Question

Introduction of carbon into a metallic lattice generally results in a harder, less ductile substance with lower electrical and thermal conductivities. Explain why this might be so.

Short answer

The introduction of carbon into a metallic lattice causes a distortion in the lattice structure due to the smaller carbon atoms occupying interstitial positions. This distortion leads to stronger atomic bonds, increasing hardness and decreasing ductility. Furthermore, the distorted lattice impedes electron mobility, resulting in lower electrical and thermal conductivities.

Step-by-step solution

Basic structure of a metallic lattice

In a metallic lattice, metal atoms are arranged in a regular repeating pattern. The electrons in the outer shells of these metal atoms are free to move, forming a 'sea of electrons.' This electron sea is responsible for the characteristic properties of metals like good electrical and thermal conductivity and ductility.

Effect of carbon on the metallic lattice structure

When carbon is introduced into the metallic lattice, it usually occupies interstitial positions between the metal atoms. Carbon atoms are smaller than the metal atoms, causing a distortion in the lattice structure. This distortion results in stronger atomic bonds, making the lattice harder and less ductile.

Effect on hardness and ductility

As the carbon atoms occupy interstitial positions and distort the lattice structure, the metal atoms are forced together, causing stronger atomic bonds. This increased bond strength makes it more difficult for the atoms to slide over one another, leading to increased hardness and decreased ductility of the metallic substance.

Effect on electrical conductivity

The presence of carbon atoms in the lattice structure also affects the electrical conductivity. Since the electrons in the outer shells of metal atoms form a 'sea of electrons,' their mobility is crucial for good electrical conductivity. The distortion in the lattice structure caused by the carbon atoms results in a decrease in electron mobility. With fewer free-moving electrons, the electrical conductivity of the metallic substance is reduced.

Effect on thermal conductivity

Similarly, the presence of carbon atoms in the lattice structure affects the thermal conductivity of the metallic substance. The distortion in the lattice structure impedes the movement of heat-carrying electrons, restricting the flow of heat throughout the material. This results in a lower thermal conductivity of the metallic substance. In conclusion, the introduction of carbon into a metallic lattice results in a harder, less ductile substance with lower electrical and thermal conductivities due to the distortion in lattice structure, the increased atomic bond strength, and the decrease in electron mobility.