Examination of Dealloying in a Domestic Water Fitting Using Light Optical/Scanning Electron Microscopy and Raman Spectroscopy
Year: 2023
Type: conference-abstract
Abstract: A leaking domestic water fitting was examined to characterize the dealloying (dezincification in brass alloys) region associated with the leak (the water system had a history of corrosion failures of the brass components). The brass alloy was not specified; based on composition, it was some form of leaded brass alloy, roughly 57Cu-40Zn-2.3Pb. The mechanism(s) associated with dezincification has either the zinc selectively leaching from the metal, leaving copper behind, or has the entire alloy going into solution and then only the copper redepositing as metallic copper (zinc either remains in solution or deposits as an oxide along with the copper). A metallographic cross-section was examined using light optical microscopy (LOM), scanning electron microscopy (SEM) and Raman spectroscopy (Raman) to see what could be learned from the dealloyed region. LOM of the dealloyed region showed different shades of gray in the oxide phases whereas SEM showed compositional variations in the different phases, some that were not readily discernable in the LOM images. A distribution of a lead-rich phase was clearly visible both the base metal (as minute “particles” of Pb) of the fitting and in the dealloying region (as coarser “islands” containing Pb+O+C). The size of the Pb-rich “islands” increased with the distance from the base metal, so right at the ID surface of the fitting, the Pb-rich phase regions were the largest. Elemental analysis of the copper-rich material within the dealloyed region showed a significantly lower Zn content, as expected with dezincification. Raman analysis of the dealloyed region (only useful in evaluating the non-metallic phases present) provided more details into the specific oxide-related materials that were present. The non-metallic phases were identified as oxides and carbonates of copper, zinc and lead, consistent with cuprite [Cu2O], rosasite [(Cu,Zn)2(CO3)(OH)2], cerussite [PbCO3] and smithsonite [ZnCO3]. With the generally accepted mechanism for dezincification of corrosion of the brass and re-depositing/plating of metallic copper, it appears that the fine lead-rich phase within the brass alloy is likewise re-depositing but as a coarser lead carbonate.
Source: Microscopy and Microanalysis
Authors: Stephen M French, Gary Johnson, Heather May
Institution: Intertek (United States)
Language: English
Subfield: Mechanical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W4385072997