Having highlighted the crucial role of the reaction environment (reducing and oxidizing atmosphere) on the ceramic approach, we illustrate the methodology used by the chemist in his quest for new phases within a binary, ternary or even quaternary diagram. The phase rule is recalled and the use of reasoned Combinatorics synthesis described. Although oxides form the basis of our reasoning, we extrapolate it to the elaboration of sulfides, chalcogenides, nitrides and borides ; the difference residing mainly in the choice of vessels, atmosphere and heating means. As the classic ceramic approach of bake and shake is very energy-intensive, more eco-friendly alternatives are being developed. These include high-temperature self-propagating synthesis (SHS) and high-temperature spontaneous combustion synthesis (SCS). In other words, temperatures of 2,000°C or even more can be obtained without any energy input, making these reactions of great interest in the context of sustainable development.
Variants of these approaches (SHS vs. SCS), which are widely used in industry and are based on highly exothermic reactions, are described using examples. The specificity of the SHS approach, which is based on metathesis reactions and often produces a spectacular pyrotechnic effect, is that it is poorly suited to the elaboration of oxides. The SCS approach was developed to fill this gap. SCS is based on the use of complexes that ignite at low temperatures, leading to spontaneous combustion and the evolution of large quantities of gas into voluminous oxide powders. This synthesis takes place from the solution, which must contain an oxidant and a fuel in a ratio equal to 1, as in a rocket engine, to release maximum energy. We apply this method to the elaboration of numerous electrode materials of controlled sizes and morphologies in order to obtain optimal electrochemical properties.
