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Ceramic materials & their processing
Ceramic materials & their processing
Ceramics materials:
 An organic compound which containing of metals and
    one or more non-metals.
   i.e. Al2O3 and pottery etc.
   Types:-
   Traditional ceramic
   Advance ceramic
   Glasses
Traditional Ceramics:
 Those ceramic which are composed of clay mineral
  (porcelain) as well as cement and glass
 Products:-
 Traditional ceramic are include pottery ,brick and tiles etc.

Advance ceramics:
 Those ceramic which are made by synthetically produced
from raw materials.
Product:-
Advance ceramic are include Al2O3 ,bio-ceramic etc.
Properties:-
 These materials are insulator of heat and electricity and
  more resistance to high temperature.
 These materials are stronger than that of metals because of
  their covalent and ionic bonding.
 These materials are less density it means they are lighter
  than metals.
 The inability of slip of ceramic materials can cause more
  difficult in the processing and performance.
 Some oxide of ceramic show magnetic behaviors such as
  Fe3O4.
 They are brittle materials.
PROCESSING OF CERAMICS AND CERMETS
 Processing of Traditional Ceramics
 Processing of New Ceramics
 Processing of Cermets
 Product Design Considerations
Types of Ceramics and Their Processing
  Ceramic materials divide into three categories:
   1. Traditional ceramics – particulate processing
   2. New ceramics – particulate processing
   3. Glasses – solidification processing
  The solidification processes for glass are covered
   in a different slide set
  The particulate processes for traditional and new
   ceramics as well as certain composite materials are
   covered in this slide set
Overview of Ceramics Particulate
Processing
 Traditional ceramics are made from minerals
  occurring in nature .
 Products include pottery, porcelain, bricks, and cement
 New ceramics are made from synthetically produced
  raw materials.
 Products include cutting tools, artificial bones, nuclear
  fuels, and substrates for electronic circuits
 The starting material for all of these items is powder
Overview of Ceramics Particulate
Processing - continued
 For traditional ceramics, the powders are usually mixed
  with water to temporarily bind the particles together and
  achieve the proper consistency for shaping
 For new ceramics, substances other than water are used
  as binders during shaping
 After shaping, the green parts are fired (sintered), whose
  function is the same as in powder metallurgy:
Figure 17.1 - Usual steps in traditional ceramics processing: (1)
   preparation of raw materials, (2) shaping, (3) drying, and (4) firing
Part (a) shows the work part during the sequence, while (b) shows the
   condition of the powders
Preparation of the Raw Material
   for Traditional Ceramics
 Shaping processes for traditional ceramics require
 the starting material to be a plastic paste
   This paste is comprised of fine ceramic powders
    mixed with water
 The raw ceramic material usually occurs in nature
 as rocky lumps, and reduction to powder is the
 purpose of the preparation step in ceramics
 processing
Fabrication Techniques:
 First of all raw material usually have to go through milling
  or grinding operation in which particle size is reduced
  which is done by crusher such as jaw or roll crusher.
 The product of crusher is to screening to made powder
 Product having desired shape of particle size.
 The powdered product must be thoroughly mixed with
  water to make plastic paste for creation of traditional
  ceramic product.
Ingredients of Ceramic Paste for Shaping
1. Clay (hydrous aluminum silicates) - usually the main
   ingredient because of ideal forming characteristics
   when mixed with water
2. Water – creates clay-water mixture with suitable
   plasticity for shaping
3. Non-plastic raw materials, such as alumina and silica -
   reduce shrinkage in drying and firing but also reduce
   plasticity of the mixture during forming
4. Other ingredients, such as fluxes that melt (vitrify)
   during firing and promote sintering, and wetting
   agents to improve mixing of ingredients
Shaping Processes
 Slip casting
    The clay-water mixture is a slurry
 Plastic forming methods
    The clay is plastic
 Semi-dry pressing
    The clay is moist but has low plasticity
 Dry pressing
    The clay is basically dry (less than 5% water) and has
     no plasticity
Figure 17.4 - Four categories of shaping processes used for traditional
ceramics, compared to water content and pressure required to form the clay
Slip Casting
A suspension of ceramic powders in water, called a slip.
