Description
Zirconium diboride (ZrB2) is a highly covalent refractory ceramic material with a hexagonal crystal structure. ZrB2 is known as a UHTC with a melting point of 3246C. This together with its relatively low density of B6.09 g/cm3 (measured density may be higher due to hafnium impurities) and good high-temperature strength makes it a contender for high-temperature aerospace applications, for example, hypersonic flight or rocket propulsion systems. It is an unusual ceramic with relatively high thermal and electrical conductivities.
Chemical Properties
Zirconium boride, also known as zirconium diboride, a gray metallic crystals or powders. Mohs hardness 8, electrical resistivity 9.2 micro-ohm-cm (20°C), excellent thermal shock resistance, poor oxidation resistance above 1100°C. It was attacked very little by cold HCl, more rapidly by HNO3, and is dissolved by aqua regia. It reacts with H2SO4 and is readily attacked by fused alkali hydroxides, carbonates, and disulfides.
Zirconium diboride (ZrB2) is a transition metal boride with a hexagonal crystal structure and P6/mmm symmetry. ZrB2 has a combination of metallic, ionic, and covalent bonds. Due to its strong covalent bonds, ZrB2 has a high melting temperature of 3250°C. This melting temperature classifies ZrB2 as an ultra-high temperature ceramic (UHTC). UHTCs have been proposed for use in many different applications due to their high melting temperatures (>3000°C), as well as their high strength and chemical inertness.
Physical properties
Gray metallic crystals, excellent
thermal shock resistance,
greatest oxidation inertness
of all refractory hardmetals.
Hot-pressed crucible for
handling molten metals such
as Zn, Mg, Fe, Cu, Zn, Cd, Sn,
Pb, Rb, Bi, Cr, brass, carbon
steel, cast irons, and molten
cryolithe, yttria, zirconia, and
alumina. Readily corroded by
liquid metals such as Si, Cr, Mn,
Co, Ni, Nb, Mo, Ta and attacked
by molten salts such as Na O, 2
alkali carbonates, and NaOH.
Severe oxidation in air occurs
above 1100–1400°C. Stable
above 2000°C in inert or
reducing atmosphere.
Uses
Zirconium boride is use to improve resistance in zirconia-based, carbon-bonded refractories in contact with ferrous melts. Used in nuclear applications, aerospace refractory, in cutting tools and to protect thermocouple tubes. It also used in use of its relatively high conductivity, especially for a ceramic.
Application
Zirconium diboride (ZrB2) is an ultra high termparature ceramic powder. With good high temperature strength, it is used in the aerospace industry for hypersonic flight or rocket propulsion. ZrB2 is a kind of senior engineering material broadly used in various fields. Refractory for aircraft and rocket applications, thermocouple protection tubes, high temperature electrical conductor, cutting tool component, coating tantalum, cathode in high-temperature electrochemical systems.
Industrial uses
Zirconium boride is a microcrystalline graypowder of the composition ZrB2. When compressedand sintered to a specific gravity ofabout 5.3, it has a Rockwell A hardness of 90,a melting point of 2980°C, and a tensilestrength of 241 to 276 MPa. It is resistant tonitric and hydrochloric acids, to molten aluminumand silicon, and to oxidation. At 1204°Cit has a transverse rupture strength of 379 MPa.It is used for crucibles and for rocket nozzles.
Synthesis
Zirconium boride powder is mainly prepared by carbothermic reduction of ZrO2 powder and carbon black or graphite powder. The reaction equation is:
3ZrO2+B4C+8C+B2O3=3ZrB2+9CO↑
Zirconium boride obtained from zirconia and boron oxide by magnesiothermic MASHS.
