Manufacturing and Microstructures Flashcards
What are the three different types of shaping routes?
- dry route
- plastic route
- wet route
What is the purpose of the shaping step in ceramic processing? sintering?
shaping - forming the green body
sintering – densification and dense body
What is the differentiating factor between the different shaping routes?
humidity content
At what temperature is the green body sintered at
2/3 of the absolute melting temp
What does sintering do?
densifies and strengthens the powder compact by diffusive mass transport which fills in the void space between the particles
how are powders produced?
submicron ceramic powders are produced by sol-gel methods (bottom up) or milling of larger particles (top down)
What are sol-gel methods?
chemical processes that synthesize solid materials from small molecules.
a colloidal suspension solution (sol) is transformed into a “gel” - a network with both liquid and solid phases
What are the types of dry shaping?
- uniaxial pressing
- isostatic pressing
- plasma spray
What are the types of plastic shaping?
- extrusion
- injection molding
*ram pressing
* viscous plastic processing (VPP)
What does near net shaping mean?
the material needs minimal shaping/machining after processing
What are the types of wet shaping?
- tape casting
- slip casting
- gelcasting
- Additive manufacturing (&subtypes)
- EPD (electrophoretic deposition)
- Hard template - Replica
- Ice templating
- particle-stabilized forms
- Hard template-sacrificial filler
**direct coagulation casting (DCC)
**pressure casting
**freeze casting
What are the differences between the different ceramic processing techniques? **test question
- humidity content
- shaping capability
- microstructure
What are the three near net shaping techniques characteristics?
- complicate geometry and 3D shapes
- green body has the final desired shape
- minimization of machining stage in green, after drying or sintering
What are 5 different microstructure types possible?
- monolithic (dense)
- porous
- coatings
- composites
- discrete phases
- continuous and discrete phases
- Lattice
How does uniaxial pressing work?
- coat the die with lubricant
- fill the die with powder
- start compaction
- eject the part
How does isostatic pressing work?
After the pressing (image)
- it’s bisque fired at <1000C (strengthens and densifies)
- green machined
- final firing
- glazing
What process is this?
isostatic pressing
What is a con of uniaxial pressing?
no way to address agglomeration
What is the firing temperature for a bisque in isostatic? what happens?
<1000 C
it slightly strengthens and slightly densifies the material
What are the NNS techniques? non?
NNS: isostatic, inj, molding, s. casting, gelcasting, freeze casting
non NNS: uniaxial, extrusion, tape casting, EPD, plasma spray
- sometimes: slip, particle-stabilized, sacrificial filler
How will fine powders vs. large particles behave during isostatic/uniaxial pressing? How is it addressed
fine powders (like flour, micron sized) are cohesive and do not flow
large particles (like sand - few hundred microns) will flow.
- they must GRANULATE the powder into about hundred micron size first flow first
** large particles (after granulation) more successful than fine powders
What does the change of pore size distribution look like during compaction?
What is this an image of?
dry pressing incomplete deformation of agglomerates
- trapped air
- fracture of a dry pressed component on the right with increasing pressure
What are 3 characteristics of plastic routes? What are some images?
- mixture of ceramic powders with polymers (up to 30 wt% of polymer additives)
- viscous paste or dough
- dough gets extruded, injected, or shaped into components
How does extrusion work? What is the polymer respect to powder percentage? How are particles held together? What are they held together by?
- a viscous plastic mixture of ceramic powder, water, and a binder are forced through a nozzle
- 15-20% polymer respect to powder
- particles held by surface tension because of the pendular rings of water-binder mixture
- binders - polyacrylamides and PVA
What is the polymer/ceramic ratio in injection molding? How is it compared to for extrusion?
30wt%
injection molding > extrusion
What are two different categories of binders that injection molding has? examples?
thermoplastic binders - polystyrene
thermosetting binders - epoxy resin
What are two main pros of wet/colloidal routes?
- dispersing the powder in a liquid (usually water) allows for improved reliability and more complex shapes to be formed
- control of the attraction/repulsion forces between particles
- SUBADVANTAGES OF THIS ON ANOTHER CARD
What are the steps to injection molding?
