Material Science Flashcards
Atomic number
number of protons in an atom
Isotope
an atom with a different number of neutrons
Anion
negatively charged ion
Cation
positively charged ion
Bonding occurs by three mechanisms:
ionic bonds, covalent bonds, metallic bonds
Ionic bonding
coulombic attraction between oppositely charged ions
Covalent bonding
sharing of electrons to fill outer shells
Metallic bonding
formation of ion cores surrounded by free electrons
Ionic bonds form between…
… metallic and nonmetallic atoms
Covalent bonds form between…
… atoms that share valence electrons in order to fill their outer shells
Metallic bonds form between the elements on the…
… left side of the periodic table
The stronger the atomic bonding..
… the higher the melting temperature, hardness, and elastic modulus
Ionically bonded materials are usually…
… electrical/thermal insulators
Metallically bonded materials usually have…
… high electrical/thermal conductivities
Crystal
periodic structure produced by repetition of atomic coordinates in three dimensions
Anisotropic
properties differ with direction and orientation
Point imperfections
vacancies, interstitials, displaced atoms
Diffusion is facilitated by…
… point imperfections
Dislocations facilitate…
… plastic deformation by slip
As temperature increases, the amplitude of…
… vibrations of atoms within a crystal increases, shaking apart the crystal
Flux (J), or rate of diffusion, is proportional to…
… the concentration gradient
Two microstructures are produced in a majority of steels:
spheriodite and pearlite
Ore
oxides/sulfides that require chemical reduction via a carbon containing gas
Refining
dissolved impurities are removed by closely controlled reoxidation and deoxidation (produces steel when iron oxide is refined)
Chemicals from which a variety of plastics are produced are refined from..
… petroleum
Annealing
reheating a material to make internal adjustments between atoms or molecules
Internal stresses are a result of…
… differential expansions between different phases and thermal gradients
The strength and hardness of steel increases with…
… carbon content
Bending depends on…
… geometry and stress level
Cracking depends on….
… geometry, stress level, and loading rate
Elastic modulus
ratio of stress to strain
Yield strength
threshold level at which initial slip occurs
In a tensile test, the area under the stress-strain curve represents…
… energy
Breakage always occurs at…
… a location of stress concentration, usually a microscopic flaw
Cyclic loading reduces…
… permissible design stresses
Endurance limit
unlimited cycling can be tolerated within the endurance limit
Creep
a slow dimensional change within a material, commonly seen in plastics (atoms migrate from compressive to tensile regions)
Spalling
thermal cracking, results from differential volume changes
Embrittlement
abrupt drop in ductility and toughness as temperature lowers (atoms cannot relocate in response to stress)
Unlike heat which energizes all of the atoms and molecules in a structure, radiation introduces…
… energy at pinpoints called thermal spikes, causing individual bonds to break and electrons be energizedq
All metals expect for gold…
… oxidize in ambient air
