An investigation into the surface layers formed on elemental zinc and oxidised α-copper–zinc alloys exposed to SO2 in humid air under hypoxic conditions

• We studied the anoxic sulphitation (AS) of metal zinc and of CuZn alloys.
• The AS of elemental zinc completes in short times at 60 °C.
• Cu–15Zn and Cu–30Zn alloys are not attacked by SO2 under same conditions.
• The AS of oxidised brasses results in non-stoichiometric double sulphites.

Elemental zinc and copper–zinc alloys capped with a mixed-oxide layer of cuprite and zincite were exposed to SO2 vapour in a humid oxygen-free atmosphere. Elemental sulphur, zinc sulphite and some zinc hydroxide are the only products which are obtained in the anoxic sulphitation of metal zinc. The pseudo-binary system Cu2SO3Cu(1−x)ZnxSO3⋅2H2O is the result of the experiments on both thermally oxidised and naturally weathered α-brasses. The outcome of competition between the high-copper and the high-zinc species strongly depends on the mass action law: the greater the ZnO to Cu2O phases ratio, the higher the substitution rate of Cu(II) for Zn(II).