Term
| What are some general PHYSICAL properties of metals? |
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Definition
| "Crystalline solids at room temperature; Hard, strong, dense, ductile, malleable, high fracture toughness" |
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Term
| What are three metals that are NOT solids at room temperature? |
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Definition
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Term
| What are some general CHEMICAL properties of metals? |
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Definition
| Form positively charged ions (cations) in solutions or reactions. Have less than four valence electrons (usually) that are loosely bound. Low ionization energies |
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Term
| What is primary bonding? What are the three types? |
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Definition
| "Primary binding is CHEMICAL bonding. (1) Covalent, (2) Ionic, (3)Metallic" |
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Term
| What are some examples of secondary bonding? Where are these most important? |
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Definition
| "Secondary bonding is due to molecules having a permanent diapole moment due to fluctuating electron distribution, induced dipoles, hydrogen bonding, covalent bonds, Van der Waals forces, etc. Secondary bonding is most important with organic polymers." |
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Term
| Which is stronger? Secondary bonding vs. Primary bonding |
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Definition
| Secondary bonding is weaker than Primary bonding. |
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Term
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Definition
| Ionic bonding = electron transfer to achieve a filled outer shell. Crystalline structure is dependent on ionic size and charge balance. |
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Term
| What are some properties of ionic materials? |
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Definition
| "Strong, high melting points, brittle" |
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Term
| Describe covalent bonding: |
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Definition
| "Electron sharing, where bonds have a defined spatial orientation. Forms molecules, usually NOT solids, most organics are covalently bound." |
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Term
| Describe metallic bonding: |
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Definition
| "Atoms are arranged in a 3D crystalline lattice structure, each atom frees one or more valence electrons which make up a ""free electron gas."" This makes metals very good conductors or heat and electricity, as well as ""metallic reflectance of light""!" |
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Term
| What are three types of metallic 3D cubic structures? |
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Definition
| "(1) Body-centered cubic, (2) Face-centered cubic, (3) Hexagonal close-packed" |
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Term
| "Describe the ""As-Cast"" condition:" |
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Definition
| "Crystallization from the liquid as it cools, involving NUCLEATION at multiple sites (polycrystalline material - HETEROGENEOUS NUCLEATION) forming GRAINS, which subsequently grow larger to form the crystalline lattice structure" |
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Term
| What two phenomena OFFSET and are involved in determining the CRITICAL RADIUS for nucleation? How do they determine this? |
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Definition
| "VOLUME Free Energy (more for liquid, less for solid) and the SURFACE Energy (higher for solid, less for liquid); Solidification REDUCES free energy proportional to VOLUME and INCREAES free energy proportional to AREA (having a surface between the solid and liquid phases). Balance results in CRITICAL RADIUS!!!" |
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Term
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Definition
| The minimum radius that must be formed by atoms clustering together to form a STABLE nucleus for crystallization that can grow. |
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Term
| How does supercooling (temperature significantly lower than freezing point) affect the critical radius? |
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Definition
| Supercooling a liquid DECREASES the critical radius which results in HOMOGENEOUS NUCLEATION with many nuclei producing many small grains/crystals |
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Term
| How does cooling a liquid at a temperature NEAR the freezing point affect critical radius and crystalline structure? |
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Definition
| No supercooling. INCREASES the critical radius which results in HETEROGENEOUS NUCLEATION with few nuclei producing few LARGE grains/crystals |
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Term
| What is a grain boundary and why is it significant? |
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Definition
| "Grain boundary = the area between grains that has no crystalline lattice structure; Region of atomic DISORDER, HIGHER ENERGY; More diffusion and corrosion at the grain boundaries!!! More grain boundaries = MORE STRENGTH!!!" |
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Term
| "What is the relationship between supercooling, grain boundaries, and the strength of a material?" |
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Definition
| "Supercooling results in smaller grains, which have more surface area at their grain boundaries. Grain boundaries INCREASE the strength of a material, so supercooling increases the strength!!!" |
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Term
| What is the relationship between grain size and yield strength? |
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Definition
| Increasing grain size DECREASES yield strength! Smaller grains have higher yeild strengths! |
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Term
| How is HETEROGENEOUS nucleation controlled/enhanced? |
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Definition
| "Using GRAIN REFINERS (elements that are added to the metal to control the grain size, such as IRIDIUM)" |
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Term
| How is HOMOGENEOUS nucleation controlled/enhanced? |
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Definition
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Term
| What is dendritic grain growth? How does it occur and what are the problems with it? |
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Definition
| Growth of grains along the major axes of the crystal. Occurs during SUPERCOOLING. Increases corrosion rate!!! |
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Term
| Where are single-crystal castings applicable? |
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Definition
| "NOT IN DENTISTRY! In electronics, solar energy, etc." |
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Term
| "During casting, where does solidification occur first? How does this affect crystal size?" |