  This slip is poured into a porous plaster of paris
  mold so that water from the mix is absorbed into the
  plaster to form a firm layer of clay at the mold surface
 The slip composition is 25% to 40% water
 Two principal variations:
   Drain casting - the mold is inverted to drain excess slip
    after a semi-solid layer has been formed, thus
    producing a hollow product
   Solid casting - to produce solid products, adequate
    time is allowed for entire body to become firm.
Figure 17.5 - Sequence of steps in drain casting, a form of slip casting:
   (1) slip is poured into mold cavity, (2) water is absorbed into plaster
   mold to form a firm layer, (3) excess slip is poured out, and (4) part
   is removed from mold and trimmed
Overview of Plastic Forming
 The starting mixture must have a plastic
  consistency, with 15% to 25% water
 Variety of manual and mechanized methods
   Manual methods use clay with more water because it
    is more easily formed
       More water means greater shrinkage in drying
   Mechanized methods generally use a mixture with
    less water so starting clay is stiffer
Plastic Forming Methods

 Hand modeling (manual method)
 Jiggering (mechanized method)
 Plastic pressing (mechanized method)
 Extrusion (mechanized method)
Hand Modeling
Creation of the ceramic product by manipulating the
  mass of plastic clay into the desired geometry
 Hand molding - similar only a mold or form is used
  to define portions of the part geometry
 Hand throwing on a potter's wheel is another
  refinement of handcraft methods
   Potter's wheel = a round table that rotates on a
    vertical spindle, powered either by motor or foot
    operated treadle
   Products of circular cross-section can be formed by
    throwing and shaping the clay, sometimes using a
    mold to provide the internal shape
Jiggering
Similar to potter's wheel methods, but hand throwing
  is replaced by mechanized techniques




Figure 17.6 - Sequence in jiggering: (1) wet clay slug is placed on a convex
mold; (2) batting; and (3) a jigger tool imparts the final product shape
Plastic Pressing
Forming process in which a plastic clay slug is pressed
  between upper and lower molds contained in metal rings
 Molds are made of porous material such as gypsum, so
  when a vacuum is drawn on the backs of the mold halves,
  moisture is removed from the clay
 The mold sections are then opened, using positive air
  pressure to prevent sticking of the part in the mold
 Advantages: higher production rate than jiggering and not
  limited to radially symmetric parts
Extrusion
Compression of clay through a die orifice to produce long
  sections of uniform cross-section, which are then cut to
  required piece length
 Equipment utilizes a screw type action to assist in
  mixing the clay and pushing it through die opening
 Products: hollow bricks, shaped tiles, drain pipes, tubes,
  and insulators
 Also used to make the starting clay slugs for other
  ceramics processing methods such as jiggering and
  plastic pressing
Semi-dry Pressing
    Uses high pressure to overcome the clay’s low plasticity
     and force it into a die cavity




Figure 17.7 - Semi-dry pressing: (1) depositing moist powder into die cavity,
(2) pressing, and (3) opening the die sections and ejection
Dry Pressing
Process sequence is similar to semi-dry pressing - the
  main distinction is that the water content of the
  starting mix is typically below 5%
 Dies must be made of hardened tool steel or
  cemented carbide to reduce wear since dry clay is very
  abrasive
 No drying shrinkage occurs, so drying time is
  eliminated and good dimensional accuracy is
  achieved in the final product
 Typical products: bathroom tile, electrical insulators,
  refractory brick, and other simple geometries
Clay Volume vs. Water Content

 Water plays an important role in most of the
  traditional ceramics shaping processes
 Thereafter, it has no purpose and must be removed
  from the clay piece before firing
 Shrinkage is a problem during drying because
  water contributes volume to the piece, and the
  volume is reduced when it is removed
Figure 17.8 - Volume of
  clay as a function of
  water content
Relationship shown here is
  typical; it varies for
  different clay
  compositions
Drying
The drying process occurs in two stages:
 Stage 1 - drying rate is rapid and constant as water
  evaporates from the surface into the surrounding
  air and water from the interior migrates by capillary
  action to the surface to replace it
   This is when shrinkage occurs, with the risk of
