glass and ceramics.pdf

MME 131:Introduction to Metallurgy and Materials

Lecture 30

Classification and Properties of Ceramic MaterialsCeramic Materials

AKMB RashidProfessor, MME DeptBUET, Dhaka

Today’s Topics

1. What are ceramics?2. Structure of ceramics3. Classification of ceramics4. Characteristics of generic ceramics5. Typical properties6. Manufacture of ceramics6. Manufacture of ceramics

© B Rashid, Dept of MME, BUET MME131 LEC30 2010 Page 02

What Are Ceramics?comes from the Greece word keramicos, which means burnt stuff

broadly classed as inorganic non metallic materialsbroadly classed as inorganic, non-metallic materials

Usually a compound, or a combination of compounds, between metallic and nonmetallic elements (mainly, O, N, C, B)

always composed of more than one element y p(Al2O3, SiO2, NaCl, SiC, etc.)

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


Typical Characteristicsof Ceramic Materials

brittlebrittle

Hard, wear-resistant, electrically and thermally insulating, refractory, chemically stable, durable, non-magnetic.

everlasting !!!load bearing ??!!

refractory, chemically stable, durable, non magnetic.

BUTThese properties are not common to ALL ceramics !!


ZrO2 toughened Al2O3 (cutting tools)

YBa Cu O (superconductor)

Some exceptions

YBa2Cu3O7 (superconductor)

(Ba,Sr)0.6Fe2O3 (magnet)

New “high-performance” ceramicsunusual properties (e g high toughness conductive)unusual properties (e.g., high toughness, conductive)need to understand structure-property relation


High melting point and high refractoriness (except glass)

Common properties

Generally electrical and thermal insulatorsGenerally hard and strong with low plasticityLow fracture toughness (brittle)Chemically inertMany are low cost (bricks)Many are low cost (bricks)Wide range of appearance


Some Property Check

Materials 1040 Soda SiliconMaterials 1040 Soda- SiliconSteel glass nitride

Density, kg m-3 7850 2480 3200Modulus, GPa 210 74 310UTS / MOR, MPa 500 50 300 – 850Fracture Toughness MPa m1/2 140 0 7 4 0Fracture Toughness, MPa m 140 0.7 4.0Softening / Melting Temp., K 1765 1000 2173


Ceramic StructureMore 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 Structures are named based on the first mineral that is discovered to have the structure. (e.g., rocksalt structure)Have low packing density

Na Cl Ti Ca ORocksaltstructure

Perovskitestructure

Based on SiO 4- tetrahedron

Silicate Structures

Based on SiO4 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.

SiO44- tetrahedron

vertex (ring)edge (chain)face (sheet)


Silicate glass – pure SiO2melts at a very high temperaturevery brittlehigh viscosity

Hard to fabricate

Crystalline silica

Modifiers (e.g., Na) are added to open up the network and

Soda-glass

p preduce the melting point


Defects in Ceramic Structure

Like metals defects such as vacancies andLike 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 new HIGH-TECH ceramics and uses1. 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 $50 billion


Silicate Ceramics: presence of glassy phase in a porous structureclay ceramics (with mullite – 3Al2O3.2SiO2)silica ceramics (with cordierite 2MgO 2Al O 2SiO )

Classification based on COMPOSITION

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

Oxide Ceramics: dominant crystalline phase, with small glassy phasesingle oxide (Al2O3), modified oxide (zirconia toughened alumina)mixed oxide (mullite, BaTiO3)

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

Glass-ceramics: partially crystallised glassSiO2-Li2O, LAS, MAS


Glassesbased on SiO2, with additions to reduce m.p. or give special properties

High-performance Advanced Ceramicsspecial ceramics having improved

h i

Classification based on APPLICATIONS

Traditional Vitreous Ceramics

or give special propertiescontainershouseholdsoptical glasses

Natural Cement & C t

toughness, wear resistance, electrical properties, etc.

cutting tool sensorgrinding laserbearing superconductor

clay-based productsporcelainsanitary waretilesbricksrefractories

Ceramicsrocks & minerals, including ice; bones

Concretea complex ceramics with many phases

structuralcomposite


GlassesAny material that has solidified and become rigid without forming a regular crystal structure is known as glass.

Usually a term applied to ceramic materials 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.

Glasses:

Crystalline materials:crystallize at melting temp, Tm.have abrupt change in sp. vol. at Tm.

do not crystallize.sp. vol. varies smoothly with T.Glass transition temp., Tg.“temperature at which glass becomes rigid enough to handle”


generally brittle(can be toughened by physical process and by

Generally term “glass” commonly applied to silicate based ceramic materials.

