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This is the complete lecture note for MME301 Thermodynamics of Materials. You can read it online below, open it in the full viewer, or download the PDF for offline study. It pairs with the course's video lectures, so you can read and watch together.
Course code: MME 301 Course title: Thermodynamics of Materials Course credit load: 2 Units Series 1: The Laws of Thermodynamics and Equilibrium in Materials ● Part 1.1: The Laws of Thermodynamics o Sub Part 1.1.1: The Zeroth and First Laws of Thermodynamics o Sub Part 1.1.2: The Second Law of Thermodynamics o Sub Part 1.1.3: The Third Law of Thermodynamics ● Part 1.2: Thermodynamics and Equilibrium in Materials o Sub Part 1.2.1: The Concept of Thermodynamic Equilibrium o Sub Part 1.2.2: Gibbs Free Energy and Equilibrium o Sub Part 1.2.3: Criteria for Equilibrium in Materials Systems ● Part 1.3: Thermodynamics and Materials Microstructure o Sub Part 1.3.1: Thermodynamic Driving Forces for Microstructural Change o Sub Part 1.3.2: Defect Concentration and Thermodynamics o Sub Part 1.3.3: Atomic Ordering and Thermodynamics ● Part 1.4: Thermochemistry Applied to Metallurgical Reactions o Sub Part 1.4.1: Enthalpy of Metallurgical Reactions o Sub Part 1.4.2: Using Thermochemical Data in Metallurgical Calculations o Sub Part 1.4.3: Thermodynamics and Material Properties Introduction Every material transformation examined throughout your materials engineering studies, melting, solidification, phase change, and microstructural evolution alike, is ultimately governed by the same fundamental thermodynamic laws, and this opening Series introduces these laws specifically as they apply to materials systems, before examining how thermodynamic
equilibrium, and departures from it, directly govern a material's own microstructure, defect content, and atomic ordering. The aim of this Series is to equip you with an understanding of the laws of thermodynamics and their application to material equilibrium, the thermodynamic influence on microstructure, defect concentration, and atomic ordering, and the application of thermochemistry to typical metallurgical reactions. We shall commence this Series with the laws of thermodynamics, before turning to thermodynamics and equilibrium in materials. We will then examine thermodynamics and materials microstructure, and conclude this Series by considering thermochemistry applied to metallurgical reactions. Series Learning Outcomes Upon completing this Series, you should be able to: ● SLO 1.1: state the laws of thermodynamics, ● SLO 1.2: explain the application of the laws of thermodynamics to material equilibrium, ● SLO 1.3: explain the concept of thermodynamic equilibrium using Gibbs free energy, ● SLO 1.4: state the criteria for equilibrium in a materials system, ● SLO 1.5: discuss how thermodynamics affects materials microstructure, ● SLO 1.6: discuss how thermodynamics affects defect concentration, ● SLO 1.7: discuss how thermodynamics affects atomic ordering, ● SLO 1.8: apply thermochemistry to typical metallurgical reactions, 1.1 The Laws of Thermodynamics 1.1.1 The Zeroth and First Laws of Thermodynamics The zeroth law of thermodynamics establishes that if two systems are each in thermal equilibrium with a third system, those two systems are genuinely in thermal equilibrium with each other, this apparently simple statement providing the fundamental logical basis for temperature itself as a meaningful, consistently comparable quantity, without which the very concept of measuring and comparing temperature would lack rigorous foundation. The first law of thermodynamics establishes conservation of energy, stating that energy can neither be created nor destroyed but only converted between forms or transferred between a system and its surroundings, this law directly underlying every energy balance calculation a materials engineer performs, from a simple heating calculation through to the considerably more elaborate thermochemical reaction calculations examined later in this Series.
