Phase transition:A brief introduction

The term phase transition (or phase change) is most commonly used to describe transitions between solid, liquid and gaseous states of matter, and, in rare cases, plasma (physics). A phase of a thermodynamic system and the states of matter have uniform physical properties. During a phase transition of a given medium certain properties of the medium change, often discontinuously, as a result of the change of some external condition, such as temperature, pressure, or others. For example, a liquid may become gas upon heating to the boiling point, resulting in an abrupt change in volume. The measurement of the external conditions at which the transformation occurs is termed the phase transition. Phase transitions are common in nature and used today in many technologies.

1. BY : PREMASHIS KUMAR SUDIPTA KUMAR DASH PHASE TRANSITION: A BRIEF INTRODUCTION SUBMITTED TO: DR.AJIT KUMAR PATRA

2. INTRODUCTION WHAT IS PHASE TRANSISION TYPES OF PHASE TRANSITION FIRST ORDER PHASE TRANSITION SECOND ORDER PHASE TRANSITION CONCLUSION CONTENTS

3. INTRODUCTION A phase is a region of space (a thermodynamic system), throughout which all physical properties of a material are essentially uniform. phase is used as a synonym for state of matter. Plasma - the "fourth phase“. A single material may have several distinct solid states capable of forming separate phases.

4. The state of a system can be described in terms of its degrees of freedom. M acroscopic quantity of gas Order of 10 23 particles Having many degrees of freedom number of thermodynamic degrees of freedom is few. A phase transition is the transformation of a thermodynamic system from one phase or state of matter to another one by heat transfer. A phase transition is achieved by changing the thermodynamic parameters. In a large class of phase transitions , the system undergoes a symmetry change .

5. TYPES OF PHASE TRANSITION

6. ORDER OF TRANSITION The order of the transformation = t he lowest derivative (n) of Gibbs free energy which shows a discontinuity at the transition point. n=1 First order n =2 Second order.

7. FIRST ORDER PHASE TRANSITION The first-order phase transitions are those that involve a latent heat. A first order phase transformation should satisfy the following two requirements: 1. There are changes in entropy and volume . 2. The first order derivatives of Gibbs function change discontinuously. The first order phase transition occurs between the triple point and critical point. For a reversible isothermal isobaric phase Transition, dg=0 i.e. = .   dG =- SdT+VdP first-order transitions are associated with "mixed-phase regimes“.

8. A t the transition point, we are changing the enthalpy of the system but not its temperature . The heat capacity C p at the transition point is infinite.  

9. The Clausius-Clapeyron equation Clausius-Clapeyron equation pertains to the relationship between the pressure and temperature for conditions of equilibrium between two phases. dP / dT = L/(T( V f -V i )) L is the specific latent heat . Clausius - Clapeyron’s equation can be used to estimate the latent heat if ,P,V and T are known.

10. SECOND ORDER PHASE TRANSITION For second order phase transition: 1 . There are no changes of entropy and specific volume . 2 . Molar Gibbs function is continuous. 3 . First order derivative of G is continuous. 4 . Second order derivatives of G changes discontinuously . The second order phase transition occurs at the critical point and At critical point the latent heat of vaporization, L is zero. EXAMPLE: Transition of a super conductor from super conducting to the normal state in zero magnetic field. Ferromagnetic to paramagnetic transition in a simple model.

11. S and V do not jump at transition) Finite discontinuity in C P (NOT infinite).

12. LAMDA TRANSITIONS T hird type of phase transition between the two liquid phases of ordinary liquid helium l and super fluid helium ll. This transition can occur at any point along the line separating these two liquid phases.   The value of Heat capacity does not change discontinuously, but its variation with temperature is different in the two phases.

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