1

Susunan Atom dan Struktur Kristal

2

The world of materials

PE, PP, PCPA (Nylon)

Polymers,elastomers

Butyl rubberNeoprene

Polymer foamsMetal foams

FoamsCeramic foams

Glass foams

Woods

Naturalmaterials

Natural fibres:Hemp, Cotton

GFRPCFRP

CompositesKFRP

Plywood

AluminaSi-Carbide

Ceramics,glasses

Soda-glassPyrex

SteelsCast ironsAl-alloys

MetalsCu-alloysNi-alloysTi-alloys

3

Material Teknik

Jumlah material teknik sangat besar: 40.000 - 80.000 jenis.

Desainer harus memilih dan menseleksi dari jumlah tersebut.

Tanpa acuan dan rujukan serta pengetahuan, memilih material menjadi masalah rumit dan kompleks.

4

FAKTOR DESAIN & PEMILIHAN MATERIAL Selain Terdapat 40.000 –

80.000 Materials, juga

Terdapat Beribu “Processing Route”

Selecting the Optimal Combination

MATERIALS

SHAPE

MANUFACTURING PROCESS

Lower Product Cost

Faster Time to Market

Reduces in Service Failures

Meski Demikian Material Selection Tidak Mudah

Faktor Faktor Yang Mempengaruhi: Cost Performance Safety Risk Aesthetics Enviromental Impact Recyclability

5

Materials vs Process

• Metal

• Polimer

• Keramik

• Komposit

• Casting

• Forging

• Welding

• Machining

• Pressing

• Injection

• Molding

Process Improvement : 10– 20 % Penghematan Production Cost

Substitusi Materials: 50 – 60 % Penghematan Production Cost

6

Substitusi Aluminium Tuang ke Polimer

Keuntungan :

1. Lebih ringan dengan reject yg kecil

2. Tidak perlu proses machining

3. Bahan bakar lebih efisien

4. Cost produksi tereduksi

Aluminium

Subsitusi Material

Nylon 66

7

Properties a Designer Might Be Interested In Mechanical Strength Ductility Impact Resistance Behavior at temperature extremes Thermal Conductivity Electrical Conductivity Wear resistance Corrosion Resistance

8

KARAKTERISTIK MATERIALS

Sifat Fisik Density

Conductivity (thermal dan heat)

Melting Temp

Coeff thermal expantion

Microstructure

Surface characteristic

Sifat Mekanik Creep Fatique Impact Efek

Perlakuan Panas Thd Sifat Mekanik

Efek Lingkungan Thd Sifat Mekanik

Corrosion/ Wear

Rate of Corrosion & Errosion/ wear

9

10

Key Relationships

Material properties depend on the material microstructure, which in turn results from its composition and processing

Processing Microstructure Properties

11

(a) Silikon single kristal.

(b) Polikristalin stainless steel menunjukan butir dan batas butir.

12

Klasifikasi material berdasarkan tipe susunan atom.

13

14

Amorphous materials - Materials, including glasses, that have no long-range order, or crystal structure.

Glasses - Solid, non-crystalline materials that have only short-range atomic order.

Glass-ceramics - A family of materials typically derived from molten inorganic glasses and processed into crystalline materials with very fine grain size and improved mechanical properties.

Amorphous Materials

15

Atomic arrangements in crystalline silicon and amorphous silicon. (a) Amorphous silicon. (b) Crystalline silicon. Note the variation in the inter-atomic distance for amorphous silicon.

16

Lattice - A collection of points that divide space into smaller equally sized segments.

Basis - A group of atoms associated with a lattice point.

Unit cell - A subdivision of the lattice that still retains the overall characteristics of the entire lattice.

Atomic radius - The apparent radius of an atom, typically calculated from the dimensions of the unit cell, using close-packed directions (depends upon coordination number).

Packing factor - The fraction of space in a unit cell occupied by atoms.

Lattice, Unit Cells, Basis, dan Crystal Structures

17

Struktur kristal adalah pola susunan tiga dimensi yang teratur dari atom-atom dalam suatu ruang.

Struktur kristal diidealisasikan sebagai kisi ruang atau kisi kristal dengan pola susunan 3D dari titik-titik lain yang sama/identik.

Pola terkecil dari susunan atom/titik dalam suatu ruang disebut sel satuan.

Sel satuan BCC Sel satuan FCC

18

Menurut A.J. Bravais, jenis kristal terbagi atas 7 sistem kristal, yaitu:

1. Kubik 2. Tetragonal 3. Rombohedral

4. Heksagonal 5. Ortorombik 6. Monoklik

7. Triklinik

Dari masing-masing sistem kristal terdapat beberapa sel satuan hingga semuanya ada 14 sel satuan.

