Material Science Flashcards
What’s a phase?
A distinct and homogeneous form of matter.
It’s a definite interface with its surroundings. It’s homogeneous in crystal structure and atomic arrangement, with the same physical and chemical properties, and is mechanically separable.
What’s the difference in the atomic packing of crystalline and non-crystalline materials?
Crystalline materials:
• Atoms pack in periodic, 3D arrays
• Typical of: metals, ceramics, some
polymers
Non-crystalline (amorphous) materials:
• Atoms have no periodic packing
• Typical of: complex structures or as a
result of rapid cooling
What’s the phase rule?
P + V = C + 2
P is number of phases in equilibrium
V is number of variables that can be chosen independently (e.g. T and P)
C is the number of components
What does a phase diagram show?
The conditions at which the distinct phases of matter can occur at equilibrium.
What’s the triple point?
The triple point (T) of a substance is the temperature and pressure at which gas, liquid, and solid coexist in thermodynamic equilibrium.
What’s the super critical phase?
A supercritical fluid is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist. It can effuse through solids like a gas, and dissolve materials like a liquid.
What technique is used to identify phases?
X-ray diffraction.
X-ray diffraction patterns are used as finger prints to identify phases.
What are the types of solid solutions?
Interstitial - the solute atoms (smaller and less abundant than solvent atoms) are arranged between solvent atoms.
Substitutional - solute atoms have replaced some solvent atoms (they’re of similar size and solvent is more abundant).
What’s a unary, binary and isomorphism system?
Unary - one component present
Binary - 2 components
Isomorphous - complete solubility of one component in another
How does the rate of cooling affect the structures of alloys/metals/compounds?
Slow rate - it has an equilibrium structure. There’s a uniform percentage of the metal throughout the structure.
Fast rate - it has a cored structure. The core solidifies first, and percentage composition of the metals in the structure vary throughout.
What’s a eutectic transformation?
When a liquid transforms into 2 solid phases.
L α + β
What’s a eutectoid transformation?
When 1 solid phase transforms into 2 other solid phases.
S α + β
What’s a peritectic transformation?
When 1 liquid and 1 solid phase transform into a second solid phase.
α + L β
