The effect of structural changes during sintering on the electric and magnetic traits of the Ni96.7Mo3.3 alloy nanostructured powder

Ni96.7Mo3.3 powder was electrochemically obtained. An X-ray diffraction analysis determined that the powder consisted of a 20% amorphous and 80% crystalline phase. The crystalline phase consisted of a nanocrystalline solid nickel and molybdenum solution with a face-centred cubic (FCC) lattice with a high density of chaotically distributed dislocations and high microstrain value. The scanning electronic microscopy (SEM) showed that two particle structures were formed: larger cauliflower-like particles and smaller dendriteshaped ones. The thermal stability of the alloy was examined by differential scanning calorimetry (DSC) and by measuring the temperature dependence of the electrical resistivity and magnetic permeability. Structural powder relaxation was carried out in the temperature range of 450 K to 560 K causing considerable changes in the electrical resistivity and magnetic permeability. Upon structural relaxation, the magnetic permeability of the cooled alloy was about 80% higher than the magnetic permeability of the fresh powder. The crystallisation of the amorphous portion of the powder and crystalline grain increase occurred in the 630 K to 900 K temperature interval. Upon crystallisation of the amorphous phase and crystalline grain increase, the powder had about 50% lower magnetic permeability than the fresh powder and 3.6 times lower permeability than the powder where only structural relaxation took place

The influence of structural changes on electrical and magnetic characteristics of amorphous powder of the nixmoy alloy

Nickel and molybdenum alloy powder was electrodeposited on a titanium cathode from a NiSO4⋅7H2O and (NH4)6 Mo7O24⋅4H2O ammonium solution. The desired chemical composition, structure, size and shape of particles in the powder samples were achieved by an appropriate choice of electrolysis parameters (current density, composition and temperature of the solution, cathode material and electrolysis duration). Metal coatings form in the current density range 15 mA cm-2<j<30 mA cm-2. If the current density is greater than 40mA cm-2 then powders form. The chemical composition of powder samples depends on the current density of electrodeposition. The molybdenum content in the powder increases with the increase of current density (in the low current density range), while in the higher current density range the molybdenum content in the alloy decreases with the increase of the current density of deposition. Smaller sized particles form at higher current density. X-ray analysis, differential scanning calorimetric and measurements of the temperature dependence of electric resistance and magnetic permeability of the powder samples were all used to establish a predominantly amorphous structure of the powder samples formed at the current density of j≥70mA cm-2. The crystalline particle content in the powder samples increases with the decrease of the current density of deposition. Powder heating causes structural changes. The process of thermal stabilization of nickel and molybdenum amorphous powders takes place in the temperature interval from 463K to 573K and causes a decrease in electrical resistance and increase in magnetic permeability. The crystallization temperature depends on the value of current density of powder electrodeposition. Powder formed at j=180 mA cm-2 begins to crystallize at 573K, while the powder deposited at j=50 mA cm-2 begins to crystallize at 673K. Crystallization of the powder causes a decrease in electric resistivity and magnetic permeability. The Curie temperature of the crystallized powders is about 10 K higher than the Curie temperature of amorphous powders

Effect of Microstructural Changes during Annealing on Thermoelectromotive Force and Resistivity of Electrodeposited Ni 85.8

Ni85.8Fe10.6W1.4Cu2.2 alloy powder containing nanocrystals of an FCC-structured solid solution of iron, tungsten, and copper in nickel embedded in an amorphous matrix was electrodeposited from an ammonia citrate solution. The alloy exhibits thermal stability in the temperature range between 25°C and 150°C. Over the range 150−360°C, the alloy undergoes intense structural relaxation which considerably increases the electron density of states and, hence, its electrical conductivity. Less intense structural relaxation takes place at temperatures between 360°C and 420°C. In the temperature range of 420°C to 460°C, relatively more intense changes in the electron density of states at the Fermi level occur, as induced by the structural relaxation resulting from the stabilization of larger less mobile tungsten atoms and copper atoms. The large decrease in electrical resistivity and the high increase in the electron density of states at the Fermi level in the temperature range 460−520°C are due to amorphous matrix crystallization and FCC-phase crystal grain growth

The phase structure and morphology of electrodeposited nickel-cobalt alloy powders

Cobalt and nickel powders of three different compositions: Ni0.8Co0.2, Ni0.55Co0.45 and Ni0.2Co0.8 were obtained by electrodeposition from an ammonium chloride-sulphate solution. It was shown that the microstructure and morphology of the powders depended on the deposition current density as well as on the bath composition. Amorphous powder of Ni0.8Co0.2 was obtained at the current density higher than 200 mA cm-2, but nanocrystalline powders having the same composition were obtained at current densities lower than 200 mAcm-2. The nanocrystalline powders with lower Ni contents (0.55 and 0.2) obtained at a current density ranging from 40 mA cm-2 to 450 mA cm-2 were solid solutions of two phases, FCC (β-Ni) and HCP (α-Co) ones. The increase of the HCP phase in the powder was a result of both the Co content increase in the powder and decrease of the deposition current density

