Effect of activating additives on the cold sintering process of (MnFeCoNiCu)₃O₄ high-entropy ceramics

Objectives. To obtain experimental data on the effect of activating additive type on the cold sintering process of (MnFeCoNiCu)₃O₄ high-entropy ceramic. The following substances were used as activating additives: ammonium acetate (CH₃COONH₄), acetic acid (CH₃COOH), ammonium chloride (NH₄Cl), potassium fluoride dihydrate (КF·2H₂O), lithium fluoride (LiF), sodium fluoride (NaF), and sodium hydroxide (NaOH).
Methods. Synthesis of the initial powder by low-temperature self-propagating method; investigation of the powder particles size distribution by laser diffraction method; analysis of the particle shape and compacted sample microstructure by scanning electron microscopy; investigation of the phase composition by X-ray phase analysis; high-entropy ceramic sample consolidation by cold sintering process. The density of the initial powder and the relative density of cold sintered samples were determined by the Archimedes method.
Results. Samples with a relative density of over 0.70 were obtained using distilled water, CH₃COONH₄ and NaOH during cold sintering at 300 °C, with a holding time of 30 min and pressure 315 MPa.
Conclusions. For the first time, the effect of the type of activating additive on the relative density of high-entropy ceramics (MnFeCoNiCu)₃O₄ samples obtained by cold sintering process has been experimentally demonstrated. The samples microstructures have pronounced differences: 20 wt % distilled water does not lead to grain growth, with only their compaction to 0.71 relative density observed; however, the addition of 0.1 wt % CH₃COONH₄ and NaOH increases the average grain size when reaching similar relative densities (0.70 and 0.71, respectively). X-ray diffraction analysis showed that the cold sintering process does not lead to a change in the phase composition of the initial (MnFeCoNiCu)₃O₄ powder, confirming the preservation of the high-entropy structure.

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