For each of the following alloy compositions, indicate whether you would expect it to be a substitutional alloy, an interstitial alloy, or an intermetallic compound: (a) Fe0.97Si0.03 (b) Fe0.60Ni0.40 (c) SmCo5.
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Identify the elements involved in the alloy composition: Iron (Fe) and Nickel (Ni).
Understand the nature of the elements: Both Fe and Ni are similar in size and are neighboring elements in the periodic table, which suggests they can replace each other in the lattice structure.
Determine the type of alloy based on the atomic sizes and properties: Since both elements are similar in size and can replace each other in the lattice, this suggests a substitutional alloy.
Consider the composition ratio: The ratio of Fe to Ni is 0.60 to 0.40, which supports the idea of a substitutional alloy where one type of atom substitutes for another in the crystal structure without distorting it.
Conclude the type of alloy: Given the similar atomic radii and the ability to form solid solutions, Fe0.60Ni0.40 is likely a substitutional alloy.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Substitutional Alloys
Substitutional alloys are formed when atoms of one metal replace or substitute for atoms of another metal in the crystal lattice. This typically occurs when the two metals have similar atomic sizes and crystal structures, allowing for a uniform distribution of the alloying elements. An example is brass, which is an alloy of copper and zinc.
Interstitial alloys are created when smaller atoms fit into the spaces (interstices) between the larger metal atoms in a crystal lattice. This type of alloy often involves a significant difference in atomic size, such as carbon atoms in iron to form steel. The presence of these smaller atoms can enhance the strength and hardness of the alloy.
Intermetallic Compounds
Intermetallic compounds are distinct phases formed between two or more metals that have a specific stoichiometric ratio and a defined crystal structure. Unlike substitutional or interstitial alloys, intermetallics exhibit unique properties and often have different physical and chemical characteristics than their constituent metals. An example is the compound Ni3Al, which has specific applications in high-temperature environments.
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