- the material mixture is heated to a temp where the polymer binder has low viscosity which allows flow
- the mixture is much more fluid than extrusion
- the mixture is forced through a nozzle into the mold cavity where it’s cooled and solidified and becomes solid
what is a colloid
small particle size suspended in a fluid and you can control the attraction/repulsion forces between
What are 5 benefits of being able to control the attraction/repulsion forces between particles?
- soft aggregates are broken apart by the repulsion and mixing
- flaws can be removed by filtration
- high green densities can be achieved by efficient packing of dispersed particles
- less shrinkage
- more versatility to prepare different microstructures
** yay more reliable ceramics
Describe the preparation of wet routes
suspensions of ceramic powders
- powders in solvent with additives
What does suspension stability depend on?
the interaction forces between particles
What are interaction forces of suspensions equal to? What defines an unstable suspension?
unstable is where the force of repulsion is less than the force of attraction
What does an unstable suspension graph look like?
What does a stable suspension graph look like? What are the parameters for it being stable?
Vrepulsion > V attraction
What are the three different types of suspension behavior?
- Newtonian
- Pseudoplastic (shear-thinning)
- Dilatant (shear-thickening)
Describe Newtonian suspension behavior?
as rate increases, viscosity is the same and shear stress increases proportionately
viscosity stays the same w rate
Describe Pseudoplastic (shear-thinning) behavior?
Viscosity decreases w increasing rate. it gets thinner when stirred faster
Describe Dilatant suspension behavior
moving the fluid gently it’s a thin liquid, but if you hit it quickly it stiffens and resists movement
What are the steps of slip casting?
- Porous mold filled with suspension
- left to dry a little and the excess is drained and trimmed
- you can have thicker, solid pieces
- pressure filtration
What are two cons of slip casting?
- complex shapes, BUT limited to constant cross section
- lengthy time in plaster of porous plastic mold*
What is this for?
slip casting and pressure filtration of sanitary white wear in a porous polymer mold
What are three pros of gelcasting?
- complex 3d shapes with dif cross sections
- closed cavity mold – low pressure injection or pouring
- molding time can be shorter than slip casting
What are the steps of gelcasting?
- liquid-like suspension containing a gellable polymer is used to fill a mould
- left to dry
- complex shaped body is removed from the mould
What is the method for forming the green body called in gelcasting?
gelation
What are the 4 components of gelcasting?
- monomer
- crosslinking agent
- initiator
- catalyst or activator
What happens in gelcasting to form the gel used?
polymerisation reaction
monomer of low MW –> polymer high MW
- formation of a tridimensional structure (w/monomer and crosslinking agent)
- becomes microgel
- becomes macrogel w ceramic particle
What do the results of gelcasting look like? What is the strength of their dried green bodies?
strength > 1MPa
What are the different parts of a tape casting machines? What are the two categories of binders commonly used in tape casting operations?
slurry comes down the reservoir, height determined by a doctor blade, the carrier sheet moves the slurry to the drying zone, then it’s stored a roll
- nonaqueous and aqueous
What could the results of tape casting look like?
What do tape casting machines look like?
What are five different types of additive manufacturing?
- Direct ink writing
- direct ink printing
- stereolithography
- slurry-based 3D printing
- slurry-based selective laser sintering
What are three subcategories of Direct ink writing?
- robocasting
- fused deposition
- freeze-form extrusion fabrication
What’s a general definition of direct ink writing?
extruding a line of suspension through a small diameter nozzle to write a shaped object on a stage
What is robocasting/how does it work? 1 What kind of slurry is used? 2 How does the rheology behave?
*type of direct ink writing
extruder has a paste/gel in it that is pushed through a nozzle onto a platform
- a colloidal slurry with dilatancy (inc V w shear) and shear-thinning behavior
- rheology (how it moves w force) - flows smoothly when force is applied but holds shape once it’s out
What is fused deposition of ceramics/how does it work?
