Because of the advantages of reaction mechanism, the rate of metal catalytic debinding is much larger than that of traditional degreasing technology.

 

Catalytic Rate

The catalytic reaction only in the gas - adhesive interface, which gradually develops to the internal external. This debinding mechanism does not produce cracks and voids, and a high debinding rate can be obtained. Moving rate of the binder interface to the interior is 2-4mm/h, which is much larger than that of the traditional one.

 

And the debinding rate of injection molding blank based on general binder is 0.2mm/h, which is 10~20 times higher than that of traditional debinding process. The effect of binder composition, catalytic gas flow rate, debinding time and debinding temperature on catalytic debinding rate was positively correlated.

 

Selection of Degreasing Catalyst

In the degreasing process, high speed inert gas (nitrogen, argon, helium and their mixture) can be introduced into the degreasing furnace to accelerate the diffusion of small molecules and regulate the degreasing rate. The degreasing rate can be controlled by controlling the concentration of the catalyst.

 

Moreover, with the decrease of the inert gas flow rate, the catalyst concentration in the degreasing zone increases, and the overall debinding rate increases as well. Therefore, the flow rate of inert gas should be controlled within a moderate range.

 

For most ceramic injection molding (CIM) powder materials, nitric acid is a suitable catalyst, as nitric acid has strong oxidizing property and strong gasification tendency. Under normal degreasing conditions, nitric acid vapor will not deposit in the capillary hole of ceramic parts after removing organic carrier, and will not corrode the furnace structure.

 

Oxalic acid can overcome the disadvantage of nitric acid, such as Y₂O₃ (sintered Si₃N₄ and SiC additives) and so on, and become another widely used catalyst. Oxalic acid is a volatile organic acid, at room temperature is solid, at 100℃ turns to  gas, more than 187 degrees of decomposition into CO, CO₂ and H₂O. Therefore, using oxalic acid as catalyst, the treatment of waste gas after catalytic reaction is relatively simple.

 

When nitric acid was used as catalyst, the removal rate was 0.7 - 1.5mmh-1, and the rate of debinding was in the order of Si₃N₄ >ZrO₂ >SiC. When the oxalic acid was used as catalyst, the degreasing rate was 0.9 - 1.5mmh-1, and the order of debinding was ZrO2 >SiC>Si3N4. It can be seen that there are great differences in the catalytic action of different catalysts. The degreasing effects of two kinds of catalysts are shown in Figure 1 and figure 2.