    warping and cracking
 Stage 2 - the moisture content has been reduced to
 where the ceramic grains are in contact
   Little or no further shrinkage occurs
Figure 17.9 - Typical drying rate curve and associated volume reduction
   (drying shrinkage) for a ceramic body in drying
Drying rate in the second stage of drying is depicted here as a straight line;
   the function is sometimes concave or convex
Firing of Traditional Ceramics
Heat treatment process that sinters the ceramic material
 Performed in a furnace called a kiln
 Bonds are developed between the ceramic grains, and
  this is accompanied by densification and reduction of
  porosity
 Therefore, additional shrinkage occurs in the
  polycrystalline material in addition to that which has
  already occurred in drying
 In the firing of traditional ceramics, a glassy phase forms
  among the crystals which acts as a binder
Glazing
Application of a ceramic surface coating to make the
  piece more impervious to water and enhance its
  appearance
 The usual processing sequence with glazed ware
  is:
   1. Fire the piece once before glazing to harden the
      body of the piece
   2. Apply the glaze
   3. Fire the piece a second time to harden the glaze
Processing of New Ceramics
 The manufacturing sequence for the new
   ceramics can be summarized in the following
   steps:
   1. Preparation of starting materials
   2. Shaping
   3. Sintering
   4. Finishing
 While the sequence is nearly the same as for the
   traditional ceramics, the details are often quite
   different
Preparation of Starting Materials
 Strength requirements are usually much greater for
  new ceramics than for traditional ceramics
 Therefore, the starting powders must be smaller
  and more uniform in size and composition, since
  the strength of the resulting ceramic product is
  inversely related to grain size
 Greater control of the starting powders is required
 Powder preparation includes mechanical and
  chemical methods
Shaping of New Ceramics
 Many of the shaping processes for new ceramics are
 borrowed from powder metallurgy (PM) and
 traditional ceramics
   PM press and sinter methods have been adapted to
    the new ceramic materials
 And some of the traditional ceramics forming
  techniques are used to shape the new ceramics,
  such as: slip casting, extrusion, and dry pressing
 The processes described here are not normally
  associated with the forming of traditional ceramics,
  although several are associated with PM
Hot Pressing
Similar to dry pressing except it is carried out at
  elevated temperatures so sintering of the product is
  accomplished simultaneously with pressing
 This eliminates the need for a separate firing step
 Higher densities and finer grain size are obtained,
  but die life is reduced by the hot abrasive particles
  against the die surfaces
Isostatic Pressing
Uses hydrostatic pressure to compact the ceramic
   powders from all directions
 Avoids the problem of nonuniform density in the
   final product that is often observed in
   conventional uniaxial pressing
 Same process used in powder metallurgy
Powder Injection Molding (PIM)
Ceramic particles are mixed with a thermoplastic
  polymer, then heated and injected into a mold cavity
 The polymer acts as a carrier and provides flow
  characteristics for molding
 Upon cooling which hardens the polymer, the mold is
  opened and the part is removed
 Because temperatures needed to plasticize the carrier
  are much lower than those required for sintering the
  ceramic, the piece is green after molding
 The plastic binder is removed and the remaining
  ceramic part is sintered
Sintering of New Ceramics
 Since the plasticity needed to shape the new
  ceramics is not normally based on water, the
  drying step required for traditional green ceramics
  can be omitted for most new ceramic products
 The sintering step is still very much required
 Functions of sintering are the same as before:
   1. Bond individual grains into a solid mass
   2. Increase density
   3. Reduce or eliminate porosity
Finishing Operations for New Ceramics
 Parts made of new ceramics sometimes require
   finishing, which has one or more of the following
   purposes:
   1. Increase dimensional accuracy
   2. Improve surface finish
   3. Make minor changes in part geometry
 Finishing usually involves abrasive processes
   Diamond abrasives must be used to cut the
     hardened ceramic materials
Reference:
 ©2002 John Wiley & Sons, Inc. M P Groover,
  “Fundamentals of Modern Manufacturing 2/e”.
