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Flashcards in Ceramics Mec207 Deck (24)
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1
Q

What is the typical process of manufacturing ceramics?

A

Powder production –> mixing –> milling –> drying –> compaction –> sintering –> finishing

2
Q

Synthesis of powders?

A
Chemical synthesis: 
-Gas phase reaction 
-Liquid phase reaction 
-Solid phase reaction 
Mechanical synthesis:
-Comminution
3
Q

What is the solid phase reaction?

A

Calcination, thermal decomposition, a reaction between solid chemicals, raw materials are mixed and heated

4
Q

Describe comminution

A

Small particles are produced by reducing the size of the larger ones

5
Q

What is the critical speed for ball mills?

A

The rotating speed which would cause media to be held against the mill lining by centripetal action.

6
Q

What is the critical speed for dry milling?

A

65-80% of Nc

7
Q

What is the critical speed for wet milling?

A

60-65% of Nc

8
Q

Disadvantage of dry milling?

A

Agglomeration can occur BUT it doesn’t need to be separated from a solution

9
Q

Advantage of wet milling?

A

Less agglomeration BUT some components may dissolve in solution, volume ratio must be carefully selected to optimise viscosity

10
Q

What is the purpose of X-Ray Diffraction?

A

It uses grain boundary information to obtain the crystal structure of a ceramic.

11
Q

What is packing density?

A

The volume occupied by the particles in an unit volume.

Packing different sized particles will make powder dense. Ideally ratio of coarse to fine of about 7

12
Q

How does thermal conductivity change with grain size?

A

Thermal conductivity increases with grain size.

13
Q

How does fracture toughness change with grain size?

A

Fracture toughness decreases with increasing grain size. Finer grains tend to obstruct dislocations in a material.

14
Q

Name the various powder analysis methods in order of grain size µm.

A
TEM - 0.001
SEM - 0.01 
OPTICAL MICROSCOPY - 1 
SEDIMENTATION - 0.1 to 100 
COULTER COUNTER - 0.5 to 400 
SIEVING - 20 to 10,000
15
Q

Equation for maximum packing density?

A

PF=PFc+(1-PFc)PFm+(1-PFc)(1-PFm)PFf

16
Q

How do grain boundaries affect phonon movement?

A

They disturb phonon movement.

17
Q

Define phonon.

A

Elastic vibration within the lattice which carries heat through the material.

18
Q

What is the critical speed equation?

A

Nc=(1/pi)((g/2(D-d))^0.5)

19
Q

At what percentage of the critical rotation speed for ball milling should your rotation speed be?

A

About 65 to 80%.

20
Q

What is the purpose of a phase diagram?

A

To identify optimum conditions for suitable aiming phases. They save energy.

21
Q

What is sintering?

A

Green compact is heated and particles merge.

  • removal of pores btw particles
  • formation of strong bonds btw particles
  • shrinkage of compact
22
Q

Equation for porosity

A

1-ρm/ρt

23
Q

Powder size ratio ball mill

A

25:1 minimum media to feed

24
Q

powder volume ratio ball mill

A

20-60% of container