14. Metals and Alloys 2 Flashcards
Definition of alloy
A combination (or mixture) of two or more metals or metal(s) with a metalloid (Fe, C)
Advantages of alloys over metals (2)
Improved mechanical properties - elastic limit, ultimate tensile strength, hardness
Improved corrosion resistance
Lower melting point than individual metal
Dental uses of alloys (4)
Steel (burs, instruments)
Amalgam (restorative material)
Gold alloy (inlays, crowns, bridges, partial dentures, wires)
Nickel chromium (crowns, bridges, wires)
Definition of phase
A physically distinct homogenous structure (can have more than one component)
Definition of one phase (2)
Grains composed of one metal only
Two metals in a homogenous mixture (solution) - solid solution (one phase)
Definition of two phases
Individual grains of two metals situated in a lattice network
Definition of solution
A homogenous mixture at an atomic scale (not a liquid)
Definition of solid solution
A common lattice structure containing two metals that are soluble in one another
Metals are normally soluble when
Molten
Upon crystallisation (cooling), metals may (3)
Be insoluble
Form an intermetallic compound with specific chemical formulation
Be soluble and form a solid solution
Features of insoluble metals upon crystallisation (2)
No common lattice
Two phases
Features of soluble metals upon crystallisation (2)
Form a common lattice
Two types
Types of solid solution (2)
Substitutional
Interstitial
Definition of substitutional solid solution
One in which the atoms of one metal replace the other metal in the crystal lattice/gain
Types of substitutional solid solution (2)
Random
Ordered
Features of random substitutional solid solution
Metal atoms similar in size, valency, crystal structure
Features of ordered substitutional solid solution
Metal atoms in regular lattice arrangements, similar in size, valency, crystal structure
Definition of interstitial solid solution
One in which atoms are markedly different in size and smaller atoms are located in spaces in the lattice/grain structure of larger atoms