The correlation of processes of crystallization and changes of free electron density amorphous alloy powder Co80Ni20

Great attention is being given today to investigations on the capabilities and structural changes of amorphous and nanocrystal materials. Structural changes of the amorphous cobalt and nickel alloy powder obtained by electrochemical deposition were investigated in this paper. The crystallization process, as determined by the DSC method, occurred in two steps. The temperature dependence of electrical resistively and magnetic susceptibility in isothermal and non-isothermal conditions within the temperature range of room temperature to 700ºC was determined for the powder samples pressed under pressure of 800 MPa. The X-ray structural examinations results correlate with those of the DSC analysis and the electrical resistively measuring

Morphological, microstructural and magnetic characteristics of electrodeposited Ni-Fe-WCu alloy powders

Nanostructured Ni-Fe-W-Cu alloy powders were electrodeposited from an alkaline ammonium citrate solution on a titanium cathode. Powder particles were dendrite- and cauliflower-shaped. The dendritic particles had a high density of branches made up of interconnected globules. XRD analysis showed that the powder contained an amorphous matrix and FCC nanocrystals of the solid solution of Fe, W and Cu in Ni. As the deposition current density increased, the mean nanocrystal size decreased, and the mean value of internal microstrain and the total weight percent of Fe and Ni in the alloy increased. The powders deposited at higher current densities exhibited higher magnetization. During annealing at temperatures up to 460°C, the powders underwent short-range ordering, which caused an increase in magnetization, whereas at temperatures above 460°C, the magnetization decreased due to the formation of large FCC crystalline grains

Influence of mechanical activation on synthesis and properties of the MgO-TiO2 system

Materials applied in electronics such as multilayer capacitors are an important field of ceramic materials. Magnesium titanate based dielectric materials are used for producing type-I capacitors. A common way of obtaining this material is a solid-state reaction during reaction sintering. The process of sintering can be enhanced if mechanical activation precedes. In this work starting powders of magnesium carbonate (MgCO3) and titanium dioxide (TiO2) with a rutile crystal modification were weighed to attain a 1:1 molar MgCO3:TiO2 ratio. Mechanical activation of the starting mixture was performed by high energy ball milling using ZrO balls and vessels with a ball to powder mass ratio of 40:1. The observed grinding times were 15, 30, 60 and 120 minutes. Powder characterization was conducted using X ray powder diffraction, DTA analysis up to 1000 o C and particle morphology changes were observed with Scanning Electron Microscopy. Isothermal sintering of compacted powders was conducted at 1100ºC during 30, 60 and 180 minutes. For specimens synthesized in such a manner, microwave dielectric properties were measured, quality factor Q, specific electrical resistivity (ρ) and the dielectric constant (Єr). In this work we explain the influence of mechanical activation on the MgCO3-TiO2 system leading to titanate formation during sintering, as well as induced changes in microwave dielectric properties

Influence of platinization of mechanically activated nuclear grade graphite powders on the hydrogen adsorption process

Non-activated powder of nuclear grade graphite and powders of nuclear grade graphite that were milled for 10, 20 and 30 minutes are doped with 0.03% of platinum. XRD analysis of injtial and activated graphite powders was used for structural characterization. Hydrogen adsorption perfonned in isothermal conditions showed that platinization of powder samples of nuclear grade graphite decreases time needed for reaching adsorbent saturation during hydration. Simultaneously it was shown that platinization, due to the hydrogen spillower effect, increases adsorption capacity in a function of mechanical activation duration

Morphological, microstructural and magnetic characteristics of electrodeposited Ni-Fe-W-Cu alloy powders

Nanostructured Ni-Fe-W-Cu alloy powders were electrodeposited from an alkaline ammonium citrate solution on a titanium cathode. Powder particles were dendrite- and cauliflower-shaped. The dendritic particles had a high density of branches made up of interconnected globules. XRD analysis showed that the powder contained an amorphous matrix and FCC nanocrystals of the solid solution of Fe, W and Cu in Ni. As the deposition current density increased, the mean nanocrystal size decreased, and the mean value of internal microstrain and the total weight percent of Fe and Ni in the alloy increased. The powders deposited at higher current densities exhibited higher magnetization. During annealing at temperatures up to 460 °C, the powders underwent short-range ordering, which caused an increase in magnetization, whereas at temperatures above 460 °C, the magnetization decreased due to the formation of large FCC crystalline grains

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

The influence of mechanochemical activation and thermal treatment on magnetic properties of the BaTiO3 -FexOy powder mixture

Powder mixture of 50 mass % of barium titanate (BaTiO3) and 50 mass % of iron (Fe) was prepared by solid-state reaction technique, i.e. ball milled in air for 60 min, 80 min, 100 min, 120 min and 150 min. During mechanochemical activation it was observed the iron powder transitsion to iron oxides. Depending on the activation time the content of iron oxides FeO, Fe2 O3 and Fe3O4 varies. Simultaneously, with the content change of the activated system, magnetic properties change as well. The XRD analysis of milled samples shown that as the activation time increase, the iron oxide percentage increases to, whereby the percentage of BaTiO3 in a total sample mass decreases. The percentage of iron oxides and BaTiO3 in annealed samples changes depending on annealing temperature. The thermomagnetic measurements performed by Faraday method shown that the powder mixture milled for 100 minutes exhibit maximum magnetization prior to annealing. The increase of magnetization maximum was observed after annealing at 540 oC with all milled samples, and at room temperature it has enhancement from 10 % to 22 % depending on the activation time. The samples milled for 100 min and 150 min and then sintered at 1200 oC exhibit magnetoelectric properties. © 2015 International Institute for the Science of Sintering (IISS). All rights reserved

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

The influence of mechanical activation on sintering process of BaCO3-SrCO3-TiO2 system

In this article the influence of mechanical activation on sintering process of bariumstrontium-titanate ceramics has been investigated. Both non-activated and mixtures treated in a planetary ball mill for 5, 10, 20, 40, 80 and 120 minutes were sintered at 1100-1400°C for 2 hours in presence of air atmosphere. The influence of mechanical activation on phase composition and crystal structure has been analyzed by XRD, while the effect of activation and sintering process on microstructure was investigated by scanning electron microscopy. It has been established that temperature of 1100°C was too low to induce final sintering stage for this system. Electrical measurements have been conducted for the densest ceramics sintered at 1400°C for 2 hours. [Projekat Ministarstva nauke Republike Srbije, br. OI172057