Sinterability of Agglomerated Powders

TLDR

Thermodynamic arguments indicate that pores vanish only when their coordination numbers fall below a critical threshold. The study introduces a concept linking powder compact sinterability to the distribution of pore coordination numbers. The authors analyze how the coordination‑number distribution depends on packing‑unit size, consolidation forces, and sintering phenomena, and how grain growth and rearrangement reduce pore coordination numbers to enable pore disappearance. The study finds that multiple‑particle packing units densify and promote grain growth during early sintering, and experimental porosimetry of sub‑micron Al₂O₃ compacts confirms this behavior.

Abstract

A concept is presented which relates the sinterability of a powder compact to its particle arrangement as defined by the distribution of pore coordination numbers, i.e., the number of touching particles surrounding and defining each void space. Previous thermodynamic arguments suggest that pores will disappear only when their coordination numbers are less than a critical value. The coordination‐number distribution of an agglomerated powder is discussed with respect to the size of the multiple‐particle packing unit, consolidation forces, and phenomena occurring during sintering. One pertinent conclusion is that the multiple‐particle packing units densify and support grain growth as sintering initiates. Grain growth and rearrangement processes decrease the coordination number of remaining pores to allow them to disappear during latter states of sintering. Porosimetry and direct observations of powder compacts of <1 μm Al 2 O 3 heat‐treated between 600° and 1600°C support this concept.