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

( g y p y p yvarying the composition or the microstructure)

Corning Glass Museum

basically contains three types of ingredients:(1) network former (SiO2, B2O3)(2) network breaker (Na2O, K2O)(3) network modifier (Al2O3)


Soda-lime Glass70% SiO2, 10% CaO, 15% Na2O, 5% MgO/Al2O3Low melting/softening point, easily formed and shaped.Windows, bottles, etc.

Borrosilicate Glass (Pyrex)80% SiO2, 13% B2O3, 4% Na2O, 3% Al2O3High temperature strength, low coefficient of thermal expansion, good thermal shock resistance.Cooking and chemical glassware

LAS Glass-CeramicLAS Glass Ceramic20% 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 thoseby processes very similar to those of 2000 years ago

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

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


1. Plastic materialsAssist forming process (deform easily without rupture, retain the imposed shape)Example: Clays, talk.

Raw Materials

p y

2. FluxesPromotes fusion during firing.Aid viscous liquid formation; to produce a glassy matrixExample: Feldspar, nepheline syenite, volcanic ash.

3. FillersProvides a rigid component to aid in forming and firing.Confer some very important physical properties (i.e. thermal expansion)Example: Silica, calcined clay, alumina, limestone, bone ash


Ceramic Typical TypicalType Composition Uses

Porcelain Electrical insulatorChina Made from clays, Tableware, Earthenware mixed with tiles, Pottery other inert materials art wareBricks Construction, refractory usesy

Stoneware

Porcelain

Pottery

Earthenware

Porcelain

China Bricks

High-performanceAdvanced 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 ceramicsinsulators, substrates, capacitors, varistors, actuators, sensors

optical ceramicsi d l ti iwindows, lasers; magnetic ceramics

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

special ceramicsnuclear reactor materials, refractories


Engineering Ceramics

high performance of engineering ceramics are resulted due to:1. full density with fewer microcracks and higher intrinsic

modulus2. high toughness (measured by fracture toughness, KIC)

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


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)


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)p g)

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


Ceramic Typical TypicalType Composition Uses

Alumina Al2O3, 3Al2O3.2SiO2 Electronic insulatorDielectric ceramics BaTiO3 CapacitorPi l t i i SiO Z S G A Ult i d i St i Piezoelectric ceramics SiO2, ZnS, GaAs Ultrasonic device, Strain

gauge, microphone Superconductors YBa2Cu3O7 Electromagnet, magnetic

resonance imaging (MRI)

Ceramic insulators

Magnetic Levitation

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 ceramicheld together by a cement (thus concrete is a ceramic-ceramic composite)

Cement Typical TypicalType Composition Uses

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


Natural Ceramicsstone is the oldest construction materials and the most durable (Pyramid, 5000 years old)behaves like any other ceramic in load bearing conditionsbehaves like any other ceramic in load-bearing conditions

ice is also a ceramicmanifestations 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 ceramicthe mineral constituent of bone is hydroxyapatite (HA), Ca10(HPO4)6(OH)2. 43 mass % of human body is HA.


Ceramic Typical TypicalType Composition UsesType Composition Uses

Limestone (marble) Largely CaCO3Sandstone Largely SiO2 Building constructionGranite Aluminium silicateIce H2O Arctic engineeringBone Ca (HPO ) (OH) HA for human boneBone Ca10(HPO4)6(OH)2 HA for human bone


Ceramic Compositesceramics

stiffness, hardness

+ Ceramic composite

toughness

Ceramic Composite Components Typical Uses

Fib l Gl l Hi h f

polymer / metal+ composite

Fibre glass Glass – polymer High-performanceCFRP Carbon – polymer structuresCermet, ZTA WC – Co, ZrO2 – Al2O3 Cutting tools, diesBone HA – collagen Animal structure



Data for CeramicsThermal

Young’s Modulus of Fracture ShockMaterials Density Modulus Rupture Toughness Resistance

Mg m-3 GPa MPa MPa m1/2 KMg m 3 GPa MPa MPa m1/2 K

Soda lime glass 2.48 74 50 0.7 84Borrosilicate 2.23 65 55 0.8 280

Porcelain, pottery 2.3-2.5 70 45 1.0 220

Diamond 3.52 1050 - - 1000Dense alumina 3.90 380 300-400 3-5 150Silicon nitride 3 2 310 300-850 4 500Silicon nitride 3.2 310 300 850 4 500Zirconia 5.6 200 200-500 4-12 500Sialon 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 -


Ceramic Fabrication Methods

SHEET GLASS MAKING

FourcaultProcess

Float Glass Process

Heat Treating Glass


(a) (b) (c)



Next Class

MME 131: Lecture 31

Polymeric Materials

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