Effects of high-temperature treatment and iron reduction index on tensile strength of basalt continuous fiber

• The tensile strengths of BFs at high temperatures were studied • BFs with higher IRIs retained better tensile strengths at high temperatures • A CaO-based crystal layer was formed on the surface of BFs • BFs with lower IRIs formed more ferric tetrahedral structures at high-temperature Iron plays an important role in enhancing the tensile strength of basalt fibers (BFs); however, the origins of tensile-strength variation at high temperatures are not well understood. In this work, we prepared BFs with different iron reduction indices (IRI = Fe 2+ /Fe total ) and explored the effects of high temperature and IRI on tensile strength. The results show that BFs with higher IRIs retained better tensile strength after high-temperature treatment at 600°C for 1 h. The surface morphology was analyzed by scanning electron microscopy to observe the nanocrystalline layers on the surface of BFs with higher IRIs, and the main composition of the crystals was CaO. The formation of nanocrystalline layers increased the tensile strength of the BFs. Moreover, results from transmission 57 Fe Mössbauer spectroscopy and Fourier transform infrared spectroscopy indicate that BFs with lower IRIs formed more ferric tetrahedral structures (Fe 3+ (tet)) after high-temperature treatment, which depolymerized Si(Al)-O-Si(Al) tetrahedral structures, resulting in lower tensile strength. A better understanding of the origin of microstructures in different iron coordination states and the tensile strength of BFs at high temperatures will assist in the development of advanced iron-bearing glass fiber products suitable for high-temperature environments.