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Advanced Ceramics > Powder Technology and Characteristics > Flashcards

Powder Technology and Characteristics Flashcards

1
Q

What are primary particles

A

individual objects of mass

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2
Q

Why is ceramic processing a powder processing?

A
  1. high melting temp so casting isn’t economical
  2. ceramics are brittle and large flaws reduce strength and casting produces large grains
  3. fine grain microstructures can be made from sintering submicron particles
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3
Q

What are the steps of the ceramic processing scheme?

A
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4
Q

What are the particles like in solids, liquids, and gasses? images

A

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

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5
Q

What is an agglomerates

A

mass of fine particles clustered together

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6
Q

what are granules

A

numerous particles forming a larger unit with a more defined shape

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7
Q

what is powder

A

group of particles

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8
Q

what is granular material

A

group of granules

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9
Q

what is pictured

A

left- agglomerate
right - granule

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10
Q

What are the three main particle characteristics? * exam question

A
  1. composition
  2. shape
  3. size
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11
Q

What is composition? What does it determine? Example characteristics?
*exam question

A
  1. one chemical phase or multiphase
  2. determines density, conductivity, chemistry
  3. dense, porous
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12
Q

What are properties of particle “shape” that are important?
*exam question

A

particle packing – affects manufacturing microstructure, properties

regular - mathematical equations
irregular - relation to regular particles through another parameter

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13
Q

What is an important aspect about the “size” of a particle? How is it divided?
*exam questions

A

surface area to volume ratio

  1. large (>10 microns) - body forces dominate: F = ma
  2. small (<10 microns) - surface forces start to be more relevant
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14
Q

What are colloidal particles? What particle characteristic is important for colloidal particles and macromolecules?

A

colloidal particles - nanometer to 1 micron

small size (<10 microns) is important & surface forces are more relevant

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15
Q

What are 4 different measurement techniques that are important for the “composition” of particles? What do they identify?

A
  1. X-Ray Fluorescence (XRF) - elemental/atomic composition
  2. X-Ray Diffraction (XRD) - phases/crystallinity
  3. Density (theoretical calculations and pycnometry) - phases
  4. Energy Dispersive Spectroscopy (EDS) - atomic composition
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16
Q

What do we measure with X-Ray Fluorescence?

A

the chemical elemental composition of materials

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17
Q

X-Ray Fluorescence

  1. What is XRF based on?
  2. What does it measure that’s characteristic of each element?
  3. What info does it NOT provide?
A
  1. the x-ray emitted from a sample excited by a primary x-ray source
  2. the dif in energies between the expelled and replacement electron
  3. doesn’t provide info on how elements are grouped together (which compounds we have/which phases they form)
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18
Q

What does a figure of XRF look like?

A
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19
Q

What is X-Ray Diffraction?

A

a powder diffraction method used to identify the phases present (types of crystals) in a material

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20
Q

How does X-Ray Diffraction work?

A

materials (or powders) have randomly oriented grains that produce diffracted beams from “different” crystalline planes that satisfy the Bragg condition

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21
Q

What is Bragg’s Law?

A
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22
Q

how do you find the planar spacing of XRD?

A
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23
Q

What do XRD results look like?

A
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24
Q

What are two ways to calculate density? when do you use which?

