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CERAMICS

BY GROUP 2

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CERAMICS

From Greek word Keramos (clay)

Compounds of metallic and non-metallicelements

Most frequently oxides, nitrides, carbidesand silicates

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2 Classes of Ceramics

TRADITIONAL CERAMICSCeramic materials that are derived from common,

naturally occurring raw materials such as clay

minerals and quartz sand.

A type of ceramic used in traditional applications

such as construction, earthenware, and glassware.

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4 CLASSIFICATION OF

CERAMICS

AMORPHOUS CERAMICS

Lacking a definite repeating form, shape or

structure

Glasses

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CRYSTALLINE CERAMICS

atoms (or ions) are arranged in a regularly repeating pattern in three

dimensions (i.e., they have long-range order)

Crystalline ceramics are the Engineering ceramics

High melting points

Strong

Hard

Brittle

Good corrosion resistance

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EXAMPLE OF CRYSTAL

STRUCTURE

Rock salt structure(AX)(NaCl) Spinel structure(AB2X4)(MgAl2O4)

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BONDED CERAMICS Individual crystals are bonded together by a glassy

matrix, as with most clay - derived products

CEMENTS some are crystalline, while others contain both

crystalline and amorphous phases

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STRUCTURES OF CERAMICS

SIMPLE CRYSTAL STRUCTURESContaining ionic or covalent bonds, or a mixture of

two.

COMPLEX SILICATE STRUCTURESThe majority of ceramic materials, in particular

those derived from clay, sand, or cement, contain

the element silicon in the from of silicates.

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CLAY

Al2Si2O5(OH)4.

TRICALCIUM SILICATECa3SiO5

ALUMINA

Al2O3

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TYPES OF CERAMIC PRODUCTS

STRUCTURALA common traditional ceramic used in the

construction industry. Structural ceramics include

brick, clay pipes, and concrete.

REFRACTORIES

A type of ceramic that can withstand extremelyhigh temperatures. Refractories are used in

industrial furnaces.

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WHITEWARESA traditional ceramic used to make pottery and

porcelain. Whiteware ceramics often have a glassy

structure.

GLASSESA type of ceramic material characterized by its

noncrystalline structure. Glasses do not solidify ata specific temperature. Instead, they gradually

solidify as the temperature decreases.

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ABRASIVES type of ceramic material that is very hard and wear

resistant. Abrasives also refer to tools used to

wear away and remove material.

SYNTHETICType of ceramic material that is made from

chemicals or artificial substances rather than fromnatural ones.

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CEMENT Bind other materials together. Used for roads, bridges,

buildings, dams, etc.

ADVANCED CERAMICSAdvanced or Technical Ceramics are parts made from oxide

ceramics, non-oxide ceramics, or composites; each providing

unique material properties of the finished piece. The majority

of these products are manufactured with high density and lowporosity and are used in high performance applications.

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3 CLASSIFICATION OF

TECHNICAL CERAMICS OXIDES

Oxidation resistant

chemically inert

electrically insulating

generally low thermal conductivity

slightly complex manufacturing

low cost for alumina

more complex manufacturing

higher cost for zirconia.

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NON-OXIDES

Low oxidation resistance

extreme hardness

chemically inert

high thermal conductivity

electrically conducting

difficult energy dependent manufacturing and high cost.

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CERAMICBASED COMPOSITE

Toughness

low and high oxidation resistance (type related)

variable thermal and electrical conductivity

complex manufacturing processes

high cost.

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PROPERTIES OF CERAMICS

MECHANICAL

Mechanical properties are important in structural

and building materials as well as textile fabrics.

They include the many properties used todescribe the strength of materials such as:

elasticity / plasticity, tensile strength,

compressive strength, shear strength, fracture

toughness & ductility (low in brittle materials),and indentation hardness.

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ELECTRICAL

Insulating properties

In contrast to Metals Ceramics have very low electricalconductivity due to Ionic-Covalent Bonding which does

not form free electrons.

Electrical conductivity

Electrical conductivity is ability of material to conduct

electric current.Most of ceramic materials are dielectric (materials,having very low electric conductivity, but supportingelectrostatic field).

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Dielectric Strength

ability of a material to prevent electronconductivity at high voltage. Dielectric strength isdetermined as value of electric field strength(expressed in v/m) at which electron conductivitybreakdown occurs.

Dielectric Constant

relative (to vacuum) ability of a material to carryalternating current (dielectric constant of vacuumequals to 1).

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Semi-conducting properties

used for manufacturing varistors (resistorswith non-linear current-voltage

characteristic, which are used for over-voltage protection) and PositiveTemperature Coefficient (PTC) Resistors.

Superconducting properties

near-to-zero electric resistivity

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THERMAL

Thermal Conductivity ()

amount of heat passing in unit timethrough unit surface in a direction normal

to this surface when this transfer is driven

by unite temperature gradient under

steady state conditions.

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Thermal Expansion (Coefficientof Thermal Expansion)

is relative increase in length per unitetemperature rise

Heat Capacity is amount of heat required toraise material temperature by one unit.

Specific Heat Capacity is amount of heatrequired to raise temperature of unit mass ofmaterial by one unit

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Thermal Shock Resistance

ability of material to withstand sharp

changes in temperature.

