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Ceramics > Powder Technology > Flashcards

Powder Technology Flashcards

1
Q

What are primary particles

A

individual objects of mass

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2
Q

What are three reasons why ceramic process is a powder processing?

A
  1. very high melting temp so casting isn’t economical
  2. casting makes large grains that reduce strength and ceramics are brittle
  3. fine grain microstructures can be produced by sintering
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3
Q

What is the ceramics processing scheme?

A

powders —> shaping (forming green body) —-> sintering (densification, dense body)

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4
Q

How are submicron ceramic powders produced?

A

sol-gel methods or milling of larger particles

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5
Q

At what temperature is the green body fired/sintered?

A

2/3 the absolute melting temperature

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6
Q

For the shaping step of the ceramic processing scheme how does humidity content behave?

A

humidity increases from dry route, plastic route, and wet route

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6
Q

What does sintering do in the ceramic processing scheme?

A

densifies and strengthens the powder compact by diffusive mass transport, which fills the void space between the particles

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7
Q

what do particles look like in solid, liquid, and gas

A

solid - typical particles
liquid - droplets (emulsion)
gas - foam

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8
Q

what is an agglomerate

A

mass of fine particles clustered together

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9
Q

what are granules

A

numerous particles forming a larger unit, more defined shape

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10
Q

what is a powder

A

a group of particles

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11
Q

define granular material

A

group of granules

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12
Q

What are three different particle characteristics that we care about

A
  1. composition
  2. shape
  3. size
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13
Q

What is “composition” for particle characteristics

A
  1. one chemical phase of multiphase
  2. determines density, conductivity, chemistry
  3. dense, porous
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14
Q

What is “shape” for particle characteristics?

A
  1. particle packing and properties
  • regular: mathematical equations
  • irregular: relation to regular particles through another parameter
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15
Q

what “size” is important for particle characteristics. what is large? small?

A

surface area to volume ratio

large (>10 microns) - body forces dominate: F=ma

small (<10 microns) - surface forces start to be more relevant

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16
Q

What number characterizes particle size

A

d

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17
Q

What is the volume of a sphere? area? circumference of a circle? area?

A

sphere
- volume : 4/3 pi r^3
- area: pi d^2

circle
- circumference: pi*d
- area: pi d^2/4

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18
Q

what is volume diameter?

A

d v , d of a sphere with the same volume as the particle

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19
Q

what is surface area diameter?

A

d s, d of a sphere with the same surface area as the particle

20
Q

What is surface-volume diameter?

A

d sv, d of a sphere with the same surface area to volume ratio as the particle

21
Q

What is sieve diameter

A

size of a sieve which the particle passes throgh

22
Q

what is stokes diameter

A

d st, d of a sphere that settles a the same velocity as the particle

23
Q

what is projected area?

A

d proj, d of a circle that has the same area as the 2D image of the particle

24
Q

what is perimeter diameter?

A

d perimeter, d with the same perimeter in 2D image

25
Q

How do you convey particle size distribution on a graph? (PSD)

Cumulative distribution? differential distribution?

A

% versus particle size (x) on a histogram

cum distribution is like a 3rd root graph going up

diff distrib is like the slope of the histogram

26
Q

what is a monodisperse particle size distribution?

A

all particles are the same size

27
Q

what is a monomodal particle size distribution?

A

only one peak, all particles are similar size

28
Q

what is bimodal particle size distribution?

A

two peaks, particles of two different sizes

29
Q

how do you identify the mode in a PSD

A

most frequent, peak in the distribution

30
Q

how do you identify the median in PSD?

A

size where 50% particles are small size and 50% are larger

determine from the percentage of the cumulative distribution of particles

31
Q

how do you identify the mean in PSD?

A

add them all up and divide

32
Q

What are four different types of distributions that aren’t particle size and mass?

A
  1. number
  2. volume
  3. surface area
  4. intensity
33
Q

how could you convert from one distribution to another?

A

shape factors

34
Q

What are the 7 different methods for determining particle size (also agglomeration)?

A
  1. microscopy
  2. sieving
  3. sedimentation
  4. centrifugation
  5. permeation
  6. resistive pulse
  7. light scattering

Mari Said sarina can probably run long

35
Q

What are the characteristics of microscopy?

A
  1. you observe and visually measure particle size/ have to sample thousands- tedious
  2. gives projected 2D image diameters
  3. optical (down to micro) or electron (down to nm)

***good to use with other techniques– to see agglomeration

36
Q

What are the characteristics of sieving?

A
  1. good for particles >25micro
  2. particles passed through sieves w diff sized hole screens/each one is weighed to determine distribution
  3. cons: particles w/high aspect ratio can pass through (L/D or D/t)
37
Q

How does sedimentation work?

A
  1. determines particle size by the rate at which particles settle in a fluid
  2. stokes law- the settling velocity of a particle falling in a fluid
  3. example: andreason pipette
38
Q

How does centrifugation work?

A
  1. centrifugal acceleration
  2. stokes diameter
39
Q

How does permeation work?

A
  1. fluid flows through a packed bed of particles
  2. mean of surface distribution found from the permeation
  3. Carman equation
40
Q

How does the resistive pulse technique work?

A
  1. voltage pulse as a particle flows through an opening
  2. amplitude of pulse varies w particle volume
    cons: limited by smallest orifice/errors if two particles pass at the same time
41
Q

How does light scattering work?

A
  1. laser light used
  2. light scattered at different angles
  3. scattering intensity depends on the angle– function of the angle
42
Q

What are most solids processed as?

A

particulates– like 60%

43
Q

How do you achieve the right particle size/distribution?

A
  • mechanical size reduction
  • very energy intensive
  • after they reach the grind limit, it’s furthered by the synthesis of particles
44
Q

What properties are size separation and classification methods based on?

A
  1. shape
  2. size
  3. density
45
Q

What is classification?

A

the separation of particles according to their settling rate in a fluid

46
Q

What are the 5 different classification methods?

A
  1. screening (and sieving)
  2. sedimentation
  3. centrifugation
  4. dry (cyclones)
  5. wet (suspensions-hydrocyclones)
47
Q

Blank

A

Ceramics (8 decks)

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