A new dewaxing method for low-pressure injection molded ceramics is presented.
Supercritical extraction with carbon dioxide was used to remove paraffin wax from the ceramic green
parts. The composition of organic additives for low-pressure injection molding feedstock and the
extraction condition for the green parts were investigated. Moreover, the properties of sintered ceramic
samples dewaxed by supercritical carbon dioxide were compared with those by thermal dewaxing. The
results show that the new binder system containing 50wt% paraffin wax, 35% bee wax and 15% stearic
acid fulfills the requirements of both low-pressure injection molding feedstocks and supercritical
dewaxing, where the feedstock has high fluidity, low viscosity and quick solidification. The efficient
extraction condition for supercritical dewaxing from the green parts is at 30MPa pressure and 45°C.
Under this condition, defect free ceramic green parts can be obtained. Dewaxing methods have significant
influence on the properties of sintered parts. The mechanical properties of the sintered sample can be
improved by supercritical dewaxing. With this method, the bending strength of sintered samples (σ =
331.6 MPa) is higher than that obtained by thermal treatment (σ = 312.3MPa). The sintered samples
dewaxed by supercritical CO2 have shown the property of higher density and less distortion compared to
the thermal dewaxing method. Moreover, with supercritical extraction the dewaxing time can be reduced
to about one tenth of the time required by thermal dewaxing.
Preparation of Al2O3 ceramics by low pressure injection molding method.