Maximum Service Temperature

Ceramic materials retain

their properties at elevated temperatures

due to the strong ionic-covalent bonding.

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MAGNETIC

Isotropic ceramic magnet - equal

magnetic properties in all directions

Anisotropic ceramic magnets -

magnetic properties in the direction of

pressing.

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OPTICAL

REFRACTION

Light that is transmitted from one medium into another,undergoes refraction.

Refractive index, (n) of a material is the ratio of the speed of lightin a vacuum (c = 3 x 108 m/s) to the speed of light in thatmaterial.

n = c/v

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CHEMICAL

Ceramics usually have a combination of

stronger bonds called ionic (occurs between a

metal and nonmetal and involves theattraction of opposite charges when electrons

are transferred from the metal to the

nonmetal); and covalent (occurs between two

nonmetals and involves sharing of atoms).

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GENERAL COMPARISON OF

MATERIALSProperty Ceramic Metal Polymer

Hardness Very High Low Very Low

Elastic modulus Very High High Low

Thermal expansion High Low Very Low

Wear resistance High Low Low

Corrosion resistance High Low Low

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GENERAL COMPARISON OF

MATERIALSProperty Ceramic Metal Polymer

Ductility Low High High

Density Low High Very Low

Electrical conductivity Depends High Lowon material

Thermal conductivity Depends High Low

on material

Magnetic Depends High Very Lowon material

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CERAMIC PROCESSING STEPS

MILLING - Millingis the process by which materials

are reduced from a large size to a smaller size.

It involves the ff:breaking up cemented material

pulverization

attritioncompression

impact

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Crushing & Grinding (to get

ready ceramic powder for

shaping)

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Ball Milling

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BATCHINGThe process of weighing oxidesaccording to recipes, and preparing them for mixing and

drying.

MIXING - occurs after batching and is performed withvarious machines, such as dry mixing ribbon mixers.

FORMING - making the mixed material into shapes

FORMING involves the ff:

EXTRUSION - a process used to create objects of a

fixed cross-sectional profile

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Pressing to make shaped parts

Slip casting

DRYING is removing the water or binder fromthe formed material.

FIRING is where the dried parts pass through

a controlled heating process, and the oxidesare chemically changed to cause sinteringand bonding.

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RIBBON MIXERS

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SLIP CASTING

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DRYING PROCESS

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APPLICATIONS OF CERAMICS

Aerospace: space shuttle tiles, thermal

barriers, high temperature glass

windows, fuel cells

Consumer Uses: glassware, windows,pottery, Corningware, magnets,

dinnerware, ceramic tiles, lenses, home

electronics, microwave transducers

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Automotive: catalytic converters, ceramic filters,airbag sensors, ceramic rotors, valves, sparkplugs, pressure sensors, thermistors, vibrationsensors, oxygen sensors, safety glass

windshields, piston rings Medical (Bioceramics): orthopedic joint

replacement, prosthesis, dental restoration,bone implants

Military: structural components for ground, airand naval vehicles, missiles, sensors

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Computers: insulators, resistors,

superconductors, capacitors, ferroelectric

components, microelectronic packaging

Other Industries: bricks, cement,membranes and filters, lab equipment

Communications: fiber optic/laser

communications, TV and radiocomponents, microphones

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EXAMPLES OF CERAMICS

Barium titanate widely used inelectromechanical transducers, ceramiccapacitors, and data storage elements.

Bismuth strontium calcium copper oxide a high-temperature superconductor

Boron nitride a graphite-like one used as alubricant, and a diamond-like one used as anabrasive.

Ferrite is used in the magnetic cores of electricaltransformers and magnetic core memory.

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Lead zirconate titanate (PZT) PZT is used as anultrasonic transducer, as its piezoelectric propertiesgreatly exceed those of Rochelle salt.

Magnesium diboride (MgB2) is an unconventionalsuperconductor.

Porcelain is used for a wide range of household andindustrial products.

Sialon (Silicon Aluminium Oxynitride) has high strength;high thermal, shock, chemical and wear resistance, andlow density. These ceramics are used in non-ferrous

molten metal handling, weld pins and the chemicalindustry.

Silicon carbide (SiC) is used as a susceptor inmicrowave furnaces, a commonly used abrasive, and asa refractory material.

Silicon nitride (Si3N4) is used as an abrasive powder.

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Steatite (magnesium silicates) is used as an electrical insulator. Titanium carbide Used in space shuttle re-entry shields and

scratchproof watches.

Uranium oxide (UO2), used as fuel in nuclear reactors.

Yttrium barium copper oxide (YBa2Cu3O7-x), another hightemperature superconductor.

Zinc oxide (ZnO), which is a semiconductor, and used in theconstruction of varistors.

Zirconium dioxide (zirconia), Its high oxygen ion conductivityrecommends it for use in fuel cells and automotive oxygen sensors.Most ceramic knife blades are made of this material.

Partially stabilised zirconia (PSZ) is much less brittle than otherceramics and is used for metal forming tools, valves and liners,abrasive slurries, kitchen knives and bearings subject to severeabrasion.

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END