Refractory Diborides of Zirconium and Hafnium

Abstract

This paper reviews the crystal chemistry, synthesis, densification, microstructure, mechanical properties, and oxidation behavior of zirconium diboride (ZrB2) and hafnium diboride (HfB2) ceramics. The refractory diborides exhibit partial or complete solid solution with other transition metal diborides, which allows compositional tailoring of properties such as thermal expansion coefficient and hardness. Carbothermal reduction is the typical synthesis route, but reactive processes, solution methods, and pre‐ceramic polymers can also be used. Typically, diborides are densified by hot pressing, but recently solid state and liquid phase sintering routes have been developed. Fine‐grained ZrB2 and HfB2 have strengths of a few hundred MPa, which can increase to over 1 GPa with the addition of SiC. Pure diborides exhibit parabolic oxidation kinetics at temperatures below 1100°C, but B2O3 volatility leads to rapid, linear oxidation kinetics above that temperature. The addition of silica scale formers such as SiC or MoSi2 improves the oxidation behavior above 1100°C. Based on their unique combination of properties, ZrB2 and HfB2 ceramics are candidates for use in the extreme environments associated with hypersonic flight, atmospheric re‐entry, and rocket propulsion.

Evidence of multiband behavior in the superconducting alloy Zr0.96V0.04B2Renosto1, Consoline2, Santos3 et al. 2013Phys. Rev. B284251View full textAdd to dashboardCite

“…The simulation of the structure and refinement of the lattice parameters were obtained using the Rietveld method, adopting as a reference the ZrB 2 phase crystallographic data reported in the literature. 17 Magnetic, electric, and thermal initial characterizations were made using a Quantum Design PPMS Evercool II. Magnetization (M) measurements were obtained with a vibrating sample measurement system in a DC external field at 50 Oe with both zero field cooling and field cooling regimes, in the temperature (T ) range from 2 to 20 K. The hysteresis loops of the M versus applied magnetic field (H ) curves were obtained at 2 K in the range −500 μ 0 H 500 Oe.…”

Comparative study of the electronic structure, phonon spectra, and electron-phonon interaction of ZrB2and TiB2

“…The various elementsε αβ are composed of real and imaginary parts as follows:ε αβ = ε (1) αβ + iε (2) αβ , where α, β ≡ x, y, z; ε xx = (n + ik) 2 ; n and k are the refractive index and extinction coefficient, respectively. The optical conductivity tensorσ αβ = σ (1) αβ + iσ (2) αβ is related to the dielectric tensor ε αβ through the equation…”

“…5,6 In particular, ZrB 2 has the lowest theoretical density among the ultra-high temperature ceramics, which makes it an attractive material for aerospace applications. 1,2,4 Titanium diboride is also potentially useful because it has many interesting physical properties, such as low density and unusual strength. 7 TiB 2 is widely accepted for applications including microelectronics, diffusion barriers, wear-and erosion-resistant coatings for cutting tools and other mechanical components.…”

“…1,2 Among them, diborides such as ZrB 2 and HfB 2 have a unique combination of mechanical and physical properties: high melting points (>3000 • C); high thermal and electrical conductivity; chemical inertness against molten metals; great thermal shock resistance. [1][2][3] Thus, although carbides typically have the highest melting points (>3500 • C), the diborides ZrB 2 and HfB 2 are more attractive candidates for high-temperature thermomechanical structural applications at temperatures ≥3000 • C. 1,2 Potential applications include thermal protective structures for leading-edge parts on hypersonic re-entry space vehicles, 1,4 propulsion systems, 1,4 furnace elements, 5 refractory crucibles, 5 and plasma-arc electrodes. 5,6 In particular, ZrB 2 has the lowest theoretical density among the ultra-high temperature ceramics, which makes it an attractive material for aerospace applications.…”

Direct current magnetron sputtered ZrB2 thin films on 4H-SiC(0001) and Si(100)

“…Zirconium diboride (ZrB2) lends its high hardness, high melting point, and low resistivity from a hexagonal crystal structure, where the boron atoms form honeycombed, graphitelike sheets that are stacked between hexagonal close packed zirconium layers [1]. The ceramic properties, demonstrated by ZrB2, originate from covalent type of bonding between the metal and boron atoms as well as between the boron atoms in the sheet, whereas the electrical conductivity stem from metal-metal bonding and electron transfer from the metal to the boron sheet to yield graphite-like conduction.…”