tailieunhanh - Concise Dictionary of Materials Science Part 5

Tham khảo tài liệu 'concise dictionary of materials science part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | where H and S are the enthalpy and the entropy respectively and T is the absolute temperature. The enthalpy H U - PV where U is the internal energy P is the pressure and V is the volume. Gibbs free energy is also known as free enthalpy. Gibbs phase rule law Interrelation between the number of components C the number of phases P and the number of degrees of freedom F in some equilibrium thermodynamic system F C - P 2 in the case of varying temperature and pressure. If the pressure is constant F C - P 1 In a binary system . at C 2 at a constant pressure the independent variables can be the temperature and the concentration of one of the components. If P 1 then F 2 which means that in a single-phase field of the corresponding phase diagram both the temperature and the composition of the phase can be changed independently as long as the system remains single-phased. If P 2 then F 1 which means that in a two-phase field only one variable can be changed independently. In the case of the arbitrarily chosen temperature the compositions of the phases are fixed and in the case of the arbitrarily chosen composition of one of the phases at a given temperature the composition of the other phase is fixed. Finally if P 3 then F 0 . in a three-phase field in binary systems it is represented by a horizontal line contacting three single-phase fields the compositions of all the phases concerned are fixed and the phase equilibrium can take place at a constant temperature only. This is the reason why all the three-phase reactions in binary systems are termed invariant. In ternary systems C 3 invariants are reactions with four participating phases whereas in a reaction with three participating phases the compositions vary in the course of the reaction and the reaction develops in a temperature range. See . eutectic and peritectic reactions. Gibbs-Thomson equation Description of an alteration in chemical potential p induced by a curved interface free surface phase boundary or .