190 5.2 Phase diagrams VIV A phase diagram describes how many and which phases of a system are present when changing the intensive parameters (pressure, temperature,composition)of the system itself. Phase diagrams are usually valid when the thermodynamic equilibrium is achieved;they can be built up using the thermodynamic equilibrium condition given by the minimum of Gibbs free enthalpy G=H-TS SINO-ITALIAN CAMPUS
SINO-ITALIAN CAMPUS 5.2 Phase diagrams A phase diagram describes how many and which phases of a system are present when changing the intensive parameters (pressure, temperature, composition) of the system itself. Phase diagrams are usually valid when the thermodynamic equilibrium is achieved; they can be built up using the thermodynamic equilibrium condition given by the minimum of Gibbs free enthalpy : G = H - TS
190> 5.2.1 Gibbs Phase rule Degree of freedom F is defined as the number of variables(pressure,temperature and composition) that are allowed to change independently without changing the number of phases in equilibrium. Gibbs Phase Rules:F=C-P+n F=number of degree of freedom(variance); C=number of components in the system (can be elements or compounds); P=number of phases present n=number of physical variables taken into account at the equilibrium,(i.e =2:pressure and temperature) BUT =1 if P=costant. SINO-ITALIAN CAMPUS
SINO-ITALIAN CAMPUS 5.2.1 Gibbs Phase rule Degree of freedom F is defined as the number of variables (pressure, temperature and composition) that are allowed to change independently without changing the number of phases in equilibrium. Gibbs Phase Rules: F=C-P+n F = number of degree of freedom (variance); C = number of components in the system (can be elements or compounds); P = number of phases present ; n= number of physical variables taken into account at the equilibrium, (i.e =2: pressure and temperature) BUT =1 if P=costant
190> F=C-P+n At triple point: 1 component 3 phases Vapore No degrees of freedom Liquido Vapore-Liquido Following the curves: 1 component Liquido-Solido 2 phases Vapore-Solido Funto triplo (Solido-Liquido-Vapore) 1 degree of freedom Solido In other places: Pressione. 1 component 1 phase 2 degrees of freedom SINO-ITALIAN CAMPUS
SINO-ITALIAN CAMPUS F=C-P+n At triple point: 1 component 3 phases No degrees of freedom Following the curves: 1 component 2 phases 1 degree of freedom In other places: 1 component 1 phase 2 degrees of freedom
190> F=C-P+n 1.000 If n=1? 100 Liquid (we) 10- Solid (Water) (Ice) 1.0 2 0.1 0.01 O Vapor (Steam) d 0.001 -20 0 20 40 60 80 100 120 Temperature("C) Figure 9.2 Pressure-temperature phase diagram for H2O. Intersection of the dashed horizontal line at 1 atm pressure with the solid-liquid phase boundary(point 2)corresponds to the melting point at this pressure (T=OC).Similarly,point 3,the intersection with the liquid-vapor boundary,represents the boiling point(T=100°C). SINO-ITALIAN CAMPUS
SINO-ITALIAN CAMPUS F=C-P+n If n=1?
190 or several materials the boundary between liquid and solid phase is an horizontal line (the melting point is independent from the pressure) The area representing the 3000 solid state of iron is divided into3 parts(a,Y,δ) 2000 ELiquido 37C 3000 Fe (CCC) 130℃ Fe y(CFC) 000 910C- Fea(CCC) 2000 Liquido Solide+6 10-2 6+Y 10 102 1537 Pressione,bar 1330 Y+a 1000 Phase transformations take place 910 at T=constant,in isothermal Tempo conditions
SINO-ITALIAN CAMPUS For several materials the boundary between liquid and solid phase is an horizontal line (the melting point is independent from the pressure) Phase transformations take place at T=constant, in isothermal conditions The area representing the solid state of iron is divided into 3 parts (α,γ,δ)