Introduction to Materials Science: Bonding, Crystal Structures, and Alloys
Ionic bond: It is between metals and nonmetals. It is given by the electrostatic attraction between charges of opposite sign.
Covalent bond: It occurs between nonmetals. There are single, double, and triple covalent bonds.
Ionic Compounds: Hard, high melting and boiling points, soluble in polar solvents, dissolved or molten state, fragile.
Metallic Compounds: Melting and boiling points vary, highly soluble in other metals, solid conductors, ductile and malleable.
Covalent Compounds:
- Molecular: Low melting and boiling points, soluble in polar and nonpolar solvents, only polar compounds are soluble in polar solvents.
- Atomic: High melting and boiling points, insoluble, non-conductors.
Crystallization: It is the transition between the solid and liquid phases.
Perfect Crystals: All atoms are at rest. No crystal is perfect.
Imperfect Crystals: Crystals with defects. The flaws affect the mechanical, chemical, and electrical properties.
Defects: Variations in the regular arrangement of atoms or molecules in a crystal. 0-Dimensional (nm), 1-Dimensional (µm), 2-Dimensional (mm), 3-Dimensional (cm)
- Stoichiometric: These defects do not change the composition of the crystal.
- Nonstoichiometric: These defects produce a change in the composition of the crystal.
- Schottky: In an ionic compound with the formula MaXb, the existence of vacant cationic positions and anionic positions.
- Frenkel: The existence of an ion in an interstitial position, which is usually empty, so its normal position becomes vacant.
Solubility: It is not different in diameter if more than 15%, if the crystal structure is similar, and not very different electronegativities.
Vacancy: Formed by a missing atom and is formed during crystallization or mobility of atoms. Atoms in crystals sometimes occupy interstitial spaces, which does not occur naturally but is induced by radiation.
Burgers Vector: A vector in the lattice indicating the direction and magnitude of displacement experienced by atoms in the network with the passage of a dislocation.
Dislocation: Linear defects that produce plastic deformation in crystalline materials.
- Edge: Line of dislocation with the Burgers vector perpendicular to the dislocation line and determining a single slip plane. Movement parallel to the Burgers vector.
- Screw: Line of dislocation with the Burgers vector parallel to the dislocation line and not determining a single slip plane. Motion perpendicular to the Burgers vector.
- Mixed: A combination of edge and screw dislocations.
Interstitial: These are the holes that are on a lattice of atoms and in which atoms arrive uninvited and they get to the photo.
Alloy: A mixture of a metal with other metals or nonmetals and is described by its components and their percentage in weight and atomic percentage.
Components: Chemical elements forming the alloy.
Binary Systems:
- Soluble in liquid and solid.
- Liquid soluble and insoluble in solid.
- Liquid soluble and partially soluble in solid.
- Systems that form intermetallic compounds.
Gibbs Phase Rule: You can calculate the number of phases that can coexist in equilibrium in any system. P + F = C + 2 where P = phases, C = components, and F = degrees of freedom.
Planco Rule: It is valid for any binary diagram.
1. A homogeneous phase is a portion of a system where intensive macroscopic properties are identical at any point in the system.
2. A homogeneous system consists of a single phase. Compact crystalline structures are also influenced by their binding characteristics.
3. A heterogeneous system consists of more than one phase.
4. A phase transition is the conversion from one phase to another.
5. Plasma is a phase that is between the liquid and gas zone, there may yet yield a material electrons.
6. Condensate is a phase that is below the solid zone, it can lead better and therefore the electrons born electronics.
7. The solid phase is formed by combining various elements or compounds in general so that the phase has uniform composition and properties that are different from those of the elements or compounds that form.
8. Sintering means to make a stronger and harder material when heated, without reaching its melting point and is molded with pressure.
9. Gibbs free energy is a state variable that combines the entropy and enthalpy and has the same units as her. It is used to predict whether a reaction is spontaneous or is in equilibrium. It is defined as G = H – TS
10. The Gibbs Phase Rule describes the number of degrees of freedom or the number of variables that must be fixed to specify the temperature and composition of a phase.
1. An alloy is a mixture of a metal with other metals or nonmetals.
2. The components are the chemical elements that form the alloy.
3. A binary alloy consists of two components.
4. The binary systems have the following characteristics: soluble in liquid and solid, liquid soluble and insoluble in solid, liquid soluble and partially soluble in solid form, and are systems that are inter-metallic compounds which are the combination of hard lattices.
5. The cooling graph cools as we see the grain and enriched in alpha and beta.
6. The eutectic reactions involving the transition from a liquid phase while the two solid phases are carried out. Eutectoid reactions occur entirely within the solid state. The following is a general expression of the above reaction: ? = A + G + heat. Where ?, Â and solid phases and g are often solid solutions.