Lecture_1 - NE 125: Introduction to Materials Science and...

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Unformatted text preview: NE 125: Introduction to Materials Science and Engineering Introduction Instructor: William K. O’Keefe, P.Eng. wkokeefe@engmail.uwaterloo.ca “Office Hours”: Mondays 1:30 to 2:20 RCH 106 Week 1 Reading: Shackelford 6th Ed, Chapters 1 & 2 Assignment 1 (handout) problem set due: 14 January 2007 Suggested (extra) problems: Shackelford 6th Ed ( 2-2, 2-5, 2-10, 2-11) Teaching Assistant (TA): Hua (Leanne) Wei h6wei@engmail.uwaterloo.ca NE 125: Introduction to Materials Science and Engineering Introduction Homework Assignments Every Monday you will receive an assignment Assignments are not marked, they are worth 0% of your grade Assignments Solutions will be made available at end of week Solutions Quizzes You will receive a 20 min quiz each week during tutorial session based on previous week’s lectures and assignment based After the tutorial, please refrain from discussing the quiz with those students who After have not yet taken the test (3 tutorial sessions) have Tutorials Tutorials (first 30 min) Previous week’s quizzes will be returned TA will go through solutions of previous week’s quizzes and homework (last 20 min) Quiz; closed book NE 125: Introduction to Materials Science and Engineering Introduction Course Grading: Quizzes Mid Term Exam Mid Final Exam 12% 12% 30% 58% 58% (Tuesday February 12th, 2008; 7 to 9 PM, location TBD) The lowest 2 quiz scores will be ignored in calculating the final mark in the course Doctor’s Certificates: Instructors have been asked to direct students who are ill or have a doctor’s note to the FirstYear Engineering Office regarding missed tests, assignments or exams. Karen Dyck, Administrative Co-ordinator, First year engineering Karen karen@engmail) will determine arrangements for make up tests karen@engmail) Office (x.36738, Job Interviews and Other Conflicts: Job Make arrangements with your TA in advance to write quiz in alternate tutorial session if you Make have a scheduled appointment which conflicts with your tutorial NE 125: Introduction to Materials Science and Engineering Introduction Course Overview: Part I Part II Part III Part IV Part Material Science, Fundamentals (Chapters 1-4, 6-9) Structural Materials for Engineering Applications (Chapters 11-14) Materials Selection for Engineering Applications (Chapter20) Introduction to Nanomaterials Synthesis crystal structure Atomic bonding Microstructure - morphology - grain size - micro porosity Material Properties Processing of material : Conditions and history eg. annealing PERFORMANCE (Engineering Application) NE 125: NE Introduction to Materials Science and Engineering Introduction Examples of Material Properties Fracture Toughness: Hardness Elastic modulus (stiffness) Ductility (vs. brittleness) Tensile Strength Thermal conductivity Electrical conductivity Corrosion Resistance Chemical compatibility Energy absorbed prior to fracture Resistance to penetration Ratio of stress to elastic strain N/m2 Plastic strain (%) prior to fracture Critical stress for failure N/m2 (eg. Stainless steels vs carbon steel) ( eg. gaskets, chemical process equipment) NE 125: Introduction to Materials Science and Engineering Introduction Classification of Materials Classification All solid materials may be classified into one of these major categories based on the All elemental constituents and atomic bonding elemental 1. Metals - one or more metallic element, sometimes non-metallic elements (C, N, O) in small amounts one 1. - good electrical conductivity, good thermal conductivity; ductile, 2. Ceramics - oxides, nitrides, carbides; good insulators; brittle; refractory (good thermal resistance) oxides, eg. Alumina (Al2O3), silica (SiO2), magnesia (MgO), eg. ), 3. Semi-conductors – intermediate between conductor and insulator; very important in electronics; important in catalysis; eg. Silicon (Si), Germanium (Ge), Titania TiO2 catalysis; 4. Polymers 4. organic macromolecules (plastics, rubber, ) organic 5. Composites - consists of two or more structural materials; ttrade off in properties; eg. reinforcement of matrix rade structural 5. Advanced Materials: 1. Biomaterials – tissue engineering, drug delivery systems, Biomaterials 7. Nanoengineered materials 7. Mechanical, electronic, magnetic, catalytic and other properties designed from the molecular level in a “bottom-up” approach as opposed to a top down approach the NE 125: NE Introduction to Materials Science and Engineering Introduction Examples of Composites Examples Automotive Tires: Reinforcement of rubber by carbon black filler to enhance mechanical properties PTFE reinforced gaskets (Durlon 9000): polymer matrix gives ductility, excellent chemical resistance and good sealing