Effect of electrodeposition current density on the microstructure and magnetic properties of nickel-cobalt-molybdenum alloy powders

Nanostructured nickel-cobalt-molybdenum alloy powders were electrodeposited from an ammonium sulfate bath. The powders mostly consist of an amorphous phase and a very small amount of nanocrystals with an mean size of less than 3 nm. An increase in deposition current density increases the amorphous phase percentage, the density of chaotically distributed dislocations and internal microstrains in the powders, while decreasing the mean nanocrystal size. The temperature range over which the structural relaxation of the powders deposited at higher current densities occurs is shifted towards lower temperatures. A change in relative magnetic permeability during structural relaxation is higher in powders deposited at higher current densities. Powder crystallization takes place at temperatures above 700oC. The formation of the stable crystal structure causes a decrease in relative magnetic permeability

Development of new material for the environmental-friendly energy generation processes

The aim of this study was to develop a new material which has high hydrogen storage capacity and hydrogen absorption/desorption rate. This material, which is based on cobalt powder onto which palladium was chemically deposited can be used in environmentally friendly energy generation processes, thus ensuring preventive protection of human health. Hydrogen absorption was investigated using differential scanning calorimetry (DSC) and by measuring hydrogen pressure under isothermal and non-isothermal conditions in a chamber containing either pure cobalt powder either cobalt powder onto which palladium was chemically deposited (Co-0.003 Pd). The mechanism of hydrogen absorption has been described. It was noticed that palladium catalyses hydrogen absorption by dissociating the adsorbed H2 molecules into H atoms more rapidly on its own atoms than on cobalt ones. The catalysis of dissociation of H2 molecules enabled hydrogen absorption into Co-0.003 Pd powder to occur at lower temperatures. The results of this study enable integration of technological and public health investigation in order to ensure preventive protection of human health through enviromental protection

Effect of milling and annealing on microstructural, electrical and magnetic properties of electrodeposited Ni-11.3fe-1.4W alloy

A nanostructured Ni-11.3Fe-1.4W alloy deposit was obtained from an ammonium citrate bath at a current density of 600 mAcm -2. XRD analysis shows that the deposit contains an amorphous matrix having embedded nanocrystals of the FCC phase of the solid solution of Fe and W in Ni with the average crystal grain size of 8.8 nm. The deposit has a high internal microstrain value and a high minimum density of chaotically distributed dislocations. The effect of milling and annealing of the Ni-11.3Fe-1.4W alloy on electrical and magnetic properties was studied. Structural changes in the alloy take place during both annealing and milling. Upon deposition, the alloy was heated to 420 °C. Heating resulted in structural relaxation which induced a decrease in electrical resistivity and an increase in magnetic permeability of the alloy. Further heating of the alloy at temperatures higher than 420 °C led to crystallization which caused a reduction in both electrical resistivity and magnetic permeability. The milling of the alloy for up to 12 hours caused a certain degree of structural relaxation and crystallization of the alloy. The increase in crystal grain size up to 11 nm and the partial structural relaxation induced a decrease in electrical resistivity and an increase in magnetic permeability of the alloy. Heating the powders obtained by milling at 420 °C led to complete structural relaxation, reduced electrical resistivity, and increased magnetic permeability. During heating of the powders obtained by milling at temperatures above 420 °C, crystallization and a significant increase in crystal grain size occurred, leading to a reduction in both electrical resistivity and magnetic permeability. The best magnetic properties were exhibited by the alloys milled for 12 hours and annealed thereafter at 420 °C. In these alloys, crystal grains were found to have an optimum size, and complete relaxation took place, resulting in a maximum increase in magnetic permeability

Corelation between the crystallisation process and change in thermoelectromotive force for the amorphous alloy Fe89.8Ni1.5Si5.2B3C0.5

Thermal and kinetic analyses of the structural changes for the amorphous alloy Fe89.8Ni1.5Si5.2B3C0.5, during the processes of non-isothermal heating and isothermal annealing, have been performed. The crystallisation process has been investigated using the method of differential scanning calorimetry (DSC). It is determined that this alloy crystalizes through three different stages. Changes in the electronic structure of the amorphous tape, for the temperature range 20 to 700ºC have been studied. This was achieved by measuring the thermoelectromotive force (TEMS), of the thermo pair made of two tapes with same chemical structure of the alloy FeNiSiBC, but different atomic structure: one is in the crystal state (CL) and the other is in the amorphous state (AM). Analysis of the temperature dependence of the electromotive force has shown the following: the investigated alloy is thermically stable up to 450ºC and changes in the atomic structure as well as equalising of the free electron density in both parts of the thermo pair AM-CL, take place in the temperature range from 450 to 550ºC. Kinetic parameters of the process were determined by measuring time dependence of the TEMS in isothermic conditions at the temperatures 450, 480 and 510ºC

Effect of heat treatment on structure and magnetic properties of Fe65.5Cr4Mo4Ga4P12C5B5.5 bulk amorphous alloy

