Does dezincification always lead to dark red spots on brass?

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Discussion Overview

The discussion revolves around the phenomenon of dezincification in brass and its visual manifestations, particularly the appearance of dark red spots and green corrosion. Participants explore the relationship between these forms of corrosion, the chemical processes involved, and the factors influencing dezincification.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that dark red spots on brass may indicate early-stage dezincification, which could lead to copper corrosion resulting in green coloration.
  • Another participant asserts that the greenish corrosion is independent of dezincification and is primarily composed of various copper compounds known as verdigris.
  • A third participant notes that white corrosion on brass is mainly due to simple zinc compounds and highlights that dezincification can cause porosity in the material, potentially leading to further corrosion.
  • It is mentioned that electrolytic corrosion may occur when brass is in contact with ferrous metals in wet conditions, adding complexity to the corrosion processes.
  • Factors influencing dezincification, such as service conditions and alloy composition, are acknowledged, with references provided for further reading.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between dark red spots and green corrosion, with no consensus reached on whether they are stages of the same process or distinct phenomena. Multiple competing perspectives remain regarding the causes and implications of these forms of corrosion.

Contextual Notes

The discussion highlights the complexity of corrosion processes in brass, with limitations noted in the assumptions about the relationships between different types of corrosion and the specific conditions that lead to dezincification.

gomerpyle
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I have a brass part that is showing signs of corrosion, namely the appearance of dark red spots. Through research I've learned that this is probably caused by dezincification, which can occur after exposure to water, acid, or salt. My question is I have noticed brass corrosion also involves the formulation of copper carbonates from the copper oxidizing (green color). Is this simply a later stage of corrosion after dezincification has taken place, i.e.: once the zinc is selectively leached away then the copper is the only element left to react? So is it a fair assumption to assume dark red sports are simply an early stage of corrosion in brass?

OR, is the greenish color of corrosion the result of a different chemical reaction causing the copper to react and not the zinc? (EX, ammonia attacking brass causing copper to react and not zinc?)
 
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The greenish color is independent of the red rot (dezincification) you see.
 
The green coloured corrosion is mostly verdigris . The actual composition of verdigris varies a lot . Usually it is a mixture of several different Copper compounds .

White coloured corrosion sometimes seen is mainly simple zinc compounds .

Dezincification causes the Brass to become porous . Sometimes areas of porosity become active sites for corrosion .

There is always the possibility of electrolytic corrosion when brass is in contact with ferrous metals in wet conditions .
 

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