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<p>Phase formation during the heat treatment of waste activated sludge (WAS)–B<sub>2</sub>O<sub>3</sub> mixtures was studied under oxygen-depleted conditions (0.4&#xa0;mPa) between 400 and 1100&#xa0;°C. During heating, WAS was transformed into highly reactive amorphous carbon, which acted as a reducing agent for WAS-derived oxides and B<sub>2</sub>O<sub>3</sub>, enabling the formation of carbides (B<sub>25</sub>C, B<sub>4</sub>C, CaC, FeC, Fe<sub>4</sub>C, Fe<sub>3</sub>C), metals (Ca, Fe), alloys (FeAl, CaSi<sub>2</sub>), and elemental phases (Si, B, C). The presence of FeAl confirms the reduction of Al<sub>2</sub>O<sub>3</sub> from clay decomposition, indicating the contribution of aluminothermic reactions. Increasing the WAS content and processing temperature (T ≥ 800&#xa0;°C) promoted amorphization, resulting in diffraction patterns characterized by complex halos. The simulation of superimposed amorphous patterns, combined with experimental results, revealed carbon, boron carbide, iron, iron carbides, and CaSi₂ as predominant phases. These results demonstrate the potential of WAS as a carbon source for the synthesis of complex carbide and alloy phases.</p> Graphical abstract <p></p>

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Formation of an amorphous C-B4C composites through low temperature processing of WAS-B2O3 mixtures

  • 期刊论文

  • 发表日期：

    2026年3月3日

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  • Mónica Torres Álvarez,
  • Abigail Parra Parra,
  • Marina Vlasova,
  • Pedro Antonio Marquez Aguilar,
  • Ulises León Silva

摘要

Phase formation during the heat treatment of waste activated sludge (WAS)–B2O3 mixtures was studied under oxygen-depleted conditions (0.4 mPa) between 400 and 1100 °C. During heating, WAS was transformed into highly reactive amorphous carbon, which acted as a reducing agent for WAS-derived oxides and B2O3, enabling the formation of carbides (B25C, B4C, CaC, FeC, Fe4C, Fe3C), metals (Ca, Fe), alloys (FeAl, CaSi2), and elemental phases (Si, B, C). The presence of FeAl confirms the reduction of Al2O3 from clay decomposition, indicating the contribution of aluminothermic reactions. Increasing the WAS content and processing temperature (T ≥ 800 °C) promoted amorphization, resulting in diffraction patterns characterized by complex halos. The simulation of superimposed amorphous patterns, combined with experimental results, revealed carbon, boron carbide, iron, iron carbides, and CaSi₂ as predominant phases. These results demonstrate the potential of WAS as a carbon source for the synthesis of complex carbide and alloy phases.

Graphical abstract