Effect of the reduction treatment on the basalt continuous fiber crystallization properties

•Basalt continuous fibers were reduced in H2 atmosphere.•Due to Fe2 +/Fe3 + ratio changing crystallization mechanism changes.•Crystallization process in the reduced basalt fibers carries slower.•The tensile strength loss of the reduced fibers is 40.4%.

Basalt continuous fibers were treated in H2/Ar atmosphere at 650 °С and 700 °C. The 57Fe Mössbauer spectroscopy indicated that after the treatment at 650 °C all ferric cations reduced to ferrous. Reduction at higher temperature leads to metallic iron formation. DSC and XRD data indicated that crystallization process in reduced basalt fibers carried slower. Glass transition temperature decreases after the reduction due to the increase of amount of ferrous cations, that act as modifiers. Due to Fe2 +/Fe3 + ratio changing spinel-like phase crystallization ability decreases. Crystallization in reduced basalt fibers starts at lower temperature. The tensile strength of reduced fibers is higher than the tensile strength of basalt continuous fibers that were annealed at the same condition in air.