01_overview Of Advanced Ceramics.pdf 6x545i

MME-467 Ceramics for Advanced Applications

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Ceramics – Definition and classification Why advanced ceramics ? Main drawbacks of advanced ceramics Deg with advanced ceramics Applications of advanced ceramics

Ceramics are a class of materials broadly defined as “inorganic, nonmetallic solids”

1. Silicate ceramics Presence of glassy phase in a porous structure

Clay-ceramics with mullite (3Al2O3.2SiO2) Silica-ceramics with cordierite (2MgO.2Al2O3.5SiO2)

2. Oxide ceramics Dominant crystalline phase, with small glassy phase

Single oxide ceramics (Al2O3, BeO, MgO, ThO2, TiO2, ZrO2) Modified oxide ceramics (ZTA – zirconia toughened alumina) Mixed oxide ceramics (spinel - MgAl2O4 etc )

3. Non-oxide ceramics Element Nitrides Carbides Borides Silicides Sialons Syalons

C in the form of graphite and diamond AIN, BN, Si3N4, TiN B4C, SiC, TiC, WC TiB2, ZrB2 MoSi2 Si3N4 with Al2O3 Si3N4 with Al2O3 and Y2O3

Have the largest range of functions of all known materials. 1. Traditional ceramics tableware, pottery, sanitary ware, tiles, bricks and clinker

2. Advanced ceramics electronic ceramics – insulators, 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

3. Special ceramics reactor ceramics – absorber materials, breeder materials, nuclear fuels refractories

Low electrical conductivity (insulation – spark plugs) Low thermal conductivity (insulation – protection tiles for Space Shuttle) Better properties at high temperatures (nuclear fusion) Wear resistance (cutting tool, roller bearing) Corrosion resistance (heat exchanger for corrosive agents) Specific properties (optical, electrical, magnetic, biomechanics)

Ref: Aldinger and Baumard, Advanced Ceramic Research: Basics Research Viewpoint

1. Low tensile strength at room temperature 2. Brittleness causing failure without prior measurable plastic deformation

3. Sub-critical crack extension can cause failure under constant or cyclic loading and a limited lifetime

Ceramic materials are applied only in such cases where the positive properties prevail over the negative ones.

Physical properties: Thermal expansion coefficient Thermal conductivity Density Electrical conductivity

Mechanical properties: Elastic constants (Young's modulus, Poisson's ratio) Tensile strength (mostly given as bending strength) Compressive strength Fracture toughness

1. Minimize tensile stresses 

Ceramic elements should be introduced at locations were compressive stresses are expected

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Sharp notches and other stress concentrators should be avoided

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External loads should not be introduced by point or line s

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Temperature gradients should be minimized

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Free expansion of thermal strains should be allowed; any restriction will result in stresses

2. A careful and accurate computation of stresses in the whole component is necessary 

In most cases this requires application of the finite element method (FEM)

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Determination of thermal stresses is of particular importance

3. The design requires a statistical analysis

UTILIZED PROPERTIES

MATERIALS

EXAMPLES

Al2O3, Al2TiO5, ZrO2, SiC, Si3N4

thermal insulation of combustion chambers, valve seats, spark plugs, turbochargers, gas turbines

Engine manufacturing wear resistance, heat insulation, low density, resistance to corrosion, electrical insulation, high temperature strength

Industrial processing engineering resistance to corrosion, wear resistance

Al2O3, SiC, ZrO2

chemical devices, drawing die, slide rings, thread guides, rolls for paper industry

UTILIZED PROPERTIES

MATERIALS

EXAMPLES

High-temperature techniques resistance to corrosion, Si3N4, SiC, Al2O3, thermal insulation, electrical C, BN, MoSi2 insulation, high temperature strength

heat exchangers, crucibles, heating conductors, protective tubes for thermocouples, loading devices for materials testing, burner units

Machining of materials Resistance to corrosion, wear resistance

Al2O3, Si3N4, SiC, B4C, TiC, TiN, BN, diamond

cutting tools, grinding wheels, sandblast nozzles

Electroceramics Aclass of ceramic materials used primarily for their electrical properties.

Further classified to: Dielectric ceramics Fast ion conductor ceramics Piezoelectric ceramics

Dielectric Ceramics  Capable of storing large amounts of electrical charge .  An electrical insulator that can be polarized by an applied electric field.  Dielectric materials can be solids, liquids, or gases.

sulfur hexafluoride (SF6)

Solid Dielectric

Liquid Dielectric

Gas Dielectric

Fast Ion Conductor Ceramics  Solids in which ions are highly mobile (Na2O. Al2O3), CaO etc

 Also known as solid electrolytes and superionic conductors.  Batteries, various sensors but primarily in solid oxide fuel cells.

Piezoelectric Ceramics In sensors they make it possible to convert forces, pressures and accelerations into electrical signals In sonic and ultrasonic transducers and actuators they convert electric voltages into vibrations or deformations.

Ferro-electric Ceramics It is the property due to which materials show spontaneous, stable polarization that can be switched hysteretically by an applied electric field. For example: BaTiO3, BiFeO3 etc. spintronics, actuators, and sensor devices etc

Magnetic Ceramics Magnetic ceramics are made of ferrites.

Crystalline minerals composed of iron oxide in combination with some other metals.  Transition metal, rare earth metal etc. Soft or hard magnets. Motors, generators, memory drum Hard disc, Floppy disc etc

Bioceramics  Ceramic products (Al2O3, ZrO2 )as implants and replacements.  Biocompatibility, non-toxic, non-inflammatory and low Young's modulus to prevent cracking of the material etc

 Dental bone implants. Artificial teeth, bones, pacemakers, kidney dialysis machines etc.

Femoral Head of a Hip Prosthesis

Hip Prosthesis

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