同济大学：《工程材料》课程电子教案（课件讲稿）Chapter 2 Material and Structure

Chap2 Material and Structure

Chap2 Material and Structure

2.1.Materials classification Materials can be classified according to: √The type of bonding The structure(crystalline or amorphous) √The properties √The application

Materials can be classified according to: The type of bonding The structure(crystalline or amorphous) The properties The application 2. 1. Materials classification

Type of bonding lonic bonding Primary covalent bonding Metallic bonding Van der walls Secondary Hydrogen bonding

Type of bonding Primary Ionic bonding covalent bonding Metallic bonding Secondary Van der walls Hydrogen bonding

(1)Primary Bonding- (a)IONIC BONDING Between metallic(M)and non metallic (X)elements: Metals gives up an electron to non metallic element M+and X ions are formed A Coulombic attraction is created The bonding is non-directional Mostly "diffused"among ceramic materials Typical example: Sodium chloride Na

(1) Primary Bonding- (a)IONIC BONDING Between metallic(M) and non metallic (X) elements: Metals gives up an electron to non metallic element M+ and X￾ions are formed A Coulombic attraction is created The bonding is non-directional Mostly “diffused” among ceramic materials Typical example: Sodium chloride

COVALENT BONDING Electrons are shared between atoms or molecules in order to saturate the valence. The simplest examples is the H,molecule,where electrons stay longer between the two nucleii rather than in the outer areas->the bonding takes place H C=C HH H H H H HHH HH HH Diamond(ceramic) monomer

(b)COVALENT BONDING Electrons are shared between atoms or molecules in order to saturate the valence. The simplest examples is the H2 molecule, where electrons stay longer between the two nucleii rather than in the outer areas→the bonding takes place Diamond(ceramic) ethylene Poly-ethylene (polymer) monomer

METALLIC BONDING Valence electrons are not properly bound to the atoms; they create a sort of "sea of electrons",keeping all the valence electrons together.The non valence electrons and the nuclei form the ion core(+) A metallic bonding is NON directional >atoms are packed one onto the other lon cores Electron cloud from valence electrons ion core Sea of valence electrons

(c)METALLIC BONDING Valence electrons are not properly bound to the atoms; they create a sort of “sea of electrons”, keeping all the valence electrons together. The non valence electrons and the nuclei form the ion core(+) A metallic bonding is NON directional →atoms are packed one onto the other

(2)SECONDARY BONDING Secondary bonding results from the interaction of atomic or molecular dipoles(separation of positive and negative portions of atom or molecule).It is weak(typically 10 KJ/mol) Physical bonding >does not involve any electron transfer 2."Permanent"dipoles 1."Temporary"dipoles Hydrogen bonding "Van der Waals" Example:water 0 Example:inert gas

(2) SECONDARY BONDING Secondary bonding results from the interaction of atomic or molecular dipoles (separation of positive and negative portions of atom or molecule). It is weak (typically 10 KJ/mol) Physical bonding →does not involve any electron transfer

2.2.Classes of materials interesting under an engineering approach (1)-METALS (2)-CERAMICS (3)-GLASSES (4)-POLYMERS (5)-COMPOSITE

2.2. Classes of materials interesting under an engineering approach (1)- METALS (2)- CERAMICS (3)- GLASSES (4)- POLYMERS (5)- COMPOSITE

(1)-Metals(I】 Main Characteristics 。Opaque Reflect light High mechanical strength 。Stiff Ductile Heat and electricity conductors Resistant to thermal shock Subject to corrosion and oxidation ·Easy to be machined

(1)-Metals(Ⅰ) Main Characteristics • Opaque • Reflect light • High mechanical strength • Stiff • Ductile • Heat and electricity conductors • Resistant to thermal shock • Subject to corrosion and oxidation • Easy to be machined

(1)-Metals(II) Made up of elements(Fe,Al,Mg,Cu,...) Typically in crystalline state Almost all in solid state at room temperature Originate alloys Example:steels Aluminum alloys,titanium

(1)-Metals(Ⅱ) Made up of elements(Fe, Al, Mg, Cu,…) Typically in crystalline state Almost all in solid state at room temperature Originate alloys Example: steels Aluminum alloys , titanium, …