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Intermetallic Compound

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Intermetallic Compound Definition

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Intermetallic compounds are substances composed of two or more elemental metals in definite proportions rather than variable proportions in the case of solid solutions. The properties and the crystal structure of the intermetallic compound thus formed are different from its constituents. 

Intermetallic compounds include electron compounds, size packing phases and zintl phases. Also, post-transition metals such as aluminium, galium etc and metalloids such as silicon, arsenic are included. However, a homogenous and heterogenous solid solution of metals and interstitial compounds are excluded under the definition of Intermetallic compounds.


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Intermetallic Alloy

Intermetallics, Intermetallic compound, Intermetallic alloy or ordered intermetallic alloy are substances created with an ordered mixture of two or more metallic elements. Intermetallics are generally hard and brittle with desirable mechanical properties.

Alloy - An alloy is an admixture of two or more metals that is to obtain a substance with the desirable properties of its components. Intermetallic materials are alloyed to obtain more desirable properties. Due to limited independent slip systems required for plastic deformation, intermetallics have cleavage or intergranular fracture modes. But intermetallic with ductile fracture modes are also present such as 15Al-40Ti. For other intermetallic alloys, boron is added to improve ductility.

Metallic alloys are possible replacements for plasmonic materials due to their large free electron densities. Gold and silver continue to be used as metallic plasmonic materials as intermetallics with more atoms in a unit cell suffer from higher optical losses. Due to the strong plasmonic performance by noble metals, their interband transitions can be shifted to another unimportant part of the spectrum by alloying two or more elements to create unique band structures. But optical properties usually get worse than get better in these cases but still alloys of noble metals have received significant attention.


Applications  of Intermetallics

Intermetallic compounds are termed exotic materials or advanced materials owing to their superior mechanical, chemical, electrical, magnetic, optical and semiconducting properties. More than 25000 distinct intermetallics are known. Some are produced in large quantities for a wide range of applications while others are produced, although not in large quantities but still essential to many billion-dollar markets. The various industry application of intermetallic compounds are as follows:

  • Intermetallics have given rise to the development of various novel materials such as alnico and hydrogen storage materials used in nickel-metal hydride batteries.

  • Nickel-base superalloys and other titanium aluminides are also being used in turbine-blade applications.

  • Titanium aluminides are also being used in very small quantities for the grain refinement of titanium alloys.

  • In microelectronics, Silicides are being used as barrier and contact layer.

  • NiAl alloys have many desirable properties such as oxidation, carburization, nitridation resistance, high thermal and electrical conductivity which makes them an attractive choice for metallizations in advanced semiconductor, surface catalysts and high vacuum circuit breakers.


Conclusion

Intermetallics are substances made up of two or more metals with a distinctive crystal structure where the metallic elements are in a fixed abundance ratio. Deviations due to precise stoichiometry are common on both sides necessitating or introducing vacancies. Usually, metal-metalloid compounds are also added in this category as they resemble the metal-metal compound properties. Intermetallics are widely used compounds and have a wide range of applications in various industries.

FAQ (Frequently Asked Questions)

1. What are the Properties of the Intermetallic Compounds?

Ans- Intermetallics are compounds made up of two or more metals in definite proportions. The properties of any intermetallic compound can be further improved by alloying it with another material.  The properties of intermetallic materials are as follows:

Intermetallics are generally brittle at room temperatures.

Intermetallic compounds have high melting points.

Intermetallics also display desirable magnetic, superconducting and chemical properties because of their strong internal order and bonding- metallic and ionic.

Intermetallics exhibit improved ductility after alloying with materials such as Boron to improve grain boundary cohesion.

Intermetallic materials are hard and highly corrosion resistant.

2. Differentiate Between Stoichiometric Intermetallic Compounds and Non-Stoichiometric Intermetallic Compounds?

Ans- The study of compounds in solid-state chemistry has been expanded to its crystal level. Governed by the law of definite proportions, the law of constant composition and the law of conservation of mass state that a chemical compound contains the same proportion of elements by mass.


Stoichiometric Compounds - Compounds obeying the laws of definite proportions, constant composition and conservation of mass are called stoichiometric compounds. Their chemical composition can be well defined in the ratio of  whole numbers


Nonstoichiometric Compounds- These compounds are derived from Stoichiometric compounds but their chemical composition can’t be represented by a ratio of well-defined natural numbers, therefore violating the law of definite proportions. These compounds, therefore, exhibit different structural and thermodynamic properties than their stoichiometric counterparts.