下水道汚泥焼却灰を原料とする燒結煉瓦の異常膨張に及ぼす炉内雰囲気の影響

概要

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The extraordinarily large expansion observed during sintering of bodies from incinerated ash of sewage sludge was investigated in connection with chemical states of iron in the bodies. The ash was pressed into a rectangular body under 100 MPa, and the body was fired at 1000℃ for 3 h in flowing Ar-O_2 (Po_2:0.1-1.0 kPa) atmosphere. The bulk density of the bodies fired in various atmospheres decreased with a decrease in oxygen partial pressure. The formation of porous black core accompanied by extraordinary expansion was observed in the bodies fired at Po_2=0.1-0.7 kPa. Reflectance spectra and the ratio of Fe^<2+> to total Fe measured by chemical analysis indicated that iron oxide in the black core was in the form of FeO or Fe_3O_4. The evolution rate of CO_2 during heating of the body was measured by using a quadruple mass spectrometer. In the case of Po_2=0.5 kPa, the evolution rate of CO_2 at 1000℃ was higher than the rate of O_2 supply through the atmospheric gas flow. The fact indicated that the ferric oxide was reduced to ferrous oxide by the residual carbon and the evolution of CO_2 occurred inside the body under lower oxygen partial pressure.
1999-06-01