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Iron(II) oxide

physical science Maturity 5-7 Next article →

Iron(II) oxide is a special kind of matter. It is an inorganic compound with the formula FeO. Many people call it ferrous oxide. It looks like a black powder. Some people think it is the same as rust. However, rust is actually a different thing called hydrated iron(III) oxide. In nature, this substance is a mineral called wüstite.

This substance has a very neat way it works. It uses a cubic, rock salt structure. In this shape, iron atoms are held by oxygen atoms. The oxygen atoms are also held by iron atoms. They form a pattern called octahedral coordination. Sometimes the mix is not perfect. This is called non-stoichiometry. This happens when some iron is replaced by iron(III).

Scientists have studied how to make this powder. One way is through thermal decomposition of iron(II) oxalate. This must happen under an inert atmosphere. This keeps iron(III) oxide from forming. You can also make it by heating Fe0.95O with metallic iron. This requires a heat of 770 °C. It also needs a pressure of 36 kbar.

We can find this powder deep underground. It makes up about 9% of the Earth's mantle. The mantle is a layer inside our planet. This powder might be electrically conductive. This could explain some changes in how the Earth rotates. These changes are not explained by other mantle models. It is a big part of our world.

People use iron(II) oxide for many helpful jobs. It is used as a pigment to add color. The FDA says it is safe for cosmetics. It is even used in some tattoo inks. You can also find it in home aquaria. It works as a phosphate remover for fish tanks. It is a very useful black powder.

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