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Exam I
Material Science Chapters 0-3
| Question | Answer |
|---|---|
| What are the six major property classifications of materials? | Mechanical, Electrical, Thermal, Magnetic, Optical, Deteriorative |
| What are three key criteria in materials selection? | In-service conditions, deterioration during operation (lifetime), and economics (cost and performance pull). |
| What are the three main classifications of solid materials? | Metals, Ceramics, Polymers |
| What are composites? | Materials made of two or more materials (e.g., fiberglass), combining the best characteristics of each. |
| What are the four advanced material classes? | Semiconductors, Biomaterials, Smart Materials, Nanomaterials |
| What are smart materials? | Materials that sense and respond to environmental changes in predetermined ways. |
| What is nanotechnology in materials? | Designing materials at the atomic/molecular level (bottom-up or top-down), with features on the nanometer scale. |
| What does “structure” of a material mean? | The arrangement of internal constituents (subatomic, atomic, microscopic, macroscopic levels). |
| What is a material property? | A material trait describing its response to an imposed stimulus (magnitude + kind of response). |
| Example of mechanical properties? | Yield stress, tensile strength, fracture stress. |
| Example of electrical property? | Resistivity of copper increases with impurities and deformation. |
| Example of thermal property? | Thermal conductivity decreases in copper when zinc is added. |
| Example of magnetic property? | Adding 3% Si to Fe improves it as a magnetic recording medium. |
| Example of optical property? | Al₂O₃ (aluminum oxide) can be transparent, translucent, or opaque depending on structure. |
| Example of deteriorative property? | Saltwater stress corrosion causing cracks in alloys. |
| What is toughness in materials? | The energy per unit volume a material absorbs before fracture (area under stress-strain curve). |
| Which materials are generally strong, ductile, and conductive? | Metals |
| Which materials are brittle, glassy, and insulators? | Ceramics |
| Which materials are soft, low strength/density, and good insulators? | Polymers |
| What were the major historical material ages? | Stone Age, Bronze Age, Iron Age, Silicon Age (possible Quantum Age). |
| Subatomic | involves electrons within the individual atoms and interactions with their nuclei |
| Atomic | organization of atoms or molecules relative to each other |
| Microscopic | large groups of agglomerated atoms |
| Macroscopic | structural elements viewed by the naked eye 25 mm 7 |
| Examples of Solidification | Casting, welding, additive manufacturing, etc |
| Examples of Deformation | Rolling, forging, extruding, drawing, forming, etc |
| Examples of Heat Treatment | Annealing, tempering, recrystallization, etc. |
| SemiConductors | Electrical properties between electrical conductors (metals and alloys) and insulators (ceramics and polymers) |
| What are the two atomic models cited in materials science? | Bohr Atomic Model and Wave-Mechanical Model |
| What is the key idea of the Bohr atomic model? | Electrons exist in discrete energy states defined by principal quantum numbers. |
| What is the key idea of the Wave Mechanical model? | Electrons behave as both waves and particles, with orbitals defined by probabilities. |
| What are the four quantum numbers? | n: principal shell l: Azimuthal (subshell: s, p, d, f) ml:Magnetic (orbital orientation) ms: spin (+.5, -.5) |
| What is the Pauli Exclusion Principle? | Each electron state can hold only two electrons, and they must have opposite spins. |
| What are valence electrons, and why are they important? | Outer electrons that determine reactivity, conductivity, and opality. |
| What trends exist across the periodic table? | Metals: conductive, ductile, solid Nonmetals: insulators, brittle, often gases/liquids |
| What is equilibrium interatomic separation? | The distance where attractive and repulsive forces balance (minimum potential energy). |
| What is bonding energy? | The energy required to separate two atoms from equilibrium. |
| How does bond energy relate to melting temperature? | Higher bond energy → higher melting temperature. |
