Zirconium dioxide (ZrO2), which is also referred to as zirconium oxide or zirconia, is an inorganic metal oxide that is mainly used in ceramic materials. Zirconium dioxide succeeds zirconium as the compound of the element zirconium that most frequently occurs in nature.
Zirconium is a heavy metal of which 0,016 % is found in the earth crust and which, thus, occurs more frequently than the elements chlorine and copper. Its great hardness, low reactivity, and high melting point have made it the oldest mineral that can be found on the earth. Zirconium does not occur massively but is bound in minerals, mainly in zircon (ZrSiO4).
Zircon is also known as a precious stone whose color may vary from colorless white to brown, green, etc., depending on the traces of impurities. Due to their high optical density, zircon (and zirconia) gems have high refraction indices. Provided they are pure and large enough, they are suited, therefore, as (cheaper) substitutes for diamonds. None of the natural isotopes of zircon is radioactive. Yet, since zircon is relatively often impurified with uranium oxides and other radioactive substances such as thorium salts, it is responsible for much of the natural radioactive radiation. Geological age determination through radioactive dating, for example, makes use of such impurities.
Zirconium dioxide is the most important zirconium compound which due to its properties is used in various products. In nature, ZrO2 occurs in the mineral form as baddeleyite, a modification in monoclinic crystal lattices (which is often found as weathered grit in gravel). Zirconium dioxide is non-magnetic and highly resistant against acids, alkaline lyes, and exogenous (chemical, thermal, and mechanical) influences.
Zirconium dioxide has a high thermal stability. It does not melt below 2680 °C, which is why it is used in high-temperature ceramics such as crucibles or furnaces. Since, in addition, it has a high mechanical stability and is very resistant to abrasion, it serves to e.g., improve the properties (especially the scratch resistance) of varnishes and coatings applied as top coats to automobiles, or as finishes to parquets and furniture. Zirconium dioxide is also found in varnishes for electronic items, in nail polishes, in ink jet printer’s inks, and other products. Besides, it is known as an abrasive and is found (like titanium dioxide) as a white pigment in porcelain.
Moreover, hip joint endoprostheses and other high-performance medical ceramics benefit from the advantages of zirconium dioxide. Dentistry makes use of its special properties when manufacturing corona frames and bridge frames, tooth root studs, and metal-free dental implants. Zirconium dioxide is the most widely used oxide ceramic next to aluminium oxide. Thanks to its electrolytic conductivity, it was used as early as in 1897 in the incandescent bodies (ceramic rods) of the Nernst lamp, an electrically powered incandescent lamp invented by the German physicist and chemist Walther Nernst.