A

Gas Pycnometry
1. powders
2. based on Boyle’s law

Archimedes’ method
1. for pieces

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25
How can density be expressed? What does this allow you to do?
express as a percentage of theoretical density allow to calculate porosity w/ astm mehtod
26
What is the symbol for theoretical density? true? apparent? bulk?
27
what is theoretical density? how would you measure it?
based on the crystal structure, the volume of the unit cell and the number of atomic weights of the ions in the volume XRD
28
What is true density? how would you measure it?
include the effect of defects and grain boundaries pycnometry
29
what is apparent density? how would you find it?
includes only the closed pores, defects, and grain boundaries combo of pycnometry and Archimedes' principle
30
what is bulk density? how do you measure it?
includes all pores (open and closed) as well as defects and grain boundaries Archimedes' principle
31
how can you find the density of simple shapes
external dimensions and weight
32
which density measurements are the largest?
33
What are the measurement techniques for shape? what do they measure?
1. Scanning Electron Microscopy SEM - shape and size 2. Transmission Electron Microscopy TEM - shape, size, phase and crystallinity
34
How do you determine the shape of regular particles? irregular? how are shapes determined?
1. regular - mathematical equations 2. irregular - relation to regular particles through another parameter 3. manufacturing, microstructure, properties
35
What does a SEM look like?
36
What do results of a SEM look like?
37
What does a TEM look like?
38
What do TEM results look like?
39
What are two quantitative shape factors used?
1. Aspect Ratio (AR) AR = (largest dimension of particle)/ smallest 2. Sphericity Shape Factor (Y with line through it) Y = surface area of sphere w same vol as particle / SA of particle
40
What is an important "size" property for particle characteristics? Large? Small?
surface area of volume ratio large: >10 microns - body forces dominate small: <10 microns - surface forces more relevant
41
What is the volume diameter of a particle? Its formula?
dv diameter of a sphere with the same volume as the particle
42
What is the surface area diameter of a particle? Its formula?
ds diameter of a sphere with the same surface area as the particle
43
What is the surface-volume diameter of a particle? Its formula?
dsv diameter of a sphere with the same SA to volume ratio as the particle
44
What is a particle size distribution PSD?
is a graphical representation to convey the information related to the size of all the particles in our system
45
What is the most common way to graphically represent a PSD?
Histogram % vs. particle size cumulative distribution and differential distribution
46
What is a monodisperse PSD?
all particles have the same size
47
What is a monomodal PSD?
only one peak, all particles similar size
48
What is a bimodal PSD?
two peaks, particles of two different sizes
49
What is the mode of PSD? How do you identify it?
- most frequently occuring size - peak of the differential distribution - find the peak of the DIFFERENTIAL frequency distribution
50
What is the median of PSD? How do you identify?
- size where half (50%) of the particles have smaller size, and half of the particles have larger size - most easily determined from the cumulative distribution - find the 50% on the y-axis of the CUMULATIVE, then the corresponding x-- here is where half the particle sizes have half smaller and half larger
51
What is the mean of PSD?
- arithmetic mean - most common definition of "average"
52
In general, does the mean = median = mode?
no
53
What are 7 different ways of determining particle size?
MSSCPRL Microscopy Sieving Sedimentation Centrifugation Permeation Resistive Pulse Light Scattering (Mari says sarina can run pretty long)
54
What is microscopy? What results does it give (2 types)? When is it recommended?
what it is 1. observe and visually measure the particle size 2. have to sample thousands of particles results 1. optical microscope (to micro meters)/electron microscope (to nm) 2. gives projected image diameters recommended 1. use with combination with other techniques to see agglomeration/ aggregation/ shape 2. correct interpretation of any other analytical technique used to measure particle size
55
How does sieving work? What are some benefits of sieving?
how it works - screens shaken mechanically over a period of time - particles smaller than the opening simply pass through the screen - weighed over a range of screens to build up a particle size distribution benefits - good for particles >25 micro m - good for industry (easy, inexpensive, and quick)
56
What is a con of sieving?
possible for particles with high aspect ratio to pass through smaller screens than their longest dimension
57
How does light scattering work? What sizes of particles? Benefits? Cons?
1. light is scattered by particles 2. scattering is suspended in a liquid 3. light measured as a function of an angle 4. intensity depends on the angle, # of particles, particle size, wavelength of light, indices of refraction, absorption of particle, and refraction index sizes - nm to mm sizes benefits - quick and modern cons - expensive laser
58
What is the bottom-up route of powders for ceramic processing?
1. synthetic routes 2. precursors (chemical, thermochemical and physical reactions) 3. several nm to a few micro 4. DEFINED shapes **basically manufacturing/creating the particles
59
What is the top-down route of powders for ceramic processing?
1. mining (w aditional thermomechanical processes of minerals) 2. comminution (crushing and grinding), followed by size separation 3. several mm to a few micro 4. IRREGULAR shapes **making existing things smaller into particles
60
What kind of processing is ceramic processing?
powder processing
61
What is key for achieving reliable ceramic components?
characterization - size, shape, chemical comp, crystal structure
62
What method should you always use for your powders?
microscopy
63
what are two different ways powders for ceramic processing can be obtained? What does it influence?
top down or bottom up - approach determines purity, shape, and size of raw materials
64
What is necessary to gather info about degree of aggregation?
particle size (mean, mode,median) and particle size distribution (differential and cumulative distributions)
65
How do you identify top-down processing?
irregular shapes
66

Advanced Ceramics (10 decks)

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