Question

1. Without looking up the actual value, rank the following metals in order of increasing melting point.

aluminum, potasium

2. The bcc unit cell of a substitutional alloy has atoms of element A at the corners of the unit cell and an atom of element B at the center of the unit cell. Write the formulas in terms of A and B. List element A first for both answers.

a. What is the formula of the alloy?

b. What would the formula of the alloy be if the positions of the two elements were reversed in the unit cell?

Answer 1

1. Potash aluminum.

2. Body Centered Cubic means that one atom of B is in the middle of a cube with A's at the corners. So you would think that the formula would be 8 A's and 1 B. But each corner is shared with the cell to the right or left, so divide by 2, meaning 4 A's and 1 B. But each corner is shared with the cell above or below, so divide by 2 again, giving 2 A's and 1 B. This is the formula.