Material science

Material Science Study Notes

ATOMIC STRUCTURE

• Definition of Solid Materials

  • All solid materials consist of atoms arranged in a characteristic pattern unique to that material.

  • Atoms are held together by attractive forces within each atom.

• Size of Atoms

  • Smallest natural occurring atom: Hydrogen

  • Largest atom: Uranium

• Useful Engineering Metallic Elements

  • Aluminum (Al), Beryllium (Be), Cadmium (Cd), Chromium (Cr), Cobalt (Co), Copper (Cu), Gold (Au), Iron (Fe), Lead (Pb), Magnesium (Mg), Manganese (Mn), Mercury (Hg), Molybdenum (Mo), Nickel (Ni), Platinum (Pt), Silver (Ag), Tin (Sn).

• Key Non-Metallic Element

  • Carbon is the primary non-metal element forming the basis of most engineering materials.

COMPOSITION OF ATOMS

• Components of Atoms

  • Atoms are composed of electrons, protons, and neutrons.

  • Protons and neutrons have roughly equal mass, while electrons have significantly less mass.

  • Charge carried by an electron: $1.6 imes 10^{-19}$ coulomb (positive charge for protons).

• Atomic Number

  • In a neutrally charged atom, the number of protons equals the number of electrons.

  • This number corresponds to the atomic number of the element.

• Nucleus and Electrons

  • Protons and neutrons are concentrated in the nucleus; electrons surround it.

  • Electrons possess energy levels and are arranged in shells.

• Electron Shells

  • Named shells: K, L, M, N, O.

  • The first quantum shell (K) is closest to the nucleus.

  • Maximum number of electrons in each shell: $2n^2$, where $n$ is the principal quantum number.

ELECTRONIC CONFIGURATION

• Subshells

  • Subshells: s, p, d, f.

  • Maximum electrons:

  • s = 2

  • p = 6

  • d = 10

  • f = 14.

• Configuration Examples

  • For a neutral atom, electrons fill the 4s subshell before the 3d subshell.

VALENCY

• Definition of Valency

  • Valency refers to the tendency of an atom to lose or gain electrons for stability.

• Ionization Process

  • 4s electrons are removed first during ionization.

  • Example for Iron (Fe):

  • Atomic number: 26.

  • Configuration:

    • Neutral: $ext{Fe: 1s}^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^6$

    • Fe²⁺: $ext{Fe}^{2+}: 1s^2 2s^2 2p^6 3s^2 3p^6 3d^6$

    • Fe³⁺: $ext{Fe}^{3+}: 1s^2 2s^2 2p^6 3s^2 3p^6 3d^5$

PERIODIC TABLE PRINCIPLES

• Periodic Behavior of Atoms

  • The behavior of atoms correlates with their position on the periodic table.

  • Elements in the same group behave similarly.

  • Group 1 elements exhibit one electron in their valence shell.

CHEMICAL BONDING

• Types of Bonds

  • Electrovalent/Ionic Bond: Typically formed by the transfer of electrons between atoms.

  • Covalent Bond: Involves sharing of electrons between two atoms for a filled orbital state (e.g., $H<em>2$, $CH</em>4$).

  • Metallic Bond: Involves a lattice of cations surrounded by a sea of delocalized electrons.

STRUCTURE OF CRYSTALLINE SOLIDS

• Classification of Solids

  • Solid materials are classified based on how regularly atoms or ions are arranged.

  • Recrystalline material has atoms in a repeating 3D pattern.

  • Crystalline structures found in metals, ceramics, and some polymers.

• Description of Atoms in Crystal Structure

  • Atoms modeled as solid spheres with well-defined diameters.

ATOMIC ARRANGEMENT

• Layer Arrangements

  • Layer arrangements may follow:

  1. Same packing as the first layer.

  2. Hexagonal closed pack (ABAB) arrangement.

  3. Face-centered cubic (ABCABC) arrangement.

• Body-Centered Cubic (BCC)

  • Arrangement fills the cavities between layers.

  • Each atom has 8 nearest neighbors.

METALLIC CRYSTAL STRUCTURES

• Unit Cell

  • Simplest repeating volume in crystal structure.

  • Common structures:

  • Face-Centered Cubic (FCC)

  • Body-Centered Cubic (BCC)

  • Hexagonal Closed Packed (HCP)

POLYMORPHISM AND ALLOTROPY

• Polymorphism

  • Multiple crystal structures of the same composition are polymorphs (e.g., Iron transforms from FCC to BCC with temperature changes).

  • Calculations of volume percentage change during transformations:

  1. For FCC to BCC:

     • Atomic radii: FCC = $1.270 ext{ Å}$, BCC = $1.241 ext{ Å}$.

• Allotropes

  • Different crystal structures of the same element (e.g., Carbon can exist as diamond and graphite).

BRAVAIS LATTICE

• Definition

  • Bravais lattices help describe internal arrangements of atoms in crystals.

  • 14 unique lattice structures exist.

MILLER INDEX

• Definition

  • Used to describe planes in crystallography by defining intercepts along axes.

• Equation for Miller Index

  • $rac{x + y + z}{u, v, w}$

    • Where h = 1/u, k = 1/v, L = 1/w.

• Identification Example

  • For intercepts 1, 1, and ∞:

    • Result in Miller index: (110).

BRAGG'S LAW

• Equation

  • $ext{l} = 2 ext{d}_{hkl} ext{sin} heta$

  • Where l = wavelength of radiation, $d_{hkl}$ = spacing between hkl planes, $heta$ = diffraction angle.

CORROSION TYPES

• General Types

  • Galvanic, Stress Cracking, General Corrosion, Localized Corrosion, Caustic Agent Corrosion.

SPECIFIC CORROSION TYPES

• Galvanic Corrosion

  • Occurs when two dissimilar metals are connected electrically.

• Crevice Corrosion

  • Comprises localized corrosion occurring in stagnant conditions under shields like washers or gaskets.

• Pitting Corrosion

  • An aggressive localized form causing pits in the material surface.

• Filiform Corrosion

  • Randomly distributed thread-like filaments form beneath protective coatings.

CORROSION PREVENTION TECHNIQUES

• Use non-corrosive metals (e.g., stainless steel).

• Ensure metal surface cleanliness and dryness.

• Apply coatings or barriers (grease, paint).

• Implement sacrificial anodes for cathodic protection.

Atoms are the smallest unit of matter that retains the properties of an element. They consist of protons, neutrons, and electrons. Protons and neutrons are located in the nucleus at the center of the atom, while electrons orbit the nucleus in defined energy levels or shells.