Abstract Scope |
Polymer binders are common processing aides, enabling shaping of loose ceramic powders during forming. Often the first step in the firing process involves thermal removal of the polymer by “binder burnout”. Binder burnout is slow and troublesome. Many firing failures are due to damage associated with the process, such as cracking, bloating, and distortions. The usual treatment of binder removal emphasizes transport in a porous medium, and considers the capillary stresses associated with this transport. A second line of reasoning involves evolution of gases from polymer degradation, and addresses damage from gas formation. This paper addresses a largely ignored aspect that could also be important: differential volume change between the low thermal expansion ceramic and the high thermal expansion polymer. I will discuss this in terms of the thermal expansion of ceramic powder-filled polymers, with examples from ceramic injection molding mixes, thermoplastic extrusion mixes, and photopolymerized ceramic suspensions. |