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MME 131: Introduction to Metallurgy and Materials

Lecture 27

Classification and Properties of Ceramic Materials

AKMB Rashid Professor, MME Dept

BUET, Dhaka

Today’s Topics

1. What are ceramics?

2. Structure of ceramics

3. Classification of ceramics

4. Characteristics of generic ceramics

5. Typical properties

6. Manufacture of ceramics

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What Are Ceramics?

comes from the Greece word keramicos, which means burnt stuff

broadly classed as inorganic, non-metallic materials

usually a compound, or a combination of compounds, between metallic and nonmetallic elements

(mainly, O, N, C, B)

bonds are either totally ionic, or combination of ionic and covalent

Typical Characteristics of Ceramic Materials

brittle

Hard, wear-resistant, electrically and thermally insulating,

refractory, chemically stable, durable, non-magnetic.

BUT

These properties are not common to ALL ceramics !!

everlasting !!!

load bearing ??!!

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ZrO2 toughened Al2O3 (cutting tools)

YBa2Cu3O7 (superconductor)

(Ba,Sr)0.6Fe2O3 (magnet)

New “high-performance” ceramics

unusual properties (e.g., high toughness, conductive)

need to understand structure-property relation

Some exceptions

High melting point and high refractoriness (except glass)

Generally electrical and thermal insulators

Generally hard and strong with low plasticity

Low fracture toughness (brittle)

Chemically inert

Many are low cost (bricks)

Wide range of appearance

Common properties

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Some Property Check

Materials 1040 Soda- Silicon

Steel glass nitride

Density, kg m-3 7850 2480 3200

Modulus, GPa 210 74 310

UTS / MOR, MPa 500 50 300 – 850

Fracture Toughness, MPa m1/2 140 0.7 4.0

Softening / Melting Temp., K 1765 1000 2173

Ceramic Structure

More than one type of atoms (cations, anions).

Complex structures, based on BCC, FCC, and HCP.

Structures are named based on the first mineral that is discovered to have the structure. (e.g., rocksalt structure)

Have low packing density (because of large anions)

Na Cl Ti Ca O Rocksalt structure

Perovskite structure

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Based on SiO44- tetrahedron

Si-O bonding is largely covalent, but overall SiO4 block has charge of -4.

Various silicate structures are formed by different ways of arranging SiO4

4- blocks.

vertex (ring)

edge (chain)

face (sheet)

SiO44- tetrahedron

Silicate Structures

Silicate glass – pure SiO2

melts at a very high temperature

very brittle

high viscosity

Hard to fabricate

Crystalline silica

Soda-glass

Modifiers / breakers (e.g., Al, Na) are added to open up / break the network and reduce the melting point

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Defects in Ceramic Structure

Like metals, defects such as vacancies and substitutional atoms are present.

Slip is difficult in polycrystalline ceramics, so defects have little effect on strength.

But, defects have significant influence on electric properties.

Classification of Ceramics

very “traditional” (clay-based and silica-based ceramics used for construction and other applications)

but also are new HIGH-TECH ceramics

1. optical (transparency) (opto-electronics)

2. electronic (piezoelectric, sensor, superconductor)

3. thermo-mechanical (engine material)

4. wear-resisting (cutting tool)

In 1974, the U.S. market for the ceramic industry was

estimated at $20 million. Today, the U.S. market is estimated

to be over $500 billion

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Silicate Ceramics: presence of glassy phase in a porous structure

clay ceramics (with mullite – 3Al2O3.2SiO2) silica ceramics (with cordierite – 2MgO.2Al2O3.2SiO2)

Oxide Ceramics: dominant crystalline phase, with small glassy phase

single oxide (Al2O3), modified oxide (zirconia toughened alumina) mixed oxide (mullite, BaTiO3)

Non-oxide Ceramics: carbon, SiC, BN, TiB2, sialon

Glass-ceramics: partially crystallised glass

SiO2-Li2O, LAS, MAS

Classification based on COMPOSITION

Traditional Vitreous Ceramics clay-based products porcelain sanitary ware tiles bricks refractories

Glasses based on SiO2, with additions to reduce m.p. or give special properties containers households optical glasses

Natural Ceramics rocks & minerals, including ice; bones

Cement & Concrete a complex ceramics with many phases structural composite

High-performance Advanced Ceramics special ceramics having improved toughness, wear resistance, electrical properties, etc. cutting tool sensor grinding laser bearing superconductor

Classification based on APPLICATIONS

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Glasses

Any material that has solidified and become

rigid without forming a regular crystal

structure is known as glass.

Usually a term applied to ceramic materials

(although metals can be formed into glasses

as well).

There is no long range order, although the

silicate tetrahedra are still linked together.

Crystalline materials: crystallize at melting temp, Tm.

have abrupt change in sp. vol. at Tm.

Glasses: do not crystallize.

sp. vol. varies smoothly with T.

Glass transition temp., Tg.

“temperature at which glass becomes rigid enough to handle”

can also be load-bearing (e.g., car window, container glass,

vacuum equipment)

basically contains three types of ingredients:

(1) network former (SiO2, B2O3)

(2) network breaker (Na2O, K2O)

(3) network modifier (Al2O3)

generally brittle (can be toughened by physical process and by

varying the composition or the microstructure)

Corning Glass Museum

general “glass” commonly applied to silicate based ceramic materials.

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Soda-lime Glass 70% SiO2, 10% CaO, 15% Na2O, 5% MgO/Al2O3

Low melting/softening point, easily formed and shaped.

Windows, bottles, etc.

Borrosilicate Glass (Pyrex) 80% SiO2, 13% B2O3, 4% Na2O, 3% Al2O3

High temperature strength, low coefficient of thermal expansion, good thermal shock resistance.

