Main Difference

The main difference between substitutional alloys and interstitial alloys is that substitutional alloys are produced by exchanging of metal atoms with another metal atom of the same size or even a bit similar in size, while interstitial alloys are produced by the addition of the smaller atoms into the holes of its metal framework or lattice.

Substitutional Alloys vs. Interstitial Alloys

Substitutional alloys are the metal alloys that are made by replacement of one metal atom into another metal atom of the same dimension, whereas interstitial alloys are metal alloys that are made by the addition of smaller sized atoms into holes of the metal frame. Substitutional alloys consist of metal atoms having similar or almost similar sizes; on the other hand, interstitial alloys consist of small metal atoms and large metal atoms of different elements. Substitutional alloys are made by atom exchange mechanism; on the contrary, interstitial alloys are made by the interstitial mechanism. Bronze is a famous example of a substitutional alloy; conversely, an example of the interstitial alloy is steel.

Comparison Chart

What are Substitutional Alloys?

The term substitutional alloys are defined as the metal alloys that are made by replacing one metal atom to another metal atom of the same sizes. The two metal substances should be mixed to produce an alloy. The type of alloy that is determined to be formed is produced by the mixing of the type and size of the substances. Therefore, the atoms of the two metals should be of alike or similar size to produce a substitutional alloy. Substitutional alloys are made by atom exchange mechanism. Here in the substitutional alloys, metal atoms in the metal dimension are substituted by other metal atoms of metal substances. However, both substituting metal atoms should be comparable or closely alike in size for this type of substitution to happen. The ratio of the difference between the size of both metal atoms should not go beyond more than 15%. Famous examples of alloy that is substitutional alloy are Bronze and Brass. Bronze is a substitutional alloy that greatly contains copper and tin metal, but many times other metal elements are also mixed with copper to produce bronze. Such additional metal elements are aluminum, arsenic, phosphorus, silicon, and manganese. Tin metal and copper that are present in bronze have nearly similar in their sizes.

What are Interstitial Alloys?

The term interstitial alloys are defined as the metal alloys that are made by the addition of smaller atoms into holes of its metal frame or lattice are called interstitial alloys. A metallic lattice or a metallic frame is considered as a metallic structure that contains a massive lattice or framework of positively charged ions and many outer lattice delocalized electrons. Interstitial alloys are formed when the metal atom is mixed with another metal substance which is the collection of small atoms that have small radii and can add in the holes of the metal lattice. The holes present in the metal lattice are generally the spaces present between the metal atoms. A few examples of these small atoms are boron, carbon, hydrogen, and nitrogen. A common example of the interstitial alloy is steel which is a metal substance that contains iron, carbon, and various other elements. In there, the small carbon elements that are discussed used to fill up the spaces present between large metal iron atoms. Steel is considered structurally a very strong and hard metal alloy due to the presence of tightly-packed structure of atoms. Interstitial alloys are made by an interstitial mechanism in which one type of atom is significant than the other type as these atoms are much smaller so they cannot replace atoms of the metal framework as for substitutional alloys. Instead, these metal atoms get stuck in spaces of the large metal atoms of the metal lattice, and spaces of large metal atoms are called interstices.

Key Differences

1. Substitutional alloys are formed by replacement of one metal atom with another metal atom of the similar sizes, while interstitial alloys are formed by injecting smaller atoms into holes of the metal frame.
2. Substitutional alloys consist of metal atoms that have comparable or almost alike sizes; on the other hand, interstitial alloys consist of small-sized metal atoms and large-sized metal atoms of different elements.
3. Substitutional alloys are made by atom exchange mechanism; on the contrary, interstitial alloys are made by the interstitial mechanism.
4. Bronze is a famous example of a substitutional alloy; conversely, an example of the interstitial alloy is steel.

Conclusion

Above discussion concludes that substitutional alloys are made by exchanging one metal atom for another metal atom of similar size and form by atom exchange mechanism, whereas interstitial alloys are made by introducing smaller atoms into the holes of the metal lattice and Form by the interstitial mechanism.