Materials Properties Electrical properties Magnetic properties Optical properties



























- Slides: 27

Materials Properties • Electrical properties • Magnetic properties • Optical properties

Electrical properties • • Ohm’s law Resistance, resistivity, conductivity • Matthiessen’s rule

Electrical resistivity

Energy bands discrete energy levels (Pauli exclusion principle) K L M splitting into energy bands (N=12)

Electron Band Structures energy conduction band gap EF valence band EF metal (e. g. Cu) metal (e. g. Mg) isolators (Egap>2 e. V) semiconductors

Conductors EF

Semiconductors (intrinsic) band gap

n-type Extrinsic Semiconductor

p-type Extrinsic Semiconductor

The p-n Diode reverse bias forward bias

Magnetic properties • Magnetic field strength, magnetic flux density, magnetization, permeability, and magnetic susceptibility

The Magnetic Field vacuum atmosphere/material

The Magnetic Moment orbital contribution => mlµB Bohr magneton: µB=9. 27 x 10 -24 Am² spin contribution => +/-µB

Diamagnetic Materials

Paramagnetic Materials

Ferromagnetic Materials

The B-H Hysteresis remanent flux density coercive force

Hard and Soft Magnetic Materials soft: alternating magnetic fields hard: permanent magnets energy product coercivity

Magnetic Storage magnetic field: induces electric current coil: magnetic field in gap

Optical properties • Transmission • Refraction • Absorption

Electro magnetic waves light = electromagnetic wave electric field E magnetic field H (perpendicular to E) wave: c=ln (const. light velocity in vacuum=300, 000 photons: E=hn (Planck constant, 6. 63 x 10 -34 J/s)

Light Interaction with Solid I 0=Itransmitted+Iabsorbed+Ireflected transparent translucent opaque heat reflection (metals): absorption (electrons excitation by DE) => re-emission of photons color (e. g. Au, Cu => only partial re-emission) refraction: transmission into transparent material => decrease in v (n=c/v), bending at interface

Absorption Itransmitted=I 0(1 -R)2 exp(-bx) reflectivity Ireflected absorption coefficient Iabsorbed Io x (transparent medium) Itransmitted

Photon Absorption in a (Semiconducting) Solid 1. hole/electron pair generation 2. hole/electron pair generation in between colored!! Egap, max=hc/lmin (>3. 1 e. V no visible light absorption=transparent) e. g. red ruby Al 2 O 3 with Cr 2 O 3 Egap, min (lmax, visible=700 nm) (<1. 8 e. V all visible light impurity levelabsorbed=opaque) in the band gap

Light Transmission in Al 2 O 3 single crystal: transparent poly-crystal: translucent with 5% pores: opaque internal reflection/refraction at grain/phase boundaries – pores polymers: scattering at boundaries betw. crystalline/amorphous regions

Effects/Applications luminescence absorbing energy => re-emitting visible light (1. 8 e. V<hv<3. 1 e. V) fluorescence (<1 s) phosphorescence (>1 s) e. g. TV (fluoresc. coating) LED (forward bias diode – recombination=> light) photoconductivity illumination => generation of charge carriers e. g. light meters, solar cells optical fibres 1/0 impulses – high information density 24000 telephone calls by two wires e. g. 30000 kg Cu corresp. to 0. 1 kg high-purified Si. O 2 glass

Laser Concepts (light amplification by stimulated emission of radiation) 1. 2. 3. 4. Xe flash lamp excite electrons from Cr 3+ ions large number of electrons falls back to intermediate state after approx. 3 ms: spontaneous emission – triggers avalanche of emissions photons parallel to the rod are transmitted to the semi-silvered end monochromatic, high-intensity coherent red beam
Magnetic materials used in electrical machines
Tyndall effect is an optical property.
Optical properties of engineering materials
Disadvantages of current transformer
Remanent magnetization
Units of magnetic flux density
Magnetic moment and magnetic field relation
Magnetic force particle
Distinguish between magnetic and nonmagnetic materials
Distinguish between magnetic and nonmagnetic materials
Whats a magnet
What are the materials
Electrical wiring materials
Unit 33 electrical principles and wiring materials
Natural materials
Useful to harmful materials
Man made map
Differentiate adopting materials and adapting materials
Direct materials budget with multiple materials
Optical properties of metals and nonmetals
Optical properties of minerals
Properties of amino acids
Perpendicular
Inherent optical properties
Magnetic properties of lanthanides
Magnetic properties of nanomaterials
Properties of nerve fibres
Electrical properties of matter