For the 900°C waste flue gas generated from printed circuit board (PCB) incineration, the flue gas contains HBr, HCl, and heavy metals, 

which makes it highly corrosive at 900°C. Ordinary stainless steel will fail rapidly under such conditions. 

The recommended material selection for the fan is as follows:

1. Impeller: Use Inconel 625 nickel-based alloy. This material can withstand temperatures up to 1100°C and effectively resists corrosion from HBr and HCl.

2. Volute (Casing): Use 253Ma heat-resistant stainless steel with an added aluminum silicate insulation layer to isolate high temperatures.

3. Bearing Housing: Adopt a forced water-cooling structure to ensure the bearing operating temperature is controlled at 80°C or below.

4. Ash Discharge Design: A large-diameter ash discharge port is set at the bottom of the fan to facilitate the regular cleaning of deposited heavy metal dust.