Abstract:
Binders are commonly used to impart green strength for pressed ceramic parts prior to sintering. It is generally assumed that a simple heat treatment in air is sufficient to remove the binder prior to sintering. A simple experiment, however, in which a droplet of binder is introduced to a pressed compact without binder, demonstrates that the binder alters the sintering of the compact in the region of the droplet. It is proposed that this alteration in sintering behavior is due to residual carbon from incomplete binder removal. To systematically evaluate binder removal, two sets of alumina compacts were prepared: one contained binder (PVA and PEG) and one without binder. The samples were both subjected to binder removal heat treatments in which the ratio of oxygen to nitrogen in the gas was altered to produce seven atmospheric conditions with oxygen levels of 0, 10, 20 (dry air), 30, 50, 75 and 100%. After the binder removal stage, the resulting samples were sintered in air at 1550°C for one-hour, densities measured, and fracture surfaces of the microstructures evaluated. The results showed that oxygen level does not have a significant impact on binder removal. However, because the samples with binder always had a lower density than the samples without binder it can be concluded another factor is hindering binder removal.