Tetapi pada umumnya logam memiliki sel satuan:

1. BCC (body centered cubic/kubus pusat badan)

2. FCC (face centered cubic/kubus pusat muka)

3. HCP (hexagonal close packed/heksagonal susunan padat)

19(c) 2003 Brooks/Cole Publishing / Thomson Learning™

7 sistem kristal yang terbagi menjadi 14 sel satuan Bravais.

20

21

Definisi lattice parameter atau parameter kisi pada sistem kubik, ortorombik dan heksagonal.

22

Susunan atom pada kristal

HCP

FCC

BCC

23

Susunan atom pada kristal

HCP

FCC

BCC

24

(a)Pembagian atom dalam unit sel

(b)Contoh: simple cubic (SC), body centered cubic (BCC), and face-centered cubic (FCC)

25

Determine the number of lattice points per cell in the cubic crystal systems. If there is only one atom located at each lattice point, calculate the number of atoms per unit cell.

Example 1 SOLUTION

In the SC unit cell: lattice point / unit cell = (8 corners)1/8 = 1

In BCC unit cells: lattice point / unit cell = (8 corners)1/8 + (1 center)(1) = 2

In FCC unit cells: lattice point / unit cell = (8 corners)1/8 + (6 faces)(1/2) = 4

The number of atoms per unit cell would be 1, 2, and 4, for the simple cubic, body-centered cubic, and face-centered cubic, unit cells, respectively.

Example 1 Determining the Number of Lattice Points

in Cubic Crystal Systems

26

Determine the number of lattice points per cell in the cubic crystal systems. If there is only one atom located at each lattice point, calculate the number of atoms per unit cell.

Example 1 SOLUTION

In the SC unit cell: lattice point / unit cell = (8 corners)1/8 = 1

In BCC unit cells: lattice point / unit cell = (8 corners)1/8 + (1 center)(1) = 2

In FCC unit cells: lattice point / unit cell = (8 corners)1/8 + (6 faces)(1/2) = 4

The number of atoms per unit cell would be 1, 2, and 4, for the simple cubic, body-centered cubic, and face-centered cubic, unit cells, respectively.

Example 1 Determining the Number of Lattice Points

in Cubic Crystal Systems

27

Kubus Pusat Badan/body centered cubic (BCC)

Pada sel satuan terlihat bahwa ada satu atom yang dikelilingi oleh 8 atom lainnya sehingga kita bisa hitung berapa jumlah atom pada sel satuan ini.

Pada BCC, ada satu atom lengkap bentuknya, kemudian ada 8 atom pada masing-masing ujung kisi.

Maka jumlah atom per sel satuan:

1 + (8 x 1/8) = 2 atom per sel satuan

28

Kubus Pusat Muka/face centered cubic (FCC)

Pada sel satuan FCC terdapat 4 atom yang terdiri dari:

6 x ½ = 3 atom

8 x 1/8 = 1 atom

29

Heksagonal Susunan Padat/hexagonal close packed (HCP)

Pada sel satuan HCP terdapat 6 atom yang terdiri dari:

3 atom dibagian tengah,

2 x 6 x 1/6 = 2 atom

Di bagian atas dan bawah: 2 x ½ = 1 atom

30

Determine the relationship between the atomic radius and the lattice parameter in SC, BCC, and FCC structures when one atom is located at each lattice point.

Example.2 Determining the Relationship between Atomic Radius and Lattice Parameters

The relationships between the atomic radius and the Lattice parameter in cubic systems

31

Example 2 SOLUTION

Referring to the Figure, we find that atoms touch along the edge of the cube in SC structures.

3

40

ra

In FCC structures, atoms touch along the face diagonal of the cube. There are four atomic radii along this length—two radii from the face-centered atom and one radius from each corner, so:

2

40

ra

ra 20

In BCC structures, atoms touch along the body diagonal. There are two atomic radii from the center atom and one atomic radius from each of the corner atoms on the body diagonal, so

32

Radius atom vs parameter kisi

atau

Panjang kisi (a):

R = radius atom

Ra 43

3

4Ra

33

Logam-logam dengan sel satuan BCC

Logam Panjang kisi(a, nm)

Radius atom(R, nm)

Krom 0.289 0.125

Besi 0.287 0.124

Molibdenum 0.315 0.136

Potasium 0.533 0.231

Natrium 0.429 0.186

Tantalum 0.330 0.143

Tungsten 0.316 0.137

Vanadium 0.304 0.132

34

Kubus Pusat Muka/face centered cubic (FCC)

Panjang kisi (a):

atau

Ra 42

2

4Ra

35

Logam Panjang kisi(a, nm)

Radius atom(R, nm)

Aluminum 0.405 0.143

Tembaga 0.3615 0.128

Emas 0.408 0.144

Timah hitam 0.495 0.175

Nikel 0.352 0.125

Platina 0.393 0.139

Perak 0.409 0.144

Logam-logam dengan sel satuan FCC