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

Abstract

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

The Effect of Temperature on the Magnetic Properties of the Electrochemically Obtained Ni_92.8 Mo_7.2 Powder Pressed at Different Pressures

“…By electrochemical codeposition from an ammonium solution of NiSO 4 and (NH 4 ) 6 Mo 7 O 24 at j=100 mA cm -2 , on a titanium cathode, nanocrystalline Ni 92.8 Mo 7.2 alloy powder was obtained [18,19]. The Ni and Mo powder consisted of a solid solution with FCC crystal lattice and grain size of about 16 nm; 30% of the powder had an amorphous structure (Fig.…”

“…The Ni and Mo powder consisted of a solid solution with FCC crystal lattice and grain size of about 16 nm; 30% of the powder had an amorphous structure (Fig. 1) [18,19]. The quantitative evaluation of the amorphous phase was obtained by the Rietveld method [20].…”

“…There are two pronounced exomaxima in the range from 630 to 870 K. The origin of the two peaks was not clear at this point. XRD analysis reveals [18,19] a) crystallization of the remained amorphous part of Ni 92.8 Mo 7.2 powder, and b) growth of the crystal grains to about 80 nm. This crystallization process was followed by a decrease in electrical resistivity.…”

“…Metallic nanocrystalline alloys with magnetic properties are especially widely applied due to specific electrical, magnetic and corrosive characteristics [1][2][3][4][5][6][7][8][9][10][11]. Electrochemical method can be used to obtain nanostructured powders whose structure differs from that of the nanostructured powders obtained by other methods [8,10,[12][13][14][15][16][17][18][19]. The appropriate choice of the electrolysis parameters results in alloy and metal powders with certain chemical composition, phase structure, size and shape of particles.…”

“…The appropriate choice of the electrolysis parameters results in alloy and metal powders with certain chemical composition, phase structure, size and shape of particles. By electrodeposition method it is possible to prepare Ni -Mo alloys with desired properties [18][19][20][21][22][23][24][25][26][27][28][29][30][31]. The properties can be essentially dependent on the structural relaxation degree.…”