characteristics, inorganic filler gives improved thermal stability for high temperature applications and increased strength strength Concrete: A composite material consisting of aggregate particles (gravel or composite sand) bound within in a solid medium. Both the matrix (cement) and reinforcing filler are ceramic. Asphalt used to pave roads is also a concrete. Reinforced concrete Add reinforcing steel rods, wires and bars (rebar) to uncured concrete to enhance mechanical strength. Enables greater capacity for tensile, compressive and shear stress capacity SEM micrograph of a fiberglass composite1 Fiberglass Glass fibres added to polymer matrix gives enhanced mechanical Glass strength. Light weight, ductile material. [1] Shackelford, J.F. “Introduction to Materials Science and Engineering”, 6th Edition,; Photo used by permission NE 125: NE Introduction to Materials Science and Engineering Introduction Polymers Polymers Polymers are organic macromolecules synthesized from smaller monmers. Consequently the structure is made Polymers up of repeating smaller units. The structure may be linear, branched or may comprise a complex 3D network (eg. gels) Good ductility, elastic properties; good insulator, good wear resistance, Examples Examples PTFE (polytetrafluoroethylene) a.k.a. (TEFLON) invented by accident in 1938 excellent chemical resistance excellent gaskets, seals, bearings, bushings, non-stick coatings and films gaskets, lowest coefficient of friction of all known structural materials lowest PET (Polyethylene terephthalate) A plastic used for beverage containers since 1958 (invented 1941). Outstanding cost effectiveness, ultra plastic high clarity bottles, toughness, can be processed in a diverse number of ways. Produced from ethylene glycol and terephthalic acid glycol n = 90 to 200 Illustrations courtesy of Wikemedia Commons, Used by permission NE 125: Introduction to Materials Science and Engineering Introduction Metals and Metallic Bonding A simple model from classical physics ignoring quantum mechanical behaviour • valence electrons are not bound by a single atom, but are delocalized and may be considered to form “a sea of electrons” • valence electrons are free to flow about the crystal lattice which consists of stationary ion cores (atomic nuclei and non valence electrons) cores • Free electrons shield ion cores from repulsive forces + + + + + - + + + + + - + + + + - + + + + + - + + + + + - - + + + + + Valence electrons are loosely bound - High thermal conductivity (k) - high electrical conductivity (σ ) Metallic lattice is less stable than ionic solids - low melting points (relative to ceramics) + -+- + + + + + --- qx ∂T =k A ∂x Heat flux T Ti T J = = σE A Electric Flux NE 125: NE Introduction to Materials Science and Engineering Introduction Ceramics and Ionic Bonding Ceramics Eg. NaCl ClNa+ ClNa+ ClCl- Ions are created by the electron transfer from Na to Cl Ions due to large difference in electronegativities due Ions are more stable, since outer shells become filled Ions (Assignment One – problem 3c) (Assignment Unlike metals, the electrons are tightly bound by the Unlike ions Cl- Cl- An Na+ and Cl- ion pair are attracted by the coloumbic force by Low electrical and thermal conductivities Low Very strong lattice energy results in very high melting Very points (eg. Al2O3 Tmp=2020°C) points =2020°C) Materials with very high temperature resistance are said to be refractory. refractory Ceramics have good insulative properties, thermal Ceramics stability, are usually hard and are strong stability, Ceramics are also brittle and subject to fracture kq1 q 2 kZ 1eZ 2e = r2 r2 2 1 k= = 8.987 x 109 Nm 2 C 4πε 0 F C= − ( ) e = 1.602 x 10 −19 C For Na+ Z1 = +1, for Cl-, Z2 = -1 NE 125: NE Introduction to Materials Science and Engineering Introduction Band Theory: Energy Level The conductive properties of metals, ceramics and semi-conductors explained. The Available States Energy Level Available States Energy Levels Available States 2p 2s 6 2 2p 2s 6N 2N 2p 2s 6N 2N 1s One Isolated Atom 2 1s N Isolated Atoms 2N 1s 2N N Interacting Atoms The energy states available to electrons are quantized. The In the case of N interacting electrons, a band of levels is created so that the quantum numbers of all electrons are unique in accordance with the Pauli Exclusion Principal are In the N interacting atoms, N new bands are created with slightly different energies. Those states which were In degenerate in the non interacting system, now have unique energies NE 125: NE Introduction to Materials Science and Engineering Introduction Band Theory: Quantization of states and the Pauli Exclusion Principle Quantization f ( Ei ) = e ( E i − E F ) / kT 1 +1 Fermi-Dirac Distribution Applies to particles which have half integral spin quantum number (Fermions) eg. an electron