Niobium carbide ( Nb C and Nb₂C) is an extremely

hard Hard may refer to: * Hardness, resistance of physical materials to deformation or fracture * Hard water, water with high mineral content Arts and entertainment * ''Hard'' (TV series), a French TV series * Hard (band), a Hungarian hard rock supe ...

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, ...

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, porcelain ...

material, commercially used in

tool bit 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 saw or water j ...

s for cutting tools. It is usually processed by

sintering 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 ...

and is a frequent additive as grain growth inhibitor in cemented carbides. It has the appearance of a brown-gray metallic powder with purple lustre. 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 engi ...

resistant.

Synthesis

Niobium carbide can be produced by the heating of niobium oxide in a vacuum at 1800 °C and adding coke.

Properties and uses

Niobium carbide has a

Young's modulus Young's modulus E, the Young modulus, or the modulus of elasticity in tension or compression (i.e., negative tension), is a mechanical property that measures the tensile or compressive stiffness of a solid material when the force is applied le ...

of approximately 452 GPa, and a shear modulus of 182 GPa. It has a Poisson's ratio of 0.227. Niobium carbide is a frequent intentional product in

microalloyed steel Microalloyed steel is a type of alloy steel that contains small amounts of alloying elements (0.05 to 0.15%), including niobium, vanadium, titanium, molybdenum, zirconium, boron, and rare-earth metals. They are used to refine the grain microstruct ...

s due to its extremely low solubility product in

austenite Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 K ...

, the lowest of all the refractory metal carbides. This means that micrometre-sized precipitates of NbC are virtually insoluble in steels at all processing temperatures and their location at grain boundaries helps prevent excessive grain growth in these steels. This is of enormous benefit, and the cornerstone of microalloyed steels, because it is their uniform, very fine grain size that ensures both toughness and strength. The only commonly occurring compound with a lower solubility and hence, greater potential for restricting the grain growth of steels is

titanium nitride Titanium nitride (TiN; sometimes known as Tinite) is an extremely hard ceramic material, often used as a physical vapor deposition (PVD) coating on titanium alloys, steel, carbide, and aluminium components to improve the substrate's surface prop ...

. Depending on grain size, niobium carbide may burn at 200-800 °C in air. A layer of niobium carbide can be created by chemical vapor deposition.

Zirconium carbide Zirconium carbide ( Zr C) is an extremely hard refractory ceramic material, commercially used in tool bits for cutting tools. It is usually processed by sintering. Properties It has the appearance of a gray metallic powder with cubic crystal ...

and niobium carbide can be used as refractory coatings in

nuclear reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat fr ...

Natural occurrence

Niobocarbide - the naturally occurring form of niobium carbide - shall be regarded as an extremely rare mineral.Mindat, http://www.mindat.org/min-7196.html

References

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