 © 1979Johnson, H.V “Manufacturing process”
Ceramic materials & their processing

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Ceramic materials & their processing

  • 3. Ceramics materials:  An organic compound which containing of metals and one or more non-metals.  i.e. Al2O3 and pottery etc.  Types:-  Traditional ceramic  Advance ceramic  Glasses
  • 4. Traditional Ceramics:  Those ceramic which are composed of clay mineral (porcelain) as well as cement and glass  Products:-  Traditional ceramic are include pottery ,brick and tiles etc. Advance ceramics:  Those ceramic which are made by synthetically produced from raw materials. Product:- Advance ceramic are include Al2O3 ,bio-ceramic etc.
  • 5. Properties:-  These materials are insulator of heat and electricity and more resistance to high temperature.  These materials are stronger than that of metals because of their covalent and ionic bonding.  These materials are less density it means they are lighter than metals.  The inability of slip of ceramic materials can cause more difficult in the processing and performance.  Some oxide of ceramic show magnetic behaviors such as Fe3O4.  They are brittle materials.
  • 6. PROCESSING OF CERAMICS AND CERMETS  Processing of Traditional Ceramics  Processing of New Ceramics  Processing of Cermets  Product Design Considerations
  • 7. Types of Ceramics and Their Processing  Ceramic materials divide into three categories: 1. Traditional ceramics – particulate processing 2. New ceramics – particulate processing 3. Glasses – solidification processing  The solidification processes for glass are covered in a different slide set  The particulate processes for traditional and new ceramics as well as certain composite materials are covered in this slide set
  • 8. Overview of Ceramics Particulate Processing  Traditional ceramics are made from minerals occurring in nature .  Products include pottery, porcelain, bricks, and cement  New ceramics are made from synthetically produced raw materials.  Products include cutting tools, artificial bones, nuclear fuels, and substrates for electronic circuits  The starting material for all of these items is powder
  • 9. Overview of Ceramics Particulate Processing - continued  For traditional ceramics, the powders are usually mixed with water to temporarily bind the particles together and achieve the proper consistency for shaping  For new ceramics, substances other than water are used as binders during shaping  After shaping, the green parts are fired (sintered), whose function is the same as in powder metallurgy:
  • 10. Figure 17.1 - Usual steps in traditional ceramics processing: (1) preparation of raw materials, (2) shaping, (3) drying, and (4) firing Part (a) shows the work part during the sequence, while (b) shows the condition of the powders
  • 11. Preparation of the Raw Material for Traditional Ceramics  Shaping processes for traditional ceramics require the starting material to be a plastic paste  This paste is comprised of fine ceramic powders mixed with water  The raw ceramic material usually occurs in nature as rocky lumps, and reduction to powder is the purpose of the preparation step in ceramics processing
  • 12. Fabrication Techniques:  First of all raw material usually have to go through milling or grinding operation in which particle size is reduced which is done by crusher such as jaw or roll crusher.  The product of crusher is to screening to made powder Product having desired shape of particle size.  The powdered product must be thoroughly mixed with water to make plastic paste for creation of traditional ceramic product.
  • 13. Ingredients of Ceramic Paste for Shaping 1. Clay (hydrous aluminum silicates) - usually the main ingredient because of ideal forming characteristics when mixed with water 2. Water – creates clay-water mixture with suitable plasticity for shaping 3. Non-plastic raw materials, such as alumina and silica - reduce shrinkage in drying and firing but also reduce plasticity of the mixture during forming 4. Other ingredients, such as fluxes that melt (vitrify) during firing and promote sintering, and wetting agents to improve mixing of ingredients
  • 14. Shaping Processes  Slip casting  The clay-water mixture is a slurry  Plastic forming methods  The clay is plastic  Semi-dry pressing  The clay is moist but has low plasticity  Dry pressing  The clay is basically dry (less than 5% water) and has no plasticity
  • 15. Figure 17.4 - Four categories of shaping processes used for traditional ceramics, compared to water content and pressure required to form the clay
  • 16. Slip Casting A suspension of ceramic powders in water, called a slip. This slip is poured into a porous plaster of paris mold so that water from the mix is absorbed into the plaster to form a firm layer of clay at the mold surface  The slip composition is 25% to 40% water  Two principal variations:  Drain casting - the mold is inverted to drain excess slip after a semi-solid layer has been formed, thus producing a hollow product  Solid casting - to produce solid products, adequate time is allowed for entire body to become firm.
