Boron carbide is a refractory material and requires extreme sintering conditions such as high temperatures and pressures during several hours to achieve fully dense sample. However, considering the environmental concerns as consequences of such processes, the energy consumption reduction during the synthesis or the sintering step can be a lever to reach sustainability in chemistry. The use of additives such as preceramic polymers, obtained through the Polymer-Derived Ceramics route (PDCs), is an innovative and promising way for enhancing densification during sintering. Indeed, the PDC route combined to the functionalization of ceramic powders with a polycarbosilane as a preceramic polymer of silicon carbide, can lead to a reduction of the sintering temperature and the dwelling time during the sintering stage [1]. Nevertheless, the synthesis and use of preceramic polymers often require organic solvents that are often toxic and hazardous.
 
The sintering additive employed in this study is silicon carbide. It is more ductile than boron carbide and aids the particle rearrangement during sintering as well as providing a better granular cohesion. The target preceramic polymer is a polycarbosilane, and the solvents commonly used to dissolve it, are toluene or hexane. They present non neglectable health risks. In a green chemistry way, the goal of this work is to reduce the use of hazardous chemical products, to prevent waste and to use benign solvents while preserving the preceramic polymer properties. This will be applied to the functionalization of boron carbide powders, by changing the current solvent used, toluene, to dissolve the polymeric ceramic precursor. The impact of the change of the solvent on the functionalization and sintering process will be studied.
 
The approach developed in this work is, in a first step, to characterize the polymeric ceramic precursor in terms of structure, composition and thermal behavior. Then a list of solvents for the replacement of traditional hazardous ones has been established according to their miscibility criteria and HSE (health safety and environment) indicators. Afterwards, the solvent influence on the stability and behavior of the preceramic polymer, has been investigated. In parallel, the impact on the reactivity of boron carbide powders, more precisely on the oxide native oxide layer, has been analyzed and put forward the dissolution of this layer. Finally, an application of the solvent change and its recyclability has been studied during the functionalization of boron carbide in the presence of a polycarbosilane, and the consequences on the sintering have been considered. Preliminary results are encouraging and point out the fact that the change of solvent does not have an effect on the preceramic polymer. In addition, the same final relative density as for toluene is achieved with the new functionalization solvents.
 
 
References
[1] H. Laadoua, N. Pradeilles, R. Lucas, S. Foucaud, and W. J. Clegg, "Preparation of ZrC/SiC composites by using polymer-derived ceramics and spark plasma sintering," Journal of the European Ceramic Society, vol. 40, no. 5, pp. 1811-1819, 2020/05/01/ 2020, doi: https://doi.org/10.1016/j.jeurceramsoc.2019.12.019.