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Definition
| "Solidification occurs around the edges of the mold first because this part cools faster. Therefore, the crystals are smaller around the edges and larger on the interior of cast objects." |
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Term
| What is the solidification shrinkage for metals? |
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Definition
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Term
| What can happen if there is a premature solidifaction of the in-gate during casting? |
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Definition
| "A VOID can develop, due to the shrinkage during solidification!" |
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Term
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Definition
| "An ""as-cast"" metal that is plastically deformed at a LOW temperature, aka ""cold-worked"", ""work-hardened"", ""strain-hardened"". ***THIS ALTERS THE MECHANICAL PROPERTIES***" |
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Term
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Definition
| "Plastic deformation occuring along the planes of atoms, resulting in the breaking of atomic bonds and establishing new ones in a different position" |
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Term
| What type of stress causes the easiest plastic deformation of a metal? |
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Definition
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Term
| Why are observed shear strengths much less than theoretical shear strengths for most metals? |
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Definition
| "DEFECTS occur within the crystalline lattice structures, which decrease the shear strength" |
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Term
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Definition
| "Equilibrium defects; Examples are vacancies, interstitials, divacancies, missing ion pairs, misplaced ions" |
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Term
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Definition
| "Non-equilibrium defects; Example is dislocations; Result in increased energy at grain boundaries, it takes less energy to deform the material under shear stress" |
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Term
| What are the two main types of defects found in metals? |
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Definition
| "POINT defects, LINE defects" |
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Term
| How does work/strain-hardening (cold-working) a metal affect its mechanical properties? |
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Definition
| "INCREASES : Proportional Limit, Hardness; DECREASES: Ductility, Grain size ; Does not change the elastic modulus!" |
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Term
| "What is annealing, and how does the amount of deformation affect the rate of this process?" |
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Definition
| Annealing = Heating a deformed metal to T > 50% (melting tempertaure) and holding it there for extended time to reverse the effects of cold working. The rate of annealing is INCREASED by a greater amount of deformation. |
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Term
| What are the three stages of annealing? |
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Definition
| "(1) Recovery, (2) Recrystallization [decreased strength, increased ductility], (3) Grain Growth [decreased strength, UNDESIREABLE]" |
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Term
| What are two dental examples of the work-hardening/annealing process? |
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Definition
| Work-hardening of DIRECT GOLD in restorations; Annealing of ORTHODONTIC WIRE |
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Term
| Why do mechanical properties change during the work-hardening/annealing process? |
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Definition
| "Work-hardening consumes dislocations and generates new ones, resulting in trapped stresses. Annealing relieves these stresses through DIFFUSION, freeing the dislocations and normalizing the grain structures." |
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Term
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Definition
| "A metal containing two or more elements (usually other metals, but can also be C, N, or H) that exhibit some liquid solubility" |
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Term
| Why are often used instead of pure metals? |
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Definition
| "To enhance mechanical properties (ex. Increase strength, reduce corrosion) and COST" |
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Term
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Definition
| All of the possible combinations of the elements that make up an alloy |
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Term
| What 2 systems are commonly used to specify composition of an alloy? |
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Definition
| Composition based on WEIGHT % or ATOMIC %; Atomic % is always a lower number than Weight % |
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Term
| "What names are used for an alloy with 2, 3, or 4 components?" |
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Definition
| "Binary, Tertiary, Quaternary" |
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Term
| What is a SOLID SOLUTION alloy? What are the two different types? |
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Definition
| An alloy with only a SINGLE SOLID PHASE; Either SUBSTITUTIONAL (atomic centers of each element within the repeating crystalline structure) or INTERSTITIAL (elements existing outside or between the crystalline lattice structure) |
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Term
| What are the two types of SUBSTITUTIONAL solid solution alloys? |
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Definition
| "RANDOM (substituted element appears randomly) and ORDERED (substituted element appears in a regular, repeating fashion)" |
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Term
| What are some factors that affect the properties of an alloy? |
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Definition
| "Atom size (must be similar for a substitutional, different for a interstitial) , Valence, Lattice type (must be compatible), Electropositivity |
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Term
| How do the cooling curves of a pure metal and alloy differ? |
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Definition
| "Pure metal has a defined melting POINT. Alloy has a melting RANGE because it is composed of two or more elements, with different individual melting points." |
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Term
| Describe a solid-solution phase diagram: |
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Definition
| "Use an ALLOY FAMILY: Temperature vs. % Element A --> % Element B; Ellipse shape, with liquid phase on top, solid phase on bottom, area within the ellipse is a mixture of solid/liquid phases" |
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