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Ceramics > Manufacturing, Forming and Shaping > Flashcards

Manufacturing, Forming and Shaping Flashcards

1
Q

What are the three (?) or humidity powder mixtures?

A
  1. dry: uniaxial, isostatic
  2. plastic: extrusion, inj, molding
  3. wet/colloidal: slip casting, gelcasting, freeze casting, tape casting, EPD
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2
Q

Shaping capability

A

NNS: isostatic, inj, molding, s. casting, gelcasting, freeze casting

non NNS: uniaxial, extrusion, tape casting, EPD

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3
Q

What are consolidation methods?

A

methods that allow you to go from liquid-like (slurry/suspension) to solid like (green body)

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4
Q

What is the consolidation method from slip casting,

A

slip casting = filtration
gelcasting = gelation (polymerization)
freeze casting = freezing
tape casting = evaporation
EPD = particle migration & deposition

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5
Q

What are characteristics of gelcasting?

A
  1. produces complex 3D shapes
  2. closed cavity mold (low pressure injection or pouring)
  3. molding time can be shortened
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6
Q

What happens in a polymerization reaction?

A

a low MW monomer turns into a polymer w/ high MW

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7
Q

what are the four components needed when forming the green body through gelation

A
  1. monomer
  2. crosslinking agent
  3. initiator
  4. catalyst or activator
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8
Q

What are two properties of gelcasted materials?

A
  1. complex shapes
  2. machinable
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9
Q

What is the mechanism for forming the green body in gelcasting?

A

gelation

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10
Q

What is the method for forming the green body in freeze casting?

A

freezing

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11
Q

What are three components needed for freeze casting?

A
  1. refrigerant
  2. cryoprotector
  3. freezing device
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12
Q

why do you need a sublimation process in freeze casting

A

to remove the frozen solvent (turn it into gas)

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13
Q

What is a cool property about freeze casting?

A

it keeps the homogeneity very well

chemical/physical and composition/shape

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14
Q

What process do you need in freeze casting? what are the steps?

A

sublimation

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15
Q

What is tape casting used for?

A

to make ceramic tapes

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16
Q

What are the parts of a tape casting machine?

A
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17
Q

What is the mechanism for forming the green body for electrophoretic deposition?

A

deposition (where particles settle out of a fluid and accumulate on a surface)

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18
Q

What are the three components needed for electrophoretic deposition?

A
  1. electrodes
  2. electrical field
  3. substrate
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19
Q

What process happens in electrophoretic deposition?

A

particle migration due to electrical field

suspension —–> substrate

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20
Q

What are the three steps in electrophoretic deposition?

A
  1. (suspension) particles electrically charged in suspensions
  2. (migration) electrical field applied through electrodes
  3. (migration) to the opposite charge electrode
  4. (deposition) overcome sep. forces and contact/adhere to each other
  5. sintering (extraction/drying)
21
Q

What does the drying/extraction step of the green body formation process for electrophoretic deposition do?

A

creates tensions that lead to the breaking of the deposited layer

22
Q

How does shaping capability behave with dry, plastic, and wet processes? price? simplicity of process? reliability?

A

low –> high
dry, plastic, wet

*price same

dry- most simple, wet- least simple

wet process most reliable

23
Q

What are some possible outcomes of electrophoretic deposition?

A
  1. thin/thick layers on substrates
  2. multilayer structures
  3. monolithic layer
  4. complex shapes
  5. functionally graded materials
24
Q

What are shaping routes a function of?

A

the humidity content of the powder mixture

25
Q

what are the dry shaping ceramic processing techniques?

A
  1. uniaxial pressing
  2. isostatic pressing
26
Q

what are the plastic shaping processing techniques?

A
  1. extrusion
  2. injection molding
  3. ram pressing
  4. viscous plastic processing (VPP)
27
Q

what are the wet shaping processing techniques?

A
  1. tape casting
  2. slip casting
  3. pressure casting
  4. gelcasting
  5. freeze casting
  6. direct coagulation casting (DCC)
  7. electrophoretic deposition (EPD)
28
Q

What are the characteristics of near-net -shaping techniques

A
  1. complicated geometry and 3D shapes
  2. green body has the final desired shape
  3. minimization of machining stage in green, after drying or sintering
29
Q

What are the three components to uniaxial pressing?

A
  1. lubricant
  2. powder
  3. compact
30
Q

What are the two types of isostatic pressing?

A

wet bag and dry bag, also cold isostatic pressing

31
Q

what are the stages in wet bag isopressing?

A
  1. filling
  2. loading
  3. pressing
  4. decompression
32
Q

what are the stages in dry bag isopressing?

A
  1. loading powder into die
  2. pressing in x-y plane
  3. ejection of pressed part through top or bottom
33
Q

What are the steps to cold isostatic pressing (CIP)?

A
  1. CIP blank
  2. firing at temp <1000C– densifies/strengthens the material
  3. final firing
  4. glaze
34
Q

How do particles behave in the dry processing routes?

A
  1. fine powders are cohesive and don’t flow
  2. large particles will flow (need to be 100 micron for flow)
35
Q

What are some defects from the dry processing routes like?

A
  1. incomplete deformation of agglomerates
  2. trapped air
  3. irregular pores
  4. deformed granules
  5. intergranular pores
36
Q

What are three characteristics of plastic processing routes?

A
  1. mixture of ceramic powders w/polymers (up to 30%)
  2. viscous dough or paste
  3. dough gets extruded, injected, shaped into components.
37
Q

How does extrusion work?

A
  1. viscous plastic mixture of ceramic powder, water, and binder is forced through a nozzle
  2. particles are held by surface tension bc of the binder mixture
  3. polycrylamides and PVA
38
Q

How does injection molding work?

A
  1. large polymer/ceramic ratio
  2. viscous feed is heated till the material can flow into the cavity under the applied pressure
  3. mixture is cooled by the cool cavity
39
Q

What is the result of wet/colloidal routes? why?

A

more reliable ceramics

dispersing the powder in a liquid (usually water) allows for improved reliability and more complex shapes to be formed

40
Q

Control of the attraction/repulsion forces in wet routes allows for what 4 things?

A
  1. soft aggregates can be broken apart
  2. flaws can be removed by filtration
  3. high green densities can be achieved from efficient packing
  4. less shrinkage
41
Q

How do you prepare suspensions for wet/colloidal routes?

A

ceramic powders and additives are put in a solvent (usually water)

42
Q

What does suspension stability depend on?

A

interaction forces between particels

43
Q

how can you identify unstable suspension between particles?

A

V repulsion < V attraction

(intermolecular potential energy)

44
Q

What do additives serve as in wet/colloidal processing?

A

stabilization mechanism

45
Q

What are three different ways additives can serve as a stabilization mechanism?

A
  1. electric double layer mechanism
  2. steric mechanism
  3. electrosteric mechanism
46
Q

What would stable suspension look like?

A

stable suspension is where V repulsion is bigger than attraction

V is potential energy between particles

47
Q

What is the process of slip casting?

A

porous mold – filled with the suspension – filtrate/plaster — excess of slurry is drained and trimmed

48
Q

What are the pros and cons of slip casting?

A

pro: complex shapes
cons: limited to constant cross section, lengthy time in plaster of the mold

Ceramics (8 decks)

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