CERAMICS Properties of Ceramic - PowerPoint Presentation

Slide1

CERAMICS Slide2

Properties of Ceramic

They are distiguished by its bonding which is ionic or covalent bonding

High elastic modulus and hardness

High melting point

Low thermal expansion

Good chemical resistance

Brittle

Thermal insulators

Electrical insulators

NonmagneticSlide3

Ceramic Structures : Crystal Structure

Factors that affect crystal structure of ceramics :

- the magnitude of the electrical charge on each of the component ions and the relative sizes of the cations and anions

- the sizes or ionic radii of the cations and anions r

C

/r

ASlide4

Ceramic Structures

Crystal structures

Atomic bonding: ionic bonding

Positive charges (metal) cation

Negative charges (non metal) anion

anion

kationSlide5

AX-Type Crystal Structures

A: cation X: anion

Rock Salt Structure

~

e.g: NaCl, MgO, MnS, LiF

~The coordination number for both

cations&anions: 6 ~Structure: FCC

Slide6

2. Cesium Chloride Structure

~The coordination number: 8

~

e.g: CsCl

Zinc Blende Structure

~The coordination

number: 4 ~atomic bonding:

covalent bonding ~e.g: ZnS, ZnTe, SiC

Slide7

A

mXp

-Type Crrystal Structure

When charges of cations and anions are not the same; where

m

and/or

p ≠ 1

AX2 e.g: CaF2, UO2, PuO

2Slide8

A

mB

n

X

p

-Type Crystal Structures

It is possible for ceramic compounds to have more than one type of cation

A & B: cation X: anionStructure: perovskitee.g: BaTiO3

(Barium titanat) cation: Ba2+, Ti4+

anion: O2-Slide9

Classification of Ceramics

Glasses : 1. Glasses

2. Glass-ceramics

Clay Products : 1. Structural clay products

2. WhitewaresRefractories : 1. Fireclay

2. Silica 3. Basic 4. Special

AbrasivesCementsAdvanced ceramicsSlide10

Glasses (1)

Glasses

They are noncrystalline silicates containing other oxides

Glass Type

Composition

SiO

2

Na

2O CaO Al2O

3 B2O3 OtherCharacteristics and ApplicationFused Silica>99.5High melting temperature, very low coefficient of expansion (thermally schok resistant)96% Silica (VycorTM)96 4Thermally shock and chemically resistant – laboratory wareBorosilicate (PyrexTM)81 3.5 2.5 13Thermally shock and cehimcally resistant – ovenwareSlide11

Glasses (2)

2. Glass-ceramics

Formed

glass ceramics : We use a process that called crystallization which is the most inorganic glasses can be made to transform from a noncrystalline state to one that is crystalline by the proper high temperature heat treatment

Properties : relatively high mechanical strength, low coefficients of thermal expansion, relatively high temperature capabilities, good dielectric properties, good biological compability

Applications : ovenware, tableware, oven windows, and rangetops, and etcSlide12

Clay Products

1. Structural clay products

Applications : building bricks, tiles, and sewer pipes

2. Whitewares

Whitewares become white after the high temperature firing

Applications : porcelain, pottery, tableware, china and plumbing fixtures (sanitary ware)Slide13

Refractories

(1)

Fireclay refractories

The primary ingredients : high purity fireclays, alumina, and silica mixtures usually containing between 25 and 45 wt% alumina.

Applications : in furnace construction, to cofine hot atmospheres and to thermally insulates structural members from excessive temperatures.

2. Silica refractories

Contains over 95% of

SiO

2

and not more than 3%

CaO both by weightWell known for their high temperature load bearing capacitiyApplications : arched roof of steel and glass making furnacesSlide14

Refractories

(2)

3. Basic

refractories

Have a high

propotions

of basic content like

CaO

and MgO

. Also contain chromium and iron compoundsApplications : use in some steel making open hearth furnaces

4. Special refractories Some of these are relatively high purity oxide materialsApplications : For example SiC are used for electrical resistance heating elementsSlide15

Abrasives

The most common examples of abrasives are diamond, silicon carbide, tungsten carbide, corundum, and silica sand

The prime requisite of this material is hardness

Applications : bonded in grinding wheels, as coated abrasives, as loose grains, etc Slide16

Cements

Cement used in construction is characterized as hydraulic and non-hydraulic

The characteristic feature in this material is when mixed with water, form a paste

Cementitious

bond develops at room temperature

Applications : mortar and concreteSlide17

Advanced Ceramics (1)

MEMS (

Microelectromechanical

Systems)

Miniature “smart” system consisting of a multitude of mechanical devices that are

integrared

with a large numbers of electrical elements on a substrate of silicon

Applications : accelerometer,

microsystem for DNA, chemical detectors, etcSlide18

Advanved

Ceramics (2)

2. Optical Fibers

Is made of extremely high purity silica

3. Ceramic Ball Bearings

Consists of balls and races that are in contact with and rub against one another when in useSlide19

Fabrication and Processing Of Ceramics (1)

Fabrication and Processing Of Glasses and Glass-ceramics

Glasses are formed at elevated temperature, hence, we have to consider the temperature viscosity

Glass forming techniques : pressing, blowing, drawing and fiber forming

After fabrication, glasses may be annealed and/or tempered to improve mechanical characteristicsSlide20

Fabrication and Processing Of Ceramics (2)

2. Fabrication and Processing of Clay Products

Commonly, there are two forming techniques,

hydroplastic

forming and slip casting

After forming, the body must be dried and then fired at elevated temperature

3. Powder Pressing

Used to fabricate both clay and non clay compositions

Three basic powder pressing : uniaxial,

isostatic, and hydro pressing

4. Tape CastingPouring the slip onto a flat surfaceA doctor blade spreads the slip into a thin tape of uniform thicknessTape thickness normally range between 0.1 and 2 mmUsually used in the production of ceramic substrates