Question

On a two-component solid-liquid phase diagram, a tie line indicates which of the following?
A. An area below which only the liquid phase exists.
B. A region where temperature is constant.
C. An area above which only the liquid phase exists.
D. A region where composition is constant.

Answer 1

Hint: First, we must know what is meant by phase diagram. Phase diagram is a graphical representation of the physical states of a substance under different conditions of temperature and pressure. As we cross the lines or curves on the phase diagram, a change of phase occurs. Next, we must know what a tie line is? The tie line on a two-component solid- liquid phase diagram is an isothermal line that connects two equilibrium phases and passes through the alloy's position on the phase diagram when it is in a two-phase field, which intersects the two adjacent solubility curves.

Complete step by step answer:

In a solid-liquid phase diagram, the solid–liquid phase boundary which is also called a fusion curve has a positive slope so that the melting point increases with pressure. This is true whenever the solid phase is denser compared to the liquid phase.
Tie Line gives information about the chemical composition of the two phases and the total amount of these two compositions must be equal to the alloy's overall composition, $$C_0$$ , which is known. Tie line is basically another name for isotherm which means constant temperature.

Hence the correct option is B; a region where temperature is constant.

Note: The lever rule is a rule which is used to determine the mole fraction or the mass fraction of each phase of a binary equilibrium phase diagram. It is used to determine the fraction of liquid and solid phases for a given binary composition and temperature that is between the liquidus and solidus line. Lever rule uses the tie line and basic scientific principle of conservation of mass to determine the ratios of the two phases that are present.