What are silicate films, and why are they a problem in copper water pipes?

Silicate films are thin layers that form on the surface of copper pipes. They are problematic because they disrupt the natural protective oxide layer that normally prevents corrosion. These films promote pitting corrosion, leading to the release of copper ions into the water, which can compromise water quality and the integrity of the pipes.

How do silicate films cause pitting corrosion in copper pipes?

Silicate films create localized corrosion cells. The copper surface beneath the silicate film acts as an anode where copper dissolves, while the surrounding copper surface and the silicate-covered area form a cathode. This electrochemical activity causes the copper to corrode, leading to the formation of pits within the pipe material. The presence of the silicate film hinders the formation of a protective oxide layer and accelerates the dissolution of copper.

What specific changes in copper dissolution occur when silicate films are present?

The presence of silicate films alters the copper dissolution process. The formation of Cu2+ ions, a typical product of copper corrosion, is hindered. Instead, Cu+ ions are primarily formed. Furthermore, the silicate film prevents the protective oxide layer from forming. This allows for accelerated copper dissolution, indicating that the film promotes corrosion rather than preventing it. The electrochemical research highlights the formation of galvanic elements on copper surfaces, especially at the phase boundary between bare copper and silicate-treated areas, leading to pit formation beneath silicate layers.

What is the role of the protective oxide layer on copper pipes, and how do silicate films affect it?

The protective oxide layer is a naturally forming barrier on copper pipes that shields the metal from corrosion. Silicate films disrupt this protective layer, preventing it from forming properly. This leaves the copper vulnerable to the corrosive effects of the surrounding water, leading to accelerated pitting corrosion and the potential for water contamination.

How does the presence of silicate films create galvanic elements on the copper surface?

The electrochemical research highlights the formation of galvanic elements on copper surfaces due to silicate film presence, especially at the phase boundary between bare copper and silicate-treated areas. These galvanic elements are created due to potential differences. The potential difference can reach 80 mV, which drives the localized corrosion. The silicate film modifies the dissolution mechanisms and hinders protective oxide layer formation, which amplifies this effect. Managing aeration cells is key to mitigate the corrosive effects.

Corroded copper pipe with silicate films.

Are Silicate Films Sabotaging Your Drinking Water? A Copper Tube Corrosion Crisis

Mira Elwood in Science & Nature September 2025 • 4 min read.

"Uncover the hidden threat of silicate films in copper water pipes and how they lead to pitting corrosion, compromising water quality."

For decades, copper tubes have been a reliable choice for water installations due to their durability and resistance to corrosion. However, recent years have seen a concerning rise in pitting corrosion within these systems, particularly in cold water tubes in specific regions, raising questions about the long-term integrity of our water infrastructure.

While factors such as sulfates, chlorides, and hydrogen carbonates are known to influence corrosion, the exact mechanisms remain elusive. A significant clue emerged during failure analyses of affected copper tubes: consistently high levels of silicates and the presence of silicate films.

This article delves into the groundbreaking research investigating the impact of silicate films on pitting corrosion. It will explore how these films disrupt the natural protective oxide layer on copper, leading to accelerated corrosion and potential water contamination.

The Insidious Role of Silicate Films in Copper Corrosion

Corroded copper pipe with silicate films.

The research confirms the presence of silicate films on copper surfaces, sparking concerns about their role in the corrosion process. Using advanced techniques like Scanning Kelvin Probe and Scanning Vibrating Electrode measurements, scientists have observed the formation of localized anodes beneath these silicate films. This is crucial because anodes are where corrosion actively occurs, as the metal dissolves into the surrounding environment.

The electrochemical activity reveals a concerning pattern. The copper surface beneath the silicate film acts as an anode, surrounded by a cathode formed by the free copper surface and the complete silicate-covered area. This creates a localized corrosion cell, where copper ions are released into the water. Further galvanostatic investigations reveal that the mechanism of copper dissolution is significantly altered by the presence of the silicate film.

Disrupted Ion Formation: The formation of Cu2+ ions, a common product of copper corrosion, is hindered under thick silicate films. Instead, only Cu+ ions are formed, indicating a shift in the electrochemical reaction.
Compromised Oxide Layer: The silicate film prevents the formation of a protective oxide layer, which normally shields the copper from corrosion. This leaves the copper vulnerable to further attack.
Accelerated Dissolution: Copper dissolution is significantly higher in the presence of a silicate film compared to a silicate-free surface, suggesting that the film promotes corrosion rather than preventing it.

This research provides critical evidence supporting the role of silicate films in the pitting corrosion of copper in cold water. By disrupting the natural protective mechanisms and accelerating copper dissolution, these films pose a significant threat to the integrity of copper water pipes and the quality of our drinking water.

Protecting Our Water: The Future of Copper Pipe Maintenance

The electrochemical research highlights the formation of galvanic elements on copper surfaces due to silicate film presence, especially at the phase boundary between bare copper and silicate-treated areas. The potential difference can reach 80 mV, leading to pit formation beneath silicate layers. The silicate layer modifies the dissolution mechanisms, indicated by potential changes during galvanostatic polarization. It also hinders protective oxide layer formation but doesn't stop copper dissolution. The key is managing aeration cells.