'Zirconia – Ceramic steel'. The title of the first scientific paper to highlight the possibilities offered by the " transformation toughening" mechanism which occurs in certain zirconia ceramics. Since the publication of this seminal work in 1975, considerable research, development, and marketing effort has been expended on this single material which offers the traditional ceramic benefits of hardness, wear resistance, and corrosion resistance, without the characteristic ceramic property of absolute brittleness.

Mechanical and Physical Properties

The fundamental properties of Technox? zirconia ceramic which are of interest to the engineer or designer are:

- High strength
- High fracture toughness
- High hardness
- Wear resistance
- Good frictional behaviour
- Non-magnetic
- Electrical insulation
- Low thermal conductivity
- Corrosion resistance in acids and alkalis
- Modulus of elasticity similar to steel
- Coefficient of thermal expansion similar to iron

Key Features of Some Advanced Technical Ceramics

Characteristics	Unit	95 Al2O3	99 Al2O3	ZrO2	SSiC	SiSiC	B4C	HPS3N4
Color		white	ivory	white	black	black	black	dark gray
Density	g/cm3	3.65	3.88	6.05	3.12	3.06	2.51	3.25
Young's Modulus	Gpa	280	350	205	400	320	420	310
Vickers Hardness	Gpa	14	20	12	25	22	36	22
Flexural Strength	Mpa	280	300	900	400	300	370	850
Compressive Strength	Mpa	1700	2000	2500	2200	2000	2900	2800
Thermal Conductivity	W/(m?K)	25	30	2.2	100	130	35-40	27
Thermal shock resistance	ΔT(C°)	220	180-200	400	350	220	130	450-650
Max. Working Temperature	C°	1500	1700	850	1500	1300	1500	1200
Volume Resistivity ( 20 C° )	Ω?cm	>10^15	>10^14	>10^12	>10^6	>10^6	_	>10^14

The usual nomenclature used to describe zirconia ceramic alloys is as detailed below

- TZP tetragonal zirconia polycrystals
- PSZ partially stabilised zirconia
- FSZ fully stabilised zirconia
- TTC transformation toughened ceramics
- ZTA zirconia toughened alumina
- TTZ transformation toughened zirconia