A Comparative Study of Saturation Induction with Current Density of Electrodeposited Fe-Ni-W Alloys
Fe-group metals have industrial application mainly in magnetic storage devices  and Micro Electromechanical Magnetic Systems (MEMS) . Tungsten (W) is incorporated in these alloys to improve their durability, hardness and resistance to high temperatures [3-4]. These alloys can also positively apply to substitute hard chrome coatings, due to high hardness .
This study addresses the preparation of Fe-Ni-W alloys by electroplating method. In order to obtain enhanced magnetic properties in deposits, different current densities are applied. The influence of current density on the induced co-deposition and magnetic properties of the Fe-Ni-W alloys have been studied and are reported here.
The Fe-Ni-W alloys were produced on Si-substrate by electroplating technique. The electrolyte was prepared by dissolving 0.2 mol/dm3 nickel sulfate, 0.1 mol/dm3 ferrous sulfate, 0.03 mol/dm3 sodium tungstate, 0.3 mol/dm3 diamonium H-citrate, 0.03 mol/dm3 citric acid, 0.16 mol/dm3 boric acid, and 0.05 mol/dm3 saccharin. Deposition was carried out at a temperature of 500C using different current densities (28, 56, and 84 mA/dm2) at constant pH 8, and solution was stirred with a magnetic stirrer during deposition. The deposition time was 15 minutes.
Composition of the deposit was determined by the energy dispersive X-ray spectroscopy (EDX) technique using the scanning electron microscope (SEM). Saturation induction (Bs) was inspected with the help of a Vibrating Sample Magnetometer (VSM).
Results and discussion
The change in composition of electrodeposited Fe-Ni-W alloys at 500C using different current densities is shown in Fig. 1. The wt% of W is nearly same, but wt% of Fe is increased with current densities. For Iron group metals (Fe, Co, and Ni) the less noble metal (here Fe) is deposited preferentially than the Ni metal, according to Brenner’s definition. In this group’s metal deposition hydrogen evaluation takes place, this leads to increase in hydroxyl ions [5-6]. The adsorption ability of Fe(OH)+ is higher than that of Ni(OH)+on the cathode surface . Therefore, formation and adsorption of metal monohydroxide ions or metal hydroxides occurred on the cathode surface, favors preferentially less noble metals in the deposition process. Followings reactions mechanism occurs [8-9]:
2H2O + 2e- → H2 + 2OH- 
M2+ + OH- → M(OH)+ 
M(OH)+ → M(OH)+ad 
M(OH)+ad +2e- → M + OH- 
Where M indicates Fe and Ni metals. The saturation induction of deposited Fe-Ni-W alloys is shown in Fig. 2. It is observed that the saturation induction is increased from 0.59 T to 0.73 T with increase in current density. The increase in saturation induction can be attributed to the increase of Fe content in deposit alloys.
1. wt% of Fe increases with increase in current density while wt% of W is approximately constant .
2. The saturation induction is increased with current density, due to increase in wt% of Fe in deposits.
This work is supported by the Hannover School for Nanotechnology grant.
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