The Mixture of Nanoparticles of RuO<inf>2</inf> and Pt Supported on Ti as an Efficient Catalyst for Direct Formic Acid Fuel Cell

© 2019, Pleiades Publishing, Ltd. Abstract: An active coating, composed of a mixture of nanocrystals of RuO2 with the rutile structure and nanocrystals of metal Pt, was thermally synthetized on a titanium substrate. Cyclic voltammograms and polarization curves showed that the catalytic activity of the coating for the formic acid oxidation in an acidic solution increased with an increase in the RuO2 content, reaching the maximum value at 50 mol % RuO2. Additionally, further increase in the RuO2 content resulted in a decline of the catalytic activity. The catalytic effect was attributed to a bifunctional mechanism and an electronic effect. The bifunctional mechanism had a dominant role and was based on the fact that Ru–OH species were formed on Ru atoms of RuO2 at more negative potentials than on Pt. Those species oxidized the adsorbed COad and HCOOad—species on adjacent Pt atoms of clusters of metal Pt and thus discharge them to oxidize new HCOOH molecules

Microstructural properties of electrochemically prepared Ni-Fe-W powders

A nanostructured Ni-Fe-W powder was obtained by electrodeposition from ammonium citrate electrolyte within the current density range of 500-1000 mA cm(-2) at the electrolyte temperature of 50 degrees C -70 degrees C. XRD analysis shows that the powder contains an amorphous matrix having embedded nanocrystals of the FCC solid solution of iron and tungsten in nickel, with an average crystal grain size of 3.4 nm, a high internal microstrain value and a high density of chaotically distributed dislocations. EDS analysis exhibits that the chemical composition of the Ni-24%Fe-11%W powder does not depend upon current density and electrolyte temperature due to the diffusion control of the process of code-position of nickel, iron and tungsten. SEM micrographs show that the electrodeposition results in the formation of two particle shapes: large cauliflower-like particles and small dendrite particles. The cauliflower-like particles contain deep cavities at hydrogen evolution sites. Cavity density increases with increasing deposition current density. Smaller powder particles are formed at higher temperatures and at higher current densities. During the first heating, relative magnetic permeability decreases reaching the Curie temperature at about 350 degrees C and after cooling exhibits a 12% increase due to the performed relaxation process. Following the second heating to 500 degrees C, the magnetic permeability of the powder is about 5% lower than that of the as-prepared powder due to crystallization of the amorphous phase of the powder and the crystal grain growth in FCC phase

The effect of temperature and frequency on magnetic properties of the Fe81B13Si4C2 amorphous alloy

In this study it was investigated influence of temperature and frequency on permeability, coercivity and power loses of Fe81B13Si4C2 amorphous alloy. Magnetic permeability measurements performed in nonisothermal and isothermal conditions was confirmed that efficient structural relaxation was occurred at temperature of 663 K. This process was performed in two steps, the first one is kinetic and the second one is diffuse. Activation energies of these processes are: Ea1 = 52.02 kJ/mol for kinetic and Ea2 = 106.9 kJ/mol for diffuse. It was shown that after annealing at 663 K coercivity decrease about 30% and therefore substantial reduction in power loses was attained. Investigated amorphous alloy satisfied the criteria for signal processing devices that work in mean frequency domain

Modelling current efficiency in an electrochemical hypochlorite reactor

A mathematical model was set up for anodic, cathodic and overall current efficiencies of an electrochemical cell for hypochlorite production acting as an ideal stirred reactor. A 0.06-0.20 mol dm(-3) NaClO hypochlorite solution was obtained in the cell by the electrolysis of 0.25-0.50 mol dm(-3) sodium chloride solution at a temperature of 20 degrees C, at a current density of 100 mA cm(-2) and at 8.3 lt pH lt 8.7. Anodic current losses occur through hypochlorite and water oxidation at the DSA anode, and cathodic current losses result from hypochlorite reduction at the titanium cathode. Theoretical dependences of the anodic current efficiency on the overall anodic current density, hypochlorite concentration and partial current density for water oxidation were established. Theoretically derived relations and the corresponding experimental results showed that oxygen evolution due to water and hypochlorite oxidation leads to reduced thickness of the anodic diffusion layer and increases the limiting diffusion current for hypochlorite oxidation. Mathematical models for the dependence of the cathodic current efficiency on the cathodic current density and hypochlorite concentration in the bulk solution were also established. The expression for the overall current efficiency of the electrochemical cell for hypochlorite production was derived on the basis of both the anodic and the cathodic current efficiency. The good agreement between experimental results and the values provided by the mathematical models has confirmed the correctness of the proposed models, suggesting that the model can be used to optimise electrolysis parameters. (The term hypochlorite is used to include both hypochlorite and undissociated hypochlorous acid.) The concentration of dissolved elementary chlorine in the slightly alkaline environment is negligible compared to hypochlorite concentration