structure of metal

8/14/2019 Structure of Metal

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METALLIC STRUCTURE

Group 2 :

NGO GIANG NAM

TRINH HOANG MINH

NGUYEN PHU HUY

Hanoi university ofTechnology

14th, December, 2009


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Main parts

1.Crystal and Metal2.Structure of Metal

3.Properties of Metal

4.Conclusion and Recommendation


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1.Crystal and metal

1.1.What is crystal?1.2.what is metal?

1.3.Applications of metal?


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1.Crystal and Metal

What is the crystal?


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Definition of Metal


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Application ofmetal

High structural strength per unit mass

Carrying large loads or resisting impactdamage

Good conductors

Carrying an electric current over a distancewith little energy lost


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2.Structure of metal (CrystalPacking)

2.1.Definition2.2.Simple Cubic

2.3. Body Centered Cubic

2.4.Faced -Centered Cubic2.5.Hexagonal Close Packing


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1.Definitions

What is crystal packing?

A model of particles organization

Describe how the particles arearranged

Based on unit cell

the simplest structure that isrepeated in the crystal


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1.1.Definitions

Why do we need it? Helps explains many properties of metal

Hardness

Density

Melting point .

Describes arrangement of metallic atoms .

Source: . .www jcrystals com


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2.1.Definitions

Key words:

Coordination number : the number of nearestneighbours of each atom .

Close Packed Crystal Structure: The most

efficient space saving way to arrangeparticles.


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2.2. Simple Cubic

Particles are arranged instraight, neat layers

Each layer oriented

directly above lowerlayers.

The atoms are in contactalong the cell edge.

Unit cell : Cubic

Sourc : . .e www jcrystals com


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2.2. Simple Cubic

atoms/unit cell = 1 Coordination number = 6

least efficient method ofpacking (52%)

Ex: Polonium (Po)

Sourc : . .es www jcrystals com


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2.3.Body-centered Cubic

Atoms at corners andbody centre of cube

The atoms are only in

contact along thebody diagonal.



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2.3.Body-centered Cubic (BCC)

Atoms/unit cell : 2. Coordination number : 8

Packing efficiency: 68%

Examples : include oneform of Fe, V, Cr, Mo,W



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2.4.Face-Centered Cubic Packing

Unit cell: face centeredcubic.

Layers are altered tobring particles closer

Layers are stacked soparticles fit in gaps


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2.4.Face-Centered Cubic Packing

Atoms /unit cell = 4

Coordination number= 12

Efficiency (74%)

Examples : Al, Ni, Cu, Ag,Pt.



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2.5.Hexagonal Close Packing

Primitive Hexagonalunit cell

Layers are stacked so

particles fit in gaps =>Close Packing



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2.5.Hexagonal Close Packing

Coordination number = 12.

Packing efficiency : 74%

Examples: Be, Mg, Ti, Zr



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3. Properties of metal

3.1. Density

3.2. Melting points and boiling points3.3. Electrical and thermal conductivity

3.4. Malleability and ductility

3.5. The hardness of metals


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3.1. Density


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3.1. Density

Heavy metal (d>5):copper, iron, gold,...

Heaviest: osmium (22.61 g/cm3 )

Light metal (d


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3.2.Melting points and boiling points

High melting and boiling points

strength of the metallic bond

number of free electrons Crystal packing

Vary from metal to metal

Highest melting point:tungsten(3,422 C,)


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Lowest point: Mercury(-38.83 C)

Group 1 metals (sodium, potassium) :low point

inefficiently packed

Less bonds

relatively large atoms


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3.3. Electrical conductivity

Metals conduct electricity well

Best : gold, silver, copper...

Application: electric wire,...

Two new terms:

Crystal grains

Grain boundary


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Crystal grains: arranged in a regular way

Grain boundary : interface between twograins grain boundary

Crystal grains

delocalised electrons:free to move throughout the

structure

Source:http://www.chemguide.co.uk


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3.3. Thermal conductivity

Good conductors of heat

Best :gold, silver,...

additional kinetic energy

transferred throughout the rest

moving electrons


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3.4. Malleability and ductility

malleable (can be beaten into sheets)

ductile (can be pulled out into wires)

roll over each other, new positions

metal is permanently changed(stress force).


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a smaller stress is put onto

back to their original positions

elastic


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3.5. The hardness of metals

atoms don't line up properly

grain boundaries

Hinder rolling of layers of atoms over eachother

Chromium is the hardest, followed by tungsten

structure of metal

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