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Chlorides and Corrosion: Why Does Chloride in Seawater Have Such a Big Impact on Metals?
Chlorides, whether in the form of chloride ions or in a covalent form bound to other molecules, are ubiquitous compounds in nature. The properties and behavior of these compounds have a significant impact on many industrial and environmental processes. Especially in seawater, the corrosion rate of metals caused by high concentrations of chloride cannot be underestimated.
Chloride has important physiological significance in biological systems, including regulating osmotic pressure and acid-base balance.
We often hear that seawater can affect the durability of metal structures, mainly because of the special properties of chloride. Chlorides usually exist as ions in water, which makes them more likely to react with oxides on metal surfaces, causing corrosion. Particularly with stainless steel, aluminum and other high-alloy materials, chlorides can exacerbate the risk of localized corrosion. Therefore, it is very necessary to understand the behavior of chlorides and how they affect the long-term stability of metals.
Characteristics and sources of chloride
Chloride occurs in many forms in nature, with particularly high concentrations in seawater. According to research, the chloride concentration in seawater is about 19,400 mg/liter, and the concentration in some inland seas is even higher. Since chlorides are usually water-soluble, they are rare in minerals found in dry climates or deep underground.
In the environment, excess chloride can cause damage to ecosystems.
The sources of chloride in seawater are not limited to the ocean itself, but also include by-products of some industrial and agricultural activities, such as the use of road salt and chloride fertilizers used for agricultural irrigation. Therefore, businesses and governments need to consider the potential impacts of chlorides when designing new infrastructure and industrial processes.
Chemical mechanism of corrosion
The process of metal corrosion caused by chloride mainly involves the interaction between chloride ions and the oxide layer on the metal surface. These chloride ions can penetrate the protective layer on the metal surface, causing so-called "localized corrosion", which is one of the most dangerous forms of corrosion.
Corrosion caused by chlorides can cause rapid deterioration of metal structures and may pose a safety hazard.
In concrete, the presence of chlorides can destroy the oxide layer protecting the steel bars, causing localized corrosion of the steel bars. This poses a potential threat to the long-term stability of buildings and bridges. Therefore, the concentration of chloride and its effect on materials are considered in the construction codes of many cities and regions.
Environmental and ecological impact
Excess chloride not only affects metals but also poses a threat to ecosystems. When the concentration of chloride is too high, it can cause acidification of water bodies and may promote the release of toxic heavy metals, affecting the survival and reproduction of aquatic plants and animals. Many studies have pointed out that the increase in salinity can prompt organisms originally living in freshwater to move to higher salinity environments, which will not only change the local ecological balance, but may also lead to the loss of biodiversity.
Chloride concentration monitoring has become an important part of water quality monitoring in various countries.
In water quality monitoring, chloride is a well-known indicator due to its stability and non-reactivity, used to detect pollution levels in rivers and groundwater. Many water quality monitoring agencies rely on chloride levels to assess potential pollution risks.
Preventive measures and future challenges
Faced with the possible corrosive effects of chloride, engineers and designers are taking various preventive measures, including using corrosion-resistant materials, strengthening protective coatings and reducing chloride exposure. These measures not only help extend the life of the structure but also reduce maintenance costs.
However, as global climate change and industrialization continue, the environmental and health challenges posed by chlorides continue to evolve. Efforts are needed to find new solutions to reduce chloride releases and monitor their effects.
How should we find the balance in the future to protect metal structures while safeguarding our environment and ecosystems?
