Zirconium dioxide

Oral Biomaterials

Crystalline zirconium dioxide (zirconium oxide), ZrO2, called zirconia (not to be confused with zircon, which is a mineral, and Zirkon™, which is a product in the market) is manufactured for use as a white pigment from minerals by conversion to Zr(SO4)2, followed by hydrolysis. ZrO2 is used also as a refractory material (crucibles, furnace lining), and it is insoluble in water, only slightly soluble in HCl and HNO3, and, however, slowly soluble in HF upon heating with 66% H2SO4.

Zirconia is considered one of the best currently known biocompatible ceramic materials along with the metallic titanium.
Zirconium dioxide, or zirconia, ZrO2, is the word in presentday dentistry. We may say that zirconia is a material of choice in contemporary restorative dentistry for several reasons. Moreover, restorative dentistry is about adhesion promotion and about durable bonding of restorations. Zirconia has found wide applications in dental restorations, such as bridges, crowns, dental implant abutments, and full dental implant systems.
Zirconia caught attraction due its superior mechanical properties as superior flexure strength (which is 1200 MPa compared to 1000 MPa for steel), high fracture toughness, high hardness, excellent fatigue, and damage resistance. The material is resistant to chemical attacks and does not react easily with strong acids, alkalis, or other corrosive material. Regarding its physical properties, ZrO2 is a white and opaque material that does not dissolve or react with water and other solvents. It is an excellent thermal and chemical insulator and is used in fuel cells.

Uses

Zirconium dioxide (ZrO2) as an abrasive is used to make grinding wheels and special sandpaper. It is also used in ceramic glazes, in enamels, and for lining furnaces and hightemperature molds. It resists corrosion at high temperatures, making it ideal for crucibles and other types of laboratory ware. ZrO2 is used as a "getter" to remove the last trace of air when producing vacuum tubes.

Chemical Properties

Heavy, white, amorphous powder. Mohs hardness 6.5, refr index 2.2. Insoluble in water and most acids or alkalies at room temperature; soluble in nitric acid and hot concentrated hydrochloric, hydrofluoric, and sulfuric acids. Most heat resistant of commercial refractories; dielectric.

Chemical Properties

Zirconium dioxide is a white, amorphous powder, insoluble in water but slightly soluble in acid.

Physical properties

Monoclinic zirconia (baddeleyite structure) stable below 1197°C, tetragonal zirconia (rutile structure) stable between 1197 and 2300°C, cubic zirconia (fluorine structure) stable above 2300°C or at lower temperature if stabilized by addition of magnesia, calcia or yttria. Maximum service temperature 2400°C. Zirconia starts to act as an oxygen anion conductor at 1200°C. Highly corrosion resistant to molten metals such as Bi, Hf, Ir, Pt, Fe, Ni, Mo, Pu, and V. Strongly attacked by liquid metals Be, Li, Na, K, Si, Ti, Zr, and Nb. Insoluble in water, but slowly soluble in HCl and HNO₃;  soluble in boiling concentrated H₂SO₄ and alkali hydroxides but readily attacked by HF.

Physical properties

White, heavy, amorphous powder or monoclinic crystals; refractive index 2.13; density 5.68 g/cm³; Mohs hardness 6.5; transforms to tetragonal structure above 1,100°C and cubic form above 1,900°C; melts at 2,710°C and vaporizes at about 4,300°C; insoluble in water; soluble in hydrofluoric acid and hot sulfuric, nitric and hydrochloric acids.

Uses

Zirconium oxide (ZrO2) is the most common compound of zirconium found in nature. It has many uses, including the production of heat-resistant fabrics and high-temperature electrodes and tools, as well as in the treatment of skin diseases. The mineral baddeleyite (known as zirconia or ZrO2) is the natural form of zirconium oxide and is used to produce metallic zirconium by the use of the Kroll process. The Kroll process is used to produce titanium metal as well as zirconium. The metals, in the form of metallic tetrachlorides, are reduced with magnesium metal and then heated to “red-hot” under normal pressure in the presence of a blanket of inert gas such as helium or argon.

Uses

Instead of lime for the oxyhydrogen light; with earths of the yttrium group in incandescent lighting (Nernst lamps); as pigment, abrasive; manufacture of enamels, white glass, refractory crucibles, and furnace linings.

Uses

Lanthanum-modified lead zirconate titanate (PLZT) fibers with a diameter of around 300 microns were produced by a thermoplastic processing method. The main use of zirconia is in the production of ceramics with other uses including as a protective coating on particles of titanium dioxide pigments, as a refractory material, in insulation, abrasives and enamels. Stabilized zirconia is used in oxygen sensors and fuel cell membranes because it has the ability to allow oxygen ions to move freely through the crystal structure at high temperatures. This high ionic conductivity (and a low electronic conductivity) makes it one of the most useful electroceramics.Zirconium dioxide is also used as the solid electrolyte in electrochromic devices. Zirconia is a precursor to the electroceramic lead zirconate titanate (PZT), which is a high-K dielectric, which is found in myriad components.

Uses

Zirconium oxide occurs in nature as the mineral baddeleyite. The oxide has many industrial applications. It is used as a refractory material. It is used in making highly reflective glazes for ceramics, glasses, linings of metallurgical furnaces, crucibles, and laboratory equipment. The oxide is used to produce oxyhydrogen and incandescent lights. Other uses are in producing piezoelectric crystals, heat-resistant fibers, and high-frequency induction coils. The hydrous oxide is used in treating dermatitis resulting from poison ivy.

General Description

Zirconium(IV) oxide (ZrO₂) which is also known as zirconia is a ceramic nanoparticle that can be used as a nano-filler. It can be incorporated in a variety of polymer and metal composites to improve the thermo-mechanical properties of the base material.

Flammability and Explosibility

Non flammable

Industrial uses

There are several types of zirconia: a pure(monoclinic) oxide and a stabilized (cubic)form, and a number of variations such asyttria- and magnesia-stabilized zirconia andnuclear grades. Stabilized zirconia has a highmelting point, about 2760°C, low thermal conductivity,and is generally unaffected by oxidizingand reducing atmospheres and mostchemicals. Yttria- and magnesia-stabilized zirconiasare widely used for equipment and vesselsin contact with liquid metals. Monoclinicnuclear zirconia is used for nuclear fuel elements,reactor hardware, and related applicationswhere high purity (99.7%) is needed.Zirconia has the distinction of being an electricalinsulator at low temperatures, graduallybecoming a conductor as temperaturesincrease.

Carcinogenicity

To simulate the chronic alpha radiation of Thorotrast, the liver of female Wistar rats was exposed to fractionated neutron irradiation at 14-day intervals (0.2Gy per fraction) over 2 years to a total dose of 10.0Gy. Before the start of irradiation, half of the animals received 120 mL of nonradioactive Zirconotrast (ZrO2), which is comparable to Thorotrast in all other physical and chemical properties. The first liver tumor was detected 1 year after the beginning of irradiation. At the end of the life span study, the incidence of irradiated animals with liver tumors was about 40%. In the animals treated additionally with ZrO2, the incidence, time of onset, and overall number of liver tumors were nearly equal, indicating that the fractionated neutron irradiation was the exclusive cause of tumor development. The lifelong-deposited ZrO2 colloid had no influence on tumor induction or development. Histological types of benign and malignant liver tumors seen in this study were the same as those seen in animals treated with Thorotrast.