Fundamental Concepts (Cont.)

3.012 Fundamentals of Materials Science Fall 2005 Lecture 2: 09.12.05 Fundamental concepts continued Today: LAST TIME .......................................................................................................................................... 2 THERMODYNAMIC VARIABLES, SYSTEMS, AND FUNCTIONS ................................................................... 3 Thermodynamic Variables ..........................................................................................................................................................3 The constituents of materials: components and phases ............................................................................................................4 Thermodynamic systems ..............................................................................................................................................................8 IDENTIFICATION OF PROCESSES .......................................................................................................... 10 Types of processes......................................................................................................................................................................10 REVERSIBLE AND IRREVERSIBLE PROCESSES ...................................................................................... 11 Reversible Processes .................................................................................................................................................................11 Irreversible processes ................................................................................................................................................................12 REFERENCES ..................................................................................................................................... 13 Reading: Engel and Reid: 1.4, 2.1, 2.2, 2.3 3.012 Fundamentals of Materials Science Fall 2005 Last Time Material State A (V0, N0) Thermodynamic forces State B (V < V0, N0) State C (V > V0, N0) State D ( V0, N > N0) Pressure Temperature Magnetic fields Light (more later) 3.012 Fundamentals of Materials Science Fall 2005 Thermodynamic variables, systems, and functions Thermodynamic Variables • Remember that classical thermodynamics is concerned with macroscopic properties • 2 types of variables o intensive Intensive variables: (P,T) (P,T) (P,T) o Extensive extensive variables: (U,V) (U,V) (2U,2V) 3.012 Fundamentals of Materials Science o Fall 2005 intensive and extensive variables form coupled pairs: • • e.g. pressure and volume P <-> V the product of one intensive variables multiplied by its coupled extensive variables is work The constituents of materials: components and phases Components • The components are the irreducible molecules, compounds, or atoms that make up a system: Example system Class of material Components Class of components 3.012 Fundamentals of Materials Science Fall 2005 phases • Phase: o examples: Stable temperature range (K) > 3013 1812-3013 1673-1812 1183-1673 < 1183 Stable phases of Fe Form of matter Gas Liquid Solid Solid Solid 1 Phase Gas Liquid Body-centered cubic Face-centered cubic Body-centered cubic Identification symbol of phase Gas Liquid δ γ α 3.012 Fundamentals of Materials Science Fall 2005 • Phases may have multiple components, and different phases may have the same components (though in different relative amounts). Phases, particularly solid phases, are often identified using Greek letters (as seen above for Fe- the solid phases are denoted δ, γ, and α). • A multiphase system is one where the components of the system exist in multiple unique forms (structure or composition) within the system. • Phases can have dimensions from macroscopic down to a few molecules: Figure removed for copyright reasons. See Fig. 6.18(a) on p. 370 of Allen, S., and E. L. Thomas. The Structure of Materials. New York, NY: Wiley, 1999. Figure removed for copyright reasons. See Fig. 2 in Bockstaller et al. "Size-selective Organization of Enthalpic Compatibilized Nanocrystals in Ternary Block Copolymer/Particle Mixtures." J. Amer. Chem. Soc. 125 (2003): 5276-5277. Figure removed for copyright reasons. See p. 198 in Mann, S. Biomineralization: Principles and Concepts in Bioinorganic Materials Chemistry. New York, NY: Oxford University Press, 2001. 3.012 Fundamentals of Materials Science • A few other useful definitions: o Mixture: o Solution: Fall 2005 3.012 Fundamentals of Materials Science Fall 2005 Thermodynamic systems • Thermodynamic systems can have boundary conditions that limit the exchange of energy or atoms/molecules with their surroundings. Some of the types of systems one may be interested in for materials science and engineering problems include: System Isolated Closed Adiabatic Open Boundary condition: 3.012 Fundamentals of Materials Science • Fall 2005 In closed multi-phase systems, molecules and energy can be exchanged among phases within the system: 3.012 Fundamentals of Materials Science Fall 2005 Identification of processes Types of processes  We’ve stated that thermodynamics is a theory for predicting what changes will happen to a material/system. A key part of making correct predictions is identifying what processes can happen within the system. o 4 Several common processes include: Process type Adiabatic Conditions Isochoric Isothermal Isobaric Isobarothermal Examples of classifying a system and process: 1. You place a thin metal film (your system) in an oven to anneal (equilibrate at elevated temperature). Type of System: Process: 2. Your system is a cold glass of water, and you place it on your porch on a sunny day. Type of System: Process: 3.012 Fundamentals of Materials Science Reversible and Irreversible Processes Reversible Processes • Reversible processes are idealized processes that: occur “forward” or “backward” with no change in the surroundings • Examples: Fall 2005 3.012 Fundamentals of Materials Science Fall 2005 Irreversible processes • Natural processes typically occur in only 1 direction spontaneously o These are irreversible processes Experiment Add a drop of food coloring to a glass of water • Process Expansion of a gas into a vacuum • Cooling of a hot object placed in a cold room • Melting of a solid at T = Tm + 100° • Observation of irreversibility Thus irreversible processes are driven in the one allowed direction by the second law 3.012 Fundamentals of Materials Science Fall 2005 References 1. 2. 3. 4. Reed-Hill, R. E. & Abbaschian, R. Physical Metallurgy Principles (PWS Publishing, Boston, 1994) 926 pp, Allen, S. & Thomas, E. L. The Structure of Materials pp, Mann, S. Biomineralization: Principles and concepts in Bioinorganic Materials Chemistry (Oxford University Press, New York, 2001) 198 pp, Carter, W. C. 3.00 Thermodynamics of Materials Lecture Notes http://pruffle.mit.edu/3.00/ (2002).