Residual porosity in ceramic bodies has what effect on mechanical properties?

• A. Residual porosity decreases both modulus of elasticity and fracture strength.
• B. Residual porosity increases thermal conductivity.
• C. Residual porosity enhances electrical conductivity.
• D. Residual porosity has no effect on mechanical properties.

Answer: (A)

Residual porosity weakens the solid network, so it reduces how well the piece carries load. The air pockets interrupt the continuous material that bears stress, which lowers stiffness (elastic modulus) because there is less solid material to resist deformation. At the same time, these pores act as stress concentrators and crack initiation sites, so the material becomes easier to crack and fracture—its fracture strength drops as porosity increases. In short, more pores mean a less stiff and weaker ceramic.

The other effects listed aren’t correct for this scenario: porosity generally lowers thermal conductivity (air gaps hinder heat flow) and does not enhance electrical conductivity (air is insulating and pores disrupt conduction paths). And porosity certainly does affect mechanical properties, so saying there’s no effect isn’t accurate.