Measuring the thickness of micaceous iron oxide coatings
Micaceous iron oxide (MIO) coatings are called for wherever maximum corrosion protection is essential: Steel bridges, power poles, and even famous structures like the Eiffel Tower or Sydney Harbour Bridge are shielded against the elements with a layer of this specific type of paint. To ensure the coating actually lasts as long as foreseen by the manufacturer, a certain layer thickness must be applied and checked.
Micaceous iron oxide (MIO) is not – as often assumed – ground iron but is rather a form of the naturally occurring mineral hematite; mixed as an additive into paint, MIO forms an additional, protective barrier against corrosion. A crystalline iron oxide mineral consisting mainly of iron III oxide, powdered MIO is flaky in texture; when suspended in viscous epoxides, the minerals align themselves parallel to the surface as the paint dries, forming a dense, nearly impenetrable shield of overlapping plates that repels water and other rust-forming elements. Known as "scale armour paint", MIO coatings are used for extremely heavy-duty applications.
Typical for MIO paint is its red-brown tint. Famous structures such as the Eiffel Tower in Paris, the Giant Ferris Wheel in Vienna, the Sydney Harbour Bridge and Istanbul’s Bosphorus Bridge are all protected with it.
While found primarily on galvanized steel parts, MIO coatings can also be used on non-galvanized steel, iron and aluminium. However, the reliability and longevity of the corrosion resistance depend on the thickness of the coatings, which are generally applied about 80-120 microns thick.
Just like with normal paint layers, the thickness of MIO coatings can be measured using the magnetic induction method, as hematite itself is antiferro-magnetic; thus, the MIO coatings are usually not magnetic either. Instruments from FISCHER’s FMP handheld series are ideally suited for this task. Due to the paint’s relatively high surface roughness, FISCHER also recommends the use of one of its robust probes with carbide metal tips, which have particularly long service life: the F20H.
The addition of platelet-shaped minerals to so-called MIO coatings boosts the corrosion protection for structures that are constantly exposed to weather. Using the handheld instruments from the FMP series and the durable F20H probe, the thickness of MIO coatings can be measured quickly and accurately. For more information, please contact your local FISCHER representative.
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