Manufacturing, Forming and Shaping

Question 1

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

Answer 1

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

Question 2

Shaping capability

Answer 2

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

non NNS: uniaxial, extrusion, tape casting, EPD

Question 3

What are consolidation methods?

Answer 3

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

Question 4

What is the consolidation method from slip casting,

Answer 4

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

Question 5

What are characteristics of gelcasting?

Answer 5

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

Question 6

What happens in a polymerization reaction?

Answer 6

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

Question 7

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

Answer 7

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

Question 8

What are two properties of gelcasted materials?

Answer 8

1. complex shapes
2. machinable

Question 9

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

Answer 9

gelation

Question 10

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

Answer 10

freezing

Question 11

What are three components needed for freeze casting?

Answer 11

1. refrigerant
2. cryoprotector
3. freezing device

Question 12

why do you need a sublimation process in freeze casting

Answer 12

to remove the frozen solvent (turn it into gas)

Question 13

What is a cool property about freeze casting?

Answer 13

it keeps the homogeneity very well

chemical/physical and composition/shape

Question 14

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

Answer 14

sublimation

Question 15

What is tape casting used for?

Answer 15

to make ceramic tapes

Question 16

What are the parts of a tape casting machine?

Answer 16

Question 17

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

Answer 17

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

Question 18

What are the three components needed for electrophoretic deposition?

Answer 18

1. electrodes
2. electrical field
3. substrate

Question 19

What process happens in electrophoretic deposition?

Answer 19

particle migration due to electrical field

suspension —–> substrate

Question 20

What are the three steps in electrophoretic deposition?

Answer 20

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)

Question 21

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

Answer 21

creates tensions that lead to the breaking of the deposited layer

Question 22

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

Answer 22

low –> high
dry, plastic, wet

*price same

dry- most simple, wet- least simple

wet process most reliable

Question 23

What are some possible outcomes of electrophoretic deposition?

Answer 23

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

Question 24

What are shaping routes a function of?

Answer 24

the humidity content of the powder mixture

Question 25

what are the dry shaping ceramic processing techniques?

Answer 25

1. uniaxial pressing 2. isostatic pressing

Question 26

what are the plastic shaping processing techniques?

Answer 26

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

Question 27

what are the wet shaping processing techniques?

Answer 27

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

Question 28

What are the characteristics of near-net -shaping techniques

Answer 28

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

Question 29

What are the three components to uniaxial pressing?

Answer 29

1. lubricant 2. powder 3. compact

Question 30

What are the two types of isostatic pressing?

Answer 30

wet bag and dry bag, also cold isostatic pressing

Question 31

what are the stages in wet bag isopressing?

Answer 31

1. filling 2. loading 3. pressing 4. decompression

Question 32

what are the stages in dry bag isopressing?

Answer 32

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

Question 33

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

Answer 33

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

Question 34

How do particles behave in the dry processing routes?

Answer 34

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

Question 35

What are some defects from the dry processing routes like?

Answer 35

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

Question 36

What are three characteristics of plastic processing routes?

Answer 36

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

Question 37

How does extrusion work?

Answer 37

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

Question 38

How does injection molding work?

Answer 38

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

Question 39

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

Answer 39

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

Question 40

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

Answer 40

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

Question 41

How do you prepare suspensions for wet/colloidal routes?

Answer 41

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

Question 42

What does suspension stability depend on?

Answer 42

interaction forces between particels

Question 43

how can you identify unstable suspension between particles?

Answer 43

V repulsion < V attraction (intermolecular potential energy)

Question 44

What do additives serve as in wet/colloidal processing?

Answer 44

stabilization mechanism

Question 45

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

Answer 45

1. electric double layer mechanism 2. steric mechanism 3. electrosteric mechanism

Question 46

What would stable suspension look like?

Answer 46

stable suspension is where V repulsion is bigger than attraction V is potential energy between particles

Question 47

What is the process of slip casting?

Answer 47

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

Question 48

What are the pros and cons of slip casting?

Answer 48

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