Abstract
The dewaxing process is used to remove an organic binder from the ceramic green bodies before sintering, which occasionally generates cracks. The crack formation behavior depends on various factors including softening and decomposition of the organic binder, generation of gases, and strength degradation of the green body thereby. Herein, this correlation was investigated to elucidate the crack formation behavior during the dewaxing process using two types of Al2O3 green bodies; one is added with polyvinyl butyral (PVB) and stearic acid (SA) and the other is with paraffin. The internal structures of Al2O3 green bodies during dewaxing were observed using optical coherence tomography (OCT), and the generated gases were analyzed simultaneously using a thermogravimetric (TG) analyzer and Fourier transform infrared (FTIR) spectroscopy (TG-FTIR). The mechanical properties of the green bodies were investigated at RT–600 °C using a thermomechanical analyzer (TMA). The weight change occurred in both the green bodies with formation of gases depending on the type of the binder. In the OCT studies, cracks were observed with substantial deformation in the PVB/SA-added green body during the dewaxing, whereas no cracks were seen in the paraffin-added one. The TMA investigation showed that the paraffin-added sample possessed higher strength and better structural stability than the PVB/SA-added one throughout the dewaxing, leading to the crack-free green body of the former. Therefore, the crack-initiation and deformation behaviors of the green bodies were significantly affected by the type of the binder used. The combination of the in-situ observations using the combined OCT-TG-FTIR system and the mechanical properties measurement using TMA was found to be effective in verifying the structural stability of the green bodies during the dewaxing.
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