• DIY

    How to Prevent Metals from Corroding Part 3

    In part three of our series, we’re looking at how to prevent corrosion with advanced electrochemical solutions.

    Preventing mental corrosion with advanced electrochemical solutions

    Use a galvanisation process:

    Galvanised metal is metal that has been coated with a thin layer of zinc to protect it from corrosion. Zinc is more chemically-active than the underlying metal, so it oxidizes when exposed to air. Once the zinc layer oxidizes, it forms a protective coating, preventing further corrosion of the metal underneath. The most common type of galvanization today is a process called hot-dip galvanization in which metal parts (usually steel) are submerged in a vat of hot, molten zinc to gain a uniform coating.

    This process involves handling industrial chemicals, some of which are hazardous at room temperature and should not be attempted by anyone other than trained professionals. If you’re keen on having your metal galvanised, we can help connect you with a professional.

    The process goes like this:

    1. The steel is cleaned with a caustic solution to remove dirt, grease and paint and then thoroughly rinsed
    2. The steel is pickled in avid to remove mill scale, then rinsed
    3. A material called a flux is applied to the steel and allowed to dry – this helps the final zinc coating adhere to the steel
    4. The steel is dipped into a vat of molten zinc and allowed to heat to the temperature of the zinc
    5. The steel is cooled in a ‘quench tank’ containing water
    Use a sacrificial anode:

    One way to protect a metal object from corrosion is to electrically attach a small, reactive piece of metal called a sacrificial anode to it. Because of the electrochemical relationship between the larger metal object and the small reactive object (which we explain below), only the small, reactive piece of metal will undergo corrosion, leaving the large, important metal object intact. When the sacrificial anode corrodes completely, it must be replaced or the larger metal object will also begin to corrode. This method of corrosion protection is often used for buried structures, like underground storage tanks, or objects in constant contact with water, like boats.

    Sacrificial anodes are made from several types of reactive metal such as zinc, aluminium and magnesium. Because of their chemical properties, zinc and aluminium are popular for metal objects living in saltwater, while magnesium is preferred in freshwater situations.

    The reason sacrificial anodes work is because of the chemistry of the corrosion process itself: when a metal object corrodes, areas that chemical resemble the anodes and the cathodes in an electrochemical cell naturally form, causing electrons to flow from the most anode parts of the metal surface into surrounding electrolytes. Since sacrificial anodes are very reactive compared to the metal used in the larger object, the object itself becomes very cathodic, making electrons flow out of the sacrificial anode, causing it to corrode alone.

    Use impressed current:

    The chemical process behind metal corrosion involves electrical currents in the form of electrons flowing out of the metal, making it possible to use an outside source of electric current to overpower the corrosive current and prevent corrosion. This process benefits from continuous negative electrical charges on the metal being protected. This charge overpowers the current, which causes electrons to flow out of the metal, halting corrosion.

    This type of protection is often used for buried metal structures like storage tanks and pipelines.

    Use anodization:

    Anodising your metal involves a special type of protective surface coating used to inhibit corrosion; it’s often applied to dyes. For instance, brightly coloured metal carabiners are dyed anodised metal surfaces. Instead of involving the physical application of the protective coating, as in the case of painting metals, anodising uses an electric current to give metal a protective coating that prevents nearly all forms of corrosion.

    The chemical process behind this is based in the fact that many metals, like aluminium, naturally form chemical products called oxides when they come into contact with oxygen, to protect them against further corrosion. The electric current used in the anodising process essentially creates a much thicker build up of this oxide on the surface, to protect it from corrosion.

    This process involves handling industrial chemicals and should not be attempted by anyone other than trained professionals. If you’re keen on having your metal galvanised, we can help connect you with a professional.

    The process goes like this:

    • The aluminium is cleaned and de-greased
    • The surface impurities are removed with a de-smut solution
    • The aluminium is lowered into an acid bath set to a specific current and temperature
    • It’s removed and rinsed
    • Then it’s submerged in a dye at 28-60 degrees C
    • Then it’s sealed by placing it in boiling water for 20 to 30 minutes
    Use a metal that exhibits passivation:

    As we mentioned above, some metals naturally form a protective oxide coating when exposed to oxygen. Some metals form this oxide coating so effectively that they eventually become relatively chemically inactive. These metals are known as passive, which is in reference to the process of passivation by which they become less reactive.

    Depending on the desired use of a passive metal object, it may not need any extra protection to make it corrosion-resistant.

    Stainless steel exhibits passivation, because it’s an alloy of ordinary steel and chromium which is effectively corrosion-proof in almost all conditions. However, it’s important to remember that passive metals can become non-passive under certain extreme conditions.