Question

Indicate whether each statement is true or false: (a) Substitutional alloys tend to be more ductile than interstitial alloys. (b) Interstitial alloys tend to form between elements with similar ionic radii. (c) Nonmetallic elements are never found in alloys.

Short answer

(a) TRUE: Substitutional alloys tend to be more ductile than interstitial alloys because they cause minimal disturbance to the original lattice structure. (b) FALSE: Interstitial alloys usually form between elements with significant differences in atomic size, not between elements with similar ionic radii. (c) FALSE: Nonmetallic elements can be found in alloys, particularly in interstitial alloys, where small nonmetal atoms can occupy the interstices within the crystal lattice.

Step-by-step solution

Statement (a)

Substitutional alloys tend to be more ductile than interstitial alloys. The given statement is TRUE. Explanation: Substitutional alloys are formed when the parent metal atoms are replaced by atoms of a different element, causing minimal disturbance to the original lattice structure. Therefore, they have similar ductility to the base metal. On the other hand, interstitial alloys are formed when atoms of one element are inserted into the interstices (holes) in the lattice structure of the base metal. This causes distortion and creates strain in the lattice, which can decrease ductility.

Statement (b)

Interstitial alloys tend to form between elements with similar ionic radii. The given statement is FALSE. Explanation: Interstitial alloys usually form between elements with significant differences in atomic size, where smaller atoms fit into the interstices of the lattice structure of larger atoms. On the other hand, substitutional alloys tend to form between elements with similar ionic radii, as they can more easily replace one another in the crystal lattice without causing significant distortion.

Statement (c)

Nonmetallic elements are never found in alloys. The given statement is FALSE. Explanation: Nonmetallic elements, such as carbon, nitrogen, or phosphorus, can be found in alloys, particularly in interstitial alloys, as small nonmetal atoms can occupy the interstices within the crystal lattice. Examples of such alloys include steel (an alloy of iron and carbon) and nitinol (an alloy of nickel and titanium with interstitial nitrogen).

Key concepts

Substitutional Alloys

Substitutional alloys are a type of alloy where some of the atoms in the metal lattice are replaced by atoms from another element. These atoms need to be similar in size to maintain the structure of the lattice. Because of this similarity in atom size, substitutional alloys closely resemble the original metal, retaining most of its properties. This includes ductility, which is the ability of a material to be stretched into a wire without breaking.

- They often form when the elements involved have similar atomic radii, allowing the replacement to occur with minimal disturbance. - Common examples include brass (copper and zinc) and bronze (copper and tin). - The uniformity in atomic sizes ensures the alloy maintains a smooth lattice structure, promoting flexibility and durability. These alloys are valuable because they combine specific properties from different metals while retaining ductility, making them useful for various industrial applications.

Interstitial Alloys

In interstitial alloys, smaller atoms fit into the spaces, known as interstices, between larger metal atoms in the crystal lattice. This occurs when the smaller atoms, which are usually significantly different in size, manage to occupy voids in the lattice. The presence of these smaller atoms in the gaps causes tension and distortion in the lattice, which often results in a decrease in ductility compared to substitutional alloys.

- They typically form between a metal with a large atomic radius and a much smaller nonmetal atom, like carbon or nitrogen. - A well-known example of an interstitial alloy is steel, which includes carbon atoms within the iron lattice. - The distortion caused by smaller atoms enhances certain properties such as hardness and strength but often at the expense of ductility. These alloys are highly beneficial when increased strength and hardness are desired, such as in construction or tool manufacturing.

Ductility

Ductility is a critical mechanical property of materials that refers to their ability to be drawn out or deformed without breaking. This quality is essential for practical applications, such as manufacturing wires or metal sheets. - Ductile materials undergo significant plastic deformation before rupture. This characteristic allows them to absorb more energy and undergo shaping processes without fracturing. - Metals are often praised for their ductility, enabling them to be easily manipulated during manufacturing processes. - Substitutional alloys tend to retain their base metals' ductility, while interstitial alloys might lose some due to the lattice strain caused by the smaller inserted atoms. Understanding ductility helps designers and engineers choose appropriate materials for applications that require flexibility and formability. Selecting the right type of alloy ensures that the final product is both efficient and durable for its intended function.