Other debinding techniques

In order to eliminate flaws inherent to thermal debinding and to shorten the duration of this stage, other techniques for the extraction of organic shaping additives have been developed. These techniques are based on an under- or overpressure of the treatment atmosphere, on microwave heating, capillary migration of molten binder, sublimation of a binder in aqueous phase, or solubilization by catalytic reaction or solvents. 

Assisted thermal debinding a) By under-pressure or over-pressure 

This technique relies on the solubility of organic additives in solvents such as trichloroethane, pentane, hexane, toluene, acetone or petroleum ether. The ceramic pieces are immersed in a solvent bath which can be preheated to temperatures of about 40 to 50°C. The solvent penetrates into the pores, solubilizes the binders and evacuates them by migration towards the surface. After the treatment, the solvent present in the porous stractuie of the piece is evaporated and the non-solubilized binder fraction is eliminated during the sintering cycle. As the soluble binder is eliminated from the surface towards the inside according to an abmpt reaction front 

This technique applies to particular binders that exhibit specific degradation (catalytic) mechanisms in certain atmospheres. BASF (Germany) has developed an injection formulation containing polyacetal binders, which are eliminated at 110°C in acid atmosphere (98% nitrogen + 2% nitric acid). This atmosphere leads to the sublimation of a part of the polyacetal binder and the crystallization of the remaining part. However, sublimation vapors reqnire a reliable reprocessing before their evacuation into the air and the debinding furnaces must have an anticorrosion treatment in order to resist nitric acid fumes. 

The techniques of depositing ceramic materials on a support (substrate) are generally excluded from books dealing with ceramic shaping processes. They are nevertheless processes involving ceramics. For this reason, the main deposition techniques are briefly described in this section. 

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