In this work, the prospects of fabrication of heating elements from heat-treated (sintered) mixtures of waste-activated sludge (WAS) and Fe2O3 under oxygen deficiency conditions are considered. During heat treatment of mixtures in the 800–900 °C temperature interval, Fe2O3 reduces to Fe3O4, Fe0.94O, and Fe. A heat treatment at 1000 °C leads mainly to the formation of amorphous iron doped with carbon, silicon, and aluminum. Based on these compacted mixtures, having different electrical resistivity (from ~ 10–4 up to 10–1 Ω·m), it is possible to fabricate heating elements, whose working temperature ranges from ~ 100 °C up to 600 °C.
Graphical Abstract
A simulation of the diffuse experimental X-ray halo obtained when waste-activated sludge (WAS) was used as the Fe2O3 reducing agent made it possible to explain the large width of the experimental halo and the change in its shape as a result of the change in the amorphous phase content. The halo consists of different sets of amorphous phase convolutions. The synthesized product was a composite consisting of amorphous iron with inclusions of amorphous oxides of aluminum and silicon, amorphous carbon, and amorphous Si, Al, and C alloys on the surface of the Fe particles. The shift in the halo makes it possible to qualitatively estimate the contributions of oxide and carbon components or alloys to the halo of amorphous iron.
It has been established that during heat treatment of mixtures of waste activated sludge (WAS) and Fe 2 O 3 under the conditions of oxygen deficiency at 800-1000 °C, reactive carbon, which initiates the reduction of Fe 2 O 3 to Fe and the formation of C-Fe x O y mixtures, forms. Based on these compacted mixtures, having different electrical resistivity (from ~ 10 -4 up to 10 -1 Ω•m), it is possible to fabricate heating elements, whose working temperature ranges from ~ 100 °C up to 600 °C. Such heating elements can be used in the construction industry to accelerate the curing of concrete and its low temperature heating.
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