  • 17. Figure 17.5 - Sequence of steps in drain casting, a form of slip casting: (1) slip is poured into mold cavity, (2) water is absorbed into plaster mold to form a firm layer, (3) excess slip is poured out, and (4) part is removed from mold and trimmed
  • 18. Overview of Plastic Forming  The starting mixture must have a plastic consistency, with 15% to 25% water  Variety of manual and mechanized methods  Manual methods use clay with more water because it is more easily formed  More water means greater shrinkage in drying  Mechanized methods generally use a mixture with less water so starting clay is stiffer
  • 19. Plastic Forming Methods  Hand modeling (manual method)  Jiggering (mechanized method)  Plastic pressing (mechanized method)  Extrusion (mechanized method)
  • 20. Hand Modeling Creation of the ceramic product by manipulating the mass of plastic clay into the desired geometry  Hand molding - similar only a mold or form is used to define portions of the part geometry  Hand throwing on a potter's wheel is another refinement of handcraft methods  Potter's wheel = a round table that rotates on a vertical spindle, powered either by motor or foot operated treadle  Products of circular cross-section can be formed by throwing and shaping the clay, sometimes using a mold to provide the internal shape
  • 21. Jiggering Similar to potter's wheel methods, but hand throwing is replaced by mechanized techniques Figure 17.6 - Sequence in jiggering: (1) wet clay slug is placed on a convex mold; (2) batting; and (3) a jigger tool imparts the final product shape
  • 22. Plastic Pressing Forming process in which a plastic clay slug is pressed between upper and lower molds contained in metal rings  Molds are made of porous material such as gypsum, so when a vacuum is drawn on the backs of the mold halves, moisture is removed from the clay  The mold sections are then opened, using positive air pressure to prevent sticking of the part in the mold  Advantages: higher production rate than jiggering and not limited to radially symmetric parts
  • 23. Extrusion Compression of clay through a die orifice to produce long sections of uniform cross-section, which are then cut to required piece length  Equipment utilizes a screw type action to assist in mixing the clay and pushing it through die opening  Products: hollow bricks, shaped tiles, drain pipes, tubes, and insulators  Also used to make the starting clay slugs for other ceramics processing methods such as jiggering and plastic pressing
  • 24. Semi-dry Pressing Uses high pressure to overcome the clay’s low plasticity and force it into a die cavity Figure 17.7 - Semi-dry pressing: (1) depositing moist powder into die cavity, (2) pressing, and (3) opening the die sections and ejection
  • 25. Dry Pressing Process sequence is similar to semi-dry pressing - the main distinction is that the water content of the starting mix is typically below 5%  Dies must be made of hardened tool steel or cemented carbide to reduce wear since dry clay is very abrasive  No drying shrinkage occurs, so drying time is eliminated and good dimensional accuracy is achieved in the final product  Typical products: bathroom tile, electrical insulators, refractory brick, and other simple geometries
  • 26. Clay Volume vs. Water Content  Water plays an important role in most of the traditional ceramics shaping processes  Thereafter, it has no purpose and must be removed from the clay piece before firing  Shrinkage is a problem during drying because water contributes volume to the piece, and the volume is reduced when it is removed
  • 27. Figure 17.8 - Volume of clay as a function of water content Relationship shown here is typical; it varies for different clay compositions
  • 28. Drying The drying process occurs in two stages:  Stage 1 - drying rate is rapid and constant as water evaporates from the surface into the surrounding air and water from the interior migrates by capillary action to the surface to replace it  This is when shrinkage occurs, with the risk of warping and cracking  Stage 2 - the moisture content has been reduced to where the ceramic grains are in contact  Little or no further shrinkage occurs
