Nowadays, there is a debate whether Zirconium is a metal or ceramic material. This post pretends to clarify the frequently asked questions from both the professionals and the patients.
Zirconium, the chemical element:
Zirconium is a chemical element with atomic number 40, located in group 4 from the periodic chart of elements. Its symbol is Zr. It is a hard metal, resistant to corrosion and similar to steel. It does not exist in nature in the pure state. It can be obtained through complex physico-chemical process. In the periodic chart, it is located next to Titanium (Ti). For this reason their properties are very similar.
Zirconium found in minerals:
The most important minerals that contain zirconium are zircon (ZrSiO4) and badeleyita (ZrO2). Zirconium is always found mixed together with Hafnium (Hf), and they are very difficult to separate them.
Occurrence and Refining:
Zirconium has a concentration of about 130 mg/kg within the earth’s crust and about 0.026 μg/L in sea water, though it is never found in nature as a native metal. The principal commercial source of zirconium is the zirconium silicate mineral, zircon (ZrSiO4), which is found primarily in Australia, Brazil, India, Russia, South Africa, and the United States. 80% of zircon mining occurs in Australia and South Africa.
Zirconium also occurs in more than 140 other recognized mineral species including baddeleyite andkosnarite. This metal is commercially produced mostly by the reduction of the zirconium(IV) chloride withmagnesium metal in the Kroll process. Commercial-quality zirconium for most uses still has a content of 1% to 3% hafnium.
Zircon mine. Australia
This zircon sand is the raw material to obtain pure METAL (Zr 99%) and the Zirconium oxide CERAMIC (ZrO2) .
Production of Pure Metal Zirconium (Zr 99%):
To obtain the pure metal, the process “Van Arkel” is used to obtain a zirconium sponge called Zirconium crystal-bar.
The “crystal-bar” can be melted to obtain the zirconium rod or ingot. The pure zirconium is mainly used in the nuclear reactors as containers for the nuclear fuel, and also to form compounds highly resistant to corrosion.
This metal is grey, shining and very resistant to corrosion. It is lighter than steel, and hardness similar to copper.
Production of zirconium oxide ceramic = Zirconia = ZrO2
Zirconium ceramic is obtained through a reductive clorination (Kroll process). At the end of this process, one can obtain zirconium oxide powder (which is a ceramic and no longer a metal).
Zirconia (ZrO2) = zirconium ceramic
ZIRCONIA is a powder that is used as pigment for white paints, and also in the abrasives. At room temperature presents a monoclínic phase. This cofiguration is extremely fragile.
To improve the properties of zirconia (ZrO2), other elements are added to the compound to stabilize the molecular structure: ex. Yttrium (Y). Through a mixture and sintering process, the final ceramic structure is stabilized. The Y-TZP is the Yttrium stabilized Tetragonal Zirconium Policrystal.
The Y-TZP ceramic is the material that is used in dentistry as ZIRCONIA (not ZIRCONIUM). Simply, it has been always easier to say zirconium than Y-TZP.
METAL vs CERAMIC
METAL Zr 99%
- Color metal grey
- Weak metallic bonds
- Thermic conductor
- Electric conductor
- easy oxidation
- chemical corrosion
- used in nuclear reactors
Y-TZP CERAMIC (ZrO2)
- Color white
- Strong cobalent bonds
- Wear resistant
- Thermic insulator
- Electric insulator
- Oxidation resistant
- No chemical corrosion
- Used in technical ceramics