Ceramic foam filters with concentrated carbon binder surfaces for copper melt filtration

In this study, the impact of coal tar pitch coatings on carbon-bonded alumina samples were investigated. The coal tar pitch coating had no effect on the bending strength of bar samples compared with an uncoated reference but a reduction of the median pore size was observed for samples coated with the coal tar pitch and coked 1x. Furthermore, differences in the measured contact angles were detected. The highest contact angles under low atmospheric pressure (<1.8 × 10 −5 mbar) were measured for 2x coked coal tar pitch-coated (Carbores P) samples (152°). A liquid coal tar pitch coating (Carbores T10) showed the lowest contact angle at 126°. Strong gas bubbling during the sand-casting trial showed the formation of a gas resulting in large pores in the cast copper samples. The strong oxidation of the carbon at the surface of the filters is regarded as the reason for the gas formation, with the oxygen originating from both the air within the filter before priming, the sand mold around it and from the oxygen dissolved in the melt.