Ferric oxides are often added to coatings and foundry moulding materials in order to suppress casting defects like pinholes. By the delivery of oxygen with T>1200°C free hydrogen and nitrogen can be bind. Castings defects resulting from thermal expansion are reduced by the addition of ferric oxide to the moulding material, because the thermal expansion of the moulding material is reduced. Usually a-Fe₂O₃ (hematite), a-FeOOH (goethite) bzw. g-FeOOH (lepidikrokite) with specific surfaces >10m²/g are used. Ferric oxide may show sperical, plate-like or needle-like shape depending upon type of production and may be also used as a rheologic additive.