electrons obey the Pauli Exclusion Principle, which states that no two electrons may occupy the electrons same quantum state at the same time ( all 4 quantum numbers n, l, ml and ms, must be unique combination) The Fermi-Dirac distribution allows the computation of the average number of electrons in a The particular quantum state “i” with energy Ei (i.e. a sub shell) particular (i.e. Note: (electrons have the same energy Ei, if they have the same principal quantum number (n) and azimuthal quantum number (l) EF denotes the Fermi energy, an important parameter in solid state physics and catalysis EF~ the energy of the electrons in the highest occupied energy state at T=0K the NE 125: NE Introduction to Materials Science and Engineering Introduction Band Theory: Band Only electrons in outermost conduction band interact with electrons from other atoms and move freely in Only the crystal lattice the The partially filled conduction band with numerous available quantum states is responsible for electrical The conductivity (and thermal conductivity) conductivity Band theory also explains why good insulators, such as diamond and other crystals are clear. Photons of Band light are not absorbed by insulators due to large band gap (forbidden energies), resulting in transmission of light. Conductors are generally opaque because electrons can be easily promoted to higher states within conduction band by absorption of light. conduction Conduction band E=EF Eg Valence band E=0 Eg The band gap represents a region of The forbidden energies. No electrons may occupy these quantum states For a semi-conductor, the thermal excitation energy E=kT, or photonic energy E=hν or energy from energy external electric field may promote electrons from the valence band to conduction band due to small band gap Eg gap : : Insulator : : Conductor : : Semiconductor A characteristic feature that defines characteristic the metals is that the highest occupied band is partially filled occupied NE 125: NE Introduction to Materials Science and Engineering Introduction Band Theory: Band n-type and p-type (Extrinsic) semiconductors Conduction band Donor impurity levels Acceptor impurity levels Valence band Donor electron “Hole” Si Si P Si Al Pure Silicon n-type semiconductor p-type semiconductor NE 125: NE Introduction to Materials Science and Engineering Introduction Band Theory: Band Extrinsic semiconductors Conduction band Donor level Ed Acceptor level Ea Valence band n-type semiconductor p-type semiconductor Replacing 1 Si atom in 5 million with a P atom increases the number of electrons in the conduction band by a factor of 1 million !!! NE 125: NE Introduction to Materials Science and Engineering Introduction Classification by Morphology: Classification Solids may be classified according to the inherent degree of molecular order or disorder 1. Crystalline – most highly structured and ordered of all solids - periodicy; unit cell is repeated in all dimensions of crystal 1. Amorphous molecular structure is completely random and disordered (Eg. glass) - the unit cell may be considered to be infinite in size Eg. Polymers; crystallinity is localized within amorphous structure 1. Semi-crystalline - 1. Liquid Crystal Polymers – eg. Liquid crystal display - do not fall into first three categories; - a structurally unique and novel state of matter neither liquid nor crystal in melt condition - complex; extended rod shaped, rigid molecules - three kinds of liquid crystals depending on orientation and order: smectic, nematic and cholesteric 1. Fractal - concept from Chaos Theory; implies order within disorder (complexity) - from Latin “fractus” which means “broken” self similarity at varying length scales (Eg. snowflakes, some forms of SiO2) - By definition, the Hausdorff (fractal) dimension D exceeds the topological dimension2 - Fractal dimension of solids can be measured experimentally by BET N2 adsorption [2] Mandelbrot, B. (1977), The Fractal Geometry of Nature, NE 125: NE Introduction to Materials Science and Engineering Introduction Review Review • Performance depends on material properties • Macroscopic material properties are governed by the microstructure • The microstructure is determined by crystal structure and processing history • Crystal structure is determined by atomic bonding • Classification of solids by atomic bonding and elemental constituents Metals, ceramics, semiconductors, polymers, composites • Classification of materials by inherent molecular disorder crystalline, amorphous, semicrystalline, liquid crystal, fractal Band Theory: • explains thermal and electrical conductivity in solids • explains light transmission in insulators • intrinsic semiconductors (silicon and germanium) • n and p type extrinsic semiconductors ...
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