This study deals with the Fe65.5Cr4Mo4Ga4P12C5B5.5 ferromagnetic bulk amorphous alloy. XRD analysis showed an amorphous structure of the as-cast sample. The same method revealed that, after annealing at 973 K for τ=10 min, the sample displayed a crystalline structure with crystalline phases formed. The crystallization process of the alloy was examined by DTA analysis. It was shown that crystallization took place in the temperature range between 810 K and 860 K with the exo-maximum peak temperature at 846 K with a heating rate of 20 Kmin-1. The method also showed that, at temperatures ranging from 753 K to 810 K, the alloy exhibited the properties of supercooled liquids. A correlation between heat-induced structural changes and magnetic properties of the alloy was determined by thermomagnetic measurements. Maximum magnetization M=3.7 Am2kg-1 of the alloy was reached after its annealing at 733 K for τ=10 min. Upon annealing, the alloy exhibited a relaxed amorphous structure. Annealing the alloy above the crystallization temperature led to a decrease in bulk magnetization. After annealing at 973 K for τ=10 min, the bulk magnetization of the alloy was M'=0.45 Am2kg-1. Accordingly, after crystallization and formation of new compounds, the magnetization of the alloy was decreased by a factor of about 7.7. The strength of the magnetic field applied during the measurements was H=10 kAm-1. The samples were tested for changes in the microstructure and hardness of both the amorphous phase and the resulting crystalline phase

Influence of the changes of free electron density on electrical and magnetic properties of the CO70Fe5Si10B15 amorphous alloy

In this study we present the results on structural relaxation of the Co70Fe5Si10B15 amorphous alloy investigated by measuring the thermo-electromotive force (TEMF) during isothermal annealing (for 600 s). A mechanical junction of the investigated alloy and a copper conductor has been constructed for measuring the thermo-electromotive force (ε). Annealing was performed at temperatures T1 = 430˚C, T2=460˚C and T3=480˚C which are about 50 to 100˚C lower than the crystallization temperature. At these temperatures structural relaxation occurred only in the amorphous alloy. The activation energy E=224 kJ/mol and rate constants k1=6.66·10-5 s-1 k2=33·10-5 s-1 and k3=76·10-5 s-1 at temperatures T1, T2 and T3 respectively, have been determined for the process. Each isothermal annealing has been followed by determination of the relative change of the electronic state density at the Fermi level as Dn1/n=2.36%, Dn2/n =3.21% and Dn3/n= 9.80%, respectively.

Synthesis and characterization of silica core/multilayered cobalt ferrite-silica shell particles for lipase immobilization

Multilayered core/shell particles were prepared by four-step deposition of cobalt ferrite layers and then deposition of external silica layer on the surface of silica core particles. The ferrite nanoparticles were obtained by co-precipitation of Co2+ and Fe3+ ions at pH=11 and pH=15, respectively. The agglomerated silica core/cobalt ferrite shell particles were obtained at extremely basic pH (pH=15), while at pH =11, monodispersed and non-aggregated core-shell particles were obtained. The poly(diallyldimethylammonium chloride)-functionalized silica core/ferrite shell particles were used as templates for deposition of mesoporous silica layers (obtained by neutralization of highly basic sodium silicate solution). The obtained porous multilayered core/shell particles were used as a host for covalent lipase immobilization inside the external silica layer. The initial activity of immobilized enzymes was about 13-fold lower than the native one, however, it showed good reusability and improved thermal stability compared to native ones

Experimental identification of the degree of deformation of a wire subjected to bending

© 2016 Authors. Published by the International Institute for the Science of Sintering. This study provides experimental verification of analytical results on maximum strain εmax in elements fabricated by bending a stainless steel wire around a cylinder with given dimensions. The method of measuring the thermal electromotive force (TEMF) of a thermocouple formed by joining the deformed metal specimen to a copper (Cu) conductor showed an increase in the thermal electromotive force coefficient (TEMFC) during heating with increasing degree of plastic deformation. For known values of plastic deformation produced by straining X5CrNi1810 stainless steel wire specimens of ∅2.8 mm diameter, the TEMF was determined as a function of the extent of deformation of the thermocouple consisting of the deformed steel wire specimen and the copper conductor. Based on the correlation (calibration curve), it was shown that the relative strain of the element fabricated by bending the same wire (made of X5CrNi1810 stainless steel, ∅2.8 mm in diameter) around the cylinder of ∅10 mm diameter is 23.8 %

Properties of MnZn ferrites prepared by powder injection molding technology

In this work, manganese zinc ferrite components were manufactured by powder injection molding-PIM technology. A fine powder consisting of Mn1-xZnxFe2O4 with small addition of hematite alpha-Fe2O3 as used in mass ferrite production was mixed with an organic binder (Solvent System) to form ferrite feedstock for powder injection molding-PIM technology. Excess of Fe2O3 was present in the starting powder in order to suppress conversion of Fe3+ to Fe2+ ions which would lower the permeability. The ferrite feedstock was injected in a mold with a cavity shaped like a small cylinder with a hole on the main axis. Injection molded samples were then solvent and thermally debinded and sintered in different atmospheres: air, argon and nitrogen. The starting powder, injected green samples and sintered samples were characterized using X-ray diffractometry, scanning electron microscopy, thermogravimetry, differential thermal analysis as well as by magnetic measurements. Rietveld refinement of measured X-ray patterns was done to detect possible phase transformations of Fe2O3 to other iron oxides through reduction by binder residues (carbon) at elevated temperatures during thermal debinding and sintering. Finally, the magnetic properties were measured by hysteresis graph and mutually compared for the injected samples that were sintered in air, argon and nitrogen. The obtained magnetic characteristics where found to be comparable with commercial samples prepared by traditional sintering technology