handbook of carbon, graphite, diamond and fullerenes

3.3 Effect of Particle (Grain) Size on Properties
AI1RL
AI4RL
AI5RL
0.075
0.025
0.010
1.72
1.82
1.90
0.0016
0.0018
0.0020
Molded Graphite 99
The size of the particle (grain size), can have a considerable effect on
the properties of molded graphite as shown in Table 5.4.
Table 5.4. Effect of Particle Size on Properties I 10 '
Particle Specific Flexural CTE*
Size Density Resistance Strength m/m°C x 10" 6
Grade** mm g/cm 3 O.cm MPa (100-600°C)
28
42
77
Notes: * CTE= coefficient of thermal expansion
**Materials are isostatically pressed grades from
The Carbon/Graphite Group Inc., St. Marys, PA
As shown in the above table, reducing particle size (grain size) results
in an substantial increase in the apparent density and, correspondingly, a
lowering of the porosity. The flexural strength is almost tripled. On the
negative side, the CTE is more than doubled, which may lead to a decrease
in thermal shock resistance. The effect on the electrical resistivity is not as
pronounced.
Particle size also affects the finishing since, during machining operations,
particles can be torn out of the surface by the tool, leaving a void and
the larger the particle, the larger the void. When a smooth finish is required
with close tolerances, a small particle size material must be selected.
3.4 Effect of Grain Orientation on Properties
The degree of grain orientation varies with the production process as
mentioned above and has a considerable effect on the properties of molded
graphite as shown in Table 5.5.
3.2
5.7
7.0