  • 29. Figure 17.9 - Typical drying rate curve and associated volume reduction (drying shrinkage) for a ceramic body in drying Drying rate in the second stage of drying is depicted here as a straight line; the function is sometimes concave or convex
  • 30. Firing of Traditional Ceramics Heat treatment process that sinters the ceramic material  Performed in a furnace called a kiln  Bonds are developed between the ceramic grains, and this is accompanied by densification and reduction of porosity  Therefore, additional shrinkage occurs in the polycrystalline material in addition to that which has already occurred in drying  In the firing of traditional ceramics, a glassy phase forms among the crystals which acts as a binder
  • 31. Glazing Application of a ceramic surface coating to make the piece more impervious to water and enhance its appearance  The usual processing sequence with glazed ware is: 1. Fire the piece once before glazing to harden the body of the piece 2. Apply the glaze 3. Fire the piece a second time to harden the glaze
  • 32. Processing of New Ceramics  The manufacturing sequence for the new ceramics can be summarized in the following steps: 1. Preparation of starting materials 2. Shaping 3. Sintering 4. Finishing  While the sequence is nearly the same as for the traditional ceramics, the details are often quite different
  • 33. Preparation of Starting Materials  Strength requirements are usually much greater for new ceramics than for traditional ceramics  Therefore, the starting powders must be smaller and more uniform in size and composition, since the strength of the resulting ceramic product is inversely related to grain size  Greater control of the starting powders is required  Powder preparation includes mechanical and chemical methods
  • 34. Shaping of New Ceramics  Many of the shaping processes for new ceramics are borrowed from powder metallurgy (PM) and traditional ceramics  PM press and sinter methods have been adapted to the new ceramic materials  And some of the traditional ceramics forming techniques are used to shape the new ceramics, such as: slip casting, extrusion, and dry pressing  The processes described here are not normally associated with the forming of traditional ceramics, although several are associated with PM
  • 35. Hot Pressing Similar to dry pressing except it is carried out at elevated temperatures so sintering of the product is accomplished simultaneously with pressing  This eliminates the need for a separate firing step  Higher densities and finer grain size are obtained, but die life is reduced by the hot abrasive particles against the die surfaces
  • 36. Isostatic Pressing Uses hydrostatic pressure to compact the ceramic powders from all directions  Avoids the problem of nonuniform density in the final product that is often observed in conventional uniaxial pressing  Same process used in powder metallurgy
  • 37. Powder Injection Molding (PIM) Ceramic particles are mixed with a thermoplastic polymer, then heated and injected into a mold cavity  The polymer acts as a carrier and provides flow characteristics for molding  Upon cooling which hardens the polymer, the mold is opened and the part is removed  Because temperatures needed to plasticize the carrier are much lower than those required for sintering the ceramic, the piece is green after molding  The plastic binder is removed and the remaining ceramic part is sintered
  • 38. Sintering of New Ceramics  Since the plasticity needed to shape the new ceramics is not normally based on water, the drying step required for traditional green ceramics can be omitted for most new ceramic products  The sintering step is still very much required  Functions of sintering are the same as before: 1. Bond individual grains into a solid mass 2. Increase density 3. Reduce or eliminate porosity
  • 39. Finishing Operations for New Ceramics  Parts made of new ceramics sometimes require finishing, which has one or more of the following purposes: 1. Increase dimensional accuracy 2. Improve surface finish 3. Make minor changes in part geometry  Finishing usually involves abrasive processes  Diamond abrasives must be used to cut the hardened ceramic materials
  • 40. Reference:  ©2002 John Wiley & Sons, Inc. M P Groover, “Fundamentals of Modern Manufacturing 2/e”.  © 1979Johnson, H.V “Manufacturing process”