Cooking and chemical glassware

LAS Glass-Ceramic 20% Li2O, 20% Al2O3, 60% SiO2, + TiO2 (nucleating agent)

Heat treatment cause glass to crystallise to form crystal/amorphous composite with greater creep resistance and very low coefficient of thermal expansion and excellent thermal shock resistance.

Cooker tops, ceramic composites

Traditional Vitreous Ceramics

pottery, porcelain, tiles, structural and refractory bricks are still made by processes very similar to those of 2000 years ago

fired products consist of a glassy phase (based on SiO2) which melts and “glues” together a complex polycrystalline multiphase (based on Al2O3) body.

formed into shape using clays in wet, plastic state, which is then dried and fired for crystallization and vitrification

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1. Plastic materials

Assist forming process (deform easily without rupture, retain the imposed shape)

Example: Clays, talk.

2. Fluxes

Promotes fusion during firing.

Aid viscous liquid formation; to produce a glassy matrix

Example: Feldspar, nepheline syenite, volcanic ash.

3. Fillers

Provides a rigid component to aid in forming and firing.

Confer some very important physical properties (eg.,thermal expansion)

Example: Silica, calcined clay, alumina, limestone, bone ash

Raw Materials

Ceramic Typical Typical Type Composition Uses Porcelain Electrical insulator China Made from clays, Tableware, Earthenware mixed with tiles, Pottery other inert materials art ware Bricks Construction, refractory uses

Earthenware

Stoneware

Porcelain

China

Pottery

Bricks

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High-performance Advanced Ceramics

Traditional ceramics are weak because they contains many pores and cracks; their elastic moduli are low because of glass phases present

Advanced ceramics exhibits superior mechanical, electrical, optical, and magnetic properties and corrosion or oxidation resistance.

electronic ceramics insulators, substrates, capacitors, varistors, actuators, sensors

optical ceramics windows, lasers; magnetic ceramics

engineering/structural ceramics have applications in mechanical engineering, chemical engineering, high-temperature technology, and in biomedical technology

special ceramics nuclear reactor materials, refractories

Engineering Ceramics

high performance of engineering ceramics are resulted due to:

1. full density with fewer microcracks and higher intrinsic modulus

2. high toughness (measured by fracture toughness, KIC)

resultant properties are comparable with those of metals, cermets, or even diamond

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Shroud ring and turbine blades

for helicopter engines (Si3N4)

Sealing rings and other

pump spares (SiC)

Cutting tools

(Al2O3, Si3N4, etc.)

Rotor (Alumina) Gears (Alumina)

Hip joint

Socket (Al2O3)

ball (ZrO2)

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Electronic Ceramics

shows unusual electrical properties

normally insulator, but can be made to

semiconductor or even superconductor by carefully

controlled addition of impurities (the process is

known as doping)

e.g., doping of Si with B or P

Ceramic Typical Typical Type Composition Uses

Alumina Al2O3, 3Al2O3.2SiO2 Electronic insulator

Dielectric ceramics BaTiO3 Capacitor

Piezoelectric ceramics SiO2, ZnS, GaAs Ultrasonic device, Strain gauge, microphone

Superconductors YBa2Cu3O7 Electromagnet, magnetic resonance imaging (MRI)

Ceramic

insulators

Magnetic

Levitation

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Cement and Concrete

used on an enormous scale in construction industries;

only brick and timber rival in volume (then steel)

very cheap – about one tenth the cost per volume

of steel

Concrete Culvert

cement is a combination of lime (CaO), silica (SiO2) and

alumina (Al2O3), which set when combined with water.

concrete is a mixture of sand and stone (aggregate)

held together by a cement (thus concrete is a ceramic-

ceramic composite)

Cement Typical Typical Type Composition Uses Portland cement CaO + SiO2 + Al2O3 Cast facing, walkways, etc. and as component of concrete, used for general construction

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Natural Ceramics

stone is the oldest construction materials and the most durable (Pyramid, 5000 years old)

behaves like any other ceramic in load-bearing conditions

ice is also a ceramic

manifestations include anything ranging from ice cubes through icebergs to the Arctic continent and the Antarctic ice cap (3 km thick, 1013 m3 vol.)

bone is also a ceramic

the mineral constituent of bone is hydroxyapatite (HA), Ca10(HPO4)6(OH)2. 43 mass % of human body is HA.

Ceramic Typical Typical Type Composition Uses Limestone (marble) Largely CaCO3 Sandstone Largely SiO2 Building construction Granite Aluminium silicate

Ice H2O Arctic engineering

Bone Ca10(HPO4)6(OH)2 HA for human bone

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Ceramic Composites

ceramics stiffness, hardness

toughness

Ceramic Composite Components Typical Uses Fibre glass Glass – polymer High-performance CFRP Carbon – polymer structures Cermet, ZTA WC – Co, ZrO2 – Al2O3 Cutting tools, dies Bone HA – collagen Animal structure

polymer / metal +

Ceramic composite

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Data for Ceramics

Thermal Young’s Modulus of Fracture Shock Materials Density Modulus Rupture Toughness Resistance Mg m-3 GPa MPa MPa m1/2 K Soda lime glass 2.48 74 50 0.7 84 Borrosilicate 2.23 65 55 0.8 280

Porcelain, pottery 2.3-2.5 70 45 1.0 220

Diamond 3.52 1050 - - 1000 Dense alumina 3.90 380 300-400 3-5 150 Silicon nitride 3.2 310 300-850 4 500 Zirconia 5.6 200 200-500 4-12 500 Sialon 3.2 300 500-830 5 510

Cement 2.4-2.5 30-50 7 0.2 <50

Ice 0.92 9.1 1.7 0.12 -

MME 131: Lecture 31 Part 2

Processing of Ceramic Materials

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