Cu redeposition and surface enrichment during the dissolution of Al-Cu Alloy in 0.1 M HCI

ABSTRACT

The enrichment of Cu on the surface of Al - 3.84% Cu alloy during the dissolution in 0.1 M HCI has been examined using open circuit potential [OCP] accompanied by scanning electron microscopy [SEM], Auger electron spectroscopy [AES] and X-ray photoelectron spectroscopy [XPS]. Results obtained during this study show that there are two types of Cu enrichment, one of them is in the form of Cu clusters, which is formed due to the outer diffusion or segregation of Cu to the alloy surface. The second type is more uniform deposition as a result of copper redeposition from solution, this data is confirmed by the AES survey point analysis, which show that the detection of Cu peak beside the disappearance of Al peak occurred at the whole surface. It is also indicated that the Cu released from the alloy surface is due to two different sources. The first occurred due to the severe galvanic attack, around the breifery of the clusters. This attack can be extended under the cluster and released. The other was attributed to the uniform redeposition of Cu on pure Al, where the disproportionation reaction of Cu[+] ions takes place on the surface, which can produce Cu[++] ions to the solution. The higher resolution multiplex of Cu using XPS analysis shows that the appearance of three peaks corresponding to Cu[°] [metallic copper], CuCI, CuCI[2] and devoid of any Al species. Accordingly the redeposit Cu on pure Al can behaves as Cu metal and dissolves also as dichlorocoprate [CuCI[2]] soluble complex beside CuCI[2]