Analysis of newly discovered substances on the vulnerable Emperor Qin Shihuang's Terracotta Army figures

Abstract In this paper, X-ray diffraction spectroscopy (XRD), Raman spectroscopy (RS), firing temperature analysis, pore size distribution analysis, Fourier infrared spectroscopy (FTIR), scanning electron microscopy-energy dispersive spectroscopy (SEM–EDS), and transmission electron microscopy (TEM) were utilized to analyze the unearthed vulnerable terracotta figures of Emperor Qin Shihuang's Terracotta Army, as well as the unknown precipitated white crystals and black substances. The results show that the firing temperature of the vulnerable terracotta figure is much lower than those of similar terracotta figures and red terracotta figures with good texture. The pore size of this kind of vulnerable pottery is smaller and the specific surface area is larger. In the pores, there is an alkaline solution containing Ca2+ that accounted for approximately 4.3% of the total mass of the sample. Along with the fracture of the delicate pottery matrix, the solution in the pores migrated to the fracture surface and chemically reacted with CO2 in the air, generating a layer of white calcium carbonate crust. The black matter on the fracture surface of the vulnerable terracotta figure is mainly composed of amorphous carbon and graphitized carbon, which shows high activity under the catalysis of Fe and Ti elements and alkaline soil. The discovery and analysis of amorphous carbon, graphitized carbon, and white calcium carbonate crystals on the fracture surface of the Qin Shihuang’s Terracotta Army provide a theoretical foundation for in-depth analysis of the terracotta warriors and horses' composition and structure, as well as scientific protection and restoration, and the stability of the original site display.