ceramic fabrication process

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CERAMIC FABRICATION
BY GOURAV ACHARYA PREETI VYAS
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DEFINATION

• Methods to produce a solid product of desired
  shape such as a film, fiber or monolith with
  desired engineering properties from suitable
  starting materials.

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IMPORTANCE

• Carefully done fabrication processes are
  responsible for better production of ceramic
  products.
• As the fabrication process govern the
  micro-structure of the product, being
  manufactured, with desired properties.

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RELATION DIAGRAM
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CLASSIFICATION

• (A)GASEOUS PHASE
• (B)LIQUID PHASE
• (C)SOLID PHASE

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(A)GASEOUS PHASE

• Gaseous Phase as a starting material
• The process can further be divided in to three
  groups.
• 1. Gas Phase Reactions
• 2. Gas to Liquid Reactions
• 3. Gas to Solid Reactions

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Fabrication processes of Gaseous Phase
Starting Materials Fabrication Method Type of Product
Between Gases Chemical vapor deposition (CVD) Films, Monoliths
Gas Liquid Directed metal oxidation Monoliths
Gas solid Reaction bonding Monoliths, mainly for production of Si3N4 Sic
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FABRICATION METHODS

• A.1. Chemical Vapor Deposition(CVD)
• Reaction between the gases.
• Production of thin, thick films or monoliths.
• Endothermic reactions(surfaces deposited may be
  heated).
• Heterogeneous precipitation for better
  densification.
• Non-oxides as well as oxides are fabricated by
  CVD.

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Table 2- Important fabrication processes through
CVD
Reaction Temperature 0C Application
SiCl4 2H2O? SiO24HCl 700 1300 Films for Semiconductor devices, optical fibers
TiCl4 O2? TiO2 2Cl2 1200 -1500 Films for electronics devices
3SiH4 4NH3? Si3N4 6H2 1000 1800 Films for Semiconductors devices
3SiCl4 4NH3? Si3N4 12HCl 1200 1800 Films for Semiconductors devices
CH3Cl3Si?SiC 3HCl 1200 -1500 Composites
NH3 BCl3? BN 3HCl 1000 1300 Monoliths
W(CO)6?WC CO2 4CO 600 -1100 Coatings
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Reactors in CVD
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A.2. Directed Metal Oxidation

• Processes involving the reaction between the gas
  liquid.
• Production of porous dense materials as well as
  composites.
• Composites with matrices not only of the oxides
  but also of
• nitrides,borides,carbides or titanates.
• Reacted product usually forms a solid protective
  coating thereby separating reactants.

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• Schematic diagram of structure
• (a)Formation of a matrix of oxide unreacted
  metal by
• direct oxidation
• (b)Oxidation in the presence of a filler.

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ADVANTAGES OF D.M.O.

• Includes matrices of
• Al2O3/Al, AlN/Al etc. or fillers of SiC,TiN,
  ZrN etc.
• The growth of the matrix involve little or no
  change in dimensions.
• Problem of shrinkage during densification, is
  avoided.

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A.3. Reaction Bonding

• The process of chemical reactions between a gas
  and solid.
• Mainly with the fabrication of
• Si3N4 SiC bodies.
• Very low shrinkage occurs during the bonding
  process.

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FLOW DIAGRAM OF RBSN
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(B)Liquid Precursor methods

• Process of converting the solution of the metal
  compound into a solid body.
• Two methods are
• (a.) SOL-GEL PROCESS
• (b.) POLYMER PYROLYSIS

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(a) SOL-GEL PROCESS

• A solution of metal compounds or a suspension of
  very fine particles in a liquid (referred to as
  Sol) is converted in to a semi-rigid mass (the
  gel).

• simple or complex oxides are produced by this
  route.
• Simple Oxides such as alumina (Al2O3), Zirconia
  (ZrO2) .
• Complex Oxides other than Silicates such as
  Barium Titanate
• HYDROLYSIS

Si(OR)4 H2O   gt   HO-Si(OR)3 R-OH
CONDENSATION
(OR)3Si-OR HOSi-(OR)3 gt (OR)3SiOSi(OR)3
R-OH
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(b) POLYMER-PYROLYSIS
Two polymerization routes are quite prominent in
use. (i) Polysilazanes with Si? N in the main
chain
(ii) Polycarbosilanes with CH2 groups separating
the Si atoms in the main chain.
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ADVANTAGES OF POLYMER PYROLYSIS

• The Pyrolysis is usually accompanied by an
  appreciable loss in mass or considerable
  shrinkage.
• More suitable for the production of films or
  fibers.
• The polymers are also being considered for use as
  binders in the injection moldings of ceramics and
  as matrices for ceramic composites.
•  Used for the commercial production of SiC
  fibers.

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(C) Fabrication from Powders

• Production of the desired bodies from an compact
  of finely divided solids(i.e. powders) by the
  action of heat.
• Divided in two most widely used methods.
• MELT CASTING
• FIRING OF COMPACTED POWDERS

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C.(1) MELT CASTING

• Melting a batch of powdered raw materials.
• Followed by cooling and forming to produce a
  solid finished shape.
• Limited to the fabrication of glasses.
• COMMON PROBLEMS
• Formation of non-equilibrium phases.
• Retention of residual glassy phase due to
  incomplete crystallization.

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PRODUCTION OF GLASS GLASS CERAMICS (MELT CASTING)
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C.(2) FIRING OF COMPACTED POWDERS

• Used for production of GLASSES (not more)
  POLYCRYSTALLINE CERAMICS.
• Traditional ceramics.
• Depends upon the physical properties of the
  starting materials.
• Plastic flow properties(according to the of
  water in body mixes)

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Production of polycrystalline ceramics
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Fig-Pressure required for making a plastic body
mix to flow at different water percentage.
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Table .- Consolidation processes according to
water percentages in body mix.
Sl.No. Condition of Body mix Water content or consistency Process
1. Liquid or thick slurry 25 to35 (a)Slip casting under gravity Drain Casting Solid Casting Drain-solid casting (b)Pressure casting High Pressure casting up to 4.0MPa Medium Pressure casting up to 0.35MPa Injection Molding Hot Molding Tape casting Electrophoresis casting
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Continue..
2. Plastic 10 to 15 (a)Soft plastic shaping Hand building Hand pinch Coiling Slab method (b)Plastic shaping Hand throwing Jiggering Jollying Motorized Jigger- Jolly Semi- Fully automatic Jigger-Jolly Roller Head Machines (c)Extrusion (d)Turning (e)Squeeze Forming
3 Semi-dry Pressing 5 to 8 (a)Mechanical Pressing (b)Tamping
4 Dry Pressing 1 to 5 (a)Hydrostatic Pressing (b)Quasisostatic Pressing (c) Isostatic Pressing (d)Ram Pressing
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? ANY QUERY
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THANKS FOR YOUR KIND ATTENTION