Chemical Properties
dark, gray, brittle solid; fcc, a=0.4640 nm; high cross section for absorption of thermal neutrons; resistivity 8.8μohm· cm; most refractory binary material known; hardness 2300kgf/mm2; used in control rods of nuclear reactors; can be prepared by heating HfO2 with lampblack under H2 at 1900°C–2300°C; used in crucible form for melting hafnium oxide, other oxides [KIR80] [HAW93] [CER91]
Usage
Used for preparation of ultra-high temperature ceramics 1 Reactant in synthesis of hafnium-containing organometallic polymers 2 Additive in alloys 3 Used in coatings 4
Uses
Used for preparation of ultra-high temperature ceramics 1 Reactant in synthesis of hafnium-containing organometallic polymers 2 Additive in alloys 3 Used in coatings 4
Physical properties
Dark gray brittle solid, most
refractory binary material
known. Controls rods in nuclear
reactors, crucible container for
melting HfO and other oxides. 2
Corrosion resistant to liquid
metals such as Nb, Ta, Mo, and
W. Severe oxidation in air above
1100–1400°C and stable up to
2000°C in helium.
Production Methods
Hafnium carbide is a dark gray, brittle solid. It can be
prepared by heating a mixture of the elements or by reacting
hafnium tetrachloride with methane at 2100 C. Sufficient
quantities of hafnium oxide or hafnium metal sponge are
obtained during the large-scale production of pure zirconium
for nuclear reactors. On an industrial scale, hafnium carbide
can be produced from the hydrided hafnium sponge at
1500–1700 ℃ or from hafnium oxide at 2000–2200 ℃ by
carburization in vacuo in the presence of hydrogen.
The resulting carbide contains almost the theoretical quantity
of carbon (6.30% °C) and a maximum of 0.1% free carbon
(219). The hafnium carbide obtained is not a true
stoichiometric compound as much as a solution of carbon
at specific interstitial sites of a face-centered cubic hafnium
lattice.
Hafnium carbide is inert to most reagents at room temperature
but is dissolved by hydrofluoric acid solutions.
Hafnium carbide reacts exothermally with halogens at
250–500 ℃to form hafnium tetrahalide, and to form hafnium
oxide with oxygen above 500℃. In the presence of hydrogen,
hafnium carbide slowly loses some of its carbon at higher
temperatures.
reaction suitability
core: hafnium
reagent type: catalyst
