Phase Diagrams And Structure Of Materials Flashcards
What is a phase?
A physically distinct, chemically homogeneous and mechanically separable region of a system
What is a component?
The chemical species that comprise the system. May be elements ions or compounds. Eg water phase diagram is a single component diagram
What is gibbs equation? What are degrees of freedom?
Degrees of freedom = number of components - number of phases + 2
Degrees of freedom: how many variables you can change and still remain in a phase. Eg. At triple point, we have 0 degrees of freedom. At freezing line (solid and liquid phase), we only have 1 degree of freedom.
F=C-P+2
What are binary phase diagrams?
When we have a mix of components (Eg. Steel). Therefore we need a three dimensional diagram. Different combo of components = different properties of the material therefore we need to be very careful
What are liquidus and solidus?
Phase boundary between liquid and two phase region is liquidus, between solid and two phase region is solidus. When solid solubility is limited we get a phase boundary called solvus. When melting points are completely different, we have a peritectic phase diagram
What is the definition of level of structure?
The internal structure can be observed at different levels of observation (degrees of magnification). Relative size must be kept in mind and the logarithmic scale of the universe is one method of comparison.
Define macro structure, microstructure, and substructure
Macro: naked eye or low magnification
Micro: optical microscopy
Substructure: scanning electron microscopy -> crystallography
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What is crystal structure?
Atoms in an orderly repetitive arrangement. Provides the details of atomic arrangement in a cell. Sufficient to describe the arrangement of a few atoms in a unit cell. Is where the majority of deterioration hapens
What is electronic structure?
The electrons in the outermost orbitals of individual atoms in the solid. SPECTROSCOPIC techniques! Controls conductivity and durability and is a major influence on mechanical and physical properties of material.
What is nuclear structure?
Studied by nuclear magnetic resonance (NMR). Can be used to look inside concrete and find the moving molecules ie water to find freeze-thaw deterioration.
What is molecular structure?
Spatial arrangement of small groups of atoms which are strongly joined together within a group or molecule. This and crystal structure exert strong influence on material behaviour and its deformation behaviour.
What are isomers?
Capability of atoms to form different geometric or structural arrangements without a change in chemical composition.
What is polymorphism? Give an example
The ability to transform between geometrical configuration. Eg. Sulphide crystal
How is a perfect structure used in crystals?
Properties of engineering materials are linked to how close their molecular crystal structures resemble a perfect structure. It means that no atoms or ions are missing from their appointed positions and no deviation from perfection. This is impossible to achieve but they provide info on theoretical predictions and actual measurements.
