Phase Equilibrium and Triple Point

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Questions and Answers

What is the significance of point 'G' in the Fe-C phase diagram?

It is the point where austenite transforms into pearlite in the solid state. (correct)

It is the point where cementite separates from austenite.

It represents the eutectic point where austenite and cementite form a eutectic mixture.

It represents the transformation temperature of γ-iron to α-iron.

What is the composition of the eutectic mixture formed at point 'B'?

0.088% carbon

0.8% carbon

2.5% carbon

4.3% carbon (correct)

What is the purpose of heat treatment of steel?

To decrease the melting point of the metal

To increase the hardness of the metal

To change the chemical composition of the metal

To relieve internal stress and change the microconstituents (correct)

What type of steel contains 0.8% carbon?

Eutectoid steel Signup and view all the answers

What does the curve OA in the Ag/Pb phase diagram represent?

The melting point curve of silver Signup and view all the answers

What is the significance of the line FG in the Fe-C phase diagram?

It represents the beginning of the change of γ-iron to α-iron. Signup and view all the answers

What is the number of phases and components in the system along curve OA?

Two phases, two components Signup and view all the answers

What is the name of the eutectic mixture formed by austenite and cementite?

Ledeburite Signup and view all the answers

What is the degree of freedom of the system at the triple point?

Zero Signup and view all the answers

What is the degree of freedom (F) along curve OA?

1 Signup and view all the answers

What is the temperature at which the eutectoid transformation occurs?

723°C Signup and view all the answers

What happens when lead is added beyond the eutectic point 'O'?

Solid Pb separates out Signup and view all the answers

What is the condition for a two-component system?

P = 1 Signup and view all the answers

Up to what percentage of carbon is regarded as pure iron?

0.088% Signup and view all the answers

What is true about the eutectic point 'O'?

The silver solution becomes saturated with lead and lead solution becomes saturated with silver Signup and view all the answers

What is the number of variables that must be specified to describe the state of the phase in a two-component system?

Three Signup and view all the answers

What is the significance of the eutectic point 'O' in the Ag/Pb phase diagram?

It is the point where the silver and lead solutions become saturated with each other Signup and view all the answers

What is the graphical representation of a binary system?

3D solid model Signup and view all the answers

What is the curve OB in the Ag/Pb phase diagram?

The freezing point curve of lead Signup and view all the answers

What is the temperature and pressure at the triple point of water?

0.0098°C and 4.58 mm Signup and view all the answers

What is the degree of freedom of the system in the areas AOB, AOC, and BOC?

Two Signup and view all the answers

What is the degree of freedom (F) along curve OB?

1 Signup and view all the answers

What is the equation for the degree of freedom in a system?

F = C - P + 2 Signup and view all the answers

What is the equilibrium that exists at any point on the curve?

Super-cooled water ↔ vapour Signup and view all the answers

Study Notes

Phase Rule and Phase Diagrams

Super cooled water can change into ice when in contact with a small particle of ice, and the curve merges into OB.
The equilibrium at any point on the curve is Super-cool water vapour.
The degree of freedom of the system is one, making it univariant.

Triple Point

The triple point is where the curves OA, OB, OC, and OA1 meet, and all three phases (ice, water, and vapour) are in equilibrium.
The temperature and pressure at the triple point of water are 0.0098°C and 4.58 mm, respectively.
The degree of freedom is zero, making it an invariant system.

Areas on the Phase Diagram

The areas AOB, AOC, and BOC contain vapour, liquid, and ice phases, respectively.
Within these single-phase areas, the system is bivariant, as predicted by the phase rule.

Two-Component System

In a two-component system, when P=1, F=C-P+2, which means three variables must be specified to describe the state of the phase.
A three-dimensional solid model phase diagram is required to represent the variables of temperature, pressure, and composition.

Iron-Carbon Phase Diagram

The transformation temperature of 910°C for γ- to α- iron changes is lowered to 723°C as the carbon content goes up to 0.8%.
The point G represents the eutectoid point, where three phases (austenite, ferrite, and cementite) co-exist in equilibrium.
The eutectic mixture of austenite and cementite is called ledeburite.

Features of Fe-C Phase Diagram

Upto 0.088% C are regarded as pure iron.
0.088% to 2% C represents steel.
Above 2% C represents cast iron.
Steel can be further divided into hypo-eutectoid steel (0.08 to 0.8% C), hyper-eutectoid steel (0.8 to 2% C), and eutectoid steel (0.8% C).

Heat Treatment of Steel

Heat treatment is a combination of heating and cooling of metal or alloy in the solid state to get desired properties.
During heat treatment, the size and shape of the grain or the composition of the phase undergoes change with respect to the micro constituents, and internal stress is relieved.

Ag/Pb System Phase Diagram

The phase diagram consists of two curves (OA and OB) and five areas (AOB, BOD, AOC, COE, and DOE).
The eutectic point is represented by 'O'.
Curve OA is the melting point curve of Ag, and curve OB is the freezing point curve of Pb.
Both curves represent univariant systems.

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Description

This quiz covers the concept of phase equilibrium and triple point, where all three phases of ice, water, and vapor are in equilibrium. It explores the relationship between temperature and pressure at this point.