CE 336 Material Properties Atomic Structure determines: Physical Properties Chemical Properties Biological Properties Electromagnetic Properties

CE 336 Physical Properties Density Mass Structure Permeability Moisture content susceptibility

CE 336 Physical Properties Specific gravity Color Texture Shape

CE 336 Chemical Properties Resistance to deterioration Oxidation Solubility

CE 336 Biological Properties Bacterial growth Hazard/exposure consideration Resistance to infestation Biodegradability

CE 336 Electromagnetic Properties Conductance Galvanic potential

CE 336 Material Selection Strength Serviceability Deflections Adaptability to future Durability

CE 336 Material and Testing Standards ASTM /ASME Standards AASHTO, State Highway, EPA, HUD, US-Army BOCA,ICBO, ICC, ISO AISC/ACI/AITC minimum quality standards, minimum application standards Some may be performance standards

CE 336 Primary Bonds Types of primary bond 1. Ionic - transfer of electrons  Metallic and non metallic elements  Sodium chloride salt 2. Covalent - sharing with adjacent atoms  Polymeric materials  Hydrogen gas 3. Metallic - mass sharing of electrons  All metal Na Cl Metal ions Electron cloud HH

CE 336 Ionic Bonds Electrons transferred Strong attractive forces between atoms Solids at room temps High melting temperature

CE 336 Ionic Bonds Solution-good conductors Solid-poor conductors Soluble in polar solvents, water Insoluble in nonpolar solvents, organic solvents.

CE 336 Ionic Bonds Low energy metals bonding to high energy nonmetals Ca+2 +O-2 = CaO Exothermic in formation

CE 336 Attractive Forces NaCl MgO

CE 336 Covalent Bonds Electrons are shared in joint orbital Can lead to small molecules with polarity No “bonding” between molecules, but some attraction and repulsion (secondary bonds).

CE 336 Covalent Bonds Gases, liquids, (mech. weak substances) Can lead to long extended networks Ceramics, diamond (high binding energy) Polymer chains (weak between chains)

CE 336 Metallic Bonds Metal – “element with 1, 2, or 3, valence electrons” No clearly defined molecules Electron cloud & Electronic bond Equilibrium of repulsive forces

CE 336 Secondary Bonds - van der Waals Bonds Weak compared to primary bonds Result from dipoles - electrostatic attraction Dipole occurs when have separation of positive and negative portion of atom or molecule Causes gasses to liquefy Water also a dipole Cl H + - H H O 105 °

CE 336 Strengths of Different Types of Bonds Bonding TypeMaterialEnergy Melt kJ/mole Temp.°C IonicNaCl CovalentSi MetallicFe HydrogenH 2 O51 0 van der WaalsCl Source: Callister, Materials Science and Engineering

CE 336 Structure of Materials Crystalline “Repeated pattern or arrangement of atoms” Ordered systems not necessarily crystalline  Laminar or small ordered systems arranged in disorganized manner Amorphous Random molecular structure

CE 336 Material Classification Metallic Solids Metallic bonding Steel, iron, aluminum, copper, other metals Crystalline Organic Solids Primarily covalent and van der Waals bonding Asphalt, plastics, wood Largely amorphous (although not entirely)

CE 336 Material Classification Inorganic Solids (ceramics) Primarily ionic and covalent bonding Portland cement, bricks, glass, aggregates, minerals Largely crystalline (but not entirely) *Note the change

CE 336 Bonding and Structure of Materials (Generally Speaking) MaterialBondingStructure SteelMetallicCrystalline Aggregates / Minerals Ionic, CovalentCrystalline, Some Amorphous Portland Cement Ionic, Covalent, van der Waals Amorphous, Crystalline AsphaltCovalent, van der WaalsAmorphous PolymersCovalent, van der WaalsAmorphous WoodCovalent, van der WaalsCrystalline, Amorphous GlassCovalentAmorphous (unaltered)

CE 336 Crystalline Structures

CE 336 Crystalline Materials Atoms arranged in repeating and regular array Unit cells  individual crystals  structural part Unit cell - smallest repeating unit Body centered cubic (BCC) Face centered cubic (FCC) Hexagonal close-packed (HCP)

CE 336 Concepts of Crystalline Structure  Coordination number Number of “nearest neighbors” Here 8 for BCC One at each corner  Atomic Packing Factor (APF) APF = Volume of atoms in cell Total volume of cell

CE 336 Body Center Cubic Structure

CE 336 Face Centered Cubic Structure

CE 336 Hexagonally Close Packed 6 around 1 on top 6 around 1 on bottom 3 at mid-height

CE 336 Body Center Cubic Structure Pure Iron (600°C to 910°C) Low Carbon Steel (723°C to ~1400°C) Some Aluminum Alloys

CE 336 Face Centered Cubic Structure Pure aluminum (-269°C to melting) Pure iron (910°C to 1403°C )

CE 336 Defects in Crystals Point Line Area Volume

CE 336 Point Defects Crystal contains many - many unit cells Explain permanent (plastic) deformation in metals Defects Interstitial  vacancy - missing  interstitial - extra Impurities Interstitial - extra  Carbon in iron Substitutional  Copper alloy in nickel Source: Callister, Materials Science and Engineering

CE 336 Lattice Defects Imperfections in arrangements of atoms edge dislocation - line defect

CE 336 Arrangements of Crystals Grain boundary Types of Interfaces?

CE 336 Amorphous Structure