Selective Dissolution of Alpha Brass in Acid Noncomplexing Media

Abstract

The electrochemical behavior of alfa brass ͑Cu3Zn͒ was studied using electrochemical and surface characterization techniques in an acidic noncomplexing medium. The alloy was prepared from pure Zn and Cu to eliminate the dezincification inhibitors and was properly heat-treated. Below a transition potential ͓E t Ϸ 0.25 V standard hydrogen electrode ͑SHE͔͒ only zinc dissolves selectively while copper remains virtually immune. Beyond E t copper dissolves rapidly along with zinc, reaching equal rates at ϳ0.3 V, beyond which copper dissolves faster than zinc. The significance of the transition potential E t is different from the critical potential, E c , which is observed with noble metal alloys. Large values of the dezincification factor ͑Z͒ were measured at potentials below E t . As the potential increases above E t , Z decreases asymptotically toward a value of Z Ϸ 1, which indicates simultaneous dissolution of zinc and copper at rates that are proportional to their mole fractions in the alloy. Electrochemical impedance spectra were modeled using a constant phase element. As the potential increases, the polarization resistance decreases while the doublelayer capacity increases. Atomic force microscopy images show roughening of the alloy surface as a result of selective dissolution of zinc. Enrichment of copper on the alloy surface was documented using X-ray photoelectron spectroscopy.The selective corrosion of alloys involves preferential dissolution of the active component of the alloy, leaving behind a fragile surface that is enriched in the more noble component. The process is actually the reverse of alloy formation and hence is often described as dealloying. It leads to serious deterioration of the surface and mechanical properties of the remaining alloy and hence increases the risk of corrosion failures, which may be costly or fatal. It is of considerable industrial importance in view of the fact that alloys ͑e.g., brasses, bronzes, cupronickels, steels, superalloys, etc.͒ form the backbone of modern industries. Under some conditions, the process leads to the formation of noble metal nanoporous structures and Raney-type catalysts. The mechanism of this process is inherently different from and more complex than the mechanism of dissolution of a single metal. [1][2][3] Copper zinc alloys ͑brasses͒ provide a favorable combination of cost, thermal, mechanical, and electrical properties. They are extensively used in Kuwait and the Gulf region in various industries, such as desalination, power generation, refineries, etc. 4 The dezincification of brass is one of the more recognized forms of the selective dissolution of alloys. 5-7 Premature failure of brass condenser tubes was recently attributed to dezincification in a power plant in Turkey. 8 Dezincification has also been documented in another power plant in Spain. 9 The corrosion behavior of brass has been the subject of active research for some decades and is still attracting increasing attention. The measurements in many of the above works were performed on com...

An in situ kinetic study of brass dezincification and corrosion

“…Conventional electrochemical methods such as potentiodynamic polarization [15,26] and electrochemical impedance spectroscopy (EIS) [15,26,27] have been used to predict the corrosion rate and to characterize the electrical properties of the interfacial structure. In situ techniques such as Raman spectroscopy [28], infrared reflection absorption spectroscopy (IRAS) [17], near normal incidence reflectance spectroelectrochemical technique (NNIRS) [29] and ultraviolet-visible (UV-vis) reflectance spectroscopy [16] can be used to observe the molecular identity of the oxide.…”