Tantalum hafnium carbide is a

refractory In materials science, a refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycrystalline, polyphase, ...

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with a general formula , which can be considered as a solid solution of

tantalum carbide Tantalum carbides (TaC) form a family of binary chemical compounds of tantalum and carbon with the empirical formula TaC''x'', where ''x'' usually varies between 0.4 and 1. They are extremely hard, brittle, refractory ceramic materials with metal ...

and

hafnium carbide Hafnium carbide ( Hf C) is a chemical compound of hafnium and carbon. Previously the material was estimated to have a melting point of about 3,900 °C. More recent tests have been able to conclusively prove that the substance has an even hig ...

Properties

Individually, tantalum and hafnium carbide have the highest

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...

s among the

binary compound In materials chemistry, a binary phase or binary compound is a chemical compound containing two different elements. Some binary phase compounds are molecular, e.g. carbon tetrachloride (CCl4). More typically binary phase refers to extended soli ...

s, and , respectively, and their "alloy" with a composition Ta₄HfC₅ has an melting point of . Very few measurements of melting point in tantalum hafnium carbide have been reported, because of the obvious experimental difficulties at extreme temperatures. A 1965 study of the TaC-HfC solid solutions at temperatures 2,225–2,275 °C found a minimum in the vaporization rate and thus maximum in the thermal stability for Ta₄HfC₅. This rate was comparable to that of

tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...

and was weakly dependent on the initial density of the samples, which were

sintered Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing ...

from TaC-HfC powder mixtures, also at 2,225–2,275 °C. In a separate study, Ta₄HfC₅ was found to have the minimum oxidation rate among the TaC-HfC solid solutions. Ta₄HfC₅ was manufactured by Goodfellow company as a 45

µm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer ( American spelling), also commonly known as a micron, is a unit of length in the International System of Uni ...

powder at a price of $9,540/kg (99.0% purity). In 2015, atomistic simulations predicted that

hafnium carbonitride Hafnium carbonitride (HfCN) is a mixed anion chemical compound of hafnium, carbon and nitrogen. With a melting point of above 4,000 °C, it is the most refractory compound known. No other substance has a higher melting point at atmospheric press ...

could have a melting point exceeding Ta₄Hf₁C₅ by 200 K. This was later verified by experimental evidence in 2020.

Structure

Individual tantalum and hafnium carbides have a rocksalt cubic lattice structure. They are usually carbon deficient and have nominal formulas TaC_x and HfC_x, with x = 0.7–1.0 for Ta and x = 0.56–1.0 for Hf. The same structure is also observed for at least some of their solid solutions. The density calculated from

X-ray diffraction X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

data is 13.6 g/cm³ for Ta_0.5Hf_0.5C. Hexagonal

NiAs Nias ( id, Pulau Nias, Nias language: ''Tanö Niha'') (sometimes called Little Sumatra in English) is an island located off the western coast of Sumatra, Indonesia. Nias is also the name of the archipelago () of which the island is the centre ...

-type structure (

space group In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it uncha ...

P63/mmc, No. 194,

Pearson symbol The Pearson symbol, or Pearson notation, is used in crystallography as a means of describing a crystal structure, and was originated by W. B. Pearson. The symbol is made up of two letters followed by a number. For example: * Diamond structure ...

hP4) with a density of 14.76 g/cm³ was reported for Ta_0.9Hf_0.1C_0.5.

References

{{hafnium compounds Refractory materials Carbides Tantalum compounds Hafnium compounds

Properties

Structure

See also

References