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Corrosion Inhibitor

Definition - What does Corrosion Inhibitor mean?

A corrosion inhibitor is a substance applied to a metal in order to reduce its corrosion rate. It is applied:

  1. on metal surfaces,
  2. in coolants, fuels, hydraulic fluids, boiler water, engine oil, and many other fluids used in industry, and
  3. in the concrete mixture when pouring concrete with steel rebar.

Safeopedia explains Corrosion Inhibitor

Iron and metals containing iron, such as steel, are most susceptible to corrosion. Titanium, copper, metallic chrome, and aluminum, on the other hand, are protected from corrosion by a thin film of oxygen on their surfaces. The oxygen reacts with the metal to form a metal oxide, which acts as a barrier against corrosion in a stable environment. Aluminum oxide, copper carbonate, titanium oxide, and chromium oxide, then, can act as protective coatings, preventing metal corrosion. Inhibitors vary by base metal (for example, zinc is a corrosion inhibitor for copper and aluminum).

Corrosion compromises safety in a number of ways—failures of bridges, aircraft, automobiles, boilers, gas pipelines, and so on. According to the National Association of Corrosion Engineers, the economic impact of corrosion totals 3 billion dollars per year in the United States.

Corrosion can contribute to contamination. Preventing corrosion is, therefore, an essential part of industrial and critical cleaning processes In the manufacture and assembly of critical components, both in and out of the cleanroom, Corrosion products on the product or the tooling can produce an uneven surface that traps contamination.

There are four types of corrosion inhibitors:

  1. Anodic Inhibitors - This type of corrosion inhibitor acts by forming a protective oxide film on the surface of the metal. It causes a large anodic shift that forces the metallic surface into the passivation region, which reduces the corrosion potential of the material. Some examples are chromates, nitrates, molybdates, and tungstate.
  2. Cathodic Inhibitors - These inhibitors slows down the cathodic reaction to limit the diffusion of reducing species to the metal surface. Cathodic poison and oxygen scavengers are examples of this type of inhibitor.
  3. Mixed Inhibitors - These are film-forming compounds that reduce both the cathodic and anodic reactions. The most commonly used mixed inhibitors are silicates and phosphates used in domestic water softeners to prevent the formation of rust water.
  4. Volatile Corrosion Inhibitors (VCI) - VCI are compounds being transported in a closed environment to the site of corrosion by the process of volatilization from a source. For example, in boilers, volatile compounds such as morpholine or hydrazine, are transported with steam to prevent corrosion in condenser tubes.
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