Worked example: Applying the first law to calculate the heat required to raise a metal sample's temperature by a specified amount directly applies conservation of energy to a genuinely practical materials engineering calculation. Application: Recognising the zeroth law as the logical foundation for temperature measurement, and the first law as the foundation for every energy balance calculation, frames why both laws matter fundamentally throughout materials thermodynamics. Fill in the blank: The first law of thermodynamics establishes that energy can neither be created nor ________ but only converted or transferred. 1.1.2 The Second Law of Thermodynamics The second law of thermodynamics establishes that the total entropy, a measure of a system's own internal disorder, of an isolated system can never decrease over time, spontaneous processes always proceeding in the direction that increases the total entropy of the system together with its surroundings, this directional requirement genuinely distinguishing the second law from the first law's own symmetric, direction-independent conservation statement. This second law directly explains why certain material processes proceed spontaneously in one direction only, heat flowing spontaneously from a hotter to a cooler body, never the reverse, and why a genuinely reliable prediction of whether a specific material transformation will actually occur spontaneously requires considering entropy change alongside the energy conservation the first law alone addresses. Worked example: Explaining why heat spontaneously flows from a hot furnace wall to cooler surrounding air, never the reverse, applies the second law's entropy-increase requirement directly to a genuinely familiar materials engineering observation. Application: Recognising that predicting spontaneous material transformation requires considering entropy change, not energy conservation alone, is the essential insight the second law adds beyond the first law's own scope. Fill in the blank: The second law of thermodynamics establishes that the total entropy of an isolated system can never ________ over time. 1.1.3 The Third Law of Thermodynamics The third law of thermodynamics establishes that a perfect crystal's entropy approaches exactly zero as its temperature approaches absolute zero, this law providing a genuinely absolute reference point from which a material's entropy at any other temperature can subsequently be calculated, exactly as the zeroth law provided the logical foundation for temperature itself as a meaningful, comparable quantity. This absolute entropy reference proves genuinely essential throughout materials thermodynamics, since many thermodynamic calculations require knowing a material's absolute entropy value, not merely an entropy change between two states, and the third law's own zero-entropy reference point at absolute zero is precisely what makes calculating this absolute value possible in the first place.
Worked example: Calculating a material's absolute entropy at room temperature by integrating measured heat capacity data from absolute zero upward directly applies the third law's zero-entropy reference point as the essential starting basis for this calculation. Application: Recognising the third law's absolute entropy reference as the essential starting point for calculating absolute, rather than merely relative, entropy values is essential throughout materials thermodynamic calculations requiring this specific quantity. Fill in the blank: The third law of thermodynamics establishes that a perfect crystal's entropy approaches exactly ________ as temperature approaches absolute zero. Figure 1.1: The four laws of thermodynamics and their essential statements. Pilot questions 1.1 1. State the zeroth law of thermodynamics and explain its significance. (Linked to SLO 1.1) 2. State the first law of thermodynamics. (Linked to SLO 1.1) 3. State the second law of thermodynamics and explain why direction matters. (Linked to SLO 1.1) 4. Explain why predicting spontaneous change requires the second law, not the first alone. (Linked to SLO 1.1) 5. State the third law of thermodynamics and explain its practical value. (Linked to SLO 1.1) 1.2 Thermodynamics and Equilibrium in Materials
1.2.1 The Concept of Thermodynamic Equilibrium Thermodynamic equilibrium describes a materials system's state once no further spontaneous change occurs within it under the given conditions, temperature and pressure most commonly, this equilibrium state representing the specific condition toward which a materials system spontaneously evolves and at which it genuinely remains until those external conditions themselves change, prompting the system to evolve toward a new equilibrium appropriate to the new conditions. Recognising whether a specific materials system has genuinely reached equilibrium, or remains instead in a metastable, non-equilibrium state that merely appears stable because its approach toward true equilibrium proceeds too slowly to observe directly, is a genuinely important practical distinction throughout materials engineering, since a metastable material's own properties can differ considerably from those its true equilibrium state would exhibit. Worked example: Recognising that a rapidly quenched metal alloy may remain in a metastable, non-equilibrium state, its properties differing from the true equilibrium structure it would eventually reach given sufficient time, illustrates this genuinely important practical distinction. Application: Distinguishing genuine equilibrium from an apparently stable but genuinely metastable state is essential before confidently predicting a material's actual properties from equilibrium thermodynamic reasoning alone. Fill in the blank: Thermodynamic equilibrium describes a system's state once no further ________ change occurs under given conditions. 1.2.2 Gibbs Free Energy and Equilibrium Gibbs free energy combines a system's enthalpy and entropy, weighted by absolute temperature, into a single quantity that a materials system at constant temperature and pressure spontaneously minimises, meaning the equilibrium state a given materials system genuinely settles into is precisely the state, among all conceivable states, that minimises this Gibbs free energy quantity under those specific conditions. This Gibbs free energy minimisation principle provides the single, unifying thermodynamic criterion this entire course applies throughout, phase equilibrium, examined in the next Series, chemical reaction equilibrium, examined later in this Series, and solution behaviour, examined in a later Series, all reducing fundamentally to finding the specific state that minimises Gibbs free energy under the relevant conditions. Worked example: Identifying the phase or state that minimises Gibbs free energy at a specified temperature and pressure directly identifies that system's genuine thermodynamic equilibrium state under those
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