CERAMICS

P.V.DEEPIKAAssistant Professor

Department of Mechanical Engineering

what is meant by ceramics? The art &technology of making objects with clay and other materials treated by firing.

DEFINITION

The various hard, brittle, heat resistant and

corrosion resistance materials made by

shaping and then firing a non metallic

mineral such as clay at a high temperature

Traditional &advanced ceramics:

Traditional ceramics includes clay products, silicate glass and cement

While the advanced ceramics consists of carbides(sic),

pure oxides(AL203),nitrides, non silicate glasses and

many othersTypes of ceramics Structural ceramics:-

Eg. Bricks

pipes

floor

roof tiles

Refractory's:Furnace liningsGas fire radiant'sSteel and glass making crucibles White wares:Table wareWall tilesDecorative ware objectsSanitary ware

APPLICATIONS Tiles used in the space

shuttle program

Gas burner nozzles

Ballistic protection

Bio medical implants

Jet engine turbine blades

Missile nose cones

Naturally occurring ceramic materials are :

These include the natural rocks Most of the rock contains the silica

Ceramics produced from the earth minerals are:

Alumina Boron carbide Chromium carbide Graphite Magnesium Silicon carbide

Mechanical properties:

Brittle Low impact strength Tensile strength is less for metals but higher than plastics

No yield strength No plastic deformation No elongation (or) reduction in area Increase in hardness and compressive strength

Diff b/w metals and ceramics: Low melting point Good electrical

conductivity Opaque and

uniform atoms High tensile

strength Good ductility Moderate hardness Non porous High density Relatively high

weight

High melting point

Poor electrical conductivity

Transparent and different size of atoms

Poor tensile strength

Poor ductility Extreme hardness Initial high

porosity Initial low

density Lower weight

CRYSTALLINE CERAMICSThe crystalline ceramics tend to be crystalline and show shear strengthCarbon: pure C has many polymorphous with vastly varying propertiesDiamond: it is similar to Zns in structure each C atom is covalently bonded to 4 other atoms in diamond cubic crystal structureGraphite: layers of hexagonally arranged and covalently bonded C atomsUses: electrodes, heating elements crucibles, casting moulds, rocket nozzles and other applicationsAmorphous ceramics: glasses(na2o, ca o, k2o etc)

Properties:

Crystalline materials are formed by either pure ionic bond (or) combination of ionic as well as covalent characteristics.

They have much higher melting point. They are harder and resistant to chemicals.

Low electrical conductivity at room temperature.

There is a net geometric configuration of atoms at the corners of the cube.

Glasses:Glass is an amorphous (non-crystalline) solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows  and drinking vessels , is soda-lime glass , composed of about 75% silica (SiO2) plus sodium oxide

 (Na2O) from soda ash, lime (CaO), and several minor additives. many glasses contain silica as their main compoundCrystalline solids have molecular structures that is repeated periodically where glass have no periodic structure

Properties: Glass is 100% recyclable Optically transparent Glasses are typically brittle and hard

ABRASIVE MATERIALS:An abrasive is a type of very hard material(it can often be a material)Abrasives are those materials used in operations such as grinding, polishing, lapping, honing, pressure blasting and other similar materialsAbrasives comes in different particles depending up on how much material needs to be removed800-very rough1200-smooth

Materials used for abrasives: Silicon carbide generally used for non ferrous materials

Aluminum oxide or alumina the most widely used abrasive generally used for ferrous alloys, high tensile materials

Cubic boron nitride Garnet usually used for machining of wood Zirconium / alumina alloys suited to carbon and stainless steels

Applications:

Abrasives are used to fine finish Used in axle shafts Used in precious metals Used in tungsten electrodes for lamp bulbss

Used in valve stems such as internal combustion

Cutting expensive materials Used in laminated magnetic cores like transformers

Also in ferrite rod of magnets

Nano materials: Nano materials is a field that takes a materials science-based approach to nanotechnology. It studies materials with morphological features on the nano scale, and especially those that have special properties stemming from their nano scale dimensions

1A0=10-10m 1 nm=10-9m

atomic/crystallographic

1 µm=10-6m micro structure

1mm=10-3m macro structure 1cm=10-2m

Nano particles range from 1 to 100 nmQuantum Dots (of CdSe) are 8 nm

Fullerenes (C60 / Buckyballs) are 1 nmDNA (width) is 2 nm

A hydrogen atom is .1 nm

Bacteria range from 1,000 to 10,000 nmRed blood cells are ~7,000 nm in dia.

White blood cells are ~10,000 nm in dia.

Ancient Nanotechnologists

SYNTHESIS AND PROCESSING OF NANO POWDERS

Top down approach: 1) High-Energy ball milling Bottom-up approach: 1) Sol-gel process 2) Liquid solid reactions 3) Gas Condensation Processing 4) Chemical Vapour Condensation

ELECTRONICS DEVICES

ELECTRONICS DEVICESiField Emitters in Flat Panel DisplayiCarbon Nanotubes TransistorsiElectrochemical DevicesiNano-Probe for AFM, STMiNano-switches and sensors MECHANICAL APPLICATIONSi As Reinforcement in Matrix from i Polymer, Ceramics, Carbon and Metal

CHEMICAL DEVICES:iHydrogen storage for Fuel CelliFilters for hydrogen from tritiumiAct as catalyst supportiSuper-capacitor & Batteries iMembrane for gas purificationiElectro-magnetic ShieldingOTHER APPLICTAIONS

i Bio–Medicali Surface Coatings i Solar Cellsi Nano-Textilei High Energy Materials

APPLICATIONS OF NANO MATERIALS:Mechanical propertiesThe large amount of grain boundaries in bulk materials made of nanoparticles allows extended grain boundary sliding leading to high plasticity.Catalytic PropertiesDue to their large surface, nanoparticles made of transition element oxides exhibit interesting catalytic properties. In special cases, catalysis may be enhanced and more specific by decorating these particles with gold or platinum clusters.

Magnetic PropertiesIn magnetic nano particles, the energy of magnetic anisotropy may be that small that the vector of magnetization fluctuates thermally; this is called super para magnetism . Such a material is free of remanence, and core city. Touching super paramagnetic particles are loosing this special property by interaction, except the particles are kept at distance. Combining particles with high energy of anisotropy with super paramagnetic ones leads to a new class of permanent magnetic materials. Optical PropertiesDistributions of non-agglomerated nano particles in a polymer are used to tune the index of refraction. Additionally, such a process may produce materials with non-linear optical properties. Gold or CdSe nano particles in glass lead to red or orange coloration. Semi-conducting nano particles and some oxide-polymer nano composites exhibit fluorescence showing blue shift with decreasing particle size.

Thank You