Temperature and frequency dependencies of the permittivities of iron- and steelmaking by-products

In the present study, the permittivities of iron and steelmaking by-products including electric arc furnace (EAF) stainless steel dust, ferrochrome converter (CRC) dust, blast furnace (BF) sludge, basic oxygen furnace (BOF) sludge, and basic oxygen furnace (BOF) slag were investigated. The cavity perturbation technique was used to measure their permittivities as a function of temperature and frequency, while thermogravimetric (TG), differential scanning calorimetry (DSC), and mass spectrometry (MS) analysis were used to interpret the permittivity results. The results showed that the BF sludge exhibited the highest permittivities, whilst the BOF slag had the lowest permittivities. Based on maximum loss tangent values and heating rates, the materials ranked: BF sludge > BOF sludge > EAF stainless steel dust > CRC dust > BOF slag. Key factors influencing permittivities included water removal, iron oxide reduction, and carbonate decomposition. Microwave heating mechanisms transitioned from dipolar rotation at the initial stage to ionic conduction at later stages.