| How does bond energy curve depth and asymmetry relate to thermal expansion? | Greater asymmetry of the energy curve → larger coefficient of thermal expansion. |
| What is ionic bonding? | Electron transfer between dissimilar atoms (metal → nonmetal); non-directional; common in ceramics. |
| What is covalent bonding? | Electron sharing between atoms of similar electronegativity; directional; found in ceramics, semiconductors, polymers. |
| What is metallic bonding? | Valence electrons form a “sea of electrons” that move freely; non-directional; explains conductivity in metals |
| What are secondary (van der Waals) bonds? | Weak, directional bonds from fluctuating or permanent dipoles; important in polymers and molecular solids. |
| What are hydrogen bonds? | A strong type of secondary bond between hydrogen and electronegative atoms. |
| What is mixed bonding? | Combination of covalent and ionic bonding, common in many materials (e.g., MgO). |
| What is electronegativity? | An atom’s tendency to attract electrons (scale: 0.9–4.1). |
| What type of bonding occurs with large electronegativity differences? | Ionic bonding. |
| What type of bonding occurs with small electronegativity differences? | Covalent bonding. |
| Which bonding type dominates ceramics? | Ionic + covalent, large bond energy, high melting point, brittle. |
| Which bonding type dominates metals? | Metallic, variable bond energy, moderate melting point, ductile. |
| Which bonding type dominates polymers? | Covalent bonding within chains; secondary bonding between chains; low melting point, flexible. |
| What does bonding energy depth determine? | Elastic modulus, melting temperature, and thermal expansion. |
| What is the mass of an electron? | 9.11×10^−31 kg |
| What is the mass of a proton or neutron? | About 1.67×10^−27kg |
| What is the atomic number z? | Number of protons (equals number of electrons in a neutral atom). |
| What is the mass number A? | Number of protons + neutrons. |
| What are isotopes? | Atoms of the same element with different numbers of neutrons (e.g., C-12, C-13, C-14). |
| : What is an atomic mass unit (amu)? | Defined as 1/12 the mass of a carbon-12 atom. |
| What is atomic weight? | The weighted average mass of all naturally occurring isotopes of an element. |
| What is Avogadro’s number? | 6.022×10^23 atoms or molecules per mole. |
| Electron Energy State | electrons have discrete energy states they tend to occupy the lowest energy state ground state fill from lowest energy |
| What does the potential energy curve show? | Energy vs. atomic separation: minimum energy corresponds to equilibrium bond distance. |
| What is equilibrium interatomic separation? | The distance where attractive and repulsive forces balance — net force = 0. |
| What is bonding energy? | The depth of the potential energy well (energy required to separate two atoms). |
| How does the slope of the force–distance curve near equilibrium relate to materials properties? | The slope determines the elastic modulus (stiffness). |
| Why does thermal expansion occur? | Because the potential energy curve is asymmetric: atoms spend more time at larger separations when vibrating. |
| How does bond energy affect thermal expansion? | Stronger bonds (deeper, more symmetric wells) → lower thermal expansion; weaker bonds → higher expansion. |
| Which type of materials typically have the lowest thermal expansion? | Ceramics (strong ionic/covalent bonds). |
| Which type of materials typically have the highest thermal expansion? | Polymers (weak secondary bonds). |
| what feature in the force vs. distance and energy vs. distance curve affects the melting temp the most? | depth of energy well |
| what feature of force or energy vs distance curve affects the coefficient of thermal expansion? | depth of energy well and asymmerty of energy distnace curve about ro |
| what feature affects elastic moduls? | slope of the force distance curve (atro) |
| formula for % ionic character is : | (1-e^ (-((xa-xb)^2)/4) * 100 |
| intermetallic | ionic + metallic |
| metalloids | covalent + metallic |
| What is the difference between crystalline and non-crystalline materials? | Crystalline: atoms arranged in periodic 3D arrays (metals, many ceramics, some polymers). Non-crystalline (amorphous): no long-range periodicity, complex structures, often from rapid cooling (glasses, many polymers |
