Abstract
The foaming mechanism of mixtures of fly ash (FA) and incinerated ash of sewage sludge was investigated in relationship with the chemical states of iron in the sintered bodies. The FA content was 20mass% of the total weight of the mixtures. The mixtures were pressed in a discus body (3cm in diameter), which was fired at 1000∼1100°Cfor 1 h in air or nitrogen. In the case of firing in nitrogen, the lowest apparent density for each fired body with 20mass% FA was 0.82 g cm-3. The large foaming was observed during firing in nitrogen but not during firing in air above 1050°C. The results of diffuse reflectance spectra and electron spin resonance measurements indicated that most of the ferric oxide in the samples fired above 1050°C in nitrogen atmosphere was reduced to ferrous oxide. The large forming was probably due to the evolution of oxygen from iron (III) oxide and the oxidation of residual carbon inside the samples after melting of the surface at high temperatures in nitrogen.
