Ceramics- Packing of Powder

Question 1

5 types of ordered packing arrangements

Answer 1

Cubic- atoms in squares
Pyramidal- cubic but above layer atoms above space between them
Orthorhombic- single layer has optimum packing (diagonal lines)
Tetragonal- orthorhombic but above layer shifted in one diagonal direction
Tetrahedral- orthorhombic but above layer has atoms above spaces in between for optimum packing

Question 2

Coordination number for each ordered packing arrangement

Answer 2

Cubic: 6
Orthorhombic: 8
Tetragonal: 10
Pyramidal: 12
Tetrahedral: 12

Question 3

Packing density for each ordered packing arrangement

Answer 3

Cubic: 52.4%
Orthorhombic: 60.5%
Tetragonal: 69.8%
Pyramidal: 74.0%
Tetrahedral: 74.0%

Question 4

Void fraction relative to packing density

Answer 4

Divide packing density by 100 and subtract this from 1

Question 5

How much of smaller particles should be added to maximise packing density?

Answer 5

Include smaller particles at 25-30% by volume

Question 6

How does size ratio between large and smaller particles affect relative packing density (PF)?

Answer 6

Larger ratio L:S means greater packing density. Maximum packing fraction achieved when ratio between nearest sizes (diameters) is greater than 7

Question 7

Formula for theoretical maximum packing fraction

Answer 7

PFmax=PFc+(1-PFc)PFm+(1-PFc)(1-PFm)PFf
PFc is packing fraction of coarse
PFm is packing fraction of medium
PFf is packing of fine

Question 8

Weight of particles corresponding to maximum packing

Answer 8

Wc=PFc x Dc
Wm=(1-PFc)PFm x Dm
Wf=(1-PFc)(1-PFm)PFf x Df
D is density of each one

Question 9

How does specific volume change when increasing infinitely coarse particles?

Answer 9

Specific volume decreases from 1.6 (no coarse) to 1 (all coarse)

Question 10

How does specific volume change when increasing infinitely fine particles?

Answer 10

Specific volume decreases from 1.6 (0 volume fraction of fine) to 0 (all fine)