| Which type of atomic packing is more stable: dense ordered or non-dense random? | Dense ordered packing (lower energy). |
| What is a unit cell? | The smallest repeating volume that contains the complete symmetry of a crystal structure. |
| What are the three most common metallic crystal structures? | BCC (Body-Centered Cubic), FCC (Face-Centered Cubic), HCP (Hexagonal Close-Packed). |
| What is the coordination number for: SC?BCC?FCC/HCP? | SC = 6, BCC = 8, FCC/HCP = 12. |
| What is the Atomic Packing Factor (APF) for: SC?BCC?FCC/HCP? | SC ≈ 0.52, BCC = 0.68, FCC/HCP = 0.74 (maximum possible). |
| What is the stacking sequence for FCC vs HCP? | FCC = ABCABC, HCP = ABAB. |
| Formula for theoretical density? | ρ=n * A /Na * Vc where 𝑛 n = atoms per unit cell, A = atomic weight, Na= Avogadro’s number, Vc = unit cell volume. |
| Which structure is denser, FCC or BCC? | FCC/HCP generally denser (higher APF), but actual density also depends on atomic weight and lattice parameter. |
| What is the difference between single crystals and polycrystals? | Single crystal: continuous periodic atomic arrangement without interruption. Polycrystal: many small crystals (grains), usually randomly oriented. |
| What is anisotropy vs isotropy? | Anisotropic: properties vary with direction (single crystals). Isotropic: properties the same in all directions (polycrystals with random orientation). |
| How can a polycrystal be anisotropic? | If grains are not random (elongated, columnar, or textured). |
| What is polymorphism? | When a material can have more than one crystal structure. |
| What is allotropy? | Polymorphism in a pure element (e.g., carbon: diamond vs graphite; iron: BCC at RT, FCC at high T). |
| What are Miller indices used for? | Describing crystallographic directions [uvw] and planes (hkl). |
| What are the steps to determine Miller indices for planes in cubic crystals? | Determine intercepts of plane with axes. Take reciprocals of intercepts. Clear fractions. Write in parentheses (hkl). |
| How are crystallographic directions represented? | By reduced integer values in brackets [uvw], with negatives indicated by a bar. |
| What is the difference between [hkl] and {hkl}? | [hkl] = a specific direction/plane; {hkl} = family of equivalent directions/planes by symmetry. |
| Why is planar density important? | It influences diffraction, diffusion, solubility, and plastic deformation. |
| What is X-ray diffraction used for in materials science? | Determining crystal structures and lattice constants. |
| What is X-ray diffraction used for in materials science? | Determining crystal structures and lattice constants. |
| Who discovered X-rays and when was diffraction first observed? | Wilhelm Röntgen (1895, Nobel Prize 1901). Diffraction observed in 1912 (von Laue). |
| What is a lattice? | A three-dimensional periodic array of points in space that represents the geometric arrangement of atoms in a crystal. |
| What is a lattice point? | A point in a lattice that represents the position of an atom, ion, or group of atoms in the crystal structure. |
| What is a crystal? | A solid material in which atoms are arranged in a periodic, repeating pattern extending in all three dimensions. |
| What is a crystal structure? | The combination of the lattice (geometry) and the basis (atoms associated with each lattice point). |
| What is a crystal system? | A classification of crystals based on unit cell geometry (lattice constants and angles). There are 7 systems (cubic, tetragonal, orthorhombic, hexagonal, rhombohedral, monoclinic, triclinic). |
| What is a coordination number? | The number of nearest-neighbor atoms surrounding a given atom in a crystal structure. |
| What is a close-packed direction? | A direction in a crystal along which atoms are in direct contact (touching each other). |
| What is the atomic packing factor (APF)? | The fraction of unit cell volume actually occupied by atoms. |
| what are polycrystals composed of? | Polycrystals are composed of a collection of many small crystals or grains which have random crystallographic orientations as a result of their solidification process. |
| What type of behavior does polycrystal display? | Polycrystals show isotropic behavior because properties are independent of the direction of measurement. |
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evelynashe
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