- a type of direct ink writing
the colloid filament blend is heated and liquified (forms shear thinning fluid) then pushed out and becomes solid with cooling
What is freeze-form extrusion fabrication process?
controlled deposition (extruded and printed layer by layer) at below the freezing point of water
How does direct inkjet printing work?
layer deposition –> drying
put droplets < 1mm thick on then the ink is solidified by a fan then the next layer is put on
How does stereolithography work?
slurry deposition –> UV curing
layer by layer the slurry is cured with a uv light (photololymerization).
- they contain photosensitized monomers which is how they solidify
How does slurry-based 3D printing work?
slurry deposition –> drying –> binder printing
spread a layer of slurry, heat it to dry excess solvent, selective print binder material
How does slurry-based selective laser sintering work?
slurry deposition –> laser scanning
slurry w two kinds of polymers, laser causes the two polymers to mix and form a water-insoluble phase w connected particles
What are porous structures?
materials where porosity have been DELIBERATELY introduced to alter their properties in a controlled matter
What is a porogen?
A substance that helps generate the porosity in porous structures
What are the most common applications for porous structures?
- membranes and filters for separation processes
- thermal and acoustic insulation
- bioscaffolds
- chemical sensors
- energy conversion
- drug delivery
- Catalysis
- absorbents
- energy storage
- photocatalysis
What are the 8 key properties of porous strucures?
- permeability
- encapsulation (and release)
- insulation
- dielectric/conduction
- damage tolerance
- lightweight
- selectivity
- adsorption
PEIDDSLA
What are the 4 ways to classify porous structures?
- pore size
- pore type
- porosity distribution
- type of material
What are the three different classifications of pore size?
- macropores/macroporosity (pore size > 50nm)
- mesopores/mesporosity (50nm<pore<2nm)
- micropores/microporosity (pore<2nm)
What are three different pore types?
- cellular ceramic
- open pores
- closed porosity
What are characteristics of the “cellular ceramic” pore type?
- volume of the pore exceeds the volume of the soild
- material just seen in the struts
- very open structures and fluids can be easily transported across the structure
- shows an “ordered” structure
What are characteristics of the “open pores” pore type?
- solid material do not totally surround the pore or void
- consecutive pores get connected through a “window”
- pores may or may not present an ordered structure
What are characteristics of “closed porosity” pore type?
- pores are not open to flow of fluid
- each pore totally surrounded by solid material
- these types of pores may or may not present a patterned structure
What are the 4 classifications of porosity distribution?
- interconnected porosity
- hierarchical porosity
- multiscale porosity
- functionally graded porosity
What is interconnected porosity?
There’s a path connecting pores, typically following a pattern or aligned in a particular direction, allowing the potential flow of a fluid across it
What is hierarchical porosity?
- a porous ceramic containing 2 or more length scales pore sizes in the same component
- the different pore size exhibit similar pore type and shape
- porous component can be described as bimodal or trimodal pore size distribution
What is multiscale porosity?
Can also be defined as “hierarchical” porous material, but commonly it makes reference to a ceramic material with different porosity type and shape and size in the same sample
What is “functionally graded porosity”?
a hierarchical or multiscale porous material where the dif pore sizes are patterned on a particular direction (ie radial distribution, unidirectional, graded, etc.)
What are the three types of materials for porous structures?
- inorganic
- organic/inorganic hybrid
- organic
What kinds of inorganic materials can make porous structures?
- ceramics
- metals
- zeolites
What kinds of organic/inorganic hybrid materials can make porous structures?
metal organic frameworks (MOFs)
What kinds of organic material can make porous structures?
- covalent-organic frameworks
- porous organic polymers
- porous molecular solids
Describe characteristics of wet/colloidal routes for green body formation of macroporous materials?
- prep of suspensions of ceramic powders
- homogeneity of mixture particles and porogens
- control of porosity and particle distribution - microstructure
- porous materials are shaped using colloidal processing techniques
What are the different types of wet/colloidal routes for macroporous ceramics?
- Hard Template - replica
- Hard template - sacrificial filler
- particle stabilized foams
- ice templating
What are the main steps of Hard Template - Replica processing?
- suspension
- shaping
- dipping polymeric sponge into suspension. number/time dippings - drying
- ceramic green sponge with same open pore microstructure as the polymeric sponge - calcination and sintering
- burn out sponge
- densify particles in struts
What are the main steps of hard template - sacrificial filler processing?
