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micaceous iron oxide (MIO)

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Paul Oman, MS, MBA - Progressive Epoxy Polymers, Inc.

Member: NACE (National Assoc. of Corrosion Engineers), SSPC (Soc. of Protective Coatings)

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micaceous iron oxide - (MIO)

MIO - Micaceous Iron Oxide - is considered an anti-corrosive additive used in many kinds of paints and coating for over 100 years and is perhaps the most important barrier pigment used in coatings to protect structural steel. Its use is much more common in Europe than in the USA. It is regularly used to protect steel surfaces from the elements and corrosion and used on steel boat hulls, bridges etc. The classic example is the Eiffel Tower in Paris. Big Ben in London and the Sidney Harbor Bridge in Australia are other examples. In the USA, MIO based coatings can be found on the Golden Gate Bridge and the San Francisco Bay Bridge. It is also used for durability and reliability on electrical and industrial equipment.

The flake-like gray or red MIO particles align parallel to the coated surface producing a layer of shield of overlapping plates (author's note: I believe this is also the mechanism for the amazing properties of our aluminum pigmented, moisture cured urethane - called Aluthane).

MIO pigment is used in paints to provide long-term durability. MIO paints have been used continuously since the early 1900's to protect steel.

MIO, also known as specular haematite and flaky haematite, is a natural mineral ore that, after it is refined, consists mainly of Fe2O3. MIO differs in form and shape from the well-known iron oxides that are used as pigments for red, yellow, brown and black pigmentation. MIO shows a flaky, lamellar structure and is dark grey with a metallic sheen. The term “micaceous” is used because the lamellar particles are similar to mica.

MIO is insoluble in water, organic solvents and alkalis and is only slightly soluble in strong acids at elevated temperatures. It is non-reactive with most chemicals and is heat-stable up to its melting point of over 1,500°C.

MIO is used widely in protective coatings due to its outstanding anti-corrosive properties. When MIO is incorporated into a coating at an appropriate level, the flakes align parallel to the substrate surface, producing a shield or barrier of overlapping plates. The flakes are impermeable—a physical barrier is formed to the ingress of the water, oxygen and ions that corrode steel and degrade the binder system. MIO flakes are strong UV absorbers and very weather-resistant. This protects the surface of the binder system from the degrading action of UV and other weathering elements. MIO reinforces the binder matrix and increases the substrate adhesion and inter-coat adhesion.

The size of MIO flakes (normally 40 to 50 µm long and 5 to 10 µm thick) dictates a dry-film thickness in excess of 50 µm to achieve a shield of overlapping flakes. For this reason, MIO is normally found in high-film-build intermediate and finishing coats.

More 3rd Party web info on MIO:

MIO article #1 - Click Here

MIO Article #3 - Click Here

Progressive Epoxy Polymers, Inc. (www.epoxyproducts.com) is pleased to offer powdered MIO in 1 quart (4 pound) units.

Find this product in our industrial catalog - Click Here

Find this product in our marine catalog - Click Here

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