An example of dealloying is the dezincification of brass. Dezincification occurs when brass, an alloy of copper and zinc, is exposed to corrosive environments, leading to the selective removal of zinc. This leaves behind a porous, weakened structure of copper, which can compromise the integrity and mechanical strength of the brass component. Dezincification often occurs in plumbing systems, where brass fittings are exposed to water containing chlorides or other aggressive chemicals.
Overview
The Basics of Dealloying
Several factors influence the occurrence and severity of selective leaching in mechanical applications. Some of which include:
- Material Properties: The composition, microstructure, and metallurgical history of the materials involved play a significant role in determining their susceptibility to dealloying.
- Environment: The chemical composition, temperature, and pH of the operating environment can affect the aggressiveness of the selective leaching process, influencing the extent of selective leaching.
- Electrochemical Factors: The electrochemical properties of the alloy components, such as their electrochemical potential difference and standard reduction potentials, can influence the rate of leaching by determining the susceptibility of the components to dissolution.
- Galvanic Coupling: The presence of galvanic coupling between the alloy components or with other metals in the system can accelerate the selective leaching process by increasing the electrochemical potential difference.
- Passive Film Formation: The presence and stability of passive films on the alloy surface can affect the dealloying process by providing a barrier to selective leaching.
- Exposure Time: Naturally, the duration of exposure to the corrosive operating environment can impact the extent of dealloying, as longer exposure times typically result in increased material loss.
As with any metal failure mode, there are several mitigation strategies that can minimize the occurrence and severity of dealloying in mechanical applications, including:
- Material Selection: Choose materials with suitable properties, such as low susceptibility to selective leaching and stable alloy compositions, to reduce the propensity for dealloying.
- Passive Coatings: Apply protective coatings or surface treatments, such as electroplated chromium or conversion coatings, to improve the corrosion resistance and provide a barrier to selective leaching.
- Environment Control: If possible, control the operating environment by reducing exposure to aggressive chemicals, minimizing temperature fluctuations, and controlling pH levels to reduce the rate of dealloying.
- Cathodic Protection: Implement cathodic protection techniques, such as sacrificial anodes or impressed current systems, to reduce the electrochemical corrosion rate and minimize the detrimental impact of dealloying.
Armoloy's Solution to Dealloying
Armoloy offers multiple metal surface treatments with varying levels of protection from the common causes of dealloying. Offering both broad-spectrum and industry-specific applications, our protective metallic coatings add significant value through increased performance and decreased revenue losses from unplanned maintenance and downtime.
Our protective coatings ensure a thin, precise coat that won’t impact production, but will improve surface hardness and prevent environmental defects. Beyond increasing wear life, Armoloy tailors our metallic coatings based on the specific requirements of your application and industry.
Dealloying is a complex and detrimental corrosion mechanism that affects a myriad of mechanical systems across an array of industries. By addressing this failure phenomenon, engineers can reduce its negative impact on numerous applications, ensuring optimal operating performance and durability.
Beyond the Lab: Metal Failures in Narrative Form
Partner With Us
Eliminate dealloying from your operations. Meet our group of curious, innovative engineers and learn how we can help improve your industry with science-based solutions.
Frequently Asked Questions
Selective leaching, also known as dealloying, is a form of corrosion where one element is selectively removed from an alloy, leaving behind a weakened, porous structure. This phenomenon occurs when certain environmental conditions favor the dissolution of one component of the alloy over others. For example, in brass, zinc can be preferentially leached out, leaving a porous copper structure. Selective leaching compromises the mechanical properties of the alloy and can lead to failure in structural applications.
Preventing selective leaching involves several strategies:
- Alloy Modification: Using alloys specifically designed to resist leaching, such as dezincification-resistant brass.
- Protective Coatings: Applying coatings to the metal surface to act as a barrier against corrosive agents.
- Corrosion Inhibitors: Adding chemicals to the environment that slow down or prevent the leaching process.
- Environmental Control: Reducing exposure to aggressive chemicals through proper design and maintenance of systems.
- Cathodic Protection: Applying a small electrical charge to counteract the electrochemical reactions that lead to selective leaching.
These measures help maintain the integrity and longevity of metal components in corrosive environments.