studied using a modified Faraday method. At room temperature, the pressed powder activated for 3 h exhibited the maximum value of magnetization, M0= 0.86 Am2/kg. Multiple heating of the pressed samples, for 10 min, was performed in a magnetic field of 20 KA/m. After cooling, the highest magnetization values were observed for the samples previously heated at 380 °C, while the maximum one (M’= 1.04 Am2/kg) corresponds to the sample activated for 3 h

Synthesis of BaFe12O19-BaTiO3 multiferroics by mechanical activation

A mixture of polycrystalline powders of Fe (70 % wt.) and BaTiO3 (30 % wt.) was ball-milled in a planetary mill under air atmosphere, for different time intervals: 60, 120, 180, 240, 300 and 360 min. During the mechanical activation, the powder was exposed to oxygen from the air, resulting in formation of iron oxides: FeO and then Fe2O3 and Fe3O4. XRD and SEM analyses of the activated powders revealed that the weight fraction of the iron oxides in the mixture and microcrystal size depend on the activation time. For the powders activated for different time intervals, average crystallite size (Dhkl), dislocation density (ρn) and average microcrystal size of BaTiO3 and Fe were determined. In order to investigate the influence of thermally induced structural changes on magnetic properties, the change of magnetic properties of the pressed activated powders during multiple heating in a magnetic field of 10KA/m was measured. Maximum magnetization of the samples was reached after heating at 620 K. Pressed powder samples were sintered at temperatures of 1100 oC and 1200 °C for 2h giving the different phase diagrams. The samples sintered at 1100 oC include BaTiO3, BaFe12O19 and BaFeO2,67 as the dominant components. The samples sintered at 1200 °C containing only two components, BaTiO3 and BaFe12O19, exhibited pronounced ferromagnetic and ferroelectric propertie

Vodonična veza u push-pull 5-supstituisanim 2-alkiliden-4-oksotiazolidinima: 1H-NMR spektroskopsko proučavanje

Application of dynamic H-1-NMR spectroscopy added to the understanding of the hydrogen bonds existing in the structurally related 5-substituted-2-alklidene-4-oxothiazolidines in polar and apolar solvents. The equilibrated mixtures of these topical push-pull alkenes in CDCl3 consist of the intramolecularly H-bonded (E)-isomer and intermolecularly H-bonded (Z)-isomer in varying proportions which depend on the solvent polarity. For the representative of the series. (Z)-2-(5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone, a concentration effect on the degree of intermolecular hydrogen bonding in apolar CDCl3 has been studied.Primenom dinamičke 1H-NMR spektroskopije došlo se do boljeg razumevanja o vrsti vodoničnih veza koje postoje u strukturno sličnim 5-supstituisanim 2-alkiliden-4-oksotiazolidinima u polarnim i apolarnim rastvaračima. Uravnotežene smese ovih tipičnih push-pull alkena u CDCl3 sadrže (E)-izomer vezan intramolekulskom vodoničnom vezom kao i intermolekulski vodoničnom vezom vezan (Z)-izomer u različitim odnosima, koji zavise od polarnosti rastvarača. U slučaju tipičnog predstavnika serije (Z)-2-(5-etoksikarbonilmetil-4-oksotiazolidin- 2-iliden)-1-feniletanona uticaj koncentracije na stepen stvaranja intermolekulske vodonične veze u apolarnom CDCl3 je takođe proučavan

Hydrogen storage in a layered flexible [Ni2(btc)(en)2]n coordination polymer

[Ni2(btc)(en)2]n coordination polymer exhibits a layered two-dimensional structure with weak interaction between the layers. Correlation of experimental measurements, DFT calculations and molecular simulations demonstrated that its structural features, primarily the inherent flexibility of the layered polymeric structure, lead to improved hydrogen storage performance at room temperature, due to significant enhancement in isosteric heats of hydrogen adsorption. Volumetric measurements of hydrogen adsorption at room temperature show up to 0.3 wt.% hydrogen absorbed at 303 K and 2.63 bar of hydrogen pressure, with isosteric heats of adsorption of about 12.5 kJ mol−1. Predicted performance at room temperature is 1.8 wt.% at 48 bar and 3.5 wt.% at 100 bar, better than both MOF-5 and NU-100, with calculated values of isosteric heats for adsorption of hydrogen in 8–13 kJ mol−1 range at both 77 K and 303 K. Grand canonical Monte Carlo calculations show that this material, at 77 K, exhibits gravimetric hydrogen densities of more than 10 wt.% (up to 8.3 wt.% excess) with the corresponding volumetric density of at least 66 gL−1, which is comparable to MOF-5, but achieved with considerably smaller surface area of about 2500 m2 g−1. This study shows that layered two-dimensional MOFs could be a step towards MOF systems with significantly higher isosteric heats of adsorption, which could provide better room temperature hydrogen storage capabilities.This is the peer reviewed version of the following article: Blagojević, V.A., Lukić, V., Begović, N.N., Maričić, A.M., Minić, D.M., 2016, “Hydrogen storage in a layered flexible [Ni2(btc)(en)2]n coordination polymer”, International Journal of Hydrogen Energy, http://dx.doi.org/10.1016/j.ijhydene.2016.08.20

Microstructure and crystal growth in thermally treated Fe73,5Cu1Nb3Si15,5B7 alloy

Thermal treatment of Fe73.5Cu1Nb3Si15.5B7 amorphous alloy induces structural changes, including crystallization of several different phases and subsequent crystal growth. X-ray diffraction combined with differential scanning calorimetry were used to investigate these, to determine kinetic parameters and mechanism of individual steps, and the dimensionality of crystal growth using Matusita-Sakka method and texture analysis. It was found that after the alloy becomes fully crystalline, crystal growth of individual phases is, in general, impeded, leading to decreased dimensionality of growth. However, this does not impact the texture, due to lack of preferred direction of crystal growth.Physical chemistry 2012 : 11th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 24-28 September 201