Zirconium carbide () is an extremely hard

refractory In materials science, a refractory (or refractory material) is a material that is resistant to decomposition by heat or chemical attack and that retains its strength and rigidity at high temperatures. They are inorganic, non-metallic compound ...

ceramic A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcela ...

material, commercially used in

tool bit In machining, a tool bit is a non-rotary cutting tool used in metal lathes, shapers, and planers. Such cutters are also often referred to by the set-phrase name of single-point cutting tool, as distinguished from other cutting tools such as a s ...

s for cutting tools. It is usually processed 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 process used with metals, ceramics, plas ...

Properties

It appears as a gray metallic powder with

cubic Cubic may refer to: Science and mathematics * Cube (algebra), "cubic" measurement * Cube, a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex ** Cubic crystal system, a crystal system w ...

crystal structure In crystallography, crystal structure is a description of ordered arrangement of atoms, ions, or molecules in a crystalline material. Ordered structures occur from intrinsic nature of constituent particles to form symmetric patterns that repeat ...

. It is highly

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

resistant. This group IV interstitial transition-metal carbide is also an example of ultra high temperature ceramics (UHTC). Due to the presence of metallic bonding, ZrC has a

thermal conductivity The thermal conductivity of a material is a measure of its ability to heat conduction, conduct heat. It is commonly denoted by k, \lambda, or \kappa and is measured in W·m−1·K−1. Heat transfer occurs at a lower rate in materials of low ...

of 20.5 W/(m·K) and an electrical conductivity of around 2.3 megasiemens per metre, both of which are similar to that for

zirconium Zirconium is a chemical element; it has Symbol (chemistry), symbol Zr and atomic number 40. First identified in 1789, isolated in impure form in 1824, and manufactured at scale by 1925, pure zirconium is a lustrous transition metal with a greyis ...

metal. The strong covalent Zr-C bond gives this material a very high melting point (~3530 °C), high

elastic modulus An elastic modulus (also known as modulus of elasticity (MOE)) is a quantity that describes an object's or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it. Definition The elastic modu ...

(~440 GPa) and

hardness In materials science, hardness (antonym: softness) is a measure of the resistance to plastic deformation, such as an indentation (over an area) or a scratch (linear), induced mechanically either by Pressing (metalworking), pressing or abrasion ...

(25 GPa). ZrC has a lower

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

(6.73 g/cm³) compared to other carbides like WC (15.8 g/cm³), TaC (14.5 g/cm³) and HfC (12.67 g/cm³). ZrC seems suitable for use in

re-entry vehicle Atmospheric entry (sometimes listed as Vimpact or Ventry) is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. Atmospheric entry may be ''uncontrolled entry ...

rocket A rocket (from , and so named for its shape) is a vehicle that uses jet propulsion to accelerate without using any surrounding air. A rocket engine produces thrust by reaction to exhaust expelled at high speed. Rocket engines work entirely ...

scramjet A scramjet (supersonic combustion ramjet) is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow. As in ramjets, a scramjet relies on high vehicle speed to compress the incoming air forcefully b ...

engines or supersonic vehicles in which low densities and high temperature load-bearing capabilities are crucial requirements. Like most carbides of

refractory metals Refractory metals are a class of metals that are extraordinarily resistant to heat and wear. The expression is mostly used in the context of materials science, metallurgy and engineering. The definitions of which elements belong to this group di ...

, zirconium carbide is sub-stoichiometric, i.e., it contains carbon vacancies. At carbon contents higher than approximately the material contains free carbon. ZrC is stable for a carbon-to-metal ratio ranging from 0.65 to 0.98. The group IV and group IVa element carbides,

TiC A tic is a sudden and repetitive motor movement or vocalization that is not rhythmic and involves discrete muscle groups. Tics are typically brief and may resemble a normal behavioral characteristic or gesture. Tics can be invisible to the obs ...

, ZrC, and

SiC The Latin adverb ''sic'' (; ''thus'', ''so'', and ''in this manner'') inserted after a quotation indicates that the quoted matter has been transcribed or translated as found in the source text, including erroneous, archaic, or unusual spelling ...

are practically inert toward attack by strong aqueous acids (e.g. HCl(aq)) and strong aqueous bases (

NaOH Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly corrosive base and alkali t ...

) even at 100 °C, however, ZrC does react with HF. The mixture of zirconium carbide and tantalum carbide is an important cermet material.

Uses

Hafnium Hafnium is a chemical element; it has symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dm ...

-free zirconium carbide and niobium carbide can be used as refractory coatings in

nuclear reactor A nuclear reactor is a device used to initiate and control a Nuclear fission, fission nuclear chain reaction. They are used for Nuclear power, commercial electricity, nuclear marine propulsion, marine propulsion, Weapons-grade plutonium, weapons ...

s. Because of a low neutron absorption cross-section and weak damage sensitivity under irradiation, it finds use as the coating of

uranium dioxide Uranium dioxide or uranium(IV) oxide (), also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear reac ...

and

thorium dioxide Thorium dioxide (ThO2), also called thorium(IV) oxide, is a crystalline solid, often white or yellow in colour. Also known as thoria, it is mainly a by-product of lanthanide and uranium production. Thorianite is the name of the mineralogical for ...

particles of

nuclear fuel Nuclear fuel refers to any substance, typically fissile material, which is used by nuclear power stations or other atomic nucleus, nuclear devices to generate energy. Oxide fuel For fission reactors, the fuel (typically based on uranium) is ...

. The coating is usually deposited by thermal

chemical vapor deposition Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high-quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (electro ...

in a

fluidized bed reactor A fluidized bed reactor (FBR) is a type of reactor device that can be used to carry out a variety of multiphase chemical reactions. In this type of reactor, a fluid (gas or liquid) is passed through a solid granular material (usually a catalyst ...

. It also has high emissivity and high current capacity at elevated temperatures, rendering it a promising material for use in thermo-photovoltaic radiators and field emitter tips and arrays. It is also used as an

abrasive An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away by friction. While finishing a material often means polishing it to gain a smooth, reflec ...

, in cladding, cermets, incandescent

filament The word filament, which is descended from Latin ''filum'' meaning " thread", is used in English for a variety of thread-like structures, including: Astronomy * Galaxy filament, the largest known cosmic structures in the universe * Solar filament ...

s and cutting tools.

Production

Zirconium carbide can be fabricated in several ways. One method is carbothermic reaction of zirconia by graphite. This results in a powder. Densified ZrC can then be made by sintering the powder of ZrC at upwards of 2000 °C. Hot pressing of ZrC can bring down the sintering temperature and consequently helps in producing fine grained fully densified ZrC. Spark plasma sintering also has been used to produce fully densified ZrC. Zirconium carbide can also be fabricated by solution based processing. This is achieved by refluxing a metal oxide with acetylacetone. Another method of fabrication is chemical vapour deposition. This is achieved by heating a zirconium sponge and passing halide gas through it. Poor oxidation resistance over 800 °C limits the applications of ZrC. One way to improve the oxidation resistance of ZrC is to make composites. Important composites proposed are ZrC- and ZrC--

. These composites can work up to 1800 °C. Another method to improve this is to use another material as a barrier layer, such as in TRISO fuel particles.

References

{{Zirconium compounds Zirconium(IV) compounds Carbides Superhard materials Refractory materials Rock salt crystal structure