4. Conclusions
Synthesis of SiC was achieved by using concentrated solar energy provided by the IER-UNAM solar furnace. For the synthesis it was used a Pyrex glass spherical vessel of 25 l capacity, designed to work with concentrated solar energy and controlled atmospheres.
The synthesis consisted in 5 steps, where the last 2 steps were performed by using concentrated solar energy. The SiO2/C composite synthesis was performed at a temperature of 700 C under nitrogen atmosphere. In this step, silica synthesized by the sol–gel method was used as a precursor of silicon, and sucrose as precursor of carbon. FTIR and XRD results confirm the formation of SiO2/C.
The last step of the synthesis was carried out at a temperature of 1500 C in argon atmosphere; in this case a graphite crucible was used to support the sample. According to the results of the characterization, the solar SiC obtained is composed mainly of cubic type SiC (b-SiC) with a minimum amount of hexagonal SiC (a-SiC). The FTIR and XRD results confirm also the existence of residual SiO2, which might be associated with unreacted silica that disappears after etching acid HF obtaining pure SiC. Results of thermal analysis (TGA/DSC) showed a more reactive carbon to form the composite SiO2/C as precursor from SiC synthesis, being more thermally stable, due it has at lowest weight loss at higher temperature (950 C); in addition, results of TGA exhibited that synthesized SiC can be considered as stable supports to effectively increase the lifetime of devices that have to withstand harsh oxidative and thermal environments. According to the results of TEM, the SiC particles system is polydisperse in size, with grains of nanometer order size. Results showed that it is feasible the use of concentrated solar energy for the synthesis of SiC with lower CO2 emissions than conventional methods. Acknowledgments