Glassy carbon (GC) is a type of non-graphitizing disordered carbon material at ambient pressure and high temperatures, which has been widely used due to its excellent mechanical properties. Here we report the changes in the microstructure and mechanical properties of GC treated at high pressures (up to 5 GPa) and high temperatures. The formation of intermediate sp(2)-sp(3) phases is identified at moderate treatment temperatures before the complete graphitization of GC, by analyzing synchrotron X-ray diffraction, Raman spectra, and transmission electron microscopy images. The intermediate metastable carbon materials exhibit superior mechanical properties with hardness reaching up to 10 GPa and compressive strength reaching as high as 2.5 GPa, nearly doubling those of raw GC, and improving elasticity and thermal stability. The synthesis pressure used in this study can be achieved in the industry on a commercial scale, enabling the scalable synthesis of this type of strong, hard, and elastic carbon materials. (C) 2020 The Chinese Ceramic Society. Production and hosting by Elsevier B.V.

Funding Information: National Key R&D Program of China, Grant Number 2018YFA0703400. National Natural Science Foundation of China (NSFC), Grant Numbers 51672238, 91963203, 51722209, 51525205. Alexander von Humboldt Foundation. 100 talents plan of Hebei Province, Grant Number E2016100013. NSF for Distinguished Young Scholars of Hebei Province of China, Grant Number E2018203349. China Postdoctoral Science Foundation, Grant Number 2017M620097.