1 3
Topics in Current Chemistry (2020) 378:6
1.2.3 Thermal Methods
The thermal methods are mainly based on thermal decomposition [39], as well as
on hydrothermal [40–43], solvothermal and microwave-assisted methods. While the
thermal decomposition consists in the simple decomposition of precursors, organic
solvents and surfactants during heat treatment to get the ferrite, the other methods
are driven by the need to lower the temperature used for crystallization in order for
the ferrite to maintain a suitable specific surface area. Hydrothermal and solvothermal usually differ in terms of solvent, aqueous vs. non-aqueous, respectively, in
which the soluble metal salts are dissolved. Temperature, pressure, synthesis duration as well as choice of solvent, of precursors and of additional surfactant are the
main synthesis parameters impacting on the physico-chemical properties of the ferrites [13, 14, 44, 45]. While the temperature can be as high as 500 °C for the thermal decomposition method, it can be decreased to 100–200 °C for solvothermal,
hydrothermal and microwave-assisted methods. However, although the microwaveassisted syntheses allow shorter reaction durations to be achieved, they suffer usually from low synthesis yields.
1.2.4 Solid‑State Reaction Methods
Besides the bottom-up chemical syntheses in solution reported above, the solid-state
reaction methods are a suitable top-down approach consisting in treating solid precursors at high temperature, usually oxides or carbonates, for inducing solid–solid
diffusion, with a further stabilization/crystallization of the ferrite defined structure. CoFe 2 O 4 , CuFe 2 O 4 , NiFe 2 O 4 and Ni 1–x Mn x Fe 2 O 4 spinel ferrites have notably
been synthesized [46–49]. However, the obtained ferrites usually suffer from low
specific surface area when compared to chemical synthesis in solution. Therefore,
the mechanical milling method has been implemented as a high-energy collision
Fig. 6 Esterification reaction occurring between citric acid and ethylene glycol in a typical Pechini process (top). Proposed schematic of the process of making metal/organic gels (bottom). Reproduced with
permission from Ref. [36]. Copyright Royal Society of Chemistry
115
Reprinted from the journal
Topics in Current Chemistry (2020) 378:6
1.2.3 Thermal Methods
The thermal methods are mainly based on thermal decomposition [39], as well as
on hydrothermal [40–43], solvothermal and microwave-assisted methods. While the
thermal decomposition consists in the simple decomposition of precursors, organic
solvents and surfactants during heat treatment to get the ferrite, the other methods
are driven by the need to lower the temperature used for crystallization in order for
the ferrite to maintain a suitable specific surface area. Hydrothermal and solvothermal usually differ in terms of solvent, aqueous vs. non-aqueous, respectively, in
which the soluble metal salts are dissolved. Temperature, pressure, synthesis duration as well as choice of solvent, of precursors and of additional surfactant are the
main synthesis parameters impacting on the physico-chemical properties of the ferrites [13, 14, 44, 45]. While the temperature can be as high as 500 °C for the thermal decomposition method, it can be decreased to 100–200 °C for solvothermal,
hydrothermal and microwave-assisted methods. However, although the microwaveassisted syntheses allow shorter reaction durations to be achieved, they suffer usually from low synthesis yields.
1.2.4 Solid‑State Reaction Methods
Besides the bottom-up chemical syntheses in solution reported above, the solid-state
reaction methods are a suitable top-down approach consisting in treating solid precursors at high temperature, usually oxides or carbonates, for inducing solid–solid
diffusion, with a further stabilization/crystallization of the ferrite defined structure. CoFe 2 O 4 , CuFe 2 O 4 , NiFe 2 O 4 and Ni 1–x Mn x Fe 2 O 4 spinel ferrites have notably
been synthesized [46–49]. However, the obtained ferrites usually suffer from low
specific surface area when compared to chemical synthesis in solution. Therefore,
the mechanical milling method has been implemented as a high-energy collision
Fig. 6 Esterification reaction occurring between citric acid and ethylene glycol in a typical Pechini process (top). Proposed schematic of the process of making metal/organic gels (bottom). Reproduced with
permission from Ref. [36]. Copyright Royal Society of Chemistry
115
Reprinted from the journal