Al-Fe Alloy Formation from Non-Aqueous Solution By Electrochemical Technique

1. Introduction

 The physical property of Fe_xAl_1-x  is not only scientific but also technological interest because of its wide variety of potential applications. However, aluminum, that is less noble than hydrogen, is not be electrodeposited from aqueous solution. Therefore, the possibility of forming an aluminum film using an organic solvent, molten salts or ionic liquid has been studied. A dimethyl sulfone (DMSO₂) is one of the most promising candidates for non-aqueous solvent.

2. Experiment

 The plating solution was composed of AlCl_３, FeCl₃ and DMSO₂. The total metal chloride ratio, (AlCl₃ + FeCl₃) / (DMSO₂ + AlCl₃ + FeCl₃), is constant at 33.3 mol%. The ratio of FeCl₃ to AlCl₃ is controlled from 10 to 30 mol%. A current density is controlled from 300 to 1000 A/m². Since a melting point of dimethyl sulfone is from to 109 ^oC, a plating temperature is necessary to be higher than this value. However, the aluminum plating was not sometimes performed at the temperature lower than 130 ^oC Results of thermal desorption spectrometry (TDS) showed that the desorption peaks of H₂O appeared at 110 and 150 ^oC. This result suggests that the water in the solution inhibits the aluminum plating. For this reason, the following plating was performed at about 180 ^oC to dehydrate. The depositions were performed in a dry glove box filled with flowing dry nitrogen. Film thickness is controlled by the deposition time. The composition of the samples was estimated using a energy dispersive X-ray spectrometry microscope (EDS, JEOL JSM-6000). The X-ray photoelectron spectroscopy (XPS) results were obtained by a Kratos Analytical AXIS ULTRA DLD equipped with an Al Kα X-ray source (hν = 1486.6 eV, 10.0 mA, 15 kV). The binding energies were calibrated with the C 1s peak at 284.8 eV.

3. Results and Discussion

 The atomic composition of the samples was determined by EDS. Figure 1 shows the effect of different FeCl₃ ratio on the Fe ratio in the films. The Fe ratio is increased with increasing the FeCl₃ ratio and reached almost 100 mol% at 20 mol% FeCl₃. The FeCl₃ ratio dependence of the Fe ratio is changed in the same manner at both 600 and 1000 A/m² of the current density. The plating films have a low Fe concentration at high current density electrodeposition, because Fe is more noble than Al. The peak intensity ratio for Fe 3p / Al 2p estimated from XPS measurements is increased with increasing in FeCl₃ ratio. This result is consistent with the result of EDS.

4. Conclusion

 Electrodeposition of Al-Fe alloy from the AlCl₃ -DMSO₂ plating solution with FeCl₃ was investigated. The total metal chloride ratio is constant at 33.3 mol%. The ratio of FeCl₃ to AlCl₃ is controlled from 10 to 30 mol%. A current density is controlled from 300 to 1000 A/m². Fe content is controllable from 0 % to almost 100 %. The significant morphological changes to the films were appeared by the addition of FeCl₃ to the plating solution.

5. Acknowledgement

 This work was partially aided by MEXT-supported Program for the Strategic Research Foundation at Private Universities.