- suspension (stuff is in there)
- shaping
- ie gelcasting, slip casting, freeze casting
- drying
- ceramic green body containing sacrificial filler
- calcination and sintering
- burn out sponge
- densify particles in struts
What do hard template- replica ceramics look like? Hard template sacrificial filler?
**be able to identify these for the exam
What are the steps of processing particle stabilized foams?
- addition of a surfactant
- incorporation of air bubbles
- particle stabilized foam
- gelcasting of the foam
What do particle stabilized foams look like?
What are the steps of ice templating?
- suspension
- freezing
- depending on the desired structure
- vacuum sublimation solvent removal green porous body.
- freeze-drying
- sintering
- result: consolidated porous structure
What does the process look like for the microstructure during ice templating?
- starting with the particles and solvent
- put in contact with the refrigerant and ice crystals start “nucleating” at the bottom
- the ice crystals start growing and pushing the particles aside “particle rejection”
- creation of the freezing front and keeps pushing particles aside
- freezing front advances until it’s all frozen
- sublimation – green body after sublimation of ice
What do the results of ice templating look like?
What are three methods to create mesoporous ceramics?
- emulsion templating
- precursors
- sol-gel (aerogels)
What kind of porosity is from ice templated?
interconnected porosity
What are 5 methods to create microporous ceramics?
- sol-gel
- polymer templating
- chemical vapor and liquid deposition
- partial sintering
- anodization
In general, what is the main role of ceramic coatings? What are two of these?
protect substrates against environmental conditions
- temperature
- chemistry
What coatings can you use to protect against temperature? chemistry (what kinds)?
Temperature: Thermal Barrier Coatings (TBCs), protect materials from elevated temperatures damage
Chemistry (oxidation, corrosion, etc.) : Environmental Barrier Coatings (EBCs), protect materials from corrosion and oxidation, in extreme environments, often at elevated temperatures
What are 5 things to consider with ceramic coatings?
- Chemistry of substrate and material
- CTE match (for thermal cycling)
- Thickness (tens of microns to several mm)
- Microstructure
- Properties of substrate and material
What is a plasma spray route?
- a dry** processing technique
- no solvent
- granulate the powders to control the flow
- inject the flow to powders on top of the substrate in the plasma jet stream
- plasma jet stream melts the powders and we put molten ceramic materials on top of the substrate we want to create
- one of the few that doesn’t need sintering
What does the microstructure look like after plasma spray
- more elongated grains
- some residual porosity
- some radial cracks
What does the coating layers usually look like?
What is electrophoretic deposition?
a mechanism for forming the green body = deposition
What components are involved in electrophoretic deposition?
- electrodes
- electrical field
- substrate
What is the mechanism for forming the green body in electrophoretic deposition?
deposition
In electrophoretic deposition, what does the electric field cause?
particle migration from the suspension to the substrate
How can you find the speed of particles in electrophoretic deposition?
What is the process of electrophoretic deposition?
suspension (organic, aqueous, sols) –>
migration (to + side) –>
deposition (overcome separation forces and come to an intimate contact – particles adhere to each other) —>
extraction and drying (apparition of tensions that leads to the breaking of the deposited layer) —>
sintering
What are 5 different possibilities for electrophoretic deposition?
- Thin/thick layers on substrates (1‐30 um)
- multilayer structures (0.1-10mm)
- monolithic layer
- complex shapes
- functionally graded materials
What kind of applications benefit from thin/thick layers on substrates
ceramic or metallic substrates
coatings
What kind of applications benefit from multilayer structures
ceramics of metallic substrates
piezoelectric for circuits
structural applications : reinforcement thermal barrier
What kind of applications benefit from monolithic layers? what’s the substrate?
graphite as substrate
autosupported materials
how does electrophoretic deposition create complex shapes?
What is a functionally graded material? How is it created?
continuous gradient in composition material by adjusting the suspension composition in teim
What 5 things do you make ceramic selection based on?
- raw material
- versatility
- microstructure
- reliability
- application
