LECTURE 2 PHASE DIAGRAM DBT 302 Heat Treatment

LECTURE 2 PHASE DIAGRAM

DBT 302 – Heat Treatment Objective • Differentiate between components and phases • Introduction of a phase diagram • Identify types of phase diagram

DBT 302 – Heat Treatment Component & Phases • Component - chemically recognizable species (Fe and C in carbon steel, H 2 O and Na. Cl in salted water). • Phase – a portion of a system that has uniform physical and chemical characteristics. • For example: a beaker of melting ice, has two phases (ice and water) but only one component (H 2 O), not H 2 and O. Universiti Malaysia Perlis Knowledge. Sincerity. Exellence

DBT 302 – Heat Treatment More About Components • Solvent - host or major component in solution • Solute - minor component. • Solubility Limit of a component in a phase is the maximum amount of the component that can be dissolved in it (e. g. alcohol has unlimited solubility in water, sugar has a limited solubility, oil is insoluble). • The same concepts apply to solid phases: Cu and Ni are mutually soluble in any amount (unlimited solid solubility), while C has a limited solubility in Fe. Universiti Malaysia Perlis Knowledge. Sincerity. Exellence

DBT 302 – Heat Treatment More About Phase • A phase is any substance that is “physically separable” from the system • Two distinct phases in a system have distinct physical or chemical characteristics (e. g. water and ice) and are separated from each other by definite phase boundaries. A phase may contain one or more components. • A single-phase system is called homogeneous, systems with two or more phases are mixtures or heterogeneous systems. Universiti Malaysia Perlis Knowledge. Sincerity. Exellence

DBT 302 – Heat Treatment PHASE DIAGRAM • A phase diagram is a graphical representation of all the equilibrium phases as a function of temperature, pressure, and composition. • A phase diagrams show what phases exist at equilibrium and what phase transformations we can expect when we change one of the parameters of the system (T, P, composition). Universiti Malaysia Perlis Knowledge. Sincerity. Exellence

DBT 302 – Heat Treatment Classification of Phase Diagram • Single Component Phase Diagram – a system formed from 1 components • Binary Phase Diagram – a system formed from 2 components • Ternary Phase Diagram – a system formed from 3 components Universiti Malaysia Perlis Knowledge. Sincerity. Exellence

DBT 302 – Heat Treatment Single Component Phase Diagram • Single phase area • Co-existence curve - boundary line between 2 phases • Ternary Point – a point at which 3 phases are in equilibrium with each other Universiti Malaysia Perlis Knowledge. Sincerity. Exellence

DBT 302 – Heat Treatment Gibbs Phase Rule F = C–P+2 • F degree of freedom – thermodynamic variable which can be changed without affecting the appearance or disappearance of phase • C number of composition • P number of phase Universiti Malaysia Perlis Knowledge. Sincerity. Exellence

DBT 302 – Heat Treatment Gibbs Phase Rule • Single phase area, F = 1– 1+2=2 • Co-existence curve, F = 1– 2+2=1 • Ternary Point, F = 1– 3+2=0 Universiti Malaysia Perlis Knowledge. Sincerity. Exellence

DBT 302 – Heat Treatment Pressure-temperature phase diagram for H 2 O: Universiti Malaysia Perlis Knowledge. Sincerity. Exellence

DBT 302 – Heat Treatment Binary Phase Diagram • Variables in Binary System: –Temperature –Pressure –Chemical composition – may be represented in atomic% (or mole fraction) or weight% (or mass fraction) Universiti Malaysia Perlis Knowledge. Sincerity. Exellence

DBT 302 – Heat Treatment Binary Phase Diagram • Because there are 1 extra variable, we cannot keep all information in 2 D • To be able to use 2 D diagram, we decide to fix the pressure (usually at 1 atm) • So, left with 2 variables; temperature on vertical axis, chemical composition on horizontal axis Universiti Malaysia Perlis Knowledge. Sincerity. Exellence

DBT 302 – Heat Treatment Binary Phase Diagram Universiti Malaysia Perlis Knowledge. Sincerity. Exellence

DBT 302 – Heat Treatment Binary Phase Diagram • Isomorphous Systems • Eutectic Phase Diagram • Peritectic Phase Diagram • Monotectic Phase Diagram Universiti Malaysia Perlis Knowledge. Sincerity. Exellence