processingporosity

Processing porosity refers to voids and pore networks that form in a material as a consequence of its manufacturing process. It is distinct from porosity that is intentionally introduced for functional reasons. Processing porosity can arise in metals, ceramics, polymers, and composites during steps such as casting, molding, debinding, sintering, foaming, or additive manufacturing.

Common causes include gas entrapment during processing, incomplete compaction or consolidation, shrinkage during solidification, binder burnout residues, and reactions that generate gas. Porosity may be open and interconnected, contributing to permeability, or closed and isolated, which lowers density and can reduce overall strength. The distribution, size, and connectivity of pores determine material performance in applications such as filtration, insulation, and structural components.

Measurement and characterization methods include density measurements via Archimedes principle, gas pycnometry for true material volume, mercury intrusion porosimetry for pore size distribution, and high-resolution micro-computed tomography for three-dimensional pore architecture. These techniques help distinguish processing porosity from intrinsic or design porosity and from porosity generated by service conditions.

Impact on properties varies with context. Processing porosity generally reduces mechanical strength and stiffness and increases permeability, but controlled porosity can be beneficial for weight reduction, thermal insulation, or fluid transport. Controls to minimize unwanted processing porosity include optimizing processing parameters (temperature, pressure, atmosphere), degassing, proper binder burnout, particle size distribution, and post-processing steps such as sintering, hot isostatic pressing, or infiltration to densify the material.