Effect of Particle Grain Size on Properties

The size of the particle (grain size), can have a considerable effect on the properties of molded graphite as shown in Table 5.4. 

Grade Particle Size mm Density g/cm Specific Resistance O.cm Flexural Strength MPa CTE m/m°Cx10 (100 - 600°C) 

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 ts pronounced. 

Particle size also affects the finishing since, during machining operations, particles can be tom 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. 

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