Materials Science and Engineering CHEG350 Fall 2024 Lecture 5 PDF

A/Prof. Ludovic (ludo) DUMEE Khalifa University, Department of Chemical Engineering [email protected] Materials Science and Engineering CHEG350 Fall 2024 Lecture 5 Chemistry of metals and metal oxides Ceramics are brittle materials...

A/Prof. Ludovic (ludo) DUMEE Khalifa University, Department of Chemical Engineering [email protected] Materials Science and Engineering CHEG350 Fall 2024 Lecture 5 Chemistry of metals and metal oxides Ceramics are brittle materials 1  Mechanical properties of materials Stress is a physical quantity that describes forces present during deformation. Strain is the relative deformation of an object when a load, or stress, is exerted on it. Strain must be applied to a specific material based on the target realistic conditions of mechanical stress.  Cannot apply stress! We only know how to apply strain (or deformation at a specific speed or strain rate)  Geometry of the sample tested matters! Changeprocess of an area change in stressdistribution onlyelastomersbehave differently2 Mechanical properties Definitions An elastic modulus is the unit of measurement of an object's or substance's resistance to being deformed elastically (i.e., non- permanently) when a stress is applied to it. Specific modulus is the modulus divided by the material density. Poisson ratio is the ratio of transverse contraction (or expansion) strain to longitudinal extension strain in the direction of stretching force. Tensile deformation is considered positive and compressive deformation is considered negative. Fatigue is the initiation and propagation of cracks in a material due to cyclic loading. Creep is the tendency of a solid material to undergo slow deformation while subject to persistent mechanical stresses. 3  Characterisation techniques – How to evaluate Morphology? Scanning Electron Microscopy (SEM) Diatoms – ceramic shells (silica) Nanogrooves E.Coli bacteria ceramics polymers must be coated Why are SEM micrographs always in B&W? 4 What are phonons (Oscillatory nature of matter)? A phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, specifically in solids and some liquids.  How heat or vibrations may move across matter  If you “excite” matter – it will move, but how? How isotropic is the heat diffusion? Do you have any anisotropy in the transfer? https://youtu.be/0TVmXFWpkqE 5  Heat conductivity values Temp expansion What affects heat transfer? 1 homogenoutity 2 Mostpolymersbehave in a viscous or elasticbehavior onlyexception is elastomers 6  d if 6 Photon diffusion in materials e É 7 Impact of chemistry on materials properties Chemistry is a cornerstone - Cohesion of materials depend on their chemistry and structure - Surface chemistry dictates most interactions with matter - Properties are induced by specific chemistry/arrangement - Predicting the right chemical structure / atomic arrangement is built design Chemical distributions - How even is chemistry within a material? - What is the impact of chemical groups distribution? - Why do we need to quantify and analyze them? - How to extract relevant information and avoid mis interpretation? main areas surface grain boundary amorphus mostly 8 Chemistry of metals Pure metals (not alloys) are solid at room temperature (20oC) expect… Mercury (Hg) and Bromide (Br). But multiple pure metals may be found liquid at temperatures