CORROSION OF BRASS IN A MARINE-ENVIRONMENT - MINERAL PRODUCTS AND THEIR RELATIONSHIP TO VARIABLE OXIDATION AND REDUCTION CONDITIONS

Minerals coating brass ammunition shells that rested at the bottom of Halifax Harbour, Nova Scotia, for 52 a have been identified by X-ray d iffraction and analytical scanning electron microscopy. The admiralty brass shells, partially buried in anoxic muds, straddle a strong Eh gr adient ranging from 0 mV to values characteristic of oxygenated seawat er. Whereas the brass surface in contact with the sediment has been pr eserved, parts of the shells exposed to seawater have corroded through out their thickness. The corrosion products identified include metalli c Cu, djurleite (Cu1.96S), cuprite (Cu2O), atacamite (Cu2Cl(OH)(3)), s pertiniite (Cu(OH)(2)) and hydrozincite Zn-5(CO3)(2)(OH)(6)). These pr oducts are those predicted thermodynamically on the basis of ambient E h and pH. However, this study also revealed the presence of a mineral not previously known to exist and tentatively identified as CU14Zn14Cl 5(SO4)5(OH)(41 .)H2O This ''new'' mineral seems to have a stability fi eld in Eh-pH diagrams similar to that of connellite (CU19Cl4(OH)(32 .) 2H(2)O). (C) 1998 Elsevier Science Ltd. All rights reserved.