Material Properties and Bonding

Material Properties and Bonding

• Metals are typically ductile and malleable, not brittle.
• Ferrous metals contain iron; non-ferrous metals do not.
• Ceramics are hard but brittle materials.
• Polymers are characterized by their chemical makeup of carbon, hydrogen, and other nonmetals.
• Composites consist of multiple material types engineered together.
• Semiconductors possess electrical properties intermediate between conductors and insulators.

Ionic Bonding

• Ionic bonds form through the transfer of electrons from one atom to another.
• Ionic bonds typically form between a metallic and a non-metallic element.
• Ionic compounds are soluble in water and slightly soluble in organic solvents.
• Ionic bonding is not directional in nature.
• A metal atom loses electrons to become positively charged when forming an ionic bond.

Covalent Bonding

• Covalent bonds form through the sharing of electrons between adjacent atoms.
• Covalent bonds typically form between two nonmetals or the same element.
• Electrons are shared between two atoms and belong to both in covalent bonds.
• Covalent bonding involves the sharing of electron pairs.
• Water (H2O) is an example of a molecule with covalent bonds.

Metallic Bonding

• Metallic bonding is found in metals and their alloys.
• A key feature of metallic bonding is the presence of free-moving electrons in an electron cloud.
• Metallic bonding gives metals high electrical and thermal conductivity.
• Metallic bonding gives metals malleability and ductility.
• Electrons move freely in an electron cloud around positive ions in metallic bonding.

Intermolecular Forces

• Van der Waals bonding is characterized by weak intermolecular forces between molecules.
• Dipole-dipole interaction is the attraction between the positive end of one polar molecule and the negative end of another.
• Polar molecule-induced dipole interaction occurs when an ion disturbs the electron arrangement of a nonpolar molecule, inducing a dipole.
• A polar molecule induces a dipole in a nonpolar molecule during dipole-induced interaction.
• Hydrogen bonding occurs between a hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom.

Crystalline and Amorphous Materials

• Crystalline materials have atoms arranged in a repeating, periodic pattern over large atomic distances.
• Materials lacking crystalline structure are non-crystalline or amorphous.
• Glass is an example of an amorphous material.
• Amorphous materials lack long-range atomic order, unlike crystalline materials with repeating patterns.
• Crystalline materials have a periodic and repeating atomic structure.
• A lattice is a 3D array of points coinciding with atom positions in a crystal.
• A lattice represents the periodic and systematic arrangement of atoms in a crystal structure.
• Amorphous solids do not exhibit a lattice structure.
• A lattice can be visualized as the points of intersection between straight lines in a 3D network.
• A lattice provides the framework for atomic arrangement in a crystal.
• In an ideal single crystal, the atomic structure repeats periodically across its whole volume.
• A polycrystalline solid is made of many individual grains or crystallites.
• Amorphous materials lack long-range order and translational symmetry, unlike crystalline materials.
• Window glass is an example of an amorphous material.
• Simple cubic is not one of the three common crystal structures found in most metals.
• The coordination number in a crystal structure represents the number of nearest-neighbor or touching atoms.
• Atomic Packing Factor (APF) is the fraction of solid sphere volume in a unit cell.
• The Body-Centered Cubic crystal structure has an APF of approximately 0.68.
• In the Face-Centered Cubic structure, atoms are at the corners and the centers of all the cube faces.
• Body-Centered Cubic structures have a coordination number of 8.
• Zinc typically exhibits a hexagonal close-packed structure.
• Metals generally have higher densities than other materials due to their close-packed structures and elements with large atomic masses.
• Complex crystal structures with less dense packing contribute to the lower density of ceramics compared to metals.
• Polymers have low density because they consist mainly of light elements (C, H, O) and exhibit low packing density due to their amorphous nature.
• The densities of composites are intermediate between those of their constituent materials.
• Polymers are generally the least dense material class.
• Pentagonal is not one of the seven crystal systems.
• In crystallography, the geometry of a unit cell is defined by three edge lengths (a,b,c) and three interaxial angles (α, β, γ).
• The cubic crystal system is characterized by all three axes being of equal length and intersecting at 90-degree angles.
• In the tetragonal crystal system, the unit cell parameters are a = b ≠ c and α = β = γ = 90°.
• The triclinic crystal system has no restrictions on the lengths of its axes or the angles between them.

Crystallography

• Miller indices (h, k, l) represent the orientation of a plane within a crystal lattice.
• Linear Atomic Density (LAD) measures the number of atoms per unit length along a specific crystallographic direction.
• Planar Atomic Density (PAD) is defined as the number of atoms per unit area on a specific crystallographic plane.
• Understanding Linear and Planar Atomic Densities is important as they influence mechanical properties like slip and diffusion rates.

Defects in Crystalline Structures

• Vacancy is classified as a point defect in a crystal lattice.
• A Frenkel defect is characterized by an ion displaced from its lattice site to an interstitial position.
• A Schottky defect involves the absence of a pair of oppositely charged ions from the crystal lattice.
• An edge dislocation is a line defect resulting from an extra half-plane of atoms inserted into a crystal.
• In a solid solution, the solvent is the element present in the greater amount.
• Copper dissolved in gold is an example of a solid solution.
• According to Hume-Rothery’s rules, the atomic radii of the solute and solvent should differ by no more than 15% for substitutional solid solution formation.
• In an interstitial solid solution, the solute atoms occupy spaces between solvent atoms.
• Color of the solute and solvent does not significantly affect solid solution formation.
• A Frenkel defect in ceramics involves a cation leaving its regular lattice site to occupy an interstitial position.
• Interstitial defects are less common for anions in ceramic structures because anions are too large to fit into interstitial sites.
• A Schottky defect in ceramic materials is a paired set of cation and anion vacancies.
• Edge dislocation is not considered a point defect in ceramics.
• A Frenkel defect involves a cation vacancy and interstitial, while a Schottky defect involves both cation and anion vacancies.
• A point defect is a missing atom or irregularity in a crystal lattice.
• Grain boundary is not a point defect in metals
• In metals, an impurity atom can be intentional or unintentional.
• The solute in a solid solution is the minor component.
• A solid solution maintains a homogeneous crystal structure through Substitutional and Interstitial means.
• Sterling silver is an example of an alloy.
• Dislocation is an example of a 1D defect.
• Dislocation seperate different crystallographic orientations
• Defect is related to errors in the stacking sequence of atomic planes
• Stacking Fault
• Dislocations is NOT a 3D defect

Material properties

• Pores in material affect: Optical, thermal, and mechanical properties
• Melting occurs when: Atomic vibrations disrupt bonds